MRI Scans
Introduction
In magnetic resonance imaging (MRI), magnetic waves (rather than x-rays) stimulate tissues of the knee to produce signals. These signals are picked up by a scanner and analyzed by a computer to create a series of cross-sectional views of the knee. An MRI is particularly helpful in detecting damage or disease of soft tissues, such as ligaments and muscles.
A typical MRI machine looks like a large, hollow tube with a table at its center. The machine is usually located in a room of its own, with the controls behind a window off to the side. The procedure is extremely safe, but requires you to remain motionless for a long time (usually 10 to 45 minutes).
People who can't tolerate confined spaces sometimes find a standard tunnel-like MRI machine upsetting. Some newer models, however, have a more "open" design: The scanner itself is overhead, but there are no walls on either side of the table to make you feel closed in.
An MRI is painless. It usually does not require an injection with special dyes. If you have anything magnetic in your body, including metal pins, clips, or plates, check with your physician to see if the MRI is appropriate - this is especially if you have a pacemaker.
Getting Ready for the Scan
Some patients do need dye injected to improve the clarity of the images. If that's the case, don't eat or drink anything for 4 to 8 hours before the test.
Even if you aren't being injected with dye, cut back on caffeine before the exam. You won't be able to get to the bathroom during the scan.
Since you're not allowed to wear any metal during the scan, leave your watch and other jewelry at home.
If you can't stand cramped spaces, your doctor can prescribe medicine to help you relax during the scan.
If you're pregnant, tell your doctor. An MRI should not harm the baby, but the doctor still needs to be aware of your condition.
Many MRI machines tend to be noisy. Ask about earplugs or headphones to block out the sound.
During the Scan
After putting on a gown, you'll lie down on the scanner's table. The table will then slide into the machine. Typically, you'll hear knocking sounds when the procedure is going on. Despite the loud noise, the technician operating the machine in the other room can hear you, if you need to talk to him.
After the Scan
If you were given medicine to relax during the test, have someone drive you home afterwards. Otherwise you can drive home yourself.
Your doctor will review the pictures and call you with the results or review the results with you at your next office visit. Here are examples of MRI scans. See below, a normal ACL (left) and a torn ACL (right).
Normal ACL (above)
Torn ACL (above)
Below are scans of a normal meniscus and two views of a damaged meniscus (frontal and side).
Normal Meniscus (above
Damaged Meniscus - Frontal View (above)
Damaged Meniscus - Side View (above)
Frequently Asked Questions
Are MRI examinations ever painful?
The magnetic waves used to make the MRI images won't cause any pain. Occasionally they make the imaged area feel warm, but this is usually not uncomfortable. If it is, let the technician know.
Will I need to be placed all of the way inside the tunnel?
No, only the area to be studied needs to be positioned in the middle of the tunnel. If your foot is being imaged, for example, your head and upper body may be placed at the upper end of the tunnel or even outside of the tunnel.
Is it OK to have someone with me during the exam?
MRI centers have different rules concerning the presence of a friend or relative. You will need to ask the technician about this. If it's OK for someone to stay with you, make sure that the individual follows the rules about metal objects on or in the body (metallic implants, pacemakers, etc.) Your companion should also leave credit cards outside the room, since the magnetic field of the MRI will erase the magnetic strips on the cards.
Why is it important to remove all metal objects prior to the exam?
The MRI produces a strong magnetic field that can displace metallic objects and disrupt the action of metallic implants. People with pacemakers and implanted brain aneurysm clips should not even enter the room during an MRI exam. Likewise, individuals with certain types of artificial heart valves or ear implants should not have an MRI. Most metal dental fillings are not affected by the magnetic field of an MRI, so they are not likely to be dislodged.
When may I talk during the exam?
While the MRI is producing the loud knocking noise, images are being taken and recorded. It is OK to talk when the knocking has stopped. You may communicate with the technician through an intercom.
Why is an injection sometimes needed prior to the exam?
To improve the accuracy of the images, a substance called Gadolinium is occasionally injected into the joint to be imaged, or into a vein. The Gadolinium improves contrast, making it easier to see the smaller structures in the knee or shoulder and increasing the accuracy of the exam.
Why is it sometimes necessary to repeat some of the images taken during an exam?
You need to keep extremely still during the examination. If the area being imaged moves while the machine is making its knocking noise, the picture will be blurry and the scan will need to be repeated.
Is a referral needed for an MRI exam?
Yes, your doctor will need to write a prescription for the exam. Depending on your coverage, the insurance company may need to approve the procedure before the exam is performed.
