Tomographic imaging of collagen fiber orientation in human tissue using depth-resolved polarimetry of second-harmonic-generation light

We propose a nonlinear optical probe method to image the distribution of collagen fiber orientation in human tissue by measuring the polarization of collagen-induced second-harmonic-generation (SHG) light (SHG polarimetry). Depth-resolved SHG polarimetry, with a depth resolution of 14 mum, was used to evaluate the cross-sectional profile of collagen fiber orientation in Achilles tendon and dentin, revealing a characteristic distribution of collagen orientation along the depth direction. We evaluated the two-dimensional (2D) lateral distribution of collagen fiber orientation in back reticular dermis and anklebone by polarization-resolved SHG imaging, and confirmed an appreciable difference in the distribution profiles of the two samples. We further extended the method to a depth-resolved measurement of the three-dimensional (3D) distribution of collagen orientation in anklebone. The proposed system promises to be a powerful tool for in vivo measurement of collagen fiber orientation in human tissue.