What Is an MRI and Why Do You Need It?
Magnetic resonance imaging (MRI) is a safe and painless test that uses a magnetic field and radio waves to produce detailed pictures of the body's organs and structures. Unlike CAT scans or X-rays, MRI doesn't use radiation.
An MRI scanner is a large doughnut-shaped magnet that often has a tunnel in the center. Patients are placed on a table that slides into the tunnel. Some hospitals and radiology centers use what are called "open" MRI machines. They have larger openings and are helpful for patients with claustrophobia (a fear of being in tight, enclosed spaces).
During the MRI exam, radio waves manipulate the magnetic position of the body's atoms, which are picked up by a powerful antenna and sent to a computer. The computer does millions of calculations to create clear, cross-sectional black-and-white images of the body. These images can be converted into three-dimensional (3-D) pictures of the scanned area that can help pinpoint problems in the body.
MRI is used to:
- provide clear images of body parts that can't be seen as well with an X-ray, CAT scan, or ultrasound. MRI is particularly helpful for diagnosing problems with the eyes, ears, heart, and circulatory system, as well as problems in joints, cartilage, ligaments, and tendons
- detect a variety of conditions, including problems of the brain, spinal cord, skeleton, chest, lungs, abdomen, pelvis, wrists, hands, ankles, and feet
- identify infections and inflammatory conditions or to rule out problems such as tumors
There's usually no need to do anything special (like fasting) before getting an MRI. However, because metal can leave a bright or blank spot on the diagnostic film, you'll need to remove any objects containing metal, such as eyeglasses, jewelry, or belts. (Don't worry, though: braces and dental fillings won't interfere with the scan.) The MRI tech may ask questions about whether you have internal metal clips from surgery or anything else that might cause a problem near the strong magnetic field.
You won't be able to take electronic devices — like music players — into the MRI room because they can interfere with the equipment.
Sometimes people get sedated (given medication so they fall asleep) during an MRI. Sedation is usually for infants and young kids who might have trouble staying still during the MRI, but sometimes sedation can help teens with claustrophobia.
If you need to get sedation, your doctor will ask you not to eat or drink anything for several hours before the MRI. If you're getting sedation, let the MRI technician know if you have any allergies, previous drug reactions, or if you might be pregnant. For most teens who need sedation, it's enough to take an oral sedative (i.e., a pill or liquid), on the way to the hospital or imaging center. But sometimes, a teen may get sedatives through an IV line into the arm or hand.
An MRI exam usually takes 20-90 minutes, depending on the type of study your doctor has asked for. You'll lie on the movable scanning table and the technician will move you into position. The table will slide into the tunnel and the technician will take images. Each scan will last a few minutes.
Sometimes a person needs to get a contrast solution to help the MRI detect specific problems. Contrast solution highlights areas of the body, such as blood vessels, and is usually given through an IV. As with sedatives, the technician will ask if you're allergic to any medications or food before giving you the contrast solution.
If you feel cold lying on the MRI table, ask for a blanket before the test starts. It's important to stay still during the actual MRI so that the images come out clearly. If an image is blurred, it may need to be done over.
The noises that the MRI makes can be loud! Although you won't be able to bring your own music player into the MRI room, some centers will give you headphones so you can listen to music. The headphones also let you talk to the technician.
Even if the MRI doesn't have headphones, it may have an intercom system so the technician can talk to you or give you instructions during the test, or a call button that you can press if you need help. Once the exam is over, the technician will help you off the table or wheel you on the table to a recovery area (if you've been sedated).
After the test is over, you'll probably be able to return to your normal routines and diet right away. Most sedation will wear off within 1-2 hours, and any contrast material should be gone from your body in about 24 hours.
MRIs are safe and easy. No health risks have been associated with the magnetic field or radio waves, since the low-energy radio waves use no radiation. The procedure can be repeated without side effects.
Allergic reactions to contrast solution are rare, and the technician and other staff are prepared to handle such cases. The same is true if a person has a reaction to any sedation.
You won't get your MRI results right away. That's because the scans need to be viewed by a radiologist who's specially trained in reading and interpreting the scans. The radiologist will send a report to your doctor, who will discuss the results with you and explain what they mean.
Reviewed by: Steven Dowshen, MD
Date reviewed: February 2009