Jelle Vlassenbroeck

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.

Virtual histology by means of high-resolution X-ray CT

Micro‐CT is a non‐destructive technique for 3D tomographic investigation of an object. A 3D representation of the internal structure is calculated based on a series of X‐ray radiographs taken from different angles. The spatial resolution of current laboratory‐used micro‐CT systems has come down over the last years from a few tens of microns to a few microns. This opens the possibility to perform histological investigations in 3D on a virtual representation of a sample, referred to as virtual 3D histology. The advantage of micro‐CT based virtual histology is the immediate and automated 3D visualization of the sample without prior slicing, sample preparation like decalcification, photographing and aligning. This not only permits a drastic reduction in preparation time but also offers the possibility to easily investigate objects that are difficult to slice. This article presents results that were obtained on punch biopsies of horse skin, (dental) alveolus of ponies and chondro‐osseous samples from the tarsus of foals studied with the new high resolution micro‐CT set‐up (HRXCT) at the Ghent University (Belgium) (http://www.ugct.ugent.be). This state‐of‐the‐art set‐up provides a 1 micron resolution and is therefore ideally suited for a direct comparison with standard light microscopy–based histology.

Development and evaluation of injection-molded sustained-release tablets containing ethylcellulose and polyethylene oxide

Purpose: It was the aim of the present study to develop sustained-release matrix tablets by means of injection molding of ethylcellulose (EC) and polyethylene oxide (PEO) mixtures and to evaluate the influence of process temperature, matrix composition, and viscosity grade of EC and PEO on processability and drug release. Methods: Formulations consisting of metoprolol tartrate (MPT, concentration: 30%), EC plasticized by dibutyl sebacate, and PEO were extruded and consequently injection molded into tablets. The influence of process temperature (120°C and 140°C), matrix composition, viscosity grade of EC (4, 10, 20, 45, and 100 mPa·s) and PEO (7 × 106, 1 × 106, and 1 × 105 Mw) on processability and drug release was determined. Results: Formulations consisting of 70% EC and 30% MPT showed incomplete drug release, whereas drug release was too fast for formulations without EC. Higher PEO concentrations increased drug release. Formulations containing 30% metoprolol, EC, and different concentrations of PEO showed first-order release rates with limited burst release. Drug release from direct compressed tablets showed faster drug release rates compared to injection-molded formulations. There was no clear relationship between the molecular weight of EC and drug release. The melting endotherm (113.9°C) of MPT observed in the differential scanning calorimeter thermogram of the tablets indicated that a solid dispersion was formed which was confirmed by X-ray diffractogram. X-ray tomography demonstrated a difference in pore structure between tablets processed at 120°C and 140°C. Conclusion: It was concluded that injection molding can be applied successfully to develop sustained-release PEO/EC matrix tablets.

A Multiresolution Approach to Iterative Reconstruction Algorithms in X-Ray Computed Tomography

In computed tomography, the application of iterative reconstruction methods in practical situations is impeded by their high computational demands. Especially in high resolution X-ray computed tomography, where reconstruction volumes contain a high number of volume elements (several giga voxels), this computational burden prevents their actual breakthrough. Besides the large amount of calculations, iterative algorithms require the entire volume to be kept in memory during reconstruction, which quickly becomes cumbersome for large data sets. To overcome this obstacle, we present a novel multiresolution reconstruction, which greatly reduces the required amount of memory without significantly affecting the reconstructed image quality. It is shown that, combined with an efficient implementation on a graphical processing unit, the multiresolution approach enables the application of iterative algorithms in the reconstruction of large volumes at an acceptable speed using only limited resources.

Extensive Jaw Mobility in Suckermouth Armored Catfishes (Loricariidae): A Morphological and Kinematic Analysis of Substrate Scraping Mode of Feeding*

