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MRI: A magnetic snapshot of your body

This imaging test uses magnets and radio waves to create images of tissues or bones in your body.

You've hurt your knee. Your doctor has diagnosed the injury as a torn ligament. But to make sure, your doctor may recommend a magnetic resonance imaging (MRI) test.

An MRI is a painless procedure that uses powerful magnets and radio waves to take pictures of your body. Along with diagnosing torn ligaments and cartilage, MRIs can also be used to detect hip, pelvic, back and brain problems, and diseases such as cancer.

Unlike some other imaging tests, such as computed tomography (CT) or x-ray scanning, an MRI does not expose you to radiation.

The MRI procedure

During an MRI, you will be asked to lie on your back on a narrow table that slides into a large tunnel-like tube inside a scanner. You will be asked to lie still. Because the scanner is very noisy, you will probably be given earplugs or headphones to block the noise, RadiologyInfo notes.

You may also have small coils placed around your head, arm or leg or on other areas of your body. The coils are used to improve the quality of the pictures being taken by the scanner, according to the National Institutes of Health (NIH).

The scanner creates a magnetic field around your body and sends radio waves to the area of your body to be scanned. The radio waves cause your tissues to resonate; different tissues emit different signals. The signals are detected by the scanner and analyzed by a computer, giving your doctor a detailed picture of the area.

You won't feel anything during the MRI. But the small space does make some people feel claustrophobic. If you don't like confined spaces, you can ask your doctor to give you a sedative before the test.

A healthcare professional will be on hand to observe the procedure. You'll be able to talk back and forth through an intercom in the scanner.

It typically takes from 30 minutes to an hour to complete an MRI, according to the American Society of Radiologic Technologists.

Preparing for an MRI

Getting ready for an MRI is simple. You usually don't need to have any tests, take any medications or go on a special diet before an MRI. But you may be asked not to eat anything for several hours before the test, depending on the part of your body being examined.

Because of the strong magnets used in an MRI, you should leave all metal objects—such as hairpins, hearing aids, eyeglasses and jewelry—outside the MRI room. You will probably be asked to wear a hospital gown or clothing without zippers, snaps or other metal fasteners. You should also take out any removable dental work before the procedure.

If you have a pacemaker, it's important to tell your doctor. The magnets used in an MRI can make the pacemaker stop working.

You should also let your doctor know if you have any other metallic objects in your body—such as ear implants, brain aneurysm clips, some artificial heart valves and recently placed artificial joints. Some transdermal drug patches also contain metal and should be removed. These items could be affected by the magnet.

An MRI is an extremely safe and effective procedure with no documented significant side effects, according to the NIH.

If you have questions or concerns about MRI, talk to your doctor before the procedure.

reviewed 7/7/2019

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