Abstract #3126

Small voxel sizes reduce extravascular dephasing from large veins in gradient-echo BOLD fMRI at 7T: a simulation study

Avery J. L. Berman^1,2, Mukund Balasubramanian^3,4, Kawin Setsompop^5,6, and Jonathan R. Polimeni^4,7,8

¹Department of Physics, Carleton University, Ottawa, ON, Canada, ²University of Ottawa Institute of Mental Health Research, Royal Ottawa Mental Health Centre, Ottawa, ON, Canada, ³Department of Radiology, Boston Children's Hospital, Boston, MA, United States, ⁴Department of Radiology, Harvard Medical School, Boston, MA, United States, ⁵Department of Radiology, Stanford University, Stanford, CA, United States, ⁶Department of Electrical Engineering, Stanford University, Stanford, CA, United States, ⁷Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, United States, ⁸Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA, United States

Synopsis

Keywords: fMRI Acquisition, High-Field MRI, BOLD fMRI; Biophysical Simulations; High-Resolution fMRI; Vasculature

Motivation: Recent ultra-high-resolution gradient-echo BOLD-fMRI data demonstrate an unexpected reduction in sensitivity to large veins at 7T, suggesting that small voxels may experience less signal loss due to extravascular dephasing.

Goal(s): To test whether a reduction in through-plane or in-plane dephasing with small voxels may measurably contribute to reduced large-vein influences in gradient-echo BOLD.

Approach: We apply biophysical simulations of simplified vascular architecture, combined with realistic image encoding gradients.

Results: While voxels adjacent to veins are still strongly influenced, smaller voxel sizes have reduced extravascular BOLD, which impacts cerebral cortical-depth profiles of activation. The direction of the imaging encoding gradients also affects these profiles.

Impact: Rencelty available ultra-high-resolution fMRI improves spatial accuracy, and may also provide an unexpected improvement in neuronal specificity. We demonstrate that small-voxel gradient-echo BOLD achieves reduced unwanted contamination from large veins, potentially providing an fMRI method with high sensitivity AND specificity.

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