In this work, we present a novel laboratory‐based microcomputed tomography (micro‐CT) experiment designed to investigate the pore‐scale drainage behavior of natural sandstone under dynamic ...conditions. The fluid distribution in a Bentheimer sandstone was visualized every 4 s with a 12 s measurement time, allowing the investigation of single‐pore and few‐pore‐filling events. To our knowledge, this is the first time that such measurements were performed outside of synchrotron facilities, illustrating the growing application potential of laboratory‐based micro‐CT with subminute temporal resolutions for geological research at the pore scale. To illustrate how the workflow can lead to an improved understanding of drainage behavior, the experiment was analyzed using a decomposition of the pore space into individual geometrical pores. Preliminary results from this analysis suggest that the distribution of drainage event sizes follows a power law scaling, as expected from percolation theory.
Key Points:
Drainage in sandstone was visualized with bench‐top micro‐CT scanner at 12 s/scan
Single‐pore and multiple pore‐filling events were analyzed by tracking gray values in individual pores
Methods presented here allow to inspect the validity of percolation theory to describe the invasion
X-ray imaging is an important tool for quality control since it allows to inspect the interior of products in a non-destructive way. Conventional x-ray imaging, however, is slow and expensive. Inline ...x-ray inspection, on the other hand, can pave the way towards fast and individual quality control, provided that a sufficiently high throughput can be achieved at a minimal cost. To meet these criteria, an inline inspection acquisition geometry is proposed where the object moves and rotates on a conveyor belt while it passes a fixed source and detector. Moreover, for this acquisition geometry, a new neural-network-based reconstruction algorithm is introduced: the neural network Hilbert transform based filtered backprojection. The proposed algorithm is evaluated both on simulated and real inline x-ray data and has shown to generate high quality reconstructions of 400 × 400 reconstruction pixels within 200 ms, thereby meeting the high throughput criteria.
In computed tomography (CT), motion and deformation during the acquisition lead to streak artefacts and blurring in the reconstructed images. To remedy these artefacts, we introduce an efficient ...algorithm to estimate and correct for global affine deformations directly on the cone beam projections. The proposed technique is data driven and thus removes the need for markers and/or a tracking system. A relationship between affine transformations and the cone beam transform is proved and used to correct the projections. The deformation parameters that describe deformation perpendicular to the projection direction are estimated for each projection by minimizing a plane-based inconsistency criterion. The criterion compares each projection of the main scan with all projections of a fast reference scan, which is acquired prior or posterior to the main scan. Experiments with simulated and experimental data show that the proposed affine deformation estimation method is able to substantially reduce motion artefacts in cone beam CT images.
In X-ray computed tomography (CT) each voxel of the reconstructed image contains a calculated grey value which represents the linear attenuation coefficient for the materials in that voxel. ...Conventional laboratory based CT scanners use polychromatic X-ray sources and integrating detectors with an energy dependent efficiency. Consequently the reconstructed attenuation coefficients will depend on the spectrum of the source and the spectral sensitivity of the detector. Beam hardening will alter the spectrum significantly as the beam propagates through the sample. Therefore, sample composition and shape will affect the reconstructed attenuation coefficients as well.
A polychromatic projection simulator has been developed at the “Centre for X-ray Tomography” of the Ghent University (UGCT) which takes into account the aforementioned variables, allowing for complete and realistic simulations of CT scans for a wide range of geometrical setups. Monte Carlo simulations of the X-ray tubes and detectors were performed to model their spectral behaviour. In this paper, the implementation and features of the program are discussed. Simulated and real CT scans are compared to demonstrate the quantitative correctness of the simulations. Experiments performed at two different UGCT scanners yield a maximum deviation of 3.9% and 6.5% respectively, between the measured and simulated reconstructed attenuation coefficients.
This work presents a framework to exploit the synergy between Digital Volume Correlation (DVC) and iterative CT reconstruction to enhance the quality of high-resolution dynamic X-ray CT (4D-µCT) and ...obtain quantitative results from the acquired dataset in the form of 3D strain maps which can be directly correlated to the material properties. Furthermore, we show that the developed framework is capable of strongly reducing motion artifacts even in a dataset containing a single 360° rotation.
