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Background: Tissue characterization of atherosclerosis by absorption-based imaging methods is limited due to low soft-tissue contrast. Grating-based phase-contrast computed tomography (PC-CT) may become an alternative for plaque assessment if the phase signal can be retrieved at clinically applicable photon energies. The aims of this feasibility study were (i) to characterize arterial vessels at low and high photon energies, (ii) to extract qualitative features and (iii) quantitative phase-contrast Hounsfield units (HU-phase) of plaque components at 53 keV using histopathology as gold standard., Materials and Methods: Five human carotid artery specimens underwent grating-based PC-CT using synchrotron radiation of either 23 keV or 53 keV and histological work-up. Specimens without advanced atherosclerosis were used to extract signal criteria of vessel layers. Diseased specimens were screened for important plaque components including fibrous tissue (FT), lipid (LIP), necrotic core (NEC), intraplaque hemorrhage (IPH), inflammatory cell infiltration (INF) and calcifications (CA). Qualitative features as well as quantitative HU-phase were analyzed., Results: Thirty-three regions in 6 corresponding PC-CT scans and histology sections were identified. Healthy samples had the same signal characteristics at 23 keV and 53 keV with bright tunica intima and adventitia and dark media. Plaque components showed differences in signal intensity and texture at 53 keV. Quantitative analysis demonstrated the highest HU-phase of soft plaque in dense FT. Less organized LIP, NEC and INF were associated with lower HU-phase values. The highest HU-phase were measured in CA., Conclusion: PC-CT of atherosclerosis is feasible at high, clinically relevant photon energies and provides detailed information about plaque structure including features of high risk vulnerable plaques., (Copyright © 2013. Published by Elsevier GmbH.)

Potential applications of grating-based X-ray phase-contrast imaging are investigated in various fields due to its compatibility with laboratory X-ray sources. So far the method was mainly restricted to X-ray energies below 40 keV, which is too low to examine dense or thick objects, but a routine operation at higher energies is on the brink of realisation. In this study, imaging results obtained at 82 keV are presented. These comprise a test object consisting of well-defined materials for a quantitative analysis and a tooth to translate the findings to a biomedical sample. Measured linear attenuation coefficients ? and electron densities ?e are in good agreement with theoretical values. Improved contrast-to-noise ratios were found in phase contrast compared to attenuation contrast. The combination of both contrast modalities further enables to simultaneously assess information on density and composition of materials with effective atomic numbers Z? > 8. In our biomedical example, we demonstrate the possibility to detect differences in mass density and calcium concentration within teeth.

In situ investigations of cracks propagating at up to 2.5 km s-1 along an (001) plane of a silicon single crystal are reported, using X-ray diffraction megahertz imaging with intense and time-structured synchrotron radiation. The studied system is based on the Smart Cut process, where a buried layer in a material (typically Si) is weakened by microcracks and then used to drive a macroscopic crack (10-1 m) in a plane parallel to the surface with minimal deviation (10-9 m). A direct confirmation that the shape of the crack front is not affected by the distribution of the microcracks is provided. Instantaneous crack velocities over the centimetre-wide field of view were measured and showed an effect of local heating by the X-ray beam. The post-crack movements of the separated wafer parts could also be observed and explained using pneumatics and elasticity. A comprehensive view of controlled fracture propagation in a crystalline material is provided, paving the way for the in situ measurement of ultra-fast strain field propagation. [ABSTRACT FROM AUTHOR]

One of the key issues to be resolved to improve the performance of silicon solar cells is to reduce crystalline defect formation and propagation during the growth‐process fabrication step. For this purpose, the generation of structural defects such as grain boundaries and dislocations in silicon must be understood and characterized. Here, in situ X‐ray diffraction imaging, historically named topography, is combined with radiography imaging to analyse the development of crystal defects before, during and after crystallization. Two individual indirect detector systems are implemented to record simultaneously the crystal structure (topographs) and the solid–liquid morphology evolution (radiographs) at high temperature. This allows for a complete synchronization of the images and for an increased image acquisition rate compared with previous studies that used X‐ray sensitive films to record the topographs. The experiments are performed with X‐ray synchrotron radiation at beamline ID19 at the European Synchrotron Radiation Facility. In situ observations of the heating, melting, solidification and holding stages of silicon samples are presented, to demonstrate that with the upgraded setup detailed investigations of time‐dependent phenomena are now possible. The motion of dislocations is recorded throughout the experiment, so that their interaction with grain boundaries and their multiplication through the activation of Frank–Read sources can be observed. Moreover, the capability to record with two camera‐based detectors allows for the study of the relationship between strain distribution, twinning and nucleation events. In conclusion, the simultaneous recording of topographs and radiographs has great potential for further detailed investigations of the interaction and generation of grains and defects that influence the growth process and the final crystalline structure in silicon and other crystalline materials. [ABSTRACT FROM AUTHOR]

