Phase retrieval based on a total‐variation‐regularized Poisson model for X‐ray ptychographic imaging of low‐contrast objects

Hard X‐ray ptychography has become an indispensable tool for observing the microscopic structure of a thick specimen. It measures diffraction patterns by scanning an X‐ray beam and visualizes the complex‐valued refractive index of the specimen by a computational reconstruction called phase retrieval...

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Bibliographic Details
Published in:Journal of applied crystallography Vol. 55; no. 4; pp. 978 - 992
Main Authors: Yatabe, Kohei, Takayama, Yuki
Format: Journal Article
Language:English
Published: 5 Abbey Square, Chester, Cheshire CH1 2HU, England International Union of Crystallography 01.08.2022
Blackwell Publishing Ltd
Subjects:
Algorithms
Computer applications
Computing costs
Diffraction
Diffraction patterns
Frequency dependence
Frequency ranges
hard X‐ray ptychography
Image quality
Image reconstruction
Mathematical models
Phase retrieval
photon noise removal
Refractivity
Silica
total variation
ISSN:1600-5767, 0021-8898, 1600-5767
Online Access:Get full text
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Summary:Hard X‐ray ptychography has become an indispensable tool for observing the microscopic structure of a thick specimen. It measures diffraction patterns by scanning an X‐ray beam and visualizes the complex‐valued refractive index of the specimen by a computational reconstruction called phase retrieval. The quality of imaging is dependent on the used phase‐retrieval algorithm, especially when the intensity of the diffraction patterns in the high‐spatial‐frequency range is low and/or when the spatial overlap of the illumination area is small. In this paper, a phase‐retrieval algorithm, AMPAM, based on the Poisson model and total variation (TV) is proposed. It applies alternating minimization using primal‐dual splitting and gradient‐descent algorithms to compute the result without matrix inversion. The imaging capability of the proposed algorithm from low‐dose and/or sparsely scanned data was investigated by numerical simulations. The proposed algorithm was compared with ADPr, which is the state‐of‐the‐art algorithm based on the TV‐regularized Poisson model. The results indicated that AMPAM can provide good‐quality images with a computational cost 7–11 times less than ADPr. In addition, ink toner and macroporous silica particles were imaged at SPring‐8 BL24XU to confirm the applicability of the algorithm to actual measurements. This paper presents a phase‐retrieval algorithm for ptychography, named AMPAM. The imaging capability of AMPAM was investigated by numerical simulations and measurements performed at SPring‐8.
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ISSN:1600-5767
0021-8898
1600-5767
DOI:10.1107/S1600576722005234