Showing papers on "Contrast transfer function published in 2023"
TL;DR: In this article , the phase-contrast transfer function (PCTF) modifies the phase contrast because it is not unity over all spatial frequency regions; therefore, the amount of phase modulation observed in the image becomes smaller than the actual value.
TL;DR: In this article , a new method is developed for 3D reconstruction of multi-material objects using propagation-based X-ray phase contrast tomography (PB-CT) with phase retrieval via the contrast transfer function (CTF) formalism.
Abstract: A new method is developed for three-dimensional (3D) reconstruction of multi-material objects using propagation-based X-ray phase-contrast tomography (PB-CT) with phase retrieval via the contrast transfer function (CTF) formalism. The approach differs from conventional PB-CT algorithms that apply phase retrieval on individual two-dimensional (2D) projections. Instead, this method involves performing phase retrieval to the CT-reconstructed volume in 3D. The CTF formalism is further extended to the cases of partially-coherent illumination and strongly absorbing samples. Simulated results demonstrate that the proposed post-reconstruction CTF method provides fast and stable phase retrieval, producing results equivalent to conventional pre-reconstruction 2D CTF phase retrieval. Moreover, it is shown that application can be highly localised to isolated objects of interest, without a significant loss of quality, thus leading to increased computational efficiency. Combined with the extended validity of the CTF to greater propagation distances, this method provides additional advantages over approaches based on the transport-of-intensity equation.
TL;DR: In this article , the authors quantified the differences in signal transfer strength between different phase contrast (PC) methods using contrast transfer function (CTF) theory and two approaches, namely a theoretical approach based on CTF theory and a computational approach using a simulator, have been used to establish several performance indices for evaluating the signal transfer strengths.
Abstract: The aim of this study is to quantify the differences in signal transfer strength between different phase contrast (PC) methods using the contrast transfer function (CTF) theory. For the quantification, two approaches, namely a theoretical approach based on CTF theory and a computational approach using a simulator, have been used to establish several performance indices for evaluating the signal transfer strength. A novel Hilbert PP (HPP) method was proposed to combine images acquired by a symmetrical pair of PPs. The performance indices were evaluated and compared for three PC methods: the novel HPP, the conventional Zernike PP (ZPP), and the Scherzer defocusing method. The results indicate that the three PC methods show similar performance in the high resolution condition, the HPP method outperforms in the medium and low resolution condition, and the ZPP method outperforms in the very low resolution condition.
TL;DR: In this article , different designs for programmable phase plates with the specific goal of correcting spherical aberration in the Transmission Electron Microscope (TEM) have been explored, and different design aspects (fill-factor, pixel pattern, symmetry) were evaluated to understand their effect on the electron probe size and current density.
Abstract: Current progress in programmable electrostatic phase plates raises questions about their usefulness for specific applications. Here, we explore different designs for such phase plates with the specific goal of correcting spherical aberration in the Transmission Electron Microscope (TEM). We numerically investigate whether a phase plate could provide down to 1 $\r{A}$ngstr\"om spatial resolution on a conventional uncorrected TEM. Different design aspects (fill-factor, pixel pattern, symmetry) were evaluated to understand their effect on the electron probe size and current density. Some proposed designs show a probe size ($d_{50}$) down to 0.66$\r{A}$, proving that it should be possible to correct spherical aberration well past the 1\AA~ limit using a programmable phase plate consisting of an array of electrostatic phase shifting elements.