Characterization of Biological Tissues by Polarization Analysis of diffused light

组织的散射特性取决于细胞大小、细胞成分和细胞结构，因此，散射光的测量可以用于组织表征、新陈代谢监测等。特别是，后向散射对亚蜂窝结构的大小和偏振态都非常敏感。用来研究生物材料散射的常规方法涉及到测角测量，但这种方法的样品必须非常薄。由于生物组织具有很强的散射特性，入射的偏振光束在经过很短的路径后变成了扩散光。本课题旨在提出一种新的方法，无需对生物组织等小体积的混浊介质进行预处理，就可以获得偏振后向散射光的二维角方向图。该系统根据成分和S…推导出具有特定角分布图案的单个散射成分散射物质的更多结构。我们尝试使用二维成像传感器来检测背向散射光的角度分布。我们开发了一个蒙特卡罗模拟来估计我们的实验系统的光子传播行为。该模拟采用Mie散射相函数，计算结果与入射光束功率归一化。模拟结果表明，这些包含散射粒子和介质信息的特征图案是由于入射点附近只有很小的体积内发生的散射现象。此外，折合散射系数μS可以作为评价扩散多次散射对二维图像影响的一个合适的指标。小针孔系统能够抑制扩散多次散射，因此，利用我们的系统可以观察到信息丰富的单次散射分量的角分布作为2D图像。我们开发了一套可以获得二维背向散射角的基本实验系统，并利用聚苯乙烯球在水中的悬浮液进行了初步的实验。验证了该系统可以获得均匀高散射材料的二维背向散射偏振光的角度方向图，其μS的值为1 mm^-1，与生物材料的结果相当。然而，与模拟预测的结果相比，偏振方向引起的光强差异并不明显。造成这种差异的原因仍未解决。为了将我们的方法应用于组织表征，实验系统应该进一步改进，并需要新的方法来将角分布的2D模式与组织结构和成分相关联。较少

The scattering properties of a tissue depend on the cell size, cell constituents and cell structure ; therefore, the measurement of scattering light can be useful for tissue characterization, metabolism monitoring and so on. In particular, backscattering is very sensitive to both the size of the subcellular structure and the polarization state. The conventional method employed to study the scattering from biological material involves goniophotometric measurement ; however, the sample for this method should be very thin. Because biological tissues have very strong scattering properties and incident polarized beam becomes diffusive light while passing through very short path.This project aims to propose new method to obtain the 2D angular pattern of polarized backscattering light from small volume of turbid media such as living tissue without pretreatment. The system derives a single scattering component that has a specific angular distribution pattern depending on the constituents and s … More tructures of the scattering substances. We attempt to detect the angular distribution of the backscattered light by using a 2D imaging sensor. We developed a Monte Carlo simulation to estimate the photon propagation behavior of our experimental system. This simulation employed Mie scattering phase function and the results were normalized with incident beam power. The simulation results showed that the characteristic patterns, which contain information on the scattering particles and medium, are due to the scattering phenomenon that occurs only in a very small volume around the incident point. Moreover, the reduced scattering coefficient μs' served as a suitable index for estimating the influence of diffusive multiple scattering on the 2D pattern. The small pinhole system enables the suppression of the diffusive multiple scattering; therefore, the angular distribution of the informative single scattering component can be observed as a 2D image by using our system. We developed a basic experimental system that could obtain the 2D angular pattern of backscattering, and preliminary experiments using suspensions of polystyrene sphere in water were performed. We verified that the proposed system could obtain the 2D angular pattern of backscattered polarized light from even high scattering materials, with a μs' value of 1 mm^<-1>, which was equivalent to that obtained from biological materials. However, difference of intensity due to polarization direction was not clear compare to the predictions by the simulation. The reason of this discrepancy remains unsolved yet. In order to apply our method for tissue characterization, the experimental system should be improved further and new approaches to relate the 2D patterns of angular distribution to the tissue structure and constituents are required. Less