Alexander Rack

ANKAphase: software for single-distance phase retrieval from inline X-ray phase-contrast radiographs.

A computer program named ANKAphase is presented that processes X-ray inline phase-contrast radiographs by reconstructing the projected thickness of the object(s) imaged. The program uses a single-distance non-iterative phase-retrieval algorithm described by David Paganin et al. [(2002), J. Microsc. 206, 33-40]. Allowing for non-negligible absorption in the sample, this method is strictly valid only for monochromatic illumination and single-material objects but tolerates deviations from these conditions, especially polychromaticity. ANKAphase is designed to be applied to tomography data (although it does not perform tomographic reconstruction itself). It can process series of images and perform flat-field and dark-field correction. Written in Java, ANKAphase has an intuitive graphical user interface and can be run either as a stand-alone application or as a plugin to ImageJ, a widely used scientific image-processing program. A description of ANKAphase is given and example applications are shown.

Status of the hard X-ray microprobe beamline ID22 of the European Synchrotron Radiation Facility

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.

LSO-Based Single Crystal Film Scintillator for Synchrotron-Based Hard X-Ray Micro-Imaging

X-ray detector systems are powerful tools: in combination with tomographic methods they provide volumetric data of samples in a non-destructive manner which is of high interest for, e.g., biology, medicine or materials research. The detector able to provide images with submicrometer spatial resolution frequently consists of a scintillator screen, light microscopy optics and a digital camera. Here, the scintillator converts the X-rays into a visible light image which is projected onto the camera by the light optics. In order to perform high resolution imaging Single Crystal Film (SCF) scintillators 1 mum to 30 mum thin are required due to the limited depth of focus of the microscopy optics. Thin SCFs can be obtained via liquid phase epitaxy (LPE). A drawback is that a detector working with SCFs suffers from low efficiency (2% at 50 keV) owing to their limited thickness. The detective quantum efficiency (DQE) is here mainly limited by the low absorption of X-rays and the light yield in the thin scintillator layer. Performances, i.e absorption, light yield, afterglow of operational systems at the European Synchrotron Radiation Facility (ESRF) using YAG:Ce (Y3Al5O12:Ce), LAG:Eu (Lu3Al5O12:Eu) and GGG:Eu (Gd3Ga5O12:Eu) scintillators will be presented and compared to new LSO:Tb (Lu2SiO5:Tb) scintillators developed in the framework of an European project , . A new concept to improve the efficiency of detection in the 20 keV - 40 keV energy range with 1 mum spatial resolution will be presented. This concept based on multilayer scintillators is realised by the LPE process as well. First results will be illustrated with X-ray images and will demonstrate the absorption efficiency improvement of the X-ray detector. The expected performance is 7 times better than the LAG-based scintillators.

Effect of β-tricalcium phosphate particles with varying porosity on osteogenesis after sinus floor augmentation in humans

This study examines the effect of two beta-tricalcium phosphate (TCP) particulate bone grafting materials with varying porosity on bone formation and on osteogenic marker expression 6 months after sinus floor augmentation. Unilateral sinus grafting was performed in 20 patients using a combination (4:1 ratio) of beta-TCP particles with 35% porosity (TCP-C) or 65% porosity (TCP-CM) and autogenous bone chips. At implant placement cylindrical biopsies were sampled and processed for immunohistochemical analysis of resin embedded sections. Sections were stained for collagen type I (Col I), alkaline phosphatase (ALP), osteocalcin (OC) and bone sialoprotein (BSP). Furthermore, the area fraction of newly formed bone as well as the particle area fraction were determined histomorphometrically first, apically close to the Schneiderian membrane and second, in the center of the cylindrical biopsies. In the TCP-CM patient group a larger amount of bone formation and particle degradation was observed in the apical area and thus at the largest distance from the crestal bone compared to the TCP-C group. Good bone bonding behaviour was observed with both materials. This was accompanied by expression of ALP, Col I, BSP and OC in the newly formed bone and osteogenic mesenchym in contact with the degrading particles. Both TCP materials supported bone formation in the augmented sinus floor. Six months after implantation of both types of beta-TCP particles, bone formation and matrix mineralization was still actively progressing in the tissue surrounding the particles. Consequently, a greater porosity appears to be advantageous for enhancing bone formation and particle degradation.

