Terminology

2D speckle-tracking echocardiography (2D-STE) is an ultrasound-based method for measuring myocardial deformation by tracking characteristic acoustic speckle patterns across successive frames of two-dimensional cardiac images. These patterns arise from interference between ultrasound echoes scattered within tissue and serve as markers of myocardial motion. Tracking their displacement allows calculation of strain, the relative change in tissue length, including longitudinal, circumferential and radial strain. The technique is used to assess global and regional ventricular function and can reveal impaired myocardial mechanics despite a preserved ejection fraction. Right ventricular free-wall longitudinal strain is a commonly used application. Measurements depend on image quality, frame rate, tracking software and imaging-plane consistency. Unlike Doppler-based strain, it does not require alignment with the ultrasound beam, but out-of-plane motion can affect tracking.

6-minute walking distance (6MWD) is the total distance a person walks in six minutes during a standardized, self-paced test, usually conducted along a flat indoor corridor. It measures functional exercise capacity by reflecting the combined effects of cardiovascular, respiratory, muscular and other factors on walking performance. Patients may slow down, stop or rest as needed while the test timer continues. The measure is used to assess functional limitation and monitor changes over time in conditions such as heart failure and pulmonary hypertension. It complements cardiac MRI measurements of ventricular structure and function but is not an imaging measurement itself. Interpretation requires attention to testing conditions, encouragement, supplemental oxygen, walking aids and non-cardiopulmonary limitations.

18F-fluorodeoxyglucose (18F-FDG) is a radioactive glucose analogue used in positron emission tomography (PET) to map tissue glucose uptake. After entering cells through glucose transporters, it is phosphorylated and largely trapped intracellularly, allowing its distribution to reflect glucose metabolism. Fluorine-18 emits positrons, whose annihilation produces paired photons detected by the PET scanner. In cardiac imaging, increased uptake can identify metabolically active inflammation, particularly in suspected cardiac sarcoidosis, and help assess treatment response. Dietary preparation and fasting are used to suppress normal myocardial glucose uptake when evaluating inflammation. FDG PET also contributes to cardiac mass characterization because many malignancies show increased glucose metabolism, although uptake is not specific for cancer. Findings are interpreted alongside anatomical and tissue information from CT, MRI, or echocardiography.

Adults with congenital heart disease (ACHD) are people who have reached adulthood with structural abnormalities of the heart or great vessels that were present at birth, whether unrepaired, surgically repaired, or treated by catheter intervention. This population includes a wide range of conditions, from simple septal defects to complex circulatory arrangements, with differing risks of heart failure, arrhythmias, pulmonary hypertension, and residual valve or vascular disease. Lifelong specialist follow-up assesses both the original abnormality and the consequences of previous treatment. Cardiac MRI is particularly useful for measuring ventricular volumes and function, quantifying blood flow and shunts, and evaluating myocardial scar. CT provides detailed assessment of vascular anatomy, coronary arteries, conduits, and other structures when clinically indicated. Imaging supports surveillance, exercise assessment, and planning of further interventions or advanced heart failure care.

Arrhythmogenic cardiomyopathy (ACM) is a myocardial disorder characterized by progressive injury and replacement of heart muscle with fibrous tissue, often accompanied by fatty tissue, creating a substrate for ventricular arrhythmias and sudden cardiac death. It commonly has a genetic basis, including variants affecting proteins involved in cell-to-cell adhesion. Disease may predominantly involve the right ventricle, the left ventricle, or both, and electrical abnormalities can precede obvious structural changes. Some patients experience inflammatory episodes with chest pain and myocardial injury resembling myocarditis. Cardiac MRI assesses ventricular volumes, systolic function, regional wall motion, and myocardial scar using late gadolinium enhancement. These findings contribute to diagnosis and risk assessment alongside electrocardiography, rhythm monitoring, family history, and genetic testing.

Alcoholic cardiomyopathy (ACM) is an acquired form of dilated cardiomyopathy caused by prolonged heavy alcohol consumption, characterized by ventricular enlargement and impaired myocardial contraction. Alcohol and its metabolites can injure cardiomyocytes through mechanisms including oxidative stress, mitochondrial dysfunction and disturbed cellular calcium handling, leading to myocyte loss and fibrosis. Patients may develop heart failure, arrhythmias and thromboembolic complications. Diagnosis relies on the alcohol exposure history, evidence of cardiac dysfunction and exclusion of other causes of cardiomyopathy. Cardiac MRI measures ventricular volumes and systolic function and can identify myocardial fibrosis using late gadolinium enhancement, although enhancement patterns are not specific enough to establish alcohol as the cause. Abstinence and guideline-directed heart failure treatment may allow improvement in ventricular function.

Acute coronary syndrome (ACS) is a spectrum of clinical conditions caused by an abrupt reduction in coronary blood flow, resulting in acute myocardial ischemia with or without infarction. It includes unstable angina, non-ST-elevation myocardial infarction and ST-elevation myocardial infarction. The usual mechanism is rupture or erosion of an atherosclerotic plaque with superimposed thrombosis. Assessment relies on symptoms, electrocardiography and serial cardiac troponin measurements, with urgent invasive coronary angiography when indicated. Coronary CT angiography can help exclude obstructive coronary disease in selected patients with suspected ACS whose initial assessment is inconclusive. Cardiac MRI can characterize myocardial injury, identify infarction and distinguish alternative diagnoses such as myocarditis or Takotsubo syndrome, particularly when coronary angiography shows no obstructive disease.

Aortic distensibility (AD) is a measure of how readily the aorta expands in response to an increase in blood pressure. It is commonly calculated as the change in aortic cross-sectional area between diastole and systole, divided by the diastolic area and pulse pressure. Higher distensibility indicates a more compliant vessel, whereas lower distensibility reflects greater aortic stiffness. Cardiac MRI can measure aortic area throughout the cardiac cycle, with blood pressure recorded to estimate the pressure driving expansion. The measurement depends on the aortic segment examined and the pressure measurement used. AD helps characterize vascular aging and arterial dysfunction and complements pulse wave velocity when assessing aortic stiffness and its relationship to cardiovascular disease.

Apparent diffusion coefficient (ADC) is a quantitative MRI measure of the effective mobility of water molecules within tissue, usually expressed in square millimetres per second. It is calculated from the reduction in MR signal produced by diffusion-sensitising gradients at different diffusion weightings. The word apparent reflects the influence of cellular membranes, tissue architecture and other barriers on water motion, rather than unrestricted diffusion alone. Lower ADC values generally indicate more restricted diffusion, although interpretation depends on tissue type, acquisition settings and contributions from microvascular perfusion. In oncology, ADC helps characterise lesions and assess treatment response alongside other imaging findings. In cardiac diffusion imaging, it characterises myocardial microstructure; diffusion tensor methods additionally describe the directional organisation of water movement.

Atrial fibrillation (AF) is a supraventricular arrhythmia characterized by disorganized atrial electrical activity and ineffective coordinated atrial contraction, usually producing an irregular ventricular rhythm. It is diagnosed electrocardiographically by the absence of distinct repeating P waves and irregular R–R intervals when atrioventricular conduction is intact. AF can cause palpitations, breathlessness and impaired cardiac function, and increases thromboembolic stroke risk through blood stasis, particularly in the left atrial appendage. Cardiac MRI can assess atrial and ventricular size, function and tissue characteristics, including atrial fibrosis using late gadolinium enhancement. Cardiac CT delineates pulmonary vein and left atrial anatomy for ablation planning and can evaluate the left atrial appendage for thrombus with appropriate contrast protocols. Irregular rhythms can complicate image acquisition and functional measurements.

Anderson-Fabry disease (AFD) is an X-linked lysosomal storage disorder caused by pathogenic variants in the GLA gene, resulting in deficient alpha-galactosidase A activity and accumulation of glycosphingolipids in multiple tissues. It can affect the heart, kidneys, nervous system and skin, with cardiac involvement causing left ventricular hypertrophy, myocardial fibrosis, conduction abnormalities and arrhythmias. Disease expression varies, and some patients present predominantly with cardiac manifestations. Cardiac MRI assesses ventricular structure and function and characterises myocardial tissue. Reduced native myocardial T1 can indicate lipid storage, while late gadolinium enhancement identifies focal myocardial injury or fibrosis, often in the basal inferolateral wall. T2 mapping can support assessment of associated myocardial inflammation. Imaging findings complement biochemical and genetic testing rather than establish the diagnosis alone.

Artificial intelligence (AI) is a field of computing that develops systems to perform tasks such as recognising patterns, making predictions and supporting decisions that ordinarily require human intelligence. In medical imaging, many AI systems use machine learning to learn statistical relationships from training data, including images, clinical measurements and patient outcomes. Applications in cardiac MRI and CT include image reconstruction and denoising, anatomical segmentation, quantification of cardiac function, disease classification and cardiovascular risk prediction. AI can also combine imaging findings with other clinical information to support differential diagnosis and treatment planning. Its outputs depend on the quality and representativeness of training data and require validation in the intended clinical population, assessment of bias and appropriate clinician oversight.

Artificial intelligence-based denoising (AID) is the use of trained computational models to reduce random noise in medical images while preserving diagnostically important structures. In CT, these models learn statistical relationships between noisy images and cleaner reference data, allowing them to suppress unwanted fluctuations while retaining anatomical edges and tissue detail. AID can be applied to reconstructed images, including those already processed with iterative reconstruction, and is distinct from the photon-counting detector hardware that acquires the data. Its clinical purpose is to improve image interpretability, particularly when noise is increased by low radiation exposure or greater patient attenuation. Performance requires validation because denoising can alter image texture, obscure small abnormalities, or affect quantitative measurements such as CT attenuation.

Amyloid light-chain (AL) amyloidosis is a systemic disorder in which monoclonal immunoglobulin light chains, usually produced by an abnormal plasma cell population, misfold and form amyloid deposits in tissues. Cardiac involvement causes myocardial infiltration and light-chain toxicity, leading to impaired relaxation, restrictive physiology, heart failure, and conduction abnormalities; reduced systolic function may occur in advanced disease. Cardiac MRI assesses ventricular structure and function and can demonstrate characteristic late gadolinium enhancement, elevated native T1, and expanded extracellular volume. These findings support recognition of cardiac amyloidosis but do not reliably distinguish AL from transthyretin amyloidosis. Diagnosis requires evaluation for monoclonal proteins and confirmation and typing of amyloid deposits when indicated, because treatment targets the underlying light-chain-producing clone.

Anomalous origin of the left coronary artery from the pulmonary artery (ALCAPA) is a congenital defect in which the left coronary artery arises from the pulmonary artery instead of the aorta. As pulmonary arterial pressure and oxygen content fall after birth, left coronary perfusion becomes inadequate, causing myocardial ischemia. In survivors with collateral vessels from the right coronary artery, blood may flow retrogradely into the pulmonary artery, producing coronary steal. Presentations include infantile heart failure, left ventricular dilation, ischemic mitral regurgitation, ventricular arrhythmias and sudden cardiac arrest. Coronary CT angiography delineates the abnormal origin and coronary course, while cardiac MRI assesses ventricular function, myocardial scar, perfusion and flow. Surgical repair aims to restore a two-coronary circulation supplied by the aorta.

Adverse left ventricular remodeling (ALVR) is a maladaptive change in the size, shape, structure, or function of the left ventricle following myocardial injury, particularly myocardial infarction. Loss of viable myocardium, infarct expansion, altered wall stress, and neurohormonal activation can lead to ventricular dilatation, a more spherical chamber, and impaired contraction. These changes may contribute to progressive heart failure and increased cardiovascular risk. Cardiac MRI assesses remodeling through reproducible measurements of ventricular volumes, mass, and ejection fraction, while tissue characterization identifies infarcted myocardium and associated injury. Serial examinations establish how ventricular structure and function evolve over time. Definitions vary across clinical and research settings, commonly using changes in indexed ventricular volumes or ejection fraction rather than a single universally accepted threshold.

Acute myocarditis (AM) is inflammation of the heart muscle with recent onset, associated with myocardial injury and most often triggered by infection or immune-mediated processes. It can present with chest pain, breathlessness, palpitations, heart failure, or electrical disturbances, including atrioventricular block and ventricular arrhythmias. Cardiac MRI provides noninvasive assessment of ventricular function and myocardial tissue injury. T2-weighted imaging and T2 mapping detect edema, while native T1 mapping, extracellular volume assessment, and late gadolinium enhancement identify changes associated with inflammation and myocardial injury. These findings support diagnosis in the appropriate clinical setting and help distinguish myocarditis from ischemic injury. Follow-up MRI can assess resolution of edema, persistent scar, and ventricular recovery; endomyocardial biopsy is reserved for selected clinical circumstances.

Acute myocardial infarction (AMI) is myocardial cell death caused by acute ischemia, most commonly following disruption of a coronary atherosclerotic plaque with thrombus formation and reduced coronary blood flow. Clinical diagnosis usually requires a rise or fall in cardiac troponin with evidence of acute myocardial ischemia, such as compatible symptoms, electrocardiographic changes or imaging findings. AMI includes presentations with and without ST-segment elevation. Cardiac MRI characterizes the location and extent of infarction using late gadolinium enhancement and assesses associated edema, microvascular obstruction and intramyocardial hemorrhage. Cine imaging measures ventricular volumes, systolic function and regional wall motion, while dedicated contrast-enhanced imaging can detect left ventricular thrombus. These findings help assess myocardial damage, complications and prognosis after infarction.

Antibody-mediated rejection (AMR) is immune-mediated injury to a transplanted organ caused by recipient antibodies directed against donor antigens, commonly human leukocyte antigens on the graft’s vascular endothelium. Antibody binding can activate complement and recruit inflammatory cells, producing microvascular injury that may impair graft function. In heart transplantation, AMR may occur with or without overt ventricular dysfunction and can contribute to chronic allograft injury. Diagnosis integrates endomyocardial biopsy findings, immunopathological evidence and testing for circulating donor-specific antibodies; antibodies alone do not establish rejection. Cardiac MRI can noninvasively assess ventricular function and myocardial tissue changes, including edema, but these findings are not specific for AMR and do not replace biopsy-based assessment when rejection is suspected.

Angiography-derived index of microcirculatory resistance (angio-IMR) is a calculated estimate of resistance in the coronary microvascular circulation obtained from invasive coronary angiography. It uses angiographic vessel geometry and estimates of coronary blood flow, often derived from contrast transit, together with pressure information or computational modelling to approximate the pressure–flow relationship across the microcirculation. Unlike conventional wire-based measurement of the index of microvascular resistance, it does not require a dedicated intracoronary pressure–temperature wire; calculation methods and requirements for induced hyperaemia vary. It is used to assess coronary microvascular dysfunction, including after reperfusion for acute myocardial infarction. Cardiac MRI provides complementary assessment of myocardial injury, infarct size and microvascular obstruction, which are related to, but distinct from, elevated microvascular resistance.

Angina with no obstructive coronary arteries (ANOCA) is a clinical syndrome of anginal symptoms in patients whose coronary arteries show no flow-limiting epicardial narrowing on coronary CT angiography or invasive angiography. It may reflect coronary microvascular dysfunction, epicardial coronary spasm, or microvascular spasm, although the underlying mechanism is not always established. Unlike ischaemia with no obstructive coronary arteries, ANOCA does not require objective demonstration of myocardial ischaemia. Stress perfusion cardiac MRI can assess myocardial blood supply and identify perfusion abnormalities consistent with ischaemia, while also evaluating ventricular function and alternative myocardial disease. Invasive coronary function testing can assess vasodilator reserve, microvascular resistance, and responses to acetylcholine to help distinguish mechanisms and guide treatment.

Apical hypertrophic cardiomyopathy (ApHCM) is a form of hypertrophic cardiomyopathy in which abnormal myocardial thickening predominantly affects the apex of the left ventricle and is not explained solely by hypertension or other loading conditions. Apical thickening can reduce the ventricular cavity and produce a characteristic spade-shaped appearance, with impaired relaxation and sometimes midventricular obstruction. It may be associated with chest pain, arrhythmias, myocardial fibrosis, or an apical aneurysm. Cardiac MRI is particularly useful when echocardiography does not clearly visualize the apex, allowing accurate assessment of wall thickness, hypertrophy distribution, ventricular function, and aneurysm formation. Late gadolinium enhancement identifies myocardial scar or fibrosis, contributing to clinical assessment and risk stratification alongside symptoms, rhythm monitoring, and other established risk factors.

Antiphospholipid syndrome (APS) is an autoimmune disorder characterized by arterial, venous or small-vessel thrombosis, or specific pregnancy complications, in association with persistently positive antiphospholipid antibodies. These include lupus anticoagulant, anticardiolipin antibodies and anti–beta-2 glycoprotein I antibodies; persistence is established by repeat testing at least 12 weeks apart. The antibodies promote clotting through effects on vascular cells, platelets and coagulation pathways. APS may occur alone or alongside another autoimmune disease, particularly systemic lupus erythematosus. Cardiac manifestations include valve abnormalities, coronary thrombosis, myocardial ischemia and intracardiac thrombi. Cardiac MRI can assess ventricular function, characterize myocardial injury and help distinguish thrombus from other intracardiac masses, but imaging does not establish APS itself. Diagnosis requires interpretation of clinical events and laboratory findings together.

Aortic regurgitation (AR) is backward flow of blood from the aorta into the left ventricle during diastole because the aortic valve does not close effectively. It can result from abnormalities of the valve leaflets or dilation of the aortic root. Chronic regurgitation produces left ventricular volume overload, leading to ventricular dilation and compensatory hypertrophy; progressive disease may cause contractile dysfunction and heart failure. Echocardiography is the primary imaging test, while cardiac MRI provides reproducible measurements of ventricular volumes, mass and ejection fraction. Phase-contrast MRI quantifies aortic forward and reverse flow to estimate regurgitant volume and fraction. MRI can also assess myocardial fibrosis, helping characterize ventricular damage and supporting decisions about surveillance and valve intervention alongside symptoms and other clinical findings.

Acute respiratory distress syndrome (ARDS) is an acute inflammatory lung injury characterised by increased alveolar–capillary permeability, pulmonary oedema, and hypoxaemic respiratory failure not primarily explained by cardiac failure or fluid overload. It can follow pneumonia, sepsis, aspiration, trauma, or other severe insults. Injury to the pulmonary endothelium and alveolar epithelium allows fluid to enter air spaces, impairs gas exchange, reduces lung compliance, and produces heterogeneous areas of collapse and aeration. Chest imaging demonstrates bilateral opacities; CT can characterise ground-glass opacity, consolidation, and the distribution of poorly aerated lung while assessing complications or alternative diagnoses. Quantitative CT can evaluate regional aeration and recruitment, while image registration and computational modelling can estimate regional deformation and mechanical stress during ventilation.

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a myocardial disease characterized by progressive loss of heart muscle cells and replacement with fibrous and fatty tissue, predominantly affecting the right ventricle, although left ventricular involvement can occur. It is commonly inherited and often associated with variants in genes encoding desmosomal proteins, which help maintain mechanical connections between heart muscle cells. The resulting tissue injury and scarring create a substrate for ventricular arrhythmias, sudden cardiac death, and ventricular dysfunction. Cardiac MRI assesses ventricular volumes, systolic function, regional wall-motion abnormalities, and myocardial scar using late gadolinium enhancement. Diagnosis integrates imaging with electrocardiographic findings, arrhythmia characteristics, family history, and genetic information; neither myocardial fat nor an isolated MRI abnormality is sufficient to establish the diagnosis.

Aortic stenosis (AS) is narrowing of the aortic valve opening that obstructs blood flow from the left ventricle into the aorta during systole. It most commonly results from progressive calcification of the valve leaflets, although congenital bicuspid valve anatomy and rheumatic disease are other causes. The obstruction increases left ventricular pressure load and can lead to hypertrophy, myocardial fibrosis, heart failure, angina or syncope. Echocardiography is the primary method for assessing severity using valve area, flow velocity and pressure gradients. Cardiac MRI provides complementary assessment of ventricular volumes, function, hypertrophy and myocardial fibrosis, and can quantify transvalvular flow. CT characterizes valve calcification and aortic anatomy and supports procedural planning for transcatheter aortic valve implantation. Interpretation of severity requires consideration of flow state and clinical symptoms.

Abdominal subcutaneous adipose tissue (ASAT) is the fat-containing connective tissue beneath the skin of the abdomen and superficial to the abdominal wall musculature and fascia. It is anatomically distinct from visceral adipose tissue, which lies within the abdominal cavity around internal organs. ASAT stores energy in adipocytes and contributes to endocrine and metabolic regulation through the release of adipokines and fatty acids. Abdominal MRI can distinguish fat from water using their different resonance frequencies, allowing segmentation and measurement of this depot without ionising radiation. CT can also quantify ASAT using its characteristic low attenuation. Measuring ASAT alongside visceral and other fat depots helps characterise body composition and investigate cardiometabolic risk beyond weight or body mass index alone.

Asymmetric septal hypertrophy (ASH) is a pattern of left ventricular thickening in which the interventricular septum is disproportionately thicker than the opposing free wall. It is a morphological finding rather than a diagnosis and is classically associated with hypertrophic cardiomyopathy, but can also occur with pressure overload, infiltrative disease, and other causes of left ventricular hypertrophy. Depending on its location and severity, septal thickening may contribute to left ventricular outflow tract obstruction, particularly when accompanied by systolic anterior motion of the mitral valve. Cardiac MRI assesses the distribution and extent of hypertrophy, measures regional wall thickness, and evaluates ventricular function. Tissue characterisation using late gadolinium enhancement and mapping techniques helps distinguish underlying causes and identify associated myocardial fibrosis or infiltration.

Arterial switch operation (ASO) is an anatomical corrective procedure for dextro-transposition of the great arteries, in which the aorta arises from the right ventricle and the pulmonary artery from the left ventricle. The great arteries are divided and reconnected to the appropriate ventricular outflow tracts, and the coronary arteries are transferred to the reconstructed aortic root. The procedure commonly includes the LeCompte maneuver, which positions the pulmonary arteries anterior to the ascending aorta. Long-term cardiac MRI assesses ventricular volumes, function and myocardial deformation, as well as blood flow and narrowing in the reconstructed pulmonary arteries. MRI and CT can also evaluate the reconstructed aortic root, while coronary CT angiography can assess transferred coronary artery anatomy when clinically indicated.

Transthyretin amyloidosis (ATTR) is a systemic disorder in which misfolded transthyretin, a protein produced mainly by the liver, forms insoluble amyloid fibrils that accumulate in tissues. It occurs either as hereditary disease caused by pathogenic variants in the transthyretin gene or as wild-type disease without such variants. Deposits commonly affect the heart and peripheral nerves, with manifestations varying by disease type. Cardiac involvement can cause increased ventricular wall thickness, impaired relaxation, heart failure and conduction abnormalities. Cardiac MRI assesses ventricular structure and function and characterises myocardial involvement through late gadolinium enhancement, native T1 mapping and extracellular volume measurement. These findings support recognition and assessment of cardiac amyloidosis but do not reliably distinguish ATTR from light-chain amyloidosis; definitive typing requires additional testing.

Transthyretin amyloid cardiomyopathy (ATTR-CM) is a disease caused by extracellular deposition of misfolded transthyretin protein as amyloid fibrils in the myocardium. It occurs with either age-related deposition of wild-type transthyretin or inherited pathogenic variants in the transthyretin gene. Amyloid accumulation increases ventricular wall thickness and stiffness, impairs diastolic filling, and can cause heart failure, conduction disease and arrhythmias. Cardiac MRI assesses ventricular structure and function and supports recognition through characteristic late gadolinium enhancement, elevated native T1 and increased extracellular volume. These findings indicate cardiac amyloid involvement but do not reliably distinguish transthyretin from light-chain amyloidosis. Diagnosis therefore integrates imaging with testing for monoclonal proteins, bone-avid tracer scintigraphy and, when necessary, tissue biopsy; genetic testing distinguishes hereditary from wild-type disease.

Angular trajectory of the vestibular aqueduct (ATVA) is an imaging measurement describing the angular course of the vestibular aqueduct, a small bony canal connecting the vestibule of the inner ear with the posterior surface of the petrous temporal bone. The aqueduct contains the endolymphatic duct, which connects to the endolymphatic sac and participates in inner-ear fluid regulation. ATVA is assessed on high-resolution temporal bone CT by identifying the aqueduct’s course relative to anatomical reference directions. Photon-counting CT can support this assessment through detailed depiction of small bony structures. The measurement is used to characterize vestibular aqueduct morphology and investigate anatomical patterns associated with disorders such as Ménière disease, rather than serving as a standalone diagnostic test.

Atrioventricular (AV) describes anatomical, electrical or mechanical relationships between the atria and ventricles of the heart. The atrioventricular valves, comprising the mitral and tricuspid valves, regulate blood flow from atria to ventricles. Electrical impulses normally pass through the AV node and His bundle, with nodal conduction slowing activation so that atrial contraction precedes ventricular contraction. Disturbances of this conduction can cause AV block, while distinct conduction pathways within or near the AV node can support reentrant tachycardia. In cardiac imaging, AV coupling refers to the functional relationship between atrial and ventricular filling, contraction and chamber remodeling. Cardiac MRI can quantify chamber volumes and myocardial deformation to assess this interaction, whereas electrical AV conduction is assessed primarily by electrocardiography and electrophysiological testing.

Atrioventricular block (AVB) is delayed or interrupted conduction of electrical impulses from the atria to the ventricles through the atrioventricular node or the His–Purkinje system. First-degree block prolongs atrioventricular conduction without losing ventricular beats; second-degree block intermittently prevents impulses from reaching the ventricles; and third-degree block produces complete atrioventricular dissociation. Causes include conduction-system degeneration, myocardial inflammation, ischemia, infiltrative disease and medications that slow conduction. Clinical effects range from no symptoms to bradycardia, syncope and hemodynamic compromise, with some patients requiring pacing. Electrocardiography establishes the diagnosis and degree of block. Cardiac MRI can investigate associated myocardial disease, including edema and non-ischemic injury or fibrosis, but does not directly measure electrical conduction or replace electrocardiographic assessment.

Arteriovenous fistula (AVF) is an abnormal or deliberately created direct connection between an artery and a vein that bypasses the intervening capillary bed. Blood flows from the higher-pressure arterial circulation into the venous system, potentially increasing venous pressure and cardiac workload. Spinal AVFs can cause venous congestion, impaired spinal cord perfusion and progressive neurological dysfunction. CT angiography can depict abnormal vessels and help localize the fistula, while catheter angiography provides detailed assessment of its vascular anatomy. Surgically created AVFs provide high-flow vascular access for hemodialysis in advanced kidney disease, but may contribute to high-output heart failure. Cardiac MRI can quantify ventricular volumes, function and blood flow when assessing the cardiovascular effects of an AVF.

Aortic valve replacement (AVR) is a procedure that replaces a diseased aortic valve with a prosthetic valve to relieve obstruction to left ventricular outflow or prevent backward flow from the aorta into the ventricle. Replacement may be performed surgically using a mechanical or biological prosthesis, or by transcatheter implantation of a biological valve in suitable patients. It is used to treat clinically significant aortic stenosis or aortic regurgitation, with timing guided by symptoms, valve severity, ventricular function and other clinical factors. Cardiac MRI can quantify regurgitant flow, ventricular volumes and systolic function, and characterize myocardial fibrosis before intervention. After replacement, it can assess changes in ventricular size, mass and function, as well as residual regurgitation when appropriate.

Body mass index (BMI) is an anthropometric measure calculated by dividing body weight in kilograms by the square of height in metres, expressed in kilograms per square metre. It is used to classify weight status and support assessment of obesity-related cardiometabolic risk, including diabetes and cardiovascular disease. BMI reflects weight relative to height but does not distinguish fat from muscle or identify the distribution of adipose tissue. Its interpretation therefore depends on factors such as age, ethnicity, muscularity and clinical context; fluid retention can also affect body weight. In cardiac imaging research, BMI commonly characterises participants or adjusts analyses, while MRI and CT can provide more direct measurements of regional adiposity and cardiac structure and function.

Balanced steady-state free precession (bSSFP) is an MRI pulse sequence that uses repeated radiofrequency excitations with balanced magnetic field gradients to maintain a steady state of magnetization. The net gradient effect over each repetition is zero along all three spatial axes, allowing signal from successive excitations to contribute coherently. Image contrast depends largely on the ratio of tissue T2 to T1 relaxation times, producing bright blood and clear contrast between blood and myocardium. Its high signal efficiency makes it widely used for cardiac cine imaging to assess ventricular volumes, ejection fraction, wall motion and valve movement, and for real-time or fetal cardiac imaging. It can be combined with different sampling trajectories and accelerated reconstruction methods, but is susceptible to banding artifacts caused by magnetic field inhomogeneity.

