Figure 3. Statistical parametric mapping (SPM)“voxel-by-voxel” subtraction analysis shows the regions in the brain where relative regional cerebral glucose utilization is significantly (n = 5, P < 0.01) less during halothane anesthesia compared with the awake baseline condition. The SPM projections (three images on the left of the figure) are “see-through” images showing sagittal, transverse, and coronal views of the three-dimensional PET data volume of voxels significant at this level. These projections are difficult for most people to visualize in three dimensions, so the SPM results are also shown rendered onto a standardized magnetic resonance image (four images on the right of the figure) for better anatomic localization. The SPM analysis shows that halothane anesthesia in humans significantly decreases relative cerebral glucose metabolism in several brain areas. R = right hemisphere, VAC = vertical line through the anterior commissure.