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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.
MRI - knee
You will wear a hospital gown or clothes without metal zippers or snaps (such as sweatpants and a t-shirt). 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 given 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 30-60 minutes, but may take longer.
You may be asked not to eat or drink anything for 4 - 6 hours before the scan.
Tell your doctor if you are afraid of close spaces (have claustrophobia). You may be given a medicine to help you feel sleepy and less anxious. Your doctor may suggest an "open" MRI, in which the machine is not as close to the body.
Before the test, tell your health care provider if you have:
Because the MRI contains strong magnets, metal objects are not allowed into the room with the MRI scanner:
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 your normal diet, activity, and medicines.
Your doctor may order this test if you have:
You may also have this test to check your progress after knee surgery.
A normal result means your knee looks okay.
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 health care provider if you have questions or concerns.
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 health care 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 a piece of metal inside your body to move or shift. For safety reasons, please don't bring anything that contains metal into the scanner room.
Tests that may be done instead of a knee MRI include:
Wilkinson ID, Paley MNJ. Magnetic resonance imaging: basic principles. In: Grainger RC, Allison D, Adam, Dixon AK, eds. Diagnostic Radiology: A Textbook of Medical Imaging. 5th ed. New York, NY: Churchill Livingstone; 2008:chap 5.
DeLee JC, Drez D Jr, Miller MD, eds. DeLee and Drez’s Orthopaedic Sports Medicine. 3rd ed. Philadelphia, Pa: Saunders Elsevier; 2009:chap 23.
Grainger RG, Thomsen HS, Morcos SK, Koh DM, Roditi G. Intravascular contrast media for radiology, CT, and MRI. In: Adam A, Dixon AK, eds. Grainger & Allison's Diagnostic Radiology: A Textbook of Medical Imaging. 5th ed. New York, NY: Churchill Livingstone; 2008:chap 2.