Cardiac CT and MRI Indications

Expansion

Cardiac CT, best for anatomy of the arteries

• CT coronary angiography: first line for stable chest pain of suspected cardiac origin. Its strength is a negative predictive value above 95 per cent, so a normal study essentially excludes obstructive coronary disease
• Calcium score: quantifies atherosclerotic burden and refines risk. A score of zero confers very low short term risk
• CT aortogram: dissection, aneurysm, and pre-procedural planning for TAVI
• CT pulmonary angiogram for pulmonary embolism
• Pericardial calcification, congenital anatomy, device and graft assessment

Limitations are ionising radiation, iodinated contrast, degradation by a fast or irregular heart rate (so beta blockade is often given), and by heavy calcification, which overestimates stenosis. It shows anatomy, not function, so a stenosis still needs functional assessment.

Cardiac MRI, best for the myocardium

• Gold standard for volumes, mass and ejection fraction, particularly for the right ventricle
• Late gadolinium enhancement distinguishes the cause of a cardiomyopathy by the pattern of scar: subendocardial or transmural in infarction, mid-wall in dilated cardiomyopathy, subepicardial in myocarditis, diffuse in amyloid
• Myocarditis, infiltration (amyloid, sarcoid, iron overload with T2* mapping)
• Viability assessment before revascularisation
• Congenital heart disease, cardiac masses, constriction versus restriction
• Stress perfusion MRI for ischaemia, with no radiation

Limitations are availability, duration, breath holding, claustrophobia, device compatibility, and gadolinium avoidance in severe renal impairment.