Phase-contrast imaging has proven to be a valuable tool when investigating weak absorbing materials like soft tissue, due to its increased contrast compared to conventional absorption-contrast imaging. While propagation-based phase-contrast is an ideal tool to achieve highest resolution at a good contrast for almost not-absorbing material, it quickly comes to its limitations on applications demanding for a high dynamic range in contrast. For those applications grating-based phase-contrast is the tool of choice, although it lacks of spatial resolution compared to inline phase-contrast or attenuation-based microCT. To reduce this gap in spatial resolution we equipped the two PETRA III beamlines P05 and P07 with a customized set of mechanics to maximize the performance of the interferometer. After latest optimization steps our system allows for phase-contrast measurements in a continuous energy range between 10 keV and 80 keV . Dependent on investigated material and energy the setup is capable to achieve a spatial resolution of 5 μm on a field of view of 6.5 mm. We will present our implementation of grating-based phase-contrast computed tomography for fast and high-resolution measurements at the PETRA III along with its recent optimization, and demonstrate its performance based on different kinds of applications.
The use of degradable magnesium based implants is becoming clinically relevant, e.g. for the use as bone screws. Still
there is a lack of analyzing techniques to characterize the in vitro degradation behavior of implant prototypes. The aim of
this study was to design an in situ environment to continuously monitor the degradation processes under physiological
conditions by time-lapse SRμCT. The use of physiological conditions was chosen to get a better approach to the in vivo
situation, as it could be shown by many studies, that these conditions change on the one hand the degradation rate and on
the other hand also the formed degradation products. The resulting in situ environment contains a closed bioreactor
system to control and monitor the relevant parameters (37°C, 5 % O<sub>2</sub>, 20 % CO<sub>2</sub>) and to grant sterility of the setup. A
flow cell was designed and manufactured from polyether etherketone (PEEK), which was chosen because of the good
mechanical properties, high thermal and chemical resistance and radiographic translucency. Sterilization of the system
including the sample was reached by a transient flush with 70 % ethanol and subsequent replacement by physiological
medium (Modified Eagle Medium alpha). As proof of principle it could be shown that the system remained sterile during
a beamtime of several days and that the continuous SRμCT imaging was feasible.
Synchrotron X-ray imaging is constantly achieving higher spatial resolution. In the field of grating-based phase- contrast imaging, these developments allow to directly resolve the interference patterns created by a phase grating without need for a analyzer grating. In this study we analyzed the performance of a single-grating interferometer and compared it to a conventional double-grating interferometer. Based on simulations and measurements of a test phantom we evaluated the sensitivity, resolution and signal to noise ratios of different setup configurations.
In this article we present the quantitative characterization of CCD and CMOS sensors which are used at the experiments
for microtomography operated by HZG at PETRA III at DESY in Hamburg, Germany. A standard commercial CCD
camera is compared to a camera based on a CMOS sensor. This CMOS camera is modified for grating-based differential
The main goal of the project is to quantify and to optimize the statistical parameters of this camera system. These key
performance parameters such as readout noise, conversion gain and full-well capacity are used to define an optimized
measurement for grating-based phase-contrast. First results will be shown.
Conventional absorption-based imaging often lacks in good contrast at special applications like visualization of
soft tissue or weak absorbing material in general. To overcome this limitation, several new X-ray phase-contrast
imaging methods have been developed at synchrotron radiation facilities. Our aim was to establish the possibility
of different phase-contrast imaging modalities at the Imaging Beamline (IBL, P05) and the High Energy
Material Science beamline (HEMS, P07) at Petra III (DESY, Germany). Here we present the instrumentation
and the status of the currently successfully established phase-contrast imaging techniques. First results from
measurements of biomedical samples will be presented as demonstration.
The unique beam characteristics of PETRA III at DESY promote novel applications for many scientific fields,
including imaging applications. For tomography these are techniques like high-speed and in-situ measurements
marked by highest density resolutions and spatial resolutions down to the nanometer range. Furthermore, the
high coherence enables phase contrast applications in an exceptional way. Therefore, the Imaging Beamline IBL
is equipped with two dedicated endstations, one for micro and one for nano tomography. In addition, a very
flexible X-ray and light optics concept is implemented. The micro tomography endstation is designed for samples
requiring (sub-) micrometer resolution. The technical specifications of the nano tomography endstation aim for
a spatial resolution of below 100 nm. The nanometer resolution will be achieved by using different combinations
of compound refractive lenses as X-ray optics. The overall setup is designed to be very flexible, which allows
also the implementation of other optical elements as well as the application of different magnifying techniques.
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.
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.
During the last few years microtomography using synchrotron radiation (SR) has become a standard technique to characterize samples 3-dimensionally in the fields of biology, medicine and materials science. The GKSS Research Center Geesthacht, Germany, is responsible for developing and running the microtomography experiments at the
SR-facility DESY, Hamburg, Germany. The application of SRμCT using attenuation-contrast at the beamlines W2/HARWI-II and BW2 of the storage ring DORIS III results in high throughput investigations. For achieving tomograms showing not only high spatial resolution but also high density resolution special emphasis was given to the stability of the used monochromators and the calibration of the total system. The influence of the photon statistic from the measurement to the tomograms is simulated and the achieved high density resolution
is demonstrated showing selected results.
Due to the high brilliance of the new storage ring PETRA III at DESY in Hamburg, the low emittance of 1 nmrad and the high fraction of coherent photons also in the hard X-ray range extremely intense and sharply focused X-ray light will be provided. These advantages of the beam fulfill excellently the qualifications for the planned Imaging BeamLine IBL and the High Energy Materials Science Beamline (HEMS) at PETRA III, i.e. for absorption tomography, phase enhanced and phase contrast experiments, for diffraction, for nano focusing, for nano tomography, and for high speed or in-situ experiments with highest spatial resolution. The existing HARWI II beamline at the DORIS III storage ring at DESY completes the GKSS beamline concept with setups
for high energy tomography (16-150 keV) and diffraction (16-250 keV), characterized by a large field of view and an excellent absorption contrast with spatial resolutions down to 2 μm.
In autumn 2005 the GKSS-Research Center Geesthacht in cooperation with Deutsches Elektronen-Synchrotron
DESY, Hamburg, started operation of the new synchrotron radiation beamline HARWI-2. The beamline is
specialized for materials science experiments using hard X-rays. Recently the fixed-exit monochromator for
imaging application was installed. Using different sets of crystals in combination with an adapted setup of the
beamline optics allow for using an intense and large monochromatic X-ray beam in the energy range of 15 to
200 keV. Investigations performing microtomography in the different energy regions are presented. Furthermore
the user experiment for microtomography operated by the GKSS at beamline BW2 was enhanced to perform
continuous tomographic investigations.
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.
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.
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.