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# The heart on CT and MRI: coronary CT, calcium score and cardiac MRI

- Modality

Heart-synchronised CT shows the coronary arteries and their calcium; cardiac MRI measures how the heart pumps and where the muscle is scarred.

Updated Nov 13, 2026

## Key points

- Cardiac CT and MRI are ECG-gated.
- CCTA: best to rule out coronary disease in low-to-intermediate probability stable chest pain; needs slow regular rhythm.
- Calcium score: non-contrast, risk tool for people without symptoms; zero is reassuring but not a chest-pain test.
- Cardiac MRI: reference standard for volumes and ejection fraction; late gadolinium enhancement shows scar and its pattern.

## What it is

The heart moves, so cardiac CT and MRI are synchronised with the ECG (gated) to catch it in the same phase of each beat. Coronary CT angiography (CCTA) injects iodinated contrast and images the coronary arteries in a few heartbeats; it needs a slow, regular rhythm, and its strength is a very high negative predictive value: a normal study practically rules out significant coronary disease in a patient with stable chest pain and low-to-intermediate probability. The coronary calcium score is a quick, low-radiation, non-contrast gated CT that measures the calcium in the coronary walls (the Agatston score); it estimates future risk in people without symptoms rather than diagnosing a narrowing. Cardiac MRI uses no ionising radiation: moving cine images measure the volumes and ejection fraction (its reference standard), and late images after gadolinium show scar or fibrosis, whose pattern separates infarction (from the inner wall outward) from myocarditis, hypertrophic cardiomyopathy, infiltrative disease and Chagas cardiomyopathy.

## How the image is made

- ECG gating: images are taken or kept only during a chosen part of the cardiac cycle, usually diastole, when the heart is still.
- CCTA: contrast timed to the coronary arteries, thin slices and reconstructions along each vessel; a slow, regular heart rate gives sharp images.
- Calcium score: a non-contrast gated CT; calcium above a density threshold is measured and added into a score (0 means none detected).
- Cardiac MRI cine: movies of the beating heart in several planes to measure chamber size, wall motion and ejection fraction.
- Late gadolinium enhancement: scar and fibrosis hold gadolinium longer and look bright minutes after the injection; oedema shows on T2 images.

## What it is good for

- CCTA: stable chest pain with low-to-intermediate probability of coronary disease; a normal study rules it out with high confidence.
- CCTA also shows anomalous coronary arteries, bypass graft patency and, in selected emergency patients, excludes coronary disease.
- Calcium score: refines risk in adults without symptoms whose risk is uncertain, to guide prevention decisions.
- Cardiac MRI: cardiomyopathies, myocarditis, viability before revascularisation, infiltrative disease, masses, pericardium and congenital disease.
- Scar pattern on MRI: subendocardial or transmural in a coronary territory = infarct; mid-wall or epicardial patches = non-ischaemic causes.

## Limitations and risks

- CCTA needs a slow, regular rhythm; atrial fibrillation, frequent ectopic beats or a fast heart rate blur the arteries.
- Heavy calcium causes blooming that overestimates narrowing; a positive or unclear CCTA often needs functional testing or invasive angiography.
- A calcium score of zero does not exclude non-calcified plaque in a young person with symptoms; it is a risk tool, not a chest-pain test.
- CCTA carries the risks of iodinated contrast and radiation; it is not the test for a patient with high probability or an acute coronary syndrome.
- Cardiac MRI is long, needs repeated breath-holds and suffers with arrhythmia; check pacemakers and other devices for MRI safety.
- Gadolinium needs caution in severe kidney disease; follow the local MRI and contrast safety protocol.

## Next step

- Stable chest pain: estimate the probability first; low-to-intermediate suits CCTA or a functional test, as chosen with cardiology.
- Chest pain with ECG changes or a rising troponin: this is not a CCTA question; call cardiology for acute coronary syndrome management.
- New heart failure or suspected myocarditis or cardiomyopathy: echocardiography first, then cardiac MRI if the cause is unclear.
- Before booking: record the rhythm and heart rate, kidney function, contrast reactions, devices and ability to hold the breath.
- Abnormal or unclear result: discuss with cardiology and the reporting radiologist before deciding on invasive angiography.

## Test yourself

Think of the answer, then tap the question to see it.

## Which patients benefit most from coronary CT angiography?

Patients with stable chest pain and low-to-intermediate probability of coronary disease, where a normal study rules it out with very high confidence.

## Why does coronary CT angiography need a slow, regular heart rhythm?

Images are gated to a still phase of the cycle; fast or irregular beats (such as atrial fibrillation) blur the small coronary arteries.

## What does the coronary calcium score measure, and for whom is it meant?

The amount of calcium in the coronary walls on a non-contrast gated CT; it refines cardiovascular risk in adults without symptoms.

## How does late gadolinium enhancement separate infarction from myocarditis?

Infarct scar starts at the inner wall (subendocardial) in a coronary territory; myocarditis gives mid-wall or epicardial patches not tied to one artery.

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## Elsewhere in DurgiPedia

- [Chest pain: ischemic, pericardial, pleural and other patterns](https://durgical.com/en/clinical-exam/chest-pain-ischemic-pericardial-pleural-and-other-patterns/)

## Connections

## Related 6

- [CT: windows, Hounsfield units and contrast phases](https://durgical.com/en/radiology/ct-windows-hounsfield-units-and-contrast-phases/)
- [MRI: T1, T2, FLAIR and diffusion](https://durgical.com/en/radiology/mri-t1-t2-flair-and-diffusion/)
- [MRI safety: implants, metal and gadolinium](https://durgical.com/en/radiology/mri-safety-implants-metal-and-gadolinium/)
- [Iodinated contrast: reactions and the kidney](https://durgical.com/en/radiology/iodinated-contrast-reactions-and-the-kidney/)
- [Which chest study to order: X-ray, CT, CT angiography or ultrasound](https://durgical.com/en/radiology/which-chest-study-to-order-x-ray-ct-ct-angiography-or-ultrasound/)
- [Cardiomegaly and pulmonary oedema on the chest X-ray](https://durgical.com/en/radiology/cardiomegaly-and-pulmonary-oedema-on-the-chest-x-ray/)

## Related conditions 6

- [Stable angina](https://durgical.com/en/conditions/stable-angina/)
- [Myocardial Infarction (Heart Attack)](https://durgical.com/en/conditions/myocardial-infarction/)
- [Hypertrophic cardiomyopathy](https://durgical.com/en/conditions/hypertrophic-cardiomyopathy/)
- [Dilated cardiomyopathy](https://durgical.com/en/conditions/dilated-cardiomyopathy/)
- [Myocarditis](https://durgical.com/en/conditions/myocarditis/)
- [Chagas cardiomyopathy](https://durgical.com/en/conditions/chagas-cardiomyopathy/)

[← All of radiology](https://durgical.com/en/radiology/)

Educational content; it does not replace a radiologist's report and is not a clinical instruction. Each study is ordered on the patient's assessment and your institution's protocols.

Sources: [Coronary CT Angiography](https://www.ncbi.nlm.nih.gov/books/NBK470279/) (StatPearls (NCBI Bookshelf), 2026); [Chest and Mediastinal Imaging](https://www.ncbi.nlm.nih.gov/books/NBK559145/) (StatPearls (NCBI Bookshelf), 2026).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/radiology/the-heart-on-ct-and-mri-coronary-ct-calcium-score-and-cardiac-mri/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/radiology/the-heart-on-ct-and-mri-coronary-ct-calcium-score-and-cardiac-mri/