Separating vessel diameter, blood velocity and oxygenation responses to activation: joint magnitude-phase analysis of phase-contrast fMRA

Motivation: Blood vessels rapidly dilate to initiate functional hyperemia, yet the diameter responses of individual mesoscale vessels in the human brain have not been measured. Goal(s): Separate interdependent effects of vessel diameter, blood velocity and oxygenation on MRI signal of individual vessels. Approach: Because both blood velocity and vessel diameter induce changes in intensity, we acquired multiple-echo single-slice phase-contrast fMRA data to measure inflow effects and estimate velocity, then applied a simple model to isolate dilation responses. Results: Inflow and oxygenation responses were separated; robust increases in blood velocity were estimated. Initial estimates of arterial diameter changes were derived. Impact: Several hemodynamic changes occur alongside neuronal activation, however existing MRI-based methods lack specificity to individual components. Here we propose a framework for estimating physiological parameters such as blood velocity and vessel diameter responses in individual arteries of human cerebral cortex.