Impact of resting physiology on the repeatability of phase contrast MRI measures of cerebral blood flow

Interpretation of clinically significant changes in total cerebral blood flow (CBF) can be confounded by normal variability in flow measures. We assessed the effects of resting end-tidal CO2 (PETCO2) on inter-session variability in total CBF as measured with phase contrast MRI. Participants were scanned twice, 1-3 weeks apart, with PETCO2 clamped at resting physiology. Clamping PETCO2 at participants’ resting respiratory physiology does not notably improve inter-session variability in flow, which was found to be consistent with previously reported values. Furthermore, inter-session changes in resting PETCO2 did not help to explain noted variability in total CBF.