Magnetic resonance imaging (MRI)

MRIs use magnetic fields and radio waves, instead of radiation, to create three-dimensional images and two-dimensional cross sections of the aorta. The images produced by MRIs are similar to X-ray images but show more information about the soft tissues of the body for a more detailed picture.

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MRIs have large tubes that are big enough for a patient lie down inside. Radio waves and strong magnetic fields are generated inside the shell of the tube and directed toward the body during an MRI scan. The body responds by emitting weak energy signals that are detected by the MRI machine. A computer converts these signals into three-dimensional images that can be manipulated to show any two-dimensional cross section.

Before the test, you must remove all accessories and clothing containing metal, including jewelry, metal fasteners, dentures, wigs, and hearing aids. Metal objects may interfere with the magnetic field of the MRI, affecting the quality of the image.

An MRI exam is painless and generally lasts between 30 and 60 minutes. The procedure involves lying on a movable table that slides into the tube. Movement can blur the images, so it is important to lie still. The space inside the tube is quite narrow, and some patients may feel claustrophobic. Often patients will be offered headphones or earplugs to help block out the loud tapping and thumping sounds made by the MRI machine and to help them relax.

Magnetic resonance angiography (MRA) is one of the newer uses of MRI. For this test, a contrast agent, similar to a dye, is injected into the arm or leg through an intravenous line. The dye makes it easier to visualize the heart and blood vessels. One advantage of the MRA is that the contrast agents are less likely to cause allergic reactions than those used during computed tomography (CT or CAT scans).

There are no known risks from the magnetic fields and radio waves produced by MRI machines. However, people who have pacemakers, cardioverter defibrillators, or other metal-containing objects inside their bodies cannot get MRIs. Also, the affects of magnetic fields on fetuses are not well understood, so getting an MRI may not be advisable for pregnant women.