With magnetic resonance imaging (MRI), a powerful magnetic field and radio waves are used to produce detailed images of the heart and chest. This expensive and sophisticated procedure is used predominantly for the diagnosis of complex heart disorders that are present at birth (congenital) and to differentiate between normal and abnormal tissue.
MRI has some disadvantages. It takes longer to produce MRI images than computed tomography (CT) images. Because of the movement of the heart, the images obtained with MRI are fuzzier than those obtained with CT. However, newer MRI scans that are timed to match specific parts of the electrocardiogram (ECG—called gated MRI) are much clearer than conventional MRI scans. MRI cannot be used when people have certain types of implanted metal objects, such as pacemakers, cochlear implants, implanted drug pumps or neural stimulators, clips in the brain used to treat aneurysms, or shrapnel.
Magnetic resonance angiography (MRA) is a type of MRI that focuses on blood vessels rather than organs. MRA produces images of blood vessels and blood flow similar in quality to those produced by conventional angiography but is not an invasive procedure. MRA can be used to detect bulges (aneurysms) in the aorta, narrowing of the arteries supplying the kidneys (renal stenosis), and a narrowing or blockage in the arteries that supply blood to the heart (coronary artery disease) or the arms and legs (peripheral artery disease). Some MRA techniques require injection of a contrast agent (a substance that makes organs and structures easier to see on MRI) into a vein in the arm. However, people with kidney problems should not receive MRA contrast due to the risk of a serious side effect that affects the skin, joints, eyes, and internal organs (nephrogenic systemic fibrosis). Newer contrast agents, which do not carry this risk, may make the test available to people with kidney problems.