High-resolution X-ray Computed Tomography Imaging Research Articles

Comparison of two ancient Egyptian Middle Kingdom statuettes from the Museo Egizio of Torino through computed tomographic measurements

X-ray Computed Tomography (CT) has a significant role as investigation tool not only in medical and industrial applications, but also in cultural heritage studies. One of the main reasons for such broad adoption of this method is its non-destructive capability to investigate the inner structure of precious and unique artefacts that would instead be damaged by traditional sampling procedures. Ordinary X-ray radiography is limited and gives only 2D images, while high-resolution X-ray CT imaging gives non-invasive access to three-dimensional (3D) information. This article focuses on the comparison of micro-CT results obtained from the analysis of two ancient Egyptian wooden statuettes representing offering bearers. The artefacts belong to the collection of the Museo Egizio of Torino as part of the funerary assemblage of Minhotep, discovered in the Asyut necropolis. For the analysis, an upgraded version of the X-ray imaging apparatus located in the Centro Conservazione e Restauro “La Venaria Reale” (CCR) was used, in order to reach a higher final resolution than the one already present and used at CCR. Thanks to this investigation, much information on the artistic technique was obtained and it was possible to highlight differences and similarities in the technical features of the two statuettes, acquiring elements to understand the specific contribution of micro-tomography in studying the finds and hypothesizing a common production method.

A mechanism for chromite growth in ophiolite complexes: evidence from 3D high-resolution X-ray computed tomography images of chromite grains in Harold's Grave chromitite in the Shetland ophiolite.

ABSTRACTA fundamental difference exists between the textures of chromite crystals in chromitites in layered complexes and ophiolites. Those in layered complexes generally have euhedral octahedral shapes except where sintered, whereas those in ophiolites generally have rounded shapes accompanied commonly by nodular and more rarely dendritic chromite. Here we describe another texture characteristic of ophiolitic chromitite. The analysis of high-resolution X-ray computed tomography images of chromitite from Harold's Grave in the Shetland ophiolite has revealed 3D hopper structures on chromite grains. In 2D, these hopper structures appear at the surface of the chromite grain as stepped inward facing edges. A study of chromitites in 2D from ten ophiolite complexes has shown that all commonly contain chromite grains displaying these stepped edges. They occur mainly in protected enclaves surrounded by chromite grains that otherwise have rounded edges. The hopper crystals and the often associated clusters of inclusions represent periods of chromite crystal growth in a chromite supersaturated magma due to the presence of a more supercooled and more volatile-rich magma than that present in most layered complexes. Subsequent exposure of chromite crystals to chromite-undersaturated magma caused corrosion, resulting in the characteristic rounded shape of the ophiolitic chromite grains.

Experimental results of fatigue testing for calibration and validation of composite progressive damage analysis methods

The Air Force Research Laboratory led a research effort to benchmark the accuracy of static and fatigue predictions of several emerging composite progressive damage analysis techniques. The static portion of this technical effort is described in detail in a previous special issue of the Journal of Composite Materials. This paper provides the details of the fatigue experiments that were conducted to calibrate and validate the computational models. Initially, in-plane and out-of-plane S–N curves were generated through coupon tests that were performed on unidirectional laminae. The challenges experienced during fatigue testing of in-plane, matrix-dominated unidirectional coupon specimens are presented in detail. The higher fidelity test data from the fiber-dominated and out-of-plane experiments are also included in this paper. Following the calibration experiments, a series of tension–tension fatigue validation tests were conducted on open-hole coupons with three different stacking sequences. Each specimen was cycled to a pre-determined number of fatigue cycles, followed by static residual strength tests in both tension and compression. This paper provides the stress–strain responses of these validation tests as well as high-resolution X-ray computed tomography images of the subsurface damage as a function of cycles. Seven analysis teams used these test results to calibrate their models and to benchmark the accuracy of their predictions of damage and residual mechanical properties.

