Unfolding the hippocampus: An intrinsic coordinate system for subfield segmentations and quantitative mapping

Jordan DeKraker, Kayla M. Ferko, Jonathan C. Lau, Stefan Köhler, Ali R. Khan
2018 NeuroImage  
The hippocampus, like the neocortex, has a morphological structure that is complex and variable in its folding pattern, especially in the hippocampal head. The current study presents a computational method to unfold hippocampal grey matter, with a particular focus on the hippocampal head where complexity is highest due to medial curving of the structure and the variable presence of digitations. This unfolding was performed on segmentations from high-resolution, T2-weighted 7T MRI data from 12
more » ... MRI data from 12 healthy participants and one surgical patient whose resected hippocampal tissue was used for histological validation. We traced a critical image feature known as the hippocampal 'dark band' in these images, then employed user-guided semi-automated techniques to detect and subsequently unfold the surrounding hippocampal grey matter. This unfolding was done by solving Laplace's equation in three dimensions of interest: longitudinal, proximaldistal, and laminar. The resulting 'unfolded coordinate space' provides an intuitive way of mapping the hippocampal subfields in 2D space (longitudinal and proximal-distal), such that similar borders can be applied in the head, body, and tail of the hippocampus independently of cross-participant variability in folding. Examination of a histological sample reveals that our unfolded coordinate system shows biological validity, and that subfield segmentations applied in this space are able to capture features not seen in manual tracing protocols. This unfolding method can also provide a standardized space for mapping tissue properties; for illustration we map hippocampal intra-cortical myelin and thickness in relation to subfield borders. Research highlights • Dark band in hippocampal head consistently detected with 7T, T2 isotropic MRI • Hippocampal grey matter unfolded using Laplace's equation in 3D • Unfolded subfields capture critical structural elements and agree with histology • Intracortical myelin and thickness mapped in unfolded coordinate space
doi:10.1016/j.neuroimage.2017.11.054 pmid:29175494 fatcat:voyz6igngbd3tjyitlgq4k26pu