Positron Imaging Laboratories, McConnell Brain Imaging Center, Montreal Neurological Institute, Montreal, Canada

Correspondence: Ernst Meyer, WB-211, Webster Pavilion, Montreal Neurological Institute, 3801 University, Montreal, Quebec, H3A 2B4, Canada.

Received 30 June 1994; Revised 25 January 1996; Accepted 26 January 1996.

Abstract

When used to measure blood flow in the brain, water leaves a residue in the vascular bed that influences the estimation of blood flow by current methods. To assess the magnitude of this influence, we developed a two-compartment model of blood flow with separate parameters for transport and vascular distribution of brain water. Maps of the water clearance. K₁ into brain tissue, separated from the circulation by a measurably resistant blood-brain barrier (BBB), were generated by time-weighted integration. Depending on the validity of the assumptions underlying the two-compartment model presented here, the maps revealed a significant overestimation of the clearance of water when the vascular residue was ignored. Maps of V_o, the estimate of the apparent vascular distribution volume of tracer H₂¹⁵O, clearly revealed major cerebral arteries. Thus, we claim that the accumulation of radioactive water in brain tissue also reflects the volume of the arterial vascular bed of the brain.