The human hippocampus is vulnerable to a range of degenerative conditions and as such, accurate in vivo measurement of the hippocampus and hippocampal substructures via neuroimaging is of great interest for understanding mechanisms of disease as well as for use as a biomarker in clinical trials of novel therapeutics. Although total hippocampal volume can be measured relatively reliably, it is critical to understand how this reliability is affected by acquisition on different scanners, as multiple scanning platforms would likely be utilized in large-scale clinical trials. This is particularly true for hippocampal subregional measurements, which have only relatively recently been measurable through common image processing platforms such as FreeSurfer. Accurate segmentation of these subregions is challenging due to their small size, magnetic resonance imaging (MRI) signal loss in medial temporal regions of the brain, and lack of contrast for delineation from standard neuroimaging procedures. Here, we assess the test-retest reliability of the FreeSurfer automated hippocampal subfield segmentation procedure using 2 S model scanners (a Siemens Trio and Prismafit Trio upgrade). T1-weighted images were acquired for 11 generally healthy younger participants (two scans on the Trio and one scan on the Prismafit). Each scan was processed through the standard cross-sectional stream and the recently released longitudinal pipeline in FreeSurfer v6.0 for hippocampal segmentation. Test-retest reliability of the volumetric measures was examined for individual subfields as well as percent volume difference and Dice overlap among scans and intra-class correlation coefficients (ICC). Reliability was high in the molecular layer, dentate gyrus, and whole hippocampus with the inclusion of three time points with mean volume differences among scans less than 3%, overlap greater than 80%, and ICC >0.95. The parasubiculum and hippocampal fissure showed the least improvement in reliability with mean volume difference greater than 5%, overlap less than 70%, and ICC scores ranging from 0.78 to 0.89. Other subregions, including the CA regions, were stable in their mean volume difference and overlap (<5% difference and >75% respectively) and showed improvement in reliability with the inclusion of three scans (ICC > 0.9). Reliability was generally higher within scanner (Trio-Trio), however, Trio-Prismafit reliability was also high and did not exhibit an obvious bias. These results suggest that the FreeSurfer automated segmentation procedure is a reliable method to measure total as well as hippocampal subregional volumes and may be useful in clinical applications including as an endpoint for future clinical trials of conditions affecting the hippocampus.

中文翻译：

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FreeSurfer 自动海马子域分割在扫描仪内和扫描仪之间的测试-再测试可靠性

人类海马体易受一系列退行性疾病的影响，因此，通过神经成像对海马体和海马体亚结构进行准确的体内测量对于理解疾病机制以及在新疗法的临床试验中用作生物标志物具有重要意义. 虽然可以相对可靠地测量总海马体积，但了解这种可靠性如何受到不同扫描仪采集的影响至关重要，因为在大规模临床试验中可能会使用多个扫描平台。对于海马次区域测量尤其如此，最近才可以通过 FreeSurfer 等常见图像处理平台进行测量。由于这些子区域的尺寸小，准确分割这些子区域具有挑战性，大脑内侧颞区的磁共振成像 (MRI) 信号丢失，并且缺乏标准神经成像程序的对比度。在这里，我们使用 2 S 模型扫描仪（Siemens Trio 和 Prismafit Trio 升级）评估了 FreeSurfer 自动海马亚区分割程序的重测可靠性。为 11 位总体健康的年轻参与者采集了 T1 加权图像（在 Trio 上进行了两次扫描，在 Prismafit 上进行了一次扫描）。每次扫描都通过标准横截面流和最近发布的 FreeSurfer v6.0 中用于海马分割的纵向管道进行处理。针对单个子域以及扫描和类内相关系数 (ICC) 之间的体积差异百分比和 Dice 重叠，检查了体积测量的重测可靠性。分子层、齿状回和整个海马的可靠性很高，包括三个时间点，扫描之间的平均体积差异小于 3%，重叠大于 80%，ICC > 0.95。下颌旁裂和海马裂的可靠性改善最少，平均体积差异大于 5%，重叠小于 70%，ICC 评分范围为 0.78 至 0.89。其他子区域，包括 CA 区域，在其平均体积差异和重叠方面保持稳定（分别<5% 和 >75%），并且在包括三个扫描后显示可靠性提高（ICC > 0.9）。扫描仪（Trio-Trio）的可靠性普遍较高，但 Trio-Prismafit 的可靠性也很高，没有表现出明显的偏差。