You will lie on a narrow table, which slides into the middle of the MRI machine. If you fear confined spaces (have claustrophobia), tell your doctor before the exam.
Small devices, called coils, are placed around the leg. These devices help send and receive the radio waves, and improve the quality of the images.
Some exams require a special dye (contrast). The dye is either given through a vein (IV) in your arm or injected directly into the joint itself (Arthrogram). 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. Several sets of images are usually needed, each taking 2 - 10 minutes. Depending on the type of equipment, the exam may take 30 minutes or longer.
Before the test, tell the radiologist if you are currently receiving dialysis, as this may affect whether you can have IV contrast.
If you fear confined spaces (have claustrophobia), tell your doctor before the exam. You may be given a medicine to help you feel sleepy and less anxious, or your doctor may recommend an "open" MRI, in which the machine is not as close to the body.
The strong magnetic fields created during an MRI can interfere with certain implants, particularly pacemakers. Persons with cardiac pacemakers cannot have an MRI and should not enter an MRI area.
You may not be able to have an MRI if you have any of the following metallic objects in your body:
- Brain aneurysm clips
- Certain artificial heart valves
- Inner ear (cochlear) implants
- Recently placed artificial joints
- Some older types of vascular stents
Tell your health care provider if you have one of these devices when scheduling the test, so the exact type of metal can be determined.
Before an MRI, sheet metal workers or any person that may have been exposed to small metal fragments should receive a skull x-ray to check for metal in the eyes.
Because the MRI contains a magnet, metal-containing objects such as pens, pocketknives, and eyeglasses may fly across the room. This can be dangerous, so they are not allowed into the scanner area.
Other metallic objects are also not allowed into 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.
An MRI of the leg causes no pain. Some people may become anxious inside the scanner. If you have difficulty lying still or are very anxious, you may be given a mild sedative. Excessive movement can blur MRI images and cause errors.
The table may be hard or cold, but you can request a blanket or pillow. The machine produces loud thumping and humming noises when turned on. You can wear ear plugs to help reduce the noise.
An intercom in the room allows you to speak to the person operating the scanner at any time. Some MRIs have televisions and special headphones that you can use to help the time pass.
There is no recovery time, unless you need sedation. After an MRI scan, you can resume your normal diet, activity, and medications.
This test provides clear pictures of parts of the leg that are difficult 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 exam
- An abnormal finding on an x-ray or bone scan
- Birth defects of the leg, ankle, or foot
- Bone infection (osteomyelitis)
- 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
- Signs of cancer or a tumor
- Signs of injury to the leg or ankle muscle, cartilage, or ligaments
- Unexplained leg, foot, or ankle pain that does not get better with treatment
Your doctor may also order a leg MRI to:
- Evaluate an infection or abscess
- Identify a mass or tumor, including cancer
- Monitor your progress after leg, foot, or ankle surgery
Results are considered normal if the leg structures being examined are normal in appearance.
Results depend on the nature of the problem. Different types of tissues send back different MRI signals. For example, healthy tissue sends back a slightly different signal than cancerous tissue.
Abnormal results may be due to:
- Achilles tendonitis
- Blood clot in the leg (deep vein thrombosis)
- Broken bone or fracture
- Infection in the bone
- Ligament, tendon, or cartilage injury
- Muscle damage
- Osteonecrosis (avascular necrosis)
- Plantar fascia rupture (See: Plantar fascitis)
- Posterior tibial tendon dysfunction
- Tumor or cancer in the bone, muscle, or soft tissue
Consult your health care provider with any questions and concerns.
MRI contains no ionizing radiation. To date, there have been no documented significant side effects of the magnetic fields and radio waves used on the human body.
The most common type of contrast (dye) used is gadolinium. It is very safe. Allergic reactions to the substance rarely occur. The person operating the machine will monitor your heart rate and breathing.
MRI is usually not recommended for acute trauma situations, because traction and life-support equipment cannot safely enter the scanner area and the exam can take quite a bit of time.
People have been harmed in MRI machines when they did not remove metal objects from their clothes or when metal objects were left in the room by others.
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 emergency cases, since it is faster and usually available right in the emergency room.