This article describes a single-shot methodology to derive an average coating thickness in multi-particle core-shell systems exhibiting high X-ray absorption. Powder composed of U-Mo alloy particles surrounded by a micrometre-thick UO2 protective layer has been used as a test sample. Combining high-energy X-ray diffraction and laser granulometry, the average shell thickness could be accurately characterized. These results have been validated by additional measurements on single particles by two techniques: X-ray nanotomography and high-energy X-ray diffraction. The presented single-shot approach gives rise to many potential applications on core-shell systems and in particular on as-fabricated heterogeneous nuclear fuels. [ABSTRACT FROM AUTHOR]

The ESRF synchrotron beamline ID22, dedicated to hard X-ray microanalysis and consisting of the combination of X-ray fluorescence, X-ray absorption spectroscopy, diffraction and 2D/3D X-ray imaging techniques, is one of the most versatile instruments in hard X-ray microscopy science. This paper describes the present beamline characteristics, recent technical developments, as well as a few scientific examples from recent years of the beamline operation. The upgrade plans to adapt the beamline to the growing needs of the user community are briefly discussed. [ABSTRACT FROM AUTHOR]

Using synchrotron X-ray diffraction, tomography and machine-learning enabled phase segmentation strategy, we have studied under operando conditions the nucleation, co-growth and dynamic interplays among the dendritic and multiple intermetallic phases of a typical recycled Al alloy (Al5Cu1.5Fe1Si, wt.%) in solidification with and without ultrasound. The research has revealed and elucidated the underlying mechanisms that drive the formation of the very complex and convoluted Fe-rich phases with rhombic dodecahedron and 3D skeleton networks (the so-called Chinese-script type morphology). Through statistical microstructural analyses and numerical modelling of the ultrasound melt processing, the research has demonstrated that a short period of ultrasound processing of just 7 s in the liquid state is able to reduce the average size of the α-Al dendrites and the Fe-containing intermetallic phases by ∼5 times compared to the cases without ultrasound. For the first time, this work has revealed fully the nucleation and growth dynamics of the convoluted morphology of the Fe-containing intermetallic phases in 4D domain. The research has also demonstrated clearly the beneficial effects of applying ultrasound to control the Fe phases' morphology in recycled Al alloys and it is one of the most effective and green processing strategies. [Display omitted] [ABSTRACT FROM AUTHOR]

Structure and composition of teeth of the saltwater crocodile Crocodylus porosus were characterized by several high-resolution analytical techniques. X-ray diffraction in combination with elemental analysis and infrared spectroscopy showed that the mineral phase of the teeth is a carbonated calcium-deficient nanocrystalline hydroxyapatite in all three tooth-constituting tissues: Dentin, enamel, and cementum. The fluoride content in the three tissues is very low (<0.1wt.%) and comparable to that in human teeth. The mineral content of dentin, enamel, and cementum as determined by thermogravimetry is 71.3, 80.5, and 66.8wt.%, respectively. Synchrotron X-ray microtomography showed the internal structure and allowed to visualize the degree of mineralization in dentin, enamel, and cementum. Virtual sections through the tooth and scanning electron micrographs showed that the enamel layer is comparably thin (100–200μm). The crystallites in the enamel are oriented perpendicularly to the tooth surface. At the dentin–enamel-junction, the packing density of crystallites decreases, and the crystallites do not display an ordered structure as in the enamel. The microhardness was 0.60±0.05GPa for dentin, 3.15±0.15GPa for enamel, 0.26±0.08GPa for cementum close to the crown, and 0.31±0.04GPa for cementum close to the root margin. This can be explained with the different degree of mineralization of the different tissue types and is comparable with human teeth. [ABSTRACT FROM AUTHOR]

When subjected to plastic deformation, grains within ductile face-centred cubic polycrystals fragment into “soft”, low dislocation density cells separated by “hard”, dislocation-rich walls. Using a narrow-bandwidth, sub-micrometre X-ray beam, we have mapped the deformation structure inside a single grain within a deformed Ni polycrystal. Dislocation multiplication and entanglement was found to vary depending on the physical dimensions of the grain. The method we use overcomes current limitations in classical X-ray topography allowing topographic images to be formed from small, highly deformed grains. [ABSTRACT FROM AUTHOR]