Progression of visual-stimulus-evoked blood velocity response timing across individual arteries and veins measured with phase-contrast fMRA

Motivation: Macrovasculature plays an important role in neurovascular coupling, yet most of what is known has focused on the communication between neurons and microvasculature. Goal(s): To measure real-time blood-velocity responses across several stages of the cerebral macrovasculature to better understand the hemodynamic response across the vascular hierarchy. Approach: A phase-contrast functional MRA (PC-fMRA) approach was used to measure visual-stimulation-induced velocity responses concurrently within multiple vessels: along major arteries, pial arteries, pial veins, major veins and sinuses. Results: Robust velocity increases were measured within individual vessels. Observed latencies in the venous responses compared with arterial responses reveal a progression of hemodynamic responses across the vasculature. Impact: We measured neuronal activity-induced blood velocity responses across several stages of the macrovasculature. The mismatches in arterial and venous hemodynamic response timing can provide insight into tissue/microvascular hemodynamics, such as microvascular blood volume changes with activation.