IMPROVED DETECTION OF FOCAL CEREBRAL BLOOD-FLOW CHANGES USING 3-DIMENSIONAL POSITRON EMISSION TOMOGRAPHY

Removal of the interplane septa and configuration of a typical multisl ice PET scanner to accept all possible coincidence lines of response l eads to a fivefold increase in sensitivity. This can be of value in re gional CBF studies using bolus O-15-labeled water injections, allowing the injected dose to be reduced by a factor of 4, while maintaining t he same number of noise equivalent counts. Thus, for a given cumulativ e dose limit, four times as many studies can be performed in a single subject. Data from the three-dimensional Hoffman brain phantom, closel y matched to count rates seen in human studies, show that for an ident ical cumulative dose, the noise in subtraction (stimulus minus baselin e) images can be reduced by a factor of 2 using three-dimensional data acquisition, with appropriate fractionation of the dose. This improve ment is dependent on axial position due to the sensitivity characteris tics of three-dimensional scans; however, there is a significant gain in the signal-to-noise ratio (SN) in all image planes. Studies perform ed in a human subject demonstrate how the factor of 2 gain in S/N lead s to improved detectability of activation sites in PET subtraction ima ges.