The application of high resolution X-ray computed tomography on naturally deformed rock salt: Multi-scale investigations of the structural inventory

X-ray computed tomography (CT) represents a useful technique providing new perspectives and insights for the structural investigation of naturally-deformed rock salt. Several samples of Permian rock salt from Gorleben, Asse and Teutschenthal (Germany) were investigated by exploiting the non-destructive nature of μCT and nCT techniques particularly for salt rocks. CT imaging enabled the visualization and quantification of anhydrite impurities, pore space and fluid phases located along grain-boundaries or trapped as intracrystalline inclusions. Disseminated grains and aggregates of anhydrite in rock salt of the Gorleben salt dome have been visualized and quantified by μCT for the first time in order to portray their spatial occurrence. The visualization of anhydrite aggregates and pore space shows no correlation between their spatial distributions. This independence excludes the anhydrite to be responsible for elevated porosity (0.87 ± 0.07 vol.-%). High-resolution nCT scans (≤1 μm voxel size) of single intracrystalline and grain-boundary fluid inclusions from Gorleben and Asse rock salt allowed the visualization and quantification of their various phase components. A major achievement is the detailed description of the morphology and shape of the fluid inclusions and of their phase components, which has not been conducted in rock salt research by high-resolution X-ray CT imaging before.

Chemical and Hydrodynamic Mechanisms for Long-Term Geological Carbon Storage

Geological storage of CO2 (GCS), also referred to as carbon sequestration, is a critical component for decreasing anthropogenic CO2 atmospheric emissions. Stored CO2 will exist as a supercritical phase, most likely in deep, saline, sedimentary reservoirs. Research at the Center for Frontiers of Subsurface Energy Security (CFSES), a Department of Energy, Energy Frontier Research Center, provides insights into the storage process. The integration of pore-scale experiments, molecular dynamics simulations, and study of natural analogue sites has enabled understanding of the efficacy of capillary, solubility, and dissolution trapping of CO2 for GCS. Molecular dynamics simulations provide insight on relative wetting of supercritical CO2 and brine hydrophilic and hydrophobic basal surfaces of kaolinite. Column experiments of successive supercritical CO2/brine flooding with high-resolution X-ray computed tomography imaging show a greater than 10% difference of residual trapping of CO2 in hydrophobic media compare...

A simulation study of high-resolution x-ray computed tomography imaging using irregular sampling with a photon-counting detector

The purpose of this study was to improve the spatial resolution for the x-ray computed tomography (CT) imaging with a photon-counting detector using an irregular sampling method. The geometric shift-model of detector was proposed to produce the irregular sampling pattern and increase the number of samplings in the radial direction. The conventional micro-x-ray CT system and the novel system with the geometric shift-model of detector were simulated using analytic and Monte Carlo simulations. The projections were reconstructed using filtered back-projection (FBP), algebraic reconstruction technique (ART), and total variation (TV) minimization algorithms, and the reconstructed images were compared in terms of normalized root-mean-square error (NRMSE), full-width at half-maximum (FWHM), and coefficient-of-variation (COV). The results showed that the image quality improved in the novel system with the geometric shift-model of detector, and the NRMSE, FWHM, and COV were lower for the images reconstructed using the TV minimization technique in the novel system with the geometric shift-model of detector. The irregular sampling method produced by the geometric shift-model of detector can improve the spatial resolution and reduce artifacts and noise for reconstructed images obtained from an x-ray CT system with a photon-counting detector.

Using High Resolution Computed Tomography to Visualize the Three Dimensional Structure and Function of Plant Vasculature

High resolution x-ray computed tomography (HRCT) is a non-destructive diagnostic imaging technique with sub-micron resolution capability that is now being used to evaluate the structure and function of plant xylem network in three dimensions (3D) (e.g. Brodersen et al. 2010; 2011; 2012a,b). HRCT imaging is based on the same principles as medical CT systems, but a high intensity synchrotron x-ray source results in higher spatial resolution and decreased image acquisition time. Here, we demonstrate in detail how synchrotron-based HRCT (performed at the Advanced Light Source-LBNL Berkeley, CA, USA) in combination with Avizo software (VSG Inc., Burlington, MA, USA) is being used to explore plant xylem in excised tissue and living plants. This new imaging tool allows users to move beyond traditional static, 2D light or electron micrographs and study samples using virtual serial sections in any plane. An infinite number of slices in any orientation can be made on the same sample, a feature that is physically impossible using traditional microscopy methods. Results demonstrate that HRCT can be applied to both herbaceous and woody plant species, and a range of plant organs (i.e. leaves, petioles, stems, trunks, roots). Figures presented here help demonstrate both a range of representative plant vascular anatomy and the type of detail extracted from HRCT datasets, including scans for coast redwood (Sequoia sempervirens), walnut (Juglans spp.), oak (Quercus spp.), and maple (Acer spp.) tree saplings to sunflowers (Helianthus annuus), grapevines (Vitis spp.), and ferns (Pteridium aquilinum and Woodwardia fimbriata). Excised and dried samples from woody species are easiest to scan and typically yield the best images. However, recent improvements (i.e. more rapid scans and sample stabilization) have made it possible to use this visualization technique on green tissues (e.g. petioles) and in living plants. On occasion some shrinkage of hydrated green plant tissues will cause images to blur and methods to avoid these issues are described. These recent advances with HRCT provide promising new insights into plant vascular function.

