Center for Biomedical Imaging, Medical University of South Carolina, Charleston, SC, USA; Department of Neurology, Medical University of South Carolina, Charleston, SC, USA; Department of Radiology and Radiological Science, Medical University of South Carolina, Charleston, SC, USA.
Center for Biomedical Imaging, Medical University of South Carolina, Charleston, SC, USA; Department of Radiology and Radiological Science, Medical University of South Carolina, Charleston, SC, USA; Department of Neuroscience, Medical University of South Carolina, Charleston, SC, USA.
Neurobiol Aging. 2018 Oct;70:265-275. doi: 10.1016/j.neurobiolaging.2018.07.006. Epub 2018 Jul 17.
Myelin breakdown and neural fiber loss occur in aging. This study used white matter tract integrity metrics derived from biophysical modeling using Diffusional Kurtosis Imaging to assess loss of myelin (i.e., extraaxonal diffusivity, radial direction, D) and axonal density (i.e., axonal water fraction) in cognitively unimpaired older adults. Tract-based spatial statistics and region of interest analyses sought to identify ontogenic differences and age-related changes in white matter tracts using cross-sectional and longitudinal data analyzed with general linear and mixed-effects models. In addition to pure diffusion parameters (i.e., fractional anisotropy, mean diffusivity, mean kurtosis), we found that white matter tract integrity metrics significantly differentiated early- from late-myelinating tracts, correlated with age in spatially distinct regions, and identified primarily extraaxonal changes over time. Percent metric changes were |0.3-0.9|% and |0.0-1.9|% per year using cross-sectional data and longitudinal data, respectively. There was accelerated decline in some late- versus early-myelinating tracts in older age. These results demonstrate that these metrics may inform further study of the transition from age-related changes to neurodegenerative decline.
髓鞘崩解和神经纤维丢失发生在衰老过程中。本研究使用基于扩散峰度成像的生物物理建模得出的白质束完整性指标来评估认知正常的老年人的髓鞘丢失（即细胞外扩散率，径向方向，D）和轴突密度（即轴突水分数）。基于束的空间统计学和感兴趣区域分析使用横断面和纵向数据，通过一般线性和混合效应模型分析，旨在确定白质束中的个体发育差异和与年龄相关的变化。除了纯扩散参数（即各向异性分数、平均扩散率、平均峰度）外，我们还发现，白质束完整性指标可显著区分早期和晚期髓鞘化束，与空间上不同区域的年龄相关，并且主要识别随时间的细胞外变化。使用横断面数据和纵向数据，分别得到的度量变化百分比为|0.3-0.9|%和|0.0-1.9|%/年。在老年时，一些晚期髓鞘化与早期髓鞘化束相比，其下降速度更快。这些结果表明，这些指标可能有助于进一步研究从与年龄相关的变化到神经退行性下降的转变。
