Extraction Of The Information About Samples' Microscopic Structures And Optical Properties By Backscattering Mueller Matrix

Polarization imaging method has been widely applied in biomedical areas,which is potentially applied in the diagnosis of precancer.Recently the research on backscattering bulk tissue polarimetry has developed rapidly,however,due to the complexity of biological tissue's microstructure,the study on its mechanism and varying regularity needs to be carried on.In this thesis,we focus on applying backscattering Mueller matrix to extract the information about the microstructural and optical properties of biological tissues systematically by combination of Monte Carlo simulation and polarization imaging experiment,to be specific,we will systematically investigate the relationship between backward polarization parameters and the microstructural and optical properties of various tissue-like models and the regularities by simulation to enhance our understanding on the physical mechanism and regularties of backward polarization imaging of tissue,and apply polarization parameters to characterize some specific physiological process extending the application of backscattering polarimetry in biomedicine.In the thesis,firstly we investigate systematically the relationship between the backward Mueller matrix polar decomposition(MMPD)derived parameters(including biattenuation,depolarization coefficient and retardance)and the microstructural parameters(including scattering coefficient,size and shape of scatterer and interstitial birefringence and so on)by Monte Carlo simulations with various simplified biological tissue models based on sphere-cylinder-birefringence model(SCBM)proposed by our group.It is found that the backward polarization features of the sample are determined jointly by its scattering and birefringence properties.Through comparing the polarization imaging regularities,and also the scattering and polarization properties of the detected photons in both forward and backward geometries,the physical mechanism of backward polarization imaging of tissue and the regularities of polarization parameters in characterizing tissue's microstructure are further illustrated,thus laying foundation for the application of backward Mueller matrix to extract the information about tissue's microstructure.Then we focus on the phenomenon of birefringence-inducing depolarization(BID)found above and investigate it systematically by Monte Carlo simulations.We examine the relationship between BID of circularly-polarized incident light and the scattering and birefringent properties of models with different scatterers imbeded in the birefringent medium.A unified parameter is discovered to describe the birefringence-induced depolarization with models only consisted of spherical scatterers and under the condition of the diffusion approximation,the physical mechanism of it is further illustrated and the quantitative fitting formula is acquired by analogy with scattering-inducing depolarization.The situations with smaller detection areas and forward detecting geometry are also investigated.This study deepens our understanding on the depolarizing mechanism of anisotropic turbid samples,potentially improving the ability and extending the application of polarization methods in characterizing tissues' microstructure and optical properties.In the last part of the thesis,we apply backscattering Mueller matrix polarimetry to investigate the dynamic variations of polarization properties of biological tissues during the process of tissue optical clearing(TOC)and analyze the possible variations of microstructural and optical properties of tissue during the process.Firstly we systematically investigate the polarization features of samples during the process of refractive index matching(RIM,a key effect of TOC)with sclera models by Monte Carlo simulations and MMPD method,indicating the potential of applying polarization methods in the study of TOC.Then backward Mueller matrix polarimetry is applied to examine in detail the polarization features of nude mouse's skin immersed in a glycerol solution(an optical clearing agent),and by simulations on different TOC mechanisms the information about the microstructural variations of the tissue during the TOC process is extracted,thus further verifying the validity of backscattering Mueller matrix in obtaining the information of tissues' microstructure and optical properties.