DZNE, German Center for Neurodegenerative Diseases, Rostock, Germany; Department for Psychosomatic Medicine, University Medicine Rostock, Rostock, Germany.
DZNE, German Center for Neurodegenerative Diseases, Rostock, Germany.
Neuroimage Clin. 2017 Oct 4;17:579-586. doi: 10.1016/j.nicl.2017.10.005. eCollection 2018.
Mean diffusivity (MD) measured by diffusion tensor imaging can reflect microstructural alterations of the brain's gray matter (GM). Therefore, GM MD may be a sensitive marker of neurodegeneration related to Alzheimer's Disease (AD). However, due to partial volume effects (PVE), differences in MD may be overestimated because of a higher degree of brain atrophy in AD patients and in cases with mild cognitive impairment (MCI). Here, we evaluated GM MD changes in AD and MCI compared with healthy controls, and the effect of partial volume correction (PVC) on diagnostic utility of MD. We determined region of interest (ROI) and voxel-wise group differences and diagnostic accuracy of MD and volume measures between matched samples of 39 AD, 39 MCI and 39 healthy subjects before and after PVC. Additionally, we assessed whether effects of GM MD values on diagnosis were mediated by volume. ROI and voxel-wise group differences were reduced after PVC. When using these ROIs for predicting group separation in logistic models, both PVE corrected and uncorrected GM MD values yielded a poorer diagnostic accuracy in single predictor models than regional volume. For the discrimination of AD patients and healthy controls, the effect of GM MD on diagnosis was significantly mediated by volume of hippocampus and posterior cingulate ROIs. Our results suggest that GM MD measurements are strongly confounded by PVE in the presence of brain atrophy, underlining the necessity of PVC when using these measurements as specific metrics of microstructural tissue degeneration. Independently of PVC, regional MD was not superior to regional volume in separating prodromal and clinical stages of AD from healthy controls.
由扩散张量成像测量的平均扩散系数（MD）可以反映大脑灰质（GM）的微观结构改变。因此，GM MD 可能是与阿尔茨海默病（AD）相关的神经退行性变的敏感标志物。然而，由于部分容积效应（PVE），AD 患者和轻度认知障碍（MCI）患者的脑萎缩程度较高，MD 的差异可能会被高估。在这里，我们评估了 AD 和 MCI 与健康对照组之间 GM MD 的变化，以及部分容积校正（PVC）对 MD 诊断效用的影响。我们在 PVC 前后确定了 AD、MCI 和健康对照组各 39 例匹配样本的感兴趣区（ROI）和体素水平的组间差异以及 MD 和体积测量的诊断准确性。此外，我们评估了 GM MD 值对诊断的影响是否通过体积来介导。PVC 后 ROI 和体素水平的组间差异减小。当在逻辑模型中使用这些 ROI 预测组间分离时，校正和未校正的 PVE GM MD 值在单预测因子模型中的诊断准确性均低于区域性体积。对于 AD 患者和健康对照组的区分，GM MD 对诊断的影响通过海马和后扣带回 ROI 的体积显著介导。我们的结果表明，在存在脑萎缩的情况下，GM MD 测量值受到 PVE 的强烈干扰，强调在将这些测量值用作微观结构组织退化的特定指标时需要进行 PVC。无论是否进行 PVC，区域 MD 在将 AD 的前驱期和临床期与健康对照组区分开来方面都不如区域体积。
