Leg MRI scan

Definition

A 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 slices.

Alternative Names

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). Make sure you take off your watch, jewelry and wallet. MRI can pull on any metallic objects. 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 to 60 minutes, but may take longer.

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:

• 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)
• Recently placed artificial joints or surgery with metal plates and screws
• Certain types of vascular stents
• Worked 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 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

This test provides detailed pictures of parts of the leg that are hard to see clearly on CT scans.

Your provider may order an MRI of the leg if you have:

• A mass that can be felt on a physical exam
• An abnormal finding on an x-ray or bone scan
• Birth defects of the leg, ankle, or foot
• Bone pain and fever
• Broken bone
• Decreased motion of the ankle joint
• Pain, swelling, or redness in a leg
• Redness or swelling of the ankle joint
• Leg pain and a history of cancer
• Leg, foot, or ankle pain that does not get better with treatment
• Instability of your ankle and foot

Normal Results

A normal result means your leg has no identified problems.

What Abnormal Results Mean

Abnormal results may be due to:

• Degenerative changes due to age
• Abscess
• Achilles tendonitis
• Arthritis
• Broken bone or fracture
• Infection in the bone
• Ligament, tendon, or cartilage injury
• Muscle damage
• Osteonecrosis (avascular necrosis)
• Plantar fascia rupture (See: Plantar fasciitis)
• Posterior tibial tendon dysfunction
• Tear or rupture of the Achilles tendon in the ankle area
• Tumor or cancer in the bone, muscle, or soft tissue

Talk to your provider about your questions and concerns.

Risks

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

It is also safe to have MRI performed during pregnancy. No side effects or complications have been proven.

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 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 do not bring anything that contains metal into the scanner room.

Considerations

Tests that may be done instead of an MRI include:

• Bone scan
• 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.

References

Kadakia AR, Aiyer AA. Imaging of the foot and ankle. In: Miller MD, Thompson SR, eds. DeLee, Drez, & Miller's Orthopaedic Sports Medicine. 5th ed. Philadelphia, PA: Elsevier; 2020:chap 112.

Kapoor G, Toms AP. Current status of imaging of the musculoskeletal system. In: Adam A, Dixon AK, Gillard JH, Schaefer-Prokop CM, eds. Grainger & Allison's Diagnostic Radiology. 7th ed. Philadelphia, PA: Elsevier; 2021:chap 38.

Kosmas C, Schreibman KL, Robbin MR. Foot and ankle. In: Haaga JR, Boll DT, eds. CT and MRI of the Whole Body. 6th ed. Philadelphia, PA: Elsevier; 2017:chap 64.