Study Of Theory And Experimental Measurement Methods Of The Depth-resolved Mueller Matrix Of Biological Tissues

Polarization sensitive optical coherence tomography(PS-OCT)is an imaging method that is a combination of optical coherence tomography and polarization measurement method to simultaneously obtain depth-resolved images of intensity and polarization parameters of sample,and has important application prospects in the fields of both biomedical research and clinical diagnosis.To this end,it is first necessary to accurately obtain the depth-resolved images of the elements of Mueller matrix of the biological tissue,reconstruct the images of the polarization parameters,and establish the relationships between the polarization information and the microstructures of the biological tissue.In this thesis,several important problems about this method are investigated,including setting up a PS-OCT system for reconstructing the images of the elements of Mueller matrix and the images of the polarization parameters of biological tissues,proposing the interpretation of the generation mechanism for the depolarization properties of the biological tissue,and establishing the relationships between the polarization information and the microstructures of biological tissues.The main research contents and innovation results are as follows:First of all,in order to obtain the depth-resolved images of the elements of Mueller matrix of biological tissues,a polarization sensitive spectral-domain optical coherence tomography(PS-SDOCT)system for detecting the elements of Mueller matrix of the tissues was built.A method of reconstructing the images of the elements of Mueller matrix of the tissues based on the elements of the Stokes vector of emitted light obtained under the incident light with four different polarization states was proposed,and the theoretical calculation,the testing and the analysis of the performance parameters of the system were completed.After that,the depth-resolved two-dimensional images of the elements of Mueller matrix of the human nail and the surrounding structures were obtained.By comparing the intensity image and the images of the elements of Mueller matrix with the images of the real structures of the nail,different microstructures can be distinguished,demonstrating the imaging performance of the system.In order to determine the relationships between the elements of Mueller matrix,the polarization parameters of the anisotropic thin-layer medium and the physical phenomena or the mechanism described by the depolarization parameters,the relationships of the polarization parameters between the differential Mueller matrix decomposition method and the polar decomposition method were established,and the form and the physical interpretation of the Mueller matrix of an anisotropic thin-layer medium measured in the transmission configuration were proposed.Based on the pseudo-polar decomposition and the serial-parallel decomposition methods,the effect of depolarization of the medium was connected with the physical phenomenon of light scattering in different directions,and an interpretation of the generation mechanism of the depolarization of the anisotropic thin-layer medium was obtained.A set of experimental data of the Mueller matrix was used as an example to verify the theoretical model of Mueller matrix of the anisotropic thin-layer media and the interpretation of the depolarization mechanism.In order to solve the problems of different values of the parameters of the same properties and data loss caused by multiple orders of the product and complex calculation steps in the matrix decomposition process,a method was proposed to obtain the polarization parameters directly from the elements of the measured Mueller matrix without the decomposition.By expressing the two Mueller-Jones matrices of the canonical decomposition with the expressions of polar decomposition with different orders,the general form of Mueller matrix with clear physical meaning and the expressions of polarization parameters of Mueller matrix elements were obtained.By analyzing the sets of experimental data of three different Mueller matrices,it is verified that the proposed expressions of the polarization parameter can be used to directly obtain the polarization parameters from the noise-containing Mueller matrix measured in the different detection conditions.In order to determine the relations between the structures of anisotropic biological tissues with a certain thickness,the polarization information and the detection methods,the Mueller matrix model was established and the expressions of three types of polarization parameters were obtained according to the propagation path of light in the medium.A Mueller matrix polarization parameter tomographic imaging method for biological tissues was proposed.The form of the Mueller matrix is the same as the symmetric decomposition,revealing the physical essence of the symmetric decomposition of the Mueller matrix of the depolarized medium.Through the use of the standard polarized optical elements and the generally isotropic biological samples,the ability and the accuracy of both the system and the proposed expressions to obtain the polarization parameters were verified.Images of the elements of Mueller matrix and polarization parameter were obtained from the biological samples ex vivo and in vivo to illustrate the application prospects of the proposed imaging method.Finally,in order to overcome the limitation of using single depolarization parameter to quantify depolarization effects and the difficulty of directly explaining depolarization mechanism at present,the relationships have been derived between the differential Mueller matrix,the weight coefficients and the Mueller-Jones matrix in the Cloude decomposition,a method was proposed for calculating the differential polarization parameters from the measured macroscopic Mueller matrix and revealing the mechanism of the depolarization properties of the tissue.By calculating the polarization parameters of the experimental data of Mueller matrix and using the built PS-OCT system to obtain the images of the elements of Mueller matrix of biological tissue and to calculate the polarization parameters,the theoretical model to interpret and quantify the depolarization of tissue was verified.