X-ray Computed Tomography System Research Articles

Thermal Battery Multi-Defects Detection and Discharge Performance Analysis Based on Computed Tomography Imaging

To address the typical structural defects that are prone to occur during the preparation and storage processes of thermal battery, experiments of battery image acquisition were designed based on X-ray computed tomography system. An improved Yolov5s network was employed to achieve high-precision automatic detection of typical defects. Through the discharge experiment of thermal battery, discharge performance curves of normal batteries and three defective batteries were constructed. The impact and mechanisms of different defects on the discharge performance were analyzed based on the voltage curve. By designing an automatic stitching scheme, the phenomenon of interlayer information overlap caused by the increase of cone angle in digital radiography images was suppressed. To address the issues of low image contrast and limited defect data in thermal battery imaging, the defect dataset was expanded using the designed image preprocessing steps and improving the contrast of the images. For subtle defects that are difficult to identify, the introduced multi-head self-attention mechanism in Transformer and the use of Focal Loss instead of cross-entropy loss function were employed to improve the recognition accuracy of subtle defects while ensuring the detection speed. The comparative experiment shows that the improved network model has higher recognition accuracy compared to Faster R-CNN, SSD, Cascade R-CNN, EfficientDet and the original Yolov5s network. The recognition accuracy of typical defects in thermal batteries can reach 98.7%.

Challenges in non-destructive X-ray CT testing of riveted joints in the automotive industry

Despite recent advancements, contemporary laboratory-based industrial computed tomography (CT) technology has not yet achieved the status of an efficient and economically viable in situ non-destructive method for examining riveted joints that are commonly used in the automotive industry. 2D X-ray or 3D CT systems can only reliably assess a rivet joint’s condition in rare, and favorable circumstances. Moreover, a comprehensive analysis to identify the obstacles preventing CT from efficiently capturing high-resolution, and contrast-rich scans of riveted joints in general is lacking. This work delves into the challenges and limitations of the technology that prevent operators from reaching the desired precision required for rigorous quality control. The study specifically addresses questions concerning in situ reachability and positioning of the sample structure, radiodensity and beam hardening, the relationship between spot size and power, and economic feasibility—all within the context of analyzing riveted joints in the automotive industry. Additionally, we provide an abstracted overview of the current industrial X-ray tube market, which informs our discussion on these specific aspects. Through a combination of experimental findings, analytical insights, and deductions, we shed light on the persistent difficulties in achieving resolutions comparable to macro-sectioning and microscopy, which are currently considered the gold standard in examining riveted joints. Our investigation further explores the potential of a photon-counting detector paired with a conventional, laboratory-based X-ray source. Furthermore, we investigate the use of a synchrotron beamline as an X-ray source in conjunction with a custom-designed detector optimized for such beam geometries. This detector employs scintillators coupled with optical magnification, functioning similarly to an X-ray microscope. Our findings and data collection conclusively reveal that commercially available CT systems still fail to meet the requirements for efficient testing, underscoring the urgent need for further research and development to enable widespread implementation.

Inline CT-Analysis of the Melting Area during Fused Filament Fabrication

In the 21st century, 3D printing has become a mainstream process for prototyping and low-volume production. Fused Filament Fabrication is the most commonly used process for 3D printing plastics. A plastic filament is melted in a nozzle and a component is built up layer by layer. As with all manufacturing processes, there is an interest in continuously optimizing and improving the FFF process. One approach is based on process simulation, which provides a better understanding of the process. Subsequently, it is always necessary to validate the simulation models with the real process. This validation has only been possible to a limited extent in the case of FFF. In this work, a method is presented that allows a non-destructive investigation of the melt behaviour during the printing process. For this purpose, a 3D printer nozzle with an extruder was integrated into an X-ray computed tomography system. Thus, a computed tomography scan can be performed during the extrusion process. By using highly absorbent tungsten filaments, sufficient contrast can be created between the metal nozzle and the plastic filament to allow analysis of the melt behaviour. This setup makes it possible to distinguish between the solid filament area and the melt area, as well as to determine the contact between the filament and the die wall. In doing so, simulations can be validated and nozzle geometries can be improved.

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.

Runtime optimization of acquisition trajectories for x-ray computed tomography with a robotic sample holder

Tomographic imaging systems are expected to work with a wide range of samples that house complex structures and challenging material compositions, which can influence image quality in a bad way. Complex samples increase total measurement duration and may introduce beam-hardening artifacts that lead to poor reconstruction image quality. This work presents an online trajectory optimization method for an x-ray computed tomography system with a robotic sample holder. The proposed method reduces measurement time and increases reconstruction image quality by generating an optimized spherical trajectory for the given sample without prior knowledge. The trajectory is generated successively at runtime based on intermediate sample measurements. We present experimental results with the robotic sample holder where two sample measurements using an optimized spherical trajectory achieve improved reconstruction quality compared to a conventional spherical trajectory. Our results demonstrate the ability of our system to increase reconstruction image quality and avoid artifacts at runtime when no prior information about the sample is provided.

