X-ray Computed Tomography Scanning Research Articles

Resolution Enhancement by Variable Zoom Trajectory in X-Ray Computed Tomography

Flat objects like electronic boards are challenging samples for high-resolution X-ray computed tomography scanning because their largest dimension significantly limits the magnification using circular trajectory scans. One way to improve spatial resolution for such samples is to utilize variable zoom trajectory. During variable zoom trajectory scanning, the source-to-object distance changes during the 360° rotation to maximize the magnification in the projections. Here, we propose an automatic variable zoom trajectory generation algorithm for arbitrary object and region of interest (ROI). We analyze how such a trajectory can enhance resolution in different cases and how isotropic is the resolution in the reconstructed volume. We demonstrate that the resolution can be improved without destroying the sample. However, the improvement is manifested mainly in directions in which we achieved the highest magnification in the projection.

Identification of TRISO Pebbles at Arbitrary Orientation Using Pairs of X-ray Radiographs

TRISO (tri-structural isotropic) fuel is anticipated to be one of the fuel types for future small modular reactors. A TRISO-fuelled pebble in a pebble bed reactor (PBR) consists of thousands of TRISO fuel particles embedded inside a graphite sphere. The diameter of each of the fuel particles is approximately 1 mm. A PBR can contain hundreds of thousands of pebbles, each with a diameter of approximately 6 cm. Unlike in traditional reactor designs, which have a relatively small number of discrete fuel assemblies, the large number of pebbles inside a PBR makes the tracking of individual fuel pebbles difficult. The distribution of TRISO particles within the pebble provides a unique fingerprint that identifies a pebble and can be used to track it. This fingerprint can be determined using a standard X-ray radiograph or a more time-consuming X-ray computed tomography scan. When an individual radiograph is used, the pebble image is compared to a library of reference images of the pebbles. To obtain a good match, the orientation of the pebble must be close to the orientation used for the reference image. As a pebble exits the reactor in a random orientation, the pebble must be reorientated before its identification can take place. This paper discusses the addition of a reference particle in the non-fuelled region of the pebble, as well as the simultaneous acquisition of pairs of radiographs at 90o with respect to each other, to aid pebble reorientation and the development of an identification framework. The framework follows a hybrid approach in which the pebble is first reorientated using machine learning techniques before being identified using traditional computer vision techniques. Other effects such as the impact of transmutation of the elements inside the fuel and the radioactivity of irradiated pebbles are also discussed.

A multi-orientation system for characterizing microstructure changes and mechanical responses of fine-grained gassy sediments associated with gas hydrates.

Fine-grained marine sediments containing veiny and nodular gas hydrates will evolve into fine-grained gassy sediments after hydrate dissociation due to climate-driven ocean warming. The mechanical properties of the fine-grained gassy sediments are basically acquired by ocean engineering design. However, they have not been fully understood, largely due to the lack of microstructure visualization. In this paper, a new system is developed to jointly conduct x-ray computed tomography scans, oedometer tests, and seismic wave testing on a single specimen with temperature being well controlled, allowing varieties of experimental data to be acquired effectively and automatically. The results show that stress history can hardly affect the undrained stiffness of fine-grained gassy sediments, while the drained stiffness of fine-grained sediments without gas bubbles is stress history dependent. After being unloaded, many microstructure changes remain, and examples include the free gas distribution being more concentrated and the connectivity among gas bubbles becoming much better. The multi-orientation system lays the foundation for further studies on the microstructure changes and mechanical responses of fine-grained gassy sediments associated with gas hydrates.

Shear-induced permeability evolution of natural fractures in granite: Implications for stimulation of EGS reservoirs

