Gureyev Timur E, Paganin David M, Quiney Harry M
School of Physics, University of Melbourne, Parkville, Victoria 3010, Australia.
School of Physics and Astronomy, Monash University, Clayton, Victoria 3800, Australia.
J Synchrotron Radiat. 2024 Jul 1;31(Pt 4):896-909. doi: 10.1107/S1600577524003886. Epub 2024 Jun 6.
Signal-to-noise ratio and spatial resolution are quantitatively analysed in the context of in-line (propagation based) X-ray phase-contrast imaging. It is known that free-space propagation of a coherent X-ray beam from the imaged object to the detector plane, followed by phase retrieval in accordance with Paganin's method, can increase the signal-to-noise in the resultant images without deteriorating the spatial resolution. This results in violation of the noise-resolution uncertainty principle and demonstrates `unreasonable' effectiveness of the method. On the other hand, when the process of free-space propagation is performed in software, using the detected intensity distribution in the object plane, it cannot reproduce the same effectiveness, due to the amplification of photon shot noise. Here, it is shown that the performance of Paganin's method is determined by just two dimensionless parameters: the Fresnel number and the ratio of the real decrement to the imaginary part of the refractive index of the imaged object. The relevant theoretical analysis is performed first, followed by computer simulations and then by a brief test using experimental images collected at a synchrotron beamline. More extensive experimental tests will be presented in the second part of this paper.
在在线（基于传播）X射线相衬成像的背景下，对信噪比和空间分辨率进行了定量分析。众所周知，相干X射线束从成像物体自由传播到探测器平面，然后根据帕加宁方法进行相位恢复，可以提高所得图像的信噪比，而不会降低空间分辨率。这导致违反了噪声分辨率不确定原理，并证明了该方法的“不合理”有效性。另一方面，当在软件中使用物平面中检测到的强度分布来执行自由空间传播过程时，由于光子散粒噪声的放大，它无法再现相同的效果。在此表明，帕加宁方法的性能仅由两个无量纲参数决定：菲涅耳数和成像物体折射率的实部衰减与虚部的比值。首先进行相关的理论分析，然后进行计算机模拟，最后使用在同步加速器光束线收集的实验图像进行简要测试。本文的第二部分将展示更广泛的实验测试。