CT-Analysis of the Melting Area in the Fused Filament Fabrication Process

3D printing has established itself in the 21st century as the process for producing prototypes and very small series. In the plastics sector, the fused filament fabrication (FFF) process is used in particular. A plastic filament is melted in a nozzle and a component is built up layer by layer. As with all manufacturing processes, there is an interest in continuously optimizing and improving the FFF process. One possibility is based on process simulations, which enable a better understanding of the entire process. Afterwards a validation of the simulation with the real process is always necessary. In the case of FFF, this validation was so far only possible to a limited extent. In this work, a method is presented that enables a non-destructive investigation of the melting behavior during the printing process. For this purpose, a 3D printer nozzle with an extruder was integrated into an X-ray computed tomography system. Thus, a computed tomography scan (CT scan) can be performed during the extrusion process. By using filaments with high absorbent tungsten, a sufficient contrast can be created between the metal nozzle and the plastic filament, which allows an analysis of the melting behavior. This setup allows to distinguish between the solid filament area and the melt area, as well as to determine contact between the filament and the nozzle wall. In this way, the simulations can be validated and nozzle geometries to be improved in the future by means of improved simulation tools.

Dimensional XCT comparison campaign on an aluminium object

An x-ray computed tomography (XCT) interlaboratory comparison campaign, involving an aluminium-machined object, whose dimensions (92 × 78 × 63 mm3) are significant for a 225 kV XCT system, was performed for the purpose of investigating the performances of industrial XCT systems for dimensional measurements in terms of accuracy, i.e. precision and trueness, and to evaluate the influence of the measurement protocol (i.e. measurement strategy), of the operator and of the software on the results by comparison to reference measurements. In this campaign, we came to the conclusion that the measurement strategy is predominant, except for distance; that the measurement process is affected by the operator only for cylindricity and coaxiality; that there is no or little influence of the software except for coaxiality and position; and that a volumetric Gaussian filter allows to improve the measurements only for some participants’ measurements Furthermore, different behaviours, in terms of precision and trueness, are observed depending on the type of measurands when performed by different operators. The diameter measurements are reproducible with XCT, lower than 30 µm which corresponds to a subvoxelic factor of 2.5 and the trueness is lower than 22 µm. The distance measurement is also reproducible with XCT, 15 µm which corresponds to a subvoxelique factor of 4.9 and the trueness is 8 µm. For these mesurands, their measurements do not depend on the used XCT system. However, the XCT reproducibility for cylindricity, coaxiality and position is worse as well as of the trueness except for the position which has a trueness of 1 µm. The process measurement should be revised regarding cylindricity and coaxiality measurements. Finally, overall, the ability of the participants to perform measurements with XCT, whatever their system, is statistically comparable except for a few measurements.

A straightforward and analytical method for precise X-ray CT magnification correction

X-ray Computed Tomography (XCT) has evolved over the last two decades from a medical imaging device to an industrial tool for dimensional metrology and quality control. Employing XCT for these purposes relies on the ability to generate an accurate 3D representation of the scanned object. An essential component of this is inputting the exact geometric magnification into the reconstruction algorithm, where failure to do so results in inaccurate dimensions, distortions, and/or image artifacts. Here, we propose a simple and accurate approach to correct the magnification of a rotation stage based XCT system using a single spherical reference sphere of well-known size. The method uses geometric relationships developed between the source, rotation stage, and detector to relate the sphere's position based on projection edges at three fixed locations on the rotation stage. The typical projection edge is difficult to locate as it is obscured by the air-to-object gray value gradient. Here, the precise edge locations are found through the convergence of several geometrically derived equations describing the sphere's edges from different perspectives. The results indicate that the method repeatedly delivered micron-level determination of geometric magnification, resulting in micron-level precision in dimensional reconstruction. The method is simple and easy to employ, without the need of multiple projections with a complex phantom or the use of a secondary instrument. It is simple and rapid enough to be performed on a scan-by-scan basis for any rotation stage based XCT instrument.

