Abstract #0395

The EPI rs-fMRI signal shows an orientation effect with respect to B0 and phase-encode axis across cortical depth

Olivia M Viessmann¹, Marta Bianciardi¹, Klaus Scheffler², Lawrence L Wald^1,3, and Jonathan R Polimeni^1,3

¹Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Harvard Medical School, Massachusetts General Hospital, Charlestown, MA, United States, ²Max Planck Institute for Biological Cybernetics, Tübingen, Germany, ³Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA, United States

The cortex exhibits a strict vascular architecture and vessel orientation to the B₀ field should impact the local susceptibility and hence the local BOLD signal. Cortical folding could thus lead to local variations in the signal. Here, we used high-resolution 7T EPI rs-fMRI dataand found substantial variations of the signal amplitdude's coefficient of variation (σ/μ) with the local cortical orientation to B₀. This effect was measurable throughout cortical depths with a maximised effect of +70% at the surface. We compare this to orientation-dependent blurring effects along the phase-encode axis, which we found to be significant too.

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