Does cerebral blood flow decline in healthy aging? A PET study with partial-volume correction

It remains a matter of controversy as to whether cerebral perfusion declines with healthy aging. In vivo imaging with PET permits quantitative evaluation of brain physiology; however, previous PET studies have inconsistently reported aging reductions in cerebral blood flow (CBF), oxygen metabolism, and glucose metabolism. In part, this may be because of a lack of correction for the dilution effect of age-related cerebral volume loss on PET measurements. Methods: CBF PET scans were obtained using [¹⁵O]H₂O in 27 healthy individuals (age range, 19-76 y) and corrected for partial-volume effects from cerebral atrophy using an MR-based algorithm. Results: There was a significant difference (P = 0.01) in mean cortical CBF between young/midlife (age range, 19-46 y; mean ± SD, 56 ± 10 mL/100 mL/min) and elderly (age range, 60-76 y; mean ± SD, 49 ± 2.6 mL/100 mL/min) subgroups before correcting for partial-volume effects. However, this group difference resolved after partial-volume correction (young/midlife: mean ± SD, 62 ± 10 mL/100 mL/min; elderly: mean ± SD, 61 ± 4.8 mL/100 mL/min; P = 0.66). When all subjects were considered, a mild but significant inverse correlation between age and cortical CBF measurements was present in the uncorrected but not the corrected data. Conclusion: This study suggests that CBF may not decline with age in healthy individuals and that failure to correct for the dilution effect of age-related cerebral atrophy may confound interpretation of previous PET studies that have shown aging reductions in physiologic measurements.