The realisation of fast X-ray computed tomography using a limited number of projection images for dimensional metrology

Due to the merit of establishing volumetric data, X-ray computed tomography (XCT) is increasingly used as a non-destructive evaluation technique in the quality control of advanced manufactured parts with complex non-line-of-sight features. However, the cost of measurement time and data storage hampers the adoption of the technique in production lines. Commercial fast XCT utilises X-ray detectors with fast detection capability, which can be expensive and result in a large amount of data. This paper discussed a different approach, where fast XCT was realised via the acquisition of a small number of projection images instead of full projection images. An established total variation (TV) algorithm was used to handle the reconstruction.The paper investigates the feasibility of using the TV algorithm in handling a significantly reduced number of projection images for reconstruction. This allows a reduction of measurement time from 52 min to 1 min for a typical industrial XCT system with an exposure time of 1 s per projection. It also enables a reduction of data size proportionally.A test strategy including both quantitative and qualitative test metrics was considered to evaluate the effectiveness of the reconstruction algorithm. The qualitative evaluation includes both the signal to noise ratio and the contrast to noise ratio. The quantitative evaluation was established using reference samples with different internal and external geometries. Simulation data were used in the assessment considering various influence factors, such as X-ray source property and instrument noise.The results demonstrated the possibility of using advanced reconstruction algorithms in handling XCT measurements with a significantly limited number of projection images for dimensional measurements. This work lays down the foundation for conducting fast XCT measurements without the need for instrument alteration or enhancement. Although the reconstruction time required is still considerable, various possibilities to improve this have been discussed.

A machine learning supported sinogram interpolation method for X-ray computed tomography

The time of an X-ray Computed Tomography (XCT) measurement is directly affected by the number of acquired X-ray projections. In general, a large number of X-ray projections, hence a large acquisition time is required to obtain a qualitative reconstruction and successive feature analysis. To expand the applicability of XCT towards low-end parts we propose a novel sinogram interpolation method that incorporates the object rotation. The method combines a forward projection model of the XCT system and a deep learning regression model to generate intermediate X-ray projections for XCT scans with a reduced number of projections. Thereby, the accompanying reconstruction artefacts can be reduced while preserving a lower acquisition time. The method is validated on simulated projections of the 3D Shepp-Logan phantom and simulated projections of real 3D printed components using the ASTRA-toolbox. Within the reconstructions, less streaking artefacts are observed and an increased contrast between different features is obtained without introducing rotational artefacts.

Adapting an XCT-scanner to enable edge illumination X-ray phase contrast imaging

Conventional X-ray computed tomography (XCT) is a non-destructive imaging technique to visualize and inspect the internal structure of materials in 3D, where materials are distinguished solely on the basis of their attenuation coefficient. However, with more specialized X-ray phase contrast imaging methods, sensitivity to complementary contrasts can be achieved, namely phase contrast and dark field contrast. Edge illumination X-ray phase contrast imaging (EI-XPCI) is a technique that is especially suited for laboratory application, because it has no strict coherence requirements for the source. While there is a wide variety of XCTscanners available on the market, a commercial EI-XPCI scanner does not yet exist. In this work, we present the procedure of outfitting an existing XCT-scanner with components to enable EI-XPCI scans and discuss the alignment procedure of these added components. Finally, phase contrast images are shown demonstrating the successful upgrade of a conventional XCT system with edge illumination based phase contrast possibilities.

Evaluation of XCT image quality

The direct visual quality of an X-ray computed tomography (XCT) image is very subjective. Metrics to quantify the image quality have been defined for X-ray radiography, but some of these no longer seem appropriate for XCT images. This has been highlighted through an XCT interlaboratory comparison campaign, performed in the XCT working group of the French Confederation for Non-destructive Testing (COFREND), on an additively manufactured part at medium-energy XCT (230-520 kV). The calculation of several of these metrics has been performed on the images acquired with nine different XCT systems to demonstrate their representativeness and compared to visual inspections. This comparison campaign confirms that several of them are no longer representative of the image quality.

The Nature of Metal Artifacts in X-ray Computed Tomography and Their Reduction by Optimization of Tomography Systems Parameters

