Motivation: The effect of field strength on the orientation dependence of relaxation rates in voxels containing distinct fiber populations remains unexplored. Goal(s): The aim was to investigate fiber orientation dependent relaxation rates in single and crossing fiber voxels across different field strengths. Approach: Four volunteers were scanned at 1.5 and 3 T to asses the anisotropy of R2, R2* and R2' in regions corresponding to single and two crossing fibers. Results: R2, R2* and R2' and their anisotropies are influenced by fiber orientation and field strength, with distinct differences observed between single and two crossing fibers. Impact: This study deepens our understanding of fiber orientation and field strength effects on relaxation rates in brain white matter, providing essential insights into underlying mechanisms leading to relaxation anisotropy. This will enable more detailed analyses of complex fiber structures.
Bauer et al. (Tue,) studied this question.