Leg MRI scan

Answer 1

Definition

A magnetic resonance imaging (MRI) scan of the leg is a noninvasive method to create detailed pictures of the leg, including the ankle, foot, and surrounding tissues.

A leg MRI also creates pictures of the knee. However, the knee is discussed in a separate article. See also: MRI of the knee.

Unlike x-raysand computed tomographic (CT) scans, which use radiation, MRI uses powerful magnets and radio waves. The MRI scanner contains the magnet. The magnetic field produced by an MRI is about 10 thousand times greater than the earth's.

The magnetic field forces hydrogen atoms in the body to line up in a certain way (similar to how the needle on a compass moves when you hold it near a magnet). When radio waves are sent toward the lined-up hydrogen atoms, they bounce back, and a computer records the signal. Different types of tissues send back different signals.

Single MRI images are called slices. The images can be stored on a computer or printed on film. One exam produces dozens or sometimes hundreds of images.

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 may be asked to wear a hospital gown or clothing without metal fasteners (such as sweatpants and a t-shirt). Certain types of metal can cause inaccurate images.

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 usually given before the test through a vein (IV) in your hand or forearm. 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 - 15 minutes. Depending on the type of equipment, the exam may take 1 hour or longer.

How to prepare for the test

You may be asked not to eat or drink anything for 4 - 6 hours before the scan.

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.

How the test will feel

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.

Why the test is performed

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

Normal Values

Results are considered normal if the leg structures being examined are normal in appearance.

What abnormal results mean

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:

• Abscess
• Achilles tendonitis
• Arthritis
• 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.

What the risks are

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 tractionand 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.

Special 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 emergency cases, since it is faster and usually available right in the emergency room.

References

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.

Diagnosis of Venous Thromboembolism. In: Gabbe SG, Niebyl JR, Simpson JL, eds. Obstetrics - Normal and Problem Pregnancies. 5th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2007:chap 41.

Lyn E, Pallin D, Antosia RE. Knee and Lower Leg. In: Marx J, ed. Rosen's Emergency Medicine: Concepts and Clinical Practice. 6th ed. St Philadelphia, Pa: Mosby Elsevier; 2006:chap 54.

Ho K, Abu-Laban RB. Ankle and Foot. In: Marx J, ed. Rosen's Emergency Medicine: Concepts and Clinical Practice. 6th ed. St Philadelphia, Pa: Mosby Elsevier; 2006:chap 55.

Bearcroft PPW. Joint Disease. In: Grainger RC, Allison D, Adam, Dixon AK, eds. Diagnostic Radiology: A Textbook of Medical Imaging. 4th ed. New York, NY: Churchill Livingstone; 2001:chap 50.

Grainger AJ, Davies M. Techniques and Imaging of Soft Tissues. In: Grainger RC, Allison D, Adam, Dixon AK, eds. Diagnostic Radiology: A Textbook of Medical Imaging. 4th ed. New York, NY: Churchill Livingstone; 2001:chap 45.

Sanders, TG. Imaging Techniques. In: DeLee JC, Drez D Jr, Miller MD, eds. DeLee and Drez's Orthopaedic Sports Medicine. 2nd ed. Philadelphia, Pa: Saunders Elsevier; 2003:chap 16.

Answer 2

Definition

A leg MRI (magnetic resonance imaging) scan of the leg is a imaging test that uses powerful magnets and radio waves to create pictures of the leg, including the ankle, foot, and surrounding tissues.

A leg MRI also creates pictures of the knee. However, the knee is discussed in a separate article. See also: MRI of the knee

MRI does not use radiation. Single MRI images are called slices. The images can be stored on a computer or printed on film. One exam produces dozens or sometimes hundreds of images.

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 may be asked to wear a hospital gown or clothing without metal fasteners (such as sweatpants and a t-shirt). Certain types of metal can cause blurry images.

You will lie on a narrow table, which slides into a tunnel-shaped scanner.

Some exams require a special dye (contrast). The dye is usually given before the test through a vein (IV) in your hand or forearm. 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, or 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)
• Recently placed artificial joints
• 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. If you have difficulty lying still or are very nervous, you may be given a medicine to relax you. Too much 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 someone 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 were given a medicine to relax. After an MRI scan, you can resume your normal diet, activity, and medications.

Why the test is performed

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 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

Normal Values

A normal result means your leg appears normal.

What abnormal results mean

Abnormal results may be due to:

• 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 fascitis)
• 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

Consult your health care provider with any questions and concerns.

What the risks are

MRI contains no radiation. To date, no side effects from the magnetic fields and radio waves have been reported.

The most common type of contrast (dye) used is gadolinium. It is very safe. Allergic reactions to the substance rarely occur. However, gadolinium can be harmful to patients with kidney problems who require 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.

Special 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 emergency cases, since it is faster and usually available right in the emergency room.

References

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.

Reviewed By

Review Date: 02/19/2011

Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine; C. Benjamin Ma, MD, Assistant Professor, Chief, Sports Medicine and Shoulder Service, UCSF Department of Orthopaedic Surgery. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.