Microfocus X-ray Computed Tomography Research Articles

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.

Gas transport parameters of differently compacted granulated bentonite mixtures (GBMs) under air-dried conditions

Granulated bentonite mixtures (GBMs) have been regarded as effective buffer materials in the deep geological disposal of radioactive waste due to their operational advantages, such as ease of transportation and in-situ placement/backfilling. Many studies have been done to characterize the hydraulic and thermal properties of GBMs as well as their swelling properties. Only limited studies, however, have investigated their gas transport properties, even though these properties affect their compactness during in-situ placement/backfilling and subsequent gas diffusion and advection in the buffer zone. The aim of this study is to understand the gas transport parameters, i.e., air permeability (ka) and gas diffusivity (Dp/Do), of tested samples compacted at different dry densities (DDs) under air-dried conditions, linking them with the measured density distribution characteristics determined by microfocus X-ray computed tomography (MFXCT) analysis. Two types of GBMs were used in this study: 1) FE-GBM (prepared from National Standard® bentonite, Wyoming, USA): this material was used in the Full-scale Emplacement (FE) experiment at the Mont Terri rock laboratory, Switzerland) and 2) OK-GBM (prepared from a bentonite, originating from Japan, with the trade name of OK bentonite, Kunimine Industries). The tested samples were firstly packed in a 100-cm3 acrylic core with different DDs, ranging from loose to dense (1.09 to 1.75 g/cm3), and scanned by MFXCT. The weighting factors, wf (fine fraction; lower density) and wc (coarse fraction; higher density) (wf + wc = 1), were determined after the peak separation of the measured CT brightness histograms from the reconstructed three-dimensional multiplanar reconstruction (MPR) images of the MFXCT analysis. The measured ka and Dp/Do were highly dependent on the DDs, the ka (ɛ) values fitted well with a power law model, and the Dp/Do (ɛ) was predicted accurately by several previously proposed models. For both FE-GBM and OK-GBM, there were good linear relationships between the gas transport parameters and wc × DD, implying that the weight of the coarse fraction controlled ka and Dp/Do. Moreover, the Kozeny-Carman model, incorporating the measured volumetric surfaces from the MFXCT analysis, was able to predict the ka values well.

Permeability analysis of hydrate-bearing sediments considering the effect of phase transition during the hydrate dissociation process

Permeability is the most important factor affecting water and gas production in hydrate-bearing sediments (HBS). In this study, we combined in-situ microfocus X-ray computed tomography (CT) and pore network model simulation to obtain insights into the dynamic permeability of the hydrate dissociation process. Microfocus X-ray CT is used to visualize the three-dimensional pore structures of the specimen. Then an equivalent pore network can be extracted, which is used as input to pore network flow simulator to simulate the water and gas flow process. Results show that secondary hydrate formation causes effective permeability keff decreases and effective connate water saturation increases as hydrate saturation Sh increases from 0.40 to 0.48. The water relative permeability krw decreases and gas relative permeability krg increases due to larger patchy hydrates (Sh = 0.33). The krw and krg are largely affected by the pore and throat sizes and pore space connectivity. Hydrate dissociation in HBS also influences its permeability anisotropy. Secondary hydrate formation causes keff decreases in the x, y, and z directions when Sh increase from 0.40 to 0.48. Large patchy hydrates influence preferential flow direction for water flow. Predicting the dynamic permeability of the hydrate dissociation process would improve pore-scale water and gas flow analyses in HBS.

Quantitative Evaluation of Soil Structure and Strain in Three Dimensions under Shear Using X-ray Computed Tomography Image Analysis.

The objective of this study is to quantitatively evaluate the soil structure behavior when under shear stress to understand the mechanism of shear zone formation using a micro-focus X-ray computed tomography (CT) scanner to visualize the internal samples without causing disturbance. A new image-analysis method was proposed to systematically evaluate the particle length and direction by fitting the particle as an ellipsoid. Subsequently, a direct shear experiment was conducted on soil materials, and shear band was scanned using a micro-focus X-ray CT scanner. After validating the proposed method, the soil structure was evaluated in the shear zone via image analysis on the CT images. Furthermore, the strain inside the specimen was evaluated using digital image correlation. The results showed that a partial change in the particle direction occurred when the volume expansion inside the shear zone exceeded the peak. In addition, the width of the shear zone was ~7.1 times the median grain size of the sand used; however, the region exhibiting a change in the direction of the particles was narrow and confined to the vicinity of the shear plane.