Cardiac amyloidosis (CA) is an infiltrative cardiomyopathy caused by extracellular deposition of misfolded proteins as amyloid fibrils within the heart. These deposits increase myocardial stiffness, impair ventricular filling and may affect atrial function, valves and the conduction system. The principal forms involve immunoglobulin light chains or transthyretin, although other hereditary amyloid proteins can cause cardiac involvement. Cardiac MRI assesses chamber structure and function and characterizes tissue using late gadolinium enhancement, native T1 mapping and extracellular volume measurement. Diffuse subendocardial or transmural enhancement and expanded extracellular volume support recognition of amyloid infiltration and help distinguish it from other causes of increased ventricular wall thickness. Imaging alone does not reliably identify the amyloid protein; typing requires appropriate laboratory, nuclear imaging, genetic or tissue investigations.

Catheter ablation (CA) is a minimally invasive procedure that treats cardiac arrhythmias by creating targeted lesions in heart tissue to interrupt abnormal electrical activity. Catheters are advanced through blood vessels into the heart, where electrical mapping helps identify treatment sites. Radiofrequency energy heats tissue, cryothermal energy freezes it, and pulsed-field ablation uses electrical pulses to disrupt cell membranes. For atrial fibrillation, the principal target is electrical isolation of the pulmonary veins, whose myocardial sleeves commonly generate arrhythmia-triggering impulses. Cardiac MRI can assess atrial and ventricular size and function, characterize myocardial scar with late gadolinium enhancement, and evaluate associated cardiomyopathy. These findings can inform clinical assessment before ablation and document subsequent changes in cardiac function and remodeling.

Coronary artery bypass grafting (CABG) is a surgical procedure that restores blood supply to the myocardium by creating alternative routes around narrowed or blocked coronary arteries. Arterial or venous conduits, commonly an internal thoracic artery or a saphenous vein, deliver blood to coronary segments beyond the obstruction. CABG is used in selected patients with coronary artery disease to relieve ischemic symptoms and, in appropriate clinical settings, improve prognosis. It may be performed alone or alongside valve surgery. Cardiac MRI can assess ventricular volumes, systolic function, inducible ischemia and myocardial scar before or after surgery. Late gadolinium enhancement helps characterize irreversible myocardial injury, while cine and perfusion imaging support evaluation of myocardial function and blood supply.

Coronary artery calcium (CAC) is mineral deposition within atherosclerotic plaques in the coronary artery walls, visible on CT as high-attenuation material because calcium strongly attenuates X-rays. Its presence indicates coronary atherosclerosis, and its burden provides information about future cardiovascular risk. CAC is commonly assessed on non-contrast, ECG-gated cardiac CT and quantified using the Agatston score, which incorporates the area and attenuation of calcified lesions. It can also be detected opportunistically on thoracic CT performed for other indications. In imaging workflows, CAC may denote the non-contrast calcium-assessment scan itself. CAC does not directly measure coronary narrowing, and its absence does not exclude non-calcified plaque. Assessment supports preventive treatment decisions alongside clinical risk factors.

Coronary artery calcium scoring (CACS) is a non-invasive CT method for quantifying calcified atherosclerotic plaque in the coronary arteries. It usually uses an electrocardiogram-gated scan without intravenous contrast, identifying calcium by its high X-ray attenuation. The commonly used Agatston score combines the area and density of detected calcifications to produce a measure of overall coronary calcium burden. Calcium scores help refine cardiovascular risk assessment and guide preventive treatment decisions, particularly when risk estimated from conventional clinical factors is uncertain. A higher score indicates a greater burden of calcified coronary atherosclerosis, but does not directly measure arterial narrowing. A score of zero does not exclude non-calcified plaque or obstructive coronary disease, especially in symptomatic or younger patients.

Coronary artery disease (CAD) is disease of the arteries supplying the heart muscle, most commonly caused by atherosclerotic plaque accumulation within their walls. Plaques may narrow the arterial lumen and limit myocardial blood flow, particularly during increased demand, or rupture or erode and trigger thrombosis, causing an acute coronary syndrome. CAD includes both obstructive and nonobstructive atherosclerosis and may be present without symptoms. Coronary CT angiography assesses coronary anatomy, stenosis severity and plaque characteristics; photon-counting CT provides an additional detector technology for this assessment. Stress perfusion cardiac MRI evaluates the functional consequences of impaired coronary blood supply by detecting inducible myocardial ischemia, while late gadolinium enhancement identifies myocardial infarction and scar. Anatomical and functional findings together help guide preventive treatment and decisions about revascularization.

Cardiac allograft vasculopathy (CAV) is a progressive disease of the coronary circulation in a transplanted heart, characterized by diffuse thickening of the arterial intima and narrowing of epicardial coronary arteries and smaller intramyocardial vessels. Immune-mediated endothelial injury, together with nonimmune cardiovascular risk factors, promotes vascular remodeling and impaired myocardial blood supply. CAV can cause ischemia, myocardial fibrosis, graft dysfunction and heart failure; typical angina may be absent because the transplanted heart is denervated. Coronary angiography and intravascular ultrasound are used to assess coronary involvement. Cardiac MRI provides complementary evaluation through ventricular function assessment, stress perfusion imaging and myocardial perfusion reserve measurement, while late gadolinium enhancement can identify associated myocardial scar.

Cone-beam CT (CBCT) is an X-ray imaging technique that acquires three-dimensional images using a cone-shaped beam and a two-dimensional detector rotating around the patient or body part. Projections obtained from multiple angles are reconstructed into a volumetric dataset, allowing structures to be viewed in different planes. CBCT provides high spatial resolution for assessing bone, teeth, small joints and implanted devices, although soft-tissue contrast is generally limited compared with conventional CT. Clinical applications include evaluating cochlear implant electrode position and surrounding temporal bone anatomy, as well as depicting joint calcifications and mineral deposits. Calcification appearance alone does not reliably establish its chemical composition. Image quality and radiation exposure depend on the scanner, field of view and acquisition protocol.

Chronic coronary syndrome (CCS) encompasses clinical presentations arising from persistent structural or functional abnormalities of the coronary circulation outside an acute coronary event. These abnormalities may cause an imbalance between myocardial oxygen supply and demand, producing exertional angina, breathlessness or silent ischemia. Causes include obstructive atherosclerotic coronary disease, coronary microvascular dysfunction, vasospasm and less common abnormalities affecting coronary blood flow. The condition is dynamic rather than necessarily stable and can progress to acute coronary syndrome. Stress perfusion cardiac MRI assesses inducible ischemia, while cine imaging and late gadolinium enhancement evaluate ventricular function and myocardial scar. Coronary CT angiography assesses coronary anatomy and atherosclerotic plaque. Management combines risk-factor modification, exercise, preventive and antianginal medication, and revascularization when appropriate.

Cardiac computed tomography (CCT) is an X-ray imaging technique that produces cross-sectional and three-dimensional images of the heart and surrounding cardiovascular structures. It measures X-ray attenuation from multiple angles and reconstructs images, usually synchronised with the electrocardiogram to reduce cardiac motion artefacts. Iodinated contrast material is commonly used to visualise the coronary arteries, cardiac chambers and major vessels, while non-contrast acquisitions can quantify coronary calcium. Clinical applications include evaluating coronary artery disease, congenital abnormalities, valve anatomy and planning structural heart interventions. When images are acquired across the cardiac cycle, CCT can also assess ventricular volumes, ejection fraction and myocardial deformation, including strain. These functional assessments require suitable temporal resolution and acquisition protocols, with attention to radiation exposure and contrast-related risks.

Coronary CT angiography (CCTA) is a noninvasive, contrast-enhanced CT examination that depicts the coronary arteries, their lumen and atherosclerotic plaque. Intravenous iodinated contrast increases X-ray attenuation within the blood, while electrocardiographic synchronisation allows images to be acquired or reconstructed during selected phases of the cardiac cycle to limit motion. Thin-section images and multiplanar reconstructions are used to assess coronary anatomy, stenosis, plaque characteristics, anomalous origins and, in suitable patients, bypass grafts or coronary stents. CCTA is used to investigate suspected coronary artery disease, inform cardiovascular risk assessment and support planning of coronary interventions. It principally assesses epicardial coronary anatomy; a normal examination does not exclude coronary microvascular dysfunction, which may require functional testing.

Cardiac diffusion tensor imaging (cDTI) is an MRI technique that characterizes myocardial microstructure by measuring the direction and magnitude of water diffusion within heart muscle. Diffusion-weighted images acquired in multiple directions are used to estimate a diffusion tensor, which describes the preferential movement of water along myocardial cell bundles rather than across them. Derived measures include mean diffusivity, fractional anisotropy and estimates of local myocardial orientation, providing information about tissue organization beyond conventional anatomical imaging. Cardiac and respiratory motion can strongly affect these measurements, so acquisitions use cardiac synchronization, respiratory motion control and specialized diffusion gradients that reduce sensitivity to tissue movement. cDTI is primarily a research tool for investigating myocardial architecture, remodeling and structural alterations associated with cardiomyopathies or ischemic injury.

Contrast-enhanced MR angiography (CE-MRA) is a magnetic resonance imaging technique that visualizes blood vessels after intravenous administration of a gadolinium-based contrast agent. The agent shortens the T1 relaxation time of blood, producing high vascular signal on rapidly acquired T1-weighted images. Acquisition is timed to the contrast bolus to emphasize the arterial or venous circulation and limit unwanted enhancement of surrounding tissues or other vessels. Three-dimensional datasets can be reformatted to assess vessel course, caliber, narrowing, occlusion, aneurysms, and congenital vascular abnormalities. In cardiovascular imaging, CE-MRA is used to evaluate the aorta, pulmonary arteries, and other major vessels without ionizing radiation. Image quality depends on bolus timing, spatial resolution, and motion control; contrast use requires consideration of kidney function and relevant safety guidance.

Computational fluid dynamics (CFD) is a numerical method for simulating fluid motion, used in cardiovascular imaging research to model blood flow within the heart and blood vessels. It solves equations governing conservation of mass and momentum within a computational representation of anatomy, using assumptions about blood properties and prescribed boundary conditions. Cardiac MRI can supply chamber geometry, time-resolved wall motion and flow measurements to construct and assess these models. CFD estimates velocity and pressure fields and derived quantities such as wall shear stress, helping characterize abnormal flow, ventricular filling and the hemodynamic effects of cardiovascular disease or interventions. Its accuracy depends on image quality, model assumptions and validation against experimental or measured flow data.

Coronary flow reserve (CFR) is the ratio of coronary blood flow during maximal vasodilation to blood flow at rest, expressing the coronary circulation’s capacity to meet increased myocardial oxygen demand. It reflects the combined effects of epicardial coronary artery disease and microvascular function, and is also influenced by resting flow and hemodynamic conditions. Invasive assessment commonly uses a coronary guidewire with Doppler velocity or thermodilution measurements before and during pharmacologically induced hyperemia. Reduced CFR indicates impaired vasodilator capacity; when obstructive coronary disease is excluded, it supports coronary microvascular dysfunction. Cardiac MRI can complement invasive testing by assessing stress myocardial perfusion, ventricular function and tissue abnormalities. CFR is interpreted alongside anatomical findings and microvascular resistance measurements to investigate ischemic symptoms and characterize coronary physiological impairment.

Congenital heart disease (CHD) comprises structural abnormalities of the heart or great vessels that arise during fetal development and are present at birth, although some are diagnosed later in life. These defects include abnormal connections, septal defects, valve malformations and underdevelopment or obstruction of cardiac chambers or vessels. Their physiological effects range from minor disturbances to substantial shunting, cyanosis, pressure or volume overload, and impaired cardiac function. Cardiac MRI assesses cardiovascular anatomy, ventricular volumes and function, blood flow, shunt magnitude and postoperative complications without ionising radiation. Flow-sensitive MRI can quantify flow through individual vessels and valves, supporting surveillance and treatment planning. Cardiac CT provides complementary high-resolution anatomical assessment, particularly of coronary arteries, extracardiac vessels and complex surgical reconstructions.

Cardiac implantable electronic devices (CIEDs) are electronic systems placed within the body to monitor heart rhythm, deliver electrical pacing, or treat dangerous arrhythmias. They include pacemakers, implantable cardioverter-defibrillators, cardiac resynchronization devices and implantable cardiac monitors. Therapeutic devices sense cardiac electrical activity and deliver impulses or shocks when indicated; resynchronization systems coordinate ventricular activation in selected patients with heart failure. Cardiac MRI can assess myocardial function, perfusion and tissue abnormalities in patients with CIEDs, but requires device identification, appropriate programming, monitoring and a device-specific safety protocol. Device generators and leads may cause MRI signal loss or distortion and CT streak artifacts, potentially obscuring adjacent anatomy or affecting quantitative measurements. Imaging protocols and artifact-reduction methods help limit these effects.

Chronic kidney disease (CKD) is an abnormality of kidney structure or function that persists for at least three months and has implications for health. It is diagnosed by sustained reduction in glomerular filtration rate or evidence of kidney damage, such as albuminuria, and classified by cause, filtration rate and albuminuria severity. CKD increases cardiovascular risk through interacting mechanisms that include hypertension, fluid overload, anemia and disturbances of mineral metabolism. Cardiac MRI can assess associated ventricular hypertrophy, chamber remodeling, systolic function and myocardial strain, while tissue characterization can help evaluate fibrosis and other myocardial abnormalities. Kidney function also informs imaging safety: the need for iodinated CT contrast or gadolinium-based MRI contrast should be assessed individually, with appropriate agent selection and precautions in advanced disease.

Coronary microvascular dysfunction (CMD) is impaired regulation of blood flow by the small coronary arteries and arterioles that supply the myocardium. It can result from endothelial dysfunction, abnormal vascular smooth muscle responses, microvascular spasm or structural remodeling, limiting the ability to increase myocardial blood flow during stress. CMD can cause myocardial ischemia and angina even without obstructive disease in the major coronary arteries and may coexist with other cardiac conditions. Stress-perfusion cardiac MRI can assess its functional consequences by measuring myocardial blood flow and perfusion reserve, although abnormal perfusion requires interpretation alongside epicardial coronary disease and other causes. Coronary CT angiography helps assess or exclude obstructive epicardial disease, while invasive coronary function testing can characterize microvascular resistance and vasomotor abnormalities.

Cardiac magnetic resonance (CMR) is a noninvasive imaging modality that uses a strong magnetic field, radiofrequency pulses and signals from hydrogen nuclei to produce images of the heart and major vessels without ionizing radiation. Acquisition is usually synchronized with the cardiac cycle to limit motion and measure ventricular volumes, myocardial mass and systolic function. Different sequences assess blood flow, perfusion, edema, iron deposition and tissue composition. Gadolinium-based contrast can reveal myocardial injury or fibrosis through late gadolinium enhancement and support perfusion assessment. CMR is used to investigate cardiomyopathies, ischemic injury, myocarditis, congenital heart disease and other cardiovascular disorders, and can complement echocardiography and biopsy in selected transplant assessments. Its tissue characterization also informs arrhythmic risk assessment and treatment planning.

Cardiac MRI extracellular volume (CMR-ECV) is a quantitative estimate of the proportion of myocardial tissue occupied by the extracellular space, including the interstitium and blood plasma. It is usually calculated from myocardial and blood T1 measurements obtained before and after administration of an extracellular gadolinium-based contrast agent, with correction for the patient’s hematocrit. Gadolinium distributes outside intact cells, allowing changes in relaxation rates to estimate the extracellular volume fraction. An increased value can reflect extracellular expansion caused by fibrosis, edema or infiltrative disease, but is not specific to any single diagnosis. CMR-ECV complements late gadolinium enhancement by quantifying diffuse as well as regional myocardial abnormalities and is used to characterize cardiomyopathies and myocardial injury, including changes following infarction.

Cardiac magnetic resonance feature tracking (CMR-FT) is a post-processing technique that quantifies myocardial motion and deformation from routinely acquired cine cardiac MRI images. Software follows image features, such as tissue patterns and myocardial boundaries, through the cardiac cycle to estimate displacement and calculate strain, the relative change in tissue length, and strain rate. It can assess longitudinal, circumferential and radial deformation of the ventricles, as well as atrial deformation associated with reservoir, conduit and contractile function. Unlike myocardial tagging, it does not require a dedicated acquisition that marks the tissue. CMR-FT complements chamber volumes and ejection fraction when evaluating cardiomyopathies, ventricular pressure or volume overload, and atrial dysfunction. Measurements depend on image quality, temporal resolution, contour placement and software implementation, so results from different analysis platforms are not necessarily interchangeable.

Cardiac MR fingerprinting (cMRF) is a quantitative MRI technique that estimates multiple myocardial tissue properties from a single acquisition. It varies acquisition settings, such as radiofrequency flip angles and preparation pulses, to produce signal evolutions that depend on tissue characteristics. These signal patterns are compared with simulated responses or analyzed using computational models to estimate parameters, most commonly T1 and T2 relaxation times. Cardiac implementations account for heart motion and variable heartbeat timing, often using electrocardiographic synchronization. Extensions can also estimate T2* and fat fraction. The resulting maps support myocardial tissue characterization, including assessment of abnormalities associated with edema, fibrosis, iron deposition, or fat. Accurate quantification depends on modeling relevant physical effects, including magnetization transfer, and the technique remains an evolving research approach.

Convolutional neural network (CNN) is a deep-learning model that processes images using learned filters applied across local regions to detect spatial patterns. Successive layers combine simple features, such as edges and textures, into more complex representations of anatomy or image structure. During training, the network adjusts its parameters using examples and a task-specific objective. In cardiac MRI, CNNs can segment cardiac chambers and myocardium, supporting measurements of ventricular volumes, mass and function. In CT, including photon-counting CT, they can reduce image noise to support interpretation of coronary anatomy and plaque. Performance depends on training data and validation; segmentation errors or alteration of subtle findings during denoising can affect clinical measurements and interpretation.

Contrast-to-noise ratio (CNR) is a quantitative measure of how clearly a structure or tissue can be distinguished from a reference tissue or background relative to image noise. It is commonly calculated as the difference between their mean image signals or CT attenuation values divided by a specified estimate of noise, usually the standard deviation measured in a suitable region of interest. Calculation methods vary, so comparisons require consistent reference tissues and noise definitions. In CT, CNR depends on factors including radiation dose, tissue composition, contrast enhancement, photon energy and reconstruction method. It is used to compare acquisition protocols and assess whether clinically relevant structures remain distinguishable when reducing radiation exposure, although it does not fully capture spatial resolution, noise texture or diagnostic performance.

Coarctation of the aorta (CoA) is a congenital narrowing of the aortic lumen, most commonly at the aortic isthmus near the insertion of the ductus arteriosus. The obstruction increases left ventricular pressure load and can cause upper-body hypertension, reduced lower-body perfusion and development of collateral arteries. Severe neonatal disease may become critical when the ductus closes, while milder disease can present later with hypertension or diminished femoral pulses. Cardiac MRI assesses the location and extent of narrowing, aortic arch anatomy, collateral circulation, blood flow and ventricular function without ionizing radiation; CT provides detailed anatomical assessment when appropriate. Treatment involves surgical repair or catheter-based intervention, including stenting in suitable patients. Lifelong surveillance is needed for recurrent narrowing, persistent hypertension and aortic aneurysm formation.

Cardiopulmonary exercise testing (CPET) is a physiological assessment that measures respiratory gas exchange during progressively increasing exercise, usually on a cycle ergometer or treadmill. Breath-by-breath measurements of oxygen uptake, carbon dioxide production and ventilation are combined with heart rate, electrocardiographic monitoring, blood pressure and symptoms to evaluate the integrated response of the cardiovascular, respiratory and muscular systems. Measures such as peak oxygen uptake, ventilatory threshold and ventilatory efficiency help quantify exercise capacity and identify patterns suggesting cardiac, pulmonary or peripheral limitations. CPET is used to investigate unexplained exertional symptoms, assess functional status and guide management in conditions including heart failure and congenital heart disease. It complements cardiac MRI by relating structural and ventricular functional findings to exercise performance.

Calcium pyrophosphate (CPP) is a calcium-containing crystalline material that can accumulate in articular cartilage, fibrocartilage and other joint tissues, usually as calcium pyrophosphate dihydrate crystals. These deposits are associated with calcium pyrophosphate deposition disease, which may be asymptomatic or cause acute inflammatory arthritis, chronic arthritis and osteoarthritis-like joint damage. Cartilage calcification visible on imaging is termed chondrocalcinosis, although this finding is not specific to CPP deposits. Identification of characteristic crystals in synovial fluid supports diagnosis. Ultrasound and CT can demonstrate deposits and their anatomical distribution. Dual-energy and photon-counting CT provide energy-dependent attenuation information that is being investigated for distinguishing CPP from other calcium-containing deposits, including basic calcium phosphate crystals.

Cardiac resynchronization therapy (CRT) is a device-based treatment that coordinates ventricular contraction in selected patients with heart failure, reduced left ventricular ejection fraction and electrical conduction delay, particularly left bundle branch block. Conventional CRT uses pacing leads to stimulate the right and left ventricles with carefully timed electrical impulses, reducing the mechanical inefficiency caused by asynchronous activation. It can improve cardiac function, symptoms and ventricular remodeling, and may be delivered by a pacemaker or a device that also provides defibrillation. Cardiac MRI can quantify ventricular volumes and function and characterize myocardial scar using late gadolinium enhancement. Scar burden and location can help assess the likelihood of response and inform pacing strategy, while follow-up imaging evaluates changes in ventricular function and remodeling.

Cardiac sarcoidosis (CS) is an inflammatory disease in which non-necrotizing granulomas affect the heart, either as part of systemic sarcoidosis or without clinically apparent involvement of other organs. Myocardial inflammation and subsequent fibrosis can disrupt electrical conduction and impair ventricular function, causing atrioventricular block, ventricular arrhythmias, heart failure, or sudden cardiac death. Cardiac MRI assesses ventricular structure and function and detects myocardial injury through late gadolinium enhancement, commonly with a patchy, nonischemic distribution. T2-based imaging can support assessment of myocardial edema, while fluorodeoxyglucose PET helps identify active inflammation. Imaging findings are interpreted alongside clinical features and other investigations because no single imaging pattern is diagnostic. Assessment informs immunosuppressive treatment, arrhythmia management, and consideration of implanted cardiac devices.

Cerebrospinal fluid (CSF) is the clear fluid that occupies the brain’s ventricles and the subarachnoid spaces surrounding the brain and spinal cord. Produced mainly by the choroid plexuses, it provides buoyancy and mechanical protection, supports chemical homeostasis, and participates in waste clearance from the central nervous system. CSF sampling allows measurement of proteins, antibodies, cells, and other biomarkers used to investigate neurological disease, infection, and inflammation. MRI can assess CSF spaces, flow, and findings associated with abnormal pressure or leakage. CT myelography uses contrast injected into the spinal subarachnoid space to identify leaks or CSF–venous fistulas, abnormal connections through which CSF drains directly into veins and may cause spontaneous intracranial hypotension.

Computed tomography (CT) is an imaging technique that uses X-rays acquired from multiple angles around the body to reconstruct cross-sectional images and three-dimensional views. Image contrast reflects differences in X-ray attenuation between tissues, with CT values conventionally expressed in Hounsfield units relative to water. These values depend on tissue composition, X-ray energy and acquisition and reconstruction settings. Intravenous iodinated contrast can enhance blood vessels and help characterize masses and other abnormalities. Cardiac CT commonly uses electrocardiographic synchronization to reduce motion and assess coronary arteries, cardiac chambers, valves, congenital abnormalities and cardiac masses. Conventional scanners use energy-integrating detectors, whereas photon-counting systems detect individual photons and can provide energy-resolved information for spectral imaging and material characterization.

CT angiography (CTA) is a noninvasive imaging technique that uses computed tomography and an intravenously injected iodinated contrast agent to visualize blood vessels. Images are acquired as contrast passes through the target circulation, increasing X-ray attenuation within the vessel lumen and allowing detailed assessment of vascular anatomy. Thin-section images and multiplanar or three-dimensional reconstructions help identify stenosis, occlusion, aneurysm, dissection, and atherosclerotic plaque. Coronary CTA assesses the coronary arteries, typically with electrocardiographic synchronization to reduce cardiac motion, while peripheral CTA maps arterial disease and supports planning and follow-up of revascularization procedures. Radiation exposure, contrast allergy, kidney function, and artifacts from calcification or metal require consideration when selecting and interpreting the examination.

Chronic thromboembolic pulmonary hypertension (CTEPH) is a form of pulmonary hypertension caused by persistent, organized thromboembolic material obstructing pulmonary arteries, together with remodeling of the smaller pulmonary vessels. These changes increase pulmonary vascular resistance, placing pressure overload on the right ventricle and potentially causing right heart failure. Diagnosis combines evidence of chronic thromboembolic obstruction with hemodynamic confirmation of precapillary pulmonary hypertension by right heart catheterization. Ventilation/perfusion imaging detects mismatched perfusion defects, while CT pulmonary angiography characterizes vascular abnormalities such as webs, stenoses and occlusions. Spectral CT can also map iodine distribution to assess regional lung perfusion. Cardiac MRI evaluates right ventricular size, function and adaptation to pressure overload. Imaging helps determine suitability for pulmonary endarterectomy or balloon pulmonary angioplasty and monitor treatment response.

CT–derived fat fraction (CTFF) is a quantitative estimate of the proportion of fat within tissue obtained from CT measurements. Fat attenuates X-rays differently from water-rich tissue, allowing its contribution to be estimated using attenuation-based calibration or spectral material decomposition. Photon-counting CT records energy-dependent attenuation information that can help separate tissue components; in bone marrow, calcium removal can support assessment of the underlying fat-containing tissue. CTFF is used to quantify hepatic steatosis and investigate bone marrow composition. Its interpretation depends on the acquisition protocol, reconstruction method and calculation model. Although MRI proton density fat fraction is often used as a reference, CTFF is derived from X-ray attenuation rather than the relative MR signals of fat and water protons.

Chronic total occlusion (CTO) is a complete blockage of a coronary artery with no forward blood flow through the occluded segment, known or presumed to have persisted for at least three months. It typically results from advanced atherosclerotic disease containing fibrous tissue and variable calcification. Collateral vessels may supply the downstream myocardium, but their presence does not ensure adequate perfusion during stress or preserved myocardial viability. Invasive coronary angiography defines the occlusion and collateral circulation, while coronary CT angiography can characterize lesion length, calcification and vessel course to support procedural planning. Cardiac MRI assesses ventricular function, inducible ischemia and myocardial scar, helping determine whether the affected myocardium may benefit from revascularization. Treatment may include medical therapy, percutaneous coronary intervention or coronary artery bypass grafting.

Cancer therapy-related cardiac dysfunction (CTRCD) is impairment of cardiac function associated with anticancer treatment, ranging from asymptomatic myocardial dysfunction to symptomatic heart failure. Treatments such as anthracyclines and HER2-targeted therapies can injure cardiomyocytes or disrupt signaling pathways needed for normal myocardial function. Assessment commonly uses changes in left ventricular ejection fraction, myocardial strain and cardiac biomarkers, interpreted alongside symptoms and baseline cardiovascular risk. Cardiac MRI provides reproducible measurements of ventricular volumes and ejection fraction, while feature tracking can assess myocardial deformation. Tissue characterization may help identify edema, fibrosis or alternative causes of dysfunction, although these findings are not specific to CTRCD. Recognition informs cardiovascular surveillance, heart failure treatment and multidisciplinary decisions about continuing or modifying cancer therapy.

Cardiovascular (CV) refers to the heart and blood vessels and to the functions, disorders, and clinical events involving this circulatory system. Cardiovascular complications include disturbances of cardiac muscle function, rhythm, valves, or vascular circulation, arising from primary heart disease or systemic conditions. Cardiovascular events are clinically significant outcomes, such as myocardial infarction, stroke, or cardiovascular death; the components of a composite endpoint depend on its specified definition. Cardiac MRI assesses cardiovascular structure, ventricular function, blood flow, perfusion, and tissue characteristics, including fibrosis and iron deposition. CT complements this assessment by depicting coronary arteries, vascular anatomy, calcification, and other structural abnormalities.

Cerebrospinal fluid–venous fistulas (CVF) are abnormal connections between the spinal subarachnoid space and adjacent veins that allow cerebrospinal fluid to drain directly into the venous circulation. They commonly arise near spinal nerve root sleeves and can cause spontaneous intracranial hypotension, often presenting with headache that worsens when upright. Unlike leaks into surrounding tissues, these fistulas generally do not produce an extradural cerebrospinal fluid collection, making routine spinal imaging insufficient to exclude them. Dynamic CT myelography or digital subtraction myelography after intrathecal iodinated contrast administration can demonstrate early contrast passage into draining veins, often with the patient positioned on their side. Accurate localization guides treatment, which may include transvenous embolization or surgical ligation.

