Jürgen Goebbels

Quantification of bone tissue regeneration employing β-tricalcium phosphate by three-dimensional non-invasive synchrotron micro-tomography — A comparative examination with histomorphometry

PURPOSE This methodical study presents a novel approach to evaluate the validity of two-dimensional histomorphometric measurements of a bone biopsy specimen after sinus floor elevation by means of high contrast, high resolution, three-dimensional and non-destructive synchrotron micro-tomography (SCT). The aim of this methodical description is to demonstrate the potential of this new approach for the evaluation of bone biopsy samples. MATERIALS AND METHODS Unilateral sinus grafting was carried out exemplarily in two patients using a combination of beta-tricalcium phosphate (beta-TCP) and autogenous bone chips. For the first patient a beta-TCP with 35% porosity and in the second with 60% porosity was used. At implant placement, 6 months after sinus grafting, a cylindrical specimen was biopsied from the augmented area. Subsequent to the histological embedding in resin the specimens were imaged using a SCT facility resulting in three-dimensional (3-D) images with approximately 4 microm spatial resolution (1.5 microm pixel size) for each patients specimen. Subsequent to the SCT acquisition, tissue sections were prepared for histomorphometric analysis. RESULTS Bone area fractions determined by two-dimensional (2-D) quantitative histomorphometry and by analysis of the corresponding 2-D slice from the SCT volume data were similar. For the first biopsy specimen (beta-TCP with 35% porosity), the bone area fractions were 53.3% and 54.9% as derived by histomorphometry and by analyzing a SCT slice, respectively. For the second biopsy specimen (beta-TCP with 60% porosity) the bone area fractions were 38.8% and 39% respectively. Although the agreement between the 2-D methods was excellent, the area fractions were somewhat higher than the volume fractions computed by 3-D image analysis on the entire SCT volume data set. The volume fractions were 48.8% (first biopsy specimen) and 36.3% (second biopsy specimen). CONCLUSION Although the agreement between the 2-D methods is excellent in terms of computing the area fractions, the structural 3-D insight which can be derived from classical 2-D methods, including histomorphometric analysis is considerably limited. This fact is emphasized by the discrepancy between the measured areas and volume fractions.

The role of material properties for the mechanical adaptation at branch junctions

Branch junctions are mechanically particularly interesting areas of trees, because they have to withstand a combination of static and dynamic loads, from the stem as well as from the branch. In the present work, the local adaptation of material properties at branch junctions was assessed by mapping microfibril angle and tissue density. Images of the density distribution were obtained by computer tomography (CT). Wide angle X-ray scattering (WAXS) was used to determine the microfibril angle distribution with high-resolution around the junctions. The stem tissue around the junctions showed increased density and microfibril angle, which points towards an optimisation for fracture toughness. The tissue at the branch bases showed low density combined with high MFA, which provides deformability and flexibility and might act as protection of the stem against load transmission from the branch.

Three-dimensional visualization of in vitro cultivated chondrocytes inside porous gelatine scaffolds: A tomographic approach

Synchrotron radiation-based microcomputed tomography (SR-microCT) has become a valuable tool in the structural characterization of different types of materials, achieving volumetric details with micrometre resolution. Biomedical research dealing with porous polymeric biomaterials is one of the research fields which can benefit greatly from the use of SR-microCT. This study demonstrates that current experimental set-ups at synchrotron beamlines achieve a sufficiently high resolution in order to visualize the positions of individual cartilage cells cultivated on porous gelatine scaffolds made by a freeze-structuring technique. Depending on the processing parameters, the pore morphology of the scaffolds investigated was changed from large-pore sized but non-ordered structures to highly directional and fine pored. The cell-seeded scaffolds were stained with a combined Au/Ag stain to enhance the absorption contrast in SR-microCT. While only some cells showed enhanced absorption contrast, most cells did not show any difference in contrast to the surrounding scaffold and were consequently not detectable using conventional greyscale threshold methods. Therefore, using an image-based three-dimensional segmentation tool on the tomographic data revealed a multitude of non-stained cells. In addition, the SR-microCT data were compared with data obtained from scanning electron microscopy, energy dispersive X-ray spectroscopy and histology, while further linking the initial cell density measured via a MTT assay to the pore size as determined by SR-microCT.

