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 structures inside the body. An MRI can give your doctor information about your knee, the bones around it, and the tissues around it, such as cartilage, ligaments, and tendons.

When you have an MRI, you lie on a table and 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 do you prepare for the test?

In general, there's nothing you have to do before this test, unless your doctor tells you to.

Tell your doctor if you get nervous in tight spaces. You may get a medicine to help you relax. If you think you'll get this medicine, be sure you have someone to take you home.

How is the test done?

• You may have contrast material (dye) put into your arm through a tube called an I.V.
• You will lie on a table that's part of the MRI scanner.
• The table will slide into the space that contains the magnet.
• Inside the scanner, you will hear a fan and feel air moving. You may hear tapping, thumping, or snapping noises. You may be given earplugs or headphones to reduce the noise.
• You will be asked to hold still during the scan. You may be asked to hold your breath for short periods.
• You may be alone in the scanning room. But a technologist will watch through a window and talk with you during the test.

How does having an MRI of the knee feel?

You won't have pain from the magnetic field or radio waves used for the MRI test. But you may be tired or sore from lying in one position for a long time.

If a contrast material is used, you may feel some coolness when it is put into your I.V.

In rare cases, you may feel:

• Tingling in the mouth if you have metal dental fillings.
• Warmth in the area being checked. This is normal. Tell the technologist if you have nausea, vomiting, a headache, dizziness, pain, burning, or breathing problems.

How long does the test take?

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

What are the risks of an MRI of the knee?

There are no known harmful effects from the strong magnetic field used for an MRI. But the magnet is very powerful. It may affect any metal implants or other medical devices you have.

Risks from contrast material

Contrast material that contains gadolinium may be used in this test. But for most people, the benefit of its use in this test outweighs the risk. Be sure to tell your doctor if you have kidney problems or are pregnant.

There is a slight chance of an allergic reaction if contrast material is used during the test. But most reactions are mild and can be treated using medicine.

If you breastfeed and are concerned about whether the contrast material used in this test is safe, talk to your doctor. Most experts believe that very little dye passes into breast milk and even less is passed on to the baby. But if you are concerned, you can stop breastfeeding for up to 24 hours after the test. During this time, you can give your baby breast milk that you stored before the test. Don't use the breast milk you pump in the 24 hours after the test. Throw it out.

What happens after the test?

• You will probably be able to go home right away. It depends on the reason for the test.
• You can go back to your usual activities right away.