In order to interpret the experimental results above, we carry on MC simulations based on the sphere birefringence model to analyze the relationship between the parameters and the fibrosis process of the liver tissues.40 In the MC simulations, there are two types of spherical scatterers, the large ones ( in diameter, scattering coefficient is ) represent the cell nuclei and the small ones ( in diameter, scattering coefficient is ) represent the organelles. According to the liver tissue samples, the thickness of the medium is and the refractive indices of the interstitial medium and scatterers are 1.33 and 1.45, respectively.37 As mentioned in Sec. 2.2, for the thin tissue slices with anisotropic fibrous structures, the birefringence effect plays the dominant role for the polarization imaging contrast mechanism.37 In addition, the experimental results have shown that from stage F1 to F4 not only the values of retardance of fibrotic regions, but also the proportion of fibrous distribution increase. Therefore, to quantitatively analyze the fibrosis process during the F1 to F4 stages, in the MC simulations, both the increases of birefringence value and proportion of fibrous distribution are considered. As shown in Fig. 10, in the simulations, the value of is increased from 0.001 to 0.0025 and the optical axis is along the -axis direction. Meanwhile, the proportion of fibrous distribution is changed from 6%, 10%, 12%, to 16% according to the experimental results. The simulated results shown in Fig. 10 demonstrate that the values of parameters and increase as the birefringence increases, which are consistent with the experimental observations. It should be pointed out that in Fig. 10, the absolute values of the parameters and are slightly lower than those in Fig. 8. In the MC simulation, there are several constant parameters used such as the thickness of the medium and the diameter of the scatterers. Actually, these parameters can be varied in different regions of the tissue samples. Since such variations are hard to estimate, we use approximately constant values of these parameters, which may influence the results of the MC simulations. It can also be observed that when changes from 0.001 to 0.0025, the mean value of parameter changes about 0.02, while the mean value of parameter changes only about 0.01, meaning that the MMPD parameter is slightly more sensitive to the variations of . Figure 11 shows that both the parameters and can reflect the orientation of the optical axis or the alignment direction of the fibers. It should be pointed out that in MC simulations, when the value of is changed from 0.001 to 0.0025, or the proportion of fibrous distribution is changed from 6% to 16%, the curves shown in Fig. 11 almost remain the same, confirming that the parameters and are insensitive to the value of .