Real-time structured polarized light imaging of dynamics of thick collagenous tissues

Collagen is the most abundant protein and the main load-bearing material in the human body. Collagen architecture and behavior under load are important for understanding their functions in healthy tissues and the pathophysiology of diseased tissues. Structured polarized light imaging (SPLI) has proved to be an effective method to quantify collagen properties of thick collagenous tissues. Compared to without using structured illumination, SPLI provides improved accuracy in quantification and enhanced contrast for visualization of collagen structures by suppressing highly scattered light from the deeper tissue. However, current SPLI requires multiples images, typically 12, which is a challenge for imaging tissue dynamics where acquisition time is highly constrained. In this study, we developed real-time SPLI to address this challenge. The real-time imaging capability was achieved with a polarization-sensitive camera, capable of acquiring images at four polarization states simultaneously at 75 frames/second. Using a rolling image processing technique, we achieved the same frame rate for visualizing tissue dynamics. The performance of real-time SPLI was validated by imaging a rotating chicken tendon. Additionally, we integrated real-time SPLI with a tissue tester and demonstrated that pig scleral tissue, under uniaxial stretching, exhibited nonlinear and region-dependent deformation.