Knee MRI scan

Definition

A knee MRI (magnetic resonance imaging) scan uses energy from strong magnets to create pictures of the knee joint and muscles and tissues.

An MRI does not use radiation (x-rays). Single MRI images are called slices. The images can be stored on a computer or printed on film. One exam produces many images.

How the Test is Performed

You will wear a hospital gown or clothes without metal zippers or snaps (such as sweatpants and a t-shirt). Please remove your watches, glasses, jewelry, and wallet. Certain types of metal can cause blurry images.

You will lie on a narrow table that slides into a large tunnel-like scanner.

Some exams use a special dye (contrast). Most of the time, you will get the dye through a vein (IV) in your arm or hand before the test. Sometimes, the dye is injected into a joint. The dye helps the radiologist see certain areas more clearly.

During the MRI, the person who operates the machine will watch you from another room. The test most often lasts 30 to 60 minutes, but may take longer. It can be loud. The technician can give you some ear plugs if needed.

How to Prepare for the Test

You may be asked not to eat or drink anything for 4 to 6 hours before the scan.

Tell your health care provider if you are afraid of closed spaces (have claustrophobia). You may be given a medicine to help you feel sleepy and less anxious. Your provider may suggest an "open" MRI, in which the machine is not as close to the body.

Before the test, tell your provider if you have:

Because the MRI contains strong magnets, metal objects are not allowed into the room with the MRI scanner:

How the Test will Feel

An MRI exam causes no pain. You will need to lie still. Too much movement can blur MRI images and cause errors.

The table may be hard or cold, but you can ask for a blanket or pillow. The machine makes loud thumping and humming noises when turned on. You can wear ear plugs to help block out the noise.

An intercom in the room allows you to speak to someone at any time. Some MRIs have televisions and special headphones to help the time pass.

There is no recovery time, unless you were given a medicine to relax. After an MRI scan, you can return to your normal diet, activity, and medicines.

Why the Test is Performed

Your provider may order this test if you have:

You may also have this test to check your progress after knee surgery.

Normal Results

A normal result means your knee looks OK.

What Abnormal Results Mean

Abnormal results may be due to a sprain or tear of the ligaments in the knee area.

Abnormal results may also be due to:

Talk to your provider if you have questions or concerns.

Risks

MRI contains no radiation. There have been no reported side effects from the magnetic fields and radio waves.

The most common type of contrast (dye) used is gadolinium. It is very safe. Allergic reactions to the substance are rare. However, gadolinium can be harmful to people with kidney problems that need dialysis. If you have kidney problems, please tell your provider before the test.

The strong magnetic fields created during an MRI can cause heart pacemakers and other implants to not work as well. It can also cause small pieces of metal inside your body to move or shift. For safety reasons, please do not bring anything that contains metal into the scanner room.

Considerations

Tests that may be done instead of a knee MRI include:


Review Date: 3/17/2019
Reviewed By: C. Benjamin Ma, MD, Professor, Chief, Sports Medicine and Shoulder Service, UCSF Department of Orthopaedic Surgery, San Francisco, CA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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