Permeability evolution of natural fractures during shearing is one of the critical issues in enhanced geothermal system (EGS). In this study, we conducted a series of numerical simulations of shear-flow tests under different normal stresses to investigate the permeability evolution and shear behavior of natural fractures during shearing. All numerical simulations in this study are executed based on a coupled hydro-mechanical pore network model (PNM) for fluid flow within the discrete element method (DEM). The numerical model uses a 33 mm × 25 mm fracture surface profile extracted from X-ray computed tomography scanning data of joints in a rock core retrieved from a 4.2-km-deep well at the Pohang EGS site. The results demonstrate a positive correlation between fracture permeability and shear displacement when the normal stress is relatively high. The central aspect of permeability evolution lies in the variation of local aperture distribution along the pathway: an increase in the variance of fracture aperture distribution leads to an increase in fracture permeability. Permeability evolution of fractures is significantly affected by normal stress, fracture roughness, and relative flow direction. Larger fracture roughness facilitates the formation of high-permeability pathways. Higher local normal stress often corresponds to lower local permeability. Moreover, high normal stress amplifies the effect of fracture roughness on permeability evolution. These findings enhance our comprehensive understanding of hydraulic-mechanical coupling effects during EGS stimulation.

Improved carbon fibers dispersion in geopolymer composites

Improved carbon fibers dispersion in geopolymer composites

Reducing Metal Artifacts in X-ray Computed Tomography Based on Metal Effect Estimation and Multiple CT Volume Fusion

In recent years, X-ray Computed Tomography (CT) has been widely used for investigating industrial parts. Many industrial parts often include metals, which cause various CT artifacts such as beam hardening artifacts, and metal artifacts. These CT artifacts lower the quality of X-ray CT images, prevent precise measurements. In order to reduce metal artifacts, here we propose using multiple X-ray CT scanning. Our multiple X-ray CT scanning method includes local artifacts estimation, proposing adequate multiple scanning angles, multiple scanned data registration and multiple CT data fusion. Based on local artifacts estimation, optimal multiple scan angles for data fusion are selected. Data registration and fusion are also based on local artifacts estimation, excluding effects of artifacts during the process. In order to demonstrate our method, we measured industrial parts which includes metals and resins, proposed optimal multiple scanning angles and conducted volume fusion. As a result, the metal artifacts in the CT volume reduced significantly compared to single X-ray CT scanning. Experiments also showed that metal artifacts in different regions are reduced by additional scans, which suggest that our scan angle selection method successfully selected optimal multiple scan angles.

Prior function designs for X-ray reconstructions from limited angular views

The objectivity of three-dimensional imaging has placed X-ray Computed Tomography (CT) into an indispensable diagnostic method in clinical and industrial applications. Despite the advances in the X-ray CT imaging, high- resolution three-dimensional reconstruction of small details in objects with large in-plane dimensions has been a fundamental challenge for the conventional X-ray CT method. An alternative scanning geometry, where X-ray source and a detector move synchronously irradiating a specimen at an inclined angle, has been proposed to address this challenge. This work presents new designs of prior (or penalty) functions developed for reconstructing the radiography data obtained under the limited angular conditions. The new prior targets reduction of shape distortion artifacts, common for laminographic reconstructions, as well as preservation of small features, such as voids, edge details, and high-density inclusions. The novel prior function designs are demonstrated on the computational phantom of a specimen scanned under tilted planar CT geometry simulating large planar dimensions of a specimen. To accommodate physical CT scanning of such specimens, a novel microfocus X-ray CT scanning device that rotates X-ray source and moves the detector synchronously while staying on the same side of the test specimen (Inclined CT), is introduced. This device allows scanning of critical areas of up to 3-meter-wide and potentially unlimited length specimens with high resolution required for identification of manufacturing and structural defects typical for modern composite structural elements used in the aerospace industry.

Nondestructive quantification of internal raster path for additively manufactured components via ultrasonic testing.

This work investigates the viability of discerning the raster pattern of additively manufactured components using high frequency ultrasonic nondestructive testing. Test coupons were fabricated from poly cyclohexylenedimethylene terephthalate glycol using the fused filament fabrication process, in which layers were deposited at various predetermined raster angles. Each printed part was scanned using spherically focused, high-resolution, ultrasonic transducers of various peak frequencies between 7.5 and 15MHz. From the captured waveform data, images are extracted to observe the raster pattern in a layer-by-layer manner, with the results from the 10MHz element yielding the best performance. An in-house MATLAB script was developed to analyze the transducer signal to investigate C-scan images at various depths throughout the component. From the resulting C-scan images, one can consistently identify the proper raster orientation within 2°-4° in each of the first 10 deposited layers, with the accuracy decreasing as a function of depth into the component. Due to signal attenuation, there is insufficient data at depths beyond the 11th and 12th layer, to properly analyze the present data sets accurately. Validation was performed using X-ray computed tomography scans to demonstrate the accuracy of the ultrasonic inspection method.

