Magnetic resonance imaging (MRI) allows your physician to see inside your body without surgery, x-rays or radiation. It is pain-free. The main component of the MRI system, or scanner, is a magnet. A radio wave antenna is used to send signals to the body and then receive signals back. These returning signals are converted into pictures by a computer attached to the scanner. Although MRI is quite safe for the majority of patients, certain patients may not be able to have an MRI. These include people with implanted medical devices such as aneurysm clips in the brain, heart pacemakers and cochlear (inner ear) implants. Also, patients with metal fragments in the eye may not be scanned.