Vuong Phong, Drucker David, Schwarz Chris, Fletcher Evan, Decarli Charles, Carmichael Owen
Proc SPIE Int Soc Opt Eng. 2013 Mar 13;8669:86693M-. doi: 10.1117/12.2006727.
Many brain aging studies use total intracranial volume (TIV) as a proxy measure of premorbid brain size that is unaffected by neurodegeneration. T1-weighted Magnetic Resonance Imaging (MRI) sequences are commonly used to measure TIV, but T2-weighted MRI sequences provide superior contrast between the cerebrospinal fluid (CSF) bounding the premorbid brain space and surrounding dura mater. In this study, we compared T1-based and T2-based TIV measurements to assess the practical impact of this superior contrast on studies of brain aging. 810 Alzheimer's Disease Neuroimaging Initiative (ADNI) participants, including healthy elders and those with mild cognitive impairment (MCI) and Alzheimer's Disease (AD), received T1-weighted and T2-weighted MRI at their baseline evaluation. TIV was automatically estimated from T1-weighted images using FreeSurfer version 4.3 (T1TIV), and an automated active contour method was used to estimate TIV from T2-weighted images (T2TIV). The correlation between T1TIV and T2TIV was high (.93), and disagreement was greater on larger heads. However, correcting a FreeSurfer-based measure of total parenchymal volume by dividing it by T2TIV led to stronger expected associations with a standardized measure of cognitive dysfunction (MMSE) in Poisson regression models among individuals with AD (=1.73 vs. 1.09) and MCI (=3.15 vs. 2.79) than a corresponding parenchymal volume measure divided by T1TIV. This effect was enhanced when the analysis was restricted to the cases where T1TIV and T2TIV disagreed the most. These findings suggest that T2-based TIV measurements may be higher fidelity than T1-based TIV measurements, thus leading to greater sensitivity to detect biologically plausible brain-behavior associations.
许多脑老化研究使用总颅内体积（TIV）作为病前脑大小的替代指标，该指标不受神经退行性变影响。T1加权磁共振成像（MRI）序列常用于测量TIV，但T2加权MRI序列在界定病前脑空间的脑脊液（CSF）与周围硬脑膜之间提供了更好的对比度。在本研究中，我们比较了基于T1和基于T2的TIV测量，以评估这种更好的对比度对脑老化研究的实际影响。810名阿尔茨海默病神经成像计划（ADNI）参与者，包括健康老年人以及轻度认知障碍（MCI）和阿尔茨海默病（AD）患者，在基线评估时接受了T1加权和T2加权MRI检查。使用FreeSurfer 4.3版从T1加权图像自动估计TIV（T1TIV），并使用自动活动轮廓法从T2加权图像估计TIV（T2TIV）。T1TIV与T2TIV之间的相关性很高（.93），并且在较大的头部上差异更大。然而，在泊松回归模型中，将基于FreeSurfer的总实质体积测量值除以T2TIV进行校正，与将相应的实质体积测量值除以T1TIV相比，在AD患者（=1.73对1.09）和MCI患者（=3.15对2.79）中，与认知功能障碍的标准化测量值（MMSE）的预期关联更强。当分析仅限于T1TIV和T2TIV差异最大的情况时，这种效应会增强。这些发现表明，基于T2的TIV测量可能比基于T1的TIV测量具有更高的保真度，从而在检测生物学上合理的脑-行为关联方面具有更高的敏感性。
