Nuclear medicine is the branch of medicine that involves the application of small amounts of radioactive substances to assess bodily functions and for diagnostic and treatment purposes. It is also called endoradiology because it records radiation energy emitted from within the body. Positron emission tomography (PET) and single photon emission computed tomography (SPECT) are the most common imaging modalities in nuclear medicine. They differ from radiological scans as the emphasis of the first is to evaluate function which is why they are called physiological imaging modalities.
Nuclear medicine imaging procedures are noninvasive and use radioactive tracers (also called radiotracers), which are radioactive atoms that are bonded tightly to a carrier molecule. Typically, they are administered into the bloodstream, but can also be inhaled as a gas or swallowed. Then, the radiotracer travels through the body and eventually accumulates in the area or organ being examined, emitting radiation in the form of gamma rays which are then detected digitally to create images of the desired area.
Nuclear medicine also includes therapeutic procedures, like the use of radioactive iodine treatment for thyroid cancer, other medical conditions affecting the thyroid gland and some neuroendocrine tumors, or the use of radioimmunological treatments for blood disorders (lymphoma). It can also be applied for palliative treatments like bone pain associated to bone tumors.