Assessment of Tribo-charging and Continuous Feeding Performance of Direct Compression Grades of Isomalt and Mannitol Powders.

Tribo-charging is often a root cause of mass flow deviations and powder adhesion during continuous feeding. Thus, it may critically impact product quality. In this study, we characterized the volumetric (split- and pre-blend) feeding behavior and process-induced charge of two direct compression grades of polyols, galenIQ™ 721 (G721) for isomalt and PEARLITOL® 200SD (P200SD) for mannitol, under different processing conditions. The feeding mass flow range and variability, hopper end fill level, and powder adhesion were profiled. The feeding-induced tribo-charging was measured using a Faraday cup. Both materials were comprehensively characterized for relevant powder properties, and their tribo-charging was investigated for its dependence on particle size and relative humidity. During split-feeding experiments, G721 showed a comparable feeding performance to P200SD with lower tribo-charging and adhesion to the screw outlet of the feeder. Depending on the processing condition, the charge density of G721 ranged from -0.01 up to -0.39 nC/g, and for P200SD from -3.19 up to -5.99 nC/g. Rather than differences in the particle size distribution of the two materials, their distinct surface and structural characteristics were found as the main factors affecting their tribo-charging. The good feeding performance of both polyol grades was also maintained during pre-blend feeding, where reduced tribo-charging and adhesion propensity was observed for P200SD (decreasing from -5.27 to -0.17 nC/g under the same feeding settings). Here, it is proposed that the mitigation of tribo-charging occurs due to a particle size-driven mechanism.

Suppression of quasiperiodicity in circle maps with quenched disorder.

We show that introducing quenched disorder into a circle map leads to the suppression of quasiperiodic behavior in the limit of large system sizes. Specifically, for most parameters the fraction of disorder realizations showing quasiperiodicity decreases with the system size and eventually vanishes in the limit of infinite size, where almost all realizations show mode locking. Consequently, in this limit, and in strong contrast to standard circle maps, almost the whole parameter space corresponding to invertible dynamics consists of Arnold tongues.

Thickness accuracy of virtually designed patient-specific implants for large neurocranial defects.

The combination of computer-aided design (CAD) techniques based on computed tomography (CT) data to generate patient-specific implants is in use for decades. However, persisting disadvantages are complicated design procedures and rigid reconstruction protocols, for example, for tailored implants mimicking the patient-specific thickness distribution of missing cranial bone. In this study we used two different approaches, CAD- versus thin-plate spline (TPS)-based implants, to reconstruct extensive unilateral and bilateral cranial defects in three clinical cases. We used CT data of three complete human crania that were virtually damaged according to the missing regions in the clinical cases. In total, we carried out 132 virtual reconstructions and quantified accuracy from the original to the generated implant and deviations in the resulting implant thickness as root-mean-square error (RMSE). Reconstructions using TPS showed an RMSE of 0.08-0.18 mm in relation to geometric accuracy. CAD-based implants showed an RMSE of 0.50-1.25 mm. RMSE in relation to implant thickness was between 0.63 and 0.70 mm (TPS) while values for CAD-based implants were significantly higher (0.63-1.67 mm). While both approaches provide implants showing a high accuracy, the TPS-based approach additionally provides implants that accurately reproduce the patient-specific thickness distribution of the affected cranial region.

Analysis and comparison of algorithms for the tomographic reconstruction of curved fibres.

We present visual methods for the analysis and comparison of the results of curved fibre reconstruction algorithms, i.e., of algorithms extracting characteristics of curved fibres from X-ray computed tomography scans. In this work, we extend previous methods for the analysis and comparison of results of different fibre reconstruction algorithms or parametrisations to the analysis of curved fibres. We propose fibre dissimilarity measures for such curved fibres and apply these to compare multiple results to a specified reference. We further propose visualisation methods to analyse differences between multiple results quantitatively and qualitatively. In two case studies, we show that the presented methods provide valuable insights for advancing and parametrising fibre reconstruction algorithms, and support in improving their results in characterising curved fibres.

