DefinitionA leg MRI (magnetic resonance imaging) scan of the leg uses strong magnets to create pictures of the leg. This may include the ankle, foot, and surrounding tissues.A leg MRI also creates pictures of the knee.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.Alternative NamesMRI – lower extremity; Magnetic resonance imaging – leg; Magnetic resonance imaging – lower extremity; MRI – ankle; Magnetic resonance imaging – ankle; MRI – femur; MRI – legHow the test is performedYou 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 testYou 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.advertisementBefore the test, tell your health care provider if you have:Brain aneurysm clipsCertain types of artificial heart valvesHeart defibrillator or pacemakerInner ear (cochlear) implantsKidney disease or dialysis (you may not be able to receive contrast)Recently placed artificial jointsCertain types of vascular stentsWorked with sheet metal (you may need tests to check for metal pieces in your eyes)Because the MRI contains strong magnets, metal objects are not allowed into the room with the MRI scanner:Pens, pocketknives, and eyeglasses may fly across the room.Items such as jewelry, watches, credit cards, and hearing aids can be damaged.Pins, hairpins, metal zippers, and similar metallic items can distort the images.Removable dental work should be taken out just before the scan.How the test will feelAn 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.Why the test is performedThis test provides detailed pictures of parts of the leg that are hard to see clearly on CT scans.Your doctor may order an MRI of the leg if you have:A mass that can be felt on a physical examAn abnormal finding on an x-ray or bone scanBirth defects of the leg, ankle, or footBone pain and feverBroken boneDecreased motion of the ankle jointPain, swelling, or redness in a legRedness or swelling of the ankle jointLeg pain and a history of cancerLeg, foot, or ankle pain that does not get better with treatmentNormal ValuesA normal result means your leg looks okay.What abnormal results meanAbnormal results may be due to:AbscessAchilles tendonitisArthritisBroken bone or fractureInfection in the boneLigament, tendon, or cartilage injuryMuscle damageOsteonecrosis (avascular necrosis)Plantar fascia rupture (See: Plantar fascitis)Posterior tibial tendon dysfunctionTear or rupture of the Achilles tendon in the ankle areaTumor or cancer in the bone, muscle, or soft tissueTalk to your health care provider about your questions and concerns.What the risks areMRI 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.advertisementThe 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 dont bring anything that contains metal into the scanner room.Special considerationsTests that may be done instead of an MRI include:Bone scanCT scan of the legPositron emission tomography (PET) scanX-ray of the legA CT scan may be preferred in an emergency. The test is faster than MRI and often available in the emergency room.ReferencesWilkinson 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 & Allisons Diagnostic Radiology: A Textbook of Medical Imaging. 5th ed. New York, NY: Churchill Livingstone; 2008:chap 2.Review Date:1/17/2013Reviewed By: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.
Leg MRI scan