Chen Zhang, Zhang Hui, Yushkevich Paul A, Liu Min, Beaulieu Christian
Department of Biomedical Engineering, Faculty of Medicine and Dentistry, University of Alberta Edmonton, AB, Canada.
Department of Computer Science and Centre for Medical Image Computing, University College London London, UK.
Front Neuroanat. 2016 Feb 16;10:9. doi: 10.3389/fnana.2016.00009. eCollection 2016.
Previous diffusion tensor imaging tractography studies have demonstrated exponential patterns of developmental changes for diffusion parameters such as fractional anisotropy (FA) and mean diffusivity (MD) averaged over all voxels in major white matter (WM) tracts of the human brain. However, this assumes that the entire tract is changing in unison, which may not be the case. In this study, a surface model based tract-specific analysis was applied to a cross-sectional cohort of 178 healthy subjects (83 males/95 females) aged from 6 to 30 years to spatially characterize the age-related changes of FA and MD along the trajectory of seven major WM tracts - corpus callosum (CC) and six bilateral tracts. There were unique patterns of regions that showed different exponential and linear rates of increasing FA or decreasing MD and age at which FA or MD levels off along each tract. Faster change rate of FA was observed in genu of CC and frontal-parietal part of superior longitudinal fasciculus (SLF). Inferior corticospinal tract (CST), posterior regions of association tracts such as inferior longitudinal fasciculus, inferior frontal occipital fasciculus and uncinate fasciculus also displayed earlier changing patterns for FA. MD decreases with age also exhibited this posterior-to-anterior WM maturation pattern for most tracts in females. Both males and females displayed similar FA/MD patterns of change with age along most large tracts; however, males had overall reached the FA maxima or MD minima later compared with females in most tracts with the greater differences occurring in the CST and frontal-parietal part of SLF for MD. Therefore, brain WM development has spatially varying trajectories along tracts that depend on sex and the tract.
以往的扩散张量成像纤维束示踪研究表明，在人类大脑主要白质（WM）束中，所有体素的扩散参数（如分数各向异性（FA）和平均扩散率（MD））的发育变化呈指数模式。然而，这假定整个纤维束是同步变化的，实际情况可能并非如此。在本研究中，将基于表面模型的纤维束特异性分析应用于178名年龄在6至30岁的健康受试者（83名男性/95名女性）的横断面队列，以在空间上表征FA和MD沿七束主要WM束（胼胝体（CC）和六对双侧束）轨迹的年龄相关变化。存在独特的区域模式，这些区域显示出不同的FA增加或MD降低的指数和线性速率，以及FA或MD沿每条纤维束趋于平稳的年龄。在CC膝部和上纵束（SLF）的额顶部分观察到FA的变化率更快。皮质脊髓束（CST）下部、联合束的后部区域（如下纵束、额枕下束和钩束）的FA也显示出较早的变化模式。在大多数女性纤维束中，MD随年龄的降低也呈现出从后到前的WM成熟模式。男性和女性在大多数大纤维束中随年龄变化的FA/MD模式相似；然而，在大多数纤维束中，男性总体上比女性更晚达到FA最大值或MD最小值，在CST和SLF额顶部分MD的差异更大。因此，脑白质发育沿纤维束具有空间变化的轨迹，这取决于性别和纤维束。