Visualization of intervertebral disc degeneration in a cadaveric human lumbar spine using microcomputed tomography.

Gross features of disc degeneration (DD) that are associated with back pain include tears in the anulus fibrosus, structural changes of the endplates, and a collapse of the anulus. The aim of this study is the detailed visualization and microstructural characterization of DD using microcomputed tomography (µCT) and a dedicated image post-processing pipeline. In detail, we investigate a cadaveric spine that shows both types of DD between L1 and L2 and between L2 and L3, respectively. The lumbar spine was obtained from a male donor aged 74 years. The complete specimen was scanned using µCT with an isometric voxel size of 93 µm. Subsequently, regions of interest (ROI) were prepared featuring each complete intervertebral disc including the adjacent endplates. ROIs were then additionally scanned with a voxel size of 35 µm and by means of magnetic resonance imaging. The collapsed endplate of the superior L2 showed explicit signs of an endplate-driven degeneration, including bony endplate failures. In contrast, the intervertebral disc between L2 and L3 showed indications of an annulus-driven DD including severe disc height loss and concentric tears. Using µCT we were able to visualize and quantify bone and cartilage features in DD. We showed that in both cases a suite of structural changes accompanies cartilage degeneration, including microstructural bony adaptions to counteract changes in the biomechanical loading regimen.

Non-Destructive Testing of Ceramic Knee Implants Using Micro-Computed Tomography.

BACKGROUND: Because of the accumulated numbers and the increasing rate of knee replacement surgeries larger numbers of revision cases are likely. Although the success rate of knee arthroplasties is high, complications like the loosening of the implant necessitate subsequent treatments. Therefore, new concepts such as metal-free ceramic implants are necessary, for example, using zirconium dioxide (ZrO2). Several studies showed that the strength of ceramic ZrO2 implants is equivalent to cobalt-chromium components. METHODS: Non-destructive testing remains challenging due to the high density (6 g/cm³) of ZrO2. In this feasibility study, we investigated 8 tibial and 8 femoral implants respectively using an industrial X-ray micro-computed tomography (XCT) system at a voxel size of 100 µm. We established a non-destructive testing protocol for ceramic knee implants optimizing scanning parameters and sample orientation using CT simulations. Finally, we used an iterative artifact reduction procedure for beam hardening correction. RESULTS: The results show that corrected image data enable the non-destructive inspection of high-density components. In this sample, none of the investigated components show any internal defects like pores or cracks. In general, XCT is a major imaging method that is able to provide a 3-dimensional representation of higher dense objects that allows the inspection of metal or ceramic knee implants. Even though we established an optimized scanning routine for tibial and femoral ceramic components, it is not possible to completely eliminate scanning artifacts of XCT. CONCLUSION: Altogether, after visual inspection, none of the beam-hardening corrected XCT data sets for femoral and tibial implants showed any defects, that is, no inclusions, cracks, or pores were detected. XCT test is therefore an essential addition to the fatigue testing since it is the only non-destroying testing method.

Dynamic Volume Lines: Visual Comparison of 3D Volumes through Space-filling Curves.

