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Phase-Contrast and Dark-Field Imaging

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A special issue of Journal of Imaging (ISSN 2313-433X).

Deadline for manuscript submissions: closed (28 February 2018) | Viewed by 62012

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Special Issue Editor

Dr. Simon Zabler

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Guest Editor

LRM–Lehrstuhl für Röntgenmikroskopie, Chair of X-ray Microscopy, University of Würzburg, 97070 Würzburg, Germany
Interests: X-ray imaging; numerical phase retrieval; micro-CT and nano-CT; signal processing; X-ray scattering; materials science; X-ray detectors; X-ray optics; acoustics
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Special Issue Information

Dear Colleagues,

Phase-contrast and dark-field imaging have been quickly-growing topics in the field of X-ray imaging for the past 15 years, both in medical and in materials communities. More than one hundred X-ray laboratories, and many synchrotron beamlines, are, today, equipped with Talbot-interferometers, Lau-interferometers or Talbot-Lau setups. However, new setups emerge every day, e.g., based on the far-field moiré effect or on transmission X-ray microscopy. Both grating-based differential phase-contrast and dark-field image contrast have been shown to provide answers to formerly unsolvable questions in the field of medical and material imaging, e.g., imaging human lung tissue at the micrometer level or calculating local fiber orientation in carbon fiber composite automotive parts. Meanwhile, tomographic reconstruction and signal processing for these new contrast modes have become vivid fields of research in mathematics and computer science. Optimizing a grating-interferometer for a given task is not an easy task and requires detailed knowledge, both of the imaging physics and of the signal response from the specimen. Furthermore, the production processes for high-aspect optical gratings are presently at their technological limits, which will have to be overcome using entirely new approaches, if we want use DPC and DIC to inspect larger parts, e.g., from aircrafts and cars.

The intent of this Special Issue is to provide a framework where scientists in several different disciplines, related to phase-contrast and dark-field imaging, can find a place to illustrate their ideas and results.

This Special Issue is primarily focused on the following topics; however, we encourage all submissions related to phase-contrast and dark-field imaging in general:

X-ray imaging setups for differential phase-contrast (DPC) and dark-field contrast
Data acquisition schemes
Signal processing of DPC, DIC and possibly higher orders
Volume image reconstruction techniques, in particular non-linear reconstruction
Imaging of anisotropic structures (e.g., fibers or tubes)
Clinical and pre-clinical results from medical scanners
Applications in materials science, biology and geology
Novel production processes for high aspect-ratio gratings and apertures
Fast and ultra-fast DPC and DIC imaging
Comparison between DPC and other phase-contrast methods, e.g., inline p.-c.
Comparison between DIC and (ultra-)small angle X-ray scattering data
Spectral and coherence properties of X-ray beams for phase-contrast and dark-field imaging
Modelling the imaging physics, in particular for dark-field image contrast (DIC)
Direct photon-counting detectors for X-ray phase-contrast and dark-field imaging
Structured anodes and compact light sources for phase-contrast and dark-field imaging

Dr. Simon Zabler
Guest Editor

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Journal of Imaging is an international peer-reviewed open access monthly journal published by MDPI.

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Keywords

Grating-based phase-contrast
Talbot-interferometry
Dark-field image contrast
X-ray scattering
X-ray phase-contrast imaging
Tomographic reconstruction techniques
Signal processing
Medical CT
Industrial CT
Micro computed tomography
X-ray detectors
X-ray optics
X-ray microscopy
X-ray tensor tomography

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Published Papers (9 papers)

