Microstructured foams are emerging as a promising class of targets, with applications ranging from laser-driven particle acceleration to inertial confinement fusion. To unlock their full potential, a deeper understanding of their properties, especially the changes and behavior of the microstructure under extreme conditions, is required. While recently advancing 3D printed foam targets can be observed by X-ray radiography, the microstructure in chemically produced targets is far below the spatial resolution of conventional radiography. To overcome this limitation, we apply grating-based X-ray dark-field imaging to observe structural changes in foams that are rapidly heated by laser-accelerated proton pulses. The experimental data is compared to synthetic dark-field values obtained from hydrodynamic simulations of a simplified foam model. Both experimental and simulation results demonstrate the viability of utilizing grating-based dark-field imaging for observing microstructural changes in foam targets.

High-quality x-ray absorption gratings are essential for grating-based x-ray phase-contrast imaging. Bidirectional angular x-ray transmission (AXT) measurements, as proposed in this work, allow for large-area and nondestructive characterization of these gratings. A custom setup consisting of two rotational axes is used to measure the transmission of x-ray absorption gratings under rotation. From the transmission values and rotation angles, pixelwise transmission profiles are reconstructed. From these transmission profiles, parameter maps that carry information about the microstructure of the grating are retrieved via a fitting procedure. Compared to unidirectional AXT measurements, more detailed and complementary parameter maps are obtained, revealing more defects and parameter variations. Apart from duty cycle, absorber height, and absorber inclination, the bidirectional measurements also provide access to grating lamella rotation on the substrate and to auxiliary structures introduced to increase grating stability. Furthermore, a novel correction technique is introduced to address projective distortions in individual radiographs caused by the rotations. This method relies on calibration phantom measurements to track the movement of registration points under the same rotations as the gratings. Based on the movement of the registration points, the distortions are reconstructed, and appropriate deformation vector fields are calculated and applied to measurement data, achieving a correction with a precision of about two pixels.

Single-shot X-ray phase-contrast imaging is used to take high-resolution images of laser-driven strong shock waves. Employing a two-grating Talbot interferometer, we successfully acquire standard absorption, differential phase-contrast, and dark-field images of the shocked target. Good agreement is demonstrated between experimental data and the results of two-dimensional radiation hydrodynamics simulations of the laser–plasma interaction. The main sources of image noise are identified through a thorough assessment of the interferometer’s performance. The acquired images demonstrate that grating-based phase-contrast imaging is a powerful diagnostic tool for high-energy-density science. In addition, we make a novel attempt at using the dark-field image as a signal modality of Talbot interferometry to identify the microstructure of a foam target.

X-ray Talbot and Talbot-Lau interferometers consisting of transmission gratings are widely used for X-ray phase imaging, which depicts soft materials. This study exploits the use of a pair of concave and convex parabolic gratings instead of a conventional rectangular phase grating to enhance the phase signal optically. To gain insight into the optimal design, signal enhancement is evaluated by directly measuring the self-image formed downstream of the pair. An increase in the differential phase signals is demonstrated as a function of the distance between the pair, and prospects for deploying this concept into a practical phase imaging technique are discussed.

Grating-based X-ray phase-contrast and in particular dark-field radiography are promising new imaging modalities for medical applications. Currently, the potential advantage of dark-field imaging in early-stage diagnosis of pulmonary diseases in humans is being investigated. These studies make use of a comparatively large scanning interferometer at short acquisition times, which comes at the expense of a significantly reduced mechanical stability as compared to tabletop laboratory setups. Vibrations create random fluctuations of the grating alignment, causing artifacts in the resulting images. Here, we describe a novel maximum likelihood method for estimating this motion, thereby preventing these artifacts. It is tailored to scanning setups and does not require any sample-free areas. Unlike any previously described method, it accounts for motion in between as well as during exposures.

A problem with high aspect ratio x-ray gratings, fabricated by the deep x-ray LIGA process, is the collapse of the metallic structure when the resist is removed. A unique method that consists of positioning perpendicular metal bridges on top of the grating (roof bridges) is described and tested as a solution. First, a theoretical study is carried out on the transmission loss of such grids as a function of the thickness, their spacing, their materials (gold or nickel), and the x-ray energy. Different processes with their own advantages and disadvantages are possible and described. To further satisfy the requirement of curved gratings, two processes are tested in detail: structuring the x-ray grating with a laser and planarization followed by restructuring a second resist layer. In both cases, a second electroplating step is performed. Finally, a grating with a 12 cm bending radius and stabilization is fabricated. To assess the quality of the grids, two complementary methods are used: scanning electron microscopy and angular x-ray transmission. The latter one is an innovatively developed measurement process specially dedicated to x-ray gratings. The results for the fabrication processes are discussed and rated. The stability provided by the roof bridges works as intended, although the overall quality of the grating is slightly reduced. (c) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 International License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

