Medical Physics, Department of Diagnostic Radiology, Faculty of Medicine, University Freiburg, Germany.
Medical Physics, Department of Diagnostic Radiology, Faculty of Medicine, University Freiburg, Germany.
Neuroimage. 2018 Nov 15;182:398-406. doi: 10.1016/j.neuroimage.2017.10.051. Epub 2017 Nov 10.
Understanding diffusion-weighted MR signal in brain white matter (WM) has been a long-sought-after goal. Modern research pursues this goal by focusing on the biological compartments that contributes essentially to the signal. In this study, we experimentally address the apparent presence of a compartment in which water motion is restricted in all spatial directions. Using isotropic diffusion encoding, we establish an upper bound on the fraction of such a compartment, which is shown to be about 2% of the unweighted signal for moderate diffusion times. This helps to eliminate such a compartment that have been assumed in literature on biophysical modeling. We also used the diffusion decay curve obtained from the isotropic encoding to establish a lower limit on the mean diffusivities of either of intra- or extra-axonal compartment as a function of their relative water fraction.
理解脑白质（WM）中的弥散加权 MR 信号一直是人们长期追求的目标。现代研究通过关注对信号有本质贡献的生物学隔室来实现这一目标。在这项研究中，我们通过实验解决了一个在所有空间方向上限制水分子运动的隔室明显存在的问题。使用各向同性弥散编码，我们确定了这种隔室的分数上限，对于中等扩散时间，该分数上限约为未加权信号的 2%。这有助于排除文献中关于生物物理建模的假设的隔室。我们还使用各向同性编码获得的扩散衰减曲线，根据其相对水分数，建立了轴内或轴外隔室的平均扩散系数的下限。
