Radionuclide scanning

A diagnostic technique based on detection of radiation emitted by radioactive substances introduced into the body. Substances are taken up to different degrees by different tissues, allowing specific organs to be studied. For example, iodine is taken up mainly by the thyroid gland, so by “tagging” a sample of iodine with a radioactive marker (radionuclide), the uptake of iodine can be monitored to investigate the functioning of the gland. A radionuclide is swallowed or injected into the blood and accumulates in the target organ. It emits radiation in the form of gamma radiation, which is detected by a gamma camera to produce an image. Cross-sectional images (“slices”) can be obtained using a computer-controlled gamma camera that rotates around the patient. This specialized form of radionuclide scanning is known as SPECT (single photon emission computed tomography). Moving images can also be made using a computer to record a series of images. Radionuclide scanning can detect some disorders at an earlier stage than other imaging techniques because changes in the functioning of an organ often occur before the structure of the organ is affected. The technique is also used to detect disorders that affect only the function of organs. Moving images can provide information on blood flow, the movement of the heart walls, the flow of urine through the kidneys, and bile flow through the liver. Radionuclide scanning is a safe procedure, requiring only minute doses of radiation that are excreted within hours. The radionuclides carry virtually no risk of toxicity or hypersensitivity.