【作者】 邓勇；

【导师】 骆清铭；

【作者基本信息】 华中科技大学 ， 生物医学工程， 2005， 博士

【摘要】 由于偏振光具有矢量性,与不具有偏振而只由强度决定的自然光比较,具有包括偏振方向在内的更多的信息,因此利用偏振光和物质相互作用而引起的各种效应,可对介质本身的某些特性进行研究。上皮组织是薄的粘膜组织,其后向散射光的偏振态是易测量的,因此偏振光散射后的偏振退化、偏振分量之间的转换能够反映组织细胞综合结构参数。本文系统地研究了用于上皮组织形态特征识别的偏振光的理论及技术应用,主要研究内容如下: 首先,从上皮组织的结构以及非典型增生、原位癌的特征出发,建立了双层散射介质的偏振后向散射光谱的理论模型。用傅立叶方法分析了表层散射体的形态学参数对光谱曲线形状及其谐波幅值的影响。分析表明:粒子直径、标准偏差主要影响光谱的波纹结构的幅值及振荡频率,而散射光谱值的大小对相对折射率最为灵敏; 且光谱基波分量及低次谐波分量的贡献依赖于粒子直径、标准偏差及相对折射率的大小。进一步,构建了该上皮组织模型的偏振后向散射光谱反演模型。针对反演模型的多参数、多极值、非线性,采用每代保留最优个体的浮点遗传算法反演。结果表明:经过70 代反演迭代,每个参数的相对误差趋于稳定,最小的达到0.02%左右,最大的达到约为0.4%,并且参数反演结果是唯一和稳定的。以组织模拟液Intralipid 为研究对象,通过测量该模型的后向漫散射光的斯托克斯矢量,研究了不同方位的线偏振光及不同旋向的圆偏振光入射时,Intralipid 的后向漫散射强度、偏振度的特征。结果表明:对不同的入射偏振态,Intralipid 的后向漫散射强度、偏振度的空间分布具有方位选择性,且介质浓度增加,后向散射强度增加,偏振度减小。进一步,提出了利用漫后向散射光随线偏振光入射方位的变化来测量上皮组织模型表层的粒子尺寸分布及相对折射率。建立了偏振后向漫散射强度随入射偏振方位变化的理论模型,并采用物理模型进行了实验验证。通过对测量数据的反演,结果证明:该方法避免了散射光谱术忽略介质折射率随波长变化的缺点,且能够同时准确地抽取表层粒子的形态参数。最后,采用Stokes Vector–Mueller Matrix 形式,建立了当无限窄的连续光束垂直入射到上皮组织模型表面时,后向单次漫散射Mueller 矩阵的理论模型。基于Mie 散射模更多还原

【Abstract】 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.更多还原