Cadmium-zinc-telluride (CZT) is a semiconductor material used to detect gamma rays in single-photon emission computed tomography (SPECT) and X-rays in photon-counting CT. Absorbed photons generate electrical charges directly within the material, without first being converted into visible light. The resulting electrical pulses allow individual photons to be counted and their energies estimated, supporting energy discrimination and spectral imaging. In cardiac SPECT, CZT detectors are used to image radiotracer uptake in the myocardium, assess perfusion, and, with suitable dynamic acquisition and tracer modeling, estimate myocardial blood flow and flow reserve. In photon-counting CT, CZT is one detector material used to acquire energy-resolved data for anatomical imaging and material differentiation. Performance depends on detector design, calibration, and photon count rate.

Diamond-Blackfan anemia syndrome (DBAS) is a rare inherited bone marrow failure disorder characterized by impaired red blood cell production, usually presenting in infancy with macrocytic anemia, low reticulocyte counts and markedly reduced erythroid precursors in the marrow. It is most often associated with pathogenic variants affecting ribosomal proteins and may also involve congenital abnormalities, growth impairment and increased cancer risk. Treatment can include corticosteroids, red blood cell transfusions and hematopoietic stem cell transplantation. Repeated transfusions can cause iron accumulation in the liver, heart and endocrine organs, requiring iron chelation. MRI provides noninvasive assessment of tissue iron: liver iron measurements guide monitoring of systemic iron burden, while cardiac T2* imaging detects myocardial iron deposition and helps guide treatment to prevent iron-related cardiac dysfunction.

Dynamic contrast-enhanced T1-weighted MRI (DCE-T1WI) is an MRI technique that repeatedly acquires T1-weighted images before, during and after intravenous administration of a gadolinium-based contrast agent. Gadolinium shortens tissue T1 relaxation, increasing signal intensity where the agent accumulates. The pattern and time course of enhancement reflect tissue perfusion, vascular permeability and contrast distribution in the extracellular space. In breast imaging, the technique depicts enhancing lesions and supports their assessment through morphology and enhancement kinetics, including early uptake and subsequent persistent enhancement, plateau or washout. It is used to detect and characterize suspicious abnormalities, evaluate disease extent and assess treatment response. Enhancement is not specific to cancer, so findings must be interpreted alongside other imaging features and clinical information.

Dilated cardiomyopathy (DCM) is a myocardial disorder characterised by left ventricular or biventricular dilatation and impaired systolic contraction that are not explained solely by abnormal loading conditions or coronary artery disease. It may arise from inherited genetic variants, inflammatory injury, toxins, metabolic disorders or other causes, although the cause can remain unknown. Reduced contractility and progressive ventricular remodelling can lead to heart failure, functional valve regurgitation, ventricular arrhythmias and thromboembolism. Cardiac MRI measures ventricular volumes, ejection fraction and myocardial mass, and helps characterise myocardial injury. Late gadolinium enhancement identifies focal replacement fibrosis, while T1 mapping and extracellular volume assessment can detect diffuse tissue abnormalities. These findings support diagnosis, evaluation of possible causes and risk assessment alongside clinical, genetic and other investigations.

Dual-energy CT (DECT) is a computed tomography technique that acquires attenuation information at two different X-ray energy spectra to distinguish materials that may appear similar on conventional CT. Because attenuation varies with photon energy and material composition, the paired measurements support material decomposition, iodine maps, virtual monoenergetic images and virtual non-contrast images. Data can be obtained using approaches such as two X-ray sources, rapid tube-voltage switching or layered detectors. Clinically, DECT helps assess tissue enhancement and perfusion, characterize selected materials and reduce some artifacts, including those near metallic implants. Its spectral information can also support estimation of tissue properties relevant to radiotherapy planning. Reconstruction accuracy depends on acquisition technique, patient size, beam hardening and the materials being assessed.

Deep learning (DL) is a branch of machine learning that uses neural networks with multiple processing layers to learn complex patterns from data. During training, model parameters are adjusted to extract features useful for tasks such as classification, prediction or image reconstruction. In medical imaging, DL can reconstruct images from undersampled MRI data, reduce noise in CT, segment cardiac structures and derive measurements or predictions from images. Accelerated cardiac MRI reconstruction can reduce acquisition time and breath-holding requirements, while predictive models can relate imaging features to subsequent clinical outcomes. DL also supports clinical analysis of non-imaging data, including speech patterns. Performance depends on training data, independent validation and robustness across patient populations and acquisition settings; outputs require appropriate clinical oversight.

Dose-length product (DLP) is a computed tomography radiation output metric that combines the volume CT dose index with the length of the scanned region. Expressed in milligray centimetres, it reflects both scanner radiation output and longitudinal scan coverage, rather than the absorbed dose to an individual patient or organ. For an examination containing multiple acquisitions, the acquisition DLP values can be summed to describe the total examination or session DLP. It is used to monitor radiation exposure, compare imaging protocols and support dose optimisation against diagnostic reference levels. DLP can also support approximate estimates of effective dose using region-specific conversion factors, although these estimates depend on patient characteristics and scan location. In CT myelography, session DLP accounts for the CT acquisitions performed during the examination.

Diabetes mellitus (DM) is a group of metabolic disorders characterized by persistent hyperglycemia caused by inadequate insulin secretion, impaired insulin action, or both. Major forms include type 1 diabetes, usually resulting from autoimmune destruction of pancreatic beta cells, and type 2 diabetes, involving insulin resistance and progressive beta-cell dysfunction. Chronic hyperglycemia contributes to microvascular injury and increases the risk of atherosclerotic cardiovascular disease and heart failure. Cardiac MRI can assess associated ventricular dysfunction, myocardial ischemia, infarction, and tissue abnormalities. Native T1 mapping and extracellular volume measurement can support assessment of diffuse myocardial changes, while late gadolinium enhancement identifies focal scar. These imaging findings are not specific to diabetes and must be interpreted alongside coronary disease, other comorbidities, and clinical information.

Duchenne muscular dystrophy (DMD) is an X-linked genetic disorder caused by pathogenic variants in the DMD gene that result in absent or severely deficient functional dystrophin, a protein that helps stabilize muscle cell membranes during contraction. It predominantly affects males and causes progressive skeletal muscle weakness, loss of mobility, respiratory muscle impairment and cardiomyopathy. Cardiac involvement includes progressive myocardial injury and fibrosis, which can precede symptoms or a measurable decline in ventricular function and may lead to dilated cardiomyopathy, heart failure and arrhythmias. Cardiac MRI assesses ventricular volumes and ejection fraction and detects myocardial fibrosis using late gadolinium enhancement, often involving the subepicardial inferolateral left ventricular wall. Native T1 mapping can provide additional information about myocardial tissue abnormalities, supporting surveillance and cardiac management.

Dynamic mode decomposition (DMD) is a data-driven computational method that represents a time-varying dataset as spatial patterns, or modes, with associated temporal frequencies and growth or decay rates. It estimates a linear evolution operator from successive data snapshots, providing a compact description of dynamics without requiring a detailed physical model. In dynamic MRI, these patterns can describe changes in the measured signal or images over time and can be incorporated into reconstruction methods. For cardiac MRI, DMD is investigated as a way to support rapid reconstruction of moving cardiac anatomy, including real-time acquisitions. Its usefulness depends on how well the estimated modes capture cardiac motion and other signal changes during acquisition.

Digital subtraction angiography (DSA) is an X-ray imaging technique that visualizes blood vessels by subtracting a pre-contrast image, called a mask, from images acquired after injection of an iodinated contrast agent. This subtraction suppresses background structures such as bone and soft tissue, making contrast-filled vessels more conspicuous. Usually performed with catheter-directed contrast injection, DSA provides high spatial and temporal resolution for assessing arterial narrowing, occlusion, aneurysms and blood flow, and for guiding endovascular procedures. It is also used to evaluate vascular implants and treatment outcomes. DSA can serve as a reference standard when assessing CT or MR angiography, but it involves ionizing radiation, iodinated contrast and, when catheter-based, vascular access risks. Patient motion can cause subtraction artifacts.

Desmoplakin (DSP) is a structural protein in desmosomes, the cell junctions that provide mechanical adhesion between adjacent cells, including cardiac muscle cells. It anchors intermediate filaments to the desmosomal complex, helping myocardial tissue withstand repeated mechanical stress. The DSP gene encodes this protein, and pathogenic variants can cause inherited arrhythmogenic cardiomyopathy, often with prominent left ventricular involvement or disease affecting both ventricles. DSP-associated cardiomyopathy may feature myocardial fibrosis, ventricular arrhythmias, heart failure, and episodes of chest pain with myocardial injury that resemble myocarditis. Cardiac MRI assesses ventricular size and function, detects fibrosis through late gadolinium enhancement, and evaluates edema during inflammatory presentations. Imaging findings are interpreted alongside clinical history, rhythm assessment, family history, and genetic testing.

Electroanatomic mapping (EAM) is an invasive technique that combines spatial tracking of intracardiac catheters with recordings of local electrical activity to create three-dimensional maps of cardiac chambers. Magnetic or impedance-based localization places electrical measurements on a reconstructed anatomical surface. Activation maps show the timing and sequence of electrical propagation, while voltage maps help identify scar and abnormal myocardial substrate, although measurements depend on catheter contact and recording conditions. During ventricular tachycardia ablation, EAM helps locate arrhythmia circuits, regions of delayed conduction and potential ablation targets. Cardiac MRI, particularly late gadolinium enhancement imaging, can provide complementary information about scar location and extent; these images may be registered with EAM to relate structural abnormalities to electrical findings and support procedural planning.

Epicardial adipose tissue (EAT) is the fat depot located between the myocardium and the visceral layer of the serous pericardium, including fat surrounding the epicardial coronary arteries. It shares a microcirculatory supply with adjacent myocardium and has no intervening fascial barrier. This tissue provides local energy storage, cushioning and metabolic signalling, while altered adipose biology can contribute to inflammation affecting nearby vessels and myocardium. Cardiac CT identifies EAT by its characteristic fat attenuation and can quantify its volume using segmentation within the pericardial boundary. Cardiac MRI can assess its distribution and volume using fat-sensitive imaging. EAT measurements are used in research to investigate relationships with obesity, coronary artery disease, atrial fibrillation and myocardial dysfunction, but are not standalone diagnostic tests.

Epicardial adipose tissue volume (EATV) is the total volume of fat between the outer surface of the myocardium and the visceral layer of the pericardium, including fat within the coronary grooves. This adipose depot lies in direct contact with the heart and coronary arteries and has metabolic, inflammatory and paracrine functions. EATV is quantified by identifying and segmenting epicardial fat across cardiac images and summing its volume. CT distinguishes fat by its characteristic low X-ray attenuation, while cardiac MRI uses fat-sensitive signal characteristics or water–fat separation techniques. Accurate measurement requires consistent anatomical boundaries and exclusion of fat outside the pericardial sac. EATV is used in research to characterize cardiac adiposity and investigate associations with obesity, coronary disease and myocardial remodeling; it is not a standalone diagnostic measure.

Erdheim-Chester disease (ECD) is a rare histiocytic neoplasm characterised by tissue infiltration with lipid-laden histiocytes, chronic inflammation and fibrosis. It is associated with acquired mutations that activate the mitogen-activated protein kinase signalling pathway, including BRAF mutations. Typical manifestations include symmetric osteosclerosis of the long bones, infiltration around the kidneys and aorta, and involvement of the heart, lungs or central nervous system. Cardiac disease can cause pericardial thickening or effusion, constrictive physiology, and infiltrative masses, particularly around the right atrium. Cardiac MRI assesses the location and extent of infiltration, tissue characteristics, ventricular function and pericardial involvement, while CT depicts vascular and extracardiac abnormalities. Diagnosis requires tissue biopsy interpreted alongside clinical and imaging findings.

Electrocardiogram (ECG) is a recording of the heart’s electrical activity obtained using electrodes placed on the skin. It detects voltage changes produced by myocardial depolarisation and repolarisation, displaying waveforms that describe cardiac rhythm, conduction and ventricular recovery. A standard 12-lead ECG provides complementary views of this activity and is used to identify arrhythmias, conduction abnormalities, signs of myocardial ischaemia and patterns suggestive of chamber enlargement or hypertrophy. Ambulatory ECG monitoring, such as Holter monitoring, records activity over longer periods to detect intermittent abnormalities. During cardiac MRI, ECG signals commonly synchronise image acquisition with the cardiac cycle and support patient monitoring. Magnetic fields, switching gradients and blood flow within the magnetic field can distort these signals, complicating waveform interpretation and requiring MRI-compatible recording equipment.

Extracellular volume (ECV) is the fraction of myocardial tissue occupied by the extracellular space, including the interstitium and blood plasma within small vessels. It is an imaging biomarker of extracellular expansion, which can occur with diffuse fibrosis, amyloid deposition or edema. Cardiac MRI estimates ECV from changes in myocardial and blood T1 relaxation rates before and after administration of an extracellular gadolinium contrast agent, corrected for hematocrit. Cardiac CT estimates the same fraction from myocardial and blood iodine enhancement, also corrected for hematocrit; spectral techniques can quantify iodine directly. ECV complements focal scar imaging by assessing diffuse tissue abnormalities and is used to characterize cardiomyopathies, particularly cardiac amyloidosis. Elevated ECV is not specific to fibrosis and must be interpreted in the clinical context.

Emergency department (ED) is a hospital-based clinical service that assesses and treats patients with acute illness or injury requiring urgent medical attention. Care includes triage, stabilization, diagnostic evaluation and decisions about discharge, observation or hospital admission. In patients with acute chest pain, evaluation commonly combines clinical assessment, electrocardiography and cardiac troponin testing to identify acute coronary syndrome and other serious causes. Coronary CT angiography may be used in selected patients to assess coronary artery disease, while other CT examinations investigate conditions such as pulmonary embolism or acute aortic disease. Cardiac MRI is generally reserved for selected, clinically stable patients requiring further characterization of myocardial injury.

End-diastolic volume (EDV) is the volume of blood contained in a cardiac chamber at the end of ventricular diastole, just before ventricular contraction. Ventricular EDV reflects chamber filling and size and is influenced by venous return, myocardial compliance and loading conditions. Cardiac MRI measures ventricular EDV by tracing the blood pool on end-diastolic cine images across contiguous slices and summing the resulting volumes. It is commonly indexed to body surface area to aid comparison between patients of different sizes. EDV supports assessment of ventricular dilatation, volume overload and remodeling, including right ventricular enlargement associated with pulmonary regurgitation. Together with end-systolic volume, it determines stroke volume and ejection fraction. Atrial volumes measured at ventricular end-diastole can also be used in indices of atrioventricular coupling.

Ejection fraction (EF) is the proportion of blood in a ventricle at the end of filling that is expelled during the subsequent contraction, usually expressed as a percentage. It is calculated by subtracting end-systolic volume from end-diastolic volume and dividing the difference by end-diastolic volume. In cardiac imaging reports, EF most commonly refers to the left ventricle and provides a global measure of systolic pump function. Cardiac MRI measures ventricular volumes from cine images covering the ventricle throughout the cardiac cycle; echocardiography and nuclear imaging can also estimate EF. Clinically, EF supports assessment of heart failure, cardiomyopathy, myocardial infarction and treatment-related cardiac dysfunction. It depends on loading conditions and does not directly measure myocardial contractility, so a preserved EF does not exclude clinically important dysfunction.

Eosinophilic granulomatosis with polyangiitis (EGPA) is a systemic disease characterized by eosinophil-rich inflammation, granulomatous inflammation and vasculitis affecting predominantly small- to medium-sized blood vessels. It typically occurs in people with asthma and blood eosinophilia and may involve the lungs, upper airways, peripheral nerves, skin, kidneys and heart. Antineutrophil cytoplasmic antibodies are present in some patients, but their absence does not exclude the diagnosis. Cardiac involvement can include eosinophilic myocarditis, cardiomyopathy, pericarditis and intracardiac thrombus. Cardiac MRI assesses ventricular function and uses tissue characterization, including edema-sensitive imaging, mapping and late gadolinium enhancement, to detect myocardial inflammation and injury. Imaging findings complement clinical assessment and laboratory tests when evaluating organ involvement and monitoring treatment response.

Electronic health records (EHR) are digital collections of patient health information maintained over time to support clinical care. They can include diagnoses, symptoms, medications, laboratory results, physiological measurements, procedures, and imaging reports, linked to dated clinical encounters. This longitudinal structure allows clinicians and researchers to follow disease progression, treatments, and outcomes, although completeness and consistency depend on how information is recorded. In cardiovascular medicine, EHR data can support identification of patients at risk of heart failure, tracking of congenital heart disease, and interpretation of cardiac MRI or CT findings alongside clinical history. For research and predictive modelling, records require careful handling of missing data, coding differences, privacy, and the timing of observations.

Energy-integrating detector (EID) is an X-ray detector used in conventional CT that measures the total energy deposited by incoming photons during each measurement interval rather than counting individual photons. Most clinical CT systems use scintillator materials to convert absorbed X-rays into visible light, which photodiodes then convert into electrical signals. Higher-energy photons contribute more strongly to the integrated signal than lower-energy photons, and individual photon energies are not directly resolved. Measurements acquired from multiple angles are reconstructed into cross-sectional images of tissue X-ray attenuation. EID technology supports routine clinical applications, including coronary CT angiography, assessment of coronary stents, and brain imaging. It provides the conventional comparator for photon-counting detectors, which register individual photons and classify them by energy.

Energy-integrating detector CT (EID-CT) is computed tomography performed with detectors that measure the combined energy deposited by incoming X-ray photons during each sampling interval, rather than counting individual photons. Most clinical systems use a scintillator to convert X-rays into light, which photodiodes convert into an electrical signal. Measurements acquired from multiple angles are reconstructed into cross-sectional images showing differences in tissue attenuation. Higher-energy photons contribute more strongly to the detector signal, and conventional acquisition does not resolve individual photon energies. EID-CT is widely used for anatomical assessment, contrast-enhanced vascular imaging, and evaluation of coronary arteries, stents, bone, and implanted hardware. Image quality depends on spatial resolution, radiation exposure, reconstruction methods, and artifacts; dual-energy implementations can also provide material-specific and virtual monoenergetic images.

Energy-integrating detector CT angiography (EID-CTA) is contrast-enhanced computed tomography used to image blood vessels with detectors that integrate the total energy deposited by incoming X-ray photons during each measurement. Conventional detectors convert X-rays into light in a scintillator, then convert that light into an electrical signal, rather than counting individual photons and measuring their energies separately. Intravenous iodinated contrast increases vascular attenuation, allowing assessment of the arterial lumen and abnormalities such as stenosis, occlusion, aneurysms and arterial outpouchings. EID-CTA is widely used for head, neck, coronary and peripheral arterial imaging. Spatial resolution and artifacts from calcification, metal or beam hardening can limit lumen assessment, particularly in small vessels or heavily calcified arteries.

Energy-integrating detector CT myelography (EID-CTM) is computed tomography of the spinal cerebrospinal fluid spaces after intrathecal administration of iodinated contrast, performed using conventional energy-integrating detectors. These detectors convert incoming X-rays into light and integrate the resulting signal, with higher-energy photons contributing more strongly than lower-energy photons. Contrast outlines the spinal subarachnoid space and nerve root sleeves, allowing assessment of their anatomy and abnormal routes of cerebrospinal fluid escape. In spontaneous intracranial hypotension, CT myelography can localize spinal cerebrospinal fluid leaks or cerebrospinal fluid–venous fistulas, in which contrast passes directly into a vein without an extradural fluid collection. Patient positioning and scan timing are tailored to the suspected leak mechanism. The examination requires a lumbar puncture and entails ionizing radiation exposure.

Endomyocardial biopsy (EMB) is an invasive procedure in which small samples of heart muscle are obtained using a catheter-mounted forceps device, usually from the right ventricular septum through venous access. The samples undergo histological examination and, when appropriate, immunohistochemical or molecular testing to identify inflammation, infiltrative deposits or other myocardial abnormalities. EMB is used to assess rejection after heart transplantation and to investigate selected cases of suspected myocarditis, unexplained cardiomyopathy or cardiac amyloidosis when tissue diagnosis may guide treatment. Cardiac MRI provides complementary information about ventricular function and tissue injury and may help identify areas for targeted sampling. Because disease can be patchy, a negative biopsy does not always exclude it; procedural risks include perforation, arrhythmia and valve injury.

Electrophysiology (EP) is the study of electrical activity in biological tissues; in cardiac practice, it focuses on the generation and conduction of impulses that control heart rhythm. Clinical cardiac electrophysiology uses surface electrocardiograms, intracardiac recordings and programmed electrical stimulation to identify arrhythmia mechanisms and guide treatment. During invasive EP procedures, electrode catheters record signals from within the heart, while electroanatomic mapping systems relate electrical timing to cardiac anatomy. Catheter ablation targets tissue responsible for initiating or sustaining abnormal rhythms. Cardiac MRI and CT can provide complementary information about chamber anatomy, myocardial scar and nearby structures for procedural planning. Electroanatomic mapping and intracardiac ultrasound can guide catheter navigation while reducing or avoiding fluoroscopy.

Exercise stress echocardiography (ESE) is an ultrasound examination that assesses cardiac structure and function during or immediately after physical exercise, usually performed on a treadmill or bicycle ergometer. Exercise increases heart rate, blood pressure and myocardial oxygen demand, allowing imaging to reveal abnormalities that may not be apparent at rest. New or worsening regional ventricular wall-motion abnormalities can indicate inducible myocardial ischemia, while Doppler measurements help assess exercise-related changes in valve function, pressure gradients and estimated pulmonary pressures. ESE is used to investigate exertional symptoms, evaluate suspected coronary artery disease and assess the functional significance of valvular disease or cardiomyopathy. In athletes, it can help distinguish physiological adaptation from disease and inform clinical evaluation of exercise-related cardiovascular risk.

Extravascular implantable cardioverter-defibrillator (EV-ICD) is an implanted device that detects and treats life-threatening ventricular arrhythmias using a lead positioned beneath the sternum, outside the heart and blood vessels. The lead is connected to a pulse generator implanted beneath the skin on the side of the chest. It senses cardiac electrical activity and delivers defibrillation shocks for ventricular fibrillation or ventricular tachycardia; it can also provide antitachycardia pacing to interrupt selected tachycardias. This configuration avoids an intravascular lead while retaining pacing capabilities unavailable in conventional subcutaneous defibrillators. EV-ICDs are used in selected patients at risk of sudden cardiac death, including survivors of cardiac arrest. MRI eligibility depends on the specific system and requires compliance with its device-specific scanning conditions.

Exercise cardiovascular MRI (ExCMR) is magnetic resonance imaging of the heart performed during or immediately after physical exercise to assess cardiovascular function under physiological stress. Exercise increases metabolic demand, heart rate and venous return, allowing assessment of responses that may not be apparent at rest. Protocols may use an MRI-compatible cycle ergometer within the scanner or exercise outside the scanner followed by rapid imaging. Real-time acquisition methods can reduce reliance on breath-holding and accommodate faster heart rates and movement. Measurements may include ventricular volumes, stroke volume, cardiac output and blood flow, helping characterize contractile reserve and exercise-related functional abnormalities. ExCMR can support evaluation of exertional symptoms and heart failure, although protocols and availability vary between specialist centres.

Fetal cardiac magnetic resonance imaging (FCMRI) is a non-invasive MRI examination used to assess the fetal heart and major blood vessels before birth. It uses magnetic fields and radiofrequency pulses to generate images without ionising radiation, generally without gadolinium contrast. Rapid acquisition and motion-compensation methods help address fetal movement and the difficulty of synchronising images to the fetal heartbeat. FCMRI complements fetal echocardiography when ultrasound assessment is limited or additional anatomical information is needed, particularly for suspected congenital heart disease and abnormalities of the aortic arch, pulmonary vessels or systemic veins. It can clarify relationships between cardiovascular and surrounding thoracic structures, supporting prenatal counselling, delivery planning and preparation for postnatal care. Its availability and diagnostic performance depend on specialist expertise, gestational age and image quality.

Fabry disease (FD) is an X-linked lysosomal storage disorder caused by pathogenic variants in the GLA gene, resulting in deficient alpha-galactosidase A activity and accumulation of globotriaosylceramide and related lipids in tissues. It can affect the heart, kidneys, nervous system and skin, with variable manifestations in both males and females. Cardiac involvement commonly includes left ventricular hypertrophy, diastolic dysfunction, conduction abnormalities and arrhythmias, and may progress to heart failure. Cardiac MRI assesses ventricular structure and function and characterises myocardial involvement: reduced native T1 can indicate lipid storage, while late gadolinium enhancement identifies myocardial injury and replacement fibrosis, often in the basal inferolateral wall. Imaging findings support diagnosis, staging and longitudinal assessment alongside genetic testing, enzyme assays and clinical evaluation.

Fractal dimension (FD) is a dimensionless quantitative measure of geometric complexity that describes how the detail of a structure changes with the scale at which it is examined. In cardiac MRI, it can be calculated from segmented ventricular contours on cine images to characterise endocardial irregularity and myocardial trabeculation. A common method, box counting, overlays grids of different box sizes on the extracted boundary and estimates how the number of boxes intersecting it scales with box size. Greater fractal dimension generally indicates a more complex boundary. Measurements depend on image resolution, segmentation, cardiac phase and the scales analysed. Cardiac applications include research into ventricular morphology in cardiomyopathies and pressure-overload conditions; FD is not a standalone diagnostic or clinical risk-stratification test.

Fluorodeoxyglucose (FDG) is a glucose analogue that, when labelled with the positron-emitting isotope fluorine-18, serves as a tracer for positron emission tomography (PET). It enters cells through glucose transporters and is phosphorylated by hexokinase, becoming largely trapped intracellularly so that its accumulation reflects glucose uptake and metabolism. Activated inflammatory cells can show increased FDG uptake, enabling assessment of myocardial inflammation, particularly in cardiac sarcoidosis and selected cases of myocarditis. Dietary preparation and fasting help suppress normal myocardial glucose uptake, improving distinction between physiological activity and inflammation. PET is commonly combined with CT for anatomical localisation and attenuation correction. FDG imaging complements cardiac MRI, which characterises myocardial oedema, injury and scar, and can support assessment of inflammatory disease activity and treatment response.

18F-fluorodeoxyglucose positron emission tomography (FDG-PET) is a nuclear imaging technique that maps tissue uptake of a glucose analogue labelled with the positron-emitting isotope fluorine-18. After intravenous injection, FDG enters metabolically active cells and is phosphorylated, becoming largely trapped within them; the scanner detects paired photons produced by positron annihilation to reconstruct its distribution. In cardiac sarcoidosis, increased uptake can identify active myocardial inflammation because activated inflammatory cells consume glucose. Dietary preparation and fasting are used to suppress normal myocardial glucose uptake, helping distinguish inflammatory activity from physiological uptake. FDG-PET complements cardiac MRI, which characterises myocardial injury and scar, and can help assess disease extent and monitor response to anti-inflammatory treatment. Uptake is not specific to sarcoidosis and requires clinical interpretation.

Fat fraction (FF) is a quantitative measure of the proportion of fat within tissue, with its precise interpretation depending on the imaging method used. Dixon MRI separates fat and water signals using differences in their resonance frequencies and estimates FF from the fat signal relative to the combined fat and water signals. Appropriate correction for confounding effects is required to obtain proton density fat fraction. CT estimates fat content from tissue X-ray attenuation, using calibration or material decomposition; spectral acquisitions can help distinguish tissue components. These measurements support assessment of hepatic steatosis and fatty replacement in skeletal muscle or myocardium. Values from different techniques are not automatically interchangeable, because acquisition settings, reconstruction methods and the underlying measurement model can influence the estimate.

Fast-interrupted steady-state (FISS) is an MRI pulse sequence that periodically interrupts short blocks of balanced steady-state free precession acquisition, modifying the signal response to off-resonance frequencies. These interruptions, combined with spoiling of residual transverse magnetization, can suppress fat signal while preserving much of the bright-blood contrast characteristic of balanced steady-state imaging. Fat suppression depends on sequence timing and magnetic field strength rather than requiring a separate fat-saturation preparation. In cardiac MRI, FISS can be incorporated into free-running three-dimensional acquisitions, with respiratory and cardiac motion resolved during reconstruction. It is used for whole-heart visualization and assessment of cardiovascular anatomy, including congenital heart disease, and can support ventricular volume and function measurements.

