Diagnostic techniques in nuclear medicine use radioactive tracers which emit gamma rays from within the body. These tracers are generally short-lived isotopes linked to chemical compounds that permit specific physiological processes to be scrutinized. They can be given by injection, inhalation, or orally.
A radioactive dose is given to the patient and the activity in the organ can then be studied either as a two-dimensional picture or, using tomography, as a three-dimensional picture. In combination with imaging devices that register the gamma rays emitted from within, they can study the dynamic processes taking place in various parts of the body. The earliest technique developed uses single photons detected by a gamma camera which can view organs from many different angles. The camera builds up an image from the points from which radiation is emitted; this image is enhanced by a computer and viewed on a monitor for indications of abnormal conditions. Single photon emission computerized tomography (SPECT) is the current major scanning technology to diagnose and monitor a wide range of medical conditions.
“Radioisotopes in Medicine.” http://www.world-nuclear.org, Feb. 2019, www.world-nuclear.org/information-library/non-power-nuclear-applications/radioisotopes-research/radioisotopes-in-medicine.aspx.