Cardiac Imaging Modalities
On this page
Direct answer
Choosing the right cardiac imaging test is itself a favourite examination question. Echocardiography is the first-line test for structure and function. Coronary CT angiography is the preferred rule-out test for coronary disease in low-to-intermediate probability patients, with a high negative predictive value and CT-derived physiology as an adjunct. Stress imaging (stress echo, SPECT, PET or perfusion MRI) tests ischaemia in intermediate-to-high probability patients. Cardiac MRI is the tissue characteriser — for myocarditis, infiltration, viability and arrhythmogenic substrate — while nuclear bone-tracer scintigraphy diagnoses transthyretin amyloidosis. Invasive fractional flow reserve remains the reference standard for lesion significance.
What you must remember
- Echocardiography: transthoracic study first for structure and function; transoesophageal for prosthetic valves, endocarditis, left atrial appendage thrombus and aortic disease; global longitudinal strain detects subclinical dysfunction — a meaningful fall during anthracycline or trastuzumab therapy prompts cardiology review.
- Coronary CT angiography: an anatomic test reported on the CAD-RADS scale; best for excluding disease in low-to-intermediate probability patients — a zero calcium score with a normal study carries an excellent prognosis; limited by heavy calcification, irregular rhythms and renal impairment.
- Stress imaging: stress echocardiography, SPECT or PET perfusion imaging and stress MRI detect flow-limiting stenosis; PET adds quantitative blood flow, exposing balanced three-vessel disease and microvascular dysfunction.
- Cardiac MRI: the gold standard for volumes and ejection fraction; late gadolinium enhancement separates ischaemic (subendocardial) from non-ischaemic (mid-wall, epicardial) disease; T1 mapping identifies amyloidosis (high values) and Anderson-Fabry disease (low); T2* quantifies iron; mapping criteria diagnose myocarditis; right ventricular findings support arrhythmogenic cardiomyopathy.
- Viability testing: the transmural extent of late gadolinium enhancement predicts recovery after revascularisation — segments with less than half-wall enhancement, stress-echo thinning or PET metabolic activity are viable.
- Nuclear adjuncts: technetium pyrophosphate or DPD scintigraphy with grade 2–3 uptake diagnoses transthyretin amyloidosis without biopsy in the right setting; FDG-PET supports cardiac sarcoidosis.
- Radiation and availability logic: echo and MRI are radiation-free; CT and nuclear studies carry dose — sequence tests sensibly and image before catheterising when non-obstructive disease is plausible.
Common confusion
The recurring confusion is anatomic versus functional testing: CT angiography excludes plaque but does not prove its haemodynamic significance, whereas stress testing demonstrates ischaemia but not anatomy — hence "CT first in low probability, stress testing in intermediate-to-high". The second confusion is which test for which question: MRI for tissue, PET for perfusion and inflammation, bone scintigraphy for amyloid.
Exam-focused takeaway
Stems ask "best next investigation": a young woman with atypical chest pain (coronary CT), new heart failure with a non-diagnostic echo (cardiac MRI), suspected amyloidosis with thick walls (bone scintigraphy plus MRI), or recurrent angina after bypass grafting. Learn each modality by its one irreplaceable strength.
Frequently asked questions
When is coronary CT angiography the test of choice?
In low-to-intermediate probability patients to rule out coronary disease, given its high negative predictive value — provided heart rate, rhythm and renal function permit a diagnostic study.
What does cardiac MRI add over echocardiography?
Tissue characterisation — late gadolinium enhancement patterns, T1 and T2 mapping — identifying myocarditis, infiltration, iron, fibrosis and right ventricular substrate beyond what functional imaging shows.
Which test diagnoses transthyretin cardiac amyloidosis non-invasively?
Grade 2–3 cardiac uptake on technetium pyrophosphate or DPD scintigraphy, in the right clinical setting and after excluding light-chain disease, avoids endomyocardial biopsy.
Why can a normal perfusion scan miss three-vessel disease?
Balanced reduction of flow in all territories produces apparently uniform tracer uptake; quantitative PET myocardial blood flow uncovers the diffuse reduction.
What defines lesion significance at catheterisation?
Fractional flow reserve of 0.80 or less (with hyperaemia) or instantaneous wave-free ratio of 0.89 or less — both identify stenoses that benefit from revascularisation.