Effect of cortical orientation relative to the magnetic field on quantitative susceptibility mapping in the grey matter

Motivation: Effect of cortex orientation relative to the magnetic field can impede quantitative susceptibility mapping (QSM) from being established as a robust measurement of cortical pathology. Goal(s): To identify the significance of cortical orientation effect in QSM and its underlying contribution from cortical myelin. Approach: QSM was performed in eight healthy subjects at isotropic 0.75mm resolution at 3T. The relationship between QSM and cortical orientation was evaluated in cortical regions across the brain. The region-specific effect strength was correlated with region-average myelin approximation. Results: Significant orientation effect was observed in most brain regions, including significant correlation between the region-specific effect strength and myelin estimation. Impact: This study represents an initial effort to uncover the cortex orientation effect in cortical grey matter QSM result towards establishing QSM as a robust clinical tool for cortical pathology.