Contrast transfer function

About: Contrast transfer function is a research topic. Over the lifetime, 934 publications have been published within this topic receiving 26533 citations.

Effect of spherical aberration in tight focusing of azimuthally polarized double ring shaped beam

Abstract: The dark core of a tightly focused azimuthally polarized beam is studied in the presence of third-order spherical aberration, using vectorial Debye-Wolf integral. Compensation for the effect of spherical aberration has been studied in the presence of defocusing. The Effect of spherical aberration on the intensity distribution can be compensated by choosing a proper value of defocusing, and this compensation generates the focal hole as same size (FWHM) and shape almost equal for the aberration free cases however it takes focal shift along the optical axis. Some results are also presented for the influence of truncation parameter of the beam, on the point spread function at different observation planes. The author expects such investigation is worthwhile for optical manipulation and material processing technologies.

Introducing the holo-TIE approach to cellular imaging.

Abstract: In this issue of Acta Crystallographica Section A, a significant advance in full-field X-ray imaging of biological samples is reported by workers from Tim Salditt’s group at GeorgAugust-University in Göttingen (Krenkel et al., 2017). Their holographic regime method, which they call the holo-TIE approach, is a significant improvement of the classical ‘transport of intensity’ (TIE) method of Paganin & Nugent (1998). Following the original development of Cloetens et al. (1999), the work described by Krenkel et al. combines data measured at multiple detector distances to fill gaps of missing frequencies in the contrast-transfer function. This idea is presented and justified using the language of variation of Fresnel numbers. The results also clearly show the respective advantages of different staining strategies relevant to biological imaging, where both resolution and contrast are key metrics. In X-ray imaging science, ‘resolution’ is defined as the highest spatial frequency capable of being measured by the instrument, limited by the solid angle passed by some aperture or by the detector, for example. The ‘contrast’, on the other hand, is a property of the sample, measured in an analogous way to the presence of density (or phase) modulations of a given spatial frequency within the sample. Both the instrument and the sample have to deliver this level of performance in order for the resulting image to contain the fine features needed for biological interpretation. In the current work, reporting holo-TIE imaging of mouse macrophage cells (Krenkel et al., 2017), OsO4 was found to create a uniform background that identifies only the approximate shape of the cytoplasm-filled regions, while BaSO4 particles were found to stand out nicely. However, while the BaSO4 particles are seen with high resolution, they are markers that may or may not report on the biological state of the sample, depending on the method of attachment and introduction to the cells. Observing the markers with high resolution does not necessarily mean that the biological functions are determined with the same level of detail.

Three-dimensional contrast-transfer-function approach in phase-contrast tomography

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.

Physical simulation system for studying contrast transfer function of remote sensor

Abstract: Studying the characteristics of target and background is very important to determine the parameters of the remote sensor and the light condition. We have established a physical simulation system for studying the contrast transfer function (CTF), allowing us to change light condition; camera parameters, such as relative aperture, TDI factor, incline angle; the target and background. We measured the CTF with different target and background, and compared the results with calculated CTF.

Aberration Correction Based on Focus Modulation Transmission Electron Microscopy and its Applications

Abstract: Three techniques of wave field reconstruction using focus modulation transmission electron microscopy are reviewed based on a fundamental concept of three-dimensional optical transfer properties. These techniques use a set of through-focus images for the processing and enable not only correction of spherical aberration but also separate imaging of the phase and amplitude components of the sample. Defocus-image modulation processing enables real-time correction of spherical aberration by combining techniques such as high-speed control of focus and high-speed image processing. Three-dimensional Fourier filtering enables correction of all Seidel aberrations including spherical aberration and higher-order aberrations with high signal-to-noise ratios. Dynamic hollow-cone illumination combined with image processing using Fourier filtering has the possibility of reducing the degradation of spatial resolution caused by chromatic aberration. Experimental data obtained by these methods are presented describing the inherent characteristics of the respective methods.