Magnetic resonance imaging (MRI) allows physicians to examine tissues and organs inside the body by observing the response of atoms exposed to a strong magnetic field. In a closed MRI, the patient lies inside a machine in a 48-inch tube; in an open--or "accessible"--MRI the patient lies on a table. More sensitive than X-ray spectroscopy, MRI does not rely upon potentially harmful radiation. Instead, a powerful electromagnet creates radio waves that cause hydrogen atoms in the body to release energy. The magnet can map this energy from almost 360 degrees, projecting images to a computer which gives an extremely high-resolution picture. Because MRI can scan through bone, it can probe the brain in search of a tumor, to assess stroke damage, or identify degeneration. It also "sees" under nerve coverings to help diagnose multiple sclerosis; reports joint injuries in muscle and ligaments...