Accurate characterization of hippocampal substructure is crucial for detecting subtle structural changes and identifying early neurodegenerative biomarkers. However, high inter-subject variability and complex folding pattern of human hippocampus hinder consistent cross-subject and longitudinal analysis. Most existing approaches rely on subject-specific modelling and lack a stable intrinsic coordinate system to accommodate anatomical variability, which limits their ability to establish reliable inter- and intra-individual correspondence. To address this, we propose HippMetric, a skeletal representation (s-rep)-based framework for hippocampal substructural morphometry and point-wise correspondence across individuals and scans. HippMetric builds on the Axis-Referenced Morphometric Model (ARMM) and employs a deformable skeletal coordinate system aligned with hippocampal anatomy and function, providing a biologically grounded reference for correspondence. Our framework comprises two core modules: a skeletal-based coordinate system that respects the hippocampus' conserved longitudinal lamellar architecture, in which functional units (lamellae) are stacked perpendicular to the long-axis, enabling anatomically consistent localization across subjects and time; and individualized s-reps generated through surface reconstruction, deformation, and geometrically constrained spoke refinement, enforcing boundary adherence, orthogonality and non-intersection to produce mathematically valid skeletal geometry. Extensive experiments on two international cohorts demonstrate that HippMetric achieves higher accuracy, reliability, and correspondence stability compared to existing shape models.

翻译：海马亚结构的精确表征对于检测细微结构变化和识别早期神经退行性生物标志物至关重要。然而，人类海马的高个体间变异性和复杂折叠模式阻碍了一致的跨个体与纵向分析。现有方法大多依赖个体特异性建模，缺乏稳定的内在坐标系以适应解剖学变异，这限制了其建立可靠的个体间与个体内对应关系的能力。为此，我们提出HippMetric，一种基于骨架表示（s-rep）的框架，用于海马亚结构形态计量以及跨个体与跨扫描的点对点对应。HippMetric建立在轴参考形态计量模型（ARMM）基础上，采用与海马解剖和功能对齐的可变形骨架坐标系，为对应关系提供生物学基础的参考。我们的框架包含两个核心模块：一个尊重海马保守纵向层状结构（其中功能单元（层）垂直于长轴堆叠）的基于骨架的坐标系，实现跨个体与跨时间在解剖学上一致的定位；以及通过表面重建、变形和几何约束的辐条优化生成的个体化s-rep，强制执行边界贴合、正交性和非相交性，以产生数学上有效的骨架几何。在两个国际队列上的大量实验表明，与现有形状模型相比，HippMetric实现了更高的准确性、可靠性和对应稳定性。