Magnetic resonance imaging (MRI) is a type of medical imaging that uses a strong magnetic field and very high frequency radio waves to produce highly detailed images, including of the heart and chest.
In cardiac imaging, MRI is used predominantly for the diagnosis of complex heart disorders that are present at birth (congenital) and to differentiate between normal and abnormal tissue. An MRI does not expose a person to radiation like a CT scan does.
MRI has some disadvantages. It takes longer to produce MRI images than computed tomography (CT) or echocardiography images. Because of the movement of the heart, the images obtained with MRI are less detailed than those obtained with CT. Like CT scans, most cardiac MRI scans are timed to match specific parts of the electrocardiogram, and people are asked to hold their breath, so motion is minimized and the images are clear enough for diagnosis. MRI cannot be used, or must be used with caution, when people have certain types of implanted metal objects, such as pacemakers, cochlear implants, implanted medication pumps, implanted neural stimulators, clips in the brain used to treat aneurysms, or shrapnel. The powerful magnet in an MRI machine can cause implanted metal objects to move, and the metal objects interfere with the MRI pictures.
Many cardiac MRI and magnetic resonance angiography 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, in some people with kidney problems, MRA contrast causes a risk of a serious side effect that affects the skin, joints, eyes, and internal organs (nephrogenic systemic fibrosis).
Cardiac MRI is especially useful for evaluating the size and function of the heart chambers, looking for inflammation and scarring in the heart muscle, clarifying complex problems with the anatomy of the heart, and evaluating how much blood is flowing through specific blood vessels.
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).
