NUCLEAR MEDICINE

medical specialty that involves the use of radioactive isotopes in the diagnosis and treatment of disease. Nuclear medicine began only after the discovery by Enrico Fermi in 1935 that stable elements could be made radioactive by bombarding them with neutrons. The atoms of the elements so bombarded capture these neutrons, thus assuming a different nuclear form while remaining the same elements. These radioisotopes have unstable nuclei, however, and dissipate excess energy by emitting radiation in the form of gamma and other rays. In isotope scanning, a radioisotope is introduced into the body, usually by means of intravenous injection. The isotope is then taken up in different amounts by different organs. Its distribution can be determined by recording the radiation it emits, and through charting its concentration it is often possible to recognize the presence, size, and shape of various abnormalities in body organs. The radiation emitted is detected by a scintillation counter, which is moved back and forth over the organ being scanned; these messages can then be electronically recorded and studied by clinicians. The radioisotope usually has a short half-life and thus decays completely before its radioactivity can cause any damage to the patient's body. Different isotopes tend to concentrate in particular organs: for example, iodine-131 settles in the thyroid gland and can reveal a variety of defects in thyroid functioning. Another isotope, carbon-14, is useful in studying abnormalities of metabolism that underlie diabetes, gout, anemia, and acromegaly. Various scanning devices and techniques have been developed, including tomography (q.v.) and magnetic resonance imaging. See also radiology.