New evaluation of species‐specific biogenic silica flux of radiolarians (Rhizaria) in the western Arctic Ocean using microfocus X‐ray computed tomography

AbstractWe studied time‐series fluxes of radiolarian particles collected by two sediment traps deployed at the eastern (Sta. NAP12t) and western (Sta. CAP12t) sides of the Chukchi Borderland in the Chukchi Sea from 04 October 2012 to 18 September 2013. In order to elucidate the contribution of radiolarian skeletons to the biogenic silica flux, a three‐dimensional (3D) imaging technique using microfocus X‐ray computed tomography (MXCT) was applied to radiolarian siliceous skeletons. We calculated volumes of individual radiolarian skeletons accurately using a 3D model of them, thereby estimating the mass of silica for each radiolarian species. The time‐series fluxes of radiolarian abundance were combined with the mass of radiolarian silica and were transformed to estimate fluxes of radiolarian silica. As a result, we found that the main carrier of radiolarian silica in the western Arctic Ocean was represented by only two species; that is, Amphimelissa setosa (averages: 55.2 wt% at Sta. NAP12t, 70.8 wt% at Sta. CAP12t) and Spongotrochus glacialis (averages: 36.7 wt% at Sta. NAP12t, 23.2 wt% at Sta. CAP12t). The total radiolarian silica flux was usually higher in the eastern side than that in the western side of the Chukchi Borderland. The contribution of radiolarian silica to the biogenic silica flux was less than 10 wt% in general during the sampling duration, but occasionally reached 19.6–34.8 wt% during the open water season. This suggests that not only diatoms but also radiolarians make a significant contribution in driving the silica cycle in the Arctic Ocean.

CHARACTERIZING PORE-STRUCTURAL PARAMETERS OF VOLCANIC ASH SOIL: COMPARISON BETWEEN NON-DESTRUCTIVE AND INDIRECT METHODS

Mass transport within porous media is governed by their pore networks, which is highlyinfluenced by pore structure parameters such as pore size distribution, porosity, pore tortuosity and porecoordination number. Micro-focus X-ray computed tomography (MFXCT) has emerged as a powerful nondestructive tool for the direct visualization and better understand soil pore geometry. In this study, soilmacropore networks (typically, pore diameter ≥ 30 µm) were visualized and gas transport parameters weremeasured for volcanic ash soils taken from Nishi Tokyo City, Japan. Especially, the study aimed to identifythe effect of moisture content on pore structural parameters based on MFXCT analysis and compare theMFXCT derived parameters to indirectly-estimated parameters from soil gas diffusion coefficient and airpermeability such as pore tortuosity-connectivity factor (XG) and equivalent pore diameter (dG) for gas flow.Both undisturbed and repacked samples were used for characterizing soil pore networks. In MFXCT analysis,the pore structural parameters such as effective pore diameter (dMFXCT), pore tortuosity (TMFXCT), andcoordination number (CMFXCT) were measured. Results showed the moisture content affected clearly porestructural parameters, TMFXCT and CMFXCT decreased with increasing soil air filled porosity, however, measureddMFXCT were independent on the moisture content. For both undisturbed and disturbed samples, the measuredTMFXCT and XG became close and plotted in a narrow range between 1:1.5 and 1.5:1. On the other hand, highvariations were observed between dMFXCT and dG, indicating that the indirectly estimated equivalent porediameter from soil gas transport parameters does not correspond to the mean diameter of soil macropore.

Advanced approach to analyzing calcareous protists for present and past pelagic ecology: Comprehensive analysis of 3D-morphology, stable isotopes, and genes of planktic foraminifers.

