Single-distance phase retrieval algorithm for Bragg Magnifier microscope

Abstract

We present an improved, single-distance phase retrieval algorithm applicable for holographic X-ray imaging of biological objects for an in-line germanium Bragg Magnifier Microscope (BMM). The proposed algorithm takes advantage of a modified shrink-wrap algorithm for phase objects, robust unwrapping algorithm as well as other reasonable constraints applied to the wavefield at the object and the detector plane. The performance of the algorithm is analyzed on phantom objects and the results are shown and discussed. We demonstrated the suitability of the algorithm for the phase retrieval on a more complex biological specimen Tardigrade, where we achieved successful phase retrieval from only a single hologram. The spatial resolution obtained by Fourier spectral power method for biological objects is ∼ 300 nm, the same value as obtained from the reconstructed test pattern. Our results achieved using the new algorithm confirmed the potential of BMM for in-vivo, dose-efficient single-shot imaging of biological objects.

Fast Fresnel propagation through a set of inclined reflecting planes applicable for X-ray imaging

“…(8) can be easily modified to account for all the free space propagations present, as well as the crystal transfer functions (see e.g. in [3]). This way, similarly as for the RCT method, the computational demands are practically independent of the number of crystals.…”

“…Various solutions to this problem have been suggested. In Chapter 2, we present two standard approaches for comparison: one optimizing for speed but with limited accuracy (used in [3,4]), and one exact treatment using heavy computational demands (used e.g. in [5]).…”

“…The application of our method is readily found in the fast and accurate forward and backward propagation through the Bragg magnifier [9], which consists of 2 or 4 crystals (reflecting planes) yielding magnified image in both directions by means of asymmetrical Bragg diffraction. Our developed method is intended to be used for phase retrieval of the X-ray images obtained by Bragg magnifier in microtomographic measurements [3,10]. Since our primary motivation is focused on the X-ray wave propagation, the inclined reflecting planes will be from now on referred to as crystals, although they are not the only possible application.…”

Subsampled phase retrieval for temporal resolution enhancement in lensless on-chip holographic video

“…Larger pixels will not only encounter aliasing issues, but also fail to realize the goal of SPR: to rely more upon the estimated sample support during image reconstruction by leaving a large fraction of hologram values unconstrained. Compared to previous interpolation schemes [17,[37][38][39], the important differentiation of SPR is that: 1) the interpolation is in a transform domain (i.e., Fresnel Transform), and 2) interpolation is achieved via constrained alternating minimization, as opposed to local neighborhood operations on each pixel. The support constraint at the sample plane is vital for filling in both the unknown amplitude and phase of the intermediately empty hologram pixels (i.e., filling in the white pixels in Fig.…”

“…Unlike traditional video, however, the operation of a lensless holographic setup is fundamentally connected to its phase-retrieval algorithm. An ideal strategy to improve lensless image readout rates would operate in tandem with phase retrieval [17]. As with the compressive video recovery schemes above, phase retrieval must also assume some prior knowledge about the imaged sample to ensure accurate algorithm convergence.…”