A significant gap in the known methods for assessing the levels of metal artifacts in X-ray computed tomography and approaches to their reduction is an almost complete disregard for the physical nature of this artifact—the proximity to zero of radioscopic transparency. The proposed work fills this gap. A mathematical model has been developed for evaluating metal artifacts in X-ray computed tomography as applied to the geometry of a parallel beam. The simulation model was transformed into an algorithm, and a Mathcad program was designed to simulate images of the internal structure of the test objects. The algorithm for estimating the studied artifact includes the stages of generating sinograms and estimating the distributions of the linear coefficient over the sections of the object based on the back projection method with filtering. The efficiency of the metal artifacts simulation algorithm is demonstrated in the example of symmetric and asymmetric objects with low- and high-density inclusions and inclusions from materials with high atomic number values. The possibility of reducing metal artifacts with the help of a rational choice of the maximum energy of X-ray radiation and the ADC bit depth is illustrated. For example, for an aluminum cylinder 200 mm in diameter with a central cylindrical cavity 80 mm in diameter, cylindrical inserts 12 mm in diameter with material densities from 1.5 g/cm3 to 10 g/cm3, and effective atomic numbers of materials from 13 to 47, the numerical simulation method proved the following: it is practically unattainable to significantly reduce the level of metal artifacts by increasing the ADC capacity to the maximum X-ray energy of 160 keV; the desired effect is achieved by simultaneously increasing the maximum X-ray energy to 225 keV and the ADC capacity to 24 or 32; increasing the maximum X-ray energy from 160 keV to 225 keV leads to an increase in the energy absorbed in the material of the test object by 26%. The results of this research can be used at the design stage of X-ray computed tomography systems designed to control objects with fragments of low radiation transparency.

Sustainable production of AlSi10Mg parts by laser powder bed fusion process

Laser powder bed fusion (L-PBF) is an additive manufacturing technology that allows producing complex and lightweight parts without the use of specific tooling during the building process. However, despite continuous developments, some problems limit its use in series production. To introduce these systems in mass production, it is necessary to solve the problems and exceed the limits related to the requirements of industrialization: higher productivity, less material consumption, less over-production, and less waste, greater stability of the process, and higher quality of the final components. In this study, good practices to reduce resource consumption are presented. The production rate of the L-PBF technique was increased to produce AlSi10Mg alloy components. All the samples were manufactured with 90-µm-layer thickness increasing productivity by approximately 65%. A design of experiments (DOE) method was used to analyze the effect of process parameters on the densification percentage. The produced samples were observed with a non-destructive process, the X-ray computed tomography system, to detect the presence of defects and pores. It has been found that a combination of parameters can induce porosities with a morphology such that after stress relieving the density increases rather than decreases as has been widely discussed in the literature. The mechanical properties are comparable with the literature values for conventional technologies. Good values of as-built surface roughness were also achieved despite the layer thickness.

Evaluation and compensation of geometrical errors of X-ray computed tomography system using a laser tracking interferometer

X-ray computed tomography (X-ray CT) is a new coordinate measuring technology that can measure both the external and internal features. However, its measuring accuracy is insufficient compared with coordinate measuring machines. To improve the measurement accuracy of the X-ray CT system, it is necessary to evaluate and compensate for each error component that influences the dimensional measurement results. In this paper, we propose a method for evaluating and compensating for the geometrical errors of the X-ray CT system, which is one of the dominant error factors, using a laser tracking interferometer. A laser tracking interferometer is not required the re-alignment of the laser path, and the data can be obtained using a common coordinate system. The proposed method was applied to a CT system designed for non-destructive testing. The result clarified that the geometrical errors of the X-ray CT system were over 100 μm. Additionally, the errors in measuring the distance between the spheres were demonstrated to be reduced by compensating for the geometrical errors of the CT system.

Initial results of in vivo CT imaging of contrast agents using MPPC-based photon-counting CT

X-ray computed tomography (CT) is an essential technology in modern medicine, as it enables three-dimensional non-destructive observation of the inside of the body. Contrast-enhanced CT scanning is widely performed for lesion-enhanced imaging. However, conventional X-ray CT systems integrate all incident X-ray signals, leading to the acquisition of monochromatic energy information and the prevention of material identification and quantitative evaluation of the concentration of contrast agents. Recently, photon counting CT (PC-CT) has been attracting attention as a new system for solving these problems. PC-CT utilizes the energy information of individual X-ray photons, enabling the identification of target materials. We have performed demonstrations combining the PC-CT system that we developed with fast scintillators and multi-pixel photon counters. In this study, we report on the initial results of in-vivo X-ray CT imaging with our established PC-CT system. We injected an iodine contrast agent into a mouse and visualized the spatial distribution of the contrast agent. Subsequently, we performed K-edge imaging and concentration mapping with the obtained CT images in multiple energy bands. The obtained images displayed successful three-dimensional contrast enhancement and a concentration map of the kidney and bladder in the mouse, indicating significant potential for the clinical application of this silicon photomultiplier-based PC-CT system.

