Effect of vascular radioactivity on regional values of cerebral blood flow: evaluation of methods for H(2)(15)O PET to distinguish cerebral perfusion from blood volume.

Abstract

To evaluate the appropriate model for calculating regional cerebral blood flow (rCBF) with PET and H(2)(15)O, the values obtained from 1- and 2-compartment analyses were compared. Dynamic PET scans were performed on 12 healthy volunteers after injection of H(2)(15)O in 2 conditions of baseline and visual stimulation. Calculation of rCBF was performed using the 2-weighted integral (WI) and autoradiographic methods for the 1-compartment analysis, and the 3-WI method was followed for the 2-compartment analysis. Arterial blood radioactivity was counted continuously and corrected for delay and dispersion. The rCBF images were transformed into the Talairach space and analyzed by statistical parametric mapping to identify regional differences in the 2 methods. The values obtained from regions of interest also were compared. Although the difference in global CBF between the 2 models was not significant, rCBF values in the large arteries and neighbor areas were significantly greater in the 2-WI method than in the 3-WI method. However, regional differences in the activation studies were not affected when the 2 methods were compared. The images of cerebral arterial blood volume (V(0)) obtained by the 3-WI method showed a significant increase in V(0) in the visual cortex during visual stimulation. These results suggest that the rCBF values in the 1-compartment analysis were affected by radioactivity in the vessels. The 3-WI method could provide rCBF values that are less influenced by vascular radioactivity and also show differences in V(0) in PET activation studies.