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 CT and mRI, it represents a new generation of computer imaging techniques that have revolutionised medicine and physiology.