Test-Retest Reliability of Cerebral Blood Flow and Blood Oxygenation Level-Dependent Responses to Hypercapnia and Hyperoxia Using Dual-Echo Pseudo-Continuous Arterial Spin Labeling and Step Changes in the Fractional Composition of Inspired Gases

Purpose: To assess the reproducibility of blood oxygenation level-dependent / cerebral blood flow (BOLD/CBF) responses to hypercapnia/hyperoxia using dual-echo pseudo-continuous arterial spin labeling (pCASL) and step changes in inspired doses. Materials and Methods: Eight subjects were scanned twice, within 24 hours, using the same respiratory manipulation and imaging protocol. Imaging comprised a 5-minute anatomical acquisition, allowing segmentation of the gray matter (GM) tissue for further analysis, and an 18-minute pCASL functional scan. Hypercapnia/hyperoxia were induced by increasing the fraction of inspired CO2 to 5% and inspired O-2 to 60%, alternately. Reproducibility of BOLD and CBF pCASL measures was assessed by computing the inter-session coefficient of variation (CV) of the respective signals in GM. Results: BOLD and CBF measures in GM were robust and consistent, yielding CV values below 10% for BOLD hypercapnic/hyperoxic responses (which averaged 1.9 +/- 0.1% and 1.14 +/- 0.02%) and below 20% for the CBF hypercapnic response (which averaged 35 +/- 2 mL/min/100g). The CV for resting CBF was 3.5%. Conclusion: It is possible to attain reproducible measures of the simultaneous BOLD and CBF responses to blood gases, within a reasonable scan time and with whole brain coverage, using a simple respiratory manipulation and dual-echo pCASL.