 MRI uses a strong magnet and radio waves to create images of the inside of the body. The subject lies on a long narrow couch inside a metal cylinder the scanner for up to 3 hours while the scanner gathers data. Earplugs are worn to muffle loud noises caused by electrical switching of radiofrequency circuits used in the scanning process. A special pad or tube may be placed over or around the region being scanned to improve the quality of the data. The subject will be asked to repeatedly move a specific joint, such as the knee, for brief periods, usually less than 5 minutes. The subject can communicate via intercom with the person performing the study at all times during the procedure, and may request to stop the study at any time. 