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Editorial

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4 pages, 177 KiB

Open AccessEditorial

Phase-Contrast and Dark-Field Imaging

by Simon Zabler

J. Imaging 2018, 4(10), 113; https://doi.org/10.3390/jimaging4100113 - 2 Oct 2018

Cited by 2 | Viewed by 3962

Abstract

Very early, in 1896, Wilhelm Conrad Röntgen, the founding father of X-rays, attempted to measure diffraction and refraction by this new kind of radiation, in vain. Only 70 years later, these effects were measured by Ulrich Bonse and Michael Hart who used them to make full-field images of biological specimen, coining the term phase-contrast imaging. Yet, another 30 years passed until the Talbot effect was rediscovered for X-radiation, giving rise to a micrograting based interferometer, replacing the Bonse–Hart interferometer, which relied on a set of four Laue-crystals for beam splitting and interference. By merging the Lau-interferometer with this Talbot-interferometer, another ten years later, measuring X-ray refraction and X-ray scattering full-field and in cm-sized objects (as Röntgen had attempted 110 years earlier) became feasible in every X-ray laboratory around the world. Today, now that another twelve years have passed and we are approaching the 125th jubilee of Röntgen’s discovery, neither Laue-crystals nor microgratings are a necessity for sensing refraction and scattering by X-rays. Cardboard, steel wool, and sandpaper are sufficient for extracting these contrasts from transmission images, using the latest image reconstruction algorithms. This advancement and the ever rising number of applications for phase-contrast and dark-field imaging prove to what degree our understanding of imaging physics as well as signal processing have advanced since the advent of X-ray physics, in particular during the past two decades. The discovery of the electron, as well as the development of electron imaging technology, has accompanied X-ray physics closely along its path, both modalities exploring the applications of new dark-field contrast mechanisms these days. Materials science, life science, archeology, non-destructive testing, and medicine are the key faculties which have already integrated these new imaging devices, using their contrast mechanisms in full. This special issue “Phase-Contrast and Dark-field Imaging” gives us a broad yet very to-the-point glimpse of research and development which are currently taking place in this very active field. We find reviews, applications reports, and methodological papers of very high quality from various groups, most of which operate X-ray scanners which comprise these new imaging modalities. Full article

(This article belongs to the Special Issue Phase-Contrast and Dark-Field Imaging)

Research

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21 pages, 4819 KiB

Open AccessArticle

Imaging with a Commercial Electron Backscatter Diffraction (EBSD) Camera in a Scanning Electron Microscope: A Review

by Nicolas Brodusch, Hendrix Demers and Raynald Gauvin

J. Imaging 2018, 4(7), 88; https://doi.org/10.3390/jimaging4070088 - 1 Jul 2018

Cited by 28 | Viewed by 8959

Abstract

Scanning electron microscopy is widespread in field of material science and research, especially because of its high surface sensitivity due to the increased interactions of electrons with the target material’s atoms compared to X-ray-oriented methods. Among the available techniques in scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) is used to gather information regarding the crystallinity and the chemistry of crystalline and amorphous regions of a specimen. When post-processing the diffraction patterns or the image captured by the EBSD detector screen which was obtained in this manner, specific imaging contrasts are generated and can be used to understand some of the mechanisms involved in several imaging modes. In this manuscript, we reviewed the benefits of this procedure regarding topographic, compositional, diffraction, and magnetic domain contrasts. This work shows preliminary and encouraging results regarding the non-conventional use of the EBSD detector. The method is becoming viable with the advent of new EBSD camera technologies, allowing acquisition speed close to imaging rates. This method, named dark-field electron backscatter diffraction imaging, is described in detail, and several application examples are given in reflection as well as in transmission modes. Full article

(This article belongs to the Special Issue Phase-Contrast and Dark-Field Imaging)

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13 pages, 3124 KiB

Open AccessArticle

Automated Analysis of Spatially Resolved X-ray Scattering and Micro Computed Tomography of Artificial and Natural Enamel Carious Lesions

by Hans Deyhle, Shane N. White, Lea Botta, Marianne Liebi, Manuel Guizar-Sicairos, Oliver Bunk and Bert Müller

J. Imaging 2018, 4(6), 81; https://doi.org/10.3390/jimaging4060081 - 15 Jun 2018

Cited by 6 | Viewed by 5362

Abstract

Radiography has long been the standard approach to characterize carious lesions. Spatially resolved X-ray diffraction, specifically small-angle X-ray scattering (SAXS), has recently been applied to caries research. The aims of this combined SAXS and micro computed tomography (µCT) study were to locally characterize and compare the micro- and nanostructures of one natural carious lesion and of one artificially induced enamel lesion; and demonstrate the feasibility of an automated approach to combined SAXS and µCT data in segmenting affected and unaffected enamel. Enamel, demineralized by natural or artificial caries, exhibits a significantly reduced X-ray attenuation compared to sound enamel and gives rise to a drastically increased small-angle scattering signal associated with the presence of nanometer-size pores. In addition, X-ray scattering allows the assessment of the overall orientation and the degree of anisotropy of the nanostructures present. Subsequent to the characterization with µCT, specimens were analyzed using synchrotron radiation-based SAXS in transmission raster mode. The bivariate histogram plot of the projected data combined the local scattering signal intensity with the related X-ray attenuation from µCT measurements. These histograms permitted the segmentation of anatomical features, including the lesions, with micrometer precision. The natural and artificial lesions showed comparable features, but they also exhibited size and shape differences. The clear identification of the affected regions and the characterization of their nanostructure allow the artificially induced lesions to be verified against selected natural carious lesions, offering the potential to optimize artificial demineralization protocols. Analysis of joint SAXS and µCT histograms objectively segmented sound and affected enamel. Full article

