Figure 6.

A summary of currently available data on the relationship of blood flow, glucose utilization, and oxygen consumption to the cellular activity of the brain during changes in functional activity is shown in this figure. The changes occurring in blood flow and glucose utilization exceed changes in oxygen consumption. The degree to which oxygen consumption actually changes, if at all, remains to be determined. PET measures the changes in blood flow. fMRI measures a BOLD (4) signal or contrast that arises when changes in blood flow exceed changes in tissue oxygen consumption.