X-ray computed tomography tracking of the calcium chloride hexahydrate crystallisation process

The research conducted on phase change materials (PCMs) for latent thermal energy storages (LTESs) is continuously growing in terms of publications, highlighting the importance of this topic. In fact, PCMs present many advantages that could help the energy transition and reduce CO2 emissions, by enhancing the performance of existing systems and better exploiting renewable energy. Therefore, it is of crucial interest to develop new and reliable methods to control LTES. Differently from sensible thermal energy storages, in LTESs the stored thermal energy is not proportional to the temperature. To really have an insight into the level of charge of these storages, it is important to know the liquid fraction, i.e., the amount of the liquid phase with respect to the whole amount of PCM. X-ray computed tomography (XCT) is a technology that allows to non-intrusively “look inside” the materials. In the current study, it was used to analyse the calcium chloride hexahydrate crystallization. This transient process of calcium chloride hexahydrate was tracked with a sequence of XCT scans, one every 6 minutes, resulting in 3D image stacks that were processed to obtain the volumetric liquid fraction evolution over time. Repeatability tests were run to evaluate the reliability of the XCT technique and the volumetric liquid fraction data was used to validate a numerical model developed within ANSYS Fluent framework. XCT offers great opportunities to study the heat and mass transfer mechanisms underlying the main issues of phase change materials, like, for example, supercooling and salt hydrate segregation.

Robust residual-guided iterative reconstruction for sparse-view CT in small animal imaging

Objective. We introduce a robust image reconstruction algorithm named residual-guided Golub–Kahan iterative reconstruction technique (RGIRT) designed for sparse-view computed tomography (CT), which aims at high-fidelity image reconstruction from a limited number of projection views. Approach. RGIRT utilizes an inner-outer dual iteration framework, with a flexible least square QR (FLSQR) algorithm implemented in the inner iteration and a restarted iterative scheme applied in the outer iteration. The inner FLSQR employs a flexible Golub–Kahan bidiagonalization method to reduce the size of the inverse problem, and a weighted generalized cross-validation method to adaptively estimate the regularization hyper-parameter. The inner iteration efficiently yields the intermediate reconstruction result, while the outer iteration minimizes the residual and refines the solution by using the result obtained from the inner iteration. Main results. The reconstruction performance of RGIRT is evaluated and compared to other reference methods (FBPConvNet, SART-TV, and FLSQR) using projection data from both numerical phantoms and real experimental Micro-CT data. The experimental findings, from testing various numbers of projection views and different noise levels, underscore the robustness of RGIRT. Meanwhile, theoretical analysis confirms the convergence of residual for our approach. Significance. We propose a robust iterative reconstruction algorithm for x-ray CT scans with sparse views, thereby shortening scanning time and mitigating excessive ionizing radiation exposure to small animals.

Diabetes disrupts osteometric and trabecular morphometric parameters in the Zucker Diabetic Sprague-Dawley rat femur.

Type 2 diabetes mellitus is increasingly becoming more prevalent worldwide together with hospital care costs from secondary complications such as bone fractures. Femoral fracture risk is higher in diabetes. Therefore, this study aimed to assess the osteometric and microarchitecture of the femur of Zucker Diabetic Sprague-Dawley (ZDSD) femur. Ten-week-old male rats (n=38) consisting of 16 control Sprague-Dawley (SD) and 22 ZDSD rats were used. The rats were terminated at 20 weeks and others at 28 weeks of age to assess age, diabetes duration effects and its severity. Bilateral femora were taken for osteometry, bone mass measurements and micro-focus X-ray computed tomography scanning to assess the trabecular number (TbN), thickness (TbTh), spaces (TbSp), bone tissue volume to total volume (BV/TV) and volume (BV). Diabetic rats had shorter (except for 20-weeks-old), lighter, narrower, and less robust bones than SD controls that wered more robust. Although cortical area was similar in all diabatic and control rats, medullary canal area was the largest in ZDSD rats. This means that the diabetic rats bones were short, light and hollow. Diabetic rats aged 20 weeks had reduced BV, BV/TV, TbN with more spacing (TbSp). In contrast, the 28 weeks old diabetic rats only showed reduced BV and TbN. Discriminant function analysis revealed, for the first time, that osteometric parameters and TbTh, TbN, and TbSp were affected by diabetes. This knowledge is valuable in the management of diabetic complications.

