Coupling between cerebral blood flow and cerebral blood volume: Contributions of different vascular compartments

A better understanding of the coupling between changes in cerebral blood flow (CBF) and cerebral blood volume (CBV) is vital for furthering our understanding of the BOLD response. The aim of this study was to measure CBF‐CBV coupling in different vascular compartments during neural activation. Three haemodynamic parameters were measured during a visual stimulus. Look‐Locker flow‐sensitive alternating inversion recovery was used to measure changes in CBF and arterial CBV (CBV(a)) using sequence parameters optimized for each contrast. Changes in total CBV (CBV(tot)) were measured using a gadolinium‐based contrast agent technique. Haemodynamic changes were extracted from a region of interest based on voxels that were activated in the CBF experiments. The CBF‐CBV(tot) coupling constant α (tot) was measured as 0.16 ± 0.14 and the CBF‐CBV(a) coupling constant α (a) was measured as 0.65 ± 0.24. Using a two‐compartment model of the vasculature (arterial and venous), the change in venous CBV (CBV(v)) was predicted for an assumed value of baseline arterial and venous blood volume. These results will enhance the accuracy and reliability of applications that rely on models of the BOLD response, such as calibrated BOLD.