# Applications of Mueller Matrix Polarimetry to Biological and Agricultural Diagnostics: A Review
## 4 Applications of MMP to Biology and Agriculture
### Biological Tissues  
The concepts and applications of tissue MMP were concisely reviewed in [20]. Inverse analysis of MMs based on scattering theory and MM polar decomposition was considered. Several medium-specific polarimetric parameters that are practical for recognizing tissue structures and their changes can be derived from the polar decomposition of MM: diattenuation, depolarization (linear, circular and total), linear retardance (and its orientation) and optical rotation. MMP increases the quality of visualization of biological tissues and, in particular, makes it possible to distinguish between cancerous and healthy tissues, while being, at the same time, a cheaper method for analysis of tissues before and after surgery [29; 30]. Microscopic imaging based on MM-derived parameters related to depolarization and retardance proved to be effective in assessing the polarization properties and structural features of biological tissues and were helpful for diagnosing pathological tissue samples [32]. In particular, measuring the retardance and depolarization of thin biopsies by MMP can be used to quantify human liver fibrosis [116]. MMP was tested as a non-invasive method for the characterization of various dermatological diseases [24; 25]. The depolarization and retardance were shown to be important polarization metrics, indicating changes in the fibrous structure of skin tissues. OCT integrated with MMP can record tissue anisotropies and is capable of measuring the polarization contrast of any biological sample, in particular, soft tissue samples [33]. MM-based polarization imaging was used for quantitative digital screening of polycrystalline structures of biological tissues in vitro [54]. It was shown that the spatial distributions of the phase of light and optical anisotropy of scattering, which are inherent in myocardial fibrillar networks at different stages of necrosis, can be effectively used as a quantitative marker of the stages of myosin fibril degradation. The use of MM calculus facilitates the calibration of fiber-optic PS-OCT to quantitatively measure the birefringence and optical axis orientation of tissues [55]. Monte Carlo simulations showed the possibility of determining the glucose concentration in turbid media using MMs [69]. Similar studies showed that linear polarization and total intensity are more sensitive to increased glucose concentration in backscatter than in forward scatter in highly turbid environments, indicating that backscatter geometry may be preferable for potential glucose detection in biomedical diagnostics. At the same time, comparative measurements with optically inactive glycerol showed that the refractive index matching effect, rather than the chiral nature of the solute, dominates the observed optical rotation caused by glucose in a highly turbid medium [112]. By multi-region segmentation of polarized light images, a radiofrequency-ablated lesion in myocardial tissue was quantified [120]. MM measurements for fluorescence and elastic scattering in the backward direction were used to study connective tissue regions of human cervical tissue [50; 51]. Fluorescence linear and circular diattenuation, together with fluorescence linear and circular polarizance, were used as parameters derived from experimental MM. Significant differences were found between precancerous and normal tissues in the fluorescence polarimetric parameters--fluorescence linear diattenuation and linear polarizance--and in the diattenuation of the elastic scattering. These parameters are much lower at higher stages of precancer, which is explained by the loss of the anisotropic orientation of the molecular structures of collagens in precancerous connective tissues. A weaker, circular diattenuation arises from the presence of chiral moiety in collagen. The progression of precancer is accompanied by the destruction of collagen cross-links, which leads to loss of anisotropic organization and reduction of the diattenuation.