XCT Images Research Articles

XCT image reconstruction by a modified superiorized iteration and theoretical analysis

ABSTRACT In this paper, we propose an improved iteration superiorization method for X-ray computed tomography image reconstruction. We simplify the classic superiorized iteration by removing two constraints imposed on the perturbation. A novel method is proposed to determine the perturbation amount and direction for the superiorized iteration simultaneously. Some theoretical properties (convergence for instance) of the superiorized iteration sequence with the proposed perturbation are analysed. We present a general proof for the convergence of ART-like iterations with summable perturbations. In addition, we prove the convergence of simultaneous iterations without the summable perturbation assumption. Experiments on simulated and real data not only verify the theoretical result but also show that the proposed algorithm is superior to the classic superiorized iteration and can reconstruct desirable images.

Effects of particle clustering on the plastic deformation and damage initiation of particulate reinforced composite utilizing X-ray CT data and finite element modeling

In this paper, a new simulation technique which can include microstructural inhomogeneity of particulate reinforced composites is proposed to accurately study deformation pattern and damage mechanism in these composites. Three dimensional microstructures constructed from XCT images incorporated into finite element modeling codes with minimal approximation to capture the effects of cluster size, local volume fraction of particles in the cluster and the distance between clusters as relevant statistical quantities describing the microstructural inhomogeneity of particulate reinforced composites. A quantitative parameter as degree of clustering is defined to consider particle clustering effect. The results indicate that the damage growth rate of composite with higher degree of clustering is significantly higher than those composites with lower degree of clustering. It is found that for region with higher degree of clustering and bigger size of clusters, the von Mises stress is higher at the same loading condition and the growth rate of plastic flow is considerably higher than the other region with lower degree of clustering. Moreover, the dislocation description of deformation in two-phase materials rationalize particle clustering effect on the yield behavior of the particulate reinforced composites and the flow stress in these composites. The macroscopic stresses that lead to the initial yielding in the matrix decrease when clusters closely proximate with bigger size and higher degree of clustering.

Examination of gas hydrate-bearing deep ocean sediments by X-ray Computed Tomography and verification of physical property measurements of sediments

Physical properties like porosity and density are important parameters for size estimations of fossil fuel reservoir in host sediments and rocks. X-ray CT based imaging and subsequent analysis of the images by using various techniques for estimations of these properties of host rocks and sediments has been attempted. However, most of those techniques tend to be biased and subjective due to complications in image processing. Here we describe a new procedure for estimating porosity and density without processing the XCT images, but using the raw data that are used for producing the images. In this study, large-size cylindrical core samples (up to 150 cm long and 6.6 cm diameter) were imaged in a matter of minutes by using a medical XCT scanner soon after their recovery from seafloor onboard drillship in order to record as realistic as possible condition of hydrate-bearing sediments. Despite some uncertainty in relative volumes of solid, liquid and gas phases at voxel level, the results obtained by this rapid and non-destructive procedure are in good agreement with those obtained by time- and sample-consuming conventional methods of physical property measurements. • XCT scanning of hydrate-bearing sediments soon after their recovery from seafloor. • New method for porosity estimation of sediments from raw XCT data (CT number). • Much faster than conventional method of porosity estimation.

Enhancing image resolution of soils by stochastic multiscale image fusion

Soil structure defines major physical properties and biophysical functions of soils. Imaging soil structure using different 2/3D techniques is a routine methodology used by soil scientists. Still, for structured soils their spatial variability and hierarchical structure imposes a significant challenge for all imaging methods in terms of field-of-view and resolution trade-off. While creating a truly multiscale 3D digital model of soil is without question of utmost importance, there is currently no single imaging method that could potentially encompass all necessary relevant soil scales within a single image. In this paper, we tested for the first time an image fusion technique to produce a multiscale soil image based on separate images obtained with different spatial resolutions. The method is based on universal soil structure descriptors, i.e. spatial correlation functions, which were shown to be very useful in soil applications. Using a relatively simple 2D test case based on X-ray tomography (XCT) images at three different scales, we show the applicability of image fusion for soil images and solve a long standing problem of imaging resolution. In total we fused seven images into a single image: one 114μm resolution macroscale XCT image (porosity <0.01), four 15μm resolution microscale XCT images (with porosities 0.039–0.049), and two 3.3μm resolution microscale XCT images (with porosities of 0.24 and 0.76). The resulting single, 15μm resolution image represented 6×6cm2 of soil structure. Its porosity increased from <0.01 to 0.073 due to representation of all pore sizes visible on the images prior to fusion. Current drawbacks of the approach are discussed and an outline is provided of its future usage to address important soil structure issues.

