High-resolution X-ray Imaging Research Articles

Dynamic Pore-Scale Modeling of Residual Trapping Following Imbibition in a Rough-walled Fracture

We present a new, fully dynamic pore-network modeling platform that is employed to conduct a systematic pore-scale study of capillary trapping under various two-phase flow conditions in a rough-walled fracture. The model rigorously solves for the fluid pressure fields, incorporates detailed descriptions of pore-scale fluid interface dynamics, and explicitly accounts for flow through wetting layers. This modeling platform further benefits from heavy parallelization and advanced domain decomposition techniques to achieve computational efficiency. We first build an equivalent pore network of a rough-walled Berea sandstone fracture using its high-resolution x-ray images. Next, to validate the dynamic model, primary drainage and imbibition simulations are conducted with fluid properties and boundary conditions matching their experimental counterparts. We show that the predicted two-phase fluid occupancy maps for both displacement processes agree well with those observed experimentally using x-ray computed tomography. Afterward, a comprehensive simulation study of flow patterns and capillary trapping during imbibition is performed under varying flow conditions, fluid properties, and initial saturations. The generated results provide significantly improved insights into the effects of wettability, gravity and viscous forces, and initial non-wetting (NW) phase saturation on the morphology and size distribution of the trapped NW phase clusters and the final residual NW phase saturation. By revealing the interplay among the capillary, buoyancy, and viscous forces, our results create a guideline on how the removal of NW phase from fractured media can be influenced by adjusting the operational settings. These findings have broad implications for predictions of capillary trapping behavior in fractured media.

In situ X-ray imaging of pore formation mechanisms and dynamics in laser powder-blown directed energy deposition additive manufacturing

Directed energy deposition (DED) additive manufacturing (AM) is receiving growing attention in many applications, such as repair, remanufacturing, and fabrication of functionally graded structures. However, the laser-matter interactions and melt pool dynamics in laser DED with powder flow are still unclear, particularly in how pores form and flow inside the melt pool during the process. Understanding the porosity formation mechanisms is critical in the qualification, certification, and overall properties of a DED AM part. Porosity is a common phenomenon and can significantly hinder the quality of DED fabricated parts, as the pores can act as sites of crack nucleation and propagation. Here, we reveal four types of pore formation mechanisms through in-situ and operando high-speed high-resolution X-ray imaging in the DED AM process. Our results confirm that porosity within the feedstock powder induces pores in the process. We also observed pore formation mechanisms unique to the laser-based, powder-blown DED process as a result of powder delivery, keyhole dynamics, melt pool dynamics, and shield gas. High-speed X-ray images provide direct evidence for pore formation mechanisms and show that the pores related to the interaction between the delivered powder and melt pool are the largest in size in laser-based powder-blown DED AM. These results will guide porosity mitigation, elimination, and control in DED AM.

Submillimetre mechanistic designs of termite-built structures.

Termites inhabit complex underground mounds of intricate stigmergic labyrinthine designs with multiple functions as nursery, food storage and refuge, while maintaining a homeostatic microclimate. Past research studied termite building activities rather than the actual material structure. Yet, prior to understanding how multi-functionality shaped termite building, a thorough grasp of submillimetre mechanistic architecture of mounds is required. Here, we identify for Nasutitermes exitiosus via granulometry and Fourier transform infrared spectroscopy analysis, preferential particle sizes related to coarse silts and unknown mixtures of organic/inorganic components. High-resolution micro-computed X-ray tomography and microindentation tests reveal wall patterns of filigree laminated layers and sub-millimetre porosity wrapped around a coarse-grained inner scaffold. The scaffold geometry, which is designed of a lignin-based composite and densely biocementitious stercoral mortar, resembles that of trabecula cancellous bones. Fractal dimension estimates indicate multi-scaled porosity, important for enhanced evaporative cooling and structural stability. The indentation moduli increase from the outer to the inner wall parts to values higher than those found in loose clays and which exceed locally the properties of anthropogenic cementitious materials. Termites engineer intricately layered biocementitious composites of high elasticity. The multiple-scales and porosity of the structure indicate a potential to pioneer bio-architected lightweight and high-strength materials.