The comparison of many members of an ensemble is difficult, tedious, and error-prone, which is aggravated by often just subtle differences. In this paper, we introduce Dynamic Volume Lines for the interactive visual analysis and comparison of sets of 3D volumes. Each volume is linearized along a Hilbert space-filling curve into a 1D Hilbert line plot, which depicts the intensities over the Hilbert indices. We present a nonlinear scaling of these 1D Hilbert line plots based on the intensity variations in the ensemble of 3D volumes, which enables a more effective use of the available screen space. The nonlinear scaling builds the basis for our interactive visualization techniques. An interactive histogram heatmap of the intensity frequencies serves as overview visualization. When zooming in, the frequencies are replaced by detailed 1D Hilbert line plots and optional functional boxplots. To focus on important regions of the volume ensemble, nonlinear scaling is incorporated into the plots. An interactive scaling widget depicts the local ensemble variations. Our brushing and linking interface reveals, for example, regions with a high ensemble variation by showing the affected voxels in a 3D spatial view. We show the applicability of our concepts using two case studies on ensembles of 3D volumes resulting from tomographic reconstruction. In the first case study, we evaluate an artificial specimen from simulated industrial 3D X-ray computed tomography (XCT). In the second case study, a real-world XCT foam specimen is investigated. Our results show that Dynamic Volume Lines can identify regions with high local intensity variations, allowing the user to draw conclusions, for example, about the choice of reconstruction parameters. Furthermore, it is possible to detect ring artifacts in reconstructions volumes.

Interactive Exploration and Visualization Using MetaTracts extracted from Carbon Fiber Reinforced Composites.

This work introduces a tool for interactive exploration and visualization using MetaTracts. MetaTracts is a novel method for extraction and visualization of individual fiber bundles and weaving patterns from X-ray computed tomography (XCT) scans of endless carbon fiber reinforced polymers (CFRPs). It is designed specifically to handle XCT scans of low resolutions where the individual fibers are barely visible, which makes extraction of fiber bundles a challenging problem. The proposed workflow is used to analyze unit cells of CFRP materials integrating a recurring weaving pattern. First, a coarse version of integral curves is used to trace sections of the individual fiber bundles in the woven CFRP materials. We call these sections MetaTracts. In the second step, these extracted fiber bundle sections are clustered using a two-step approach: first by orientation, then by proximity. The tool can generate volumetric representations as well as surface models of the extracted fiber bundles to be exported for further analysis. In addition a custom interactive tool for exploration and visual analysis of MetaTracts is designed. We evaluate the proposed workflow on a number of real world datasets and demonstrate that MetaTracts effectively and robustly identifies and extracts fiber bundles.

Virtual reconstruction of modern and fossil hominoid crania: consequences of reference sample choice.

Most hominin cranial fossils are incomplete and require reconstruction prior to subsequent analyses. Missing data can be estimated by geometric morphometrics using information from complete specimens, for example, by using thin-plate splines. In this study, we estimate missing data in several virtually fragmented models of hominoid crania (Homo, Pan, Pongo) and fossil hominins (e.g., Australopithecus africanus, Homo heidelbergensis). The aim is to investigate in which way different references influence estimations of cranial shape and how this information can be employed in the reconstruction of fossils. We used a sample of 64 three-dimensional digital models of complete human, chimpanzee, and orangutan crania and a set of 758 landmarks and semilandmarks. The virtually knocked out neurocranial and facial areas that were reconstructed corresponded to those of a real case found in A.L. 444-2 (A. afarensis) cranium. Accuracy of multiple intraspecies and interspecies reconstructions was computed as the maximum square root of the mean squared difference between the original and the reconstruction (root mean square). The results show that the uncertainty in reconstructions is a function of both the geometry of the knockout area and the dissimilarity between the reference sample and the specimen(s) undergoing reconstruction. We suggest that it is possible to estimate large missing cranial areas if the shape of the reference is similar enough to the shape of the specimen reconstructed, though caution must be exercised when employing these reconstructions in subsequent analyses. We provide a potential guide for the choice of the reference by means of bending energy.

MObjects--a novel method for the visualization and interactive exploration of defects in industrial XCT data.