Progressive internal erosion during triaxial shearing: an X-ray micro-computed tomography study

Fines removal during internal erosion results in the permeability increase and strength reduction of granular soils. This study examines internal erosion during shearing of granular soils under triaxial loading conditions using a specially designed apparatus and X-ray computed tomography scans. Two gap-graded soil samples with different fines content are tested and scanned multiple times to characterise sample- and pore-scale volume change and fines content using image-processing techniques. Results show that internal erosion increases gradually with axial strain and has a complex impact on permeability increase due to the spatial variation of fines content. Triaxial shearing induces both pore contraction and dilation, destabilises the clogging of fine particles and promotes internal erosion. Also, the erosion of force-supporting fine particles at a high fines content facilitates pore contraction. The progressive internal erosion due to mechanical disturbance leads to the formation of a flow channel from the upstream loading platen throughout the sample, resulting in a dramatic increase in permeability. Overall, this study provides novel insights regarding the interplay between the hydro-mechanical processes during shearing under constant seepage.

Analysis of permeability anisotropy of marine hydrate-bearing sediments using fractal theory combined with X-CT

Permeability anisotropy plays a crucial role in accurately predicting fluid productions during hydrate exploitation. However, the mechanisms governing permeability anisotropy have yet to be fully elucidated. This study conducted experiments on methane hydrate formation/dissociation in both unsaturated and saturated quartz sands, followed by X-ray computed tomography scanning and pore structure characterizations. Fractal parameters, encompassing fractal dimension, tortuosity fractal dimension, and maximum pore diameter, were employed to characterize the evolution of pore structure and changes in permeability anisotropy. Results show that the fractal dimension and maximum pore diameter decreased, while the tortuosity fractal dimension increased with the increase of hydrate saturation. Larger maximum pore diameter and smaller tortuosity fractal dimension in the horizontal direction become more pronounced with increasing hydrate saturation, resulting in heightened permeability anisotropy (kh/kv). The permeability anisotropy increases from 1.77 to 3.20 with hydrate saturation increasing from 0 to 0.38 in unsaturated sands, and from 1.47 to 4.70 with hydrate saturation increasing from 0 to 0.49 in saturated sands. Gas and water relative permeability anisotropy also amplifies with increasing hydrate saturation. Extrapolating to field tests, the findings suggest that horizontal wells present a more favorable option for gas production, especially in reservoirs with high hydrate saturation.

Effects on Lung Tissue After Breast Cancer Radiation: Comparing Photon and Proton Therapies

PurposeIn breast cancer, improved treatment approaches that reduce injury to lung tissue and early diagnosis and intervention for lung toxicity are increasingly important in survivorship. The aims of this study are to (1) compare lung tissue radiographic changes in women treated with conventional photon radiation therapy and those treated with proton therapy (PT), (2) assess the volume of lung irradiated to 5 Gy (V5) and 20 Gy (V20) by treatment modality, and (3) quantify the effects of V5, V20, time, and smoking history on the severity of tissue radiographic changes. Patients and MethodsA prospective observational study of female breast cancer patients was conducted to monitor postradiation subclinical lung tissue radiographic changes. Repeated follow-up x-ray computed tomography scans were acquired through 2 years after treatment. In-house software was used to quantify an internally normalized measure of pulmonary tissue density change over time from the computed tomography scans, emphasizing the 6- and 12-month time points. ResultsCompared with photon therapy, PT was associated with significantly lower lung V5 and V20. Lung V20 (but not V5) correlated significantly with increased subclinical lung tissue radiographic changes 6 months after treatment, and neither correlated with lung effects at 12 months. Significant lung tissue density changes were present in photon therapy patients at 6 and 12 months but not in PT patients. Significant lung tissue density change persisted at 12 months in ever-smokers but not in never-smokers. ConclusionPatients treated with PT had significantly lower radiation exposure to the lungs and less statistically significant tissue density change, suggesting decreased injury and/or improved recovery compared to photon therapy. These findings motivate additional studies in larger, randomized, and more diverse cohorts to further investigate the contributions of treatment modality and smoking regarding the short- and long-term radiographic effects of radiation on lung tissue.

