Motivation: Substantial variability has been reported in cerebrovascular reactivity (CVR) under hypercapnia and hypoxia, but it is unclear whether such variability stems from individual physiology or methodological considerations. Goal(s): We aimed to assess agreement of ASL-CVR with phase contrast (PC-CVR) and evaluate regional contributions. Approach: ASL and PC cerebral blood flow were collected under normal respiration, hypoxia, and hypercapnia. CVR metrics in PC and ASL were compared. Regional and overall CVR were compared. Results: ASL-CVR was significantly lower than PC-CVR, likely due to labeling efficiency changes. Similar regions in hypoxia and hypercapnia correlated with overall CVR, suggesting that regional differences do not drive variability. Impact: We show that ASL measures of cerebrovascular reactivity are significantly lower than phase-contrast measures, and atypical CVR values found in ASL may result from changes in labeling efficiency. Hypoxic CVR variability does not seem to be driven by regional differences.
Johnson et al. (2025) studied this question.