In vivo visualizations of drought-induced embolism spread in Vitis vinifera.

Long-distance water transport through plant xylem is vulnerable to hydraulic dysfunction during periods of increased tension on the xylem sap, often coinciding with drought. While the effects of local and systemic embolism on plant water transport and physiology are well documented, the spatial patterns of embolism formation and spread are not well understood. Using a recently developed nondestructive diagnostic imaging tool, high-resolution x-ray computed tomography, we documented the dynamics of drought-induced embolism in grapevine (Vitis vinifera) plants in vivo, producing the first three-dimensional, high-resolution, time-lapse observations of embolism spread. Embolisms formed first in the vessels surrounding the pith at stem water potentials of approximately -1.2 megapascals in drought experiments. As stem water potential decreased, embolisms spread radially toward the epidermis within sectored vessel groupings via intervessel connections and conductive xylem relays, and infrequently (16 of 629 total connections) through lateral connections into adjacent vessel sectors. Theoretical loss of conductivity calculated from the high-resolution x-ray computed tomography images showed good agreement with previously published nuclear magnetic resonance imaging and hydraulic conductivity experiments also using grapevine. Overall, these data support a growing body of evidence that xylem organization is critically important to the isolation of drought-induced embolism spread and confirm that air seeding through the pit membranes is the principle mechanism of embolism spread.

Metasomatic origin of diamonds in the world's largest diamondiferous eclogite

The world's largest diamondiferous eclogite (8.8 kg, UD-111/02) from the Udachnaya kimberlite, Siberia, is the subject of this investigation. High-resolution X-ray computed tomography (HRXCT), chemistry of host minerals and diamond inclusions, stratigraphy of the diamonds (cathodoluminescence zoning), and carbon isotopes have been obtained. HRXCT images, 3-d models, and subsequent detailed dissection of this Group B eclogite revealed linear distributions of diamonds along alteration zones. Both unusual multiple-diamond clusters with dodecahedral morphologies, and distinctive internal zoning recorded by cathodoluminescence analyses are indicative of multiple stages of diamond growth and resorption in UD-111-02. Carbon-isotope ratios ( δ 13C) of 16 diamonds have a total range of ~ 7‰ (− 2.0 to − 9.2‰), with the majority at − 5.4‰. Diamond core values are variable and include the lightest (− 9.2‰) and heaviest δ 13C (− 2.0‰) values, suggesting that cores formed from distinct carbon sources, or grew under different conditions. In contrast, the rims of all diamonds have similar δ 13C values (average − 5.2‰ with a 2SD of 1.2‰), suggesting that they formed under uniform conditions. Mineral inclusions in diamonds display compositional variations. These lines of evidence, considered together, indicate that diamonds in this eclogite were formed by several events, most likely from multiple metasomatic fluids. Furthermore, it is becoming increasingly evident that in most diamondiferous eclogites, diamonds are not synchronously formed with their host eclogites.

Deterministic Modeling of Fluid Flow through a CT-scanned Fracture Using Computational Fluid Dynamics

Modeling flow through fractures is a major challenge in the design of recovery mechanisms from naturally fractured reservoirs, since proper structural characterization of fracture networks and fracture transport properties are rarely available. We investigate single-phase flow dynamics in a rough fracture model constructed from high-resolution X-ray computed tomography images, using computational fluid dynamics. Flow simulations gave a detailed description of pressure and velocity fields and showed that this approach can be used for the deterministic analysis of single-phase flow through fractures. Our results demonstrate the formation of preferential flow channels and their correlation with local structural characteristic of the fracture.

