Mah Alyssa, Geeraert Bryce, Lebel Catherine
Biomedical Engineering Program, University of Calgary, Calgary, Alberta, Canada.
Alberta Children's Hospital Research Institute, and Owerko Centre; University of Calgary, Calgary, Alberta, Canada.
PLoS One. 2017 Aug 17;12(8):e0182340. doi: 10.1371/journal.pone.0182340. eCollection 2017.
Diffusion tensor imaging (DTI) studies have provided much evidence of white and subcortical gray matter changes during late childhood and early adolescence that suggest increasing myelination, axon density, and/or fiber coherence. Neurite orientation dispersion and density imaging (NODDI) can be used to further characterize development in white and subcortical grey matter regions in the brain by improving specificity of the MRI signal compared to conventional DTI. We used measures from NODDI and DTI to examine white and subcortical gray matter development in a group of 27 healthy participants aged 8-13 years. Neurite density index (NDI) was strongly correlated with age in nearly all regions, and was more strongly associated with age than fractional anisotropy (FA). No significant correlations were observed between orientation dispersion index (ODI) and age. This suggests that white matter and subcortical gray matter changes during late childhood and adolescence are dominated by changes in neurite density (i.e., axon density and myelination), rather than increasing coherence of axons. Within brain regions, FA was correlated with both ODI and NDI while mean diffusivity was only related to neurite density, providing further information about the structural variation across individuals. Data-driven clustering of the NODDI parameters showed that microstructural profiles varied along layers of white matter, but that that much of the white and subcortical gray matter matured in a similar manner. Clustering highlighted isolated brain regions with decreasing NDI values that were not apparent in region-of-interest analysis. Overall, these results help to more specifically understand patterns of white and gray matter development during late childhood and early adolescence.
扩散张量成像（DTI）研究提供了大量证据，表明在儿童晚期和青少年早期，白质和皮质下灰质发生了变化，这表明髓鞘形成增加、轴突密度增加和/或纤维连贯性增加。与传统DTI相比，神经突方向离散度和密度成像（NODDI）可通过提高MRI信号的特异性，进一步表征大脑白质和皮质下灰质区域的发育情况。我们使用NODDI和DTI的测量方法，对一组27名年龄在8至13岁的健康参与者的白质和皮质下灰质发育情况进行了研究。神经突密度指数（NDI）在几乎所有区域都与年龄密切相关，并且与年龄的相关性比分数各向异性（FA）更强。未观察到方向离散度指数（ODI）与年龄之间存在显著相关性。这表明在儿童晚期和青少年期，白质和皮质下灰质的变化主要由神经突密度（即轴突密度和髓鞘形成）的变化主导，而不是轴突连贯性的增加。在脑区内，FA与ODI和NDI均相关，而平均扩散率仅与神经突密度相关，这为个体间的结构变异提供了更多信息。对NODDI参数进行数据驱动的聚类分析表明，微观结构特征沿白质层变化，但大部分白质和皮质下灰质以相似的方式成熟。聚类分析突出显示了在感兴趣区域分析中不明显的、NDI值降低的孤立脑区。总体而言，这些结果有助于更具体地了解儿童晚期和青少年早期白质和灰质的发育模式。