In grating-based X-ray Talbot interferometry, the wave nature of X-ray radiation is exploited to generate phase contrast images of objects that do not generate sufficient contrast in conventional X-ray imaging relying on X-ray absorption. The phase sensitivity of this interferometric technique is proportional to the interferometer length and inversely proportional to the period of gratings. However, the limited spatial coherency of X-rays limits the maximum interferometer length, and the ability to obtain smaller-period gratings is limited by the manufacturing process. Here, we propose a new optical configuration that employs a combination of a converging parabolic micro-lens array and a diverging micro-lens array, instead of a binary phase grating. Without changing the grating period or the interferometer length, the phase signal is enhanced because the beam deflection by a sample is amplified through the array of converging-diverging micro-lens pairs. We demonstrate that the differential phase signal detected by our proposed set-up is twice that of a Talbot interferometer, using the same binary absorption grating, and with the same overall inter-grating distance.

Zielsetzung Die Dunkelfeldbildgebung mit Röntgenstrahlen ist ein neuartiges interferometrisches Verfahren, das eine Visualisierung der Alveolarstruktur ermöglicht. Im klinischen Kontext ist das Verfahren bislang auf radiographische Anwendungen beschränkt und konnte noch nicht für CT Bildgebung umgesetzt werden. In ersten Studien konnte bereits gezeigt werden, dass die Dunkelfeld-Bildgebung des Thorax konventionelle Radiographie ergänzt und verbessert. Ziel dieser technischen Machbarkeitsstudie ist es daher, einen Dunkelfeld-CT-Prototyp für Thorax Scans zu entwickeln. Für einen potentiellen klinischen Einsatz muss ein solcher Scanner dosiskompatible und schnelle Messungen im Sekundenbereich ermöglichen.

X-ray computed tomography (CT) is one of the most commonly used three-dimensional medical imaging modalities today. It has been refined over several decades, with the most recent innovations including dual-energy and spectral photon-counting technologies. Nevertheless, it has been discovered that wave-optical contrast mechanisms-beyond the presently used X-ray attenuation-offer the potential of complementary information, particularly on otherwise unresolved tissue microstructure. One such approach is dark-field imaging, which has recently been introduced and already demonstrated significantly improved radiological benefit in small-animal models, especially for lung diseases. Until now, however, dark-field CT could not yet be translated to the human scale and has been restricted to benchtop and small-animal systems, with scan durations of several minutes or more. This is mainly because the adaption and upscaling to the mechanical complexity, speed, and size of a human CT scanner so far remained an unsolved challenge. Here, we now report the successful integration of a Talbot-Lau interferometer into a clinical CT gantry and present dark-field CT results of a human-sized anthropomorphic body phantom, reconstructed from a single rotation scan performed in 1 s. Moreover, we present our key hardware and software solutions to the previously unsolved roadblocks, which so far have kept dark-field CT from being translated from the optical bench into a rapidly rotating CT gantry, with all its associated challenges like vibrations, continuous rotation, and large field of view. This development enables clinical dark-field CT studies with human patients in the near future.

X-ray phase imaging with grating interferometers, such as the Talbot interferometer, is widely performed even with a laboratory X-ray source. However, the achievable spatial resolution is normally limited by the period of gratings. In this work, two laboratory-based apparatuses are developed to overcome the constraint of the spatial resolution. One is the combination of a commercially available FZP-based X-ray imaging microscope and Lau interferometer optics. The two-step deconvolution approach is explained to attain phase tomography. The other is a sub-period super-resolution X-ray phase imaging, which is based on the sample-scanning scheme across the beamlet array formed by a triangular phase grating. A proof-of-concept result of the super-resolution approach is presented.

In our work, we evaluated the effective dose values for first clinical dark-field chest radiography, both for examinations of the reference person and a certain patient collective consisting of 92 patients. Unfortunately, the histogram in Figure 4 consists of more patients than introduced in the running text, as more of the participants in the ongoing studies were mistakenly included. In the published Figure 4, instead of data points of 92 patients, data points of additional patients are included. This changes the mean value, as indicated by a dashed line, from 38.7 μGy (correct value as given in Figure legend and running text) to 41.1 μGy (as depicted in published Figure 4). The corrected version can be found in the attached Figure 1. Figure legend is not subject to change. Please note that this does not change the message of the paper. All dose values in the running text and figure legends are correct. The reported effective dose value for the reference person is correct. The reported effective dose values for the first 92 patients are correct. Even by including more patients, the recorded mean value is below the reference value, therefore we fulfill the legal requirements regarding the local diagnostic reference level (DRL).