(This article belongs to the Special Issue Phase-Contrast and Dark-Field Imaging)

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18 pages, 3347 KiB

Open AccessArticle

Optimization Based Evaluation of Grating Interferometric Phase Stepping Series and Analysis of Mechanical Setup Instabilities

by Jonas Dittmann, Andreas Balles and Simon Zabler

J. Imaging 2018, 4(6), 77; https://doi.org/10.3390/jimaging4060077 - 7 Jun 2018

Cited by 16 | Viewed by 4940

Abstract

The diffraction contrast modalities accessible by X-ray grating interferometers are not imaged directly but have to be inferred from sine-like signal variations occurring in a series of images acquired at varying relative positions of the interferometer’s gratings. The absolute spatial translations involved in the acquisition of these phase stepping series usually lie in the range of only a few hundred nanometers, wherefore positioning errors as small as 10 nm will already translate into signal uncertainties of 1–10% in the final images if not accounted for. Classically, the relative grating positions in the phase stepping series are considered input parameters to the analysis and are, for the Fast Fourier Transform that is typically employed, required to be equidistantly distributed over multiples of the gratings’ period. In the following, a fast converging optimization scheme is presented simultaneously determining the phase stepping curves’ parameters as well as the actually performed motions of the stepped grating, including also erroneous rotational motions which are commonly neglected. While the correction of solely the translational errors along the stepping direction is found to be sufficient with regard to the reduction of image artifacts, the possibility to also detect minute rotations about all axes proves to be a valuable tool for system calibration and monitoring. The simplicity of the provided algorithm, in particular when only considering translational errors, makes it well suitable as a standard evaluation procedure also for large image series. Full article

(This article belongs to the Special Issue Phase-Contrast and Dark-Field Imaging)

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6 pages, 644 KiB

Open AccessArticle

Single-Shot X-ray Phase Retrieval through Hierarchical Data Analysis and a Multi-Aperture Analyser

by Marco Endrizzi, Fabio A. Vittoria and Alessandro Olivo

J. Imaging 2018, 4(6), 76; https://doi.org/10.3390/jimaging4060076 - 6 Jun 2018

Cited by 1 | Viewed by 3837

Abstract

A multi-aperture analyser set-up was recently developed for X-ray phase contrast imaging and tomography, simultaneously attaining a high sensitivity and wide dynamic range. We present a single-shot image retrieval algorithm in which differential phase and dark-field images are extracted from a single intensity projection. Scanning of the object is required to build a two-dimensional image, because only one pre-sample aperture is used in the experiment reported here. A pure-phase object approximation and a hierarchical approach to the data analysis are used in order to overcome numerical instabilities. The single-shot capability reduces the exposure times by a factor of five with respect to the standard implementation and significantly simplifies the acquisition procedure by only requiring sample scanning during data collection. Full article

(This article belongs to the Special Issue Phase-Contrast and Dark-Field Imaging)

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7 pages, 8818 KiB

Open AccessArticle

Applications of Laboratory-Based Phase-Contrast Imaging Using Speckle Tracking Technique towards High Energy X-Rays

by Tunhe Zhou, Fei Yang, Rolf Kaufmann and Hongchang Wang

J. Imaging 2018, 4(5), 69; https://doi.org/10.3390/jimaging4050069 - 11 May 2018

Cited by 6 | Viewed by 5121

Abstract

The recently developed speckle-based technique is a promising candidate for laboratory-based X-ray phase-contrast imaging due to its compatibility with polychromatic X-rays, multi-modality and flexibility. Previously, successful implementations of the method on laboratory systems have been shown mostly with energies less than 20 keV on samples with materials like soft tissues or polymer. Higher energy X-rays are needed for penetrating materials with a higher atomic number or that are thicker in size. A first demonstration using high energy X-rays was recently given. Here, we present more potential application examples, i.e., a multi-contrast imaging of an IC chip and a phase tomography of a mortar sample, at an average photon energy of 40 keV using a laboratory X-ray tube. We believe the results demonstrate the applicability of this technique in a wide range of fields for non-destructive examination in industry and material science. Full article

(This article belongs to the Special Issue Phase-Contrast and Dark-Field Imaging)

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14 pages, 6162 KiB

Open AccessArticle

Improved Reconstruction Technique for Moiré Imaging Using an X-Ray Phase-Contrast Talbot–Lau Interferometer

by Maria Seifert, Michael Gallersdörfer, Veronika Ludwig, Max Schuster, Florian Horn, Georg Pelzer, Jens Rieger, Thilo Michel and Gisela Anton

