Dynamic Susceptibility Contrast MRI and Arterial Spin Labeling reveals blood volume dependence of BOLD-based Cerebrovascular Reactivity

Motivation: Cerebrovascular reactivity (CVR) measured via BOLD-MRI indicates vascular health but may be biased by cerebral blood volume (CBV), considering that CBV largely differs between grey (GM) and white matter (WM). Goal(s): This study aimed to evaluate CBV dependency of BOLD-CVR, hypothesizing that BOLD-CVR would exhibit CBV-related differences between GM and WM. Approach: BOLD-CVR and CBF-CVR data were compared to relative CBV (rCBV) from Dynamic Susceptibility Contrast MRI (3T-MRI). GM-WM differences and correlations between BOLD-CVR and rCBV were assessed. BOLD signal dependence on baseline venous CBVV,0 was simulated. Results: BOLD-CVR showed significant rCBV dependency, confirming that baseline rCBV significantly affects BOLD-CVR outcomes. Impact: BOLD-CVR, a promising marker of vascular health, may be biased by CBV. Using pCASL-CBF and DSC-rCBV data and simulations, we revealed the dependency of BOLD-CVR on rCBV. Therefore, CBV should be considered when interpreting CVR assessments, especially in diagnostic applications.