This paper describes an advanced visualization method for the analysis of defects in industrial 3D X-Ray Computed Tomography (XCT) data. We present a novel way to explore a high number of individual objects in a dataset, e.g., pores, inclusions, particles, fibers, and cracks demonstrated on the special application area of pore extraction in carbon fiber reinforced polymers (CFRP). After calculating the individual object properties volume, dimensions and shape factors, all objects are clustered into a mean object (MObject). The resulting MObject parameter space can be explored interactively. To do so, we introduce the visualization of mean object sets (MObject Sets) in a radial and a parallel arrangement. Each MObject may be split up into sub-classes by selecting a specific property, e.g., volume or shape factor, and the desired number of classes. Applying this interactive selection iteratively leads to the intended classifications and visualizations of MObjects along the selected analysis path. Hereby the given different scaling factors of the MObjects down the analysis path are visualized through a visual linking approach. Furthermore the representative MObjects are exported as volumetric datasets to serve as input for successive calculations and simulations. In the field of porosity determination in CFRP non-destructive testing practitioners use representative MObjects to improve ultrasonic calibration curves. Representative pores also serve as input for heat conduction simulations in active thermography. For a fast overview of the pore properties in a dataset we propose a local MObjects visualization in combination with a color-coded homogeneity visualization of cells. The advantages of our novel approach are demonstrated using real world CFRP specimens. The results were evaluated through a questionnaire in order to determine the practicality of the MObjects visualization as a supportive tool for domain specialists.

Projection-based metal-artifact reduction for industrial 3D X-ray computed tomography.

Multi-material components, which contain metal parts surrounded by plastic materials, are highly interesting for inspection using industrial 3D X-ray computed tomography (3DXCT). Examples of this application scenario are connectors or housings with metal inlays in the electronic or automotive industry. A major problem of this type of components is the presence of metal, which causes streaking artifacts and distorts the surrounding media in the reconstructed volume. Streaking artifacts and dark-band artifacts around metal components significantly influence the material characterization (especially for the plastic components). In specific cases these artifacts even prevent a further analysis. Due to the nature and the different characteristics of artifacts, the development of an efficient artifact-reduction technique in reconstruction-space is rather complicated. In this paper we present a projection-space pipeline for metal-artifacts reduction. The proposed technique first segments the metal in the spatial domain of the reconstructed volume in order to separate it from the other materials. Then metal parts are forward-projected on the set of projections in a way that metal-projection regions are treated as voids. Subsequently the voids, which are left by the removed metal, are interpolated in the 2D projections. Finally, the metal is inserted back into the reconstructed 3D volume during the fusion stage. We present a visual analysis tool, allowing for interactive parameter estimation of the metal segmentation. The results of the proposed artifact-reduction technique are demonstrated on a test part as well as on real world components. For these specimens we achieve a significant reduction of metal artifacts, allowing an enhanced material characterization.

A comparative study of high resolution cone beam X-ray tomography and synchrotron tomography applied to Fe- and Al-alloys.

X-ray computed tomography (XCT) has become a very important method for non-destructive 3D-characterization and evaluation of materials. Due to measurement speed and quality, XCT systems with cone beam geometry and matrix detectors have gained general acceptance. Continuous improvements in the quality and performance of X-ray tubes and XCT devices have led to cone beam CT systems that can now achieve spatial resolutions down to 1 µm and even below. However, the polychromatic nature of the source, limited photon flux and cone beam artefacts mean that there are limits to the quality of the CT-data achievable; these limits are particularly pronounced with materials of higher density like metals. Synchrotron radiation offers significant advantages by its monochromatic and parallel beam of high brilliance. These advantages usually cause fewer artefacts, improved contrast and resolution.Tomography data of a steel sample and of two multi-phase Al-samples (AlSi12Ni1, AlMg5Si7) are recorded by advanced cone beam XCT-systems with a µ-focus (µXCT) and a sub-µm (nano-focus, sub-µXCT) X-ray source with voxel dimensions between 0.4 and 3.5 µm and are compared with synchrotron computed tomography (sXCT) with 0.3 µm/voxel. CT data features like beam hardening and ring artefacts, detection of details, sharpness, contrast, signal-to-noise ratio and the grey value histogram are systematically compared. In all cases µXCT displayed the lowest performance. Sub-µXCT gives excellent results in the detection of details, spatial and contrast resolution, which are comparable to synchrotron-XCT recordings. The signal-to-noise ratio is usually significantly lower for sub-µXCT compared with the two other methods. With regard to measurement costs "for industrial users", scanning volume, accessibility and user-friendliness sub-µXCT has significant advantages in comparison to synchrotron-XCT.

