🤖 AI Summary
To address the lack of observer-independent, quantifiable descriptors for neural fiber patterns in three-dimensional polarized light imaging (3D-PLI), this paper introduces CL-3D—the first self-supervised representation learning framework tailored for 3D-PLI. Methodologically, we propose a 3D contextual contrastive learning objective that constructs positive sample pairs from spatially adjacent brain tissue slices in volume reconstruction and design image augmentation strategies specifically adapted to 3D-PLI parameter maps, enabling fiber-configuration-sensitive and cross-slice-robust representation learning. Evaluated on macaque occipital lobe data, the learned representations accurately discriminate canonical fiber configurations (e.g., U-fibers), support zero-shot and few-shot classification, homogeneous fiber cluster retrieval, and query-based structural localization. Moreover, they significantly enhance downstream tasks including multimodal correlation analysis, clustering, and cortical mapping.
📝 Abstract
Abstract A comprehensive understanding of the organizational principles in the human brain requires, among other factors, well-quantifiable descriptors of nerve fiber architecture. Three-dimensional polarized light imaging (3D-PLI) is a microscopic imaging technique that enables insights into the fine-grained organization of myelinated nerve fibers with high resolution. Descriptors characterizing the fiber architecture observed in 3D-PLI would enable downstream analysis tasks such as multimodal correlation studies, clustering, and mapping. However, best practices for observer-independent characterization of fiber architecture in 3D-PLI are not yet available. To this end, we propose the application of a fully data-driven approach to characterize nerve fiber architecture in 3D-PLI images using self-supervised representation learning. We introduce a 3D-Context Contrastive Learning (CL-3D) objective that utilizes the spatial neighborhood of texture examples across histological brain sections of a 3D reconstructed volume to sample positive pairs for contrastive learning. We combine this sampling strategy with specifically designed image augmentations to gain robustness to typical variations in 3D-PLI parameter maps. The approach is demonstrated for the 3D reconstructed occipital lobe of a vervet monkey brain. We show that extracted features are highly sensitive to different configurations of nerve fibers, yet robust to variations between consecutive brain sections arising from histological processing. We demonstrate their practical applicability for retrieving clusters of homogeneous fiber architecture, performing classification with minimal annotations and query-based retrieval of characteristic components of fiber architecture such as U-fibers.