【作者】 丁飞；

【导师】 陈志强；

【作者基本信息】 清华大学 ， 核科学与技术， 2008， 硕士

【摘要】 X射线相衬成像(X-ray phase-contrast imaging)技术是X射线成像领域的最新研究方向之一,不同于传统的X射线成像技术,相衬成像利用X射线的相移信息来反映观测物内部的电子密度变化,从而揭示物体的内部结构。自90年至今,相衬成像技术已经发展了多种成像技术,其中,衍射增强成像(DEI)方法和光栅相衬成像方法现已成为目前相衬成像方法中的研究焦点之一。这两种方法分别通过完整晶体或光栅来测量X射线穿过物体后的一阶相移信息(也称为折射角信息),而如何精确地测量X射线的一阶相移信息则是这两种相衬成像方法的关键核心问题。本论文分别对这两种相衬成像方法的一阶相移信息提取方法进行深入的研究:在衍射增强成像的一阶相移信息提取方法的研究方面,首先,在北京同步辐射装置上衍射增强成像系统的基础上,应用Maksimenko提出的利用两幅DEI图像进行相移信息提取的非线性相位提取思路,研究了利用高斯函数表征摇摆曲线下的非线性提取(GEDEI)方法,提出了对DEI图像进行近似预处理的方法,并推导了相关的一阶相移信息近似提取公式。模拟和真实实验数据验证了GEDEI算法的有效性,并证明了GEDEI方法比几何光学近似方法能得到更好的一阶相移信息。其次,在利用多幅DEI图像进行相移信息提取方法方面,提出了多项式拟合(PCF)相移信息提取方法。PCF方法很好地避免了高斯曲线拟合(GCF)方法高计算复杂度,在计算速度上比GCF方法提高了10倍。在光栅相衬成像的一阶相移信息提取方法的研究方面,首先,介绍了本实验室所搭建的基于莫尔偏折法的光栅相衬成像系统的基本原理与系统构成,以及相应的相位步进测量方法。在此基础上,研究了正弦函数拟合(SCF)方法与多项式拟合(PCF)方法这两种算法,并实验验证了它们的有效性。其次,探讨了条纹扫描(FS)方法应用于基于摩尔偏折法的光栅相衬成像系统的可行性,获得了初步的结果,通过与SCF方法、PCF方法的性能比较,证实了这一方法的有效性。更多还原

【Abstract】 Hard X-ray phase-contrast imaging is a newborn non-destructive testing and diagnostic technology in medicine, biology and materials science. In order to reveal the internal structure of objects, this technology is adopted to capture the X-ray phase-shift information to observe the electron density of objects. Theoretically, the transmitted beam will change along its direction of propagation slightly because of the refractive index’s gradients of the sample.In Diffraction Enhanced Imaging and Grating phase-contrast imaging technology .The key problem of these technologies is how to extract phase information which is expressed by refraction angle images from a series of original images measured in different position of the rocking curve (RC) or displacement curve.Study on the DEI technology and the modality of rocking curve, based on the extension method which is presented by Maksimenko, we provide the analytic formula of GEDEI in case of the rocking curve which can be fitted by Gaussian function approximately. Furthermore, in order to make the GEDEI formula can be solved in a nutshell, we present a predigest process on the DEI images. In the end, the extraction results on simulation data and columnar model proved that the GEDEI algorithm with a pretreatment approximation is accredited. And the extraction results of GEDEI are better than the GOA method.GCF method in DEI provides the most approximate refraction-angle values in exist methods, but it has a high computational complexity due to the nonlinear multiplex iterative process. So the enormous calculation time obviously limits the practical applications of GCF method. In order to speed up the computation time, this paper presented a theoretical and experimental study on polynomial curve fitting (PCF) method for refraction-angle extraction in DEI. In conclusion, PCF method can obtain most approximate refraction-angle values and its computational speed is 10 times faster than GCF method. Study on the traditional grating phase-contrast imaging technology based on the Talbot self-imaging principle in the third part of this paper, we introduce a new grating phase-contrast imaging system based on the Moirés deflection principle. Based on this system, we presented a theoretical and experimental study on the sine curve fitting (SCF) method and polynomial curve fitting (PCF) method for refraction-angle extraction in the experimental system. Then we tried to apply the fringe scan method to extract the refraction-angle in this new experimental system. In conclusion, the comparisons of PCF SCF and FS methods proved that the FS method is the fastest and the best exaction method for this moirés deflection-based grating phase-contrast imaging system.更多还原