Susceptibility Effects in White Matter: Orientation Dependence Under a Plurality of Contrast Mechanisms

Sean Foxley¹, Way Cherng Chen¹, Karla L. Miller¹

In this present study, we focus on measurements that are sensitive to the distribution of frequencies within a voxel: multi-GRE magnitude spectra and BSSFP profile asymmetries. The latter method detects asymmetries in the BSSFP frequency profile, which are driven by asymmetries in the underlying frequency distribution (as collected with multi-GRE). We compare multi-GRE- and BSSFP-based metrics for tracts with approximately parallel or perpendicular orientations, demonstrating orientation dependence that suggests a single underlying source. Calculation of the multi-GRE spectral and BSSFP profile asymmetries corroborate previously reported orientational dependence of the signal T₂^* decay, but also suggest a more complicated underlying effect.