We describe the rationale for selecting graphite as a substrate material suitable for manufacturing curved high-aspect ratio metallic x-ray gratings and experimentally validate that its properties satisfy requirements relevant for clinical phase-contrast and dark-field x-ray imaging. Selection criteria applied to two candidate materials graphite and polyimide were compliance to bending, mechanical tenacity of the attachment of the lamellar grating structure to the substrate, the substrate material's x-ray robustness, and the compatibility with the x-ray LIGA process used to manufacture the grating structures. In contrast to other standard materials such as silicon wafers with titanium layer, graphite wafers could be bent to smaller radii and are natively electrically conductive. While polyimide wafers allowed for even smaller bending radii, we found their high risk of grating structure detachment to be a strong detractor. Minimum achievable bending radii were 55 and 70 mm for pure graphite wafers and graphite wafers with mounted grating structure, respectively. Electron microscopy of graphite surface and cross-sections revealed a fine porous structure conducting to a very stable metal-wafer interface. Grating structures with heights of more than 200 mu m were bonded to graphite wafers and their integrity confirmed in flat as well as in bent state using microfocus x-ray imaging. We conclude that graphite is a very well-suited substrate material for manufacturing curved x-ray gratings. (c) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 International License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Imaging of the focal spot size in X-ray generators can be achieved by means of a pinhole in a highly attenuating material, such as gold. For microfocus generators with spot sizes of only around 10 microns or less, the material must be very thin to avoid an impractical aspect ratio. With a 90 kV source, only 11% attenuation is attained with 5 µm gold. For a pinhole that is smaller than the focal spot, the signal-to-noise ratio (SNR) may be less than 1. To image the focal spot of a medical X-ray generator, a coded aperture has been used previously to reduce the exposure time required, however the same technique does not appear to have been used to increase the SNR when the attenuation is very low. Such a method is used here, using a no-two-holes-touching variation of a modified uniformly redundant array (MURA). In a prototype sample, with only 5 µm gold having 2.75 µm holes, the focal spot of a microfocus X-ray generator used in a micro-CT system could be clearly visualised and quantified. Directionality of the aberrations made focussing of the X-ray spot more intuitive and reduced the time required to obtain an optimal, quantifiable focus.

The advent of hard X-ray free-electron lasers enables nanoscopic X-ray imaging with sub-picosecond temporal resolution. X-ray grating interferometry offers a phase-sensitive full-field imaging technique where the phase retrieval can be carried out from a single exposure alone. Thus, the method is attractive for imaging applications at X-ray free-electron lasers where intrinsic pulse-to-pulse fluctuations pose a major challenge. In this work, the single-exposure phase imaging capabilities of grating interferometry are characterized by an implementation at the I13-1 beamline of Diamond Light Source (Oxfordshire, UK). For comparison purposes, propagation-based phase contrast imaging was also performed at the same instrument. The characterization is carried out in terms of the quantitativeness and the contrast-to-noise ratio of the phase reconstructions as well as via the achievable spatial resolution. By using a statistical image reconstruction scheme, previous limitations of grating interferometry regarding the spatial resolution can be mitigated as well as the experimental applicability of the technique.

Grating-based x-ray dark-field and phase-contrast imaging allow extracting information about refraction and small-angle scatter, beyond conventional attenuation. A step towards clinical translation has recently been achieved, allowing further investigation on humans. After the ethics committee approval, we scanned the full body of a human cadaver in anterior-posterior orientation. Six measurements were stitched together to form the whole-body image. All radiographs were taken at a three-grating large-object x-ray dark-field scanner, each lasting about 40 s. Signal intensities of different anatomical regions were assessed. The magnitude of visibility reduction caused by beam hardening instead of small-angle scatter was analysed using different phantom materials. Maximal effective dose was 0.3 mSv for the abdomen. Combined attenuation and dark-field radiography are technically possible throughout a whole human body. High signal levels were found in several bony structures, foreign materials, and the lung. Signal levels were 0.25 ± 0.13 (mean ± standard deviation) for the lungs, 0.08 ± 0.06 for the bones, 0.023 ± 0.019 for soft tissue, and 0.30 ± 0.02 for an antibiotic bead chain. We found that phantom materials, which do not produce small-angle scatter, can generate a strong visibility reduction signal. We acquired a whole-body x-ray dark-field radiograph of a human body in few minutes with an effective dose in a clinical acceptable range. Our findings suggest that the observed visibility reduction in the bone and metal is dominated by beam hardening and that the true dark-field signal in the lung is therefore much higher than that of the bone.

