radiology, branch of medicine specializing in the use of X rays, gamma rays, radioactive isotopes, and other forms of radiation in the diagnosis and treatment of disease. X ray machines and fluoroscopes are essential in diagnosing bone fractures, tumors, and other abnormalities of the internal organs. The computerized axial tomography (CAT) scan uses computer technology to focus X rays on precise sections of the body. Magnetic resonance imaging (MRI) utilizes supercooled magnets to concentrate and focus radiation in very small areas of the body, rendering sharp detail. Radioactive isotopes are also employed in diagnosis, e.g. iodine–131 is used to confirm cases of suspected thyroid disorder. In radiotherapy, X rays, gamma rays, and other radiation sources are used in the treatment of cancer and related diseases.