Regional Cerebral Perfusion Assessed with 81mKr and Emission Computerized Tomography

Functional images of brain perfusion can be obtained by a steady-state method which exploits the peculiar physical characteristics of the radioactive gas 81mKr.2 This is a very short half-lived isotope (13 sec half-life), which can be continuously produced either in the gaseous or the solution phase from its parent 81Rb (4.6 hours half-life). It emits 190 keV γ rays, an ideal energy for recording with an Anger γ camera. Because of its short half-life, continuous carotid infusion of 81mKr in solution will never eventually result in the equilibrium of this diffusible tracer within the brain; during continuous infusion continuous recording of the activity over the brain will therefore reflect at any time regional arrival of tracer, which is a linear function of regional perfusion. Thus, when used in conjunction with an ordinary Anger γ camera, it provides images of cerebral perfusion in two dimensions.