Polarization Method For Morphological Feature Recognition Of Epithelial Tissue

As the polarized light holding the vector properties includes some more informations than the natural light only holding intensity information, some properties about the media are studied by use of the various polarization effects brought from the interaction of polarized light with the matter. The epithelium consists of a thin surface layer, its polarization state of backscattering light is easily measured, therefore, the depolarization properties of polarized light backscattered and the conversion between the polarization components can reveal total structure parameters about tissue and cell lines. In this thesis, the theories and techniques of polarized light for morphology feature recognitionof mucosal tissue are systematically and thoroughly studied. The main parts are included as following. Firstly, according to the structure properties of epithelial tissue, the theoretical model of singly backscattering spectra based on Mie scattering theory is established for a two-layer scattering media. The propertiess of scattering spectra are analysed by simulation calculation. The influences of mean diameter, size distribution and relative refractive index of the particles of the uppermost layer on the singly backscattering spectra are further studied by Fourier waveform analysis method. The results show that, The mean diameter and size distribution have influence on the amplitude and frequency of ripple structure for the spectra, spectra value are most sentive to the relative refractive index. The contributions of wave component of different orders are dependence on the mean diameter, size distribution and relative refractive index of the particles. Furthermore, the invertion model of polarized light backscattering spectra is established for the epitheliumlike tissue phantom. This invertion model is of multiple parameters, multiple extreme values and nonlinear. The determination of all unknown parameters needs to solve a nonlinear inverse problem. A nonlinear inversion method—Floating genetic algorithms (FGAs) that is applied to invert polarization light backscattering spectra is used. Our results show that, for diameter, standard deviation and refractive index, the minimal relative errors of three estimated statistical quantities are about 0.02%, the maximal relative errors are about 0.4% with 70 iteration epochs. The errors gradually decrease with iteration epoch increases. Moreover, the inversion results have the advantages of high precision, stability and robustness. The properties of backscattering intensity and degree of polarization from the Intralipid suspensions are investigated for the linearly polarized light with different input azimuth angle, the circularly polarized light with the different rotary direction by measuring the Stokes vectors of the diffuse backscattered light exiting the sample. The results show that, the intensity and DOP patterns depend on the orientation of linearly polarized incident light and the rotary direction of circularly polarized incident light. And as the concentrations increasing, the DOP decrease and the intensity increases. Furthermore, a new method is proposed for measuring the morphological parameters in an epithelium-like tissue phantom. A theoretical model for diffuse backscattering intensity dependent on the azimuth are presented, then two-layer physical models are used to validate. By inverting the metrical data, The experimental results demonstrate that, the size and refractive index of the scatters of the top layer can be determined by measuring and analyzing the azimuth dependence of parallel and perpendicular components of diffusely backscattered light from an epithelium-like phantom, and with comparing of the light-scattering spectroscopy, this method avoid the significant disadvantage of the refractive index dependent on wavelength. Lastly, Single-scattering diffuse backscattering Mueller matrices expression based on Stokes vectors of the backscattered light are derived when a narrow pencillike beam is perpendicular to the surface of the epithelial tissue phantom. Using only Mie theory of light scattering by sphere, the properties distribution pattern of single-scattering Mueller matrices and the correlation with particle number density, particle diameter are discussed. The results indicate that the azimuthal variations gradually disappear when the particle number density increases, and the particle size and particle number density are varied, all of the Mueller matrices elements intensity patterns dependence on radial is similar, similarly exponential function for any azimuth angle.