X-ray phase-contrast radiography and tomography enables to increase contrast for weakly absorbing materials.
Recently, x-ray grating interferometers were developed which extend the possibility of phase-contrast imaging
from highly brilliant radiation sources like third-generation synchrotron even to non-coherent sources. Here,
we present a setup of an x-ray grating interferometer designed and installed at low-coherence wiggler source
at the GKSS beamline W2 (HARWI II) operated at the second-generation synchrotron storage ring DORIS at
the Deutsches Elektronen-Synchrotron (DESY, Hamburg, Germany). The beamline is dedicated to imaging in
materials science. Equipped with the grating interferometer, it is the first synchrotron radiation beamline with
a three-grating setup combining the advantages of phase-contrast imaging with monochromatic radiation with
very high flux and a sufficiently large field of view for centimeter sized objects. Examples of radiography on
laser-welded aluminum and magnesium joints are presented to demonstrate the high potential of the new gratingbased
setup in the field of materials science. In addition, the results of an off-axis phase-contrast tomography of
a human urethra with 15 mm in diameter are presented showing internal structures, which cannot be resolved
by the conventional tomography in absorption mode.
In this paper we describe the design of different X-ray Talbot interferometers that have been built at the tomography
beamline ID19 of the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, and give a short review of
performance characteristics, of current developments, and of the results obtained with these instruments so far. Among the
applications so far, soft-tissue imaging has been a particular focus, as demonstrated in a recent paper by Schulz et al. <i>(J.
Roy. Soc. Interface</i>, in press).
The basic principles of x-ray image formation in radiography have remained essentially unchanged since R¨ontgen
first discovered x-rays over a hundred years ago. The conventional approach relies on x-ray absorption as
the sole source of contrast and draws exclusively on ray or geometrical optics to describe and interpret image
formation. This approach ignores another, potentially more useful source of contrast, namely phase and scattering
information. Phase-contrast imaging techniques, which can be understood using wave optics rather than ray
optics, offer ways to augment or complement standard absorption contrast by incorporating phase information.
The recent development of grating based phase- and darkfield-contrast imaging with x-rays1 pawed the way for many potential applications to medical imaging and structure determination in material science.
Here we present our recent contributions to the field of interferometric phase-contrast and dark-field x-ray imaging. We introduce a new material dependent scattering parameter, the <i>Linear Diffusion Coefficient</i>, and a quantitative mathematical formalism to extend the dark-field x-ray images into three dimensions by tomographic reconstruction. Further, the results of two experiments that illustrate the potential of dark-field imaging for computed tomography are shown.
Using laser welding in fabrication of metallic airframes reduces the weight and hence fuel consumption. Currently only limited parts of the airframes are welded. To increase laser beam welded parts, there is the need for a better understanding of crack propagation and crack-pore interaction within the welds. Laser beam welded Al-alloys may contain isolated small process pores and their role and interaction with growing crack need to be investigated. The present paper presents the first results of a crack propagation study in laser beam welded (LBW) Al-alloy T-joints using synchrotron radiation based micro computed tomography (SRμCT). A region-of-interest technique was used, since the specimens exceeded the field of view of the X-ray detector. As imaging with high density resolution at high photon energies is very challenging, a feasibility measurement on a small laser weld, cut cylindrically from the welded region of a T-joint, was done before starting the crack-propagation study. This measurement was performed at the beamline HARWI-II at DESY to demonstrate the potential of the SRμCT as non-destructive testing method. The result has shown a high density resolution, hence, the different Al alloys used in the T-joint and the weld itself were clearly separated. The quantitative image analysis of the 3D data sets allows visualizing non-destructively and calculating the pore size distribution.
Knowledge on the geometry of pore networks of intra-aggregate soil pore spaces are of great value for many soil environmental processes. Advances in non-invasive 3D imaging techniques such as synchrotron-radiation-based microtomography offer an excellent opportunity to study the interrelationship of the pore network geometry with
physical processes at a spatial resolution of a few micrometers. This paper presents results of a quantitative 3D pore space geometry analysis of small scale (~5mm across) soil aggregates from contrasting soil management systems. Soil aggregates have been scanned at the SR-μCT facility operated by the GKSS Research Center at HASYLAB / DESY (Hamburger Synchrotron Strahlungslabor / Deutsches Elektronen Synchrotron) in Hamburg/Germany. The achieved
isotropic voxel resolution of the scans ranged from 2.4 to 5.4 μm. Three-dimensional reconstructions of the soil aggregates were analysed for various pore space features using a suite of algorithms based on mathematical morphology. Results have shown expected differences in distributions of pore size, throat size, channel length and width as well as tortuosity and connectivity of the intra-aggregate pores with potential implications for soil functions. Underlying image transformations and methods of visualization and quantification of soil pore networks will be discussed in view of their robustness and possible application of such information in soil related research fields.
Phase-contrast imaging using grating interferometers has been developed over the last few years for x-ray energies of up to 28 keV. We have now developed a grating interferometer for phase-contrast imaging that operates at 60 keV x-ray energy. Here, we show first phase-contrast projection and CT images recorded with this interferometer using an x-ray tube source operated at 100 kV acceleration voltage. By comparison of the CT data with theoretical values, we find that our measured phase images represent the refractive index decrement at 60 keV in good agreement with the theoretically expected values. The extension of phase-contrast imaging to this significantly higher x-ray energy opens up many new
applications of the technique in industry, medicine, and research.