In situ investigation of the discharge of alkaline Zn–MnO2 batteries with synchrotron x-ray and neutron tomographies

Zn–MnO2 alkaline batteries were investigated in situ at different stages of electric discharge by synchrotron tomography with monochromatic x rays and by neutron tomography. The spatial distribution and the changes in the morphology of different components of a battery caused by the reduction of MnO2, the dissolution of Zn, and the nucleation and growth of ZnO are investigated with high spatial resolution around several micrometers with x rays. Neutron tomography is used to monitor the changes in the spatial distribution of hydrogen in the MnO2 matrix and provides complementary information about the process.

Trimodal low-dose X-ray tomography

X-ray grating interferometry is a coherent imaging technique that bears tremendous potential for three-dimensional tomographic imaging of soft biological tissue and other specimens whose details exhibit very weak absorption contrast. It is intrinsically trimodal, delivering phase contrast, absorption contrast, and scattering (“dark-field”) contrast. Recently reported acquisition strategies for grating-interferometric phase tomography constitute a major improvement of dose efficiency and speed. In particular, some of these techniques eliminate the need for scanning of one of the gratings (“phase stepping”). This advantage, however, comes at the cost of other limitations. These can be a loss in spatial resolution, or the inability to fully separate the three imaging modalities. In the present paper we report a data acquisition and processing method that optimizes dose efficiency but does not share the main limitations of other recently reported methods. Although our method still relies on phase stepping, it effectively uses only down to a single detector frame per projection angle and yields images corresponding to all three contrast modalities. In particular, this means that dark-field imaging remains accessible. The method is also compliant with data acquisition over an angular range of only 180° and with a continuous rotation of the specimen.

Why are metal foams stable

Although metal foams are becoming accepted engineering materials, the reason for their stability in the liquid state is still under dispute. Liquid metal foams contain solid constituents which according to the existing models stabilize foam films by either modifying the curvature of the liquid/gas (L∕G) interfaces, or by forming particle bridges across metallic films and transmitting repulsive “disjoining” forces mechanically. Using high-resolution synchrotron tomography and a quantitative three-dimensional image analysis the authors show that there is little evidence for such curvature changes or particle bridges. The authors conclude that the main stabilizing action must be due to interactions between neighboring particles attached to L∕G interfaces.

Comparative study of multilayers used in monochromators for synchrotron-based coherent hard X-ray imaging

A systematic study is presented in which multilayers of different composition (W/Si, Mo/Si, Pd/B(4)C), periodicity (from 2.5 to 5.5 nm) and number of layers have been characterized. In particular, the intrinsic quality (roughness and reflectivity) as well as the performance (homogeneity and coherence of the outgoing beam) as a monochromator for synchrotron radiation hard X-ray micro-imaging are investigated. The results indicate that the material composition is the dominating factor for the performance. By helping scientists and engineers specify the design parameters of multilayer monochromators, these results can contribute to a better exploitation of the advantages of multilayer monochromators over crystal-based devices; i.e. larger spectral bandwidth and high photon flux density, which are particularly useful for synchrotron-based micro-radiography and -tomography.

Fast processes in liquid metal foams investigated by high-speed synchrotron x-ray microradioscopy

Rupture of an individual film in an evolving liquid metal foam is investigated by means of high-speed x-ray radioscopy using white synchrotron radiation. At a frame rate of 5000frames∕s, the rupture event is spread over three to four images. The images show that the remnants of the rupturing film are pulled into the surrounding plateau borders in 600±100μs which conforms well with a liquid movement governed by inertia and not by viscosity. Within one order of magnitude, the viscosity of the liquid involved must be similar to the viscosity of pure liquid aluminium.

Quantitative X-ray phase-contrast computed tomography at 82 keV

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.