Fast strain-encoded cardiovascular magnetic resonance (fSENC) is a rapid cardiac MRI technique that measures myocardial strain, the relative change in myocardial length during contraction and relaxation. It applies a spatial modulation of magnetization perpendicular to the imaging plane and detects shifts in its frequency as the myocardium deforms, encoding strain into image intensity. Rapid acquisition allows strain imaging within a single heartbeat and can reduce reliance on breath-holding. Images acquired in different cardiac orientations provide regional and global longitudinal or circumferential strain measurements for either ventricle. These measurements help characterize systolic dysfunction in cardiomyopathies, ischemic heart disease and congenital heart disease, including abnormalities that may not be apparent from ejection fraction alone. The technique measures mechanical deformation rather than fibrosis directly and does not inherently require contrast administration.

Feature tracking (FT) is an image-analysis method that measures cardiac motion and deformation by following identifiable tissue patterns and anatomical boundaries across successive frames of cine cardiac MRI. Software tracks features within or along the myocardium throughout the cardiac cycle to estimate displacement and strain, the relative change in tissue length. It can quantify longitudinal, circumferential and radial ventricular strain, as well as atrial deformation, using routine cine images without dedicated myocardial tagging acquisitions. These measurements complement chamber volumes and ejection fraction when assessing ventricular or atrial function in cardiomyopathies, pulmonary hypertension and treatment-related cardiac injury. Results depend on image quality, temporal resolution, contour placement and software implementation, so measurements from different analysis packages are not necessarily interchangeable.

Global circumferential strain (GCS) is a measure of the average relative change in myocardial length around the circumference of a ventricle during contraction, usually reported for the left ventricle. It describes circumferential shortening relative to the end-diastolic reference length and is expressed as a percentage. Under the usual sign convention, systolic shortening produces negative values, with more negative values indicating greater shortening. In cardiac MRI, GCS can be derived from short-axis cine images using feature tracking or from dedicated deformation imaging methods such as myocardial tagging. It complements ejection fraction by characterising myocardial mechanics and can help assess dysfunction associated with infarction, cardiomyopathy or cardiotoxic treatment. Measurements depend on loading conditions, image quality and analysis method, so values from different techniques or software are not necessarily interchangeable.

Gadolinium (Gd) is a metallic element used in chelated contrast agents, principally for MRI, and investigated as a contrast material for spectral photon-counting CT. In MRI, its paramagnetic properties shorten nearby water-proton relaxation times, helping depict blood vessels, tissue perfusion and extracellular contrast accumulation. In CT, gadolinium attenuates X-rays and has a characteristic K-edge, an abrupt increase in attenuation when photon energy exceeds the binding energy of its innermost electrons. Energy-resolved measurements can exploit this feature to distinguish gadolinium from other materials, including calcium and iodine. This provides a basis for experimental vascular contrast imaging and material decomposition. Gadolinium-enhanced coronary CT remains investigational rather than a routine replacement for iodinated contrast, and administration requires attention to agent-specific safety and renal function.

Global longitudinal strain (GLS) is the average relative change in myocardial length along the ventricular long axis during contraction, most commonly reported for the left ventricle. It reflects longitudinal myocardial shortening and is expressed as a percentage relative to the reference length, usually at end-diastole. Under the usual signed convention, systolic shortening produces negative values, with less negative values generally indicating impaired longitudinal contraction. GLS can be measured using speckle-tracking echocardiography or cardiac MRI techniques such as feature tracking of cine images. It complements ejection fraction by detecting abnormalities in myocardial deformation that may precede a reduction in overall pump function. Clinical applications include assessing cardiomyopathies, ischemic injury and cancer therapy-related cardiac dysfunction. Interpretation depends on loading conditions, image quality and the analysis method.

Hypertrophic cardiomyopathy (HCM) is a myocardial disease characterized by increased left ventricular wall thickness that is not explained solely by abnormal loading conditions, such as hypertension or aortic stenosis. It is often inherited and associated with variants in genes encoding cardiac sarcomere proteins. Myocyte hypertrophy, disarray, and fibrosis can impair ventricular relaxation, cause dynamic left ventricular outflow tract obstruction, and predispose to atrial and ventricular arrhythmias. Cardiac MRI defines the distribution and extent of hypertrophy, including apical forms, and measures ventricular volumes, mass, and function. Late gadolinium enhancement identifies focal replacement fibrosis, while tissue mapping can help characterize more diffuse myocardial abnormalities. These findings support diagnosis, distinguish alternative causes of wall thickening, and contribute to clinical risk assessment and management.

Hemodynamic forces (HDF) are the forces associated with intraventricular pressure gradients that accelerate and decelerate blood during cardiac contraction and relaxation. Their magnitude, direction and timing describe how ventricular wall motion coordinates blood movement toward the outflow tract and during filling. Cardiac MRI can estimate these forces from time-resolved velocity measurements using fluid-dynamic equations, or from cine images using models incorporating ventricular geometry, endocardial motion and valve dimensions. Measurements commonly characterize forces along the ventricular long axis and transverse directions, sometimes normalized to ventricular volume. HDF analysis provides a non-invasive assessment of ventricular mechanics that complements volumes, ejection fraction and myocardial strain. It is used in research to characterize altered contraction, filling and remodeling, but is not a standalone diagnostic test.

Heart failure (HF) is a clinical syndrome in which structural or functional cardiac abnormalities impair ventricular filling or blood ejection, causing symptoms such as breathlessness, fatigue and exercise intolerance, often with signs of fluid retention. It results from elevated cardiac filling pressures, inadequate cardiac output, or both, and can occur with reduced, mildly reduced or preserved left ventricular ejection fraction. Common causes include coronary artery disease, hypertension, valve disease and cardiomyopathies. Cardiac MRI measures ventricular volumes, ejection fraction and myocardial mass, while tissue characterization can identify infarction, inflammation, fibrosis or infiltrative disease underlying the syndrome. Cardiac CT can assess coronary arteries and relevant structural abnormalities. Imaging supports diagnosis, identification of the cause and treatment planning alongside clinical assessment and biomarkers.

Heart failure with preserved ejection fraction (HFpEF) is a clinical syndrome in which symptoms and signs of heart failure occur despite a left ventricular ejection fraction of at least 50%, with objective evidence of elevated cardiac filling pressures or structural or functional abnormalities supporting the diagnosis. Impaired ventricular relaxation and increased stiffness commonly limit filling and raise pressures, particularly during exercise, although vascular dysfunction and other mechanisms also contribute. A preserved ejection fraction does not imply normal cardiac function. Cardiac MRI can quantify chamber volumes, ventricular mass and atrial remodeling, assess myocardial fibrosis through late gadolinium enhancement and tissue mapping, and identify alternative or contributing conditions such as cardiac amyloidosis, hypertrophic cardiomyopathy or ischemic injury.

Heart failure with reduced ejection fraction (HFrEF) is a clinical syndrome in which symptoms and signs of heart failure are associated with a left ventricular ejection fraction of 40% or less. Impaired ventricular contraction reduces the proportion of blood ejected with each heartbeat and may cause elevated cardiac filling pressures, breathlessness, fatigue and fluid retention. Common causes include coronary artery disease, previous myocardial infarction and non-ischaemic cardiomyopathy. Echocardiography is usually the initial imaging test, while cardiac MRI provides accurate measurements of ventricular volumes and ejection fraction and characterises myocardial tissue to help identify the underlying cause. Late gadolinium enhancement can reveal patterns of infarction or non-ischaemic scarring. Management includes guideline-directed drug therapy and, in selected patients, implanted devices or interventions targeting the cause.

Hypertensive heart disease (HHD) is the structural and functional damage to the heart caused by sustained elevation of systemic arterial blood pressure. Chronic pressure overload increases left ventricular wall stress, promoting myocardial hypertrophy, interstitial fibrosis and impaired relaxation, which can progress to heart failure with preserved or reduced ejection fraction. Cardiac MRI assesses ventricular mass, wall thickness, chamber volumes and systolic function, helping distinguish hypertensive remodeling from other causes of myocardial thickening, including hypertrophic cardiomyopathy. Native T1 mapping and extracellular volume measurements can support assessment of diffuse myocardial tissue abnormalities, while late gadolinium enhancement identifies focal replacement fibrosis. Imaging findings must be interpreted alongside blood pressure history and other clinical information because these features are not specific to hypertension.

High-intensity interval training (HIIT) is a structured form of exercise that alternates short bouts of vigorous activity with periods of lower-intensity exercise or rest. Exercise intensity is commonly prescribed relative to an individual’s measured exercise capacity, heart rate, or perceived exertion. Repeated high-intensity efforts stimulate cardiovascular and skeletal-muscle adaptations that can improve cardiorespiratory fitness and oxygen utilization. HIIT is used in selected rehabilitation and preventive exercise programs, with clinical assessment and appropriate supervision particularly important for people with cardiovascular disease or congenital heart disease. Cardiopulmonary exercise testing can guide exercise prescription and assess changes in peak oxygen uptake, while cardiac MRI can evaluate associated changes in ventricular volumes, mass, and systolic function. Protocols vary and should be tailored to clinical status and exercise tolerance.

Hemorrhagic myocardial infarction (hMI) is myocardial infarction complicated by bleeding into the damaged heart muscle, typically following reperfusion of severely ischemic tissue. Injury to the coronary microvasculature allows red blood cells to escape into the infarcted myocardium, often in association with microvascular obstruction. Breakdown of these cells can leave iron-containing deposits that persist after the acute infarct has healed. Cardiac MRI can characterize this injury using T2*-weighted imaging or T2* mapping, because blood breakdown products and residual iron alter local magnetic susceptibility, causing signal loss and shortening T2*. Late gadolinium enhancement provides complementary assessment of infarct location and extent. Detecting hemorrhage and chronic iron deposition helps characterize infarct severity and tissue changes associated with adverse ventricular remodeling.

Hypertrophic obstructive cardiomyopathy (HOCM) is a form of hypertrophic cardiomyopathy in which abnormal myocardial thickening produces dynamic obstruction of the left ventricular outflow tract. Hypertrophy commonly involves the interventricular septum, and systolic anterior motion of the mitral valve can further narrow the outflow tract and cause mitral regurgitation. Obstruction varies with loading conditions and contractility and may cause exertional breathlessness, chest pain or syncope. The underlying disease is often associated with inherited variants affecting sarcomeric proteins. Echocardiography assesses the outflow pressure gradient at rest and with provocation. Cardiac MRI characterises the distribution of hypertrophy, ventricular function and myocardial fibrosis using late gadolinium enhancement, while supporting differentiation from conditions that mimic hypertrophic cardiomyopathy, including cardiac amyloidosis.

Hypertension (HTN) is a sustained elevation of systemic arterial blood pressure, diagnosed using repeated standardized measurements in the clinic or with home or ambulatory monitoring. It increases the pressure against which the left ventricle must pump, promoting myocardial hypertrophy, interstitial fibrosis and impaired relaxation, and can contribute to heart failure, coronary artery disease, stroke and kidney damage. Most cases are primary, without a single identifiable cause, while secondary hypertension results from an underlying disorder or medication. Cardiac MRI does not diagnose hypertension itself but can assess its cardiac consequences by measuring ventricular mass, volumes and function. Native T1 mapping and extracellular volume measurement can help characterize diffuse myocardial changes, while late gadolinium enhancement can identify focal scar and support evaluation of alternative causes of hypertrophy.

Ischemia/reperfusion (I/R) is the sequence of inadequate tissue blood supply followed by restoration of perfusion. In the myocardium, ischemia limits oxygen delivery, impairs energy production and, if prolonged, causes cardiomyocyte death. Reperfusion is essential to salvage viable muscle, but it can also contribute to injury through oxidative stress, calcium overload, mitochondrial dysfunction and inflammation. Myocardial ischemia/reperfusion injury can involve cardiomyocyte death, microvascular obstruction and intramyocardial hemorrhage despite reopening of the supplying coronary artery. Cardiac MRI assesses its consequences using cine imaging for ventricular function, late gadolinium enhancement for infarcted tissue, T2-based imaging for edema and T2*-based imaging for hemorrhage. Contrast-enhanced imaging can also identify microvascular obstruction, helping characterize tissue damage after acute myocardial infarction.

Invasive coronary angiography (ICA) is a catheter-based X-ray procedure that visualizes the coronary artery lumen after direct injection of iodinated contrast material. A catheter is introduced through an artery, usually at the wrist or groin, and advanced to the coronary artery openings. Contrast outlines the blood-filled lumen, allowing fluoroscopic images from different projections to reveal stenoses, occlusions and narrowing within previously implanted stents. ICA is used to investigate suspected or established coronary artery disease and to guide coronary revascularization, which may be performed during the same session. It commonly serves as an anatomical reference for coronary CT angiography. Because lumen narrowing alone does not establish its physiological significance, invasive pressure measurements or complementary functional imaging may be needed to determine whether a lesion causes myocardial ischemia.

Implantable cardioverter-defibrillator (ICD) is an implanted electronic device that monitors cardiac rhythm and treats life-threatening ventricular tachycardia or ventricular fibrillation by delivering an electrical shock or, in suitable systems, antitachycardia pacing. It consists of a pulse generator and electrodes that sense cardiac electrical activity and deliver therapy. ICDs are used to prevent sudden cardiac death in selected patients at high arrhythmic risk or after a serious ventricular arrhythmia not attributable to a reversible cause. Cardiac MRI can inform risk assessment by measuring ventricular function and identifying myocardial scar or other structural abnormalities, but implantation decisions integrate imaging with clinical criteria. MRI in patients with an ICD requires assessment of the device and leads, appropriate programming, monitoring, and a dedicated safety protocol.

Ischemic cardiomyopathy (ICM) is myocardial disease caused by coronary artery disease, typically characterized by left ventricular systolic dysfunction and adverse remodeling following myocardial infarction, chronic ischemia, or both. Ventricular dysfunction may reflect irreversible scar as well as viable but persistently underperfused myocardium with reduced contractility. Cardiac MRI measures ventricular volumes, ejection fraction, and regional wall motion, while late gadolinium enhancement identifies replacement scar through contrast accumulation in expanded extracellular spaces. Ischemic scar typically involves the subendocardium and may extend through the myocardial wall in a coronary arterial distribution. Assessing scar location and transmural extent helps characterize myocardial viability and the substrate for ventricular arrhythmias, supporting decisions about revascularization, heart failure management, and ventricular tachycardia ablation.

Interventional cardiac MRI (iCMR) is the use of magnetic resonance imaging to guide catheter-based cardiovascular procedures rather than solely to obtain diagnostic images. MRI uses magnetic fields and radiofrequency pulses to generate images with soft-tissue contrast, while rapid acquisition and reconstruction allow visualization of cardiac anatomy and device position during an intervention. Applications include guiding cardiac catheterization, measuring intracardiac pressures alongside MRI-derived blood flow, and supporting selected electrophysiological ablation procedures. Unlike fluoroscopic guidance, iCMR does not use ionizing radiation and can provide additional information about myocardial tissue and procedural effects. It requires appropriately MR-compatible or MR-conditional instruments, specialized monitoring, and measures to limit device heating and imaging artifacts. Its availability remains limited to specialized centers.

Ischemic heart disease (IHD) is a group of conditions in which blood supply to the heart muscle is insufficient to meet its oxygen needs. It most commonly results from atherosclerotic narrowing or acute thrombosis of the coronary arteries, although coronary vasospasm and microvascular dysfunction can also cause myocardial ischemia. Clinical manifestations include angina, myocardial infarction and chronic ventricular dysfunction due to ischemic injury or scarring. Cardiac MRI assesses ventricular function, detects inducible ischemia with stress perfusion imaging and identifies infarcted myocardium using late gadolinium enhancement. Coronary CT angiography evaluates coronary anatomy, atherosclerotic plaque and luminal narrowing. These imaging findings help establish the cause and extent of disease and guide medical treatment or consideration of revascularization.

Idiopathic inflammatory myopathies (IIM) are a heterogeneous group of acquired, immune-mediated disorders characterized by skeletal muscle inflammation or injury, commonly causing muscle weakness. They include dermatomyositis, antisynthetase syndrome, immune-mediated necrotizing myopathy, inclusion body myositis and polymyositis. Depending on the subtype, manifestations may also involve the skin, lungs, joints and heart. Cardiac involvement can include myocarditis, myocardial fibrosis, ventricular dysfunction, conduction abnormalities and arrhythmias, sometimes without overt cardiac symptoms. Diagnosis integrates clinical findings, muscle enzymes, autoantibodies, imaging and, when appropriate, muscle biopsy. Cardiac MRI helps assess suspected myocardial involvement by measuring ventricular function and identifying edema and nonischemic myocardial injury through T1 and T2 mapping and late gadolinium enhancement. Imaging findings require interpretation alongside symptoms, electrocardiography and cardiac biomarkers.

Interstitial lung disease (ILD) is a heterogeneous group of disorders characterised by inflammation and/or fibrosis of the lung interstitium, often with accompanying involvement of alveoli and small airways. These changes can impair gas exchange and reduce lung compliance, causing exertional breathlessness, dry cough and restrictive physiological abnormalities. ILD may arise in association with autoimmune diseases, including idiopathic inflammatory myopathies, environmental or occupational exposures, medications, or conditions without an identified cause. High-resolution chest CT is central to assessment, demonstrating the distribution and pattern of abnormalities such as ground-glass opacity, reticulation, traction bronchiectasis and honeycombing. CT findings help guide diagnosis, estimate disease extent and monitor progression, alongside clinical evaluation and pulmonary function testing; selected patients require tissue sampling.

Iterative metal artifact reduction (iMAR) is a CT reconstruction method that reduces streaks and shading caused by metallic implants, hardware or dental materials. Metal strongly attenuates X-rays, producing beam hardening, photon starvation and inconsistencies in the projection data that can obscure adjacent anatomy. iMAR identifies metal and iteratively corrects affected data using information from less corrupted projections and reconstructed images. Implementations may offer presets tailored to different implant types or anatomical regions. It is used to improve assessment of tissues near orthopedic prostheses, spinal instrumentation and dental restorations, and can support evaluation of nearby vessels on CT angiography. It can be combined with virtual monoenergetic reconstruction, but residual artifacts or newly introduced distortions require comparison with images reconstructed without metal artifact reduction.

Intramyocardial hemorrhage (IMH) is bleeding into the myocardial tissue caused by disruption of the microvasculature, most commonly within a severely injured infarct after restoration of coronary blood flow. Damage to capillary walls allows red blood cells to escape into the interstitial space, often in association with microvascular obstruction. Breakdown of hemoglobin produces iron-containing compounds that alter magnetic susceptibility and shorten T2 and particularly T2* relaxation times. Cardiac MRI can therefore identify hemorrhagic regions as areas of reduced signal or shortened relaxation times within an otherwise edematous infarct. T2*-based imaging is particularly useful, while conventional T2-weighted imaging may also show a dark infarct core. IMH indicates severe reperfusion injury and is assessed alongside infarct size, ventricular function and microvascular obstruction when characterizing myocardial damage and prognosis.

Inflammatory myopericardial syndrome (IMPS) is an umbrella term encompassing inflammation of the myocardium, the pericardium, or both, including myocarditis, pericarditis and overlapping presentations. These conditions may arise from infectious, immune-mediated or other causes and can present with chest pain, electrocardiographic abnormalities, elevated cardiac troponin, arrhythmias or heart failure. The clinical phenotype depends on the predominant tissue involved and the severity of injury. Cardiac MRI supports diagnosis by identifying myocardial oedema and non-ischaemic injury using tissue mapping and late gadolinium enhancement, while also assessing ventricular function, pericardial inflammation and effusion. Findings are interpreted alongside symptoms, laboratory tests and other investigations. Endomyocardial biopsy is reserved for selected presentations where identifying the underlying pathology may influence treatment.

Index of microvascular resistance (IMR) is an invasive physiological measure of resistance in the coronary microcirculation, the small vessels that regulate myocardial blood flow. It is obtained during coronary catheterization using a pressure- and temperature-sensitive guidewire under maximal vasodilation, usually induced with adenosine. IMR is calculated from distal coronary pressure multiplied by the mean transit time of injected saline, with transit time serving as an inverse surrogate for blood flow. Higher values indicate greater microvascular resistance, although interpretation depends on the clinical setting and measurement conditions. IMR helps assess coronary microvascular dysfunction and microvascular injury after reperfusion of myocardial infarction. It complements cardiac MRI assessment of perfusion, infarction and microvascular obstruction by providing a vessel-specific physiological measurement rather than a tissue image.

Ischemia with no obstructive coronary arteries (INOCA) is a clinical syndrome in which myocardial ischemia occurs despite the absence of flow-limiting narrowing in the major epicardial coronary arteries. It commonly reflects coronary microvascular dysfunction, epicardial coronary spasm, or a combination of these mechanisms, which impair oxygen delivery to the myocardium. Patients may experience angina or other ischemic symptoms, and the condition is not necessarily benign. Coronary CT angiography or invasive angiography can assess epicardial coronary anatomy, while stress perfusion cardiac MRI or positron emission tomography can evaluate myocardial perfusion and flow reserve. Invasive coronary function testing, including vasodilator assessment and acetylcholine provocation, can help identify the underlying mechanism and guide treatment.

Iron overload cardiomyopathy (IOC) is myocardial disease caused by excessive iron accumulation within cardiac cells, leading to oxidative injury, impaired contraction and relaxation, and disturbances of electrical conduction. It can occur with hereditary disorders of iron regulation, repeated blood transfusions, or other conditions associated with systemic iron overload. Clinical manifestations include diastolic dysfunction, dilated cardiomyopathy, heart failure and arrhythmias. Cardiac MRI assesses myocardial iron primarily using T2* mapping: iron alters local magnetic fields and accelerates signal decay, producing shorter T2* values as iron burden increases. MRI also measures ventricular volumes and function to assess the consequences of iron deposition. These measurements support diagnosis, risk assessment and monitoring of iron-removal treatment, because circulating iron markers and hepatic iron burden do not reliably establish the degree of cardiac involvement.

Image quality levels (IQL) are selectable CT scanner settings that specify a target image quality for exposure control, rather than measurements of image quality in the reconstructed images. On systems using this terminology, the selected level guides tube current modulation according to patient attenuation and the acquisition protocol. Higher settings generally request greater radiation exposure to reduce quantum noise, whereas lower settings permit more noise to limit dose. Actual image quality also depends on patient size, tube voltage, filtration, spatial resolution, and reconstruction method. In photon-counting CT, these settings help tailor examinations to the diagnostic task and patient population, including pediatric imaging. Phantom measurements of radiation dose and signal-to-noise ratio can support protocol optimization across available levels.

Iterative reconstruction (IR) is a family of computational methods that forms CT images through repeated updates to an initial image estimate, rather than relying solely on a direct analytical reconstruction. Algorithms may compare predicted X-ray projection data with measured data and use models of acquisition physics, detector response and statistical noise to refine the image. Regularization constrains these updates to suppress noise while preserving clinically useful structures. In photon-counting CT, IR is used to manage image noise, particularly in low-dose examinations and high-resolution imaging with small detector pixels. Reconstruction strength and kernel selection influence spatial resolution, noise texture and the visibility of vessels and other anatomical details, so settings must be matched to the diagnostic task.

In-stent restenosis (ISR) is recurrent narrowing of an artery within a previously implanted stent, usually caused by neointimal tissue growth or the development of atherosclerotic changes within that tissue, termed neoatherosclerosis. Mechanical factors, such as stent underexpansion, can also contribute to narrowing of the treated segment. ISR may impair blood flow and cause recurrent ischemic symptoms, with clinical consequences depending on whether the affected vessel supplies the heart, brain or another territory. CT angiography assesses the contrast-filled lumen within the stent, although metal-related blooming and beam-hardening artifacts can obscure it. High-resolution photon-counting CT can improve visualization of the stent lumen. Invasive angiography provides direct assessment of luminal narrowing, while intravascular imaging can clarify its underlying mechanism and guide treatment.

Inferior vena cava (IVC) is the large systemic vein that returns blood from the abdomen, pelvis and lower limbs to the right atrium. It forms from the union of the common iliac veins, ascends through the retroperitoneum, receives the renal and hepatic veins, and passes through the diaphragm before entering the heart. Its anatomy and patency are important when assessing venous obstruction, intravascular masses and congenital abnormalities, including anomalous pulmonary venous drainage. CT and MRI can delineate its course, calibre, connections and surrounding structures, while contrast-enhanced imaging helps distinguish thrombus from enhancing tissue and assess stenosis. Flow-sensitive cardiac MRI can additionally evaluate venous flow and quantify associated abnormal circulatory connections.

Intravascular ultrasound (IVUS) is a catheter-based imaging technique that uses a miniature ultrasound transducer positioned inside a blood vessel to produce cross-sectional images of its lumen and wall. High-frequency sound waves are emitted and reflected by surrounding tissues, allowing assessment of vessel dimensions, atherosclerotic plaque burden, remodeling, and calcium. In coronary practice, IVUS complements angiography, which primarily depicts the lumen, and guides selection, placement, and optimization of stents during percutaneous coronary intervention. It can help identify plaque-related abnormalities or coronary dissection when investigating ischemic presentations without obstructive coronary disease. Compared with optical coherence tomography, IVUS generally offers greater tissue penetration but lower spatial resolution. It may also be combined with near-infrared spectroscopy to assess plaque structure alongside lipid content.

Joint space width (JSW) is the measured distance between opposing articular bone surfaces in a joint, used as an indirect indicator of the intervening cartilage and other joint tissues. It is not a direct measurement of cartilage thickness, because cartilage is generally not separately delineated on routine radiographs or non-contrast CT. CT enables three-dimensional assessment of this distance across joint surfaces, whereas radiographs show a projected joint space that depends on positioning and beam angle. JSW analysis helps assess structural changes in arthritis, particularly joint space narrowing associated with cartilage loss. Measurements depend on joint anatomy, loading, alignment, image resolution and the method used to identify bone surfaces, so these factors matter when comparing examinations or interpreting regional differences.

Kawasaki disease (KD) is an acute systemic vasculitis that predominantly affects young children and has a particular tendency to involve the coronary arteries. Its cause is unknown, and diagnosis is clinical, based on persistent fever with characteristic mucocutaneous features, conjunctival inflammation, extremity changes and cervical lymphadenopathy; incomplete presentations also occur. Cardiovascular complications include coronary artery dilatation or aneurysms, thrombosis, stenosis and myocardial ischemia, as well as acute myocardial inflammation and ventricular dysfunction. Echocardiography is the first-line cardiac imaging test. Cardiac MRI can assess ventricular volumes and function, myocardial perfusion and tissue injury without ionizing radiation. Coronary CT angiography provides detailed assessment of coronary anatomy, particularly when echocardiographic visualization is limited. Imaging supports risk stratification and surveillance of persistent coronary abnormalities.

Kinetic energy (KE) is the energy associated with blood motion within the heart or vessels. In cardiac MRI, it can be estimated from time-resolved, three-dimensional velocity measurements acquired with 4D flow imaging. For each voxel, kinetic energy is calculated as one-half of the blood mass multiplied by the squared velocity magnitude; summing these contributions within a segmented chamber gives its total blood kinetic energy at a particular phase of the cardiac cycle. Measurements may also be normalized to chamber volume or stroke volume. Intracardiac kinetic energy describes the changing energetics of ventricular filling and ejection and is used in research to characterize altered flow in ventricular dysfunction and remodeling. It depends on both blood velocity and the volume included, making accurate chamber contours and consistent acquisition methods important.

Left atrial (LA) refers to the left atrium, the cardiac chamber that receives oxygenated blood from the pulmonary veins and delivers it to the left ventricle through the mitral valve. Its function comprises reservoir filling during ventricular systole, passive conduit flow during early ventricular diastole, and active contraction during late diastole in sinus rhythm. Cardiac MRI assesses left atrial size, volumes, emptying function, and myocardial deformation using cine imaging and feature-tracking strain analysis. These measurements help characterize atrial remodeling associated with ventricular dysfunction, valvular disease, cardiomyopathy, and other conditions. Left atrial strain reflects deformation rather than stiffness directly; stiffness assessment generally combines deformation or volume measurements with information about filling pressure.

Left atrial appendage (LAA) is a muscular, trabeculated pouch projecting from the left atrium, with a narrow opening into the atrial cavity and variable shape and size. It contributes to atrial reservoir function and contains pectinate muscles. Reduced appendage contraction and blood stasis, particularly during atrial fibrillation or atrial flutter, can promote thrombus formation and subsequent systemic embolism, including ischemic stroke. Transesophageal echocardiography assesses its anatomy, blood flow and possible thrombus. Contrast-enhanced cardiac CT also evaluates the appendage; delayed imaging helps distinguish persistent thrombus from incomplete contrast mixing caused by slow flow. Cardiac MRI can provide complementary anatomical and tissue assessment. Appendage imaging supports thrombus exclusion before selected cardiac procedures and planning for left atrial appendage occlusion. Congenital absence is a rare anatomical variant.