J. Imaging 2018, 4(5), 62; https://doi.org/10.3390/jimaging4050062 - 1 May 2018

Cited by 16 | Viewed by 7851

Abstract

X-ray phase-contrast imaging is a promising method for medical imaging and non-destructive testing. Information about the attenuation, small-angle scattering and phase-shifting properties of an object can be gained simultaneously in three image modalities using a Talbot–Lau interferometer. This is a highly sensitive approach for retrieving this information. Nevertheless, until now, Talbot–Lau interferometry has been a time-consuming process due to image acquisition by phase-stepping procedures. Thus, methods to accelerate the image acquisition process in Talbot–Lau interferometry would be desirable. This is especially important for medical applications to avoid motion artifacts. In this work, the Talbot–Lau interferometry is combined with the moiré imaging approach. Firstly, the reconstruction algorithm of moiré imaging is improved compared to the standard reconstruction methods in moiré imaging that have been published until now. Thus, blurring artifacts resulting from the reconstruction in the frequency domain can be reduced. Secondly, the improved reconstruction algorithm allows for reducing artifacts in the reconstructed images resulting from inhomogeneities of the moiré pattern in large fields of view. Hence, the feasibility of differential phase-contrast imaging with regard to the integration into workflows in medical imaging and non-destructive testing is improved considerably. New fields of applications can be gained due to the accelerated imaging process—for example, live imaging in medical applications. Full article

(This article belongs to the Special Issue Phase-Contrast and Dark-Field Imaging)

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15 pages, 6003 KiB

Open AccessArticle

Non-Destructive Testing of Archaeological Findings by Grating-Based X-Ray Phase-Contrast and Dark-Field Imaging

by Veronika Ludwig, Maria Seifert, Tracy Niepold, Georg Pelzer, Jens Rieger, Julia Ziegler, Thilo Michel and Gisela Anton

J. Imaging 2018, 4(4), 58; https://doi.org/10.3390/jimaging4040058 - 14 Apr 2018

Cited by 23 | Viewed by 7806

Abstract

The analysis of archaeological findings reveals the remaining secrets of human history. However, it is a challenging task to investigate and simultaneously preserve the unique remains. Available non-destructive examination methods are limited and often insufficient. Thus, we considered X-ray grating interferometry as a non-destructive and advanced X-ray imaging method to retrieve more information about archaeological findings. In addition to the conventional attenuation image, the differential phase and the dark-field image are obtained. We studied the potential of the scattering-sensitive dark-field and the phase-shift sensitive differential phase image to analyse archaeological findings. Hereby, the focus lies on organic remnants. Usually, the organic materials have vanished due to decomposition processes, but the structures are often preserved by mineralisation and penetration of corrosion products. We proved that the combination of the attenuation and the dark-field image in particular, enables a separation of structural properties for fabric remnants. Furthermore, we achieved promising results for the reconstruction of sub-pixel sized fibre orientations of woven fabric remnants by employing the directional dark-field imaging method. We conclude from our results that a further application of X-ray dark-field imaging on wet organic findings and on the distinction of different types of organic remnants at archaeological findings is promising. Full article

(This article belongs to the Special Issue Phase-Contrast and Dark-Field Imaging)

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Review

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36 pages, 10943 KiB

Open AccessReview

State of the Art of X-ray Speckle-Based Phase-Contrast and Dark-Field Imaging

by Marie-Christine Zdora

J. Imaging 2018, 4(5), 60; https://doi.org/10.3390/jimaging4050060 - 25 Apr 2018

Cited by 86 | Viewed by 12973

Abstract

In the past few years, X-ray phase-contrast and dark-field imaging have evolved to be invaluable tools for non-destructive sample visualisation, delivering information inaccessible by conventional absorption imaging. X-ray phase-sensing techniques are furthermore increasingly used for at-wavelength metrology and optics characterisation. One of the latest additions to the group of differential phase-contrast methods is the X-ray speckle-based technique. It has drawn significant attention due to its simple and flexible experimental arrangement, cost-effectiveness and multimodal character, amongst others. Since its first demonstration at highly brilliant synchrotron sources, the method has seen rapid development, including the translation to polychromatic laboratory sources and extension to higher-energy X-rays. Recently, different advanced acquisition schemes have been proposed to tackle some of the main limitations of previous implementations. Current applications of the speckle-based method range from optics characterisation and wavefront measurement to biomedical imaging and materials science. This review provides an overview of the state of the art of the X-ray speckle-based technique. Its basic principles and different experimental implementations as well as the the latest advances and applications are illustrated. In the end, an outlook for anticipated future developments of this promising technique is given. Full article

(This article belongs to the Special Issue Phase-Contrast and Dark-Field Imaging)

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