positronemitting

Positronemitting refers to radionuclides that decay by emitting positrons (beta-plus decay). The emitted positron travels a short distance in matter and annihilates with an electron, producing two gamma photons with 511 keV each emitted in roughly opposite directions. This coincidence gamma radiation is exploited in positron emission tomography (PET).

Common positron emitters include fluorine-18, carbon-11, nitrogen-13, oxygen-15, rubidium-82, and gallium-68. Fluorine-18 has a half-life of about 110 minutes, carbon-11 about 20 minutes, nitrogen-13 about 10 minutes, oxygen-15 about 2 minutes, gallium-68 about 68 minutes, and rubidium-82 around 75 seconds. They are produced in cyclotrons (F-18, C-11, N-13, O-15) or via generators (Ga-68 from Ge-68/generator; Rb-82 from Sr/Rb generator). The choice of radionuclide depends on the biological tracer and the imaging window.

In medical imaging, positron emitters are used to create PET scans by attaching them to biologically active molecules to study metabolism, receptor binding, or perfusion. The best-known tracer is [18F]fluorodeoxyglucose ([18F]FDG), which maps glucose metabolism and is widely used in oncology, neurology, and cardiology. Other tracers target neurotransmitter systems, hypoxia, or tissue perfusion.

Safety and logistics: because of short half-lives, radiopharmaceuticals are produced near the point of use and administered in small activity amounts. Radiation exposure is carefully managed, and regulatory controls govern production, handling, and disposal.