MRI of the Knee: About Your Child's Test

What is it?

MRI (magnetic resonance imaging) is a test that uses a magnetic field and pulses of radio wave energy to make pictures of the organs and other parts inside the body. An MRI can give the doctor information about your child's knee, the bones around it, and the tissues around it, such as cartilage, ligaments, and tendons.

Your child will lie on a special table. The table moves into the MRI machine.

Why is this test done?

An MRI of the knee can help find problems such as damage to the ligaments and cartilage around the knee. The MRI also can look for the cause of unexplained knee pain, the knee giving out for no reason, or infections in or around the knee.

How can you prepare for the test?

Let your child know that an MRI doesn't hurt. But he or she may feel warm near the area being imaged.

An MRI machine can be loud. Your child may get earplugs or headphones during the test. If you join your child in the room, you may need hearing protection as well.

Ask the doctor if your child will need sedation to help relax before the test. You can also ask if your child will swallow a contrast material before the test.

The doctor will tell you if your child should stop eating or drinking before the test.

How is the test done?

Before the test

• Your child will remove all metal objects from their body. These include hearing aids, jewelry, watches, and hairpins.
• Your child will take off all or most of their clothes and then change into a gown.
• If your child does leave some clothes on, make sure that the pockets are empty.
• Your child may have contrast materials (dye) put into the arm through a tube called an I.V. This dye helps doctors see specific organs and blood vessels and most tumors. If a dye is used, your child may feel a quick sting or pinch when the I.V. is started.
• Many children need a sedative to help them relax and stay still during the test.

During the test

• Your child will lie on their back on a table that is part of the MRI scanner.
• The table will slide into the space that contains the magnet.
• Inside the scanner, your child may hear a fan and feel air moving. They may hear tapping, thumping, or snapping noises.
• Your child will be asked to hold still during the scan. And your child may be asked to hold their breath for short periods. You may need to help your child do these things.
• Your child will be kept safe and comfortable during the test. You may be able to stay in the room with your child. A technologist will watch through a window and talk with your child during the test.

What happens during the test?

• Your child may have contrast dye put into his or her arm through a tube called an I.V.
• Your child will lie on a table that is part of the MRI scanner.
• The table will slide into the space that contains the magnet.
• Inside the scanner, your child may hear a fan and feel air moving. They may hear tapping, thumping, or snapping noises.
• Your child will be asked to hold still during the scan. And your child may be asked to hold their breath for short periods. You may need to help your child do these things.
• Your child will be kept safe and comfortable during the test. You may be able to stay in the room with your child. A technologist will be watching through a window and talking with your child during the test.

How long does the test take?

The test usually takes 30 to 60 minutes. But it can take as long as 2 hours.

What happens after the test?

• Your child will probably be able to go home right away, depending on the reason for the test. If your child is in the hospital, he or she will be taken back to his or her room.
• If your child had medicine to help relax (sedation), he or she may be unsteady after the test. An older child may have trouble walking. A baby may be unsteady when sitting or crawling. It takes time (sometimes a few hours) for the medicine effects to wear off. Common side effects include nausea, vomiting, and feeling sleepy or cranky.
• If a dye was used, it may make your child feel warm and flushed. It may leave a metallic taste in the mouth. Some people feel sick to their stomach or get a headache.
• You will be able to go home when your child is awake and the radiologist says it is safe to leave.