Merck Manual

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Radionuclide Scanning


Mustafa A. Mafraji

, MD, Rush University Medical Center

Reviewed/Revised Nov 2023

Radionuclide scanning is a type of medical imaging that produces images by detecting radiation after a radioactive material is administered.

During a radionuclide scan, a small amount of a radionuclide attached to another substance (together, called a radioactive tracer) is administered, usually by injection. The radionuclide gives off small amounts of radiation that is measured during the scan to create images. Unlike other types of medical imaging, radionuclide scanning can sometimes provide information about how a tissue is functioning, as well as what it looks like.

Procedure for Radionuclide Scanning

Labeling with a radionuclide

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:

  • Iodine 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.

Tracking the radionuclide

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, during, and after the procedure

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.

Uses of Radionuclide Scanning

Radionuclide scanning can be used to evaluate many parts of the body: thyroid gland, liver and gallbladder, lungs, urinary tract, bone, brain, and certain blood vessels.

Because the body metabolizes many of the substances (such as iodine) used to label the radionuclide, radionuclide scanning can sometimes provide information about how a tissue is functioning, as well as what it looks like.

Various radionuclides are used to image different parts of the body or types of disorders, as for the following:

Variations of Radionuclide Scanning

Single-photon emission computed tomography (SPECT)

SPECT is similar to computed tomography but uses radionuclide gamma rays rather than x-rays.

For SPECT, the person lies on a motorized table. A rotating gamma camera takes images from many different angles (tomograms), each representing a slice of the body, and a computer is used to construct them into 2- and 3-dimensional images. These images help doctors more precisely locate structures and abnormalities.

Depending on the area being evaluated, people may be asked to restrict what they eat or drink before the test. The test usually takes 30 to 90 minutes.

Disadvantages of Radionuclide Scanning

The amount of radiation exposure from radionuclide scanning depends on which radionuclide is used and how much is used. For example, with a lung scan, the dose is similar to that used in about 100 single-view chest x-rays. Other scans may involve more or less radiation.

Radionuclide scanning can take hours to do because of the need to wait between injection and scan to give the radionuclide time to reach the target tissue.

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