Cardiac imaging helps doctors examine the structure and function of the heart. Different types of scans are used depending on the clinical question. The most commonly used imaging tests include echocardiography, cardiac CT, myocardial perfusion imaging, and cardiac MRI. Each has its advantages, limitations, and specific indications.
Echocardiography is an ultrasound-based test that uses sound waves to produce real-time images of the heart. It shows how the heart chambers and valves function and is often used to assess ejection fraction, wall motion, and valve disease. It is safe, non-invasive, and does not use radiation or contrast. Limitations include poor image quality in patients with obesity or lung disease.
Cardiac CT, often used for coronary angiography, provides detailed images of the coronary arteries. It uses X-rays and requires injection of an iodine-based contrast agent. This contrast highlights the vessels, allowing detection of narrowing or calcification. The test is quick and highly sensitive for coronary artery disease. However, it involves exposure to ionising radiation. Patients with iodine allergy or severe kidney dysfunction may not be suitable for contrast administration.
Myocardial perfusion imaging, a type of nuclear scan, assesses blood flow to the heart muscle at rest and under stress. A small amount of radioactive tracer is injected, and a gamma camera captures images. Areas with reduced tracer uptake may indicate reduced blood supply. It is useful in diagnosing ischaemia and evaluating risk in coronary artery disease. It involves radiation exposure and is not recommended during pregnancy. It may be less accurate in obese patients or those with significant breast or diaphragmatic tissue.
Cardiac MRI provides high-resolution images of the heart’s structure and function without radiation. It is particularly useful for assessing myocardial tissue, detecting fibrosis, and diagnosing cardiomyopathies. Gadolinium-based contrast is often used to enhance image quality. This contrast is generally safe but should be avoided in patients with advanced kidney disease due to the risk of nephrogenic systemic fibrosis. MRI is contraindicated in patients with non-MRI-compatible implants or metal fragments. It may also be difficult for those with claustrophobia or those unable to remain still for extended periods.
Contrast agents are used in cardiac CT and MRI to improve the visibility of blood vessels and tissue detail. In CT, contrast enhances artery walls to detect narrowing or plaques. In MRI, gadolinium highlights areas of scarring or inflammation. While generally safe, contrast use carries risks, especially in patients with kidney disease or allergies.
Radiation exposure is a concern in CT and nuclear imaging. Though the doses are low, repeated exposure over time can slightly increase the risk of cancer. For this reason, tests involving radiation are only recommended when the expected benefit outweighs the risk.
Each cardiac imaging test has specific uses and contraindications. Selection depends on the clinical scenario, patient characteristics, and diagnostic goals. Proper test selection ensures accurate diagnosis while minimising risk.