Coupled x-ray high-speed imaging and pressure measurements in a cavitating backward facing step flow

The two-phase flow generated behind a cavitating backward-facing step is studied using the combination of three experimental techniques: wall-pressure measurements, global high-speed imaging with visible light, and high spatial and temporal resolution x-ray imaging. Three zones are identified based on the topology of the vapor fraction maps, that correspond to vaporization, transport, and condensation. Simultaneous pressure and void fraction measurements reveal that extreme events are associated with a change from a shear layer mode to a wake mode, with a temporal signature that is heavily affected by the presence of the vapor phase.

Pore-scale imaging of displacement patterns in an altered-wettability carbonate

High-resolution X-ray imaging combined with a steady-state flow experiment is used to demonstrate how pore-scale displacement affects macroscopic properties in an altered-wettability microporous carbonate, where porosity and fluid saturation can be directly obtained from the grey-scale micro-CT images. The resolvable macro pores are largely oil-wet with an average thermodynamic contact angle of 120°. The pore-by-pore analysis shows locally either oil or brine almost fully occupied the macro pores, with some oil displacement in the micro-porosity. We observed a typical oil-wet behaviour consistent with the contact angle measurement. The brine tended to occupy the larger macro pores, leading to a higher brine relative permeability, lower residual oil saturation, than under water-wet conditions and in a mixed-wet sandstone. The capillary pressure was negative and seven times larger in the carbonate than the sandstone, despite having a similar average pore size. These different displacement patterns are principally determined by the difference in wettability.

Absolute throughput calibration of multiple spherical crystals for the Orion High-REsolution X-ray spectrometer (OHREX).

We present absolute throughput analysis of several crystals for the Orion High-REsolution X-ray (OHREX) imaging crystal spectrometer using ray tracing and experimental measurements. The OHREX spectrometer is a high-resolution x-ray spectrometer designed to measure spectral line shapes at the Orion laser facility. The spectrometer is fielded with up to two spherical crystals simultaneously covering two independent spectral ranges. Each crystal has a nominal radius of curvature of R = 67.2 cm and is fielded at a nominal Bragg angle of 51.3°. To cover different bands of interest, several different crystals are available, including Ge (111), KAP, and several cuts of quartz, whose resolving power λ/Δλ exceeds 10 000. The calibrated response of the available crystals has previously been reported from measurements at the EBIT-I electron beam ion trap at Lawrence Livermore National Laboratory. Here, we model the absolute throughput of each crystal using ray tracing and verify the results using experimental data for the quartz (101¯1) crystal.

Deep learning for early detection of pathological changes in X-ray bone microstructures: case of osteoarthritis

Texture features are designed to quantitatively evaluate patterns of spatial distribution of image pixels for purposes of image analysis and interpretation. Unexplained variations in the texture patterns often lead to misinterpretation and undesirable consequences in medical image analysis. In this paper we explore the ability of machine learning (ML) methods to design a radiology test of Osteoarthritis (OA) at early stage when the number of patients’ cases is small. In our experiments we use high-resolution X-ray images of knees in patients which were identified with Kellgren–Lawrence scores progressing from 1. The existing ML methods have provided a limited diagnostic accuracy, whilst the proposed Group Method of Data Handling strategy of Deep Learning has significantly extended the diagnostic test. The comparative experiments demonstrate that the proposed framework using the Zernike-based texture features has significantly improved the diagnostic accuracy on average by 11%. This allows us to conclude that the designed model for early diagnostic of OA will provide more accurate radiology tests, although new study is required when a large number of patients’ cases will be available.

Oriented-Structured CsCu2I3 Film by Close-Space Sublimation and Nanoscale Seed Screening for High-Resolution X-ray Imaging.