The impacts of CaCO3 deposition in natural wood on its viscoelastic properties

In this study, we discuss the methods used for depositing calcium carbonate (CaCO3) and the resulting 2D and 3D particle distributions of CaCO3 in two types of wood, which were quantified using scanning electron microscopy (SEM) and X-ray computed tomography (CT). We also present the results of dynamic mechanical analysis (DMA), which was used to measure the impact of CaCO3 deposition on the viscoelastic properties of the wood. X-ray CT scanning showed that CaCO3 deposits inside the wood scaffold with increased amounts as the deposition cycles were iterated. However, DMA results did not indicate significant improvement in storage moduli (E′) of CaCO3 deposited wood. SEM images revealed that the particles did not fill all the voids to provide stress transfer between the wood scaffold and the particles, indicating a lack of composite action between the wood and CaCO3 components. To address this issue, we hypothesized that heat-pressing would lead to a mechanical bond between the particles and the matrix. After heat-pressing, DMA results showed a dramatic increase in E′ not only in CaCO3 deposited wood samples but also in control wood samples. In other words, the densification of the structure led to significant increases in E′, primarily due to densification, while the impact of the presence of CaCO3 particles was minimal. This is mainly because the volume fraction of the deposited CaCO3 particles is small as compared to the total volume of the composite.

Projection-Angle-Sensor-Assisted X-ray Computed Tomography for Cylindrical Lithium-Ion Batteries.

X-ray computed tomography (XCT) has become a powerful technique for studying lithium-ion batteries, allowing non-destructive 3D imaging across multiple spatial scales. Image quality is particularly important for observing the internal structure of lithium-ion batteries. During multiple rotations, the existence of cumulative errors and random errors in the rotary table leads to errors in the projection angle, affecting the imaging quality of XCT. The accuracy of the projection angle is an important factor that directly affects imaging. However, the impact of the projection angle on XCT reconstruction imaging is difficult to quantify. Therefore, the required precision of the projection angle sensor cannot be determined explicitly. In this research, we selected a common 18650 cylindrical lithium-ion battery for experiments. By setting up an XCT scanning platform and installing an angle sensor to calibrate the projection angle, we proceeded with image reconstruction after introducing various angle errors. When comparing the results, we found that projection angle errors lead to the appearance of noise and many stripe artifacts in the image. This is particularly noticeable in the form of many irregular artifacts in the image background. The overall variation and residual projection error in detection indicators can effectively reflect the trend in image quality. This research analyzed the impact of projection angle errors on imaging and improved the quality of XCT imaging by installing angle sensors on a rotary table.

Direct voxel classification from x-ray projections for 3D pore detection applied to laser sintered parts

X-ray computed tomography (XCT) is a validated and frequently used tool to verify part geometry and to perform a non-destructive inspection of additive manufacturing parts. However, the acquisition of a large number of x-ray projections generates long inspection times. This conflicts with a high throughput of the production process and hinders the integration of XCT as an in-line quality control procedure for low-end parts. In this paper, we propose a method to obtain three-dimensional (3D) information of the internal pores from a limited view or limited angle scan. The method combines a forward projection model of a cone-beam x-ray system and a deep learning neural network to directly classify each individual voxel, based on the x-ray projections in order to avoid the reconstruction and segmentation step. Accompanying reconstruction artifacts for limited view and limited angle XCT scans are thereby reduced, while preserving 3D information of the pores, defects or inclusions inside the material. The method is validated on real x-ray projections of polymer laser sintered industrial parts and shows a significant reduction in the required x-ray projections, hence acquisition time.

