The technique of radionuclide scanning produces images using radiation emitted from a substance within the body. The radioactive substance, called radionuclide, is introduced into the body (usually by intravenous injection) and taken up by the organ or tissue to be imaged. A counter positioned outside the body detects the radiation that is emitted by the radionuclide and transmits this information to a computer. The computer then converts the information into images. Radionuclide scanning is used both to image the structure of many internal organs and to provide a measure of their function. SPECT scanning and PET scanning are two specialized forms of radionuclide scanning.

Radionuclide scans show parts of the body as areas of colour of varying intensity. Areas of intense colour are called hot spots; these are areas where there is a high uptake of radionuclide. Areas of less intense colour, called cold spots, are areas where the radionuclide uptake is low. The greater the amount of tissue activity, the greater the uptake of radionuclide.

How it is done?

During a radionuclide scan you will be asked to lie on a motorized bed that will move you past a special camera that can detect the radiation emitted by the radionuclide. The camera relays the information to a computer that builds up an image. Most radionuclide scans take about 45 minutes to an hour to perform.

Radionuclide scanning may be used to detect abnormal levels of activity in organs such as the thyroid gland, where it is used to look for thyroid nodules, and the kidneys. Changes in the function of a tissue or organ often develop before structural changes occur, and radionuclide scanning can detect some diseases at a significantly earlier stage than most other imaging techniques. For example, a radionuclide scan of bone can detect infection of bone tissue weeks before it would become apparent on an ordinary X- ray. Radionuclide scans are particularly useful for assessing how well a treatment has worked. Scans may be done before and after a particular treatment to compare the function of an organ.

Two particular types of radionuclide scanning may be used to look at the function of the heart. Thallium scanning reveals areas of the heart muscle with a poor blood supply and is used to look at the activity of the heart muscle during exercise. MUGA (multiple-gated acquisition scanning) is a technique in which the blood flow into and out of the heart is measured to assess how efficiently the heart pumps blood around the body.

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