X-rays are introduced from outside the body but, in nuclear medicine, the radioactive substance works from inside the body, being swallowed or injected to diagnose or treat a disease.

The radioactive substance travels to a targeted area in the body and gives off energy in the form of gamma rays. A special camera detects the energy and records precise details of the body’s interior, which can be used in detecting disease or monitoring an existing condition. Nuclear medicine helps diagnose many disorders, including cancer, gallbladder disease, heart conditions, and brain maladies such as Alzheimer’s disease.

The same radioactive elements that help identify disease through imaging also power nuclear medicine’s targeted therapies. Radioactive iodine, for example, has been employed for more than 50 years to treat hyperthyroidism (overactive thyroid). Since the thyroid naturally absorbs iodine from the bloodstream, radioactive iodine also has long been used to combat thyroid cancer by “nuking” tumor cells. Nuclear medicine also is used to treat bone pain from certain cancers, including non-Hodgkin lymphoma.

Doctors use the smallest amount of radiation possible and have found that its benefits outweigh the risks. It’s also worth noting that radiation exits the body relatively quickly—often within a few days.

Nuclear medicine was born from scientific contributions to physics, chemistry, medicine, and engineering. Its storied past includes the invention of the X-ray in 1895 and, three years later, Marie and Pierre Curie’s discovery of radioactivity. In the 1950s, nuclear medicine began to be used more widely among clinicians as an imaging tool. By 1971, most organs could be visualized using the technology, and nuclear medicine was recognized as a medical specialty by the American Medical Association.