Often, the orthopaedic surgeon may recommend a hard-soled sandal for further protection. A magnet creates a steady field which causes protons in the body to line up and spin in the same direction. As the protons move back to their aligned positions, they release energy. A receiver coil measures the energy released by the protons when they are disturbed. It is these measurements which give us information about the condition of the tissue in which the protons lie.
Information is also available about the type of tissue being imaged.
The computer reconstructs this information into an image. These screens are then recorded on film. MRIs are generally not used upon pregnant women or people who have cardiac pacemakers, aneurysm clips or some metal implants. MR images were approved by the United States' Food and Drug Administration in the 1980s, but chemists and physicists have used the principles of magnetic resonance since the 1940s for such things as characterizing chemical compounds. The cartilage, which will appear glossy and smooth in a normal anatomic finding, will present as a frayed and rough surface.