Nowadays, X-ray tube-based high-resolution CT systems are widely used in scientific research and industrial applications. But the potential, convenience and economy of these lab systems is often underestimated. The present paper shows the comparison of sophisticated conventional μCT with synchrotron radiation-based μCT (SRμCT). The different aspects and characteristics of both approaches like spatial and density resolution, penetration depth, scanning time or sample size is described in detail. The tube-based μCT measurements were performed with a granite-based
nanotom®-CT system (phoenix|x-ray, Wunstorf, Germany) equipped with a 180 kV - 15 W high-power nanofocus® tube with tungsten or molybdenum targets. The tube offers a wide range of applications from scanning low absorbing samples in nanofocus® mode with voxel sizes below 500 nm and highly absorbing objects in the high power mode with focal spot and voxel sizes of a few microns. The SRμCT measurements were carried out with the absorption contrast set-up
at the beamlines W 2 and BW 2 at HASYLAB/DESY, operated by the GKSS Research Center. The range of samples examined covers materials of very different absorption levels and related photon energies for the CT scans. Both quantitative and qualitative comparisons of CT scans using biomedical specimens with rather low X-ray absorption such
as parts of the human spine as well as using composites from the field of materials science are shown.
The position of the rotation axis (center of rotation) is an important input parameter for the reconstruction of tomography data. We have recently presented a method for the determination of the center of rotation from sinogram data recorded in parallel-beam tomography, which is based on scoring of reconstructions with image metrics. The influence of noise on the metric value is investigated by simulation using a circular computer phantom. Limits on the precision of the method are discussed by calculation of the metric signal and its noise level. It is shown that for typical count rates and resolutions used in microtomographic imaging, the method enables to determine the center of rotation with a precision of better than 0.06 pixel.
The structure of wood based medium density fiberboard (MDF) has been studied using synchrotron radiation-based
x-ray microtomography (SRμCT.) Fully automated 3D segmentation and analysis routines have been
developed in order to gain information about individual fibers, the distribution of the fiber material, fiber
orientation, fiber surfaces and size and location of contact areas. Representative samples of the analyzed volume
data are presented to demonstrate the results of the implemented methods using the VIGRA image processing
The X-ray microtomography system which is operated at the Hamburger Synchrotronstrahlungslabor HASYLAB of the Deutsches Elektronen-Synchrotron DESY in Hamburg, Germany, is presented. At the DORIS storage ring synchrotron radiation at the wiggler beamlines BW2, W2, and BW5 was used to run the microtomography apparatus as a user experiment. The development of tomography scanning techniques to investigate samples which are larger than the field of view of the X-ray detector is demonstrated for dental implants using the photon
energy of 90 keV at the high energy beamline BW5. In cooperation with DESY the GKSS Research Center is setting up the high energy beamline HARWI-2 at the DORIS storage ring of DESY. This beamline will allow for tomography experiments using monochromatic X-rays from 20 to 200 keV with a beam size of 70•10 mm<sup>2</sup>. Furthermore the GKSS is operating a neutron radiography facility GENRA at the research reactor Geesthacht FRG, Geesthacht, Germany. It is intended to extend this facility by a tomography station. The combination of synchrotron radiation based microtomography with neutron tomography will allow for the development of new
techniques to give new insight in the 3-dim. behavior of samples especially in materials science.
Synchrotron radiation based X-ray microtomography was applied for the morphometric analysis of polyurethane scaffolds (polymer foams) intended for the use as a biocompatible replacement material. The X-ray microtomography apparatus used for this study is described in detail. The full data evaluation process including X-ray image recording, tomographic reconstruction and the subsequent data reduction steps is explained. The 3-dim. segmentation of the scaffolds and the results of the morphometric analysis are presented.
This study explores the application of conventional micro tomography (μCT) and synchrotron radiation (SR) based μCT to evaluate the bone around titanium dental implants. The SR experiment was performed at beamline W2 of HASYLAB at DESY using a monochromatic X-ray beam of 50 keV. The testing material consisted of undecalcified bone segments harvested from the upper jaw of a macaca fascicularis monkey each containing a titanium dental implant. The results from the two different techniques were qualitatively compared with conventional histological sections examined under light microscopy. The SR-based μCT produced images that, especially at the bone-implant interface, are less noisy and sharper than the ones obtained with conventional μCT. For the proper evaluation of the implant-bone interface, only the SR-based μCT technique is able to display the areas of bony contact and visualize the true 3D structure of bone around dental implants correctly. This investigation shows that both conventional and SR-based μCT scanning techniques are non-destructive methods, which provide detailed images of bone. However with SR-based μCT it is possible to obtain an improved image quality of the bone surrounding dental implants, which display a level of detail comparable to histological sections. Therefore, SR-based μCT scanning could represent a valid, unbiased three-dimensional alternative to evaluate osseointegration of dental implants.