Comparison of pulsed and pseudocontinuous arterial spin‐labeling for measuring CO 2 ‐induced cerebrovascular reactivity

Purpose: To compare the performance of pulsed and pseudocontinuous arterial spin‐labeling (PASL and pCASL) methods in measuring CO 2 ‐induced cerebrovascular reactivity (CVR). Materials and Methods: Subjects were scanned using both ASL sequences during a controlled hypercapnia procedure and visual stimulation. CVR was computed as the percent CO 2 ‐induced increase in cerebral blood flow (Δ%CBF) per mmHg increase in end‐tidal PCO 2 . Visually evoked responses were expressed as Δ%CBF. Resting CBF and temporal signal‐to‐noise ratio were also computed. Regionally averaged values for the different quantities were compared in gray matter (GM) and visual cortex (VC) using t ‐tests. Results: Both PASL and pCASL yielded comparable respective values for resting CBF (56 ± 3 and 56 ± 4 mL/min/100g) and visually evoked responses (75 ± 5% and 81 ± 4%). Values of CVR determined using pCASL (GM 4.4 ± 0.2, VC 8 ± 1 Δ%CBF/mmHg), however, were significantly higher than those measured using PASL (GM 3.0 ± 0.6, VC 5 ± 1 Δ%CBF/mmHg) in both GM and VC. The percentage of GM voxels in which statistically significant hypercapnia responses were detected was also higher for pCASL (27 ± 5% vs. 16 ± 3% for PASL). Conclusion: pCASL may be less prone to underestimation of CO 2 ‐induced flow changes due to improved label timing control. J. Magn. Reson. Imaging 2012;36:312–321. © 2012 Wiley Periodicals, Inc.