# Review on Complete Mueller Matrix Optical Scanning Microscopy Imaging
## 3 Mueller Matrix Applications
### Biomedical Diagnosis and Tissue Organization  
Recently, many works have been focused on developing MM polarimeter to investigate the modification of the tissues induced by pathology at the cellular level [71; 72; 73]. Indeed, MM offers the capability of tracking changes at distance in a non-invasive and label free way since no high power is required for detecting the polarized light. Coupling with SLM, a better contrast emerged from this technique, resolving sub-microscopic objects optical properties giving the capability of quantifying pathologies at early stages.  
Cancers induce drastic modifications in cells size and collagen organization. Actually, the scoring of pathologies are performed by specialists and the accuracy of the analysis in completely operator dependant. This is the reason that the recent emerging methods proposed to automatize the measurements and the interpretation of the results through statistical interpretation and machine learning. The approach is almost the same and consists in measuring the associated physical changes to the cancer that exhibit strong polarimetric effects comparatively to the healthy area. Thus, MM provides an interesting method for imaging confined localized structures and bring quantitative methods for staging the pathologies. It is the purpose of the applications proposed in Figure 6.  
More particularly, the work in Figure 6i proposed a statistical approach for scoring liver fibrosis biopsies by analyzing the retardance and depolarization parameters compared to the SHG response. This pathology induces an accumulation of the type I and III fibrillar collagen through the extracellular matrix in the hepatic tissue. The non-linear signal erases from the anisotropic arrangement in the collagen structure and are correlated to the retardance images as observed. Based only on this parameter, it is impossible to distinguish the different arrangement in the collagen fibers, different from the random accumulation in the fibrosis or from the organized collagen composing blood vessels. Based on a pure visual interpretation, this can leads a bad scoring of the fibrosis. However, it is well stated that the random distribution of deterministic objects (here pure birefringent) leads to depolarization, MM gives the opportunity of discriminating the two kinds of organization through this parameter. Furthermore, Figure 6 ii shows that this discrimination can be done on the image extracted from the retardance orientation (i.e., birefringent fast axis) where it is possible to follow the rotation of the fiber in space with high imaging contrast. It could be of interest in the case the experiment requires the tracking of a specific polarimetric change under certain conditions as it has be done for fixed zebrafish reported in Figure 6 iii [45]. This work has proposed to acquire a detailed fingerprint at different developmental stages and interpret all the MM parameters. This is key in understanding the morphological changes of the animal during development. It has been shown that each parameters could be use as a specific markers for local structures since the physical effects are reliable to a dedicated structure and organization. For zebrafish, it has been proven than the imaging contrast from Pd comes from the thickness heterogeneity while the R values erases from the tissues and muscles.