Tension-Based Optical Coherence Elastography: Mapping the Micro-Scale Strain Tensor Resulting from Tensile Loading

Many load-bearing tissues, e.g., tendon, ligament, and muscle, are primarily subjected to tensile loading. Characterizing the micro-scale mechanical properties of these tissues under tensile loading can help to improve our understanding of the link between tissue mechanics and tissue function. Optical coherence elastography (OCE) maps the three-dimensional (3-D) micro-scale mechanical properties of tissue and has shown promise in many applications. However, demonstrations of tensile loading in OCE, i.e., tension-based OCE, are limited and are typically not sensitive to mechanical heterogeneity in the submillimeter range. In this paper, we present a tension-based OCE technique to image the micro-scale strain tensor in tissue under tensile loading. We use a complex cross-correlation method to measure 3-D displacement and propose segmentation-aided multi-directional weighted least squares method to map the strain tensor in samples that contain non-solid regions. We validate our technique using finite element analysis and demonstrate close correspondence with experimental results using a phantom containing a circular cut-out. We demonstrate tension-based OCE on ex vivo bovine tendon tissue, co-registered with histology, revealing that the microstructural heterogeneity of tissue can result in large local strain in tensor components other than that along the direction of the applied load.