Positron emission tomography positron emission tomography
(Science: radiology) A highly specialised research imaging
technique using short lived radioactive substances - usually
those made with a cyclotron. This technique is very sensitive in
picking up active tumour tissue but does not measure the size of
it. Tomographic images are formed by computer analysis of
photons detected from annihilation of positrons emitted by
radionuclides incorporated into biochemical substances; the
images, often quantitated with a colour scale, show the uptake
and distribution of the substances in the tissue, permitting
analysis and localization of metabolic and physiological
function. Because the half-lives of the radionuclides are so
short (20 minutes to 2 hours), and the equipment expensive, pET
is rarely used in a clinical setting. But since its development
in the mid-1970s, it has proved the most important tool yet
devised for experimental investigation of the living brain,
whether healthy, traumatised, or diseased. With C