Proton energy and scattering angle radiographs to improve proton treatment planning: a Monte Carlo study

The novel proton radiography imaging technique has a large potential to be used in direct measurement of the proton energy loss (proton stopping power, PSP) in various tissues in the patient. The uncertainty of PSPs, currently obtained from translation of X-ray Computed Tomography (xCT) images, should be minimized from 3–5% or higher to less than 1%, to make the treatment plan with proton beams more accurate, and thereby better treatment for the patient. With Geant4 we simulated a proton radiography detection system with two position-sensitive and residual energy detectors. A complex phantom filled with various materials (including tissue surrogates), was placed between the position sensitive detectors. The phantom was irradiated with 150 MeV protons and the energy loss radiograph and scattering angles were studied. Protons passing through different materials in the phantom lose energy, which was used to create a radiography image of the phantom. The multiple Coulomb scattering of a proton traversing different materials causes blurring of the image. To improve image quality and material identification in the phantom, we selected protons with small scattering angles. A good quality proton radiography image, in which various materials can be recognized accurately, and in combination with xCT can lead to more accurate relative stopping powers predictions.

Microstructure of chemically modified wood using X-ray computed tomography in relation to wetting properties

Abstract X-ray computed tomography (XCT) was utilized to visualize and quantify the 2D and 3D microstructure of acetylated southern yellow pine (pine) and maple, as well as furfurylated pine samples. The total porosity and the porosity of different cell types, as well as cell wall thickness and maximum opening of tracheid lumens were evaluated. The wetting properties (swelling and capillary uptake) were related to these microstructural characteristics. The data show significant changes in the wood structure for furfurylated pine sapwood samples, including a change in tracheid shape and filling of tracheids by furan polymer. In contrast, no such changes were noted for the acetylated pine samples at the high resolution of 0.8 μm. The XCT images obtained for the furfurylated maple samples demonstrated that all ray cells and some vessel elements were filled with furan polymer while the fibers largely remained unchanged. Furfurylation significantly decreased the total porosity of both the maple and pine samples. Furthermore, this was observed in both earlywood (EW) and latewood (LW) regions in the pine samples. In contrast, the total porosity of pine samples was hardly affected by acetylation. These findings are in line with wetting results demonstrating that furfurylation reduces both swelling and capillary uptake in contrast to acetylation which reduces mostly swelling. Furfurylation significantly increased the cell wall thickness of both the maple and pine samples, especially at higher levels of furfurylation.

A dual-phase bilayer oxygen permeable membrane with hierarchically porous structure fabricated by freeze-drying tape-casting method

A bilayer oxygen permeable membrane consisting of hierarchically porous Ce0.9Gd0.1O1.95-(La0.8Sr0.2)0.95MnO3−δ (GDC-LSM) support and dense GDC-LSM film has been fabricated by a combined freeze-drying tape-casting and screen-printing method followed by co-sintering. Two dimensional (2D) SEM-BSE and reconstructed three dimensional (3D) XCT images indicated that the porous GDC-LSM support (870-µm-thick) contains graded straight pores with low tortuosity factor, promoting fast gas diffusion in the support, while the dense GDC-LSM film with a thickness of 30µm provides a short path for the bulk transport of oxygen ions and electrons. However, the oxygen flux of the asymmetric GDC-LSM membrane is only 81% higher than that of the 900-µm-thick dense GDC-LSM symmetric membrane, indicating that the oxygen transport becomes limited by the surface oxygen exchange process for the GDC-LSM asymmetric membrane with a 30-µm-thick dense GDC-LSM film. When the permeate side surface is modified with Ce0.8Sm0.2O1.9-La0.6Sr0.4Co0.2Fe0.8O3−δ (SDC-LSCF), the oxygen permeation flux of the GDC-LSM asymmetric membrane is significantly enhanced from 0.105 to 0.780mLcm−2min−1, while the activation energy is substantially decreased from 219.6±8.7 to 138.1±3.3kJmol−1, due to enhanced surface oxygen exchange kinetics. Furthermore, the coated asymmetric membrane shows 1100% higher oxygen flux than the coated symmetric membrane. When the sweep gas is switched from helium to CO2, although the adsorption of CO2 on the permeate side surface leads to a slight decrease in oxygen permeation flux, a high oxygen permeation flux of 0.659mLcm−2min−1 can still be achieved, demonstrating that the coated GDC-LSM asymmetric membrane is promising for oxy-fuel combustion application.

