Abstract #1439

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

Divya Varadarajan^1,2, Zhangxuan Hu^1,2, Daniel E. P. Gomez^1,3, Sebastien Proulx^1,2, Paul Wighton¹, Avery J. L. Berman⁴, and Jonathan R. Polimeni^1,2,5

¹Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, United States, ²Department of Radiology, Harvard Medical School, Boston, MA, United States, ³Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States, ⁴Medical Physics, Carleton University, Ottawa, ON, Canada, ⁵Harvard-MIT Program in Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA, United States

Synopsis

Keywords: fMRI Acquisition, fMRI Acquisition, fMRI contrast mechanisms; fMRI physics; Ultra-High field fMRI; functional MR angiography

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.

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