Magnetic Resonance Imaging (MRI)

What is magnetic resonance imaging (MRI?)

Magnetic resonance imaging (MRI) is a special test that produces very clear, detailed pictures of the organs and structures in your body. The test uses a powerful magnetic field, radio waves, and a computer to create images in cross-section. While an X-ray is very good at showing bones, an MRI shows soft tissues such as ligaments and cartilage and organs such as your eyes, brain, and heart.

When is it used?

Healthcare providers use MRI to see problems in the brain and spinal cord and to see the size and location of tumors. It can be used to examine joints and soft tissues. MRI is also helpful in diagnosing diseases and disorders of the eyes and ears.

Injuries show up well on an MRI. For example, an MRI may show whether you have torn ligaments or torn cartilage in your knee and help your healthcare provider decide whether or not you need surgery. It is also useful for injuries involving the shoulder, back, or neck.

An MRI may also be used to evaluate:

  • nerve disorders, such as multiple sclerosis
  • diseases of blood vessels, and
  • problems with the adrenal glands, kidneys, prostate gland, and bladder.

How do I prepare for the procedure?

No special preparation is needed. You may eat normally and take any usual medicines. For the test, wear loose, comfortable clothing without metal fastenings such as zippers or clasps because metal will interfere with the test. Do not wear jewelry. If you have any metal in your body (such as plates or screws from a previous surgery) tell your healthcare provider. If you have a pacemaker you may or may not be able to have an MRI, depending on the type of pacemaker. If you have any metal fragments in or around your eyes you cannot have an MRI because the test may injure your eyes. If you have anxiety or claustrophobia (trouble with small or crowded spaces), let your provider know. If you wear a transdermal patch (medicated skin patch), you may need to remove it before the MRI. Some patches contain metals in the backing of the patches. They could overheat during an MRI scan and cause skin burns. Talk with your provider about this.

What happens during the procedure?

You lie down on a cushioned bed that moves into a tunnel-shaped magnet that is open on both ends. If you get nervous when you are in small closed spaces your provider may need to give you a medicine to help you feel less nervous, or go to a site with an open MRI scanner. You will have to be very still during the procedure so the pictures will not be blurry.

Sometimes you are given a shot of a fluid called gadolinium before getting an MRI. This causes any abnormal areas to become very bright and easier to see.

Most MRIs take between 25 and 40 minutes. You will hear loud knocking and a whirring sound while the pictures are being taken. You will wear earplugs or listen to music so that the noise doesn't sound so loud. You will be able to speak with the person doing the test through a sound system so you can let him or her know if you are having any problems.

When the test is over you may go home. Your healthcare provider will schedule a visit with you to discuss the results.

What are the benefits and risks?

An MRI is painless. There is no radiation. If you were given a shot of gadolinium, there is a chance you will have an allergic reaction, but this is very rare.

Although there is no evidence that an MRI will hurt a baby during the first trimester of pregnancy, the National Radiological Protection Board recommends not using it at this time of pregnancy. MRI may be used safely later in pregnancy.

Reviewed for medical accuracy by faculty at the Wilmer Eye Institute at Johns Hopkins. Web site:
Written by Pierre Rouzier, MD, for RelayHealth.
Adult Advisor 2012.1 published by RelayHealth.
Last modified: 2010-01-08
Last reviewed: 2011-06-07
This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.
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