School of Biomedical Engineering, The University of Sydney, Sydney, Australia.
Brain and Mind Centre, The University of Sydney, Sydney, Australia.
Magn Reson Med. 2022 Dec;88(6):2485-2503. doi: 10.1002/mrm.29413. Epub 2022 Aug 31.
Characterization of cerebral cortex is challenged by the complexity and heterogeneity of its cyto- and myeloarchitecture. This study evaluates quantitative MRI metrics, measured across two cortical depths and in subcortical white matter (WM) adjacent to cortex (juxtacortical WM), indicative of myelin content, neurite density, and diffusion microenvironment, for a comprehensive characterization of cortical microarchitecture.
High-quality structural and diffusion MRI data (N = 30) from the Human Connectome Project were processed to compute myelin index, neurite density index, fractional anisotropy, mean diffusivity, axial diffusivity, and radial diffusivity from superficial cortex, deep cortex, and juxtacortical WM. The distributional patterns of these metrics were analyzed individually, correlated to one another, and were compared to established parcellations.
Our results supported that myeloarchitectonic and the coexisting cytoarchitectonic structures influence the diffusion properties of water molecules residing in cortex. Full cortical thickness showed myelination patterns similar to those previously observed in humans. Higher myelin indices with similar distributional patterns were observed in deep cortex whereas lower myelin indices were observed in superficial cortex. Neurite density index and other diffusion MRI derived parameters provided complementary information to myelination. Reliable and reproducible correlations were identified among the cortical microarchitectural properties and fiber distributional patterns in proximal WM structures.
We demonstrated gradual changes across the cortical sheath by assessing depth-specific cortical micro-architecture using anatomical and diffusion MRI. Mutually independent but coexisting features of cortical layers and juxtacortical WM provided new insights towards structural organizational units and variabilities across cortical regions and through depth.
大脑皮层的细胞和髓鞘结构十分复杂且具有异质性，这给其结构特征的描述带来了挑战。本研究旨在评估定量 MRI 指标，这些指标跨越两个皮层深度以及皮层附近的皮质下白质（WM）（皮质旁 WM）进行测量，可反映髓鞘含量、神经丝密度和扩散微环境，从而全面描述皮层微结构。
对来自人类连接组计划的高质量结构和扩散 MRI 数据（N=30）进行处理，以从浅层皮层、深层皮层和皮质旁 WM 计算髓鞘指数、神经丝密度指数、各向异性分数、平均扩散系数、轴向扩散系数和径向扩散系数。单独分析这些指标的分布模式，彼此之间进行相关性分析，并与已建立的脑区划分进行比较。
我们的研究结果支持这样一种观点，即髓鞘结构和并存的细胞结构影响水分子在皮层中的扩散特性。全皮层厚度显示出与先前在人类中观察到的相似的髓鞘模式。在深层皮层中观察到更高的髓鞘指数和相似的分布模式，而在浅层皮层中观察到较低的髓鞘指数。神经丝密度指数和其他扩散 MRI 衍生参数提供了髓鞘的补充信息。在近端 WM 结构中，皮层微观结构和纤维分布模式之间确定了可靠且可重复的相关性。
我们通过使用解剖学和扩散 MRI 评估深度特异性皮层微观结构，证明了在皮层鞘中存在逐渐的变化。皮层层和皮质旁 WM 的相互独立但并存的特征为跨皮层区域和深度的结构组织单元和变异性提供了新的见解。
