Nuclear medicine is a branch of medicine based on the nuclear properties of matter. The procedures involved in diagnosis, such as medical imaging, and therapy use radiopharmaceuticals (drugs labeled with radionuclides). These drugs emit low levels of radiation that can be detected and provide a description of the biological process at the cellular level or measurements of the extent of the process of interest.
Radionuclides
The radioactive material used in nuclear medicine are injected, inhaled, or ingested depending on their purpose. Each drug has a pre-determined dose at which it is effective but presents minimal risk to the patient. There are medical community guidelines, depending on the country and facility, covering the use of radioactive material (and X-rays) in patient diagnosis and care, limiting exposure during the course of a year to below the limit of harm. Most diagnostic radionuclides also have short half-lives, which prevents patients from being exposed to the radiation for long periods of time.
The common radionuclides, many of which are chemical isotopes, used in therapy and diagnosis are iodine-131, gallium, thallium-201, technetium-99m, indium-111, and barium.
Therapy
Iodine-131, also known as radioiodine, is harmful when taken in by healthy individuals. It is a component of radioactive fallout such as that observed after the Chernobyl incident in the 1980s. It accumulates in the thyroid and can cause cancer as it degrades. This radionuclide is useful as a thyroid-specific agent to treat cancer. By accumulating in the thyroid it destroys the cancerous cells. It can also be used to treat thyrotoxicosis (hyperthyroidism), keeping the thyroid gland from being overactive.
Gallium is an element most notably used in superconductors such as those found in light emitting diodes (LEDs). However gallium salts have medicinal purposes. Gallium nitrate is used to treat arthritis. Gallium maltolate is in clinical trials as a cancer treatment as well as inflammatory and infectious diseases. And there is some hope that gallium may be a new antibiotic.
Diagnosis
Tracer studies are diagnostic techniques using radionuclides to trace the system of interest. Probes and/or imaging can determine the location where a radiocompound migrates or where it accumulates. The specific uses of chemical isotopes include thallium-201 in stress tests to test for coronary artery disease and blood flow to the heart, iodine-131 to observe that the thyroid gland is functioning properly, technetium-99m to visualize bone fractures, gallium salts or gallium-67 to images sites of inflammation, internal bleeding, and cancer cell division, and indium-111 to monitor the activity of white blood cells and identify abscesses.
One of the more well known diagnostic nuclear medicine techniques is barium imaging. A mixture is ingested and then the gastrointestinal imaged to identify disorders, such as colitis.
Nuclear Medicine
Using isotopes that target specific area of the body or pathology, radiologists and nuclear medicine technicians can use the chemicals to treat or diagnose many medical conditions. Though the techniques use radiation, the risk is minimized by decades of use and testing encompassed by guidelines for use.
