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What Is an MRI?

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Updated January 21, 2009

An MRI

The patient lies on a table that rolls into the MRI machine

Photo © A.D.A.M.
Definition: MRI (magnetic resonance imaging) allows doctors to see inside the body without cutting anything open. MRI uses a large magnet and radio waves to look at organs and structures inside the body. It does not use radiation like an x-ray. An MRI can help doctors diagnose many types of medical conditions, especially problems with the brain and spinal cord, the heart, and other organs deep inside the body. It is particularly effective at distinguishing the body's soft tissues.

For an MRI, you will lie on a table that slides inside a tunnel in a large machine. Dye may be injected into your vein to help highlight certain structures. During the test, the magnet in the machine moves from side to side and makes humming, bumping, or banging sounds. This is very noisy, so you may wear earplugs. The test takes a long time (about an hour), and you must lie still the entire time. An MRI is painless but some people find it difficult to lie still in the tunnel, so sedative medication is sometimes given prior to the test to relax the patient.

People who have metal in their bodies (pacemaker, bullet, prosthesis, etc.) may not be able to have an MRI. Talk to your radiologist or medical provider if this applies to you before getting an MRI.

Also Known As: NMR (nuclear magnetic resonance)

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