Achieving Traceability of Industrial Computed Tomography

Achieving traceability is crucial for complex measurement techniques, especially for coordinate measuring machines (CMMs). For CMMs using tactile probes, traceability can for certain measurements be achieved using model-based uncertainty budgets. Up to now, uncertainty simula-tions could be used applicable only for tactile CMM measurements of regular geometries, but are available as an add-on for different CMMs. This procedure is accepted by guidelines and inter-national standards (VDI/VDE 2617-7, supplement 1 [1] to GUM). Furthermore, empirical ap-proaches to assess the measurement uncertainty by means of calibrated workpieces or prior know-ledge exist or are under development. These approaches can as a matter of principle also be used for CMMs featuring computed tomography (CT). In this paper, the empirical assessment of the mea-surement uncertainty of the upcoming measurement technology CT [2, 3] will be discussed uniting the present approaches and the current knowledge, with the focus being on the applicability of con-cepts for users in industry. For this purpose, the influences on dimensional CT measurements are analyzed and evaluated, taking the measurement data of a current industrial micro CT system as a basis.

Synchrotron radiation and laboratory micro X-ray computed tomography—useful tools for the material identification of prehistoric objects made of ivory, bone or antler

Archaeological bone, ivory and antler, as well as objects manufactured from them, are largely studied to extract as much information as possible from these materials. Among others, one key question in archaeology is the exact identification of the material. Even if the identification of different kinds of osseous material seems to be trivial in many cases, it can be a difficult issue when small, heavily carved and more or less altered ancient objects are concerned. This study was focused on the determination of parameters allowing the distinction of archaeological ivory, bone and antler in order to identify the raw material used for the manufacture of prehistoric objects. The high performance of synchrotron radiation (SR) and laboratory-based micro X-ray computed tomography (microCT), providing highly resolved three-dimensional information on the micromorphology, permitted the establishment of such distinctive features of modern references of ivory, antler, land mammal and whale bones: ivory shows characteristic tubular pores with a diameter of about 1 to 2 μm, bone and antler show typical osteon structures. In our measured references, antler shows on average larger and more elongated shaped pores of the osteons compared to terrestrial mammal bone. This feature however depends very much on the original localization of the studied sample within the antler. Whale bones can be distinguished from the other osseous materials by a cancellous, osteoporotic-like structure with irregularly distributed rounded porosities with diameters reaching up to 500 μm. These characteristics have also been tested on determined Palaeolithic fragments, as diagenetic changes during burial have to be considered and may lead to the modification of the parameters established on the basis of modern bone references. In general, the chemical composition of bone objects can change drastically over time while micromorphological features, as evidenced by microCT, seem to be less susceptible to such alterations. In addition, microCT enables the comparison of inner and possibly less altered parts of the objects, and can be considered as completely non-destructive for small mineralised prehistoric objects. In this study, specific morphological features allowing the distinction of ivory and of whale bone from other bone and antler material were determined, even for altered materials dating back to Palaeolithic periods. Thus, we provide, in addition to archaeozoological, chemical and isotopic markers, a new non-destructive tool to identify some raw materials used for the fabrication of osseous objects ranging from recent to prehistoric periods.

Wassermanagement in Brennstoffzellen — die Bedeutung von hochauflösenden zerstörungsfreien Untersuchungsmethoden

Kurzfassung Ein effektives Wassermanagement ist ein wichtiger Aspekt in der Entwicklung von Brennstoffzellen hinsichtlich Langzeitstabilität und Optimierung der Leistungsfähigkeit. Eine zentrale Rolle spielt dabei die Gasdiffusionslage, die für die gleichmäßige Verteilung der Reaktionsgase auf die elektrochemisch aktive Schicht (Katalysator) sorgen soll. In diesem Beitrag werden gemeinsame Forschungsaktivitäten des Helmholtz-Zentrums Berlin für Materialien und Energie (Entwicklung bildgebender Verfahren) sowie des Zentrums für Sonnenenergie- und Wasserstoff-Forschung (ZSW, Entwicklung von Brennstoffzellen) vorgestellt. Im Rahmen dieser Kooperation werden die Entstehung, die Verteilung und der Transport von flüssigem Wasser, kurz das Wassermanagement, unter Betriebsbedingungen untersucht. Mittels Synchrotronradiografie und -tomografie werden kleinste Wassercluster in der Gasdiffusionslage detektiert. Die gewonnenen Erkenntnisse dienen der Modifikation und einer gezielten Auswahl der eingesetzten Materialien.

