Measuring Cerebral Blood Flow: Theory

This chapter describes the theory for quantitative measurement of cerebral blood flow. Cerebral blood flow is perfusion flow that can be measured using radioisotope-labeled tracers. There are two types of tracers, transit-type and plug-type. The transit-type tracers (diffusible tracers and nondiffusible tracers) travel through the vessels and the mean transit time (MTT) is used for cerebral blood flow calculation. The plug-type tracers (microsphere tracers and chemical microsphere tracers) are trapped in the vessels before they can transit, and the density of the plugged tracer is used for cerebral blood flow calculation. Accurate calculation needs to consider the partition coefficient and first-pass extraction. In tracer kinetics, a compartment model and an accurate input function are necessary. The kinetic model is applied to oxygen-15 gas studies, FDG studies, neurotransmission ligand analysis, and various other tracers. When analyzing cerebral blood flow, it is possible to use either the absolute or relative value.