Normalized cerebrovascular reactivity mapping using hypercapnia and hyperoxia challenges

Motivation: Cerebrovascular reactivity (CVR) is an important biomarker of brain's vascular function.. BOLD-based CVR mapping techniques are susceptible to multiple BOLD confounding factors. Goal(s): To develop a normalized CVR mapping approach using BOLD MRI with both hypercapnia and hyperoxia challenges and obtain CBF-CVR, which is independent of BOLD confounding factors while maintaining its superior sensitivity. Approach: A proof-of-principle study was first performed in 7 healthy subjects, followed by a test-retest reproducibility study in 11 subjects. Results: CBF-CVR obtained from the normalized CVR approach showed smaller inter-voxel coefficient of variance (CoV) and gray matter/white matter ratio than BOLD-CVR, and also reduced inter-subject variations. Impact: The normalized CVR approach, using hypercapnia and hyperoxia challenges with BOLD acquisition to obtain CBF-CVR, can provide a more direct index of the microvascular function and would be practical and promising in clinical applications of cerebrovascular diseases.