Timm Weitkamp
European Synchrotron Radiation Facility
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Publication
Featured researches published by Timm Weitkamp.
Optics Express | 2005
Timm Weitkamp; Ana Diaz; Christian David; Franz Pfeiffer; Marco Stampanoni; Peter Cloetens; Eric Ziegler
Using a high-efficiency grating interferometer for hard X rays (10-30 keV) and a phase-stepping technique, separate radiographs of the phase and absorption profiles of bulk samples can be obtained from a single set of measurements. Tomographic reconstruction yields quantitative three-dimensional maps of the X-ray refractive index, with a spatial resolution down to a few microns. The method is mechanically robust, requires little spatial coherence and monochromaticity, and can be scaled up to large fields of view, with a detector of correspondingly moderate spatial resolution. These are important prerequisites for use with laboratory X-ray sources.
Journal of Synchrotron Radiation | 2011
Timm Weitkamp; D. Haas; D. Wegrzynek; Alexander Rack
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.
Applied Physics Letters | 2005
Timm Weitkamp; B. Nöhammer; Ana Diaz; Christian David; Eric Ziegler
We present an interferometric method to measure the shape of a hard-x-ray wavefront. The interferometer consists of a phase grating as a beam splitter and an absorption grating as a transmission mask for the detector. The device can be used to measure wavefront shape gradients corresponding to radii of curvature as large as several dozens of meters, with a lateral resolution of a few microns. This corresponds to detected wavefront distortions of approximately 10−12m or λ∕100. The device was used with 12.4 keV x rays to measure the slope error and height profile of an x-ray mirror. Surface slope variations with periods ranging from less than 1 mm to more than 1 m can be detected with an accuracy better than 0.1μrad.
Journal of the Royal Society Interface | 2010
Georg Schulz; Timm Weitkamp; Irene Zanette; Franz Pfeiffer; Felix Beckmann; Christian David; Simon Rutishauser; Elena Reznikova; Bert Müller
Human brain tissue belongs to the most impressive and delicate three-dimensional structures in nature. Its outstanding functional importance in the organism implies a strong need for brain imaging modalities. Although magnetic resonance imaging provides deep insights, its spatial resolution is insufficient to study the structure on the level of individual cells. Therefore, our knowledge of brain microstructure currently relies on two-dimensional techniques, optical and electron microscopy, which generally require severe preparation procedures including sectioning and staining. X-ray absorption microtomography yields the necessary spatial resolution, but since the composition of the different types of brain tissue is similar, the images show only marginal contrast. An alternative to absorption could be X-ray phase contrast, which is known for much better discrimination of soft tissues but requires more intricate machinery. In the present communication, we report an evaluation of the recently developed X-ray grating interferometry technique, applied to obtain phase-contrast as well as absorption-contrast synchrotron radiation-based microtomography of human cerebellum. The results are quantitatively compared with synchrotron radiation-based microtomography in optimized absorption-contrast mode. It is demonstrated that grating interferometry allows identifying besides the blood vessels, the stratum moleculare, the stratum granulosum and the white matter. Along the periphery of the stratum granulosum, we have detected microstructures about 40 µm in diameter, which we associate with the Purkinje cells because of their location, size, shape and density. The detection of individual Purkinje cells without the application of any stain or contrast agent is unique in the field of computed tomography and sets new standards in non-destructive three-dimensional imaging.
X-RAY OPTICS AND MICROANALYSIS: Proceedings of the 20th International Congress | 2010
Timm Weitkamp; Paul Tafforeau; Elodie Boller; Peter Cloetens; Jean‐Paul Valade; Pascal Bernard; Françoise Peyrin; Wolfgang Ludwig; L. Helfen; J. Baruchel
The ESRF synchrotron beamline ID19, dedicated to full‐field parallel‐beam imaging techniques such as phase‐contrast and absorption microtomography and X‐ray topography, is one of the most versatile instruments of its kind. This paper presents key characteristics of ID19 in its present form, names examples for research and development performed on the beamline, and outlines the plans for an upgrade on the beamline in coming years, to adapt to the growing needs of the user community. The technical goals envisioned include an increase in available beam size and maximum photon energy, and a substantial increase in flux density for applications using beams of small and intermediate size.
Applied Physics Letters | 2000
V. Aristov; M. Grigoriev; S. Kuznetsov; Leonid Shabel'nikov; Vecheslav Yunkin; Timm Weitkamp; Christoph Rau; I. Snigireva; A. Snigirev; Martin Hoffmann; E. Voges
Silicon refractive planar parabolic lenses with minimized absorption were fabricated by a combination of photolithography and dry-etching techniques. Focusing and spectral properties of the lenses were studied with synchrotron radiation in the energy range 8–25 keV at the European Synchrotron Radiation Facility. A focal spot of 1.8 μm with a gain of 18.5 and transmission of more then 80% was measured at 15.6 keV. The spectral characteristics were analyzed taking into account material dispersion and photon-energy attenuation in the hard x-ray range.
Proceedings of the National Academy of Sciences of the United States of America | 2012
Irene Zanette; Martin Bech; Alexander Rack; G. Le Duc; P. Tafforeau; Christian David; Juergen Mohr; Franz Pfeiffer; Timm Weitkamp
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.
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment | 2001
Brit Salbu; T. Krekling; Ole Christian Lind; D.H. Oughton; Michael Drakopoulos; A. Simionovici; I. Snigireva; A. Snigirev; Timm Weitkamp; F. Adams; Koen Janssens; V.A. Kashparov
Abstract For the first time different high energy microanalysis techniques were combined to characterise individual micrometer sized radioactive particles. It was shown that particle characteristics including weathering rates and mobilisation of associated radionuclides are source specific and release-scenario dependent. Fuel particles released during the explosion are characterised by UO 2 -cores with surrounding layer of reduced U with low weathering rates. In contrast, fuel particles released during the subsequent fire show UO 2 -core with surrounding layers of oxidised U 2 O 5 /U 3 O 8 with high weathering rates
European Journal of Radiology | 2008
Timm Weitkamp; Christian David; O. Bunk; Jens Bruder; Peter Cloetens; Franz Pfeiffer
X-ray phase and absorption radiographs and tomograms of the heart of a rat were taken with an X-ray grating interferometer with monochromatic synchrotron radiation at a photon energy of 17.5 keV. The phase images show largely superior quality with respect to the absorption images taken with the same dose, particularly much better contrast and contrast-to-noise ratio. Different tissues can clearly be distinguished. The results demonstrate the potential of grating interferometry for two- and three-dimensional X-ray imaging of biological soft tissue in an aqueous environment.
Zeitschrift Fur Medizinische Physik | 2010
Martin Bech; Torben Heick Jensen; Oliver Bunk; Tilman Donath; Christian David; Timm Weitkamp; Géraldine Le Duc; Alberto Bravin; Peter Cloetens; Franz Pfeiffer
Here we review our recent progress in the field of X-ray dark-field and phase-contrast imaging using a grating interferometer. We describe the basic imaging principles of grating-based phase-contrast and dark-field radiography and present some exemplary results obtained for simple test objects and biological specimens. Furthermore, we discuss how phase-contrast and dark-field radiography can be combined with the concept of computed tomography, and yield highly detailed three-dimensional insights into biomedical sample. Exemplary results obtained with standard X-ray tube sources and highly brilliant synchrotron sources are presented.