Kaden Enrico, Kruggel Frithjof, Alexander Daniel C
Centre for Medical Image Computing, University College London, UK.
Department of Biomedical Engineering, University of California, Irvine, California, USA.
Magn Reson Med. 2016 Apr;75(4):1752-63. doi: 10.1002/mrm.25734. Epub 2015 May 13.
This article presents a simple method for estimating the effective diffusion coefficients parallel and perpendicular to the axons unconfounded by the intravoxel fiber orientation distribution. We also call these parameters the per-axon or microscopic diffusion coefficients.
Diffusion MR imaging is used to probe the underlying tissue material. The key observation is that for a fixed b-value the spherical mean of the diffusion signal over the gradient directions does not depend on the axon orientation distribution. By exploiting this invariance property, we propose a simple, fast, and robust estimator of the per-axon diffusion coefficients, which we refer to as the spherical mean technique.
We demonstrate quantitative maps of the axon-scale diffusion process, which has factored out the effects due to fiber dispersion and crossing, in human brain white matter. These microscopic diffusion coefficients are estimated in vivo using a widely available off-the-shelf pulse sequence featuring multiple b-shells and high-angular gradient resolution.
The estimation of the per-axon diffusion coefficients is essential for the accurate recovery of the fiber orientation distribution. In addition, the spherical mean technique enables us to discriminate microscopic tissue features from fiber dispersion, which potentially improves the sensitivity and/or specificity to various neurological conditions. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc.
本文介绍一种简单方法，用于估计平行和垂直于轴突的有效扩散系数，且不受体素内纤维方向分布的干扰。我们也将这些参数称为每轴或微观扩散系数。
扩散磁共振成像用于探测潜在的组织材料。关键观察结果是，对于固定的b值，扩散信号在梯度方向上的球面均值不依赖于轴突方向分布。通过利用这一不变性特性，我们提出一种简单、快速且稳健的每轴扩散系数估计方法，我们称之为球面均值技术。
我们展示了人脑白质中轴突尺度扩散过程的定量图谱，该图谱已排除了纤维分散和交叉的影响。这些微观扩散系数是在体内使用一种广泛可用的现成脉冲序列估计的，该序列具有多个b值壳层和高角梯度分辨率。
每轴扩散系数的估计对于准确恢复纤维方向分布至关重要。此外，球面均值技术使我们能够区分微观组织特征与纤维分散，这可能提高对各种神经疾病的敏感性和/或特异性。《磁共振医学》由威利期刊公司出版。