Effect of superhydrophobic surfaces on bubble column flow dynamics

Bubbly flow in bubble column reactors promotes mixing necessary for many chemical processes. We show that if superhydrophobic-coated material is introduced into a bubble column, there can be a substantial difference in gas holdup and earlier initiation of churn-turbulent flow which can alter larger-scale mixing without a need to change the superficial gas velocity. Addition of superhydrophobic surface can also cause bubbles to (directly or indirectly assisted by the surface) escape faster to the free surface resulting in a reduced void fraction (i.e., reduced gas holdup). As the flow becomes optically opaque at few percent gas phase volume fraction, we utilize two dual plane wire mesh sensors to obtain velocity profiles and bubble size distributions, in addition to the traditional pressure and level based gas holdup measurements to calculate average phase fraction. Additionally, a custom build photon-counting dual energy threshold X-ray computed tomography system is employed to get a higher resolution measurement of the time average phase fraction non-intrusively. We report satisfactory agreement between these techniques with differences arising for understood reasons, and use the insight thus yielded to discuss the effect of superhydrophobic surfaces on bubble column flow dynamics.

Dimensional X-Ray computed tomography: Apparent feature form error and its effect on measurement tasks

X-ray computed tomography (XCT) provides a unique set of dimensional measurement capabilities suitable for assessing complex geometry. However, due to the origins of XCT as a medical imaging method and qualitative non-destructive examination technique, only recently has XCT been rigorously investigated as a dimensional metrology tool. Although the data produced via XCT may be leveraged with conventional coordinate metrology techniques, the instrument physics and volumetric reconstruction methods which govern the accuracy and precision of the data are complex, workpiece-specific, and non-negligible. In particular, there is minimal prior work which has studied complex multi-step metrology tasks such as datum reference frame (DRF) construction and feature position measurement. In this work, a qualified artifact was used to evaluate the fitness of XCT for such a task. Multiple XCT systems were used, and multiple instrument magnification levels compared. The form error of planar and cylindrical features was evaluated. Further, the influence of individual feature reconstruction on the development of datums and upstream position measurements was studied. It was found that negative, i.e., bore-like, and positive, i.e., pin-like configurations of certain features were subject to distinct XCT artifact effects which caused upstream measurement errors when these features were used to construct a DRF. High magnification and X-ray scatter produced high spatial frequency noise in surface reconstruction while beam hardening and beam penetration distance variation produced gross apparent form error. The latter was associated with greater measurement errors in feature position measurement within an DRF.

Ultrasound shear-wave computed tomography for elasticity imaging

Shear-wave elasticity imaging (SWEI) has been routinely used for measuring the elastic properties of tissues. It is potentially applicable to three-dimensional (3D) cell culture systems and may outperform existing methods such as atomic force microscopy and shear rheology in terms of being contactless and having higher spatial resolution and penetration. However, applying clinical SWEI to 3D cell culture systems requires the developments of high-frequency SWEI systems operating at >20 MHz that are compatible with the scale of cell culture systems, and C-scan 3D SWEI well suited to such observations. In this study, we implemented a computed tomography (CT) technique for SWEI (called SWCT) by leveraging the scanning scheme used in first-generation x-ray CT systems, that is, translation and rotation of a 20-MHz push probe and a 40-MHz imaging probe to obtain time-of-flight projections for multiple viewing directions. Compared with conventional B-scan SWEI, the proposed reconstruction method allows high-resolution, robust, 3D C-scan imaging of the shear-wave speed distribution. Three phantoms with different inclusions (half circle, thin strip, and cylinder) were imaged using 3D SWCT to a depth of 13 mm. The estimated shear-wave speed for the strip phantom using SWCT was 1.23 ± 0.20 m/s (mean ± standard deviation) in the background and 2.27 ± 0.11 m/s for the inclusion, which suggests the feasibility of SWCT for improving elasticity measurements of cell culture systems.

In-situ X-ray tomographic imaging and controlled steering of microcracks in 3D nanopatterned structures

An experimental approach to control the fracture behavior of 3D nanopatterned structures in real time and to describe the microcrack propagation in solids quantitatively is presented. The three-dimensional details of the complicated failure mechanism are unveiled with high resolution using a method that integrates a micro-scale fracture mechanics test into a nano X-ray computed tomography system, to allow in-situ 3D imaging of the kinetics of damage mechanisms in integrated circuits. With the unique combination of a miniaturized micro-mechanical experiment and high-resolution X-ray imaging, the critical energy release rate at the crack tip of materials is determined quantitatively in sub-100 nm dimension, which allows to reveal scale-dependent mechanical properties. The ability of controlled microcrack steering in engineered materials and structures into regions with high fracture toughness is demonstrated. This unique characterization capability promises broad applications for design and manufacturing of robust microchips in future technology nodes, and it is applicable to the study of a broad variety of 3D nanostructured material systems.