Magnetic Resonance Imaging (MRI) of the Knee
Magnetic resonance imaging (MRI) is a test done with a large machine that uses a magnetic field and pulses of radio wave energy to make pictures of the knee . Muscles, ligaments, cartilage, and other joint structures are often best seen with an MRI. In many cases MRI gives information about structures in the body that cannot be seen as well with an X-ray, ultrasound, or CT scan.
For an MRI test, you are placed inside the magnet so that your knee is inside the strong magnetic field. MRI can find changes in the structure of organs or other tissues. It also can find tissue damage or disease, such as infection or a tumor. Pictures from an MRI scan are digital images that can be saved and stored on a computer for further study. The images also can be reviewed remotely, such as in a clinic or an operating room. Photographs or films of selected pictures can also be made.
In some cases, a contrast material may be used during the MRI scan to show certain structures more clearly in the pictures. The contrast material may be used to check blood flow, find some types of tumors, and show areas of inflammation or infection. The contrast material may be put in a vein (IV) in your arm or directly into your knee.
There are two main types of MRI-the standard MRI machine and the open MRI machine .
Why It Is Done
Magnetic resonance imaging (MRI) of the knee is done to:
MRI may also find a bone fracture when X-rays and other tests do not give a clear answer. MRI is done more commonly than other tests to check for certain bone and joint problems.
How To Prepare
Before your MRI test, tell your doctor and the MRI technologist if you:
- Are allergic to any medicines. The contrast material used for MRI does not contain iodine. If you know that you are allergic to the contrast material used for the MRI, tell your doctor before having another test.
- Are or might be pregnant.
- Have metal screws in your knee from a past knee surgery.
- Have any metal implanted in your body. This helps your doctor know if the test is safe for you. Tell your doctor if you have:
- Heart and blood vessel devices such as a coronary artery stent, pacemaker, ICD (implantable cardioverter-defibrillator), or metal heart valve.
- Metal pins, clips, or metal parts in your body, including artificial limbs and dental work or braces.
- Any other implanted medical device, such as a medicine infusion pump or a cochlear implant.
- Cosmetic metal implants, such as in your ears, or tattooed eyeliner.
- Had recent surgery on a blood vessel. In some cases, you may not be able to have the MRI test.
- Have an intrauterine device (IUD) in place. An IUD may prevent you from having the MRI test done.
- Become very nervous in confined spaces. You need to lie very still inside the MRI magnet, so you may need medicine to help you relax. Or you may be able to have the test done with open MRI equipment. It is not as confining as standard MRI machines. You may need medicine to help you relax.
- Have any other health conditions, such as kidney problems or sickle cell anemia, that may prevent you from having an MRI using contrast material.
- Wear any medicine patches. The MRI may cause a burn at the patch site.