Marine protists play an important role in oceanic ecosystems and biogeochemical cycles. However, the difficulties in culturing pelagic protists indicate that their ecology and behavior remain poorly understood; phylogeographic studies based on single-cell genetic analyses have often shown that they are highly divergent at the biological species level, with variable geographic distributions. This indicates that their ecology could be complex. On the other hand, the biomineral (calcareous) shells of planktic foraminifers are widely used in geochemical analyses to estimate marine paleoenvironmental characteristics (i.e., temperature), because the shell chemical composition reflects ambient seawater conditions. Among the pelagic protists, planktic foraminifers are ideal study candidates to develop a combined approach of genetic, morphological, and geochemical methods, thus reflecting environmental and ecological characteristics. The present study precisely tested whether the DNA extraction process physically and chemically affects the shells of the planktic foraminifer Globigerinoides ruber. We used a nondestructive method for analyzing physical changes (micro-focus X-ray computed tomography (MXCT) scanning) to compare specimens at the pre- and post-DNA extraction stages. Our results demonstrate that DNA extraction has no significant effect on shell density and thickness. We measured stable carbon and oxygen isotopes on the shell of each individual in a negative control or one of two DNA-extracted groups and detected no significant differences in isotopic values among the three groups. Moreover, we evaluated isotopic variations at the biological species level with regard to their ecological characteristics such as depth habitat, life stages, and symbionts. Thus, our examination of the physiochemical effects on biomineral shells through DNA extraction shows that morphological and isotopic analyses of foraminifers can be combined with genetic analysis. These analytical methods are applicable to other shell-forming protists and microorganisms. In this study, we developed a powerful analytical tool for use in ecological and environmental studies of modern and past oceans.

Linking pore network structure derived by microfocus X-ray CT to mass transport parameters in differently compacted loamy soils

Mass transport in soil occurs through the soil pore network, which is highly influenced by pore structural parameters such as pore-size distribution, porosity, pore tortuosity, and coordination number. In this study, we visualised the networks of meso- and macro-pores (typical pore radius r ≥ 10 μm) using microfocus X-ray computed tomography (MFXCT) and evaluated pore structural parameters of two loamy soils from Japan and New Zealand packed at different degrees of compaction. The effect of compaction on pore structural parameters and relationships between pore structural parameters and measured mass transport parameters were examined. Results showed a clear influence of compaction on pore structural parameters, with the MFXCT-derived mean pore radii and pore tortuosities decreasing and the mean pore coordination number increasing with increasing dry bulk density. Especially, pores with r > 80 µm became finer or were not well formed due to compaction. The MFXCT-derived pore structural parameters were not well correlated with the equivalent pore radii from measured water retention curves. However, volumetric surface areas and pore-network connectivity-tortuosity factors derived from MFXCT allowed a fair prediction of several important mass transport parameters such as saturated hydraulic conductivities, soil-gas diffusion coefficients, and soil-air permeabilities. Further studies are needed to link micro-pores with radii smaller than the X-ray CT resolution to meso- and macro-pores visualised by X-ray CT to improve the prediction of mass transport parameters in soil.

Nondestructive evaluation of egg-to-adult development and feeding behavior of the bamboo powderpost beetle Dinoderus minutus using X-ray computed tomography

The life history and feeding biology of the bamboo powderpost beetle Dinoderus minutus remain poorly understood because the beetles’ oviposition, development, and feeding take place inside bamboo culms. In this study, X-ray computed tomography (CT) was employed to nondestructively quantify the progression of larval body size and tunnel size from the first instar to pupation. Eggs of D. minutus laid between laminates of nutrient-containing filter paper were easily collected. The newly hatched larvae were inoculated singly into pieces of internodes of madake (Phyllostachys bambusoides). The pieces were scanned using a microfocus X-ray CT system every 3–5 days to visualize the beetles’ bodies and tunnels with resolutions of 18–60 μm/voxel. CT scans were continued after adult eclosion to analyze pre-mating adult feeding. The collected eggs were 0.84 ± 0.06 mm (mean ± SD) in length and the egg duration lasted 5.0 ± 0.8 days. Based on CT images, the larvae grew to 3.53 ± 0.23 mm in body length and turned into pupae of 3.42 ± 0.09 mm. The larvae bored tunnels with a length of 80.2 ± 4.8 mm and a volume of 68.0 ± 7.0 mm3 over the larval period of 61 ± 11 days. Newly emerged adults remained in the bamboo pieces to feed before making exit holes in 8 ± 1 days after adult eclosion. During this period, they bored tunnels at rates of 2.64 ± 0.58 mm/day in length and 4.87 ± 1.10 mm3/day in volume.

