Coupling between regional blood flow and oxygen utilization in the normal human brain. A study with positron tomography and oxygen 15.

Using the oxygen 15 continuous-inhalation technique and positron emission tomography (PET), the regional cerebral blood flow (rCBF), oxygen extraction fraction (rOEF) and oxygen utilization (rCMRO2) were measured in 19 control subjects. The rCBF and rCMRO2 values, computed for small regions of interest (ROI), were within accepted normal ranges. Larger, more convenient ROI provided values for gray and white matter regions that were, respectively, lower and higher than those found using small ROI. The rOEF values were not affected by the ROI size, but seemed to slightly overestimate real OEF. These findings may be explained by (1) the partial volume effect, and (2) some limitations of the 15O steady state model. The 15O-PET technique therefore provides representative but clinically useful physiological indexes. In addition, our study demonstrated the normal coupling between local oxygen supply and demand.