Regional asymmetries of cerebral blood flow, blood volume, and oxygen utilization and extraction in normal subjects

Positron emission tomography (PET) and ¹⁵O-labeled radiotracers were used to measure regional CBF, cerebral blood volume (CBV), CMRO₂, and oxygen extraction in 32 right-handed subjects at rest. Mean left hemispheric CBF (46.2 ± 6.8 ml/100 g/min) and CMRO₂ (2.60 ± 0.59 ml/100 g/min) were significantly lower than right hemispheric values (47.4 ± 7.2 and 2.66 ± 0.61 ml/100 g/min, respectively; p < 0.0001 for both), whereas left and right hemispheric CBV and oxygen extraction were not significantly different. We further investigated these asymmetries by comparing left- and right-sided values for specific cortical and subcortical regions. We found that left-sided CBF and CMRO₂ were significantly lower than right-sided values for sensorimotor, occipital, and superior temporal regions, whereas only left-sided CBF values were lower for anterior cingulum. CBV was asymmetric for the anterior cingulate and midfrontal regions, and oxygen extraction was asymmetric for the sensorimotor area. No asymmetries were observed in inferior parietal cortex, thalamus, putamen, or pallidum. Knowledge of these normal physiological asymmetries is essential for proper interpretation of PET studies of physiology and pathology. Furthermore, the ability to detect asymmetries with PET may lead to a better understanding of the lateralization of specific functions in the human brain.