Nuclear medicine uses radiopharmaceuticals and imaging techniques like SPECT and PET to diagnose and treat diseases. Radiopharmaceuticals are produced through cyclotron bombardment, reactor irradiation, or radioactive decay of parent isotopes. They localize in target organs and tissues and can be imaged. Common radiotracers used in diagnosis include technetium-99m, fluorine-18, iodine-123, indium-111, and gallium-67 to image organs like the heart, brain, thyroid, and sites of infection or cancer. Radiopharmaceuticals like iodine-131, strontium-89, and yttrium-90 are also used in therapy to treat hyperthy