An all-inorganic lead-free halides Cs-Cu-I system, represented by Cs3Cu2I5 and CsCu2I3, has attracted attention for their good photophysical characteristics recently. Successive works had reported their application potential in light-emitting devices. However, there is no report for CsCu2I3 in X-ray scintillation detectors so far. We notice that CsCu2I3 may be advantageous in such an application due to the one-dimensional crystal structure, the congruent-melting feature, and the high spectral matching to some photosensors. In this work, we explore the scintillation properties and imaging application of CsCu2I3 in X-ray scintillator detector. The oriented structure is designed to enhance the imaging performance of a CsCu2I3 detector. Close-space sublimation process and nanoscale seed screening strategy are employed to realize this design by producing a large-area (25 cm2) CsCu2I3 thick film layer with the oriented nanorod structure. This CsCu2I3 detector eventually achieves a high spatial resolution of 7.5 lp mm-1 in X-ray imaging.

Evaluation of granule structure and strength properties of green packed beds in iron ore sintering using high-resolution X-ray tomography and uniaxial compression testing

The strength properties of green sinter beds, including the Young’s modulus and maximum bed strain, were evaluated using uniaxial compression tests. The green-sinter-bed samples were scanned using X-ray computed tomography (XCT), and the geometry characteristics of the granules were quantified by XCT image analysis. The orthogonal array method was applied to determine the concomitant effects of the moisture, hydrated lime, and concentrate contents on the bed strength characteristics. Less bed strain was observed when the granules had a thin adhering layer and increased interlock contacts, which had a great capacity to resist the applied load collectively. The optimal combination for decreasing the bed maximum strain was 5.8% moisture, 2% hydrated lime, and 0% concentrate. The moisture and concentrate contents were the most significant factors determining the green bed strength. Increasing the moisture and concentrate contents produced granules with a thicker and more deformable adhering layer, resulting in a more compact bed. The addition of hydrated lime inhibited rearrangement, deformation, and fracture of the granules in green sinter bed during compression.

Defect-correlated fatigue resistance of additively manufactured Al-Mg4.5Mn alloy with in situ micro-rolling

Hybrid in situ rolled wire + arc additive manufacturing (HRAM) is a potential 3D printing method that combines traditional wire and arc additive manufacturing (WAAM) with in situ micro-rolling. Here, the manufacturing defects and mechanical and fatigue strength were explored for an HRAM- and WAAM-processed Al-Mg4.5 Mn alloy. The results show that advanced HRAM can result in significant grain refinement and enhance the material failure resistance compared with standard WAAM. High-resolution X-ray tomography was adopted to identify the defect density, morphology, distribution, and size, which showed that the defect population and size produced by HRAM were considerably lower than those produced by WAAM. Based on high-cycle fatigue tests, fatigue failure was observed entirely from metallurgical defects. Finite element simulations of the defect images based on computed tomography scans showed that lack-of-fusion defects are more dangerous than gas porosity in terms of increasing the local stress. Finally, the defect-controlled fatigue lifetime was predicted by combining the peaks-over-threshold method with a modified NASGRO model.

X-ray computed tomography using partially coherent Fresnel diffraction with application to an optical fiber.

A reconstruction algorithm for partially coherent x-ray computed tomography (XCT) including Fresnel diffraction is developed and applied to an optical fiber. The algorithm is applicable to a high-resolution tube-based laboratory-scale x-ray tomography instrument. The computing time is only a few times longer than the projective counterpart. The algorithm is used to reconstruct, with projections and diffraction, a tilt series acquired at the micrometer scale of a graded-index optical fiber using maximum likelihood and a Bayesian method based on the work of Bouman and Sauer. The inclusion of Fresnel diffraction removes some reconstruction artifacts and use of a Bayesian prior probability distribution removes others, resulting in a substantially more accurate reconstruction.

X-ray image super-resolution reconstruction based on a multiple distillation feedback network

The super-resolution reconstruction of X-ray images is one of the hot issues in the field of medical imaging. Due to the limitations of X-ray machines, the acquired images often have some problems, such as blurred details, unclear edges and low contrast, which seriously affect doctors’ interpretations of X-ray images. In view of the above problems, an X-ray image super-resolution reconstruction method based on a multiple distillation feedback network is proposed. In the feature extraction stage, the shallow features of X-ray images are extracted through 3 × 3 and 1 × 1 convolutional layers, and a multiple distillation feedback module is designed, which iteratively upsamples and downsamples to fully extract the texture details of X-ray images. Subpixel convolution is used to improve the resolution and the residual convolution is used to predict the corresponding residual image. In the image reconstruction stage, the residual image is fused with the transposed convolution upsampled image, and the Laplacian pyramid structure is used to progressively reconstruct high-resolution X-ray images. The experimental results show that the proposed method can suppress noise and reduce artifacts. Its peak signal-to-noise ratio (PSNR), structural similarity (SSIM) and information fidelity criteria (IFC) were all higher than those of the comparison methods, and its subjective visual was better.

