Dependence of the EPI and bSSFP resting-state fMRI signals on the cortical orientation relative to B0: Initial observations at 9.4 Tesla

The spatial specificity of fMRI with GRE-EPI is significantly affected by large draining veins on the cortical surface. They cause susceptibility changes that are strongest when the veins are oriented perpendicular to B0. Since they follow the cortical curvature, their orientation to B0 can be approximated by the cortical orientation. Previous studies have shown a high dependence of the GRE-EPI signal on the cortical orientation, reflecting its disadvantage of being sensitive to these veins. In this preliminary two-subject study, this phenomenon is investigated with GRE-EPI and bSSFP in different cortical depths to experimentally explore the sensitivity of bSSFP to microvasculature.