Refraction computed tomography

Abstract For the first time metal matrix composites have been investigated by 3D computed tomography combined with enhanced interface contrast due to X-ray refraction. The related techniques of refraction topography and refraction computed tomography have been developed and applied during the last decade to meet the actual demand for improved non-destructive characterization of high performance composites, ceramics and other low-density materials and components. X-ray refraction is an optical effect that can be observed at small scattering angles of a few minutes of arc as the refractive index n of X-rays is nearly unity (n = 1 − 10−6). Due to the short X-ray wavelength, the technique determines the amount of inner surfaces and interfaces of nanometer dimensions. The technique can solve many problems in understanding micro and sub microstructures in materials science. Applying 3D refraction computed tomography, some questions could be clarified for a better understanding of fatigue failure mechanisms under cyclic loading conditions.

Fabric studies on contaminated mineral layers in composite liners

Abstract The fabric of mineral liner materials that had been exposed to organic compounds over a 12-year period was investigated as part of a wider research project. Macromorphological and micromorphological changes in the fabric were identified using computed tomography and polarisation microscopy. Special care was taken to ensure artefact free sampling and sample preparation, in particular, the drying method used, has a substantial influence on the quality of the thin sections. Fabric changes due to contaminant permeation over several years are, by and large, relatively small and their intensity is material specific. Silty clay CML1, in particular, contains a somewhat greater number of fissures and voids in comparison with the original material. The superposition of various processes in both test procedures and sample preparation may lead to fabric changes which can impede interpretation of the results.

The high-resolution synchrotron-based imaging stations at the BAMline (BESSY) and TopoTomo (ANKA)

The BAMline at the BESSY light source in Berlin and the TopoTomo beamline at the ANKA synchrotron facility in Karlsruhe (both Germany) operate in the hard X-ray regime (above 6 keV) with similiar photon flux density. For typical imaging applications, a double multilayer monochromator or a filtered white beam is used. In order to optimise the field of view and the resolution of the available indirect pixel detectors, different optical systems have been installed, adapted, respectively, to a large field of view (macroscope) and to high spatial resolution (microscope). They can be combined with different camera systems, ranging from 16-bit dynamic range slow-scan CCDs to fast CMOS cameras. The spatial resolution can be brought substantially beyond the micrometer limit by using a Bragg magnifier. The moderate flux of both beamlines compared to other 3rd generation light sources is compensated by a dedicated scintillator concept. For selected applications, X-ray beam collimation has proven to be a reliable approach to increase the available photon flux density. Absorption contrast, phase contrast, holotomography and refraction-enhanced imaging are used depending on the application. Additionally, at the TopoTomo beamline digital white beam synchrotron topography is performed, using the digital X-ray pixel detectors installed.

Correction techniques for 2D detectors to be used with high-energy x-ray sources for CT, part II

In 1997 we presented some correction techniques for image intensifier images. In the mean time flat panel detectors are often used instead of. The visible contrast of the 16bit flat panel is much higher then with the same digitisation from intensifier images. This misleads users of CT-systems with flat panel detectors to expect far better results. Nevertheless all of the previously described corrections have to be done here too, if an artefact free image is the aim. This gets most important, if an automated evaluation shall be used to extract features from CT images. The main advantage of the new proposed correction technique is that the detector intrinsic scattered radiation (stray light) is corrected with a fast two dimensional filter. Also the right interaction with other corrections like beam hardening and object-scattered radiation is of importance, examples will be shown. The corrected 2D detector images enhances the quality of cone beam CT results in respect to their geometrical distinctness so that geometrical measurements and reverse engineering results get comparable with 2D CT measurements. Results are shown on the µ-CT scanner for bigger objects or for objects with higher X-ray absorption which was set up at BAM. The system is equipped with a bipolar 320kV micro focus tube and a flat panel detector of amorphous Si with 400mm side length, room and system temperatures are regulated.