Single MRI images are called slices. The images can be stored on a computer or printed on film. One exam produces many images.
MRI - lower extremity; Magnetic resonance imaging - leg; Magnetic resonance imaging - lower extremity; MRI - ankle; Magnetic resonance imaging - ankle; MRI - femur; MRI - leg
How the test is performed
You will be asked to wear a hospital gown or clothes without metal zippers or snaps (such as sweatpants and a t-shirt). Some types of metal can cause blurry images.
You will lie on a narrow table that slides into a tunnel-like scanner.
Some exams use a special dye (contrast). Most of the time, you will get the dye through a vein 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.
How to prepare for the test
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:
Brain aneurysm clips
Certain types of artificial heart valves
Heart defibrillator or pacemaker
Inner ear (cochlear) implants
Kidney disease or dialysis (you may not be able to receive contrast)
Tear or rupture of the Achilles tendon in the ankle area
Tumor or cancer in the bone, muscle, or soft tissue
Talk to your health care provider about your questions and concerns.
What the risks are
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 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 an MRI include:
CT scan of the leg
Positron emission tomography (PET) scan
X-ray of the leg
A CT scan may be preferred in an emergency. The test is faster than MRI and often available in the emergency room.
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 24.
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.
C. Benjamin Ma, MD, Assistant Professor, Chief, Sports Medicine and Shoulder Service, UCSF Department of Orthopaedic Surgery. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, Bethanne Black, Stephanie Slon, and Nissi Wang.