X-ray Computed Tomography Device Research Articles

Improving accuracy reconstruction of parts through a capability study: A methodology for X-ray Computed Tomography Robotic Cell

Aeronautical performance is enhanced by increasingly complex and lightweight composite parts. The improvement of their manufacturing must ensure the quality measured by Non-Destructive Testing. To evaluate the health of aeronautical parts that are a few meters long, we built a high dimensional robotic cell including two industrial robots positioned on 5-meter-tracks equipped with X-ray Computed Tomography devices. Our main objective is to reconstruct the interior of the parts and detect any anomaly that may have occurred during life cycle or manufacturing (such as porosity or inclusions). In this way, the objective is to present a methodology, firstly, to evaluate the raw process capability and secondly, to assess the improved process capability. The raw process capability uses geometrical identification and we demonstrate that without proper identification, some defects can remain hidden. Three strategies are then developed. The first one involves improving the robot behavior model, which takes into account a thermo-geometrical model, including backlash compensation. Due to possible repositioning problems and to ensure the correct knowledge of the source with respect to the detector, the second strategy involves a real-time test phantom located on the detector named the comb prototype. Finally, a large-sized steel balls phantom is designed to allow a calibration in the full workspace of the robots. This phantom is also used to accurately determine the axis of the rotary horizontal-axis support on which the large parts to be controlled are fixed. We demonstrate that such an architecture, for reconstructing a perfect sphere, leads to an initial mean radius error of 0.05 mm which we improve to 0.016-0.017 mm with our methodology.

Mesoscopic damage mechanism and a constitutive model of shale using in-situ X-ray CT device

With the continuous development of shale gas engineering in China, an accurate and adequate understanding of shale damage mechanism has become a critical scientific problem addressed by rock mechanics. So far, many researchers have studied the fracturing process and mechanism of shale in multi-scales. The mesoscopic structural characteristics of shale during loading can be obtained using the in-situ X-ray computed tomography (CT) technology. Some scholars have observed the structure evolution of shale under in-situ uniaxial compression conditions, but the quantitative investigation of damage evolution and constitutive model of shale still requires further studies. Given this, the in-situ micro-CT device was adopted to study the macroscopic mechanical response and the mesoscopic structural evolution of Longmaxi shale under uniaxial compression conditions. The evolution law of the damage variable with the axial strain was analysed according to the characterisation of the damage variable based on the CT image grey variance. In combination with the macroscopic stress-strain curve shape, evolution stage of the mesoscopic void, evolution of the damage variable, mesoscopic mechanism of the macroscopic mechanical response was investigated, and a damage constitutive model of shale under the uniaxial compression test was proposed. The conclusion of this study can provide a foundation for further research into the multi-scale failure mechanism of shale and exert theoretical guidance significance on shale gas fracturing engineering practice.

Wavelet based medical image super resolution using cross connected residual-in-dense grouped convolutional neural network

In clinical analysis and diagnosis, high resolution (HR) computed tomography (CT) images are required for proper treatment of a patient. Developing HR medical images by X-ray CT devices require extended radiation exposure with large radiative dosages, putting the patient at potential risk of inducing cancer. So, radiation exposure should be reduced. However, photon starvation and beam hardening in low-dose X-rays will cause severe artifacts. Thus, an accurate reconstruction of low-dose X-ray CT images is required. To this end, we propose a wavelet based multi-channel and multi-scale cross connected residual-in-dense grouped convolutional neural network (WCRDGCNN) for accurate super resolution (SR) of medical images. The adopted filter groups reduce the connection weights, thereby reducing the computational complexity. Gradient vanishing problem is tackled by using residual and dense skip connections. The extensive experimentation results on benchmark datasets show that our method outperforms the state-of-the-art SR methods.

X-Ray Nanotomography of Individual Pulp Fibre Bonds Reveals the Effect of Wall Thickness on Contact Area

Fibre bonds play an essential role in various properties of paper. Much research has focused on their strength, but the determination of the actual contact area also provides a challenge. Many of the research methods rely on optical tools, which are restricted by the wavelength of light that is utilised. Novel X-ray computed tomography devices utilise X-rays in studying the inner structure of materials, and surpass the optical methods in terms of resolution, allowing detection of even smaller details and variations in distance between the fibres in the bond intersection area. X-ray nanotomography was used to image 26 individual cellulose fibre bonds made of springwood and summerwood fibres of refined bleached softwood kraft pulp. Various dimensional properties of the bonds were measured, most importantly the relative contact area (apparent contact area/intersection area), whose values showed wide variation from 6.4 to 85% with an average of 57.7%. Although the summerwood bonds had a somewhat smaller intersection and contact area than springwood bonds, there were no significant differences in the relative contact area between the bond types. This suggests that the effect of relative and absolute contact area on the strength differences between bond types seems to be minor.

