Wolf Johannes, Sperl Jonathan I, Schaff Florian, Schüttler Markus, Yaroshenko Andre, Zanette Irene, Herzen Julia, Pfeiffer Franz
Lehrstuhl für Biomedizinische Physik, Physik-Department & Institut für Medizintechnik, Technische Universität München, 85748 Garching, Germany.
GE Global Research, 85748 Garching, Germany.
Biomed Opt Express. 2015 Nov 12;6(12):4812-24. doi: 10.1364/BOE.6.004812. eCollection 2015 Dec 1.
X-ray grating interferometry requires gratings with periods in the micrometer range and allows the acquisition of the dark-field contrast. The analyzer grating is designed to match the period of the interference pattern in order to translate it into a measurable intensity modulation. In this study, we explore the influence of a sample-induced mismatch between the interference pattern and the analyzer grating on the dark-field contrast. We propose a formula for the calculation of the signal due to a period mismatch and present estimations varying periods and detector pixel size. Furthermore, numerical simulations of the X-ray wave-front demonstrate that the wave-front curvature, described by the lens-term, e.g. behind a parabolic lens or edges of a sample can change the period of the interference pattern. Our results give a concrete explanation for the formation of a dark-field contrast from object edges and thus allow a better understanding of the dark-field signal obtained with a grating interferometer.
X射线光栅干涉测量法需要周期在微米范围内的光栅，并能够获取暗场对比度。分析光栅的设计目的是匹配干涉图样的周期，以便将其转换为可测量的强度调制。在本研究中，我们探讨了样品引起的干涉图样与分析光栅之间的失配对暗场对比度的影响。我们提出了一个用于计算由于周期失配产生的信号的公式，并给出了不同周期和探测器像素尺寸的估计值。此外，X射线波前的数值模拟表明，由透镜项描述的波前曲率，例如在抛物面透镜后面或样品边缘处，会改变干涉图样的周期。我们的结果为物体边缘形成暗场对比度提供了具体解释，从而有助于更好地理解使用光栅干涉仪获得的暗场信号。
