What is an Isotope Scan?

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  • Written By: Constance Simmons
  • Edited By: Jenn Walker
  • Last Modified Date: 25 September 2019
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An isotope scan is a medical procedure that produces pictures of the inside of the body. During the procedure a radioactive substance is ingested. This substance migrates to the area of the body being scanned. A special camera and computer is then used to create pictures. The isotope, or radioactive substance used, and the procedure vary slightly depending on the part of the body being targeted.

The first step in an isotope scan is to transfer the isotope into the body. This is done a variety of ways, which include injection into a vein, inhalation, or drinking a liquid that contains the isotope. The type of isotope used and the way it enters into the body depends on the body part that is targeted.

The images produced by isotope scans are made from gamma rays. Gamma rays are given off by the radioactive substance inside the patient. These rays are picked up by a special camera and then sent to a computer. The computer then creates a picture using the different intensities of gamma rays provided by the camera.


Isotope scans are effective in diagnosing conditions because the radioactive agents are drawn to the most active tissues. This enables doctors to see a clear picture of the tissue that is active and healthy versus the inactive tissue. Areas of activity are called hot spots, while areas with little cellular activity are referred to as cold spots. Hot spots appear as red on the image and cold spots are blue.

Isotope scans are used to create images of the bones, lungs, thyroid, and kidneys. The procedure accesses the activity in each one of these organs. For example, if the scan shows clusters of activity in the thyroid, there is then evidence of some hyperactivity of the gland.

There is little preparation needed for this procedure. Each individual’s physician or hospital will give detailed instructions. Once the isotope is taken, it then takes time for it to reach the intended body part. When it has reached the organ, the pictures are taken. The amount of pictures taken will vary depending on the individual’s condition. Having an isotope scan can take several hours.

There is little risk involved in having an isotope scan. Women who are pregnant or nursing should not have the procedure due to the risks of exposing the fetus or child to radiation. Other than pregnant or nursing women, there is no need for worry because the amount of radiation is not significant enough to cause damage. The radioactive substance is naturally expelled from the body, usually within a few days.


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