Cardiac CT or MRI

Cardiac CT and cardiac MRI are advanced imaging tests that show the heart and the blood vessels around it in far greater detail than an ultrasound can. They answer different questions and are chosen accordingly — CT is the better look at the coronary arteries themselves, while MRI is the better look at the heart muscle.

A CT scanner takes rapid X-ray images from many angles and reconstructs them into cross-sections of the heart. Timed with your heartbeat and combined with iodine-based contrast given through an IV, it produces a coronary CT angiogram — a non-invasive picture of the coronary arteries showing narrowing and plaque.

It is often used to evaluate chest pain in someone at low to intermediate risk, because a normal result is very reliable at ruling out significant coronary blockage and can spare a patient an invasive catheterization. It is also used to map anatomy before procedures such as TAVR or an ablation.

To keep the arteries sharp, a slow, steady heart rate helps, so a beta blocker is often given beforehand, and nitroglycerin under the tongue may be used to widen the arteries. You will be asked to hold your breath for a few seconds during the scan. The contrast commonly causes a warm flush and a metallic taste that passes in moments.

An MRI uses a strong magnetic field and radio waves — no X-rays — and excels at characterizing the heart muscle itself. It is the reference standard for measuring chamber volumes and ejection fraction, and gadolinium contrast can reveal scar tissue in a pattern that helps distinguish a previous heart attack from an inflammatory or infiltrative cause of a weakened heart.

It is commonly ordered for unexplained cardiomyopathy, suspected myocarditis, infiltrative disease such as amyloidosis or sarcoidosis, and congenital heart disease. The scan is longer than a CT, often 45 to 90 minutes, and involves lying still inside a tube while the machine makes loud knocking sounds; headphones are provided, and repeated breath-holds are required.

• Any kidney problems — both contrast agents are cleared by the kidneys, and a recent blood test is usually needed
• A previous reaction to contrast dye or an iodine or shellfish allergy
• Whether you might be pregnant
• For MRI, any implanted device or metal: pacemaker, defibrillator, some stents and clips, cochlear implants, or metal fragments in the eye. Many modern cardiac devices are MRI-conditional and can be scanned with preparation, but the device details must be known in advance
• If you have difficulty with enclosed spaces, say so early — it can be planned for

Images are reconstructed and read after your visit, and your cardiologist will discuss what they show alongside the rest of your evaluation.