DEM modelling of sequential fragmentation of zeolite granules under oedometric compression based on XCT observations

The objective of our research is to define a new Discrete Element Method (DEM) that can describe the processes involved in particle breakage and the resulting macroscopic behaviour of the particulate assembly, by directly observing and characterizing breakage mechanisms. To this aim, an oedometer compression test is performed on a dry granular assembly of zeolite, while acquiring 3D images of the specimen at several strain levels with an x-ray computed tomography device. We construct a DEM model that reproduces experimental observations, mainly: axial splitting is the main breakage mode; fragments are subjected to further breakage; very few fragments pass through the breakage plane. A fragment size limit is defined to reduce the computational cost associated with large numbers of breakage generations. We simulate the oedometer test for the same initial microstructure as in the lab test and with realistic particle mechanical properties, and compare the results to the 3D images. The numerical results show that our proposed model can capture the size evolution, shape change and mechanical response of the tested specimens.

Unloading during the infusion process: Direct measurement of the dual-scale fibrous microstructure evolution with X-ray computed tomography

Composites manufacturing using the infusion process involves an unloading phenomenon due to the vacuum bag flexibility. Additionally, during impregnation, woven or non-crimp fabrics exhibit a dual-scale flow. Usual modeling of both phenomena assumes that the fibrous preform is a continuous medium with a varying permeability. Nonetheless, the permeability is affected by the meso-pores size and spatial distribution, which depend on the compaction state. This paper proposes an experimental method to quantify the evolution of a given dual-scale fibrous microstructure under several controlled flow-induced compaction states. A downsized setup has been designed to conduct in situ infusion of quasi-unidirectional fabrics inside a X-ray Computed Tomography device. The downsized setup reproduces large scale infusion phenomena. Using image processing tools, it is observed that, while the stack thickness increases between dry and saturated states, tows swell and displace. The impact of this microstructural reorganization on the in-plane permeability is also identified.

Digitization of natural objects with micro CT and photographs.

In this paper, we present a three-dimensional (3D) digitization technique for natural objects, such as insects and plants. The key idea is to combine X-ray computed tomography (CT) and photographs to obtain both complicated 3D shapes and surface textures of target specimens. We measure a specimen by using an X-ray CT device and a digital camera to obtain a CT volumetric image (volume) and multiple photographs. We then reconstruct a 3D model by segmenting the CT volume and generate a texture by projecting the photographs onto the model. To achieve this reconstruction, we introduce a technique for estimating a camera position for each photograph. We also present techniques for merging multiple textures generated from multiple photographs and recovering missing texture areas caused by occlusion. We illustrate the feasibility of our 3D digitization technique by digitizing 3D textured models of insects and flowers. The combination of X-ray CT and a digital camera makes it possible to successfully digitize specimens with complicated 3D structures accurately and allows us to browse both surface colors and internal structures.

Determination of thermal diffusivity of persimmon flesh tissue using three-dimensional structure model based on X-ray computed tomography

Computed tomography (CT) images were acquired for an intact fruit and the cell tissues of persimmon flesh using two types of X-ray CT devices. The relationship between the porosity and mean CT value for small tissue samples having a volume of 0.3 mm × 0.3 mm × 0.3 mm was investigated. The three-dimensional microstructure of the issue was reconstructed using image processing software and heat transfer simulation was carried out based on the real structure model. The effective thermal conductivity of the tissue was determined by comparing the results of the three-dimensional (3D) model simulation with those of the homogeneous model simulation and was related to the porosity of the sample. The Brailsford model was selected as the most suitable model to predict the effective thermal conductivity of the tissue. The porosity, thermal conductivity and moisture distributions were visualized for an intact fruit based on analysis of high-resolution X-ray image.

The correlation of local deformation and stress-assisted local phase transformations in MMC foams

Cellular structures are of growing interest for industry, and are of particular importance for lightweight applications. In this paper, a special case of metal matrix composite foams (MMCs) is investigated. The investigated foams are composed of austenitic steel exhibiting transformation induced plasticity (TRIP) and magnesia partially stabilized zirconia (Mg-PSZ). Both components exhibit martensitic phase transformation during deformation, thus generating the potential for improved mechanical properties such as strength, ductility, and energy absorption capability. The aim of these investigations was to show that stress-assisted phase transformations within the ceramic reinforcement correspond to strong local deformation, and to determine whether they can trigger martensitic phase transformations in the steel matrix. To this end, in situ interrupted compression experiments were performed in an X-ray computed tomography device (XCT). By using a recently developed registration algorithm, local deformation could be calculated and regions of interest could be defined. Corresponding cross sections were prepared and used to analyze the local phase composition by electron backscatter diffraction (EBSD). The results show a strong correlation between local deformation and phase transformation.