Left atrial appendage occlusion (LAAO) is a procedure that closes or excludes the left atrial appendage from the circulation to reduce thromboembolic stroke risk in selected patients with atrial fibrillation. Impaired atrial contraction can cause blood stasis and thrombus formation within this pouch, allowing emboli to enter the systemic circulation. Occlusion may be achieved percutaneously with an implanted closure device or surgically by clipping, ligating or removing the appendage. Cardiac CT and transesophageal echocardiography assess appendage anatomy, exclude thrombus and guide device selection and placement; cardiac MRI can also provide anatomical measurements for planning. Follow-up imaging evaluates closure completeness, residual flow around a device and device-related thrombus. Antithrombotic treatment after the procedure depends on the technique and the patient’s clinical circumstances.

Left atrioventricular coupling index (LACI) is an imaging-derived measure calculated by dividing left atrial volume by left ventricular volume, with both measured at ventricular end-diastole, and often expressed as a percentage. It describes the size of the left atrium relative to the left ventricle at the same point in the cardiac cycle, rather than using the maximum atrial volume. A higher value indicates a relatively larger atrium, which may reflect altered chamber remodeling and impaired ventricular filling. Cardiac MRI can determine these volumes from cine images; echocardiography and cardiac CT can also assess them. LACI is investigated as a marker of atrioventricular remodeling and prognosis in heart failure and cardiomyopathies, but does not directly measure filling pressure.

Left anterior descending (LAD) refers to the coronary artery that usually arises from the left main coronary artery and runs in the anterior interventricular groove toward the cardiac apex. Its diagonal and septal branches supply much of the anterior left ventricular wall, the anterior interventricular septum and often the apex. Acute LAD occlusion can cause myocardial infarction, with the extent of injury depending on the obstruction’s location and coronary anatomy. Coronary CT angiography assesses its course, lumen and atherosclerotic plaque, while cardiac MRI evaluates associated perfusion abnormalities, ventricular dysfunction and myocardial injury or scar. LAD ligation is also used in experimental models to produce regional myocardial ischemia or infarction.

Left atrial strain (LAS) is a quantitative measure of left atrial myocardial deformation during the cardiac cycle, expressed as a percentage change in length relative to a reference state. Reservoir strain describes atrial stretching as the chamber receives pulmonary venous blood during ventricular systole; conduit and contraction strain describe deformation during passive emptying and active atrial contraction. In cardiac MRI, strain can be estimated by feature tracking of the atrial wall on cine images, commonly in long-axis views. LAS reflects atrial function and is influenced by atrial compliance, ventricular filling pressures, and loading conditions. It can help assess atrial dysfunction in cardiomyopathy and other cardiovascular diseases, complementing atrial volume measurements. Values depend on the strain phase, reference timing, image quality, and analysis software.

Left bundle branch area pacing (LBBAP) is a cardiac pacing technique in which a lead is advanced from the right ventricular side deep into the interventricular septum to stimulate the left bundle branch, its branches, or adjacent left ventricular septal myocardium. It encompasses both direct conduction-system pacing and left ventricular septal pacing without confirmed conduction-system capture. By activating the left ventricle through or near its conduction network, it aims to preserve or improve ventricular electrical synchrony. It is used for bradycardia pacing and, in selected patients, cardiac resynchronization. Cardiac MRI can characterize septal scar that may affect lead placement or pacing response, while cardiac CT can assess lead-tip depth and its relationship to septal anatomy.

Left bundle branch block (LBBB) is a cardiac conduction abnormality in which electrical activation through the left bundle branch is delayed or interrupted. The left ventricle is consequently activated through slower alternative pathways, producing a characteristic widened QRS complex on the electrocardiogram and potentially causing mechanical dyssynchrony. LBBB may accompany structural heart disease or occur without an identifiable underlying disorder; its effects on ventricular contraction can contribute to impaired systolic function and heart failure. Cardiac MRI assesses associated ventricular size, function, myocardial scar and underlying cardiomyopathy, while cine imaging and feature tracking can characterize altered contraction and myocardial strain. In selected patients with heart failure, LBBB is relevant to decisions about cardiac resynchronization therapy or conduction-system pacing.

Left circumflex (LCX) refers to the coronary artery that usually branches from the left main coronary artery and runs in the left atrioventricular groove, between the left atrium and left ventricle. Through its branches, it supplies the lateral and posterolateral left ventricular walls, with the extent of its territory depending on coronary dominance and individual anatomy. Narrowing or occlusion can cause myocardial ischemia or infarction in this territory. Coronary CT angiography assesses its course, lumen, atherosclerotic plaque and surrounding tissues. Cardiac MRI evaluates the consequences of impaired blood supply, including regional wall-motion abnormalities, perfusion defects and myocardial scar identified by late gadolinium enhancement.

Low-dose (LD) describes a CT acquisition protocol designed to reduce patient exposure to ionizing radiation while preserving image quality sufficient for the clinical task. Radiation output can be lowered by adjusting tube current, tube voltage, scan coverage or other acquisition settings, often alongside automatic exposure control and reconstruction methods that manage increased image noise. Photon-counting detectors can support dose-efficient imaging by directly counting X-ray photons and using their energy information. Low-dose protocols are used in chest imaging and selected CT angiography examinations when diagnostic requirements permit reduced radiation exposure. The designation is relative to the examination and patient rather than a universal dose threshold. Low-dose refers to radiation exposure and should not be confused with a low-contrast protocol, which reduces the amount of administered contrast medium.

Late gadolinium enhancement (LGE) is a cardiac MRI technique that identifies myocardial injury and replacement fibrosis by imaging delayed retention of a gadolinium-based contrast agent. Gadolinium distributes in the extracellular space and shortens T1 relaxation time; regions with expanded extracellular space or altered contrast washout appear bright on T1-weighted images acquired after a delay. Inversion-recovery sequences suppress the signal from normal myocardium, making abnormal tissue conspicuous. The location and distribution of enhancement help distinguish ischemic injury, which typically involves the subendocardium in a coronary territory, from nonischemic patterns seen in cardiomyopathies and inflammatory disease. LGE supports assessment of myocardial viability, scar burden and arrhythmic risk, but it does not directly measure diffuse interstitial fibrosis and must be interpreted alongside other imaging and clinical findings.

Late gadolinium enhancement cardiac magnetic resonance (LGE-CMR) is a cardiac MRI technique that identifies tissue injury and scar by acquiring images after administration of a gadolinium-based contrast agent. Gadolinium distributes in the extracellular space and is retained longer in areas with expanded extracellular volume, such as fibrosis or necrosis, than in normal myocardium. Inversion-recovery sequences suppress the signal from normal myocardium, making affected tissue appear bright. The location, distribution and extent of enhancement help distinguish ischemic from nonischemic injury, assess myocardial scar and support evaluation of arrhythmia substrates and ablation planning. Three-dimensional acquisitions can also assess atrial fibrosis and ablation-related scar, although the thin atrial wall makes measurement technically challenging. Enhancement must be interpreted alongside other imaging findings and the clinical context.

Liver iron concentration (LIC) is the amount of iron per unit mass of liver tissue, conventionally expressed relative to dry tissue weight. It is a quantitative marker of hepatic iron accumulation used to assess iron overload, including hereditary hemochromatosis and transfusion-related iron loading, and to monitor treatment such as iron chelation. MRI estimates LIC indirectly because iron accelerates transverse relaxation, increasing R2 and R2* and shortening T2 and T2*. Validated calibration methods translate these relaxation measurements into tissue iron concentration. Chemical shift–encoded MRI can estimate R2* alongside liver fat, provided relevant confounding effects are addressed. Spectral CT methods can also investigate hepatic iron through its energy-dependent X-ray attenuation. LIC reflects hepatic iron burden but does not directly establish myocardial iron loading, which requires separate assessment.

Late iodine enhancement (LIE) is a cardiac CT technique that depicts myocardial tissue retaining iodinated contrast on images acquired several minutes after contrast administration. Iodine distributes within the extracellular space, so areas with expanded extracellular volume, such as infarct scar, fibrosis or infiltrative disease, may show greater delayed enhancement than normal myocardium. Enhancement patterns help distinguish ischemic injury, typically involving the subendocardium in a coronary distribution, from nonischemic myocardial abnormalities. Spectral CT, including photon-counting CT, can generate iodine maps that improve visualization and support quantification of delayed iodine distribution. LIE provides tissue characterization complementary to coronary CT angiography and may be useful when cardiac MRI is unsuitable, although image quality, radiation exposure and contrast requirements must be considered.

Large language model (LLM) is a deep-learning system trained on large collections of text to interpret and generate language, including clinical and radiological text. Most contemporary models use transformer architectures, which learn contextual relationships between tokens and generate responses by predicting successive tokens. In medical imaging, LLMs can extract information from referral notes, classify imaging requests, structure reports and interpret textual descriptions of imaging findings. These applications may support CT protocol selection, assessment of factors affecting cardiac MRI quality and diagnostic decision support. A text-based LLM does not directly assess image pixels unless combined with an image-processing component. Outputs require clinical validation because models can generate plausible but incorrect statements, omit relevant information and reproduce biases in their training data.

Left main (LM) refers to the proximal segment of the left coronary artery, which usually arises from the left aortic sinus and divides into the left anterior descending and left circumflex coronary arteries. It supplies blood to a large portion of the left ventricular myocardium through these branches, so significant narrowing can jeopardize an extensive myocardial territory. Left main coronary artery disease most commonly results from atherosclerosis and is clinically important when planning revascularization. Coronary CT angiography can assess its origin, course, lumen dimensions and plaque burden. Vasodilator stress perfusion cardiac MRI evaluates the downstream physiological consequences of coronary disease by detecting impaired myocardial perfusion, rather than directly measuring left main stenosis.

Lupus myocarditis (LM) is inflammation of the heart muscle associated with systemic lupus erythematosus, an autoimmune disease that can affect multiple organs. Immune-mediated injury involving autoantibodies, immune complexes and inflammatory pathways can damage cardiomyocytes and impair cardiac function. Manifestations range from subclinical myocardial involvement to chest pain, arrhythmias, heart failure or cardiogenic shock. Diagnosis integrates clinical findings, electrocardiography, cardiac biomarkers and imaging while considering alternative causes, including coronary artery disease and infection. Cardiac MRI can assess ventricular function and identify myocardial edema and nonischemic injury using T1 and T2 mapping and late gadolinium enhancement. These findings support recognition of myocardial inflammation but are not specific to lupus. Endomyocardial biopsy may be considered in selected cases, although sampling can miss patchy inflammation.

Low-Rank Adaptation (LoRA) is a parameter-efficient method for adapting pretrained neural networks to medical-imaging tasks without updating all of their original weights. It represents changes to selected weight matrices as the product of two smaller, low-rank matrices, which are trained while the underlying pretrained weights remain fixed. This reduces the number of trainable parameters and the memory required for fine-tuning compared with updating the full model. In cardiac MRI research, LoRA can adapt foundation models for tasks such as cardiac structure segmentation or generation of synthetic images and anatomical label maps. Its outputs can support image analysis and downstream measurements, but their anatomical accuracy and reliability require validation before clinical use.

Left ventricular (LV) refers to the left ventricle, the muscular cardiac chamber that receives oxygenated blood from the left atrium through the mitral valve and ejects it into the aorta through the aortic valve. Its contraction generates the pressure required to supply the systemic circulation. In cardiac imaging, the term describes chamber size, wall thickness, mass, pumping function, myocardial deformation, and associated abnormalities such as scar or thrombus. Cardiac MRI measures ventricular volumes and ejection fraction from cine images and assesses myocardial strain, tissue characteristics, and remodeling. Contrast-enhanced sequences help identify infarction, fibrosis, and intracavitary thrombus. LV assessment is central to evaluating myocardial infarction, cardiomyopathies, valvular disease, and heart failure.

Left ventricular aneurysm (LVA) is a localized outward bulging of the left ventricular wall that remains akinetic or expands paradoxically during systole. A true aneurysm contains thinned, scarred myocardial tissue and most commonly develops after a transmural myocardial infarction, when damaged muscle is replaced by fibrous scar and undergoes adverse remodeling. It can impair ventricular pumping, contribute to heart failure, provide a substrate for ventricular arrhythmias, and promote mural thrombus formation through blood stasis. Cardiac MRI characterizes the aneurysm’s size, location, wall motion, and effect on ventricular function; late gadolinium enhancement identifies myocardial scar, while dedicated imaging can detect thrombus. Distinguishing a true aneurysm from a pseudoaneurysm, which represents a contained ventricular rupture, is important because their risks and management differ.

Left ventricular diastolic dysfunction (LVDD) is an abnormality of ventricular relaxation, restoring forces or chamber stiffness that impairs filling during diastole and may elevate left ventricular filling pressure. It can occur despite a preserved ejection fraction and is associated with conditions such as hypertension, hypertrophic cardiomyopathy and diabetes. LVDD is not synonymous with heart failure, which requires a compatible clinical syndrome. Echocardiography is the principal assessment method, integrating mitral inflow, tissue Doppler velocities and other indicators of filling pressure. Cardiac MRI provides complementary information through ventricular mass, myocardial tissue characterisation, left atrial size and function, and flow measurements. These findings help characterise underlying myocardial disease and its effects on filling, although MRI does not routinely replace guideline-based echocardiographic assessment.

Left ventricular end-diastolic diameter (LVEDD) is a linear measurement of the internal width of the left ventricular cavity at the end of ventricular filling, when its volume is greatest. It reflects ventricular chamber size and is used to assess dilation and structural remodeling in conditions such as heart failure, dilated cardiomyopathy and valvular disease. In cardiac MRI, LVEDD can be measured on cine images at end-diastole using a defined imaging plane and consistent anatomical landmarks; echocardiography also commonly provides this measurement. Interpretation depends on body size, sex, age and the measurement method. Because a single diameter does not capture the ventricle’s full three-dimensional geometry, MRI assessment generally considers LVEDD alongside ventricular volumes, myocardial mass, wall thickness and ejection fraction.

Left ventricular ejection fraction (LVEF) is the percentage of blood in the left ventricle at the end of diastole that is expelled during the subsequent systolic contraction. It is calculated as end-diastolic volume minus end-systolic volume, divided by end-diastolic volume, and expressed as a percentage. LVEF is a widely used measure of global left ventricular systolic function, although it depends on loading conditions and does not directly measure myocardial contractility. Cardiac MRI measures LVEF by delineating ventricular blood-pool volumes on cine images across the cardiac cycle. Clinically, LVEF helps classify heart failure, monitor cardiomyopathy and treatment-related cardiac dysfunction, and inform device and treatment decisions. A preserved LVEF does not exclude myocardial injury, regional dysfunction or impaired diastolic function.

Left ventricular global longitudinal strain (LVGLS) is a quantitative measure of myocardial deformation that describes overall shortening of the left ventricle along its long axis, from base to apex, during systole. It is expressed as the percentage change in longitudinal length relative to a reference length, usually at end-diastole; shortening conventionally produces a negative value. Global strain combines measurements across ventricular segments to summarise longitudinal systolic function. In cardiac MRI, it can be derived by feature tracking on cine images, and comparable measurements can be obtained from suitably acquired multiphase cardiac CT or echocardiography. LVGLS helps identify and characterise systolic dysfunction, including abnormalities not apparent from ejection fraction alone. Interpretation depends on loading conditions, image quality, analysis method, and software-specific reference ranges.

Left ventricular hypertrophy (LVH) is an increase in left ventricular myocardial mass, often accompanied by thickening of the ventricular walls. It may develop in response to chronic pressure overload, such as hypertension or aortic stenosis, or occur with hypertrophic cardiomyopathy and other myocardial disorders. Infiltrative or storage diseases can produce a similar thickened-wall appearance through tissue deposition rather than enlargement of muscle cells alone. The distribution may be concentric, asymmetric, or predominantly apical, and can affect ventricular relaxation, outflow, and myocardial mechanics. Cardiac MRI measures wall thickness, ventricular mass, volumes, and function, while tissue characterization with late gadolinium enhancement and parametric mapping helps distinguish underlying causes and identify fibrosis. CT can also assess ventricular morphology when clinically indicated.

Left ventricular hypertrabeculation (LVHT) is a morphological feature characterized by prominent muscular trabeculae and deep recesses along the inner surface of the left ventricle. It may occur as an isolated anatomical variant, accompany cardiomyopathy, or develop in settings of altered cardiac loading, such as pregnancy or intensive athletic training. LVHT describes an imaging appearance rather than, by itself, establishing a distinct cardiomyopathy or proving abnormal embryonic myocardial development. Cardiac MRI depicts the trabeculated and compact myocardial layers, measures ventricular size and function, and assesses associated fibrosis or thrombus. Echocardiography also identifies trabeculations and recesses. Imaging criteria overlap with those historically used for left ventricular non-compaction, so interpretation requires clinical context, family history, and associated functional or tissue abnormalities to avoid overdiagnosis.

Left ventricular mass (LVM) is the total mass of the myocardium forming the left ventricle, excluding the blood within its cavity. Cardiac MRI measures it by tracing the inner and outer myocardial boundaries on cine images covering the ventricle, calculating myocardial volume, and multiplying that volume by an assumed myocardial tissue density. Consistent handling of papillary muscles and trabeculations is important because segmentation conventions affect the result. LVM reflects myocardial growth and remodeling associated with pressure or volume overload, cardiomyopathy, and physiological adaptation to exercise. It is used to assess ventricular hypertrophy and monitor structural changes over time or after treatment. For comparison between individuals, LVM is often indexed to body surface area, producing the left ventricular mass index.

Left ventricular mass index (LVMI) is the mass of the left ventricular myocardium normalized to body size, most commonly by dividing it by body surface area and reporting it in grams per square metre. Indexing helps distinguish pathological increases in myocardial mass from differences attributable to body size. Cardiac MRI measures left ventricular mass by delineating the endocardial and epicardial borders on end-diastolic cine images, calculating myocardial volume, and multiplying that volume by myocardial density. Echocardiography estimates mass from ventricular dimensions or volumetric measurements. LVMI is used to identify and monitor left ventricular hypertrophy and remodeling associated with hypertension, valvular disease, cardiomyopathy, and chronic kidney disease. Interpretation requires reference ranges appropriate to the imaging method, sex, and indexing convention.

Left ventricular non-compaction (LVNC) describes a morphological phenotype characterized by prominent left ventricular trabeculations, deep intertrabecular recesses communicating with the ventricular cavity, and a relatively thin compacted myocardial layer. Historically attributed to arrested embryonic myocardial compaction, it is now recognized that excessive trabeculation does not necessarily indicate a developmental disorder or cardiomyopathy. Similar appearances can occur in healthy individuals and in physiological adaptation, as well as alongside inherited or acquired myocardial disease. Cardiac MRI assesses trabecular morphology, ventricular volumes and systolic function, and myocardial fibrosis using late gadolinium enhancement. Imaging criteria alone are insufficient to establish clinically significant disease; interpretation incorporates symptoms, family history, genetic findings, arrhythmias, and associated ventricular dysfunction to distinguish an isolated morphological trait from a pathological cardiac phenotype.

Left ventricular outflow tract (LVOT) is the passage through which blood leaves the left ventricle and enters the aorta during systole. It lies immediately below the aortic valve, between the basal interventricular septum and the anterior mitral leaflet and adjacent fibrous structures. Its geometry and relationship to the mitral valve influence blood flow and susceptibility to obstruction, particularly in hypertrophic cardiomyopathy, where septal thickening and systolic anterior motion of the mitral valve can narrow the passage dynamically. Echocardiography assesses its anatomy and Doppler flow velocities, while cardiac MRI characterizes surrounding myocardium, structural abnormalities and flow. Phase-contrast and four-dimensional flow MRI can quantify LVOT velocities, although measurements depend on acquisition settings and alignment. CT can delineate its anatomy and associated aneurysmal or pseudoaneurysmal changes.

Left ventricular outflow tract obstruction (LVOTO) is a fixed or dynamic impediment to blood flow from the left ventricle toward the aortic valve, producing a pressure gradient during systole. Dynamic obstruction commonly involves narrowing of the outflow tract by a hypertrophied basal septum and systolic anterior motion of the mitral valve, and varies with ventricular loading conditions and contractility. It occurs in hypertrophic cardiomyopathy and can also complicate Takotsubo syndrome. Clinically, it may contribute to breathlessness, chest pain, syncope or hemodynamic instability. Doppler echocardiography is the principal method for assessing the pressure gradient, while cardiac MRI characterizes ventricular anatomy, mitral valve motion and myocardial tissue. Phase-contrast and four-dimensional flow MRI can assess outflow velocities and flow patterns.

Left ventricular reverse remodeling (LVRR) is a reduction in pathological left ventricular enlargement accompanied by improvement in ventricular structure and systolic function, often following treatment of heart failure or its underlying cause. It reflects partial reversal of maladaptive changes driven by myocardial injury, neurohormonal activation and abnormal loading conditions. In dilated cardiomyopathy, it is commonly assessed through decreases in ventricular dimensions or volumes and an increase in left ventricular ejection fraction, although specific criteria vary. Cardiac MRI provides reproducible measurements of ventricular volumes, mass and function, while late gadolinium enhancement and parametric mapping characterize myocardial tissue abnormalities that may influence recovery. LVRR is clinically relevant when monitoring treatment response, assessing prognosis and reassessing management, but does not necessarily indicate complete myocardial recovery or elimination of arrhythmic risk.

Left ventricular thrombus (LVT) is a blood clot formed within the cavity of the left ventricle, usually attached to an area of damaged or poorly contracting myocardium. It develops through a combination of blood stasis, endocardial injury and increased coagulation tendency, particularly after myocardial infarction or in severe left ventricular systolic dysfunction. Thrombi commonly occur near the ventricular apex and may cause systemic embolism, including ischemic stroke. Cardiac MRI assesses their location, size and relationship to myocardial scar or ventricular aneurysm. Contrast-enhanced imaging, particularly late gadolinium enhancement with a long inversion time, helps distinguish thrombus from myocardium and intracardiac masses because thrombus generally lacks contrast uptake. Echocardiography is commonly used initially, while MRI can clarify uncertain findings and support treatment planning and follow-up.

Major adverse cardiovascular events (MACE) is a composite clinical outcome used to evaluate cardiovascular prognosis and the effects of treatment. It commonly includes cardiovascular death, nonfatal myocardial infarction and nonfatal stroke, although some studies include additional outcomes such as heart failure hospitalisation or coronary revascularisation. The exact components must therefore be checked in each study, because MACE is not a universally standardised endpoint. An event is generally recorded when a patient experiences any prespecified component. In cardiac imaging research, MRI measures of ventricular function, myocardial deformation and scar, and CT measures of coronary atherosclerosis, may be assessed for their ability to predict subsequent MACE and improve risk stratification.

Mitral annular disjunction (MAD) is an abnormal separation between the attachment of the posterior mitral valve leaflet at the left atrial wall and the adjacent left ventricular myocardium. This altered junction can permit excessive motion of the posterior annulus and abnormal mechanical stress on the basal ventricular wall and papillary muscles. MAD often accompanies mitral valve prolapse but can occur without it; its presence alone does not establish a high risk of arrhythmia. Echocardiography and cardiac MRI assess the separation dynamically, particularly during systole, and characterize associated valve motion and ventricular function. Cardiac MRI can also detect myocardial fibrosis using late gadolinium enhancement, helping evaluate patients with ventricular arrhythmias or suspected arrhythmic mitral valve prolapse.

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a chronic liver condition defined by hepatic steatosis together with at least one cardiometabolic risk factor, such as excess adiposity, abnormal glucose regulation, hypertension or dyslipidaemia, within specified alcohol-consumption limits. Insulin resistance and altered lipid metabolism promote triglyceride accumulation in hepatocytes; some patients develop steatohepatitis, fibrosis and ultimately cirrhosis. Assessment includes identifying metabolic risk factors, evaluating alcohol exposure and other causes of liver disease, and estimating fibrosis risk. MRI proton density fat fraction provides a quantitative measure of hepatic fat, while CT can detect steatosis and spectral CT techniques can estimate fat content. Liver fat measurements alone do not establish inflammation or fibrosis. MASLD is also associated with increased cardiovascular risk.

Myocardial blood flow (MBF) is the volume of blood delivered to heart muscle per unit time and tissue mass, usually expressed in millilitres per minute per gram. It reflects coronary blood supply relative to myocardial metabolic demand and is influenced by coronary artery narrowing, microvascular function, perfusion pressure and cardiac workload. Quantitative perfusion cardiac MRI estimates MBF by tracking the first passage of a gadolinium-based contrast agent through the blood pool and myocardium and applying tracer kinetic modelling. PET measures the same physiological quantity using radiotracers. Measurements at rest and during pharmacological stress help assess ischemia and coronary microvascular dysfunction; their ratio provides myocardial perfusion reserve. Resting MBF may also be interpreted in relation to heart rate and systolic blood pressure.

Material decomposition (MD) is a computational method in spectral CT that separates measured x-ray attenuation into contributions from selected basis materials or physical interaction components. It exploits differences in how materials attenuate x-rays across photon energies, using measurements from multiple energy channels in photon-counting CT or different spectra in dual-energy CT. The resulting material maps can estimate concentrations of substances such as iodine, distinguish contrast agents from other tissues, and support virtual non-contrast imaging. Material decomposition can also provide information for estimating tissue properties relevant to proton therapy planning, including stopping power. Its accuracy depends on spectral calibration, the chosen material model, and measurement noise; decomposition can amplify noise and is affected by how distinctly the materials’ energy-dependent attenuation patterns differ.

Modified Dixon (mDixon) is an MRI acquisition and reconstruction technique that separates water and fat signals using their different resonance frequencies. Images acquired at different echo times capture differences in the relative phase of water and fat, allowing reconstruction of water-only and fat-only images while accounting for magnetic field inhomogeneity. Modified implementations allow more flexible echo timing than conventional Dixon methods. In MR angiography, water-only reconstruction suppresses surrounding fat to improve vessel conspicuity and support assessment of vascular anatomy and dimensions. It can be incorporated into three-dimensional, contrast-enhanced acquisitions with cardiac and respiratory motion control, including imaging of children with congenital heart disease. The Dixon method itself does not specify the cardiac phase or contrast timing.

Metabolic syndrome (MetS) is a cluster of interrelated cardiometabolic abnormalities that increases the risk of type 2 diabetes and atherosclerotic cardiovascular disease. It comprises central adiposity, elevated blood pressure, elevated fasting glucose, high triglycerides and low high-density lipoprotein cholesterol. Common diagnostic criteria require at least three of these five features, with thresholds depending on the guideline and population. Insulin resistance, visceral fat accumulation and associated inflammatory and metabolic disturbances contribute to its development. Diagnosis relies on clinical measurements and blood tests rather than imaging. Cardiac MRI can assess associated changes in ventricular structure, function and myocardial tissue characteristics, while coronary CT can evaluate coronary atherosclerosis when clinically indicated.

Myocardial flow reserve (MFR) is the ratio of myocardial blood flow during maximal vasodilator stress to myocardial blood flow at rest, expressing the coronary circulation’s capacity to increase blood supply above baseline demand. It reflects the combined effects of flow-limiting epicardial coronary disease, diffuse atherosclerosis and coronary microvascular function rather than identifying any one mechanism alone. MFR is measured using quantitative perfusion imaging, particularly positron emission tomography, and can also be assessed with validated dynamic SPECT or cardiac MRI methods. Reduced MFR indicates impaired coronary vasodilator capacity and can support assessment of ischemic heart disease or coronary microvascular dysfunction. Interpretation requires consideration of resting flow, adequacy of pharmacological stress and the accompanying absolute blood-flow measurements.

Metabolically healthy obese (MHO) describes an obesity phenotype in which an individual meets criteria for obesity but has relatively preserved metabolic health, typically without major abnormalities in blood pressure, glucose regulation, or blood lipids. Definitions vary across clinical and research settings, particularly in the metabolic abnormalities permitted and whether insulin resistance is assessed. This phenotype distinguishes metabolic status from body size alone and may reflect differences in fat distribution, adipose tissue function, and insulin sensitivity. It does not imply absence of cardiovascular risk or guarantee that metabolic health will persist. Cardiac MRI can characterize associated cardiac structure and function through measurements of chamber volumes, myocardial mass, and ventricular performance, but imaging is not required to establish the phenotype.

Myocardial infarction (MI) is irreversible death of heart muscle cells caused by prolonged myocardial ischemia, when oxygen delivery is insufficient to meet tissue demand. In clinical practice, it most commonly results from coronary plaque disruption with thrombosis, although other mechanisms can impair coronary blood flow or produce an oxygen supply–demand imbalance. Infarcted myocardium undergoes inflammation, repair and scar formation, potentially leading to ventricular remodeling, impaired contraction, arrhythmias or intracardiac thrombus. Cardiac MRI assesses ventricular function and infarct extent, with late gadolinium enhancement identifying injured or scarred myocardium in a characteristic ischemic distribution. Additional MRI sequences can assess edema, microvascular obstruction and intramyocardial hemorrhage. Experimental coronary ligation models reproduce ischemic myocardial injury to study healing and remodeling.