Development of a modular system to provide confidence in porosity analysis of additively manufactured components using x-ray computed tomography

X-ray computed tomography (XCT) offers a promising non-destructive method to assess high value components that are additively manufactured (AM) for space-based imaging. However, AM components can be often challenging to measure and the true resolution of the XCT system used is both non-trivial to determine and may change locally. To solve this, we used high precision micro-machining to manufacture a cylindrical reference pin with internal holes. This pin can then be inserted into any component via subtractive machining, prior to the XCT process. A pre-existing AM flexure is modified to allow our modular system to be implemented. This allows XCT scanning and porosity analysis of similar components (similar geometry and manufacturing process) to be refined and adjusted based on the known internal micro-machined hole size. Analysis of the XCT volumetric data is implemented using a Python script developed for Avizo 2022.1, to compare and suggest the ideal threshold grey value (GV). The plugin threshold comparison is semi-automatic and 15 times faster than a manual comparison. Study findings showed how different calibrated micro-machined hole sizes (30 μm–120 μm) needed different thresholding values (188 GV–195 GV). Challenges and future studies related to traceability of the suggested method are discussed.

Feasibility of diagnosing osteoporosis using routine computed tomography scans for hip fractures: Correlation with histopathological diagnosis of head and neck regions.

The aim of this study was to demonstrate the feasibility of diagnosing osteoporosis through routine computed tomography (CT) by assessing the association between the histopathological assessment of femoral head specimens extracted from patients who underwent surgery for intertrochanteric fractures and the Hounsfield unit (HU) measurements derived from preoperative CT scans. Forty-eight patients who presented to our clinic between November 2019 and May 2020 with hip fractures and underwent partial prosthesis fixation were included in this retrospective study. Hounsfield unit measurements were performed on the head and neck regions using dual-energy x-ray absorptiometry (DEXA) and CT scans, respectively. The trabecular ratio per unit area was calculated using the Nikon Imaging Software (NIS-Elements ) program in the pathology laboratory from digitally captured images of the removed head and neck specimens. The mean HU receiver operating characteristic analysis had a sensitivity of 77% and a specificity of 87%, with a cutoff value of 77.68. There was a moderate correlation between the mean trabecular density and the mean HU of the femoral head (P=0.013, r=0.340). Additionally, there was a significant correlation between the mean HU and the T-score of the head, although this correlation was not found with the maximum-minimum HU. Although there was a significant correlation between trabecular density and mean HU, the correlation coefficient indicated a moderate relationship. This relationship was also observed between the inferior sections of the head and the trabecular density and HU (P=.018). However, no significant correlation was found between the T-score and the trabecular structure of the head (P=.977). The results of the present study suggest that conventional CT has the potential to serve as a diagnostic tool for osteoporosis and may offer a more precise and accurate method for evaluating the success of intraosseous implants when compared to T-scores without the need for additional tests or procedures.

X-ray computed tomography – Measured pore characteristics and hydro-physical properties of soil profile as influenced by long-term tillage and rotation systems

Soil hydro-physical properties and pore characteristics are crucial for crop production as they determine water, air, and nutrients transfer. Long-term tillage and crop rotation studies provide valuable insights into the effects of management practices on various soil properties. Because of the inherent differences between the surface and sub-surface soils, the impact of management systems can be pronounced differently at different soil depths. Though many studies have reported the tillage and rotation effects on soil hydro-physical properties, their vertical impacts to a depth of 40 cm were less explored. This study aims to assess the impact of long-term tillage and crop rotations on soil hydro-physical properties and pore characteristics to a depth of 40 cm utilizing the X-ray Computed Tomography (XCT) technique. Intact soil cores of 7.6 cm height × 7.6 cm ∅ were collected from tillage [no-till (NT); reduced-till (RT); conventional-till (CT)] and crop rotation [continuous corn (CC) – Zea mays L. and corn-soybean (CS) – Glycine max [Merr.] L.] plots of 0–40 cm depth (each sample for 10 cm increment). The XCT scanning allowed us to investigate the soil pore size distribution, porosity, number of branches, and average branch length. Measured hydro-physical properties in the study include bulk density (ρb), plant available water content (PAW), saturated hydraulic conductivity (Ksat), and water retention. XCT image analysis revealed that NT with CC/CS rotation increased the number of macropores at surface and sub-surface depths. However, the number of mesopores was higher with NT × CS. In addition, NT lowered the ρb by 9.6 % and increased the PAW by 28 % compared to the CT. Ksat was higher under NT × CS at 0–10 cm and had a strong positive correlation with the XCT-measured number of macropores. Therefore, we conclude that NT with CS rotation can potentially improve soil pore characteristics and hydro-physical properties, leading to enhanced soil function.