Optical coherence tomography and elastography for tissue imaging and stiffness differences in soft- and stiff-conditioned breast tumors

Breast cancer is the most diagnosed cancer in women and a leading cause of cancer-related death worldwide. Early detection is essential for improving outcomes, but current imaging methods can be limited in their ability to distinguish tumors at early stages or in certain tissue types. Tumor progression is often associated with changes in the extracellular matrix that lead to increased tissue stiffness, making biomechanical measurements a promising detection and prognostic biomarker. Optical coherence elastography (OCE), an extension of optical coherence tomography (OCT), enables highresolution, non-invasive mapping of tissue stiffness and may serve as a complementary tool for cancer detection. In this study, we applied OCE to evaluate tissue biomechanics in an intraductal mouse model of breast cancer. MCF7 human breast cancer cells were pre-conditioned in either soft (0.5 kPa) or stiff (8 kPa) polyacrylamide hydrogels to simulate distinct tumor microenvironments before injection. Mammary glands were explanted, and imaging was performed ex vivo using a Thorlabs TEL221 spectral-domain OCT system. OCE was conducted using a simplified optical palpation approach, where a transparent silicone reference layer was placed on the tissue surface and compressed axially. Reference layer deformation was tracked across increasing compressions, and stress maps (which are related to tissue stiffness) were generated and overlaid on en face OCT projections for spatial context. Stress maps showed low average stress in normal mammary tissue, and increased stress in tumors from both soft- and stiffconditioned cells. In this small study, there was no significant difference in average tissue stress related to mechanical preconditioning, however there was large heterogeneity in tissue stress. Future work will focus on quantifying tissue strain to enable absolute stiffness measurements and implementation of endoscopic OCE in vivo.