Comparison of CO2 in Air Versus Carbogen for the Measurement of Cerebrovascular Reactivity with Magnetic Resonance Imaging

Hannah Hare¹, Michael Germuska¹, Daniel P. Bulte¹

This study consisted of a direct comparison between cerebrovascular reactivity (CVR) to 5% CO₂ in air and 5% CO₂ in oxygen (carbogen). We found that CVR as measured by BOLD and ASL response are correlated for CO₂ in air but not under a carbogen stimulus. In addition flow CVR as measured by ASL is strongly affected by inspired oxygen fraction and is not consistent between these two stimuli. We conclude that BOLD imaging should not be used in conjunction with a carbogen stimulus to measure CVR, and that flow CVR values acquired with carbogen and CO₂/air are not directly comparable.