About "Axial" and "Radial" Diffusivities
About "Axial" and "Radial" Diffusivities
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DOI：
10.1002/mrm.21965
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发表时间：
2009-05-01
影响因子：
3.3
通讯作者：
Cercignani, Mara
中科院分区：
文献类型：
--
作者：
Wheeler-Kingshott, Claudia A. M.;Cercignani, Mara
本文介绍了潜在的问题所产生的使用“轴向”和“径向”的扩散系数，来自扩散张量的特征值，和他们的解释的基本生物物理性质，如髓鞘和轴突密度。显示了模拟和体内数据。模拟表明，在“径向”扩散率的变化，可以导致一个虚构的“轴向”扩散率的变化，反之亦然，在体素的特点是交叉纤维。体内数据比较了四个不同受试者（两个健康受试者和两个受多发性硬化症影响的受试者）的主特征向量的方向，并且显示了在低各向异性、严重病理和部分体积的区域中，配准数据集的对应体素的主特征向量之间的角度α大于45度。此外，存在白色物质病理区域，其中“径向”扩散率比相应的正常组织的扩散率大10%，并且其中与健康情况相比，主特征向量的方向改变超过45度。这应该强烈阻止研究人员解释的基础上的组织结构的“轴向”和“径向”扩散率的变化，除非伴随着在每个数据集研究的数学和几何特性的彻底调查。Magn Reson Med 61：1255-12609 2009. (C)2009 Wiley-Liss，Inc.
This article presents the potential problems arising from the use of "axial" and "radial" diffusivities, derived from the eigenvalues of the diffusion tensor, and their interpretation in terms of the underlying biophysical properties, such as myelin and axonal density. Simulated and in vivo data are shown. The simulations demonstrate that a change in "radial" diffusivity can cause a fictitious change in "axial" diffusivity and vice versa in voxels characterized by crossing fibers. The in vivo data compare the direction of the principle eigenvector in four different subjects, two healthy and two affected by multiple sclerosis, and show that the angle, alpha, between the principal eigenvectors of corresponding voxels of registered datasets is greater than 45 degrees in areas of low anisotropy, severe pathology, and partial volume. Also, there are areas of white matter pathology where the "radial" diffusivity is 10% greater than that of the corresponding normal tissue and where the direction of the principal eigenvector is altered by more than 45 degrees compared to the healthy case. This should strongly discourage researchers from interpreting changes of the "axial" and "radial" diffusivities on the basis of the underlying tissue structure, unless accompanied by a thorough investigation of their mathematical and geometrical properties in each dataset studied. Magn Reson Med 61: 1255-12609 2009. (C) 2009 Wiley-Liss, Inc.