Motivation: Recent in-vivo human and ex-vivo animal tissue research suggests that the Myelin Water Fraction (MWF) may depend on the angle of fibers relative to the main magnetic field. Goal(s): To investigate MWF orientation dependence in human spinal cord tissue. Approach: 9.4T multi-echo T2 relaxation data was collected from ex-vivo human spinal cord tissue rotated compared to B0. MWF in white matter was compared between 9 different angles. Results: MWF varied with orientation. The average COV of mean white matter (WM) MWF across 4 samples was 12.9%. Most samples had a consistent WM MWF vs. angle pattern. Impact: We observed variations in myelin water fraction (MWF) at different cord orientations relative to the B0 field, suggesting that MWF is dependent on fiber orientation. Further work should focus on methods to correct for orientation dependence when scanning in-vivo.
Joseph et al. (Tue,) studied this question.