Impact of time-of-day on diffusivity measures of brain tissue derived from diffusion tensor imaging.
Impact of time-of-day on diffusivity measures of brain tissue derived from diffusion tensor imaging.
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一天中的时间对源自扩散张量成像的脑组织扩散率测量的影响。
DOI：
10.1016/j.neuroimage.2018.02.026
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发表时间：
2018
期刊：
影响因子：
5.7
通讯作者：
Pierpaoli,Carlo
中科院分区：
文献类型：
--
作者：
Thomas,Cibu;Sadeghi,Neda;Nayak,Amrita;Trefler,Aaron;Sarlls,Joelle;Baker,ChrisI;Pierpaoli,Carlo
最近报道了大脑结构和功能特性的 MRI 测量的昼夜波动。这些波动可能具有生理起源，因为它们是使用不同的 MRI 模式检测到的，并且不能用通常已知的干扰 MRI 测量的因素来解释。虽然初步证据表明，基于扩散张量成像 (DTI) 的大脑结构特性测量值会随着时间 (TOD) 的变化而波动，但其潜在机制尚未得到研究。在这里，我们使用纵向受试者内设计来研究一天中的时间对 DTI 测量的影响。除了使用传统的单指数张量模型来评估与 TOD 相关的波动之外，我们还使用了双室张量模型，该模型使我们能够直接评估 DTI 测量值的任何变化是否是由于 CSF/自由水体积分数的增加或由于实质内水扩散率的增加所致。我们的结果表明，使用传统的单指数张量模型测量的痕量或平均扩散率往往会从早上到下午扫描灰质/脑脊液界面处系统地增加，最明显的是大脑的主要裂隙和脑沟。有趣的是，在最近对类淋巴系统的一项研究中，发现这些相同的区域在鞘内注射脑脊液造影剂后显示出晚期增强。迹线的增加也会影响 DTI 的扩散率测量，例如径向和轴向扩散率，但不会影响分数各向异性。双室分析表明，从 PM 到 AM 的扩散率测量值的增加是由类 CSF 自由水体积分数的增加驱动的。总而言之，我们的研究结果为大脑结构特性的 MRI 测量中昼夜波动的可能生理起源提供了重要的见解。
Diurnal fluctuations in MRI measures of structural and functional properties of the brain have been reported recently. These fluctuations may have a physiological origin, since they have been detected using different MRI modalities, and cannot be explained by factors that are typically known to confound MRI measures. While preliminary evidence suggests that measures of structural properties of the brain based on diffusion tensor imaging (DTI) fluctuate as a function of time-of-day (TOD), the underlying mechanism has not been investigated. Here, we used a longitudinal within-subjects design to investigate the impact of time-of-day on DTI measures. In addition to using the conventional monoexponential tensor model to assess TOD-related fluctuations, we used a dual compartment tensor model that allowed us to directly assess if any change in DTI measures is due to an increase in CSF/free-water volume fraction or due to an increase in water diffusivity within the parenchyma. Our results show that Trace or mean diffusivity, as measured using the conventional monoexponential tensor model tends to increase systematically from morning to afternoon scans at the interface of grey matter/CSF, most prominently in the major fissures and the sulci of the brain. Interestingly, in a recent study of the glymphatic system, these same regions were found to show late enhancement after intrathecal injection of a CSF contrast agent. The increase in Trace also impacts DTI measures of diffusivity such as radial and axial diffusivity, but does not affect fractional anisotropy. The dual compartment analysis revealed that the increase in diffusivity measures from PM to AM was driven by an increase in the volume fraction of CSF-like free-water. Taken together, our findings provide important insight into the likely physiological origins of diurnal fluctuations in MRI measurements of structural properties of the brain.