类同轴法相衬成像是X射线成像领域最新前沿技术和研究热点之一，它能检测对X射线弱吸收的轻元素物质，空间分辨率可达微米甚至亚微米量级，和传统X射线吸收成像技术相比具有不可替代的优势，并且在医学、生物学、材料科学等学科上的初步实验上获得了成功。因此，类同轴法相衬成像的课题研究具有重要的研究价值和应用前景。本文在深入研究并总结类同轴法相衬成像原理的基础上，对类同轴法相衬成像进行了计算机模拟与实际成像实验，并研究了类同轴法相衬成像的CT技术，模拟实现了CT重建。论文所做的工作及成果可概括如下：首先，在类同轴法相衬成像的原理基础上，从基本的光学理论以及电磁波传播理论出发，导出了类同轴法相衬成像的基本原理，并且通过几种模型来进行阐述，包括傅里叶光学模型、互强度理论模型以及稳相法解析模型。其次，在计算机模拟以及成像实验方面，通过对不同成像位置的效果比较，得到了最适宜的成像位置，这个位置与X射线以及物体本身的参数有关。并且在成像实验中成功地观察到了相位信息所体现的效应，实现了类同轴法相衬成像。最后，在类同轴法CT成像的研究上，阐述了直接滤波反投影的重建算法，不通过相位恢复的过程而直接可以重建出物体内部的折射率相位因子 的分布。计算机模拟实验的结果表明，这种直接滤波反投影算法能重建出与实际值相当接近的相位因子分布。
In-line phase contrast imaging is one of up-to-date subjects in the X-ray imaging filed. It can inspect weakly absorbing low-Z samples and its special resolution is on the order of microns or even sub-microns. So In-line phase contrast imaging has its particular advantages over traditional X-ray absorption imaging technology. The primary experiments on In-line phase contrast imaging have been done successfully in medical, biological and material fields. Thus, the research on In-line phase contrast imaging has significant value and perspective.Based on in-depth study and development on formation of In-line phase contrast imaging, this dissertation focuses on simulation and experiment of it. CT technique of In-line phase contrast imaging is also studied, and CT reconstruction is realized. The main work of the dissertation is summarized as follows:First, from basic optics and electromagnetic wave theory, principle of In-line phase contrast imaging is presented. Several models are used in this process, including Fourier optics model, mutual-intensity model and stationary phase analytical model.Second, proper imaging position is obtained by comparing effects of simulated images at different positions. The proper position is related to parameters of X-ray and the sample itself. In experiment, phase effect is successfully observed, and In-line phase contrast imaging is realized.Third, direct filter backprojection reconstruction algorithm for CT is presented. It could reconstruct the distribution of index phase factor in sample without phase retrieval. The reesults of computer simulation indicate that the new algorithm can reconstruct phase factor quite accurately.
