Publications of the ultrafast X-ray imaging group at IPS
Alaribe L., Fauler A., Cecilia A., Santos Rolo T.D., Fiederle M., Burger A.
in International Journal of Microwave and Wireless Technologies, 1576 (2013). DOI:10.1557/opl.2013.1143
© Materials Research Society 2013. Much has been reported on the excellent performance of the Eu2+ activated SrI2-scintillator in spectroscopic applications, like the high light yield (97 660 ph/MeV) and good energy resolution (2.7% FWHM at 662 keV). The exploitation of these properties for other application fields is limited by the hygroscopic nature of the SrI2. Single crystal scintillating screens exhibit high spatial resolution, this combined with the high density, high effective atomic number, and the high light yield of the SrI2 could be used for high resolution X-ray imaging. Some of the questions we tried to answer in this work are the following: owing to the excellent performance of the SrI2-scintillator in spectroscopic applications, how would it perform in X-ray imaging applications. X-ray images are described based on their (spatial) resolution and contrast, how would they look like when recorded using the SrI2-scintillator detector. First a packaging technique was developed that protected the hygroscopic screens during the measurements. Our results show a high resolution of the images obtained with thin SrI2-scintillator screens both in 2D radiography and 3D tomography measurements. With these results, we think that the SrI2-scinitillator is not only a candidate for spectroscopic applications, but also for high resolution X-ray imaging purposes.
Myagotin A., Voropaev A., Helfen L., Hanschke D., Baumbach T.
in IEEE Transactions on Image Processing, 22 (2013) 5348-5361, 6631501. DOI:10.1109/TIP.2013.2285600
Computed laminography (CL) was developed to use X-rays from synchrotron sources for high-resolution imaging of the internal structure of a flat specimen from a series of 2-D projection images. The projections are acquired by irradiation of the sample under different rotation angles where the object rotation axis is inclined with respect to the beam direction. This yields for laterally extended objects a more uniform average transmitted intensity during sample rotation compared with computed tomography (CT). The reconstruction problem of CL cannot be reduced to a data-efficient 2-D case (as for parallelbeam CT) since each single slice perpendicular to the rotation axis requires a 2-D region on the detector as input data for all projection directions. This paper describes a computationally efficient reconstruction procedure based on filtered backprojection (FBP) adapted to the CL acquisition geometry. From the Fourier slice theorem, we derive a framework for analytic image reconstruction and outline implementation details of the generic FBP algorithm. Different approaches reducing the reconstruction time by means of parallel and distributed computations are considered and evaluated. © 2013 IEEE.
Moosmann J., Altapova V., Helfen L., Hanschke D., Hofmann R., Baumbach T.
in Journal of Physics: Conference Series, 425 (2013), 192003. DOI:10.1088/1742-6596/425/19/192003
Considering a pure and not necessarily weak phase object, we review a noniterative and nonlinear single-distance phase-retrieval algorithm. The latter exploits the fact that a well-known linear contrast-transfer function, which incorporates all orders in object-detector distance, can be modified to yield a quasiparticle dispersion. Accepting a small loss of information, this algorithm also retrieves the high-frequency parts of the phase in an artefact free way. We point out an extension of this highly resolving quasiparticle approach for mixed objects by assuming a global attenuation-phase duality. Tomographically reconstructing two developmental stages in Xenopus laevis, we compare our approach with a linear algorithm, based on the transport-of-intensity equation, which suppresses high-frequency information.
Hanschke D., Helfen L., Altapova V., Danilewsky A., Baumbach T.
in Applied Physics Letters, 101 (2012), 244103. DOI:10.1063/1.4769988
Synchrotron radiation laminography with X-ray diffraction contrast enables three-dimensional imaging of dislocations in monocrystalline wafers. We outline the principle of the technique, the required experimental conditions, and the reconstruction procedure. The feasibility and the potential of the method are demonstrated by three-dimensional imaging of dislocation loops in an indent-damaged and annealed silicon wafer. © 2012 American Institute of Physics.
Vogelgesang M., Chilingaryan S., Rolo T.D.S., Kopmann A.
in Proceedings of the 14th IEEE International Conference on High Performance Computing and Communications, HPCC-2012 – 9th IEEE International Conference on Embedded Software and Systems, ICESS-2012 (2012) 824-829, 6332254. DOI:10.1109/HPCC.2012.116
Current synchrotron experiments require state-of-the-art scientific cameras with sensors that provide several million pixels, each at a dynamic range of up to 16 bits and the ability to acquire hundreds of frames per second. The resulting data bandwidth of such a data stream reaches several Gigabits per second. These streams have to be processed in real-time to achieve a fast process response. In this paper we present a computation framework and middleware library that provides re-usable building blocks to implement high-performance image processing algorithms without requiring profound hardware knowledge. It is based on a graph structure of computation nodes that process image transformation kernels on either CPU or GPU using the OpenCL sub-system. This system architecture allows deployment of the framework on a large range of computational hardware, from netbooks to hybrid compute clusters. We evaluated the library with standard image processing algorithms required for high quality tomographic reconstructions. The results show that speed-ups from 7x to 37x compared to traditional CPU-based solutions can be achieved with our approach, hence providing an opportunity for real-time on-line monitoring at synchrotron beam lines. © 2012 IEEE.
