Luc Van Hoorebeke

Three-dimensional analysis of high-resolution X-ray computed tomography data with Morpho+

Three-dimensional (3D) analysis is an essential tool to obtain quantitative results from 3D datasets. Considerable progress has been made in 3D imaging techniques, resulting in a growing need for more flexible, complete analysis packages containing advanced algorithms. At the Centre for X-ray Tomography of the Ghent University (UGCT), research is being done on the improvement of both hardware and software for high-resolution X-ray computed tomography (CT). UGCT collaborates with research groups from different disciplines, each having specific needs. To meet these requirements the analysis software package, Morpho+, was developed in-house. Morpho+ contains an extensive set of high-performance 3D operations to obtain object segmentation, separation, and parameterization (orientation, maximum opening, equivalent diameter, sphericity, connectivity, etc.), or to extract a 3D geometrical representation (surface mesh or skeleton) for further modeling. These algorithms have a relatively short processing time when analyzing large datasets. Additionally, Morpho+ is equipped with an interactive and intuitive user interface in which the results are visualized. The package allows scientists from various fields to obtain the necessary quantitative results when applying high-resolution X-ray CT as a research tool to the nondestructive investigation of the microstructure of materials.

HECTOR : a 240kV micro-CT setup optimized for research

X-ray micro-CT has become a very powerful and common tool for non-destructive three-dimensional (3D) visualization and analysis of objects. Many systems are commercially available, but they are typically limited in terms of operational freedom both from a mechanical point of view as well as for acquisition routines. HECTOR is the latest system developed by the Ghent University Centre for X-ray Tomography (http://www.ugct.ugent.be) in collaboration with X-Ray Engineering (XRE bvba, Ghent, Belgium). It consists of a mechanical setup with nine motorized axes and a modular acquisition software package and combines a microfocus directional target X-ray source up to 240 kV with a large flat-panel detector. Provisions are made to install a line-detector for a maximal operational range. The system can accommodate samples up to 80 kg, 1 m long and 80 cm in diameter while it is also suited for high resolution (down to 4 μm) tomography. The bi-directional detector tiling is suited for large samples while the variable source-detector distance optimizes the signal to noise ratio (SNR) for every type of sample, even with peripheral equipment such as compression stages or climate chambers. The large vertical travel of 1 m can be used for helical scanning and a vertical detector rotation axis allows laminography experiments. The setup is installed in a large concrete bunker to allow accommodation of peripheral equipment such as pumps, chillers, etc., which can be integrated in the modular acquisition software to obtain a maximal correlation between the environmental control and the CT data taken. The acquisition software does not only allow good coupling with the peripheral equipment but its scripting feature is also particularly interesting for testing new and exotic acquisition routines.

Development of injection moulded matrix tablets based on mixtures of ethylcellulose and low-substituted hydroxypropylcellulose

The objective of this study was to produce sustained-release matrix tablets by means of injection moulding and to evaluate the influence of matrix composition, process temperature and viscosity grade of ethylcellulose on processability and drug release by means of a statistical design. The matrix tablets were physico-chemically characterized and the drug release mechanism and kinetics were studied. Formulations containing metoprolol tartrate (30%, model drug), ethylcellulose with dibutylsebacate (matrix former and plasticizer) and L-HPC were extruded and subsequently injection moulded into tablets (375mg, 10mm diameter, convex-shaped) at different temperatures (110, 120 and 130 degrees C). Dissolution tests were performed and tablets were characterized by means of DSC, X-ray powder diffraction studies, X-ray tomography, porosity and hardness. Tablets containing 30% metoprolol and 70% ethylcellulose (EC 4cps) showed an incomplete drug release within 24h (<50%). Formulations containing L-HPC and EC in a ratio of 20/50 and 27.5/42.5 resulted in nearly zero-order drug release, while the drug release rate was not constant when 35% L-HPC was included. Processing of these formulations was possible at all temperatures, but at higher processing temperatures the drug release rate decreased and tablet hardness increased. Higher viscosity grades of EC resulted in a faster drug release and a higher tablet hardness. The statistical design confirmed a significant influence of the EC and L-HPC concentration on drug release, while the processing temperature and EC viscosity grade did not affect drug release. Tablet porosity was low (<5%), independent of the formulation and process conditions. DSC and XRD demonstrated the formation of a solid dispersion. The hydration front in the tablets during dissolution was visualized by dynamic X-ray tomography, this technique also revealed an anisotropic pore structure through the tablet.

