Sometimes seeing things from the outside doesn't tell the whole story. It may look okay, but on the inside it may not be okay. Nuclear medicine is an area of radiology that allows doctors to see from the outside how the body is working inside. One imaging technique, called a PET scan, actually shows which part of the brain we are using as we are using it. For example, listening to music, looking at pretty pictures, or expressing one’s opinion. Here's how it works: small radioactive tracers injected, swallowed or inhaled into the body are trapped and photographed by a special camera. Once the tracers make a quick lap around the system, they are exhaled or passed through the body without leaving a trace. When radiologists want to see the body in action, nuclear medicine creates a picture of good health.