Se-Hong Oh1, Jongho Lee1
1Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, United States
Recent MRI studies have demonstrated that the relative orientation of white matter fibers to the B0 field significantly affects R2* measurement. In this work, the origin of this effect was investigated by measuring R2 and R2* in multiple orientations and fitting the results to a magnetic susceptibility-based model and a magic angle-based model. To further explore the source of magnetic susceptibility effect, the contribution of tissue iron to the orientation dependent R2* contrast was investigated. Additionally, R2* was measured in basal ganglia area to confirm there is no orientation dependence in deep gray matter. Our results suggest that myelin is a primary source for R2* contrast because of its highly oriented structure and large susceptibility value.