From Vascular Corrosion Cast to Electrical Analog Model for the Study of Human Liver Hemodynamics and Perfusion

Hypothermic machine perfusion (HMP) is experiencing a revival in organ preservation due to the limitations of static cold storage and the need for better preservation of expanded criteria donor organs. For livers, perfusion protocols are still poorly defined, and damage of sinusoidal endothelial cells and heterogeneous perfusion are concerns. In this study, an electrical model of the human liver blood circulation is developed to enlighten internal pressure and flow distributions during HMP. Detailed vascular data on two human livers, obtained by combining vascular corrosion casting, micro-CT-imaging and image processing, were used to set up the electrical model. Anatomical data could be measured up to 5-6 vessel generations in each tree and showed exponential trend lines, used to predict data for higher generations. Simulated flow and pressure were in accordance with literature data. The model was able to simulate effects of pressure-driven HMP on liver hemodynamics and reproduced observations such as flow competition between the hepatic artery and portal vein. Our simulations further indicate that, from a pure biomechanical (shear stress) standpoint, HMP with low pressures should not result in organ damage, and that fluid viscosity has no effect on the shear stress experienced by the liver microcirculation in pressure-driven HMP.

Three-Dimensional X-Ray Imaging and Analysis of Fungi on and in Wood

As wood is prone to fungal degradation, fundamental research is necessary to increase our knowledge aiming at product improvement. Several imaging modalities are capable of visualizing fungi, but the X-ray equipment presented in this article can envisage fungal mycelium in wood nondestructively in three dimensions with submicron resolution. Four types of wood subjected to the action of the white rot fungus Coriolus versicolor (Linnaeus) Quélet (CTB 863 A) were scanned using an X-ray-based approach. Comparison of wood volumes before and after fungal exposure, segmented manually or semiautomatically, showed the presence of the fungal mass on and in the wood samples and therefore demonstrated the usefulness of computed X-ray tomography for mycological and wood research. Further improvements to the experimental setup are necessary to resolve individual hyphae and enhance segmentation.

Bronnikov-aided correction for x-ray computed tomography

When a very-low-absorbing sample is scanned at an x-ray computed tomography setup with a microfocus x-ray tube and a high-resolution detector, the obtained projection images contain not only absorption contrast but also phase contrast. While images without a phase signal can be reconstructed very well, such mixed phase and absorption images give rise to severe artifacts in the reconstructed slices. A method is described that applies a correction to these mixed projections to remove the phase signal. These corrected images can then be processed using a standard filtered backprojection algorithm to obtain reconstructions with only few or no phase artifacts. This new method, which we call the Bronnikov-aided correction (BAC), can be used in a broad variety of applications and without much additional effort. It is tested on a biological and a pharmaceutical sample, and results are evaluated and discussed by comparing them with those of conventional reconstruction methods.

X-ray tomography as a tool for detailed anatomical analysis

Abstract• Wood identification, anatomical examination and retrieval of quantitative information are important aspects of many research disciplines. Conventional light microscopy with a camera and (semi)-automatic image analysis software is an often used methodology for these purposes. More advanced techniques such as fluorescence, scanning electron, transmission electron, confocal laser scanning and atomic force microscopy are also part of the toolset answering to the need for detailed imaging.• Fast, non-destructive visualization in three dimensions with high resolution combined with a broad field of view is sought-after, especially in combination with flexible software.• A highly advanced supplement to the existing techniques, namely X-ray sub-micron tomography, meets these requirements. It enables the researcher to visualize the material with a voxel size approaching < 1 μm for small samples (< 1 mm). Furthermore, with tailor-made processing software quantitative data about the wood in two and three dimensions can be obtained. Examples of visualization and analysis of four wood species are given in this paper, focusing on the opportunities of tomography at micron and sub-micron resolution.• X-ray computed tomography offers many possibilities for material research in general and wood science in specific, as a qualitative as well as a quantitative technique.Résumé• L’identification du bois, l’observation anatomique et l’obtention d’informations quantitatives sont des aspects importants dans différentes disciplines scientifiques. La microscopie optique conventionnelle couplée à l’acquisition et au traitement semi automatique des images est souvent utilisée pour atteindre ces objectifs. Des techniques plus récentes comme la fluorescence, la microscopie électronique par balayage ou par transmission, la microscopie confocale ou encore à force atomique constituent une panoplie d’outils répondant à ces besoins d’imagerie fine.• Il y a une forte demande d’outils non destructifs de visualisation 3D à haute résolution combinés à un large champ de vision et surtout avec des logiciels flexibles.• En complément avancé à ces techniques la tomographie RX submicrométrique remplit ces conditions. Elle permet au chercheur de visualiser le matériau avec une taille de voxel inférieure au micron pour de petits échantillons dont la taille est inférieure au mm. En outre, à l’aide de logiciels de traitement adaptés, des données quantitatives peuvent être obtenues pour le bois en deux et trois dimensions. Dans ce papier on présente des exemples de visualisation et d’analyse pour quatre essences en focalisant sur les possibilités de tomographie aux échelles micrométrique et submicrométrique.• La tomographie RX offre de nombreuses possibilités pour la recherche en science des matériaux en général et en sciences du bois en particulier, que ce soit pour les approches qualitatives ou pour les approches quantitatives.

