A magnetic resonance imaging test (MRI) uses magnetism and radio waves to create a detailed image of what the doctor needs to see inside your body -- such as tumors, injuries, infections, and more. There are certain precautions and preparation tasks that you will need to be aware of before the test. MRI magnets may react with any metal in your body, including pacemakers. Discuss these risks with your doctor. Follow the links below to find WebMD's comprehensive coverage about how an MRI is done, what an MRI scan looks like, what to expect, and much more.