title: Origin of B0 orientation dependent R2(*) (=1/T2(*)) in white matter.
abstract: 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 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 and in vivo at body temperature. The results suggest that the B0 dependent 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 the in-vivo and in-vitro conditions.
authors: Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors: Se-Hong
authors: SH
authors: Oh
authors: Young-Bo
authors: YB
authors: Kim
authors: Zang-Hee
authors: ZH
authors: Cho
authors: Jongho
authors: J
authors: Lee
mesh_terms: D000465:Algorithms; D016880:Anisotropy; D001479:Basal Ganglia / Q000502:physiology; D001831:Body Temperature; D001921:Brain / Q000166:cytology / Q000502:physiology*; D002102:Cadaver; D003337:Corpus Callosum / Q000502:physiology; D004574:Electromagnetic Fields; D006801:Humans; D007501:Iron / Q000502:physiology; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009412:Nerve Fibers / Q000502:physiology*; D059629:Signal-To-Noise Ratio; D013696:Temperature
chemical_list: D007501:Iron
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