Comparison of CO <inf>2</inf> in air versus carbogen for the measurement of cerebrovascular reactivity with magnetic resonance imaging
Hare HV., Germuska M., Kelly ME., Bulte DP.
Measurement of cerebrovascular reactivity (CVR) can give valuable information about existing pathology and the risk of adverse events, such as stroke. A common method of obtaining regional CVR values is by measuring the blood flow response to carbon dioxide (CO 2)-enriched air using arterial spin labeling (ASL) or blood oxygen level-dependent (BOLD) imaging. Recently, several studies have used carbogen gas (containing only CO 2 and oxygen) as an alternative stimulus. A direct comparison was performed between CVR values acquired by ASL and BOLD imaging using stimuli of (1) 5% CO 2 in air and (2) 5% CO 2 in oxygen (carbogen-5). Although BOLD and ASL CVR values are shown to be correlated for CO 2 in air (mean response 0.11±0.03% BOLD, 4.46±1.80% ASL, n=16 hemispheres), this correlation disappears during a carbogen stimulus (0.36±0.06% BOLD, 4.97±1.30% ASL). It is concluded that BOLD imaging should generally not be used in conjunction with a carbogen stimulus when measuring CVR, and that care must be taken when interpreting CVR as measured by ASL, as values obtained from different stimuli (CO 2 in air versus carbogen) are not directly comparable. © 2013 ISCBFM.