Aggarwal Manisha, Kageyama Yusuke, Li Xu, van Zijl Peter C
Russell H. Morgan Department of Radiology and Radiological Science, Division of MR Research, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Magn Reson Med. 2016 Jun;75(6):2455-63. doi: 10.1002/mrm.26208. Epub 2016 Mar 28.
To investigate B0 -field-orientation dependent white matter contrast in the human brainstem based on R2 * and frequency difference (Δf) mapping from gradient echo (GRE) imaging at 11.7T.
Multi-echo GRE data were acquired from two fixed human brainstem specimens at multiple orientations with respect to the static B0 field. The B0 -orientation dependent modulation curves of R2 * and Δf measurements between short and long echo time regimes were used to reconstruct maps of three-dimensional (3D) white matter orientation vectors. The results were compared with maps from diffusion MRI, susceptibility tensor imaging, and histological staining of the same specimens.
R2 * and Δf maps demonstrated distinct and significant contrast modulation between the corticospinal tract (CST) and transverse pontine fibers (TPF) dependent on B0 orientation. Interleaved fiber orientations of the CST and TPF could be sensitively resolved based on field-orientation-dependent fitting of the R2 * and Δf measurements. The fitted 3D orientation vector maps and peak-to-peak amplitude of R2 * and Δf modulation exhibited close correspondence to primary eigenvector and anisotropy maps derived from diffusion MRI. The amplitude of B0 -orientation dependent R2 * modulation was significantly (P < 0.005) higher in the CST compared with TPF, while fractional anisotropies were comparable.
The findings of this study demonstrate the potential of B0 -orientation dependent susceptibility-induced R2 * and Δf contrasts to probe tract-specific orientation and microstructure in white matter. Magn Reson Med 75:2455-2463, 2016. © 2016 Wiley Periodicals, Inc.
基于11.7T梯度回波（GRE）成像的R2*和频率差（Δf）映射，研究人脑干中与B0场方向相关的白质对比度。
从两个固定的人脑干标本获取多回波GRE数据，标本相对于静态B0场有多个方向。利用短回波时间和长回波时间状态之间R2*和Δf测量的与B0方向相关的调制曲线，重建三维（3D）白质方向向量图。将结果与相同标本的扩散MRI、磁化率张量成像和组织学染色图进行比较。
R2和Δf图显示，皮质脊髓束（CST）和脑桥横纤维（TPF）之间存在明显且显著的与B0方向相关的对比度调制。基于R2和Δf测量的与场方向相关的拟合，可以灵敏地分辨出CST和TPF的交错纤维方向。拟合的3D方向向量图以及R2和Δf调制的峰峰值与扩散MRI得出的主特征向量图和各向异性图密切对应。与TPF相比，CST中与B0方向相关的R2调制幅度显著更高（P<0.005），而分数各向异性相当。
本研究结果表明，与B0方向相关的磁化率诱导的R2*和Δf对比度在探测白质中特定束的方向和微观结构方面具有潜力。《磁共振医学》75:2455 - 2463, 2016。©2016威利期刊公司。
