Foxley Sean, Wildenberg Gregg, Sampathkumar Vandana, Karczmar Gregory S, Brugarolas Pedro, Kasthuri Narayanan
Department of Radiology, University of Chicago, Chicago, Illinois, USA.
Department of Neurobiology, University of Chicago, Chicago, Illinois, USA.
Magn Reson Med. 2021 Feb;85(2):667-677. doi: 10.1002/mrm.28440. Epub 2020 Jul 27.
Dysmyelinating diseases are characterized by abnormal myelin formation and function. Such microstructural abnormalities in myelin have been demonstrated to produce measurable effects on the MR signal. This work examines these effects on measurements of voxel-wise, high-resolution water spectra acquired using a 3D echo-planar spectroscopic imaging (EPSI) pulse sequence from both postmortem fixed control mouse brains and a dysmyelination mouse brain model.
Perfusion fixed, resected control (n = 5) and shiverer (n = 4) mouse brains were imaged using 3D-EPSI with 100 µm isotropic resolution. The free induction decay (FID) was sampled every 2.74 ms over 192 echoes, for a total sampling duration of 526.08 ms. Voxel-wise FIDs were Fourier transformed to produce water spectra with 1.9 Hz resolution. Spectral asymmetry was computed and compared between the two tissue types.
The water resonance is more asymmetrically broadened in the white matter of control mouse brain compared with dysmyelinated white matter. In control brain, this is modulated by and consistent with previously reported orientationally dependent effects of white matter relative to B . Similar sensitivity to orientation is observed in dysmyelinated white matter as well; however, the magnitude of the resonance asymmetry is much lower across all directions.
Results demonstrate that components of the spectra are specifically differentially affected by myelin concentration. This suggests that water proton spectra may be sensitive to the presence of myelin, and as such, could serve as a MRI-based biomarker of dysmyelinating disease, free of mathematical models.
脱髓鞘疾病的特征是髓鞘形成和功能异常。髓鞘中的这种微观结构异常已被证明会对磁共振信号产生可测量的影响。这项工作研究了这些影响，这些影响来自使用3D回波平面光谱成像（EPSI）脉冲序列从死后固定的对照小鼠脑和脱髓鞘小鼠脑模型中获取的体素级高分辨率水光谱测量。
使用具有100 µm各向同性分辨率的3D-EPSI对灌注固定、切除的对照（n = 5）和颤抖（n = 4）小鼠脑进行成像。在192个回波上每2.74 ms对自由感应衰减（FID）进行采样，总采样持续时间为526.08 ms。对体素级FID进行傅里叶变换以产生具有1.9 Hz分辨率的水光谱。计算并比较两种组织类型之间的光谱不对称性。
与脱髓鞘白质相比，对照小鼠脑白质中的水共振展宽更不对称。在对照脑中，这受到白质相对于B的先前报道的取向依赖性影响的调节并与之一致。在脱髓鞘白质中也观察到对取向的类似敏感性；然而，在所有方向上共振不对称的幅度要低得多。
结果表明，光谱成分受到髓鞘浓度的特异性差异影响。这表明水质子光谱可能对髓鞘的存在敏感，因此可以作为基于MRI的脱髓鞘疾病生物标志物，无需数学模型。