Loricariidae, or suckermouth armored catfishes, possess upper and lower jaws that are ventrally oriented and that bear teeth that touch the substrate from which algae and other food items are scraped. The ventral orientation and the highly specialized morphology of the jaws, characterized by protrusible upper jaws and left‐right decoupled lower jaws, are observed in Pterygoplichthys disjunctivus, the species investigated here. Kinematic data of the scraping feeding movements, obtained by external high‐speed and x‐ray recordings, are used to quantify jaw movement, especially to test for upper jaw mobility and versatility during substrate scraping. Our results show that the mobility of the jaws is indeed high compared with what is standard for catfishes. The upper jaws ability to perform a substantial degree of rostrocaudal movement is quite unique for catfishes. The ventromedially oriented lower jaws, with the teeth and the coronoid process at opposite sides, display an extensive mobility: they rotate around the suspensorial articulation and around their longitudinal axis, resulting in an extended scraping movement and thereby covering a large surface area. The lower jaws also show a left‐right asymmetry in their movements during scraping. Thus, our results suggest that the extreme morphological specializations of the jaws in loricariid catfishes are linked to an increased mobility and functional versatility, allowing these animals to efficiently scrape algae from substrates with irregular surfaces.

A comparative and critical study of X-ray CT and neutron CT as non-destructive material evaluation techniques

Abstract X-ray computerized tomography (CT) has traditionally been used as a medical diagnostic tool. This non-destructive technique has developed as an important research tool for a wide variety of scientific subjects. For material research ‘medical’ CT, microCT and, very recently, nano- or submicroCT have been used as non-destructive material evaluation techniques for engineering and geological purposes. The fact that X-ray CT visualizes the internal structure of natural building stones and yields information on porosity values and pore-size distributions is a major advantage for the study of their conservation. The penetration of fluids like water, consolidants or water repellents inside porous materials is important when dealing with conservation and restoration research. Recently, high-speed neutron tomography has been introduced as a visualization technique for fluids inside porous materials. High-speed neutron tomography can be used as a complementary technique to X-ray tomography as elements like hydrogen, which have a weak attenuation for X-rays, are easy to detect using neutrons. In this paper the basic principles of computerized tomography and more specifically X-ray and neutron tomography are discussed. In addition, application possibilities, advantages and limitations of medical CT, X-ray microCT and high-speed thermal neutron CT are outlined.

Correcting phase contrast artefacts in X-ray CT imaging

When going to higher resolution in X-ray transmission CT, one of the biggest problems is the appearance of phase contrast. Achieving high resolution usually means scanning very small and thus very low absorbing objects, especially in medical and biological applications. Since the absorption signal for such samples becomes very small, the contribution of the phase contrast signal to the projection image is no longer negligible. This phase signal, which is due to small angle refraction of the X-rays in the sample, results in severe artifacts in the reconstructed slices when using conventional reconstruction algorithms for transmission CT. The appearance of such phase artifacts can be prevented by using a method called Bronnikov Aided Correction, which applies a filtering operation on the projection images that almost completely removes the phase signal. This method is used to reconstruct a CT scan of a horse biopsy. Results are compared with those of a standard reconstruction.

UGCT: the new CT facility of the Ghent University (Belgium)

TheUGCTX-ray tomography facility is a cooperation between theRadiation Physics research group (Department of Subatomic and Radiation Physics, Ghent University) and the Sedimentary Geology and Engineering Geology research group (Department of Geology and Soil Science, Ghent University). The facility operates a number of setups offering a wide range of spatial resolutions, X-ray energies and sample sizes. First there is a state-of-the-art transmission typeX-ray tubewith sub-micron focal spot size (900 nm) for extreme-high resolution CT with resolutions down to 1micron for samples up to 4 mm diameter. Secondly a high-power water-cooled X-ray tube is available with an energy between 30 and 160 keV for regular micro-CT applications with resolutions down to 3micron. For large and/or heavy samples up to 40 cm diameter, a dedicated beamline is available at the linear electron accelerator with high-energy X-rays up to 10MeV. The setups are built in room-size bunkers, allowing flexible experimental conditions such as conditioned environments or experimental equipment for real-time sample conditioning. In addition the facility also operates a desktop micro-CT scanner from Skyscan (model 1072) and a medical CT scanner from Philips (Tomoscan SR5000) for particular applications. The facility has several detectors available which are suited for the various applications. For nanoandmicro-CT imaging, a high-resolution 16 bit CCD camera (4K x 2.7K 9μ pixels, 1:1 fiber-optic coupling) and a 12 bit flat panel CMOS detector (1024x512 50μ pixels) are available. For high-speed applications a 6’’ large-field image intensifier can be used. For high-energy applications, a 1Kx1K CCD camera is used which is lens-coupled to a large scintillator that is optimized for high energies. m26.o01