Hrivňak Stanislav, Hovan Andrej, Uličný Jozef, Vagovič Patrik
Department of Biophysics, Faculty of Science, P. J. Šafárik University, Jesenná 5, 04154 Košice, Slovakia.
European XFEL GmbH, Holzkoppel 4, 22869 Schenefeld, Germany.
Biomed Opt Express. 2018 Aug 21;9(9):4390-4400. doi: 10.1364/BOE.9.004390. eCollection 2018 Sep 1.
We present a generalization of the non-iterative phase retrieval in X-ray phase contrast imaging applicable for an arbitrary linear shift-invariant (LSI) imaging system with a non-negligible amount of free space propagation (termed as Fresnel-like). Our novel approach poses no restrictions on the propagation distance between optical elements of the system. In turn, the requirements are only demanded for the transfer function of the optical elements, which should be approximable by second-order Taylor polynomials. Furthermore, we show that the method can be conveniently used as an initial guess for iterative phase retrieval, resulting in faster convergence. The proposed approach is tested on synthetic and experimentally measured holograms obtained using a Bragg magnifier microscope - a representative of Fresnel-like LSI imaging systems. Finally, the algorithm is applied to a whole micro-tomographic scan of a biological specimen of a tardigrade, revealing morphological details at the spatial resolution of 300 nm - limiting resolution of the actual imaging system.
我们提出了一种适用于任意线性平移不变（LSI）成像系统的X射线相衬成像中非迭代相位恢复的推广方法，该系统具有不可忽略的自由空间传播量（称为类菲涅耳）。我们的新方法对系统光学元件之间的传播距离没有限制。反过来，只对光学元件的传递函数有要求，该传递函数应由二阶泰勒多项式近似。此外，我们表明该方法可以方便地用作迭代相位恢复的初始猜测，从而实现更快的收敛。所提出的方法在使用布拉格放大镜显微镜（类菲涅耳LSI成像系统的代表）获得的合成全息图和实验测量全息图上进行了测试。最后，该算法应用于缓步动物生物样本的全微断层扫描，以300nm的空间分辨率揭示形态细节——这是实际成像系统的极限分辨率。
