context: If you have pain, weakness, or swelling around your knee, you may need a knee MRI. This test can help your doctor see what might be causing your symptoms. MRI stands for magnetic resonance imaging. It's a type of scan that uses a magnetic field, radio waves, and a computer to create detailed pictures of the inside of your body. Unlike an X-ray, which takes pictures of your bones, a knee MRI lets your doctor see your bones, cartilage, tendons, ligaments, muscles, and even some blood vessels. The test can show a range of problems, including: Damaged cartilage Torn tendons or ligaments Bone fractures Osteoarthritis Infections Tumors Your doctor may also order an MRI to see if you need knee surgery, or to see how well you're healing after surgery. A typical MRI machine looks like large, hollow tube. Wearing a hospital gown or loose-fitting clothes, you'll lie on an exam table that slides into the tube. For a knee MRI, you'll go in feetfirst, and only your lower body will be in the tube. Expect to hold still for around 15 to 45 minutes, sometimes longer, while the machine makes images of your knee. In some cases, you'll get a special dye injected into your arm before the exam. It's called a contrast agent, and it helps make the images of your knee even clearer. You may feel a cool sensation after you get the injection. During the exam, you're usually alone in the room. An MRI technologist will be outside, performing the exam from a computer. She can see you the whole time and will talk to you via a two-way intercom. You won't feel anything during the scan. But if it's your first MRI, you may be surprised by how loud it is. The machine makes thumping, knocking, and humming sounds. The technologist will probably offer you headphones or earplugs. If she doesn't, you can ask for them. After the exam, the technician will send images to a radiologist, who will send a report to your doctor. You'll be able to drive yourself home and continue your day as you normally would. You should not wear metal during the scan. It can interfere with the machine's magnetic field. Be sure to remove any items with metal before the exam, such as: Jewelry Hairpins Zippers Body piercings Watches Hearing aids Pocketknives Eyeglasses If you have metal inside your body, like from shrapnel or a medical device, be sure to tell your doctor or the technologist about it before you have the MRI. You may still be able to get the test. But there are some types of metal implants that mean you should not get the test: Cochlear implant Most cardiac defibrillators and pacemakers Some types of metal clips, such as those that treat brain aneurysms MRIs are safe for most people. But keep these concerns in mind: Claustrophobia: Tell your doctor if you have fear of tight spaces. You may need to take medicine before the test to calm your anxiety. The MRI technologist does not provide this medicine, so you'll need to mention it to your doctor beforehand. Pregnancy: Let your doctor know if there's any chance you're pregnant. While MRIs are considered safe for pregnant women, they're usually not recommended during the first trimester. Pregnant women should not get an injection of contrast dye unless it's absolutely necessary. Allergic reaction: If you get the contrast dye before the exam, there is a small risk you could have an allergic reaction. Your medical team can treat it quickly with medications, so be sure to tell the doctor or MRI technologist if you have any allergic symptoms, such as itching, a skin rash, trouble breathing, or a change in your heartbeat.