SPECT cerebral blood flow tracers

There are two groups of cerebral blood flow tracers: the freely diffusible and the ones which are trapped. The Xenon 133 is the only representative of the freely diffusible ones. This radioactive gas allows absolute quantification, in ml / 100 g / min, of the cerebral blood flow. Nevertheless, its physical characteristics and the need of dedicated acquisition devices have limited its use. Among the tracers which are trapped in the brain, only two are presently commercially available: HMPAO and ECD. There is a stable, flow dependent, uptake of these tracers in the brain without redistribution. Conventional gamma cameras can therefore be used and brief phenomena like epileptic seizures can be imaged. However, the behavior of these two tracers is different. (author)