1. Healthy volunteers who have metal objects in their body that are not MRI-safe. These include the following objects: 1) pacemakers or other implanted electrical devices; 2) brain stimulators; 3) some types of dental implants; 4) aneurysm clips (metal clips on the wall of a large artery); 5) metallic prostheses (including metal pins and rods, heart valves, and cochlear implants; 6) implanted delivery pump; 7) permanent eye liner; or 8) shrapnel fragments.