A radionuclide scan is an imaging technique that uses a small dose of a radioactive chemical (isotope) called a tracer that can detect cancer, trauma, infection or other disorders. In a radionuclide scan, the tracer either is injected into a vein or swallowed. Once the tracer enters the body, it travels through the bloodstream to the organ being targeted, such as the thyroid, heart or bones. Different tracers tend to collect in different organs. The tracer emits gamma rays, which are similar to X-rays. These gamma rays are detected by a gamma camera and analyzed by a computer to form an image of the target organ. Sites of potential problems send out more intense gamma rays and appear as bright spots on the scan. Types of radionuclide scans include PET scans, gallium scans and bone scans.
A radionuclide scan is painless, except for a mild skin prick if the tracer is injected. Once the tracer is given, it takes several hours for the isotope to travel to the target organ. During this time, the patient usually can leave the test facility and return for the scan itself, which can last one to five hours.