Radionuclide imaging is a technique that allows physicians to obtain very clear images of various parts of the body. In cancer patients, it most often is used to help locate tumors and to determine how far a cancer has spread (metastasized).

To obtain the images generated in this technique, tiny amounts of radioactive materials (called “tracers”) are introduced into the patient’s body. The tracers emit a type of energy called gamma rays, which are detected by special devices.

For example, a positron emission tomography (PET) scan uses machines called photomultiplier-scintillator detectors to detect the gamma rays. Another test, single photon emission computed tomography (SPECT), uses a gamma camera to detect the energy. The information detected and recorded by these machines is then analyzed and reconstructed by computers to create very clear images of the target area of the patient’s body.

For most people, the tracer is harmless and is flushed from the body after the test. Patients are often encouraged to drink lots of liquids and to urinate frequently to help flush the tracer from the body. For most people, the amount of radiation received during radionuclide imaging is considered safe. However, there are a number of people who should avoid radionuclide imaging, including women who are pregnant or breastfeeding.