context: Widespread use of MRI (magnetic resonance imaging) has revolutionized the ability to diagnose multiple sclerosis. Disease-related changes in the brain or spinal cord are detected by MRI in more than 90% of people suspected of having MS. MRI is a test that produces very clear pictures of the human body without the use of X-rays. It uses a large magnet, radio waves and a computer to produce these images. MRI can often detect damaged areas in the brain or spinal cord that would be missed by other imaging techniques such as a CAT scan. To detect MS. MRI is considered the best test to help diagnose MS. However, 5% of people with MS do not have abnormalities detected on MRI; thus, a "negative" scan does not completely rule out MS. In addition, some common changes of aging may look like MS on a MRI. To track the progress of disease. Although they aren't widely needed, people with MS may get repeat scans to determine the status of their disease and how well their medications are working. Yes. The MRI exam poses no risk to the average person if appropriate safety guidelines are followed. Many people who have had heart surgery and people with the following medical devices can be safely examined with MRI (the metals used in these surgeries are not "magnetic" and the person can be safely placed in the MRI machine): Artificial joints Staples Many cardiac valve replacements (check with your doctor) Disconnected medication pumps Vena cava filters Brain shunt tubes for hydrocephalus Some conditions may make an MRI exam a bad idea. Tell your doctor if you have any of the following conditions: Heart pacemaker Cerebral aneurysm clip (metal clip on a blood vessel in the brain) Pregnancy Implanted insulin pump (for treatment of diabetes), narcotics pump (for pain medication), or implanted spinal cord stimulators for chronic pain Metal in the eye or eye socket Cochlear (ear) implant for hearing impairment Implanted spine stabilization rods (newer titanium rods and plates are fine) Severe lung disease (such as tracheomalacia or bronchopulmonary dysplasia) Heartburn Obesity (weighing more than 300 pounds may limit which machine can be used) Not able to lie on your back for 30 to 60 minutes Claustrophobia (which can be handled with sedation) Allow two hours for your MRI exam. In most cases, the procedure takes 40 to 80 minutes; during that time, several dozen images may be taken. Personal items such as your watch, wallet (including any credit cards with magnetic strips that can be erased by the magnet), and jewelry should be left at home if possible or removed prior to the MRI scan. Secured lockers are available to store personal possessions. You may be asked to wear a hospital gown during the MRI scan. As the MRI scan begins, you will hear the equipment making a variety of different sounds, including a muffled thumping sound or banging sound that will last for several minutes at a time. Other than that sound, you should experience no unusual sensations during the scanning. Certain MRI exams require an injection of a contrast material. This helps identify abnormalities in certain parts of the body on the scan images. Feel free to ask questions and tell the technologist or doctor if you have any concerns. Your doctor will discuss the test results with you. Most imaging centers will give you a copy of your scan on a CD disk that you can take to your doctor at your next appointment. It is a good idea to let your doctor know that you have completed your scan, so that he or she can contact the imaging center to get your report. Generally, you can resume your usual activities immediately.