Comparison of BOLD and ASL-derived Measures of Cerebrovascular Reactivity Acquired During Breath-Hold

Motivation: Breath-hold BOLD fMRI may be regarded as a proxy of deoxygenated cerebral blood volume (CBVdHb), instead of cerebrovascular reactivity (CVR) when blood flow changes are uniform in response to breath-hold. Goal(s): We aimed to test this assumption in healthy volunteers. Approach: We measured the spatial uniformity of CVR derived from arterial spin labelling and BOLD fMRI data acquired simultaneously during a breath-holding task. Results: Breath-hold induced a more uniform fractional increase in CBF than in BOLD signal. Thus, the spatial variability in apparent BOLD-CVR is likely due to variation in CBVdHb with little variability arising from spatial differences in vascular reactivity. Impact: Under isometabolic conditions in healthy volunteers, owing to the uniform change in blood flow induced by breath-hold, it is possible to infer maps of deoxygenated cerebral blood volume based on BOLD fMRI breath-hold data.