Three-dimensional pore geometry and permeability anisotropy of Berea sandstone under hydrostatic pressure: connecting path and tortuosity data obtained by microfocus X-ray CT

Abstract Void space and permeability are two primary factors controlling the movement and storage of fluids in rock and sediments. To investigate fluid flow anisotropy in Berea sandstone, permeability was measured in three perpendicular directions under effective confining pressure as a function of pore pressure. Permeability anisotropy was observed slightly in the normal and in two parallel directions to the bedding planes. We introduced microfocus X-ray computed tomography (CT) as a non-destructive tool and the three-dimensional medial axis (3DMA) method to quantify the flow-relevant geometric properties of the voids structure. Using this apparatus and structure analysis software, we obtained the distributions of pore size, throat size and the number of connecting paths between two faces in an arbitrary region of Berea sandstone. Using these data, we also evaluated the number of connecting paths between two faces and tortuosity within an arbitrary region, and discussed the relationship between permeability anisotropy and voids geometry.

Verifying the potential of micro-focus X-ray computed tomography in the study of ancient bone tool function

The results of 22 micro-focus X-ray computer tomography (micro-CT) scans of one-hundred-year-old bone arrowheads and link-shafts are presented. These data build on previous experimental research that sought to establish a new use-trace method for identifying archaeological bone arrowheads where surface damage is lacking. The results presented here confirm the potential of micro-CT for imaging bone micro-structure but highlight the variable conditions under which micro-cracks and fatigue fractures may develop. Micro-cracks associated with impact crushing occur more often than those associated with bending forces, but cannot be used in isolation to ascribe hunting function. Link-shafts are more likely to develop micro-structural damage unrelated to hunting activities. In order for micro-structural damage to be informative about the nature of use, a ‘tool’ must have been frequently used in order for sufficient damage to accrue.

High-resolution X-ray computed tomography of through silicon vias for RF MEMS integrated passive device applications

This paper presents our exploration of microfocus and high-resolution X-ray computed tomography (CT) on open high-aspect ratio through Silicon via (TSV) test structures, the interior wall covered with a ~10μm thick conformal Cu plating, using state-of-the-art and commercially available X-ray systems. Goal of our research is to better understand the physical failure mechanisms of defective open TSVs, in order to further improve the yield of TSV production for integrated passive devices (IPD) to be used in radio frequency microelectromechanical system (RF MEMS) applications.Micrometer-sized defects were non-destructively identified in some of the open TSVs (i.e. Cu plating thickness deviations, incomplete plating and large voids) using microfocus X-ray CT, which were then verified by destructive mechanical cross-sectioning. With high-resolution X-ray CT, which has almost an order of magnitude better resolution, (sub) micron-sized defects in TSVs were directly non-destructively identified and localized, without the need for further destructive inspection techniques for confirmation. The Cu plating thickness variations, in TSVs all connected to a large-area redistribution layer, were found to be design related; based on these failure analysis findings, a new electroplating procedure has been established.

Segmentation of multi-phase X-ray computed tomography images

X-ray computed tomography (CT) is useful for non-destructively visualising internal features of non-transparent objects. In addition, it provides quantitative information about the geometry and spatial distribution of an object’s constituent materials. However, X-ray CT images include blurs and noises. Herein, the authors focus on the partial volume effect that causes blurs depending on image resolution. Artificial materials (e.g., thin wire and threads) and natural materials (e.g., oil sand) were observed using a microfocus X-ray CT scanner. A maximum likelihood thresholding method considering the partial volume effect based on histogram data was applied for segmenting two- and three-phase X-ray CT images. Relative errors in measured cross-sectional areas of aluminium wires and nylon threads were evaluated for verifying the segmentation method. Occupancy ratios of each phase of oil sand to its bulk volume were quantified. The introduced segmentation method estimates the volume of each constituent of two- and three-phase porous materials with reasonable accuracy.