Real-Time Anomaly Detection in Packaged Food X-Ray Images Using Supervised Learning

Physical contamination of food occurs when it comes into contact with foreign objects. Foreign objects can be introduced to food at any time during food delivery and packaging and can cause serious concerns such as broken teeth or choking. Therefore, a preventive method that can detect and remove foreign objects in advance is required. Several studies have attempted to detect defective products using deep learning networks. Because it is difficult to obtain foreign object-containing food data from industry, most studies on industrial anomaly detection have used unsupervised learning methods. This paper proposes a new method for real-time anomaly detection in packaged food products using a supervised learning network. In this study, a realistic X-ray image training dataset was constructed by augmenting foreign objects with normal product images in a cut-paste manner. Based on the augmented training dataset, we trained YOLOv4, a real-time object detection network, and detected foreign objects in the test data. We evaluated this method on images of pasta, snacks, pistachios, and red beans under the same conditions. The results show that the normal and defective products were classified with an accuracy of at least 94% for all packaged foods. For detecting foreign objects that are typically difficult to detect using the unsupervised learning and traditional methods, the proposed method achieved high-performance real-time anomaly detection. In addition, to eliminate the loss in high-resolution X-ray images, the false positive rate and accuracy could be lowered to 5% with patch-based training and a new post-processing algorithm.

A Semantic Segmentation Method for Buffer Layer Defect Detection in High Voltage Cable

A semantic segmentation method based on the fully convolutional network is proposed to detect the buffer layer defect in high voltage cable automatically. One hundred seventy-seven high-resolution X-ray images of cables are collected. FCN-8s and VGG16 backbone are adopted. The results indicated that the FCN-8s achieves the mIoU to 0.67 on the test set, proving to be an efficient way to detect the buffer layer defects.

Recent Development in X-Ray Imaging Technology: Future and Challenges.

X-ray imaging is a low-cost, powerful technology that has been extensively used in medical diagnosis and industrial nondestructive inspection. The ability of X-rays to penetrate through the body presents great advances for noninvasive imaging of its internal structure. In particular, the technological importance of X-ray imaging has led to the rapid development of high-performance X-ray detectors and the associated imaging applications. Here, we present an overview of the recent development of X-ray imaging-related technologies since the discovery of X-rays in the 1890s and discuss the fundamental mechanism of diverse X-ray imaging instruments, as well as their advantages and disadvantages on X-ray imaging performance. We also highlight various applications of advanced X-ray imaging in a diversity of fields. We further discuss future research directions and challenges in developing advanced next-generation materials that are crucial to the fabrication of flexible, low-dose, high-resolution X-ray imaging detectors.

Tracking based, high-resolution single-shot multimodal x-ray imaging in the laboratory enabled by the sub-pixel resolution capabilities of the MÖNCH detector

The simultaneous retrieval of x-ray attenuation, phase, and scattering using multimodal imaging techniques is finding increasing use in a range of applications, from medicine to materials science. Most techniques rely on the mechanical movement of an optical element (e.g., a grating or a mask) to obtain the multimodal images. While single-shot approaches exist, they typically employ detector pixels smaller than the grating period, often with low detection efficiency, and are limited in resolution unless either the sample or the optical element is displaced in various positions and multiple frames are collected. In this paper, we replace mechanical motion with the MÖNCH detector's capability to reach sub-pixel resolutions by interpolating between neighboring pixels collecting the charge generated by a single x-ray event. This enabled us to obtain the pilot demonstration of a laboratory-based high-resolution, single-shot multimodal imaging technique capable of simultaneously retrieving attenuation, directional differential phase, and scatter images, without any mechanical movement. We show that our proof-of-concept setup enables a single-shot resolution of 19.5 μm and that the resulting images provide sufficient information to produce a reliable sample thickness map. Furthermore, we demonstrate that the setup is capable of producing single-shot directional scattering images, while leaving open the option to further increase the resolution by using sample dithering.

