Cerebrovascular Reactivity Under Hypercapnia and Hypoxia: Comparing Whole-Brain and Regional Measurements from Phase-Contrast and ASL MRI

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.