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引用次数: 0
摘要
对在线(基于传播)X 射线相位对比成像的信噪比和空间分辨率进行了定量分析。众所周知,相干 X 射线光束从成像物体到探测器平面的自由空间传播,然后按照帕加宁方法进行相位检索,可以在不降低空间分辨率的情况下提高成像结果的信噪比。这就违反了噪声分辨率不确定性原理,证明了该方法 "不合理 "的有效性。另一方面,如果在软件中使用检测到的物体平面上的强度分布来执行自由空间传播过程,则由于光子射出噪声的放大,无法再现同样的效果。这里的研究表明,帕加宁方法的性能仅由两个无量纲参数决定:菲涅尔数和成像物体折射率的实减与虚部之比。首先进行相关的理论分析,然后进行计算机模拟,最后利用同步辐射光束线收集的实验图像进行简要测试。本文的第二部分将介绍更广泛的实验测试。
Signal-to-noise and spatial resolution in in-line imaging. 1. Basic theory, numerical simulations and planar experimental images.
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.
期刊介绍:
Synchrotron radiation research is rapidly expanding with many new sources of radiation being created globally. Synchrotron radiation plays a leading role in pure science and in emerging technologies. The Journal of Synchrotron Radiation provides comprehensive coverage of the entire field of synchrotron radiation and free-electron laser research including instrumentation, theory, computing and scientific applications in areas such as biology, nanoscience and materials science. Rapid publication ensures an up-to-date information resource for scientists and engineers in the field.