Anisotropy of Longitudinal Relaxation in White Matter: Comparison of T1 and Magnetization Transfer

Motivation: Studies on the orientation dependence of T1 have led to contradictory observations, indicating that this effect is not well understood. Goal(s): Our primary objective was to meticulously explore the orientation dependency of T₁ under precisely controlled and stable conditions. Approach: Comprehensive T1 (inversion recovery) and magnetization-transfer (MT) experiments were performed in fixed spinal-cord samples, with systematic variation of the fiber-to-field angle θFB . Results: No relevant T1 variation with θFB was observed in the IR experiments. However, a clear orientation dependence was consistently observed in all MT experiments,Impact: Precise quantitative MR measurements in spinal cord with varying fiber-to-field angle showed no consistent orientation dependence of T1 but a clear effect for the MT saturation, indicating the MT effects may be responsible for the previously observed T1 anisotropy.