Centre for Cognitive Neuroimaging, Donders Institute for Brain, Cognition and Behaviour, Radboud University, Nijmegen, the Netherlands; Department of Cognitive Neuroscience, Radboudumc, Nijmegen, the Netherlands.
Translational and Molecular Imaging Institute Translational and Molecular Imaging Institute and Brain Imaging Center, Icahn School of Medicine at Mount Sinai, New York, NY, USA.
Neuroimage. 2019 Jan 15;185:27-34. doi: 10.1016/j.neuroimage.2018.10.023. Epub 2018 Oct 9.
Intracortical myelin is a key determinant of neuronal synchrony and plasticity that underpin optimal brain function. Magnetic resonance imaging (MRI) facilitates the examination of intracortical myelin but presents with methodological challenges. Here we describe a whole-brain approach for the in vivo investigation of intracortical myelin in the human brain using ultra-high field MRI.
Twenty-five healthy adults were imaged in a 7 Tesla MRI scanner using diffusion-weighted imaging and a T-weighted sequence optimized for intracortical myelin contrast. Using an automated pipeline, T values were extracted at 20 depth-levels from each of 148 cortical regions. In each cortical region, T values were used to infer myelin concentration and to construct a non-linearity index as a measure the spatial distribution of myelin across the cortical ribbon. The relationship of myelin concentration and the non-linearity index with other neuroanatomical properties were investigated. Five patients with multiple sclerosis were also assessed using the same protocol as positive controls.
Intracortical T values decreased between the outer brain surface and the gray-white matter boundary following a slope that showed a slight leveling between 50% and 75% of cortical depth. Higher-order regions in the prefrontal, cingulate and insular cortices, displayed higher non-linearity indices than sensorimotor regions. Across all regions, there was a positive association between T values and non-linearity indices (P < 10). Both T values (P < 10) and non-linearity indices (P < 10) were associated with cortical thickness. Higher myelin concentration but only in the deepest cortical levels was associated with increased subcortical fractional anisotropy (P = 0.05).
We demonstrate the usefulness of an automatic, whole-brain method to perform depth-dependent examination of intracortical myelin organization. The extracted metrics, T values and the non-linearity index, have characteristic patterns across cortical regions, and are associated with thickness and underlying white matter microstructure.
皮质内髓鞘是决定神经元同步性和可塑性的关键因素，而这些因素是大脑最佳功能的基础。磁共振成像（MRI）有助于检查皮质内髓鞘，但存在方法学挑战。在这里，我们描述了一种使用超高场 MRI 对人类大脑皮质内髓鞘进行活体研究的全脑方法。
25 名健康成年人在 7 特斯拉 MRI 扫描仪上进行成像，使用扩散加权成像和优化的 T 加权序列进行皮质内髓鞘对比。使用自动化流水线，从 148 个皮质区域中的每个区域提取 20 个深度级别的 T 值。在每个皮质区域中，T 值用于推断髓鞘浓度，并构建非线性指数作为衡量髓鞘在皮质带中空间分布的指标。研究了髓鞘浓度和非线性指数与其他神经解剖学特性的关系。还使用相同的方案对 5 名多发性硬化症患者进行了评估，作为阳性对照。
皮质内 T 值在外脑表面和灰白质边界之间呈下降趋势，在皮质深度的 50%至 75%之间呈现出轻微的水平化。前额叶、扣带和脑岛等高级区域的非线性指数高于感觉运动区域。在所有区域中，T 值与非线性指数之间存在正相关（P < 10）。T 值（P < 10）和非线性指数（P < 10）均与皮质厚度相关。仅在最深的皮质水平，髓鞘浓度越高与皮质下各向异性分数增加相关（P = 0.05）。
我们证明了一种自动的、全脑的方法在进行皮质内髓鞘组织的深度依赖检查方面的有效性。提取的度量指标 T 值和非线性指数在皮质区域之间具有特征性模式，与厚度和潜在的白质微观结构相关。
