[Radioactive Isotope] Radioisotopes are atoms with an unstable nucleus, which try to reach a more stable state by emitting radiation. Through one or more steps down its decay chain a more stable number of protons and neutrons is reached. Approximately 3,800 natural and artificial (fission, generator) radioisotopes exist. Radioisotopes are commonly used in science, industry, and nuclear medicine.

See also Isotope, Decay and Decay Chain.

Cerebral metabolic imaging can be accomplished with positron emission computer tomography (PET), magnetic resonance spectroscopy, and functional magnetic resonance imaging.
PET uses positron-emitting radioisotopes of elements with short half-live such as fluorine-18, oxygen-15, nitrogen-13, and carbon-11 as tracers to image and to measure the cerebral metabolism.

Decay chain or decay series is a series of decays that certain radioisotopes go through before reaching a stable form. For example, the production of technetium-99m (daughter nuclide with a half-life of 6 hours) from molybdenum-99 (parent nuclide with a half-life of 66 hours) in a generator is part of a decay chain.

See also Decay and Generator.

(FDG) Fluorodeoxyglucose F18 is a type of radioactive glucose (sugar). FDG is the most common radioisotope used in PET/CT scanning.

A generator is used in nuclear medicine to provide a radioisotope used for a scintigraphic procedure. A generator contains a radionuclide (e.g. molybdenum) that decays to another radionuclide (decay product, e.g. technetium) that can be extracted and used. The original radionuclide is firmly bound in the generator and remains behind.

See also Eluate