In the first study comparing high angular resolution diffusion MRI (dMRI) in the human brain to axonal orientation measurements from polarization-sensitive optical coherence tomography (PSOCT), we compare the accuracy of orientation estimates from various dMRI sampling schemes and reconstruction methods. We find that, if the reconstruction approach is chosen carefully, single-shell dMRI data can yield the same accuracy as multi-shell data, and only moderately lower accuracy than a full Cartesian-grid sampling scheme. Our results suggest that current dMRI reconstruction approaches do not benefit substantially from ultra-high b-values or from very large numbers of diffusion-encoding directions. We also show that accuracy remains stable across dMRI voxel sizes of 1 mm or smaller but degrades at 2 mm, particularly in areas of complex white-matter architecture. We also show that, as the spatial resolution is reduced, axonal configurations in a dMRI voxel can no longer be modeled as a small set of distinct axon populations, violating an assumption that is sometimes made by dMRI reconstruction techniques. Our findings have implications for in vivo studies and illustrate the value of PSOCT as a source of ground-truth measurements of white-matter organization that does not suffer from the distortions typical of histological techniques.

中文翻译：

---

从离体人脑中的偏振敏感光学相干断层扫描中了解扩散 MRI 的基本权衡

在第一项将人脑中的高角分辨率扩散 MRI (dMRI) 与偏振敏感光学相干断层扫描 (PSOCT) 的轴突方向测量值进行比较的研究中，我们比较了来自各种 dMRI 采样方案和重建方法的方向估计的准确性。我们发现，如果仔细选择重建方法，单壳 dMRI 数据可以产生与多壳数据相同的精度，并且仅比完整的笛卡尔网格采样方案略低精度。我们的结果表明，当前的 dMRI 重建方法并不能从超高 b 值或非常大量的扩散编码方向中受益。我们还表明，精度在 1 mm 或更小的 dMRI 体素尺寸上保持稳定，但在 2 mm 时会下降，特别是在复杂的白质架构领域。我们还表明，随着空间分辨率的降低，dMRI 体素中的轴突配置不再可以建模为一小组不同的轴突群，这违反了 dMRI 重建技术有时做出的假设。我们的研究结果对体内研究有影响，并说明了 PSOCT 作为不受组织学技术典型扭曲影响的白质组织的真实测量来源的价值。