Propagation-based phase contrast imaging (PB-PCI) with an X-ray lab source is a powerful technique to study low absorption samples, e.g. soft tissue or plastics, on the micrometer scale but is often limited by the low flux and coherence of the source. The setup geometry is essential for the performance since there is a trade-off where a short source distance yields a high contrast-to-noise ratio (CNR) but a low relative fringe contrast. While theoretical optimization strategies based on Fresnel propagation have been reported, there is a need for experimental testing of these models. Here, we systematically investigate this trade-off experimentally using two different setups with high-resolution detectors: a custom-built system with a Cu X-ray source and a commercial system (Zeiss Xradia) with a W source. The fringe contrast, CNR and fringe separation for a low-absorption test sample were measured for 130 different combinations of magnification and overall distances. We find that these figures-of-merit are sensitive to the magnification and that an optimum can be found that is independent of the overall source-detector distance. In general, we find that the theoretical models show excellent agreement with the measurements. However, this requires the complicated X-ray spectrum to be considered, in particular for the broadband W source.

中文翻译：

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基于X射线传播的相衬成像几何结构的实验优化

具有X射线实验室源的基于传播的相衬成像（PB-PCI）是研究微米级低吸收样品（例如软组织或塑料）的一项强大技术，但通常受其低通量和相干性的限制资源。设置几何形状对于性能至关重要，因为需要权衡取舍，在这种情况下，较短的光源距离会产生较高的对比度-噪声比（CNR），但会产生较低的相对条纹对比度。尽管已经报告了基于菲涅耳传播的理论优化策略，但仍需要对这些模型进行实验测试。在这里，我们使用高分辨率探测器的两种不同设置，系统地研究了这种折衷方案：带有Cu X射线源的定制系统和带有W源的商业系统（Zeiss Xradia）。边缘对比，针对130种不同的放大倍率和总距离，对低吸收率测试样品的CNR和条纹分离进行了测量。我们发现这些品质因数对放大倍数敏感，并且可以找到一个最佳信号，该信号与总的源-探测器距离无关。通常，我们发现理论模型与测量结果显示出极好的一致性。但是，这需要考虑复杂的X射线光谱，特别是对于宽带W源。我们发现理论模型与测量结果显示出极好的一致性。但是，这需要考虑复杂的X射线光谱，特别是对于宽带W源。我们发现理论模型与测量结果显示出极好的一致性。但是，这需要考虑复杂的X射线光谱，特别是对于宽带W源。