Magnetic resonance imaging (MRI) can give your doctor clear pictures without X-rays. This test uses a large magnet, radio waves, and a computer to make images. An MRI can take 15 minutes to more than an hour, depending on the number of images made. For certain MRIs, you’ll need a shot of a contrast material to help make clearer images. Because an MRI uses magnets, some people, such as people who have pacemakers, shouldn’t have one.