Surface extraction from multi-material components for metrology using dual energy CT.

This paper describes a novel method for creating surface models of multi-material components using dual energy computed tomography (DECT). The application scenario is metrology and dimensional measurement in industrial high resolution 3D x-ray computed tomography (3DCT). Based on the dual source / dual exposure technology this method employs 3DCT scans of a high precision micro-focus and a high energy macro-focus x-ray source. The presented work makes use of the advantages of dual x-ray exposure technology in order to facilitate dimensional measurements of multi-material components with high density material within low density material. We propose a workflow which uses image fusion and local surface extraction techniques: a prefiltering step reduces noise inherent in the data. For image fusion the datasets have to be registered. In the fusion step the benefits of both scans are combined. The structure of the specimen is taken from the low precision, blurry, high energy dataset while the sharp edges are adopted and fused into the resulting image from the high precision, crisp, low energy dataset. In the final step a reliable surface model is extracted from the fused dataset using a local adaptive technique. The major contribution of this paper is the development of a specific workflow for dimensional measurements of multi-material industrial components, which takes two x-ray CT datasets with complementary strengths and weaknesses into account. The performance of the workflow is discussed using a test specimen as well as two real world industrial parts. As result, a significant improvement in overall measurement precision, surface geometry and mean deviation to reference measurement compared to single exposure scans was facilitated.

Surface area analysis of dental implants using micro-computed tomography.

OBJECTIVES: In this study, we present and evaluate a micro-computed tomography (micro-CT)-based method for the calculation of the potential bone/implant contact area (p-BICA) on the surface of dental implants. MATERIAL AND METHODS: For seven commercially available implants (Ankylos implant, Brånemark System, Frialit CELLplus, Replace((R)) Select Tapered, Straumann Solid screw, XiVE S CELLplus, 3i Osseotite XP Threaded Miniplant, the p-BICA surface is determined by means of three-dimensional X-ray computed-tomography and computer-based data processing. Measurements were repeated two times, and the stability and repeatability of the measurement method were evaluated. RESULTS: Our analysis revealed a p-BICA of 118 mm(2) for the XiVE S CELLplus implant, 134 mm(2) for the Ankylos, 136 mm(2) for the Frialit CELLplus, 138 mm(2) for the Brånemark System, 139 mm(2) for the Replace((R)), 159 mm(2) for the 3i Osseotite XP and 199 mm(2) for the Straumann Solid screw implant. The measurement method proved to be stable and led to reproducible results. CONCLUSIONS: The micro- and macrostructure of dental implants define the surface and the p-BICA. Precise determination of this parameter can be achieved by means of the micro-CT-based method as presented in this study. The value of p-BICA lies in the predictability of industrial design before preclinical and clinical testing. Based on this method, dental implant properties become comparable even if geometrical details are not disclosed by the manufacturer.

A model for clubfoot based on micro-CT data.

The pathological anatomy of idiopathic clubfoot has been investigated for more than 180 years using anatomy, computed tomography (CT), histology and microscopy. Seven idiopathic clubfeet and two normal feet of aborted fetuses were dissected in the present study, with special emphasis on the shape of the cartilage and bones. A three-dimensional (3D) micro-CT system, which generates a series of X-ray attenuation measurements, was used to produce computed reconstructed 3D data sets of each of the separated bones. Based on the micro-CT data scans a high-definition 3D colour printing system was used to make a four times enlarged clubfoot model, precisely presenting all the bony malformations. This model reflects the complexity of the anatomy of this disease and is designed to be used in the workshops of orthopaedic surgeons and physiotherapists, for training in new surgical and manipulation techniques.