Alaribe L., Disch C., Fauler A., Engels R., Keller E., Cecilia A., Dos Santos Rolo T., Hamann E., Fiederle M.
in IEEE Transactions on Nuclear Science, 59 (2012) 2193-2195, 6303848. DOI:10.1109/TNS.2012.2212208
Much work is going on presently to improve the crystal growth and packaging of the Eu 2+ activated SrI 2 scintillator, thanks to its excellent scintillation properties like high light yield and good energy resolution. Larger crystals are needed for spectroscopic applications, and proper packaging is important for long-time field use and application in other areas due to its hygroscopic nature. In this paper, we report on the successful growth of a SrI 2Eu[6mol%] single crystal in silica ampoule to prevent melt hydration and oxygen contamination using the vertical Bridgman technique. The scintillation properties of a 0.314 cm 3SrI 2:Eu sample are presented, showing a light output of ∼ 80000 ph/MeV. A 360 μm sample was investigated for X-ray imaging applications; we also show how the sample was prepared for the measurement and the result of this preliminary investigation. © 2012 IEEE.
Riedel A., Dos Santos Rolo T., Cecilia A., Van De Kamp T.
in Zoological Journal of the Linnean Society, 165 (2012) 773-794. DOI:10.1111/j.1096-3642.2012.00825.x
Two genera of extinct weevils, Sayrevilleus Gratshev & Zherikhin from Cretaceous New Jersey amber and Baltocar Kuschel from Eocene Baltic amber, are recognized as close relatives based on similarities revealed by the use of synchrotron tomography and the availability of new amber inclusions. The subfamily Sayrevilleinae Legalov stat. nov. is characterized by possessing mandibles with an external cutting edge and an inner blunt edge. The subfamily is placed in the family Attelabidae (s.l.), although some characters also suggest a possible relationship with the ‘higher weevils’ comprising Caridae, Brentidae, and Curculionidae. Sayrevilleus is transferred from the tribe Auletini of Rhynchitinae to Sayrevilleinae, and Sayrevilleus grimaldii Gratshev & Zherikhin is redescribed. Baltocar Kuschel is transferred from Caridae to Sayrevilleinae and revised, its type species, Baltocar succinicus (Voss), is redescribed and three new species, Baltocar groehni Riedel sp. nov., Baltocar hoffeinsorum Riedel sp. nov., and Baltocar subnudus Riedel sp. nov. are described based on eight well-preserved inclusions. The genera Orapauletes Legalov and Zherichiniletes Legalov previously assigned to Sayrevilleini are regarded as Curculionoidea incertae sedis. The Sayrevilleinae were distributed over areas of North America and Europe at least since the Late Cretaceous (c.90Mya) and were probably relatively diverse until the Eocene (c.44Mya). It is speculated that they became extinct through competition with Curculionidae, which used a similar oviposition strategy. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 165, 773-794. © 2012 The Linnean Society of London.
Moosmann J., Altapova V., Hanschke D., Hofmann R., Baumbach T.
in AIP Conference Proceedings, 1437 (2012) 57-62. DOI:10.1063/1.3703343
For coherent X-ray imaging, based on phase contrast through free-space Fresnel propagation, we discuss two noniterative, nonlinear approaches to the phase-retrieval problem from a single-distance intensity map of a pure-phase object. On one hand, a perturbative set-up is proposed where nonlinear corrections to the linearized transport-of-intensity situation are expanded in powers of the object-detector distance z and are evaluated in terms of the linear estimate. On the other hand, a nonperturbative projection algorithm, which is based on the (linear and local) contrast-transfer function (CTF), works with an effective phase in Fourier space. This effective phase obeys a modified CTF relation between intensity contrast at z > 0 and phase contrast at z = 0: Unphysical singularities of the local CTF model are cut off to yield ‘quasiparticles’ in analogy to the theory of the Fermi liquid. By identifying the positions of the zeros of the Fourier transformed intensity contrast as order parameters for the dynamical breaking of scaling symmetry we investigate the phase structure of the forward-propagation problem when interpreted as a statistical system. Results justify the quasiparticle approach for a wide range of intermediary phase variations. The latter algorithm is applied to data from biological samples recorded at the beamlines TopoTomo and ID19 at ANKA and ESRF, respectively. © 2012 American Institute of Physics.
Myagotin A., Ershov A., Helfen L., Verdejo R., Belyaev A., Baumbach T.
in Journal of Synchrotron Radiation, 19 (2012) 483-491. DOI:10.1107/S0909049512015099
A novel image-processing procedure is proposed for the analysis of sequences of two-dimensional projection images. Sudden events like the merging of bubbles in an evolving foam can be detected and spatio-temporally located in a given projection image sequence. The procedure is based on optical flow computations extended by a forward-backward check for each time step. Compared with prior methods, efficient suppression of noise or false events is achieved owing to uniform foam motion, and the reliability of detection is thus increased. The applicability of the proposed procedure in combination with synchrotron radiography is illustrated by a series of characteristic studies of foams of different kind. First, the detection of single-bubble collapses in aqueous foams is considered. Second, a spatial distribution of coalescence events in metals foamed in casting molds is estimated. Finally, the structural stability of polymer foams containing admixed solid nanoparticles is examined. © 2012 International Union of Crystallography.
Altapova V.R., Ershov A., Rolo T.d.S., Reznikova E., Mohr J., Pivovarov Y.L., Pichugin V.F., Baumbach G.T.
in Journal of Surface Investigation, 6 (2012) 394-397. DOI:10.1134/S1027451012050035
The imaging methods used at the ANKA Synchrotron Light Source (Institute for Synchrotron Radiation, Karlsruhe Institute of Technology) are briefly reviewed. Examples of recent applications of the phase-contrast imaging method using a grating interferometer and fast radiography with optic flow data analysis to study static and moving biological objects are presented. © 2012 Pleiades Publishing, Ltd.