The Palatal Dentition in Squamate Reptiles: Morphology, Development, Attachment, and Replacement

Abstract The palatal dentition in squamate reptiles is poorly known compared to the marginal dentition. We surveyed species representing all squamate families for the occurrence of palatal teeth. For those exhibiting palatal teeth, we investigated palatal tooth arrangement, morphology, development, attachment, and replacement patterns using SEM, high-resolution X-ray computed tomography imaging, and histology. We found substantial variability in the presence of palatal teeth and in the arrangement and number of palatal tooth rows at familial, generic, and specific levels among nonophidian lizards. However, snakes exhibit much more uniformity in both these respects. These patterns of variability have implications for trade-offs between phylogenetic, functional, and developmental constraints. When numerous, palatal teeth in most nonophidian lizards are either arranged in fields or loosely organized rows near the back of the oral cavity. In contrast, palatal teeth in snakes and in the “lizards” Shinisaurus a...

Effect of steam injection on pore structure and distribution in coke samples produced by delayed coking ☆

Porous structure of the petroleum coke produced in delayed coking technique is investigated by high-resolution X-ray computed tomography imaging. Cokes analyzed for these studies were produced from decant oil with and without steam injection. Images taken at different regions along the length of the coke columns have been used to characterize and quantify porosity and pore size (>20 μm)/shape distribution within the coke samples. Fractal analysis was performed to investigate the pore complexity distribution within the coke and to compare the two coke samples produced by different methods. High-resolution X-ray computed tomography was utilized also to scan a 1.1 cm section in the middle of the steam treated coke in volume mode to scan 80 images in one scan. Multi-planar reconstruction and 3D rendering of the pores were used to understand how the flow channels are developed and the degree of connectivity. Results showed that each coke sample shows a wide range of pore sizes and shapes that vary along the length of the coke samples. This variation in the coke that is not subjected to steam is more pronounced. Quantification of macropore size distribution shows that, in each coke sample the middle sections are the most similar regions in terms of pore size distribution and porosity. In general, steam injected coke has larger pores. Box counting fractal analysis in the cokes shows that pore distribution has fractal scaling at the locations scanned and helps in the interpretation of the pores at different locations in terms of their complexity in the distribution and shapes.

Assessing the accuracy of high-resolution X-ray computed tomography of primate trabecular bone by comparisons with histological sections.

Different lines of evidence suggest that trabecular bone architecture contains a functional signal related to an organism's locomotor behavior. An understanding of the interspecific and intraspecific variation in extant nonhuman primate trabecular structure is needed to evaluate its usefulness as a tool to reconstruct the locomotor habits of extinct primates. High-resolution X-ray computed tomography (HRXCT) is a new imaging approach with a resolution in the tens of microns that allows nondestructive access to the internal structure of bony elements. Previous studies indicate that such resolution is necessary to accurately quantify structural parameters of trabecular bone. The primary goal of this study was to test the accuracy of HRXCT by comparing stereological measurements from HRXCT images and histological thin sections of cancellous bone taken from the proximal femur and humerus of baboons. To this end, 11 bone samples were scanned on an HRXCT scanner and then thin-sectioned to reveal the scanned plane. HRXCT images were thresholded using a modified half-maximum height protocol. The stereological measurements included bone volume fraction (BV/TV), trabecular number (Tb.N), bone surface to volume ratio (BS/BV), trabecular thickness (Tb.Th), and trabecular spacing (Tb.Sp). The measurement errors on the HRXCT images were 10.90% for BV/TV, 6.06% for Tb.N, 14.19% for BS/BV, 14.33% for Tb.Th, and 7.09% for Tb.Sp, but none of these measurements were significantly different from the histological standards (alpha = 0.05). A second goal of this study was to examine the influence of thresholding, a necessary step in any morphometric study using computed tomography, on the accuracy of the quantitative morphometry. Threshold values derived from a modified half-maximum height protocol showed that parameters derived from the region of interest (area in which stereological measurements were later taken) produced better reconstructions of the actual bone structure than threshold values derived from more inclusive areas of bone. We conclude that HRXCT can accurately reconstruct the complex architecture of trabecular bone, and that thresholding is a nontrivial step in trabecular bone studies, with even slight changes in the protocol greatly affecting the morphometric data. HRXCT represents a valuable analytical tool that should be of interest to a great many researchers in physical anthropology because it allows nondestructive access to internal morphology, thereby preserving valuable and limited skeletal collections.