Origin of B0orientation dependent R2(=1/T2) in white matter

• Published in: NeuroImage (Orlando, Fla.) Vol. 73; p. 71
• Main Authors: Oh, Se-Hong, Kim, Young-Bo, Cho, Zang-Hee, Lee, Jongho
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Limited 01.06.2013
• Subjects: Medical research
• ISSN: 1053-8119; 1095-9572
• DOI: 10.1016/j.neuroimage.2013.01.051

Recent MRI studies have demonstrated that the relative orientation of white matter fibers to the B0field significantly affects R2*measurement. In this work, the origin of this effect was investigated by measuring R2and R2*in multiple orientations and fitting the results to magnetic susceptibility-based models and magic angle-based models. To further explore the source of magnetic susceptibility effect, the contribution of tissue iron to the orientation dependent R2*contrast was investigated. Additionally, the effects of temperature on R2*and orientation dependent R2*contrasts were studied to understand the differences reported between a fixed specimen at room temperature andin vivoat body temperature. The results suggest that the B0dependent R2*variation is better explained by the magnetic susceptibility-based model with susceptibility anisotropy. However, extracting tissue iron did not reduce the orientation dependent R2*contrast, suggesting iron is not the origin of the contrast. This leaves susceptibility effects from myelin as the most probable origin of the contrast. Temperature showed large contribution on both R2*and orientation dependent R2*contrasts, explaining a portion of the contrast difference between thein-vivoandin-vitroconditions.