special subjects
Radionuclide Scanning
Procedure for Radionuclide Scanning
For scanning, a radionuclide is used to label a substance that accumulates in a specific part of the body. Different substances are used depending on which part of the body is to be evaluated. A substance may accumulate because the body uses (metabolizes) it, as for the following: Thyroid hormones is used to make thyroid hormones and thus accumulates in the thyroid gland. Diphosphonate accumulates where bone is repairing or rebuilding itself. Or a substance may abnormally accumulate in a specific area, as for the following: Red blood cells accumulate in the intestine when the intestine is bleeding rapidly. White blood cells accumulate in areas that are inflamed or infected. The combination of the radionuclide and the substance it labels is called a radioactive tracer. With imaging, doctors can see where the tracer collects and gives off radiation, which is detected by special scanners or cameras, such as a gamma camera. The camera produces a flat image of where the tracer collects. Sometimes a computer analyzes the radiation to produce a series of 2-dimensional images that look like slices of the body. Usually, the tracer is injected in a vein, but for some tests, the tracer is swallowed, inhaled, or injected under the skin (subcutaneously) or into the joint. Imaging is done after the tracer has had time to move to the target tissues (which may be almost immediately or take up to several hours). Before some tests (such as a gallbladder scan), the person is asked to refrain from eating and drinking for several hours. Clothing does not usually need to be removed. The person must lie still during the scanning, which usually takes about 15 minutes. However, sometimes a scan needs to be repeated after a time, often hours later. After the test, drinking extra fluids to help the body eliminate the radionuclide is recommended. Normal activities can be resumed immediately. A radionuclide in the body can sometimes set off radioactivity detectors that are used for security purposes. Detectors may be carried by police or be in place around transportation centers and in other high-security areas. How long the radionuclide can set off detectors varies depending on the radionuclide but is typically a few days or less. To prevent problems with security, a doctor often gives people a note documenting that they have had radionuclide scanning. 