Positron emission tomography (PET) is a gamma imaging technique that uses radiotracers that emit positrons, the antimatter counterparts of electrons.
In PET the gamma rays used for imaging are produced when a positron meets an electron inside the patient’s body, an encounter that annihilates both electron and positron and produces two gamma rays travelling in opposite directions.
By mapping gamma rays that arrive at the same time the PET system is able to produce an image with high spatial resolution.
Another advantage of PET over procedures that employ gamma emitting tracers is the greater availability of suitable isotopes.
Positron emitting isotopes of biologically active elements such as fluorine, carbon and oxygen are all available.
Fluorine-18 in particular, can be used to make a radioactive analogue of glucose which is preferentially taken up by brain and cancer cells making an ideal tool for detecting tumours. PET can also be used to map brain function and the diagnosis of conditions such as Alzheimer’s disease.
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