Temporal dynamics and spatial specificity of arterial and venous blood volume changes during visual stimulation: Implication for BOLD quantification

Determination of compartment-specific cerebral blood volume (CBV) changes is important for understanding neurovascular physiology and quantifying blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI). In isoflurane-anesthetized cats, we measured the spatiotemporal responses of arterial CBV (CBV_a) and total CBV (CBV_t) induced by a 40-second visual stimulation, using magnetization transfer (MT)-varied BOLD and contrast-agent fMRI techniques at 9.4 T. To determine the venous CBV (CBV _v) change, we calculated the difference between CBV_t and CBV_a changes. The dynamic response of CBV_a was an order of magnitude faster than that of CBV_v, while the magnitude of change under steady-state conditions was similar between the two. Following stimulation offset, ΔCBV_a showed small poststimulus undershoots, while ΔCBV_v slowly returned to baseline. The largest CBV_a and CBV_t response occurred after 10 seconds of simulation in cortical layer 4, which we identified as the stripe of Gennari by T 1-weighted MRI. The CBV_v response, however, was not specific across the cortical layers during the entire stimulation period. Our data indicate that rapid, more-specific arterial vasodilation is followed by slow, less-specific venous dilation. Our finding implies that the contribution of CBV_v changes to BOLD signals is significant for long, but not short, stimulation periods.