Myocardial infarction with nonobstructive coronary arteries (MINOCA) is a clinical syndrome meeting diagnostic criteria for acute myocardial infarction despite coronary angiography showing no stenosis of 50% or greater in a major epicardial coronary artery. It is initially a working diagnosis that requires investigation of the underlying mechanism and exclusion of alternative causes of myocardial injury. Potential mechanisms include plaque disruption with transient thrombosis, coronary vasospasm, microvascular dysfunction, coronary embolism and spontaneous coronary artery dissection. Cardiac MRI helps identify ischemic injury through myocardial edema and a subendocardial or transmural late gadolinium enhancement pattern, while distinguishing nonischemic conditions such as myocarditis and Takotsubo syndrome. Intravascular imaging and coronary functional testing can provide complementary evidence, allowing treatment to be directed toward the identified cause.

Multisystem inflammatory syndrome in children (MIS-C) is a systemic inflammatory illness associated with preceding SARS-CoV-2 infection, typically developing several weeks after infection. It is characterized by persistent fever, elevated inflammatory markers, and involvement of multiple organ systems, with no more likely alternative diagnosis. Manifestations may include gastrointestinal symptoms, rash, conjunctivitis, shock, myocardial dysfunction, and coronary artery abnormalities. The syndrome is thought to reflect a dysregulated immune response rather than direct acute viral injury alone. Echocardiography is used to assess ventricular function, valves, pericardial effusion, and coronary arteries. Cardiac MRI can complement this assessment by measuring ventricular volumes and function and characterizing myocardial edema or injury using mapping techniques and late gadolinium enhancement, particularly when evaluating suspected myocardial involvement or persistent cardiac abnormalities.

Machine learning (ML) is a branch of artificial intelligence in which computational models learn patterns from data to perform tasks such as classification, measurement or prediction without explicitly programmed rules for every case. In clinical medicine, inputs can include speech features, patient characteristics, laboratory results and imaging measurements. In cardiac MRI, models may analyse images directly or combine derived measures, such as ventricular function and myocardial scar burden, with other clinical variables to estimate disease or arrhythmic risk. Deep learning is a subset of machine learning that uses multilayer neural networks. Reliable clinical application requires evaluation on independent data, assessment of bias and generalisability, and interpretation alongside established clinical evidence rather than treating model predictions as definitive diagnoses.

Modified Look-Locker Inversion-Recovery (MOLLI) is a cardiac MRI technique for measuring myocardial T1, the time constant describing recovery of longitudinal magnetization after radiofrequency excitation. It acquires images at different times after inversion pulses, synchronized to the cardiac cycle, usually within a breath-hold. The resulting signal measurements are fitted to a recovery curve to produce a quantitative T1 map. Native T1 mapping requires no contrast agent and helps characterize myocardial abnormalities associated with edema, fibrosis and infiltrative disease. When combined with post-contrast T1 measurements and hematocrit, it can estimate myocardial extracellular volume. MOLLI values depend on field strength, acquisition settings, heart rate and tissue properties, so interpretation requires reference ranges appropriate to the scanner and protocol.

Myocardial perfusion imaging (MPI) is a nuclear medicine examination that assesses blood supply to the heart muscle using single-photon emission computed tomography (SPECT) or positron emission tomography (PET). An injected radiotracer distributes within the myocardium according to blood flow and tracer-specific uptake mechanisms, allowing regional perfusion to be evaluated at rest and during exercise or pharmacological stress. A defect present during stress but improving at rest suggests inducible ischemia, whereas a persistent defect may indicate infarct scar, although attenuation artifacts and viable but poorly perfused myocardium can complicate interpretation. MPI supports diagnosis and risk assessment in coronary artery disease and helps guide management. ECG-gated acquisitions can assess ventricular function, while PET can also quantify myocardial blood flow and flow reserve.

Myocardial perfusion reserve (MPR) is the ratio of myocardial blood flow during maximal or near-maximal vasodilator stress to myocardial blood flow at rest. It reflects the coronary circulation’s capacity to increase blood supply above baseline demand, integrating the effects of epicardial coronary arteries and the microvasculature. Quantitative perfusion cardiac MRI estimates these flows by tracking the first passage of gadolinium contrast through the myocardium at rest and during pharmacological stress. Reduced MPR can indicate obstructive coronary artery disease, coronary microvascular dysfunction or diffuse vascular disease, including cardiac allograft vasculopathy. Interpretation depends on both stress and resting flow, because elevated resting cardiac workload can lower the ratio without necessarily indicating impaired maximal flow. MPR supports assessment of ischemia and cardiovascular risk.

Mitral regurgitation (MR) is the backward flow of blood from the left ventricle into the left atrium during ventricular systole because the mitral valve does not close completely. Primary MR results from abnormalities of the valve apparatus, including mitral valve prolapse, whereas secondary MR arises from altered ventricular or atrial geometry that impairs leaflet coaptation. Persistent regurgitation causes volume overload and may lead to left atrial enlargement, ventricular remodeling, pulmonary hypertension and heart failure. Echocardiography is the first-line imaging method for assessing valve anatomy and severity. Cardiac MRI provides reproducible ventricular volumes and can quantify regurgitant volume and fraction, commonly by comparing left ventricular stroke volume with aortic forward flow, particularly when echocardiographic findings are uncertain or discordant.

Magnetic resonance angiography (MRA) is an MRI technique that depicts blood vessels and assesses their anatomy without ionising radiation. It can use gadolinium-based contrast to shorten blood T1 relaxation time, or non-contrast methods that exploit blood movement, such as time-of-flight and phase-contrast imaging. These approaches distinguish flowing blood from surrounding tissues, allowing assessment of vessel narrowing, occlusion, aneurysms and vascular malformations. MRA is used to investigate peripheral artery disease, plan vascular interventions and monitor treated vessels or aneurysms. Some techniques also quantify blood velocity and flow. Image quality depends on the acquisition method and can be affected by slow or turbulent flow, motion and metallic implants; device-related artefacts may limit assessment after endovascular treatment.

Magnetic resonance imaging (MRI) is a non-invasive imaging technique that uses a strong magnetic field, radiofrequency pulses and magnetic field gradients to produce images without ionising radiation. The magnetic field aligns hydrogen nuclei, and radiofrequency excitation generates signals whose relaxation and spatial encoding allow tissues to be distinguished and localised. In cardiovascular practice, MRI assesses cardiac anatomy, ventricular volumes and function, blood flow, perfusion and myocardial tissue characteristics, including oedema, fibrosis and scar. Imaging is commonly synchronised with the cardiac cycle using an electrocardiogram or another triggering method to reduce motion effects. Contrast agents containing gadolinium may be used for selected examinations, while many anatomical and functional sequences require no contrast. MRI is particularly useful for evaluating cardiomyopathies and congenital cardiovascular abnormalities.

Microvascular obstruction (MVO) is severely impaired blood flow through the myocardial microcirculation following acute myocardial infarction, despite restoration of flow in the supplying epicardial coronary artery. It reflects microvascular injury caused by ischemia and reperfusion, including endothelial swelling, capillary damage, distal embolization and compression by tissue edema. MVO is a tissue-level manifestation of the no-reflow phenomenon and may coexist with intramyocardial hemorrhage. On contrast-enhanced cardiac MRI, it appears as a region of reduced or absent gadolinium enhancement within the surrounding enhanced infarct, visible on early post-contrast imaging or late gadolinium enhancement images. Assessing its presence and extent helps characterize infarct severity and provides prognostic information about adverse ventricular remodeling and subsequent cardiovascular risk.

Mitral valve prolapse (MVP) is a structural abnormality in which one or both mitral valve leaflets displace into the left atrium during ventricular systole, conventionally by more than 2 mm beyond the mitral annular plane on an appropriate long-axis view. It commonly reflects degenerative changes in the leaflets and supporting chordae, including myxomatous disease or fibroelastic deficiency, and may cause mitral regurgitation through impaired leaflet coaptation. Echocardiography is the primary diagnostic test. Cardiac MRI complements echocardiography by assessing ventricular size and function, quantifying regurgitation, and identifying associated mitral annular disjunction and myocardial fibrosis using late gadolinium enhancement. Although many patients have a benign course, a subset develops clinically important regurgitation or ventricular arrhythmias, making assessment of valve anatomy and myocardial involvement relevant to management.

Normalized iodine concentration (NIC) is a quantitative contrast-enhanced spectral CT measure calculated by dividing the iodine concentration in a tissue or lesion by that in a reference structure, usually a blood vessel imaged during the same acquisition. Dual-energy and photon-counting CT can distinguish iodine from other materials through its energy-dependent X-ray attenuation, producing iodine maps from which these measurements are obtained. Normalization helps reduce variation related to contrast delivery and circulating iodine levels, although results still depend on acquisition timing, reference selection and measurement technique. NIC provides a relative indicator of tissue enhancement and vascular contrast distribution. In oncological imaging, it is used to investigate tumour vascularity, characterize lesions and assess treatment-related changes; it is not a direct measurement of blood flow.

Non-ischemic cardiomyopathy (NICM) is a group of disorders affecting heart muscle in which structural or functional abnormalities are not primarily caused by coronary artery disease or myocardial ischemia. Causes include genetic abnormalities, inflammation, toxic exposures and infiltrative diseases; some cases remain unexplained. These disorders can impair ventricular contraction or relaxation and produce myocardial fibrosis, creating a substrate for heart failure and ventricular arrhythmias. Cardiac MRI measures ventricular volumes and function and characterizes myocardial tissue using late gadolinium enhancement and mapping techniques. The distribution of enhancement can help distinguish non-ischemic injury from infarction and suggest an underlying cause. MRI findings contribute to diagnosis, arrhythmic risk assessment and treatment planning, alongside clinical findings, electrocardiography and genetic evaluation when appropriate.

Non-ischemic dilated cardiomyopathy (NIDCM) is a myocardial disorder characterized by left ventricular enlargement and impaired systolic contraction that are not explained by coronary artery disease or abnormal loading conditions, such as significant valve disease or hypertension. The right ventricle may also be affected. Causes include genetic abnormalities, inflammatory injury, toxins and metabolic disorders, although the cause may remain unidentified. Cardiac MRI accurately measures ventricular volumes, mass and ejection fraction and helps distinguish ischemic from non-ischemic patterns of myocardial injury. Late gadolinium enhancement identifies focal fibrosis, while native T1 mapping and extracellular volume assessment can characterize diffuse myocardial abnormalities. These findings support diagnosis, assessment of arrhythmic risk and monitoring of reverse remodeling during treatment.

N-terminal pro–B-type natriuretic peptide (NT-proBNP) is a biologically inactive peptide released into the circulation when the precursor of B-type natriuretic peptide is cleaved. It is produced predominantly by cardiac muscle cells in response to increased myocardial wall stress associated with pressure or volume loading. Measurement in blood helps support or exclude a diagnosis of heart failure and provides information about prognosis and disease severity, but it is not specific to a single cardiac disorder. Concentrations are influenced by age, renal function, atrial fibrillation and obesity, so interpretation requires clinical context. In cardiac MRI assessment, NT-proBNP complements measurements of ventricular volumes, ejection fraction, myocardial strain and tissue characteristics by providing a biochemical indicator of cardiac stress.

Osteoarthritis (OA) is a chronic disease of synovial joints characterized by progressive loss and alteration of articular cartilage, remodeling of subchondral bone, osteophyte formation, and variable synovial inflammation. It affects the whole joint and commonly causes pain, stiffness, and reduced function through interacting mechanical, biological, and inflammatory processes. Imaging supports assessment of structural damage: radiographs show joint space narrowing and osteophytes, while MRI depicts cartilage, bone marrow lesions, menisci, and other soft tissues. CT provides detailed three-dimensional assessment of bone, joint geometry, and mineralized deposits, supporting structural analysis and biomechanical modeling. Spectral CT techniques can investigate differences in the composition of joint calcifications, although identifying specific crystal types noninvasively remains an area of research.

Optical coherence tomography (OCT) is a high-resolution imaging technique that uses near-infrared light and low-coherence interferometry to generate cross-sectional images of tissue. In coronary imaging, a catheter directs light at the vessel wall and measures reflected signals, revealing the arterial lumen, superficial plaque structure and implanted stents. Blood must usually be displaced by a brief contrast flush because it scatters light. OCT can identify fibrous caps, plaque rupture, features consistent with plaque erosion, intracoronary thrombus and calcium, and can assess stent expansion and apposition during percutaneous coronary intervention. It complements cardiac MRI by investigating coronary causes of myocardial injury, including myocardial infarction with nonobstructive coronary arteries. Its finer spatial resolution than intravascular ultrasound is balanced by more limited tissue penetration.

Out-of-hospital cardiac arrest (OHCA) is the abrupt loss of effective cardiac pumping and circulation occurring outside a hospital, typically causing unresponsiveness and absent normal breathing. It may result from ventricular fibrillation, pulseless ventricular tachycardia, pulseless electrical activity or asystole. Causes include coronary ischemia, structural heart disease, primary electrical disorders and noncardiac conditions such as severe hypoxemia. Immediate cardiopulmonary resuscitation and, when indicated, defibrillation are essential to restore circulation and limit brain injury. After stabilization, investigations seek the underlying cause and guide prevention of recurrence. Cardiac MRI can assess ventricular function and identify myocardial infarction, inflammation, fibrosis or cardiomyopathy, while coronary CT angiography may help evaluate coronary anatomy in selected patients.

Obstructive sleep apnea (OSA) is a sleep-related breathing disorder characterized by recurrent partial or complete collapse of the upper airway during sleep despite continued respiratory effort. These episodes cause reduced airflow or pauses in breathing, often accompanied by intermittent hypoxemia, sleep fragmentation, and sympathetic nervous system activation. Symptoms may include loud snoring, witnessed breathing pauses, and excessive daytime sleepiness. Diagnosis generally uses polysomnography or an appropriate home sleep apnea test, with severity commonly graded by the frequency of apneas and hypopneas. OSA is associated with hypertension, atrial fibrillation, and other cardiovascular disorders. Cardiac MRI is not a diagnostic test for OSA but can assess associated ventricular remodeling, function, myocardial tissue characteristics, and aortic stiffness.

Pulmonary artery (PA) refers to the vessel carrying blood from the right ventricle toward the lungs for gas exchange. The main pulmonary artery, or pulmonary trunk, arises beyond the pulmonary valve and divides into right and left pulmonary arteries, which branch within the lungs. In normal postnatal circulation, these vessels carry deoxygenated blood through a low-pressure, low-resistance vascular system. Cardiac MRI and CT can assess pulmonary artery diameter, cross-sectional area, branching anatomy, and relationships to surrounding structures. Phase-contrast and four-dimensional flow MRI quantify blood flow and characterize flow patterns, while pulse wave velocity measurements can assess arterial stiffness. These assessments support evaluation of congenital heart disease, postoperative anatomy, pulmonary hypertension, and pulmonary artery narrowing or dilatation.

Peripheral artery disease (PAD) is narrowing or occlusion of arteries supplying the limbs, most commonly the lower extremities, usually caused by atherosclerosis. Reduced arterial blood flow can cause exertional muscle pain known as intermittent claudication, while severe disease may produce ischemic rest pain, nonhealing wounds, or gangrene. Acute limb ischemia can result from sudden thrombosis or embolism. Assessment combines clinical examination and physiological testing, such as the ankle–brachial index, with imaging when anatomical detail is needed. Duplex ultrasound evaluates blood flow and stenosis, while CT angiography and MR angiography map arterial lesions and distal runoff for treatment planning. Photon-counting CT angiography can provide high-resolution vascular images, although calcification and artifacts remain important considerations when assessing lumen patency.

Pulmonary arterial hypertension (PAH) is a form of precapillary pulmonary hypertension caused by disease of the small pulmonary arteries, with elevated pulmonary vascular resistance and normal left-sided filling pressure. It is defined haemodynamically by a mean pulmonary arterial pressure above 20 mmHg, pulmonary arterial wedge pressure of 15 mmHg or less, and pulmonary vascular resistance above 2 Wood units at right heart catheterization. Progressive vascular narrowing and remodelling increase right ventricular afterload, potentially leading to right ventricular dilatation, dysfunction and heart failure. Cardiac MRI assesses right ventricular volumes, mass, ejection fraction, myocardial strain and pulmonary arterial flow, supporting evaluation of disease severity and treatment response. It also characterizes ventricular interaction, including septal displacement and reduced left ventricular filling, but does not replace catheterization for haemodynamic diagnosis.

Photon-counting CT (PCCT) is a computed tomography technique that uses semiconductor detectors to count individual X-ray photons and classify them by energy. Unlike conventional energy-integrating detectors, which convert X-rays into light before measuring the combined signal, photon-counting detectors directly convert absorbed photons into electrical pulses. This enables energy-resolved imaging and small detector elements that support high spatial resolution. Spectral data can be used to generate virtual monoenergetic images, iodine maps and other material-specific reconstructions. Clinically, PCCT is used to assess coronary arteries, characterize lesions and depict fine anatomical structures, including bone and lung tissue. Its spectral reconstructions can also help manage metal artifacts, although image quality depends on acquisition settings, reconstruction methods and the clinical task.

Photon-counting detector CT angiography (PCCTA) is contrast-enhanced computed tomography of blood vessels performed using detectors that directly convert individual X-ray photons into electrical signals and sort them by energy. Intravenous iodinated contrast is timed to enhance the vessels of interest, allowing assessment of their lumen, course and surrounding anatomy. Compared with conventional energy-integrating detector systems, photon-counting technology supports high spatial resolution and energy-resolved imaging, which can be used for material decomposition and specialized vascular reconstructions. Clinical applications include evaluating intracranial aneurysms, arterial stenosis and other vascular abnormalities, as well as planning interventions. Multiplanar and three-dimensional reconstructions aid assessment of vascular morphology and dimensions, while dedicated spectral reconstructions can support vessel wall visualization. Image quality depends on acquisition settings, contrast timing, motion and reconstruction technique.

Photon-counting detector (PCD) is an X-ray detector that registers individual incident photons and classifies them by energy using electronic thresholds. In CT, semiconductor materials directly convert absorbed X-rays into electrical pulses, whose amplitudes reflect the deposited photon energy. Unlike energy-integrating detectors, which combine the energy contributed by many photons, PCDs provide photon counts in distinct energy bins, enabling spectral imaging and material decomposition. Their small detector elements support high spatial resolution, while energy thresholds help exclude electronic noise. Clinically, PCD-based CT is used to assess vascular anatomy, calcification, stents, prosthetic valves and other fine structures, and to generate iodine maps and virtual monoenergetic images. Detector response variation and high photon flux can affect spectral accuracy and require calibration and correction.

Photon-counting detector CT myelography (PCD-CTM) is an imaging technique that combines intrathecal iodinated contrast administration with CT performed using photon-counting detectors. Contrast is introduced into the spinal subarachnoid space, usually by lumbar puncture, to outline cerebrospinal fluid pathways and reveal abnormal contrast escape. The detectors directly convert individual X-ray photons into electrical signals and sort them by energy, supporting high spatial resolution and spectral imaging. PCD-CTM is used to investigate spinal cerebrospinal fluid leaks and cerebrospinal fluid–venous fistulas, particularly in patients with spontaneous intracranial hypotension. For fistula detection, patient positioning and scan timing help demonstrate contrast passing from the subarachnoid space into adjacent veins. Findings can localize the abnormal connection and guide targeted treatment.

Percutaneous coronary intervention (PCI) is a catheter-based procedure used to restore blood flow through a narrowed or occluded coronary artery without open-heart surgery. Access is usually obtained through the radial or femoral artery, and a guidewire is advanced across the coronary lesion under X-ray angiographic guidance. Balloon dilation enlarges the lumen, and a stent is commonly implanted to maintain vessel patency. PCI is used urgently to reperfuse myocardium in acute myocardial infarction and electively in selected patients with coronary artery disease to relieve ischemic symptoms. Coronary CT angiography can characterize coronary anatomy and support procedural planning, while cardiac MRI can assess ventricular function, infarct extent, myocardial viability, and microvascular obstruction after reperfusion.

Patent ductus arteriosus (PDA) is persistence after birth of the ductus arteriosus, a fetal vascular connection between the proximal descending aorta and the pulmonary artery near its left branch. This vessel normally closes after birth as oxygen levels rise and circulating prostaglandin effects diminish. A persistent connection usually produces a left-to-right shunt, increasing pulmonary blood flow and left heart volume load; a large longstanding shunt can cause pulmonary vascular disease and pulmonary hypertension, sometimes progressing to shunt reversal. Echocardiography is generally the initial diagnostic test. CT angiography depicts ductal size, shape, calcification and relationships to adjacent vessels, supporting closure planning. Cardiac MRI can quantify shunt flow and ventricular volumes and assess the associated cardiovascular consequences without ionizing radiation.

Pancreatic ductal adenocarcinoma (PDAC) is a malignant epithelial tumour of the pancreas that shows ductal differentiation and typically forms infiltrating glands within dense fibrous stroma. It is the most common pancreatic malignancy and can invade adjacent vessels and organs, spread to lymph nodes and distant sites, and recur after surgical resection. Contrast-enhanced CT is central to diagnosis, staging, assessment of vascular involvement and surgical planning, and surveillance after treatment. The tumour often enhances less than surrounding pancreatic tissue because of its stromal composition and relatively low perfusion. After surgery, recurrent tumour may resemble benign fibrosis on imaging. Spectral CT, including photon-counting CT, can provide iodine-sensitive measurements and energy-dependent images to support assessment of suspicious postoperative tissue alongside clinical findings and other investigations.

Proton density fat fraction (PDFF) is a quantitative measure of tissue fat content, defined as the proportion of mobile protons attributable to fat relative to the total mobile protons attributable to fat and water. In liver MRI, it is commonly measured using chemical shift–encoded acquisitions that separate water and fat signals through their different resonance frequencies. Accurate estimation accounts for confounding factors such as T1 bias, T2* signal decay and the multiple spectral peaks of fat. PDFF provides a noninvasive measure of hepatic steatosis and supports assessment and longitudinal monitoring of metabolic dysfunction-associated steatotic liver disease and other liver conditions. It also serves as a reference for evaluating CT-based fat quantification, but does not directly measure liver inflammation or fibrosis.

Pulmonary endarterectomy (PEA) is a surgical procedure that removes organized thromboembolic material and the affected inner lining from the pulmonary arteries in patients with operable chronic thromboembolic pulmonary hypertension. This material obstructs pulmonary blood flow, increasing pulmonary vascular resistance and the pressure load on the right ventricle. Surgery is performed using cardiopulmonary bypass, typically with deep hypothermia and periods of circulatory arrest to provide a bloodless field for precise dissection. Restoring arterial patency can reduce pulmonary pressures and allow right ventricular recovery, although residual pulmonary hypertension may persist. CT pulmonary angiography helps define the distribution and surgical accessibility of disease, while cardiac MRI assesses right ventricular volumes, mass, function, and postoperative remodeling.

Positron emission tomography (PET) is a nuclear imaging technique that maps the distribution of a positron-emitting radiotracer to assess physiological and molecular processes. When a positron annihilates with an electron, two photons are emitted in approximately opposite directions; detectors record these coincident photons to reconstruct the tracer distribution. The tracer determines what is measured, such as myocardial perfusion, glucose metabolism or inflammatory activity. Cardiovascular PET is used to quantify myocardial blood flow and flow reserve, evaluate myocardial viability, and investigate selected inflammatory disorders. It can also characterize metabolic changes associated with pulmonary hypertension and ventricular remodeling. PET is commonly combined with CT for attenuation correction and anatomical localization, while MRI provides complementary assessment of cardiac structure, function and tissue characteristics.

Papillary fibroelastomas (PFE) are benign cardiac tumors composed of branching, avascular fronds with collagen and elastic tissue cores covered by endothelium. They usually arise from heart valves but can occur on other endocardial surfaces. Although often incidental, mobile left-sided lesions can cause systemic embolization, including ischemic stroke, through tumor fragments or associated thrombus. Echocardiography, particularly transesophageal echocardiography, is central to identifying their attachment, mobility and relationship to valves. Cardiac CT and MRI can complement echocardiography by defining location and surrounding anatomy, although small size and rapid motion may limit detection and MRI tissue characterization. Imaging helps distinguish these lesions from thrombi, vegetations and other cardiac masses and informs decisions about surgical excision.

Patent foramen ovale (PFO) is a persistent flap-like communication between the right and left atria caused by incomplete fusion of the septum primum and septum secundum after birth. Unlike an atrial septal defect, it does not represent missing septal tissue. It is usually clinically silent, but transient or sustained right-to-left shunting can allow venous emboli to enter the systemic circulation, causing paradoxical embolism, or permit deoxygenated blood to bypass the lungs, causing hypoxemia. Positional shunting may produce platypnea-orthodeoxia, with breathlessness and reduced oxygen saturation when upright. Contrast echocardiography with agitated saline, often combined with provocative maneuvers, is the principal diagnostic test. Cardiac MRI and CT can assess associated cardiac anatomy and alternative causes of shunting but are not primary tests for detecting a small PFO.

Pulmonary hypertension (PH) is a haemodynamic condition defined by a mean pulmonary arterial pressure greater than 20 mmHg at rest, measured by right heart catheterization. It can result from pulmonary arterial disease, left heart disease, lung disease or hypoxia, chronic pulmonary arterial obstruction, or multifactorial mechanisms. Pre-capillary and post-capillary forms are distinguished using pulmonary arterial wedge pressure and pulmonary vascular resistance. Increased pulmonary vascular load can cause right ventricular hypertrophy, dilatation and eventual failure. Cardiac MRI assesses right ventricular volumes, mass, ejection fraction and myocardial deformation, and measures blood flow through the pulmonary artery. These measurements support evaluation of disease severity, ventricular adaptation and treatment response, but MRI does not replace catheterization for definitive haemodynamic diagnosis.

Plaque-to-myocardium signal intensity ratio (PMR) is a dimensionless cardiac MRI measurement that compares the signal intensity of a coronary atherosclerotic plaque with that of reference myocardium on the same T1-weighted images. It is calculated by dividing plaque signal intensity by myocardial signal intensity, providing a relative measure of plaque brightness rather than an absolute tissue property. High plaque signal on T1-weighted imaging can reflect T1 shortening associated with methemoglobin in intraplaque hemorrhage, although the ratio alone does not establish plaque composition. PMR is used mainly in research to characterize high-intensity coronary plaques and investigate their relationship with adverse coronary events and plaque features on coronary CT angiography. Measurements depend on acquisition technique and region-of-interest placement, and classification thresholds vary across protocols.

Primary percutaneous coronary intervention (PPCI) is an emergency catheter-based procedure to restore blood flow through an acutely occluded coronary artery in patients with ST-elevation myocardial infarction, without preceding fibrinolytic treatment. Under fluoroscopic guidance, a catheter is advanced through an arterial access site, usually the radial or femoral artery, and coronary angiography identifies the culprit lesion. A guidewire crosses the obstruction, and balloon dilation and usually stent implantation reopen the artery. Rapid reperfusion limits myocardial injury, although microvascular damage can persist despite successful restoration of flow in the larger vessel. Cardiac MRI after PPCI can quantify ventricular function and infarct extent, identify microvascular obstruction and intramyocardial hemorrhage, and assess subsequent ventricular remodeling.

Peripartum cardiomyopathy (PPCM) is a form of heart failure caused by left ventricular systolic dysfunction that develops toward the end of pregnancy or in the months following delivery, without another identifiable cause. Left ventricular ejection fraction is typically below 45%, although the ventricle need not be dilated. Its mechanisms are incompletely understood and may involve vascular dysfunction, oxidative stress, hormonal factors and genetic susceptibility. Presentation ranges from breathlessness and peripheral edema to arrhythmias, thromboembolism or cardiogenic shock. Echocardiography is the initial imaging test, while cardiac MRI can accurately quantify ventricular volumes and function, identify intracardiac thrombus and characterize myocardial tissue. Late gadolinium enhancement can demonstrate focal myocardial injury or fibrosis, but its absence does not exclude PPCM. Serial imaging helps assess recovery and guide ongoing management.