Owing to the development of X-ray focusing optics during the past decades, synchrotron-based X-ray microscopy techniques allow the study of specimens with unprecedented spatial resolution, down to 10 nm, using soft and medium X-ray photon energies, though at the expense of the field of view (FOV). One of the approaches to increase the FOV to square millimetres is raster-scanning of the specimen using a single nanoprobe; however, this results in a long data acquisition time. This work employs an array of inclined biconcave parabolic refractive multi-lenses (RMLs), fabricated by deep X-ray lithography and electroplating to generate a large number of long X-ray foci. Since the FOV is limited by the pattern height if a single RML is used by impinging X-rays parallel to the substrate, many RMLs at regular intervals in the orthogonal direction were fabricated by tilted exposure. By inclining the substrate correspondingly to the tilted exposure, 378000 X-ray line foci were generated with a length in the centimetre range and constant intervals in the sub-micrometre range. The capability of this new X-ray focusing device was first confirmed using ray-tracing simulations and then using synchrotron radiation at BL20B2 of SPring-8, Japan. Taking account of the fact that the refractive lens is effective for focusing high-energy X-rays, the experiment was performed with 35 keV X-rays. Next, by scanning a specimen through the line foci, this device was used to perform large FOV pixel super-resolution scanning transmission hard X-ray microscopy (PSR-STHXM) with a 780 ± 40 nm spatial resolution within an FOV of 1.64 cm × 1.64 cm (limited by the detector area) and a total scanning time of 4 min. Biomedical implant abutments fabricated via selective laser melting using Ti–6Al–4V medical alloy were measured by PSR-STHXM, suggesting its unique potential for studying extended and thick specimens. Although the super-resolution function was realized in one dimension in this study, it can be expanded to two dimensions by aligning a pair of presented devices orthogonally.

X-ray backlighters allow the capture of sharp images of fast dynamic processes due to extremely short exposure times. Moiré imaging enables simultaneously measuring the absorption and differential phase-contrast (DPC) of these processes. Acquiring images with one single shot limits the X-ray photon flux, which can result in noisy images. Increasing the photon statistics by repeating the experiment to gain the same image is not possible if the investigated processes are dynamic and chaotic. Furthermore, to reconstruct the DPC and transmission image, an additional measurement captured in absence of the object is required. For these reference measurements, shot-to-shot fluctuations in X-ray spectra and a source position complicate the averaging of several reference images for noise reduction. Here, two approaches of processing multiple reference images in combination with one single object image are evaluated regarding the image quality. We found that with only five reference images, the contrast-to-noise ratio can be improved by approximately 13% in the DPC image. This promises improvements for short-exposure single-shot acquisitions of rapid processes, such as laser-produced plasma shock-waves in high-energy density experiments at backlighter X-ray sources such as the PHELIX high-power laser facility.

Abstract. Background: X-ray grating interferometry is an emerging imaging technique that strongly relies on fine grating structures. A common method to fabricate compatible gratings is deep x-ray lithography (DXRL). Aim: To develop a method to fabricate grating structures by DXRL, which does not require a synchrotron source. Approach: The synchrotron source is replaced by a conventional x-ray tube. The fabrication process is adapted for the divergent beam by cylindrically bending mask and substrate. Results: A 10-μm period absorption grating with 80-μm-thick gold lamellae is successfully fabricated from an intermediate 110-μm high structured resist. This grating is characterized and implemented in a preclinical Talbot-Lau interferometer designed for medical thorax imaging. Conclusion: This approach can overcome the strong dependence on synchrotron facilities for the fabrication of gratings for x-ray grating interferometry. As x-ray tubes are more widely available, this is a cost-efficient and scalable alternative suitable for industrial production.

Einführung: Eine Röntgenaufnahme wird häufig für die initiale Untersuchung oder zur Verlaufsbeurteilung des Thorax angewandt. Die Erkennung von strukturellen Schäden, insbesondere bei frühen Formen, ist jedoch begrenzt. Die Dunkelfeldtechnik (X-ray dark-field imaging, XDF) ermöglich die Erfassung von kohärenter Kleinwinkelstreuung, wodurch Dichtefluktuationen wie z. B. an den Alveolarmembranen sichtbar werden. Durch diese Studie sollen die ersten Eindrücke mit dieser neuen Technik vorgestellt werden.