INTERRUPTED IN-SITU COMPRESSIVE DEFORMATION EXPERIMENTS ON MMC FOAMS IN AN XCT: EXPERIMENTS AND ESTIMATION OF DISPLACEMENT FIELDS

The mechanical properties of a metal-matrix composite foam are investigated by interrupted in-situ compressive deformation experiments within an X-ray computed tomography device (XCT). Each in-situ experiment generates a sequence of reconstructed 3D images of the foam microstructure. From these data, the deformation field is estimated by registring the images corresponding to three consecutive steps. To this end, the generic registration framework of the itk software suite is exploited and combined with several image preprocessing steps. Both segmented (binary) images having just two grey values for foreground (strut structure) and background (pore space) and the result of the Euclidean distance transform (EDT) on pore space and solid phase are used. The estimation quality is evaluated based on a sequence of synthetic data sets, where the foam’s microstructure is modelled by a random Laguerre tessellation. For large deformations, a combination of non-rigid registration for the EDT images and partwise-rigid registration on strongly deformed regions of the binary images, yields surprisingly small estimation errors.

New High Stopping Power Thin Scintillators Based on ${\rm Lu}_{2}{\rm O}_{3}$ and ${\rm Lu}_{3}{\rm Ga}_{5-{\rm x}}{\rm In}_{\rm x}{\rm O}_{12}$ for High Resolution X-ray Imaging

X-ray computed tomography devices and X-ray diffraction techniques are powerful tools: the former provide volumetric data of samples during a non-destructive examination for biology and material science, and the latter measure grain orientation and strain, as well as crystalline phase identification and structure refinement. Today, the European Synchrotron Radiation Facility (ESRF) provides increasingly higher energy beams, up to 150 keV combined with higher brilliance (1013 X-ray photons/sec). This means that detectors suffer from low X-ray absorption at high spatial resolution (1-10 μm) and from radiation damage in tomography and diffraction applications. In addition, more and more experiments in medicine require the absorbed dose by the sample to be reduced. In this context, more efficient scintillators are developed and evaluated at the ESRF. In order to perform sub-micrometer and micrometer resolution imaging scintillators 1 μm to 500 μm thin are required. Single Crystal Film scintillators (SCF), 1 μm to 100 μm can be obtained via Liquid Phase Epitaxy for sub-micrometer resolution. Transparent ceramics, 100 μm to 500 μm thick are promising candidates for X-ray imaging requiring high X-ray absorption and good contrast with micrometer resolution. Commonly available scintillators, such as CdWO4 and YAG:Ce suffer from low efficiency, therefore new scintillators with higher light yield and stopping-power are required. A first test was carried out to evaluate an Europium doped Lutetium Oxide ceramic for micrometer resolution and new SCFs of Lu3Ga5-xInxO12:Eu for sub-micrometer resolution are investigated. Performance of Lu2O3 and LuInGG, i.e absorption, light yield, afterglow, spatial resolution will be presented and compared to standard screens (YAG, GGG). First results will be illustrated with X-ray images and will demonstrate the absorption efficiency improvement at high spatial resolution.

An Educational Experiment System for Simulated CT Device with Coherent Light

Today, X-ray computed tomography (CT) devices are used in a wide range of fields including medical and industrial applications. It is not easy for students in engineering fields including electrical and electronic engineering to understand the electrical and image analysis principles of X-ray CT devices. Also, in teaching facilities that educate the radiographers who actually work with this equipment in medical fields, testing and training are usually done using real X-ray CT devices. Since these devices are large and have a complex internal structure, students are currently limited with regard to the types of testing and training that they are able to perform. This makes it difficult for medical students to gain a proper understanding of the principles behind X-ray CT devices. There is consequently a need for a simple educational test system that enables engineering and medical students to understand how X-ray CT devices work. We report on the construction of an educational test system that simulates an X-ray CT device based on optical heterodyne detection using laser light for simulation experiments, and on the construction of a system that is capable of performing image reconstruction experiments using data obtained with this test system. We also report on a test system that is capable of acquiring simulated X-ray CT images.

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 1μm 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 3.5μm and are compared with synchrotron computed tomography (sXCT) with 0.3μm/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.

X-ray computed tomography to quantify tree rooting spatial distributions

Poor root development due to constraining soil conditions could be an important factor influencing health of urban trees. Therefore, there is a need for efficient techniques to analyze the spatial distribution of tree roots. An analytical procedure for describing tree rooting patterns from X-ray computed tomography (CT) data is described and illustrated. Large irregularly shaped specimens of undisturbed sandy soil were sampled from various positions around the base of trees using field impregnation with epoxy resin, to stabilize the cohesionless soil. Cores approximately 200 mm in diameter by 500 mm in height were extracted from these specimens. These large core samples were scanned with a medical X-ray CT device, and contiguous images of soil slices (2 mm thick) were thus produced. X-ray CT images are regarded as regularly-spaced sections through the soil although they are not actual 2D sections but matrices of voxels ∼0.5 mm×0.5 mm×2 mm. The images were used to generate the equivalent of horizontal root contact maps from which three-dimensional objects, assumed to be roots, were reconstructed. The resulting connected objects were used to derive indices of the spatial organization of roots, namely: root length distribution, root length density, root growth angle distribution, root spatial distribution, and branching intensity. The successive steps of the method, from sampling to generation of indices of tree root organization, are illustrated through a case study examining rooting patterns of valuable urban trees.