Advanced MRI Section and Cerebral Microcirculation Unit, Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA.
Proc Natl Acad Sci U S A. 2010 Mar 16;107(11):5130-5. doi: 10.1073/pnas.0910222107. Epub 2010 Mar 2.
Recent advances in high-field (>or=7 T) MRI have made it possible to study the fine structure of the human brain at the level of fiber bundles and cortical layers. In particular, techniques aimed at detecting MRI resonance frequency shifts originating from local variation in magnetic susceptibility and other sources have greatly improved the visualization of these structures. A recent theoretical study [He X, Yablonskiy DA (2009) Proc Natl Acad Sci USA 106:13558-13563] suggests that MRI resonance frequency may report not only on tissue composition, but also on microscopic compartmentalization of susceptibility inclusions and their orientation relative to the magnetic field. The proposed sensitivity to tissue structure may greatly expand the information available with conventional MRI techniques. To investigate this possibility, we studied postmortem tissue samples from human corpus callosum with an experimental design that allowed separation of microstructural effects from confounding macrostructural effects. The results show that MRI resonance frequency does depend on microstructural orientation. Furthermore, the spatial distribution of the resonance frequency shift suggests an origin related to anisotropic susceptibility effects rather than microscopic compartmentalization. This anisotropy, which has been shown to depend on molecular ordering, may provide valuable information about tissue molecular structure.
近年来，高场（>或=7T）MRI 的发展使得研究人类大脑纤维束和皮质层精细结构成为可能。特别是，旨在检测源自局部磁导率变化和其他来源的 MRI 共振频率偏移的技术极大地改善了这些结构的可视化。最近的一项理论研究[He X，Yablonskiy DA（2009）Proc Natl Acad Sci USA 106：13558-13563]表明，MRI 共振频率不仅可以报告组织成分，还可以报告磁化率夹杂物的微观分区及其相对于磁场的方向。这种对组织结构的敏感性可能会极大地扩展传统 MRI 技术提供的信息量。为了研究这种可能性，我们使用实验设计研究了人类胼胝体的死后组织样本，该设计允许将微观结构效应与混杂的宏观结构效应分离。结果表明，MRI 共振频率确实取决于微观结构的方向。此外，共振频率偏移的空间分布表明与各向异性磁化率效应有关的起源，而不是微观分区。已经表明这种各向异性取决于分子有序性，它可能为组织分子结构提供有价值的信息。