An alternative acquisition geometry for X-ray computed tomography (CT) is investigated as a solution to in-line non-destructive quality inspection in a high throughput production environment. The ...sample movement during acquisition combines a translation, typically horizontal, along one axis and a rotation about a second axis perpendicular to the first, and is shown to produce theoretically exact CT reconstructions. A methodology is presented to evaluate the design of a conveyor belt implementation for this acquisition scheme, investigating the trade-off between reconstruction quality and throughput. The methodology was applied in both a simulated version and an experimental mock-up of the conveyor belt implementation for a specific food sample, but can be extrapolated to any type of sample. Throughput, for the food sample, is predicted to be in a practically usable range of up to 5 samples per second. As a general conclusion, higher throughput can be reached with larger inspection stations while maintaining image quality.
•In-line conveyor belt X-ray CT combining the translation and rotation of a sample.•Conditions for theoretically exact reconstructions of conveyor belt CT data are met.•Parametric design methodology to evaluate reconstruction quality and throughput.•Simulation and mock-up implementation of a conveyor belt CT inspection station.•Larger CT inspection stations achieve higher throughputs while conserving image quality.
We present a new approach to 3‐dimensional chemical imaging based on X‐ray computed micro tomography (CT), which enables the analysis of the internal elemental chemistry. The method uses a ...conventional laboratory‐based CT scanner equipped with a semiconductor detector (CdTe). Based on the X‐ray absorption spectra, elements in a sample can be distinguished by their specific K‐edge energy. The capabilities and performance of this new approach are illustrated with different experiments, i.e. single pure element particle measurements, element differentiation in mixtures, and mineral differentiation in a natural rock sample. The results show that the method can distinguish elements with K‐edges in the range of 20 to 160 keV, this corresponds to an element range from Ag to U. Furthermore, the spectral information allows a distinction between materials, which show little variation in contrast in the reconstructed CT image.
Piecewise linear fitting, the technique proposed in this paper, performs data reduction on a large dynamic CT dataset and it already takes a step in the direction of the data analysis and ...characterization that needs to be performed afterwards. In addition, it drastically improves the signal-to-noise ratio. This is demonstrated on two complementary samples: a Bentheimer sandstone and a pharmaceutical tablet.
This technique is developed for dynamic high-resolution CT scanning or 4D-μCT, a tool to study dynamic processes in situ on the micro-scale. We propose to start from the low quality reconstruction and perform a piecewise linear fit in the time direction for each voxel. This effectively uses the nearby temporal information, regardless of the nature of the dynamic process, without introducing spatial correlation.
•A post-reconstruction data reduction technique for 4D CT data is proposed.•The result can be used for the analysis of the microstructural behaviour.•The signal-to-noise ratio is highly improved while maintaining spatial resolution.•The technique is very generic and can be applied in a large variety of materials.
The effect of low molecular weight gelatin peptides on the shrinkage of thawed mousses was investigated. Changes promoted by freezing-thawing processes were evaluated through texture and volume ...measurements and through X-ray analysis of the bubble distribution. Freezing provoked collapse of the standard reference recipe mousse and of the reference recipe mousse with 2% milk powder added, but samples containing 2% gelatin peptides showed no shrinkage. The bubble size and bubble number distribution of the different mousses were measured based on high-resolution X-ray tomography. Results indicated that the volume losses experienced by the controls were almost entirely caused by the disappearance of air bubbles having a diameter smaller than 50 μm. Hence, this fraction of over-pressurised air bubbles is extra stabilised by the matrix due to the additional presence of gelatin peptides. Moreover, gelatin peptides were found to inhibit ice crystal growth, which resulted in smaller ice crystals that are believed to be less destructive to the microstructure of the freeze-thawed mousses.
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•Gelatin peptides protect frozen mousses against collapse and volume loss.•Gelatin peptides fortify the microstructure by stabilising air bubbles.•Gelatin peptides have a most profound effect on the <50 μm fraction air bubbles.•Gelatin peptides inhibit ice crystal growth.
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