Positron emission tomography (PET)

Positron emission tomography (PET) is a nuclear medicine imaging technique which produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide (tracer), which is introduced into  body on a biologically active molecule.

 The positron emitted by the nuclide encounters an electron and annihilated with it to produce a pair of gamma photons which move in opposite directions. Radionuclides used in PET scanning are typically isotopes with short half lives such as carbon-11 (~20 min), nitrogen-13 (~10 min), oxygen-15 (~2 min), and fluorine-18 (~110 min).These radio-nuclides are incorporated either into compounds normally used by the body such as glucose (or glucose analogues), water or ammonia.