Protein quantitative trait loci (pQTL) are genomic regions containing genetic variants statistically associated with differences in protein abundance, commonly measured in blood plasma. These associations can reflect genetic effects on protein production, processing, secretion or clearance. Loci near the gene encoding the measured protein are termed cis-pQTL, whereas more distant loci are termed trans-pQTL. In cardiovascular research, pQTL help connect inherited genetic variation with circulating proteins, disease susceptibility and quantitative traits measured by cardiac MRI. They can serve as genetic instruments in Mendelian randomization, while colocalization analysis assesses whether protein and disease associations may share a causal variant. Such analyses support investigation of disease mechanisms and potential therapeutic targets, but an association alone does not establish causality.

Pulmonary regurgitation (PR) is backward flow of blood from the pulmonary artery into the right ventricle during diastole because the pulmonary valve does not close effectively. It may result from congenital valve abnormalities, pulmonary hypertension, or previous surgical or catheter-based treatment of congenital heart disease, particularly reconstruction of the right ventricular outflow tract. Chronic significant regurgitation causes right ventricular volume overload, which can lead to ventricular dilatation, impaired function, exercise intolerance, and arrhythmias. Echocardiography assesses valve anatomy and regurgitant flow, while cardiac MRI quantifies backward and forward pulmonary arterial flow using phase-contrast imaging to calculate regurgitant volume and fraction. MRI also measures right ventricular volumes and systolic function, supporting surveillance and decisions about pulmonary valve replacement.

Phase-sensitive inversion recovery (PSIR) is an MRI technique that uses phase information to preserve the sign of the longitudinal magnetization following an inversion pulse. Unlike magnitude-only inversion recovery, which displays both positive and negative magnetization as positive signal, PSIR distinguishes them using a reference acquisition and phase-sensitive reconstruction. This makes image contrast less sensitive to the precise inversion time chosen to suppress normal myocardium. In cardiac MRI, PSIR is commonly used for late gadolinium enhancement imaging, where differences in gadolinium retention highlight myocardial injury or expanded extracellular space. It helps delineate infarction and non-ischaemic fibrosis and supports assessment of scar distribution and extent. PSIR can be incorporated into two-dimensional or three-dimensional acquisitions, including motion-corrected free-breathing protocols.

Pulmonary transit time (PTT) is the time taken for blood to pass through the pulmonary circulation from the right side of the heart to the left side. In cardiac MRI, it is commonly estimated during first-pass perfusion imaging by measuring the interval between the arrival or peak signal of an injected gadolinium contrast bolus in right-sided and left-sided cardiac blood pools. The measurement reflects the relationship between pulmonary blood volume and blood flow, and is influenced by cardiac output, ventricular function and pulmonary vascular conditions. Prolonged PTT can indicate impaired cardiopulmonary haemodynamics, but is not specific to a single disease. It is used as an adjunctive functional measure in evaluating heart failure and other cardiovascular disorders, with interpretation dependent on the acquisition and analysis method.

Premature ventricular contractions (PVC) are early heartbeats initiated by electrical activity in the ventricles rather than by the normal sinus-node impulse. They interrupt the usual cardiac rhythm and typically appear on an electrocardiogram as premature, broad QRS complexes, often followed by a compensatory pause. PVCs may arise from a single focus or multiple ventricular sites and can occur in otherwise healthy hearts or alongside structural heart disease. Frequent PVCs can contribute to ventricular dysfunction, while symptoms and underlying myocardial abnormalities influence clinical assessment. Cardiac MRI evaluates ventricular size and function and can identify scar or other tissue abnormalities associated with ventricular ectopy. Irregular beats can also impair ECG-gated cine imaging. Selected symptomatic or clinically significant PVCs may be treated with medication or catheter ablation.

Pulmonary vein isolation (PVI) is a catheter ablation procedure for atrial fibrillation that electrically disconnects myocardial tissue extending into the pulmonary veins from the surrounding left atrium. These myocardial sleeves commonly generate electrical triggers that initiate atrial fibrillation. Ablation creates a barrier to conduction around the pulmonary vein openings, using thermal energy, such as radiofrequency heating or cryothermal cooling, or pulsed electric fields that cause irreversible electroporation of myocardial cells. The procedural endpoint is electrical isolation rather than anatomical closure of the veins. Cardiac CT or MRI can delineate left atrial and pulmonary venous anatomy for procedural planning. Late gadolinium enhancement cardiac MRI can characterize post-ablation tissue injury and scar, although thin atrial walls and imaging artifacts can limit assessment.

Pulmonary valve replacement (PVR) is a surgical or transcatheter procedure that replaces a dysfunctional pulmonary valve with a prosthetic valve to treat significant pulmonary regurgitation, stenosis, or both. It is commonly considered in patients with repaired tetralogy of Fallot, in whom chronic regurgitation can cause right ventricular volume overload, progressive enlargement, and impaired function. Restoring valve competence reduces regurgitant flow and right ventricular loading. Cardiac MRI supports surveillance and decisions about intervention by quantifying pulmonary regurgitant fraction, right ventricular volumes and ejection fraction, and associated cardiovascular anatomy. Timing integrates these imaging findings with symptoms, exercise capacity, arrhythmias, and other clinical factors. CT can complement assessment of the right ventricular outflow tract and coronary anatomy when planning transcatheter replacement.

Pulmonary vascular resistance (PVR) is the resistance that the pulmonary circulation presents to blood flow from the right ventricle toward the left atrium. It is calculated by subtracting pulmonary arterial wedge pressure, an estimate of left atrial pressure, from mean pulmonary arterial pressure and dividing the difference by cardiac output, conventionally expressed in Wood units. PVR reflects the combined effects of pulmonary vascular tone, vessel narrowing or obstruction, and structural remodeling, and contributes to right ventricular afterload. It is used to characterize pulmonary hypertension and assess pulmonary vascular responses to exercise or treatment. Right heart catheterization provides the pressures needed for its calculation, while cardiac MRI complements assessment by measuring pulmonary blood flow, right ventricular volumes, and ventricular function.

People with HIV (PWH) are individuals living with human immunodeficiency virus infection, regardless of symptoms, treatment status or degree of viral suppression. HIV infects immune cells, particularly CD4-positive T lymphocytes, and can cause progressive immune deficiency if untreated. Antiretroviral therapy suppresses viral replication but does not eradicate infection. Cardiovascular assessment in this population considers traditional risk factors alongside chronic immune activation, inflammation and treatment-related metabolic effects. Cardiac magnetic resonance can evaluate ventricular structure and function, myocardial perfusion, and tissue abnormalities such as edema or fibrosis. Specialized stress protocols can also assess coronary vascular responses. HIV status alone does not establish cardiovascular disease, and imaging findings must be interpreted in the context of symptoms, immune status and other clinical information.

Pulse wave velocity (PWV) is the speed at which the pressure wave generated by ventricular contraction travels along an artery. It reflects arterial stiffness: a pulse wave generally travels faster through a stiffer arterial wall, although the measurement also depends on blood pressure and vessel properties. PWV is calculated by dividing the distance between two arterial measurement sites by the time taken for the wave to pass between them. Cardiovascular magnetic resonance can estimate aortic PWV using phase-contrast flow measurements at different aortic locations and the intervening vessel path length. Non-imaging methods also measure PWV from arterial pulse recordings. Clinically, PWV supports assessment of vascular aging, cardiovascular risk, and the arterial load imposed on the heart.

Quantum iterative reconstruction (QIR) is a proprietary iterative image-reconstruction algorithm used in photon-counting computed tomography to reduce image noise while retaining diagnostically useful detail. It accounts for the statistical behavior of detected X-ray photons and iteratively refines reconstructed images rather than relying solely on conventional filtered back projection. Selectable reconstruction strengths control the degree of noise reduction, with stronger settings potentially affecting image texture and the appearance of fine structures. QIR supports imaging with thin slices and high spatial resolution, where noise can otherwise limit interpretation. In cardiac CT, it is used to improve visualization of coronary arteries, atherosclerotic plaques and coronary stents. Its performance depends on radiation dose, reconstruction kernel, slice thickness and the diagnostic task.

Quantitative perfusion cardiac magnetic resonance (QP-CMR) is an MRI technique that measures myocardial blood flow by analysing the passage of a gadolinium-based contrast agent through the heart muscle. Rapid images acquired during the first passage of contrast provide signal-intensity curves from the blood pool and myocardium; mathematical models use these curves to estimate blood flow per unit mass of tissue. Measurements can be obtained at rest and during pharmacological stress, allowing assessment of myocardial perfusion reserve. Unlike visual perfusion interpretation, quantification provides numerical flow estimates that can help identify diffuse or balanced perfusion abnormalities. QP-CMR is used to evaluate myocardial ischaemia, coronary microvascular dysfunction and the physiological consequences of coronary artery disease without ionizing radiation. Accuracy depends on acquisition methods, motion correction and modelling assumptions.

Quantitative susceptibility mapping (QSM) is an MRI post-processing technique that estimates the spatial distribution of magnetic susceptibility, a property describing how material becomes magnetized in an applied magnetic field. It uses phase information, typically from gradient-echo acquisitions, to measure local magnetic field variations and mathematically reconstruct their underlying susceptibility sources after removing background field contributions. Susceptibility is influenced by substances such as iron, calcium and deoxygenated hemoglobin, allowing QSM to provide information complementary to conventional anatomical and relaxation-based imaging. In cardiac and vascular research, it is used to investigate myocardial tissue changes, including iron deposition or hemorrhage, and to estimate blood oxygenation from susceptibility differences. Cardiac applications remain technically challenging because of respiratory motion, cardiac motion and strong susceptibility differences near the lungs.

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease characterized by persistent inflammation of synovial joints, typically causing symmetrical pain, swelling, and stiffness and potentially leading to cartilage loss, bone erosions, and deformity. Immune-mediated inflammation can also affect tissues outside the joints, including the lungs, blood vessels, and heart. Cardiovascular manifestations include pericarditis and, less commonly, myocardial or valvular involvement; patients also have increased cardiovascular risk related partly to chronic inflammation and accelerated atherosclerosis. Cardiac MRI can assess ventricular function and characterize suspected myocardial inflammation or fibrosis using tissue mapping and late gadolinium enhancement. Cardiac CT can evaluate coronary disease and delineate structural abnormalities when clinically indicated.

Right atrial (RA) refers to the right atrium, the cardiac chamber that receives systemic venous blood through the superior and inferior venae cavae and most cardiac venous blood through the coronary sinus. It directs blood through the tricuspid valve into the right ventricle. Right atrial function comprises reservoir filling during ventricular systole, passive conduit flow during early ventricular diastole, and active contraction during late diastole in sinus rhythm. Cardiac MRI can assess right atrial size, volumes, emptying, and phasic myocardial deformation using cine imaging and feature tracking. Late gadolinium enhancement imaging can also evaluate atrial tissue remodeling, although the thin atrial wall makes assessment technically challenging. These measurements help characterize right-sided hemodynamic burden, atrial dysfunction, and remodeling associated with arrhythmias or cardiomyopathy.

Right bundle branch block (RBBB) is an intraventricular conduction abnormality in which electrical activation through the right bundle branch is delayed or interrupted. The right ventricle is consequently activated later than the left ventricle, largely through impulses spreading across the ventricular myocardium. Complete RBBB produces a widened QRS complex with characteristic changes in the right precordial and lateral ECG leads; incomplete RBBB has a similar pattern with less QRS prolongation. It may occur without structural heart disease or accompany conditions affecting the right ventricle or conduction system. Cardiac MRI does not diagnose the electrical block but can assess ventricular size, systolic function, myocardial scar and associated structural disease. Feature-tracking analysis can characterize ventricular deformation and mechanical consequences of altered activation.

Right coronary artery (RCA) is a major epicardial artery that usually originates from the right aortic sinus and travels in the right atrioventricular groove. It supplies much of the right ventricle and, depending on coronary dominance, portions of the inferior left ventricular wall and interventricular septum. It also commonly supplies the sinoatrial and atrioventricular nodes. In right-dominant anatomy, it gives rise to the posterior descending artery. Coronary CT angiography depicts its origin, course, calibre, atherosclerotic plaque and surrounding tissues, and can assess selected coronary stents and complications. Cardiac MRI can evaluate coronary anatomy in selected settings and assess the downstream effects of impaired RCA blood supply through myocardial perfusion, ventricular function and scar imaging.

Regurgitant fraction (RF) is the proportion of blood ejected through a heart valve that flows backward because the valve does not close effectively, expressed as a percentage. It is calculated by dividing regurgitant volume by the total forward stroke volume associated with that valve. In cardiac MRI, phase-contrast flow imaging can measure forward and reverse flow across the aortic or pulmonary valve, while atrioventricular valve regurgitation is commonly quantified by comparing ventricular stroke volume with forward flow through the corresponding outflow vessel. Four-dimensional flow MRI can also assess regurgitant flow using retrospectively positioned measurement planes. RF helps quantify valve regurgitation severity and complements ventricular volumes, function, symptoms, and other imaging findings when assessing hemodynamic burden and planning surveillance or treatment.

Right heart catheterization (RHC) is an invasive procedure in which a catheter is advanced through a vein into the right atrium, right ventricle and pulmonary artery to measure cardiovascular pressures and blood flow. Measurements typically include right atrial pressure, pulmonary artery pressure, pulmonary artery wedge pressure and cardiac output, allowing calculation of pulmonary vascular resistance. Pulmonary artery wedge pressure provides an indirect estimate of left atrial pressure when measured under appropriate conditions. RHC is central to confirming and classifying pulmonary hypertension and evaluating selected patients with heart failure or congenital heart disease. Cardiac MRI complements these measurements by assessing ventricular volumes, function and flow; in specialized settings, real-time MRI can guide catheter placement without ionizing radiation.

Region-of-interest (ROI) is a selected area or volume within a medical image that identifies tissue or anatomy for measurement, analysis or targeted processing. It may be drawn manually, generated automatically or refined by an observer. In MRI, an ROI can sample pixel values from quantitative maps, such as native T1 or extracellular volume maps, to characterize tissue within a specified organ. In cardiac perfusion imaging, an ROI can localize the left ventricle for subsequent segmentation or analysis. Its size, shape and placement affect results through tissue heterogeneity, motion and partial-volume effects, in which a pixel contains more than one tissue type. Consistent placement and exclusion of unwanted structures or artifacts help make measurements reproducible and clinically interpretable.

Region-optimized virtual coils (ROVir) is an MRI signal-processing technique that combines data from multiple physical receive-coil channels into virtual channels optimized for a selected anatomical region. Spatial information from coil data is used to calculate linear combinations that retain signal from the region of interest while suppressing signal from surrounding tissues. Unlike conventional coil compression, which primarily preserves overall signal information, ROVir explicitly prioritizes spatial selectivity. This can reduce the number of channels needed for reconstruction and limit interference from anatomy outside the target region. In cardiac MRI, it can focus reconstruction on the heart, including in fetal and pediatric imaging, and can be combined with motion compensation and accelerated reconstruction methods.

Repaired tetralogy of Fallot (rTOF) is the postoperative state of a congenital heart defect comprising a ventricular septal defect, overriding aorta, right ventricular outflow tract obstruction and right ventricular hypertrophy. Surgical repair closes the septal defect and relieves outflow obstruction, but residual lesions and long-term complications may persist. These include pulmonary regurgitation, recurrent outflow obstruction, right ventricular dilatation or dysfunction, and atrial or ventricular arrhythmias. Lifelong surveillance is therefore required even after successful repair. Cardiac MRI provides reproducible measurements of right and left ventricular volumes and function, quantifies pulmonary regurgitation using flow imaging, and assesses outflow tract and pulmonary artery anatomy. It can also identify myocardial scar and helps guide decisions about pulmonary valve replacement and other interventions alongside symptoms, exercise testing and rhythm assessment.

Right ventricular (RV) refers to the anatomy or function of the right ventricle, the cardiac chamber that receives systemic venous blood from the right atrium and pumps it through the pulmonary valve into the pulmonary circulation. Its thin wall and complex shape are adapted to the relatively low resistance of the normal pulmonary vascular bed. Increased pressure or volume loading can cause ventricular enlargement, hypertrophy, and impaired contraction. Cardiac MRI assesses RV size and systolic function by measuring end-diastolic and end-systolic volumes and calculating ejection fraction from cine images. Flow measurements can quantify associated valve regurgitation and shunts. RV assessment is important in pulmonary hypertension, repaired congenital heart disease such as tetralogy of Fallot, cardiomyopathies, and surveillance for treatment-related cardiac dysfunction.

Right ventricular–pulmonary arterial (RV-PA) describes the functional relationship between the right ventricle and the pulmonary arterial circulation, most commonly discussed as RV-PA coupling. Coupling reflects how effectively right ventricular contractility matches the load imposed by the pulmonary circulation to maintain forward blood flow. It is conventionally quantified as the ratio of ventricular end-systolic elastance, a measure of contractility, to effective arterial elastance, a measure of afterload. Uncoupling occurs when ventricular adaptation becomes inadequate for the imposed load and can accompany right ventricular failure. Cardiac MRI measures right ventricular volumes, ejection fraction and pulmonary flow, providing noninvasive surrogates of coupling rather than direct pressure–volume assessment. These measures help characterize right ventricular adaptation in pulmonary hypertension, heart failure and valvular disease.

Right ventricular dysfunction (RVD) is impairment of the right ventricle’s ability to fill adequately or eject blood into the pulmonary circulation. It may reflect reduced myocardial contractility, abnormal relaxation, or excessive loading from increased pulmonary vascular resistance or valve disease. Causes include pulmonary hypertension, left-sided heart failure, myocardial ischemia, and cardiomyopathy. RVD can reduce forward blood flow and contribute to systemic venous congestion, but it is not synonymous with symptomatic right heart failure. Cardiac MRI assesses right ventricular size, volumes, ejection fraction, regional wall motion, and blood flow without relying on geometric assumptions about the ventricle’s complex shape. Tissue characterization can help identify underlying myocardial disease. Functional measurements should be interpreted alongside loading conditions and clinical findings, because they do not measure intrinsic contractility alone.

Right ventricular outflow tract (RVOT) is the portion of the right ventricle that channels blood toward the pulmonary valve and pulmonary artery. Its muscular, funnel-shaped component, called the infundibulum, leads to the pulmonary valve, through which blood enters the pulmonary circulation during ventricular contraction. RVOT narrowing is an important feature of tetralogy of Fallot, and surgical repair may alter its shape or involve a patch or conduit. Subsequent problems can include residual obstruction, pulmonary regurgitation, and dilation or aneurysmal change. Cardiac MRI assesses RVOT anatomy alongside right ventricular volumes and function. Phase-contrast and four-dimensional flow MRI characterize blood flow, quantify pulmonary regurgitation, and help evaluate the consequences of repaired congenital heart disease and guide follow-up or further intervention.

Segment Anything Model (SAM) is a foundational artificial intelligence model for image segmentation, the task of assigning pixels to an anatomical structure, lesion or other region of interest. It combines an image encoder, which extracts visual features, with a prompt encoder and mask decoder to generate segmentation masks from inputs such as points or bounding boxes. Originally trained on large collections of predominantly non-medical images, SAM often requires adaptation and validation for medical imaging because tissue appearance and image contrast differ from its original training data. In MRI and CT workflows, adapted versions can support delineation of organs, tumours and cardiac structures. These masks can assist quantitative analysis, including myocardial motion and strain assessment when combined with appropriate motion-estimation methods.

Short-axis (SAX) is a cardiac imaging plane oriented perpendicular to the long axis of the left ventricle, typically defined from the apex toward the centre of the mitral valve. In cardiac MRI, a stack of short-axis slices from the ventricular base to the apex provides cross-sectional views of the ventricular cavities and myocardium. Cine acquisitions show these sections throughout the cardiac cycle, allowing assessment of wall motion, myocardial thickening and ventricular contraction. Tracing the ventricular borders across the slice stack at end-diastole and end-systole enables calculation of ventricular volumes, ejection fraction and myocardial mass. Short-axis images also support myocardial strain and motion analysis and provide a standard orientation for evaluating the distribution of abnormalities on tissue-characterisation sequences.

Spontaneous coronary artery dissection (SCAD) is a nontraumatic, noniatrogenic separation within the coronary arterial wall that is not caused by atherosclerotic plaque rupture. Bleeding into the vessel wall, with or without an intimal tear, creates an intramural hematoma or false lumen that can compress the true lumen and reduce myocardial blood flow. It can cause acute coronary syndrome, myocardial infarction, ventricular arrhythmias, or cardiogenic shock. Invasive coronary angiography is the principal diagnostic test, with intravascular imaging used selectively when the diagnosis remains uncertain. Coronary CT angiography can help assess selected cases or follow healing, although small or distal vessels may be difficult to evaluate. Cardiac MRI assesses associated ventricular dysfunction and myocardial injury, including infarction detected by late gadolinium enhancement, rather than directly establishing the coronary wall diagnosis.

Sudden cardiac death (SCD) is an unexpected death attributed to a cardiac cause, typically occurring within one hour of symptom onset when witnessed, or within 24 hours of last being seen alive and well when unwitnessed. It commonly results from ventricular tachycardia or ventricular fibrillation, which abruptly prevents effective circulation, although other cardiac mechanisms can cause it. Underlying conditions include coronary artery disease, cardiomyopathies and inherited electrical disorders. Cardiac MRI supports risk assessment by measuring ventricular function and identifying myocardial scar or fibrosis, particularly through late gadolinium enhancement. These findings are interpreted alongside clinical history, rhythm monitoring and, where appropriate, genetic testing to guide preventive management, including consideration of an implantable cardioverter-defibrillator; MRI findings alone do not determine an individual’s risk.

Single-energy CT (SECT) is computed tomography performed using one X-ray energy spectrum, typically generated at a single tube voltage. Although the beam contains photons spanning a range of energies, their attenuation is combined into one set of reconstructed images rather than separated into distinct energy datasets. Tissue attenuation is expressed in Hounsfield units and reflects both tissue composition and the X-ray spectrum. SECT is widely used for anatomical assessment, including contrast-enhanced abdominal and pelvic imaging. Unlike dual-energy CT, it cannot independently separate materials using energy-dependent attenuation information. In proton radiotherapy planning, SECT images can support estimation of tissue stopping power through calibrated relationships between CT numbers and stopping-power ratios, with uncertainty from tissue composition and beam-hardening effects.

Spontaneous intracranial hypotension (SIH) is a clinical syndrome usually caused by spontaneous loss of cerebrospinal fluid through a spinal dural leak or a cerebrospinal fluid–venous fistula, which drains fluid directly into a vein. Reduced cerebrospinal fluid volume diminishes buoyant support of the brain and can produce downward displacement of intracranial structures and compensatory venous enlargement. The characteristic symptom is an orthostatic headache that worsens upright and improves when lying down, although other presentations occur and measured cerebrospinal fluid pressure may be normal. Brain MRI can demonstrate diffuse pachymeningeal enhancement, brain sagging and subdural collections. Spinal imaging and CT myelography are used to localize the source of fluid loss, including fistulas, and guide targeted treatment such as an epidural blood patch, embolization or surgery.

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by autoantibody production, immune-complex formation, and inflammation that can affect multiple organs, including the skin, joints, kidneys, blood cells, and cardiovascular system. Its clinical course commonly includes periods of increased disease activity and remission. Cardiac manifestations include pericarditis, myocarditis, valvular abnormalities, and accelerated atherosclerotic disease; myocardial involvement may occur without obvious symptoms. Cardiac MRI can assess ventricular size and function and characterize myocardial injury using T1 and T2 mapping, extracellular volume measurement, and late gadolinium enhancement. These techniques help identify edema and fibrosis, although imaging findings require interpretation alongside symptoms, laboratory markers, and other clinical evidence and are not specific to SLE.

Septal-to-lateral wall thickness ratio (SLR) is a dimensionless imaging measure calculated by dividing interventricular septal thickness by left ventricular lateral wall thickness. It describes the distribution of myocardial thickening rather than the overall amount of hypertrophy, with higher values indicating a relatively thicker septum. In cardiac MRI, wall thickness is generally measured at end-diastole on appropriately aligned cine images, avoiding trabeculations and oblique sections that can distort measurements. SLR helps characterize asymmetric septal hypertrophy and compare ventricular morphology across hypertrophic cardiomyopathy and other causes of left ventricular hypertrophy. Interpretation depends on the myocardial segments and measurement method used, and the ratio alone does not establish a diagnosis; absolute wall thickness, ventricular geometry, clinical context and tissue characterization must also be considered.

Secondary mitral regurgitation (SMR) is backward flow of blood from the left ventricle into the left atrium during systole caused by altered ventricular or atrial geometry rather than primary disease of the mitral leaflets. Ventricular dilation or regional remodeling can displace the papillary muscles, tether the leaflets and impair valve closure; atrial enlargement can dilate the mitral annulus and similarly reduce leaflet coaptation. SMR commonly accompanies ischemic or non-ischemic cardiomyopathy and may also occur with atrial fibrillation. Echocardiography assesses valve anatomy, severity and suitability for intervention. Cardiac MRI provides complementary measurements of regurgitant volume and fraction, ventricular size and function, and myocardial scar. Multimodality assessment helps guide heart failure treatment and selection for transcatheter repair, replacement or surgery.

Simultaneous multi-slice (SMS) is an MRI acquisition technique that excites and records signals from several slices at the same time rather than acquiring each slice separately. Radiofrequency pulses excite multiple slice locations, and reconstruction separates their overlapping signals using the spatial sensitivity patterns of receiver coils, often aided by controlled shifts in slice encoding. This parallel acquisition can shorten scan times or increase anatomical coverage within a given acquisition period. In cardiac MRI, SMS can support cine imaging, late gadolinium enhancement imaging and diffusion tensor imaging, potentially reducing breath-hold demands or enabling faster free-breathing acquisitions. Image quality depends on reliable slice separation, with noise amplification and residual signal leakage between slices representing important limitations.

Signal-to-noise ratio (SNR) is a quantitative measure of the strength of useful image signal relative to random noise in an imaging system. It is commonly estimated by dividing the mean signal in a region of interest by an appropriate estimate of noise standard deviation, although measurement methods differ between CT and MRI and depend on reconstruction and acquisition techniques. In CT, noise is strongly influenced by detected photon counts, radiation dose, and reconstruction settings; in MRI, SNR depends on factors including field strength, receiver coils, voxel size, sequence parameters, and acquisition time. SNR helps evaluate image quality and optimize protocols, including dose reduction in CT and sequence design in cardiac MRI. It does not alone determine diagnostic quality, because spatial resolution, contrast, and artifacts also matter.

Spectral photon-counting CT (SPCCT) is a computed tomography technique that uses energy-resolving detectors to count individual X-ray photons and sort them into energy bins. Unlike conventional energy-integrating detectors, photon-counting detectors directly convert absorbed X-rays into electrical signals, preserving information about photon energy. Differences in energy-dependent attenuation allow material decomposition, virtual monoenergetic image reconstruction and, with suitable energy thresholds, identification of materials by their characteristic K-edge absorption. SPCCT can support assessment of vascular disease, tissue enhancement and small lesions through high spatial resolution and material-specific contrast. It is also used experimentally to image labelled cells and nanoparticle contrast agents. Its performance depends on detector energy resolution, photon count rate, acquisition settings and reconstruction methods; experimental contrast agents are not necessarily approved for clinical use.

Single-photon emission computed tomography (SPECT) is a nuclear imaging technique that reconstructs three-dimensional maps of an administered radiotracer’s distribution from gamma photons detected at multiple angles around the patient. Tracer uptake reflects the physiological process being examined rather than anatomy alone. In cardiology, myocardial perfusion SPECT compares tracer distribution during stress and at rest to identify inducible ischemia and fixed defects that may indicate infarction or scar. Electrocardiographic gating can also provide ventricular volumes, ejection fraction and regional wall motion. Other tracers assess myocardial metabolism; iodine-123 BMIPP reflects fatty acid handling and can reveal persistent metabolic abnormalities after transient ischemia, termed ischemic memory. SPECT complements anatomical coronary imaging by demonstrating functional or metabolic consequences of impaired myocardial blood supply.

Stopping power ratio (SPR) is the ratio of a material’s stopping power for charged particles, here protons, to that of water at the same particle energy. Stopping power describes the mean energy lost per unit distance as a proton travels through matter, primarily through interactions with electrons. In proton radiotherapy planning, tissue SPR values are used to calculate water-equivalent path lengths and predict where the proton beam deposits its dose. CT estimates SPR indirectly from X-ray attenuation, using calibrated relationships or estimates of electron density and tissue composition. Dual-energy and photon-counting CT provide spectral information that can support these estimates through material decomposition. Accurate SPR mapping helps limit uncertainty in proton range; beam hardening, image noise, and tissue composition can affect the calculation.