Evaluation of larval growth process and bamboo consumption of the bamboo powder-post beetle Dinoderus minutus using X-ray computed tomography

The bamboo powder-post beetle Dinoderus minutus is a major pest of felled bamboo in Japan. In this study, X-ray computed tomography (CT) was utilized to non-destructively trace the movement of the larvae of D. minutus inside infested bamboo specimens and to evaluate the bamboo consumption of the larvae. The infested specimens, which had been enclosed with adult D. minutus beetles, were scanned using a microfocus X-ray CT system every 2 to 5 days. Larvae and other stages of the beetles were clearly recognizable in the CT images with a voxel size of 61.9 μm, and they were distinguishable from the bamboo, insect tunnels, and frass. The larvae were traced until pupation, and the length and volume of their tunnels were measured to evaluate their bamboo consumption. The tunnel length and volume bored by one larva was estimated to be 0.98 mm and 1.06 mm3 (0.70 mg of oven-dry mass) per day within the average observation period of 22 days, respectively, and the active larval period was estimated to be 39 days in our experimental conditions.

Internal skeletal analysis of the colonial azooxanthellate scleractinian Dendrophyllia cribrosa using microfocus X-ray CT images: underlying basis for its rigid and highly adaptive colony structure.

Dendrophyllid Scleractinia exhibit a variety of colonial morphologies, formed under the strict constraints on (1) budding sites, (2) orientations of the directive septa of offsets, (3) inclination of budding direction, and (4) those constraints in every generation. Dendrophyllia cribrosa exhibits a sympodial dendroid form, characteristically large coralla, and occasional fusions of adjacent branches within the same colony. Adjacent corallites are bound and supported by coenosteum skeleton. This study examined the inner skeletal structures at the junctions of fused branches using a non-destructive microfocus X-ray computed tomography (CT) imaging approach, and considered the reasons for the large colonial sizes and their adaptive significance. Three-dimensional reconstructions of two-dimensional X-ray CT images reveal that individual corallites are not directly connected in fused parts. Additionally, no completely buried individuals were found within fused skeleton. When adjacent branches approach one another, constituent corallites change their growth directions to avoid collisions between the branches. The adjacent branches fuse without a reduction in the number of constituent corallites, leading to the establishment of reticular and rigid colonial structures. In addition, a nearly even distribution of individuals on the colony surface facilitates efficient intake of nutrients. Thus, the growth of large D. cribrosa colonies involves avoidance of collision between constituent individuals, the reinforcement of colonial structure, and efficient uptake of nutrients. These observations provide insights on the dynamics of interrelationships between colony-making mechanisms and the adaptive strategies required under habitat conditions such as specific current activities.

Visualization of O2 on Aqueous Li-Air Battery by Using Microfocus X-ray CT

The reaction products associated with charge/discharge processes are key issues to improve the performance of Li-air battery. Although LiO2, Li2O2, and other Li organic compounds have been previously investigated, the production of O2 during the charge process and its ability to cause reduction of the electrode area have not been discussed. In this study, experimental visualization of the inside of an air cathode was realized using microfocus X-ray computed tomography (CT), and the production of O2 in aqueous electrolyte by the charge reaction was visualized. As a result, we show that the wettability of the porous cathode carbon electrode strongly affected the behavior of produced gas.

