Adult age differences in subcortical myelin content are consistent with protracted myelination and unrelated to diffusion tensor imaging indices.
Adult age differences in subcortical myelin content are consistent with protracted myelination and unrelated to diffusion tensor imaging indices.
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DOI：
10.1016/j.neuroimage.2016.08.047
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发表时间：
2016-12
期刊：
影响因子：
5.7
通讯作者：
Raz N
中科院分区：
文献类型：
--
作者：
Arshad M;Stanley JA;Raz N
死后研究表明，皮质下白色物质的髓鞘形成持续到中年，随后在成年后期逐渐下降。然而，到目前为止，建立年龄-髓鞘关联的倒U型模式被证明是困难的，因为研究白色物质的最常见方法，扩散张量成像（DTI），通常只显示健康成年人的DTI指数和年龄之间的线性关联。在这里，我们使用一种新的方法估计髓鞘水分数（MWF）的基础上建模的短自旋自旋（T2）弛豫分量从多回波T2弛豫成像数据和评估皮质下髓鞘含量内六个白色物质束的健康成人（N=61，年龄18-84岁）的样本。髓鞘含量与年龄呈二次曲线关系，与尸检研究结果雅阁。相比之下，DTI衍生的指数，经常被引用的髓鞘，分数各向异性（FA）和径向扩散率（RD）的代理，表现出线性或零与年龄的关系。此外，MWF的年龄差异的大小在整个白色物质束变化。髓鞘含量估计MWF是无关的FA和相关的RD只在压部。这些发现与髓鞘形成在整个青年期持续到中年的观点一致。结果表明，DTI不能作为一个特定的代理髓鞘的白色物质束。
Post mortem studies suggest protracted myelination of subcortical white matter into the middle age followed by gradual decline in the late adulthood. To date, however, establishing the proposed inverted-U pattern of age-myelin association proved difficult, as the most common method of investigating white matter, diffusion tensor imaging (DTI), usually reveals only linear associations between DTI indices and age among healthy adults. Here we use a novel method of estimating Myelin Water Fraction (MWF) based on modeling the short spin-spin (T2) relaxation component from multi-echo T2 relaxation imaging data and assess subcortical myelin content within six white matter tracts in a sample of healthy adults (N=61, age 18–84 years). Myelin content evidenced a quadratic relationship with age, in accord with the pattern observed postmortem studies. In contrast, DTI-derived indices that are frequently cited as proxies for myelination, fractional anisotropy (FA) and radial diffusivity (RD), exhibited linear or null relationships with age. Furthermore, the magnitude of age differences in MWF varied across the white matter tracts. Myelin content estimated by MWF was unrelated to FA and correlated with RD only in the splenium. These findings are consistent with the notion that myelination continues throughout the young adulthood into the middle age. The results demonstrate that DTI cannot serve as a specific proxy for myelination of white matter tracts.
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