Mueller matrix characterization on anisotropy in tissue optical models

Most of real tissues have anisotropic microstructures or anisotropic optical features. The variation of tissue anisotropy can be an effective character to describe some abnormal conditions in tissues, so it is meaningful for the extraction and comparison of parameters for anisotropy evaluation. In this paper, based on our previously proposed sphere-cylinder scattering model, we simulate and investigate the propagation and scattering of polarized light in tissue models using polarization-sensitive Monte Carlo simulation. Focusing on anisotropic tissues, we consider two type disturbance of highly ordered cylindrical elements: cylinders with a distribution of the orientation angle and the existence of the isotropic elements like spheres. By analyzing the corresponding backscattering Mueller matrices with the changes of structural parameters in our tissue model, we extract a characteristic parameter to describe the symmetry of certain Mueller matrix elements. According to the simulation, the characteristic is less sensitive to the size of cylindrical scatterers, and is especially suitable for the case of detecting the small scale isotropic perturbation in a highly anisotropic medium. The results presented in this paper confirm the feasibility of this new anisotropy factor to measure the degree of tissue anisotropy, and imply the validity of applying it in distinguishing some pathological changes.