Effects of polymer infiltration processing (PIP) temperature on the mechanical and thermal properties of Nextel 312 fibre SiCO ceramic matrix composites

Effects of the polymer infiltration processing (PIP) temperature between 850 and 1050 °C on the mechanical and thermal properties of Nextel 312 fibre SiCO ceramic matrix composite were studied. The aim was to optimise the material system for its proposed application as a mechanical gas-seal at temperatures up to 900 °C. The microstructure and its failure behaviour at room temperature were characterised using electron microscopy (SEM, TEM), X-ray diffraction and high resolution X-ray Tomography, with mechanical testing by nano-indentation, fibre-push out and flexural bending. Thermo-gravimetric analysis quantified the thermal stability. Processing at 950 °C or above gave a combination of high effective elastic modulus, good resistance to mechanical damage from tensile strain and good thermal stability.

Geometry assessment of ultra-short pulsed laser drilled micro-holes

Ultra-short pulsed laser ablation enables a defined generation of micro-holes. A parameter study on the ablation characteristics of copper clearly reveals a benefit for green wavelength with lower threshold fluence, simultaneously increasing the Rayleigh length. The use of a circular drilling method allows a defined manufacturing of micro boreholes and micro through-holes with 35 μm diameter of up to 165 μm and 300 μm length. Introducing high-resolution micro-computed X-ray tomography studying the micro-hole evolution and adjacent geometrical transformations reveals micrometer resolution and high usability. The conical geometry evolving up to an aspect ratio of 5:1 fits well to established models known for percussion drilling. However, increasing the number of pulses leads to non-conical geometry evolution, and this resulting geometry is studied for the first time. Henceforth, the exact geometrical evolution from conical to cylindrical shape upon laser drilling can be resolved revealing the impact of multiple reflections at the generated steep flanks.

Characterization of high-temperature nuclear fuel-coolant interactions through X-ray visualization and image processing

High-resolution X-ray imaging was employed at the JAEA MELT facility to visualize a kilogram-scale interaction between a jet of high temperature molten stainless steel and sodium, mimicking a sodium-cooled fast-neutron reactor in the aftermath of a core-disruptive accident. A novel software, SPECTRA, has been developed for the quantitative characterization of jet quenching and fragmentation. Tracking and 3D reconstruction of the melt phase traversing the imaging window enabled the detection of 72% of the debris mass recovered post-experiment. The rebounding of melt fragments confirmed a solid outer crust at the melt-coolant interface, while a thermal fragmentation event induced rapid vapor expansion. Jet fragmentation is best explained by the vaporization of coolant entrained within the melt jet generating an internal over-pressure sufficient for fragmentation of the crust. Thermal fragmentation produced missiles with velocities exceeding that of the jet, and a bimodal debris size distribution of coarse jet shells and finer fragments.

Plug for the parasitophorous duct: a solution of two conundra

BackgroundWe present two conundra in the biology of intraerythrocytic malaria parasite: how an apparent open parasitophorous duct provide direct access of only a select set of serum proteins to the parasitophorous vacuole, and how proteases mediate membrane lysis to allow merozoite egress.SolutionWe posit the existence of a parasitophorous vacuolar duct plug that is originally formed from a tight junction (or parts thereof) between merozoite apical surface and red blood cell plasma membrane, which by moving over the parasite surface towards the posterior end draws the parasite into the host cell interior, and by remaining at the passage orifice provides a location of transporter(s) for import of serum proteins into parasitophorous vacuole and an opening for merozoite egress upon its dissolution/dismantling through protease(s) action.ConclusionThis notion obviates the need of a distinct intact parasitophorous vacuolar membrane, which in the proposed model is an extension of the red blood cell membrane but still forms an intracellular compartment for parasite growth and development. The model is testable using existing high-resolution electron and X-ray tomography tools.