Investigation of localized deformation in partially saturated sand under triaxial compression using microfocus X-ray CT with digital image correlation

In this paper, localized deformation in partially saturated sand was investigated quantitatively using microfocus X-ray computed tomography (CT) and an image analysis of the CT images. Triaxial compression tests on a partially saturated dense Toyoura sand specimen were carried out under a low confining pressure and under drained conditions for both air and water. The development of localized deformation was observed macroscopically using microfocus X-ray CT, and the displacement field over the entire specimen was quantified by an image analysis of the CT images with the digital image correlation (DIC) technique. The progressive development of shear bands is discussed with reference to these images. In addition, the region of localization was observed microscopically by partial CT scanning on a micron scale with high spatial resolution. Changes in the particulate structures are also discussed herein. The DIC image analysis of the partial CT images provided a microscopic displacement field and indicated that very fine localized shear deformation developed before the shear bands had become visible in the macroscopic investigation.

Correlating Gas Transport Parameters and X-Ray Computed Tomography Measurements in Porous Media

Gas transport parameters and X-ray computed tomography (CT) measurements in porous medium under controlled and identical conditions provide a useful methodology for studying the relationships among them, ultimately leading to a better understanding of subsurface gaseous transport and other soil physical processes. The objective of this study was to characterize the relationships between gas transport parameters and soil-pore geometry revealed by X-ray CT. Sands of different shapes with a mean particle diameter (d 50) ranging from 0.19 to 1.51 mm were used as porous media under both air-dried and partially saturated conditions. Gas transport parameters including gas dispersivity (α), diffusivity (D P/D 0), and permeability (k a) were measured using a unified measurement system (UMS). The 3DMA-Rock computational package was used for analysis of three-dimensional CT data. A strong linear relationship was found between α and tortuosity calculated from gas transport parameters ( ), indicating that gas dispersivity has a linear and inverse relationship with gas diffusivity. A linear relationship was also found between k a and d 50/T UMS 2, indicating a strong dependency of k a on mean particle size and direct correlation with gas diffusivity. Tortuosity (T MFX) and equivalent pore diameter (d eq.MFX) analyzed from microfocus X-ray CT increased linearly with increasing d50 for both Granusil and Accusand and further showing no effect of particle shape. The T UMS values showed reasonably good agreement with T MFX values. The k a showed a strong relationship when plotted against d eq.MFX/T MFX 2, indicating its strong dependency on pore size distribution and tortuosity of pore space.

Evaluation of Porosity and Its Variation in Porous Materials Using Microfocus X-ray Computed Tomography Considering the Partial Volume Effect

The physical properties of two-phase materials depend on their internal structure. Therefore, segmentation of the structure of such materials is important in material sciences. In this study, we used a maximum likelihood thresholding method that considered the partial volume effect —i.e., the effect of mixels (mixed pixels)— to calculate the porosities of packed glass beads and the Berea sandstone using microfocus X-ray computed tomography (CT) images. We also examined the effects of scanning conditions on the segmentation results and assessed the porosity of possible packing structures of the glass beads to be segmented to be 33–37% based on histogram data. Moreover, we evaluated the porosity of the Berea sandstone to be 18%.Then, we examined variation in the porosity of biogrouted packing of glass beads using a microfocus X-ray CT scanner and histogram-based image analysis with the same thresholding method. Our results indicated that the ratio of grouted to ungrouted geomaterial porosities was 0.98, whereas the value estimated by measuring changes in the concentration of calcium ions was 0.98–0.99. Thus, we have confirmed that the proposed method can evaluate small changes in porosity with high accuracy.

Investigation of self-sealing in high-strength and ultra-low-permeability concrete in water using micro-focus X-ray CT

High-strength and ultra-low-permeability concrete (HSULPC) is thought to be useful as a radioactive waste package. Thus, a high confining ability is desirable. For cementitious materials, sealing of cracks may occur in water due to the precipitation of calcium compounds. This can affect the confining ability. In this study, the sealing of a crack in HSULPC in water was investigated using micro-focus X-ray computed tomography (CT). The sealing by precipitation occurred only around the end of the specimen. Sealed regions of the crack were identified using three-dimensional image registration and CT image subtraction of images obtained for the specimen before and after it was immersed in water to evaluate temporal changes of the sealing deposits in the crack. The sealing deposits increased as the HSULPC specimen was kept in water longer. It was concluded that cracks in HSULPC in water are sealed by precipitation.