Perfusion characteristics of the human hepatic microcirculation based on three-dimensional reconstructions and computational fluid dynamic analysis

The perfusion of the liver microcirculation is often analyzed in terms of idealized functional units (hexagonal liver lobules) based on a porous medium approach. More elaborate research is essential to assess the validity of this approach and to provide a more adequate and quantitative characterization of the liver microcirculation. To this end, we modeled the perfusion of the liver microcirculation using an image-based three-dimensional (3D) reconstruction of human liver sinusoids and computational fluid dynamics techniques. After vascular corrosion casting, a microvascular sample (±0.134 mm(3)) representing three liver lobules, was dissected from a human liver vascular replica and scanned using a high resolution (2.6 μm) micro-CT scanner. Following image processing, a cube (0.15 × 0.15 × 0.15 mm(3)) representing a sample of intertwined and interconnected sinusoids, was isolated from the 3D reconstructed dataset to define the fluid domain. Three models were studied to simulate flow along three orthogonal directions (i.e., parallel to the central vein and in the radial and circumferential directions of the lobule). Inflow and outflow guidances were added to facilitate solution convergence, and good quality volume meshes were obtained using approximately 9 × 10(6) tetrahedral cells. Subsequently, three computational fluid dynamics models were generated and solved assuming Newtonian liquid properties (viscosity 3.5 mPa s). Post-processing allowed to visualize and quantify the microvascular flow characteristics, to calculate the permeability tensor and corresponding principal permeability axes, as well as the 3D porosity. The computational fluid dynamics simulations provided data on pressure differences, preferential flow pathways and wall shear stresses. Notably, the pressure difference resulting from the flow simulation parallel to the central vein (0-100 Pa) was clearly smaller than the difference from the radial (0-170 Pa) and circumferential (0-180 Pa) flow directions. This resulted in a higher permeability along the central vein direction (k(d,33) = 3.64 × 10(-14) m(2)) in comparison with the radial (k(d,11) = 1.56 × 10(-14) m(2)) and circumferential (k(d,22) = 1.75 × 10(-14) m(2)) permeabilities which were approximately equal. The mean 3D porosity was 14.3. Our data indicate that the human hepatic microcirculation is characterized by a higher permeability along the central vein direction, and an about two times lower permeability along the radial and circumferential directions of a lobule. Since the permeability coefficients depend on the flow direction, (porous medium) liver microcirculation models should take into account sinusoidal anisotropy.

Novel gelatin–PHEMA porous scaffolds for tissue engineering applications

In the present work, novel bicomponent polymeric hydrogels based on methacrylamide-modified gelatin (MAG) and 2-hydroxyethyl methacrylate (HEMA) have been prepared by cross-linking polymerization using photoinitiation. Five types of novel hydrogels have been prepared using different MAG/HEMA ratios between 1/0.5 and 1/10 w/w. Subsequently, porous scaffolds were obtained via a cryogenic treatment followed by freeze-drying. Physico-chemical measurements as well as in vitro degradation tests have been performed in order to correlate the material composition with the corresponding properties. Among the properties studied we have to mention the water uptake capacity, the rheological properties and the enzyme-mediated degradation behaviour. The results indicate that the HEMA content in the initial polymerization mixtures modulates the architecture of the porous scaffolds from straightforward, top-to-bottom oriented channels for hydrogels possessing the lowest HEMA content to a complex and dense internal porosity of the channels the case of higher HEMA loaded materials. While aiming at tissue engineering applications, it is important to notice that the covalently bound gelatin sequences significantly improve the biocompatibility of PHEMA based hydrogels.

Biomechanical determinants of bite force dimorphism in Cyclommatus metallifer stag beetles

In the stag beetle family (Lucanidae), males have diverged from females by sexual selection. The males fight each other for mating opportunities with their enlarged mandibles. It is known that owners of larger fighting apparatuses are favoured to win the male–male fights, but it was unclear whether male stag beetles also need to produce high bite forces while grabbing and lifting opponents in fights. We show that male Cyclommatus metallifer stag beetles bite three times as forcefully as females. This is not entirely unexpected given the spectacular nature of the fights, but all the more impressive given the difficulty of achieving this with their long mandibles (long levers). Our results suggest no increase in male intrinsic muscle strength to accomplish this. However, morphological analyses show that the long mandibular output levers in males are compensated by elongated input levers (and thus a wider anterior side of the head). The surplus of male bite force capability is realized by enlargement of the closer muscles of the mandibles, while overall muscle force direction remained optimal. To enable the forceful bites required to ensure male reproductive success, male head size and shape are adapted for long input levers and large muscles. Therefore, the entire head should be regarded as an integral part of male armature.