Standard-resolution (SR) denotes CT acquisition or reconstruction configured for routine spatial resolution rather than an ultra-high-resolution mode. Spatial resolution describes the ability to distinguish small, closely spaced structures and depends on detector sampling, acquisition geometry, reconstruction settings and image voxel size. In photon-counting CT, standard-resolution imaging uses the detector’s photon-counting capabilities without necessarily exploiting its finest available spatial sampling. It provides angiographic images for evaluating vessel patency, luminal narrowing and surrounding anatomy after administration of iodinated contrast material. Compared with ultra-high-resolution imaging, it generally balances anatomical detail against image noise and data volume. Very small vessels, narrow residual lumens and fine features of implanted vascular devices may require higher spatial resolution for confident assessment.

Systemic sclerosis (SSc) is a chronic autoimmune connective tissue disease characterized by small-vessel dysfunction, immune activation, and progressive fibrosis of the skin and internal organs. It can affect the lungs, gastrointestinal tract, kidneys, and heart, with clinical patterns ranging from limited to diffuse cutaneous disease. Cardiac involvement may include myocardial inflammation and fibrosis, microvascular ischemia, ventricular dysfunction, arrhythmias, and pericardial disease; pulmonary hypertension can also place strain on the right ventricle. Cardiac MRI assesses ventricular size and function and characterizes myocardial injury using edema-sensitive imaging, T1 and T2 mapping, extracellular volume measurement, and late gadolinium enhancement. These findings help identify cardiac involvement and distinguish features suggesting active inflammation from established fibrotic damage, alongside clinical assessment and other investigations.

Statistical shape modeling (SSM) is a computational method for describing anatomical shape and its variation across a population using corresponding landmarks or surface points derived from medical images. Structures segmented from cardiac MRI or CT are typically aligned to reduce differences in position and orientation, with size normalization applied when appropriate. Statistical methods, commonly principal component analysis, then identify a mean shape and the main patterns of variation around it. In cardiovascular imaging, SSM can characterize cardiac chambers, great vessels and surgically reconstructed anatomy, capturing complex three-dimensional geometry beyond individual diameters or angles. Shape measurements can be compared with blood-flow measurements, clinical characteristics or outcomes to investigate anatomical remodeling and support assessment of congenital heart disease and postoperative anatomy.

Soluble suppression of tumorigenicity 2 (sST2) is a circulating form of the ST2 receptor, encoded by the IL1RL1 gene, that is measured in blood as a biomarker of tissue stress, inflammation and cardiovascular risk. Unlike membrane-bound ST2, sST2 acts as a decoy receptor for interleukin-33, potentially limiting signaling that can protect the myocardium against hypertrophy and fibrosis. Circulating concentrations may rise with myocardial stress and inflammatory disease, but are not specific to cardiac injury and can reflect extracardiac processes. In heart failure, sST2 provides prognostic information alongside clinical assessment and other biomarkers. In research assessing cardiac involvement in systemic disease, it complements imaging rather than replacing it; cardiac MRI directly evaluates ventricular structure, function and myocardial tissue abnormalities.

Spatiotemporally constrained reconstruction (STCR) is an MRI reconstruction method that uses spatial and temporal relationships within a dynamic image series to recover images from undersampled data. It combines consistency with the acquired MRI signals with mathematical constraints that discourage implausible variation across neighboring pixels and successive frames. These constraints help suppress undersampling artifacts while retaining anatomical structure and motion, although their strength must be balanced against excessive smoothing. In cardiac MRI, STCR can support accelerated cine and real-time imaging, where rapid acquisition is needed to depict the beating heart. It is useful for reconstructing dynamic examinations when breath-holding or reliable cardiac gating is difficult, including fetal cardiac imaging, but computational demands can limit immediate image availability.

Speckle-tracking echocardiography (STE) is an ultrasound image-analysis technique that measures myocardial motion and deformation by tracking characteristic speckle patterns across successive frames of cardiac images. These patterns arise from interference between ultrasound echoes scattered within tissue and serve as natural markers for following myocardial regions throughout the cardiac cycle. STE estimates strain, the relative change in tissue length, in longitudinal, circumferential and radial directions, as well as strain rate and rotational mechanics. Global, regional and, with suitable software, layer-specific measurements help assess ventricular systolic function and detect mechanical abnormalities that may not be apparent from ejection fraction alone. Unlike tissue Doppler measurements, STE is relatively independent of insonation angle, although accuracy depends on image quality, frame rate and analysis software. Its deformation measurements can be compared with cardiac MRI feature tracking.

ST-elevation myocardial infarction (STEMI) is an acute myocardial infarction characterized by persistent ST-segment elevation on the electrocardiogram in an appropriate clinical context, usually caused by abrupt coronary artery occlusion following atherosclerotic plaque disruption and thrombosis. The resulting interruption of myocardial blood flow causes ischemia and, if sustained, irreversible cardiomyocyte injury. STEMI requires urgent reperfusion, preferably by primary percutaneous coronary intervention, to restore blood flow and limit myocardial damage. Cardiac MRI after stabilization can quantify ventricular function and infarct extent using cine imaging and late gadolinium enhancement. Additional sequences assess myocardial edema, microvascular obstruction and intramyocardial hemorrhage, helping characterize reperfusion injury, estimate prognosis and evaluate subsequent ventricular remodeling. MRI must not delay emergency reperfusion treatment.

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disease characterized by persistent hyperglycemia arising from insulin resistance and progressive impairment of pancreatic beta-cell insulin secretion. Also abbreviated T2D, it is distinct from type 1 diabetes, which usually results from autoimmune beta-cell destruction. Diagnosis is based on established blood glucose or glycated hemoglobin criteria. T2DM increases the risk of coronary artery disease, heart failure, kidney disease and microvascular complications, and may contribute to myocardial dysfunction even without obstructive coronary disease. Cardiac MRI can assess ventricular structure and function, myocardial strain, perfusion and tissue characteristics, including fibrosis through late gadolinium enhancement and extracellular volume mapping. These measurements help characterize cardiac involvement and associated cardiovascular disease rather than diagnose diabetes itself.

T2-weighted (T2W) magnetic resonance imaging is an imaging technique in which tissue contrast predominantly reflects differences in T2, the time constant describing decay of transverse magnetization through interactions between spins. Pulse sequence timing emphasizes these differences, so tissues with increased mobile water, such as edematous myocardium, generally appear brighter. In cardiac MRI, T2-weighted imaging is used to assess myocardial edema associated with acute infarction, myocarditis and other acute myocardial injuries. Intramyocardial hemorrhage within reperfused infarcted tissue can appear as a dark core within surrounding bright edema because blood breakdown products accelerate transverse signal decay. Interpretation requires attention to motion, blood signal and other artifacts; T2* imaging provides complementary sensitivity to hemorrhage, while T2 mapping enables quantitative assessment of tissue relaxation.

Transcatheter aortic valve implantation (TAVI), also called transcatheter aortic valve replacement (TAVR), is a catheter-based procedure that places a biological prosthetic valve within the native aortic valve, most commonly to treat severe aortic stenosis. The prosthesis is delivered through a blood vessel, usually the femoral artery, and expanded within the diseased valve without surgical removal of its leaflets. CT is used before implantation to measure the aortic annulus, assess calcification and coronary artery positions, and evaluate vascular access. After implantation, echocardiography is the principal method for assessing valve function. Cardiac MRI can quantify residual aortic regurgitation and ventricular function, while CT can assess prosthesis position, leaflet motion, and suspected complications such as leaflet thrombosis.

Tuberculosis (TB) is an infectious disease caused by bacteria of the Mycobacterium tuberculosis complex, usually transmitted through inhalation of airborne particles from a person with infectious pulmonary disease. Although it most commonly affects the lungs, infection can involve other organs through lymphatic or bloodstream spread. Cardiac involvement most often affects the pericardium, causing inflammation, effusion and sometimes fibrosis that restricts cardiac filling, known as constrictive pericarditis; myocardial involvement is uncommon. Cardiac MRI can assess pericardial thickening, oedema and enhancement, ventricular interaction and associated myocardial injury, helping characterise inflammation and constrictive physiology. CT can complement MRI by depicting pericardial calcification and thoracic disease. Imaging supports assessment but does not establish the microbiological diagnosis.

Transesophageal echocardiography (TEE) is an ultrasound examination in which a probe is passed through the mouth into the esophagus to obtain detailed images of the heart and nearby vessels. The probe transmits high-frequency sound waves and detects returning echoes, while Doppler techniques assess blood flow. The esophagus lies close to the heart, allowing imaging with less interference from the lungs, ribs and chest wall than transthoracic echocardiography. Multiplanar two-dimensional and three-dimensional views help characterize valve disease, intracardiac masses, septal defects and left atrial appendage thrombus. TEE also guides selected cardiac interventions and provides intraoperative assessment. It usually requires fasting, topical throat anesthesia and often sedation; esophageal disease may limit its use. Cardiac CT and MRI provide complementary anatomical and tissue information.

Inversion time (TI) is the interval between an inversion radiofrequency pulse and the subsequent excitation or acquisition reference point in an inversion-recovery MRI sequence. The inversion pulse reverses longitudinal magnetization, which then recovers toward equilibrium at a rate governed by the tissue’s T1 relaxation time. Selecting an appropriate TI allows a tissue’s magnetization to approach zero when sampled, suppressing or nulling its signal. In cardiac MRI, TI is commonly adjusted to null normal myocardium during late gadolinium enhancement imaging, making areas of myocardial injury or fibrosis more conspicuous. It can also be selected to suppress blood-pool signal, with the required timing influenced by contrast agents and sequence design. Phase-sensitive inversion recovery reduces sensitivity to imperfect TI selection by preserving magnetization polarity.

Transient ischemic attack (TIA) is a transient episode of focal neurological dysfunction caused by ischemia of the brain, spinal cord, or retina, without acute infarction. It usually results from temporary arterial occlusion by an embolus or local thrombosis, producing symptoms such as unilateral weakness, speech disturbance, or loss of vision. Symptom resolution does not eliminate the need for urgent assessment, because TIA can signal an increased risk of subsequent ischemic stroke. Evaluation includes brain and vascular imaging to identify infarction, arterial stenosis, or other causes, together with assessment for cardiac embolic sources. MRI with diffusion-weighted imaging helps distinguish TIA from ischemic stroke. Cardiac imaging may support investigation of suspected structural heart disease or intracardiac thrombus, although cardiac MRI is not routinely required for every TIA.

Transjugular intrahepatic portosystemic shunt (TIPS) is an image-guided procedure that creates a low-resistance channel between a branch of the portal vein and a hepatic vein using a stent within the liver. Access is obtained through the jugular vein, and the shunt diverts portal blood into the systemic venous circulation, reducing portal pressure. It is used to treat selected complications of portal hypertension, particularly variceal bleeding and refractory ascites. By increasing venous return to the heart, TIPS can raise cardiac preload and precipitate heart failure in susceptible patients; diversion of blood away from hepatic processing can also cause hepatic encephalopathy. Cardiac MRI can quantify ventricular volumes, function, and myocardial tissue characteristics when evaluating cardiovascular adaptation or suspected dysfunction before or after placement.

True non-contrast (TNC) refers to CT images acquired without intravenous contrast administration, usually before any contrast-enhanced scanning. Image attenuation therefore reflects the tissues and materials present without the added contribution of an iodinated contrast agent. TNC imaging provides a reference for measuring native tissue attenuation and distinguishing calcification, fat, hemorrhage and other intrinsically dense or low-density findings. In cardiac imaging, it is used for coronary artery calcium scoring, which quantifies calcified coronary plaque. In abdominal imaging, liver attenuation on TNC CT can help assess hepatic steatosis. Unlike virtual non-contrast or virtual non-iodine images, which are reconstructed by computationally removing iodine-related signal from contrast-enhanced acquisitions, TNC images are directly acquired and do not depend on iodine-subtraction accuracy.

Tetralogy of Fallot (TOF) is a congenital heart defect comprising a ventricular septal defect, an overriding aorta, right ventricular outflow tract obstruction, and right ventricular hypertrophy. The outflow obstruction promotes right-to-left shunting through the septal defect, which can cause cyanosis; its severity depends largely on the degree of obstruction. Surgical repair closes the septal defect and relieves the outflow obstruction, but residual pulmonary regurgitation or stenosis can lead to right ventricular enlargement, dysfunction, and arrhythmias. Cardiac MRI is central to long-term assessment after repair, providing reproducible ventricular volumes and function, pulmonary regurgitant fraction, and evaluation of the outflow tract and pulmonary arteries. These measurements inform surveillance and decisions about pulmonary valve replacement.

Tissue phase mapping (TPM) is a velocity-encoded MRI technique that measures the speed and direction of myocardial motion throughout the cardiac cycle. Motion-sensitive magnetic field gradients encode tissue velocity in the phase of the MR signal, allowing myocardial velocities to be resolved into radial, circumferential and longitudinal components. Cardiac gating links these measurements to systole and diastole, while regional analysis characterizes differences in contraction, relaxation and timing between myocardial segments. Spatial changes in the measured velocity field can also be used to derive strain rate, which describes how rapidly tissue deforms. TPM is used primarily in cardiac research to assess regional and global ventricular mechanics, including mechanical dyssynchrony and dysfunction associated with cardiomyopathy or congenital heart disease.

Transcatheter pulmonary valve replacement (TPVR) is a minimally invasive procedure in which a prosthetic valve mounted within a supporting frame is delivered through a catheter and implanted in the right ventricular outflow tract. It treats clinically significant pulmonary regurgitation or obstruction, commonly in patients with repaired congenital heart disease and a dysfunctional surgical conduit, bioprosthetic valve, or suitable native outflow tract. The implanted valve restores forward flow toward the pulmonary arteries while limiting backward flow into the right ventricle. Cardiac MRI quantifies pulmonary regurgitation, right ventricular volumes and function, and outflow tract anatomy to inform timing and planning. CT can further define anatomy, calcification, and relationships to the coronary arteries, helping assess device suitability and procedural risks.

Tricuspid regurgitation (TR) is backward flow of blood from the right ventricle into the right atrium during ventricular systole because the tricuspid valve does not close effectively. It may result from primary abnormalities of the valve leaflets or supporting structures, or arise secondarily from annular dilation and leaflet tethering associated with right atrial or right ventricular enlargement. Persistent regurgitation causes right-heart volume overload and can contribute to systemic venous congestion, reduced forward cardiac output, and right ventricular dysfunction. Echocardiography is the principal method for assessing valve anatomy and regurgitation severity. Cardiac MRI provides reproducible measurements of right ventricular volumes and function and can quantify regurgitant volume by comparing right ventricular stroke volume with forward pulmonary arterial flow, while accounting for associated lesions.

Transthoracic echocardiography (TTE) is a non-invasive ultrasound examination of the heart performed with a transducer placed on the chest wall. The transducer emits high-frequency sound waves and detects echoes from cardiac tissues to produce real-time images, while Doppler techniques assess blood flow direction and velocity. Standard views allow assessment of chamber size, wall thickness, ventricular contraction, valve anatomy and function, and pericardial abnormalities. TTE is commonly the first-line imaging test for suspected structural heart disease, heart failure, and valvular disease, and is used for serial monitoring. Image quality depends on the available acoustic windows. Cardiac MRI can complement TTE when ultrasound images are limited or more detailed tissue characterization and ventricular volume measurements are needed.

Transthyretin (TTR) is a transport protein produced mainly by the liver that circulates as a tetramer and carries thyroxine and retinol-binding protein. Destabilization of the tetramer can allow individual subunits to misfold and aggregate into amyloid fibrils that accumulate in tissues. Both age-related deposition of wild-type transthyretin and inherited pathogenic variants can cause transthyretin amyloidosis, which commonly affects the heart and may also involve peripheral nerves. Cardiac deposition can increase ventricular wall thickness, impair relaxation and produce heart failure or conduction abnormalities. Cardiac MRI assesses the resulting structural changes and tissue abnormalities using late gadolinium enhancement, native T1 mapping and extracellular volume measurement, but does not independently identify the amyloid protein type. Typing requires appropriate scintigraphy and laboratory evaluation or tissue analysis.

Takotsubo syndrome (TTS) is an acute cardiac syndrome characterized by transient regional ventricular systolic dysfunction, usually involving the left ventricle and extending beyond a single coronary artery territory. It often follows emotional or physical stress, although an identifiable trigger is not required. Excess sympathetic activation and catecholamine-mediated myocardial stunning are implicated in its pathophysiology. The presentation can resemble acute myocardial infarction, with chest pain, electrocardiographic abnormalities and elevated cardiac biomarkers. Cardiac MRI assesses ventricular function and wall-motion patterns, detects myocardial edema with T2-weighted imaging or mapping, and helps distinguish the syndrome from infarction and myocarditis through tissue characterization, including late gadolinium enhancement. Imaging also evaluates complications such as ventricular thrombus and left ventricular outflow tract obstruction, while follow-up documents functional recovery.

Tricuspid valve (TV) is the right atrioventricular valve, situated between the right atrium and right ventricle and normally composed of anterior, posterior and septal leaflets. Its leaflets are supported by chordae tendineae and papillary muscles, which help prevent leaflet prolapse during ventricular contraction. The valve opens during diastole to permit right ventricular filling and closes during systole to limit backward flow into the right atrium. Congenital abnormalities, including Ebstein anomaly and abnormal leaflet tissue, can impair valve competence or obstruct inflow. Echocardiography is the primary imaging method for assessing valve anatomy and function. Cardiac MRI complements it by quantifying right ventricular volumes and function, evaluating associated congenital abnormalities and estimating tricuspid regurgitation.

Ultra-high-resolution (UHR) refers to a CT acquisition and reconstruction approach designed to depict smaller anatomical details than standard-resolution imaging. In photon-counting CT, small detector elements directly convert individual X-ray photons into electrical signals, enabling finer spatial sampling. Realizing this resolution also requires suitable acquisition geometry, reconstruction kernels and sufficiently small reconstructed voxels; it is not achieved simply by enlarging an image. UHR imaging can improve visualization of small vessels, aneurysm morphology, fine pulmonary structures and other high-contrast anatomical features. Its benefits must be balanced against image noise, radiation dose and reconstruction requirements, because smaller voxels generally contain fewer detected photons. The term describes spatial resolution rather than spectral performance or a universally fixed voxel size.

Ultra-high-resolution photon-counting CT angiography (UHR-PCCTA) is contrast-enhanced imaging of blood vessels using a photon-counting CT scanner operated in an acquisition mode designed for high spatial resolution. Its detectors directly convert individual X-ray photons into electrical signals and classify them by energy, while small detector elements enable detailed depiction of vascular structures. Intravenous iodinated contrast opacifies the vessel lumen, allowing assessment of arterial narrowing, occlusion, aneurysms and treated vessels. The technique can help evaluate vessels adjacent to implants, including intracranial flow diverters and orthopedic prostheses, although metal artifacts may still limit interpretation. Fine-resolution imaging requires careful selection of radiation dose, reconstruction settings and contrast timing because smaller reconstructed voxels can increase image noise.

Ultra-high-resolution photon-counting detector CT (UHR-PCD-CT) is computed tomography that uses photon-counting detectors with small detector elements to produce images with high spatial resolution. These detectors convert individual X-ray photons directly into electrical pulses and classify them by energy, rather than measuring their combined energy through an intermediate light signal. Fine detector sampling and suitable image reconstruction improve the depiction of small structures and can reduce partial-volume effects and blooming around calcium or metallic stents. Clinical applications include assessment of coronary plaque, coronary stent lumens, and pulmonary nodules. The achievable detail depends on acquisition settings, reconstruction method, patient motion, and radiation dose; finer resolution generally increases image noise unless compensated by dose or noise-reduction techniques.

Ultra-low dose (ULD) describes a CT acquisition protocol designed to substantially reduce ionizing radiation exposure relative to conventional protocols for the same clinical task. It is a relative designation rather than a universally standardized dose threshold. Dose reduction typically involves lowering tube current, selecting an appropriate tube voltage, and tailoring acquisition settings to patient size and diagnostic requirements. Iterative reconstruction and efficient detector technology, including photon-counting detectors, can help preserve diagnostically useful images despite fewer detected photons. ULD chest CT may be used for selected lung assessments, particularly when limiting cumulative exposure or imaging children. Its suitability depends on whether image quality remains adequate for the intended task, because increased noise can impair detection of subtle abnormalities and affect quantitative measurements.

Ultrasound (US) is a diagnostic imaging technique that uses high-frequency sound waves to produce real-time images of tissues without ionizing radiation. A transducer transmits sound pulses and receives echoes reflected from tissue boundaries; echo timing and strength determine the location and appearance of structures. Doppler techniques assess motion, particularly blood flow, through changes in the frequency of returning echoes. Ultrasound is used to evaluate organs, soft tissues, blood vessels, and joints, and to guide procedures. In orbital imaging, it can assess ocular and selected orbital abnormalities. In musculoskeletal imaging, it can demonstrate synovitis, effusions, and patterns of crystal deposition. Its performance depends on operator skill and acoustic access, with bone and gas limiting visualization of deeper structures.

Ventricular arrhythmias (VA) are abnormal heart rhythms originating in the ventricles rather than the normal sinus node–atrial conduction pathway. They range from premature ventricular contractions to ventricular tachycardia and ventricular fibrillation, with sustained forms potentially causing hemodynamic collapse or sudden cardiac death. Mechanisms include abnormal impulse formation and re-entry through electrically heterogeneous myocardium, often associated with scar, inflammation or cardiomyopathy. Diagnosis relies on electrocardiography, ambulatory monitoring or recordings from implanted cardiac devices. Cardiac MRI helps identify underlying structural disease, quantify ventricular function and characterize myocardial injury or fibrosis using late gadolinium enhancement and tissue mapping. These findings inform arrhythmic risk assessment and may support decisions about implantable cardioverter-defibrillators or catheter ablation alongside clinical and electrophysiological evaluation.

Visceral adipose tissue (VAT) is fat located within the abdominal cavity around internal organs, including fat in the mesentery and omentum, rather than beneath the skin. It is a metabolically active tissue that stores energy and releases fatty acids, hormones and inflammatory mediators. Excess visceral fat is associated with insulin resistance, metabolic dysfunction and increased cardiovascular risk, and its distribution provides information not captured fully by body mass index or waist circumference. MRI can distinguish fat from water using chemical-shift techniques and quantify visceral fat area or volume through segmentation of abdominal images. CT can also measure this depot using its characteristic low attenuation. Imaging assessment helps characterise body composition and investigate relationships between abdominal adiposity, cardiac structure and cardiometabolic disease.

Video-assisted thoracoscopic surgery (VATS) is a minimally invasive approach to operations within the chest using a thoracoscope, a camera-equipped instrument that provides a magnified view of the operative field on a monitor. The surgeon introduces the thoracoscope and surgical instruments through small chest-wall incisions rather than a conventional open thoracotomy; uniportal VATS uses a single incision. It is used for procedures such as lung biopsy, anatomical lung resection, pleural surgery and thymectomy. Chest CT supports preoperative assessment by defining lesions, surrounding anatomy and disease extent, while tissue sampling may be needed for diagnosis or staging. VATS generally reduces chest-wall trauma compared with open surgery, although conversion to an open approach may be necessary for safety or technical reasons.

Viscous energy loss (vEL) is the irreversible conversion of mechanical energy in flowing blood into heat through internal friction associated with spatial differences in flow velocity. In cardiac imaging, it can be estimated from the three-dimensional velocity fields acquired with time-resolved three-dimensional phase-contrast MRI, commonly called 4D flow CMR. Calculations use velocity gradients and an assumed blood viscosity to estimate the rate of energy dissipation within a defined region, which may be integrated over time. This measure helps characterize intracardiac and vascular flow efficiency, including altered flow after congenital heart disease repair. Estimates depend on spatial resolution, velocity noise, and segmentation boundaries, and do not necessarily capture all energy losses associated with unresolved turbulent flow.

Ventricular fibrillation (VF) is a life-threatening cardiac arrhythmia in which rapid, disorganized electrical activity in the ventricles prevents coordinated contraction and effective blood circulation, causing cardiac arrest. It arises from unstable ventricular activation involving multiple wavefronts or rapidly firing sources, sometimes triggered by abnormal impulses from the Purkinje conduction system. VF can occur with myocardial ischemia, cardiomyopathy, myocardial scar, or inherited electrical disorders, including in hearts without evident structural disease. Immediate treatment requires cardiopulmonary resuscitation and defibrillation. After stabilization, cardiac MRI can assess ventricular function and identify scar, inflammation, or other structural substrates contributing to arrhythmic risk. Longer-term management may include an implantable cardioverter-defibrillator, treatment of the underlying cause, and catheter ablation for recurrent episodes in selected patients.

Virtual monoenergetic images (VMI) are CT images computationally reconstructed from spectral data to approximate the appearance of an image acquired with X-ray photons of a single selected energy. Dual-energy and photon-counting CT provide energy-dependent attenuation information, which is used to estimate material composition and calculate attenuation at the chosen energy, usually expressed in kiloelectronvolts. Lower-energy images increase iodine contrast and can improve the visibility of contrast-enhanced vessels and lesions, although image noise may increase. Higher-energy images can reduce beam-hardening and some metal artifacts, but generally provide less iodine contrast. Energy selection therefore depends on the diagnostic task, patient size and reconstruction method. VMI support vascular and abdominal imaging, assessment near metallic implants, and attenuation-based tissue measurements; they are not images acquired with a truly monochromatic X-ray beam.

Virtual non-contrast (VNC) refers to CT images computationally reconstructed from contrast-enhanced spectral acquisitions to approximate the appearance of images obtained without intravenous contrast. Dual-energy and photon-counting CT distinguish materials through differences in their energy-dependent X-ray attenuation. Material decomposition uses this information to estimate and subtract the iodine contribution, producing images that retain the estimated attenuation of other tissues. VNC images can support assessment of baseline tissue attenuation, urinary stones, and calcification, and may reduce the need for a separate unenhanced acquisition in selected protocols. They are not interchangeable with true non-contrast images in all settings: residual iodine, altered calcium attenuation, and reconstruction-dependent artifacts can affect interpretation and quantitative measurements, particularly coronary artery calcium scoring.

Virtual non-iodine (VNI) refers to CT images reconstructed from contrast-enhanced spectral data by computationally removing the contribution of iodine while aiming to preserve calcium-containing structures. Spectral CT distinguishes materials through their different energy-dependent X-ray attenuation; material decomposition uses this information to separate iodine from other tissues. In photon-counting CT, energy-resolved detector measurements support this processing. VNI reconstruction is designed to reduce the inadvertent removal of calcium that can occur with conventional virtual non-contrast methods. Clinical applications include evaluating urinary calculi and estimating coronary artery calcium from contrast-enhanced examinations. VNI images are derived rather than directly acquired unenhanced images, and residual iodine, calcium preservation and quantitative accuracy depend on the reconstruction algorithm and acquisition conditions.

Ventricular septal defect (VSD) is a congenital opening in the interventricular septum that permits blood flow between the left and right ventricles. Flow usually passes from left to right because left ventricular pressure is higher, increasing pulmonary blood flow and potentially causing left-sided chamber enlargement, pulmonary hypertension, and heart failure. The physiological effect depends on the defect’s size, location, and pulmonary vascular resistance. Perimembranous defects lie near the aortic and tricuspid valves, whereas muscular defects involve the muscular septum. Echocardiography is the primary diagnostic test; cardiac MRI can quantify shunt flow and ventricular volumes, while CT can clarify anatomy when needed. Clinically significant defects may require surgical patch closure or catheter-based closure.

Ventricular tachycardia (VT) is a cardiac arrhythmia consisting of three or more consecutive beats originating in the ventricles, usually at a rate above 100 beats per minute. It can arise from re-entry through myocardial scar, abnormal automaticity, or triggered electrical activity. VT is classified as nonsustained when it terminates within 30 seconds and sustained when it lasts longer or requires earlier termination because of haemodynamic instability. It may cause palpitations, syncope, circulatory collapse, or progression to ventricular fibrillation. Electrocardiography establishes the rhythm diagnosis, while cardiac MRI assesses underlying structural disease and identifies myocardial scar or fibrosis using late gadolinium enhancement. Scar distribution can inform risk assessment and help plan catheter ablation; treatment may also include antiarrhythmic medication and an implantable cardioverter-defibrillator.

Wall shear stress (WSS) is the tangential force per unit area that flowing blood exerts on the inner surface of a blood vessel. It depends on blood viscosity and the spatial gradient of blood velocity immediately adjacent to the vessel wall. In cardiovascular imaging, time-resolved three-dimensional phase-contrast MRI, commonly called 4D flow MRI, measures blood velocities throughout the cardiac cycle, allowing regional WSS to be estimated along a segmented vessel surface. WSS influences endothelial function and vascular remodeling, making its distribution relevant to research on aortic dilation, valve-related flow disturbances and vascular disease. MRI-derived estimates depend on spatial resolution, wall segmentation and modeling assumptions; they are principally research measurements rather than standalone clinical diagnostic criteria.