The fiber orientation density function (fODF) in white matter is a primary physical quantity that can be estimated with diffusion MRI. It has often been employed for fiber tracking and microstructural modeling. Requirements for the construction of high fidelity fODFs, in the sense of having good angular resolution, adequate data to avoid sampling errors, and minimal noise artifacts, are described for fODFs calculated with fiber ball imaging. A criterion is formulated for the number of diffusion encoding directions needed to achieve a given angular resolution. The advantages of using large b-values (≥6000 s/mm²) are also discussed. For the direct comparison of different fODFs, a method is developed for defining a local frame of reference tied to each voxel's individual axonal structure. The Matusita anisotropy axonal is proposed as a scalar fODF measure for quantifying angular variability. Experimental results, obtained at 3 T from human volunteers, are used as illustrations.

中文翻译：

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来自纤维球成像的高保真纤维取向密度函数

白质中的纤维取向密度函数 (fODF) 是可以通过扩散 MRI 估计的主要物理量。它经常被用于纤维跟踪和微结构建模。对于使用光纤球成像计算的 fODF，描述了构建高保真 fODF 的要求，即具有良好的角分辨率、足够的数据以避免采样误差以及最小的噪声伪影。为实现给定角分辨率所需的扩散编码方向的数量制定了标准。使用大b值（≥6000 s/mm ²) 也进行了讨论。为了直接比较不同的 fODF，开发了一种方法来定义与每个体素的单个轴突结构相关的局部参考框架。提出了 Matusita 各向异性轴突作为量化角度变化的标量 fODF 测量。以 3 T 从人类志愿者获得的实验结果用作说明。