Regional cerebral blood flow: estimation by means of nonmetabolized diffusible tracers--an overview.

Visualization and measurement of functional activity throughout the human brain has been made possible by position emission tomography (PET) using tracers, the accumulation of which in the various regions of the brain are functions of regional blood flow or energy metabolism. Certain principles and mathematical expressions describing the exchange of diffusible, nonmetabolized substances between capillary and brain, published nearly 40 years ago, have been useful in this development.