Kitchen M J, Pavlov K M, Siu K K W, Menk R H, Tromba G, Lewis R A
School of Physics, Monash University, Victoria 3800, Australia.
Phys Med Biol. 2007 Jul 21;52(14):4171-87. doi: 10.1088/0031-9155/52/14/010. Epub 2007 Jun 15.
Analyser-based phase contrast imaging can provide radiographs of exceptional contrast at high resolution (<100 microm), whilst quantitative phase and attenuation information can be extracted using just two images when the approximations of geometrical optics are satisfied. Analytical phase retrieval can be performed by fitting the analyser rocking curve with a symmetric Pearson type VII function. The Pearson VII function provided at least a 10% better fit to experimentally measured rocking curves than linear or Gaussian functions. A test phantom, a hollow nylon cylinder, was imaged at 20 keV using a Si(1 1 1) analyser at the ELETTRA synchrotron radiation facility. Our phase retrieval method yielded a more accurate object reconstruction than methods based on a linear fit to the rocking curve. Where reconstructions failed to map expected values, calculations of the Takagi number permitted distinction between the violation of the geometrical optics conditions and the failure of curve fitting procedures. The need for synchronized object/detector translation stages was removed by using a large, divergent beam and imaging the object in segments. Our image acquisition and reconstruction procedure enables quantitative phase retrieval for systems with a divergent source and accounts for imperfections in the analyser.
基于分析器的相衬成像可以在高分辨率（<100微米）下提供对比度极高的射线照片，而当满足几何光学近似条件时，仅使用两张图像就可以提取定量的相位和衰减信息。通过用对称的皮尔逊VII型函数拟合分析器摇摆曲线，可以进行解析相位恢复。与线性或高斯函数相比，皮尔逊VII型函数对实验测量的摇摆曲线的拟合效果至少好10%。使用ELETTRA同步辐射设施中的Si(1 1 1)分析器，在20 keV下对一个测试体模（一个空心尼龙圆柱体）进行成像。我们的相位恢复方法比基于摇摆曲线线性拟合的方法能产生更准确的物体重建。当重建未能映射预期值时，通过计算高木数可以区分几何光学条件的违反和曲线拟合程序的失败。通过使用大的发散光束并对物体进行分段成像，消除了对同步物体/探测器平移台的需求。我们的图像采集和重建程序能够对具有发散源的系统进行定量相位恢复，并考虑了分析器中的缺陷。
