Prior to a nuclear medicine scan, patients are given a tiny amount of radioactive substance, called a radionuclide, either orally or by injection. The amount of radioactive compound used is very small, quickly eliminated from the body and poses no threat to the patient or anyone coming in contact with that individual.
As the radionuclide moves throughout the body and eventually lands in the tissue or organ being studied, it emits gamma rays. A special gamma camera detects the rays and works with a powerful computer to produce images and measurements of the organ or tissue being studied. The amount of radionuclide that collects in the organ or tissue, and therefore the amount of gamma rays emitted, is linked to the metabolic activity occurring there. Cancer cells, which divide rapidly, tend to be "hot spots" of metabolic activity and therefore absorb more of the radionuclide and emit more gamma radiation.