Nuclear magnetic resonance imaging. A procedure in which radio waves and a powerful magnet linked to a computer are used to create detailed pictures of areas inside the body. These pictures can show the difference between normal and diseased tissue. NMRI makes better images of organs and soft tissue than other scanning techniques, such as computed tomography (CT) or X-ray. NMRI is especially useful for imaging the brain, the spine, the soft tissue of joints and the inside of bones. Also called nuclear magnetic resonance imaging, magnetic resonance imaging and MRI.