Magnetic resonance imaging: A procedure that uses magnetism, radio waves, and a computer to create pictures of areas inside the body. Abbreviated MRI. An MRI is painless and has the advantage of avoiding x-ray radiation exposure. There are no known risks of an MRI. The benefits of an MRI relate to its precise accuracy in detecting structural abnormalities of the body. Patients with heart pacemakers, metal implants, or metal chips or clips in or around the eyes cannot be scanned with MRI because of the effect of the magnet.
