Magnetic Resonance Imaging (MRI) of the Heart

(MRI Scan of the Heart, Cardiac MRI)

Procedure Overview

What is magnetic resonance imaging (MRI) of the heart?

Magnetic resonance imaging (MRI) is a diagnostic procedure that uses a combination of a large magnet, radiofrequencies, and a computer to produce detailed images of organs and structures within the body.

How does MRI work?

The MRI machine is a large, cylindrical (tube-shaped) machine that creates a strong magnetic field around the patient. This magnetic field, along with a radiofrequency, alters the hydrogen atoms' natural alignment in the body. Computers are then used to form two-dimensional (2D) images of the heart's structure based on the activity of the hydrogen atoms. Cross-sectional views can be obtained to reveal further details. MRI does not use radiation, as do x-rays or computed tomography (CT scans).

A magnetic field is created and pulses of radio waves are sent from a scanner. The radio waves knock the nuclei of the atoms in the body out of their normal position. As the nuclei realign back into proper position, they send out radio signals. These signals are received by a computer that analyzes and converts them into an image of the part of the body being examined. This image appears on a viewing monitor. Some MRI machines look like narrow tunnels, while others are more open.

MRI may be used instead of a CT scan in situations where organs or soft tissue are being studied, because with MRI scanning bones do not obscure the images of organs and soft tissues, as does CT scanning.

Other related procedures that may be used to assess the heart include resting or exercise electrocardiogram (ECG), Holter monitor, signal-averaged ECG, cardiac catheterization, chest x-ray, computed tomography (CT scan) of the chest, electrophysiological studies, myocardial perfusion scans, radionuclide angiography, and ultrafast CT scan. Please see these procedures for additional information.

Reasons for the Procedure

MRI of the heart may be performed for further evaluation of signs or symptoms that may suggest:

  • atherosclerosis - a gradual clogging of the arteries over many years by fatty materials and other substances in the blood stream

  • cardiomyopathy - an enlargement of the heart due to thickening or weakening of the heart muscle

  • congenital heart disease - defects in one or more heart structures that occur during formation of the fetus, such as a ventricular septal defect (hole in the wall between the two lower chambers of the heart)

  • congestive heart failure - a condition in which the heart muscle has become weakened to an extent that blood cannot be pumped efficiently, causing buildup (congestion) in the blood vessels, lungs, feet, ankles, and other parts of the body

  • aneurysm - a dilation of a part of the heart muscle or the aorta (the large artery that carries oxygenated blood out of the heart to the rest of the body), which may cause weakness of the tissue at the site of the aneurysm

  • valvular heart disease - malfunction of one or more of the heart valves that may cause an obstruction of the blood flow within the heart

  • cardiac tumor - a tumor of the heart that may occur on the outside surface of the heart, within one or more chambers of the heart (intracavitary), or within the muscle tissue of the heart

There may be other reasons for your physician to recommend an MRI of the heart.

Risks of the Procedure

Because radiation is not used, there is no risk of exposure to radiation during an MRI procedure.

Due to the use of the strong magnet, MRI cannot be performed on patients with implanted pacemakers, some older intracranial aneurysm clips, cochlear implants, certain prosthetic devices, implanted drug infusion pumps, neurostimulators, bone-growth stimulators, certain intrauterine contraceptive devices, or any other type of iron-based metal implants. MRI is also contraindicated in the presence of some internal metallic objects such as bullets or shrapnel, as well as surgical clips, pins, plates, screws, metal sutures, or wire mesh.