Phase segmentation of X-ray computer tomography rock images using machine learning techniques: an accuracy and performance study

Abstract. Performance and accuracy of machine learning techniques to segment rock grains, matrix and pore voxels from a 3-D volume of X-ray tomographic (XCT) grayscale rock images was evaluated. The segmentation and classification capability of unsupervised (k-means, fuzzy c-means, self-organized maps), supervised (artificial neural networks, least-squares support vector machines) and ensemble classifiers (bragging and boosting) were tested using XCT images of andesite volcanic rock, Berea sandstone, Rotliegend sandstone and a synthetic sample. The averaged porosity obtained for andesite (15.8 ± 2.5 %), Berea sandstone (16.3 ± 2.6 %), Rotliegend sandstone (13.4 ± 7.4 %) and the synthetic sample (48.3 ± 13.3 %) is in very good agreement with the respective laboratory measurement data and varies by a factor of 0.2. The k-means algorithm is the fastest of all machine learning algorithms, whereas a least-squares support vector machine is the most computationally expensive. Metrics entropy, purity, mean square root error, receiver operational characteristic curve and 10 K-fold cross-validation were used to determine the accuracy of unsupervised, supervised and ensemble classifier techniques. In general, the accuracy was found to be largely affected by the feature vector selection scheme. As it is always a trade-off between performance and accuracy, it is difficult to isolate one particular machine learning algorithm which is best suited for the complex phase segmentation problem. Therefore, our investigation provides parameters that can help in selecting the appropriate machine learning techniques for phase segmentation.

SU‐C‐207A‐03: Development of Proton CT Imaging System Using Thick Scintillator and CCD Camera

Purpose:In the treatment planning of proton therapy, Water Equivalent Length (WEL), which is the parameter for the calculation of dose and the range of proton, is derived by X‐ray CT (xCT) image and xCT‐WEL conversion. However, about a few percent error in the accuracy of proton range calculation through this conversion has been reported. The purpose of this study is to construct a proton CT (pCT) imaging system for an evaluation of the error.Methods:The pCT imaging system was constructed with a thick scintillator and a cooled CCD camera, which acquires the two‐dimensional image of integrated value of the scintillation light toward the beam direction. The pCT image is reconstructed by FBP method using a correction between the light intensity and residual range of proton beam. An experiment for the demonstration of this system was performed with 70‐MeV proton beam provided by NIRS cyclotron. The pCT image of several objects reconstructed from the experimental data was evaluated quantitatively.Results:Three‐dimensional pCT images of several objects were reconstructed experimentally. A finestructure of approximately 1 mm was clearly observed. The position resolution of pCT image was almost the same as that of xCT image. And the error of proton CT pixel value was up to 4%. The deterioration of image quality was caused mainly by the effect of multiple Coulomb scattering.Conclusion:We designed and constructed the pCT imaging system using a thick scintillator and a CCD camera. And the system was evaluated with the experiment by use of 70‐MeV proton beam. Three‐dimensional pCT images of several objects were acquired by the system.This work was supported by JST SENTAN Grant Number 13A1101 and JSPS KAKENHI Grant Number 15H04912.

Development of proton CT imaging system using plastic scintillator and CCD camera

A proton computed tomography (pCT) imaging system was constructed for evaluation of the error of an x-ray CT (xCT)-to-WEL (water-equivalent length) conversion in treatment planning for proton therapy. In this system, the scintillation light integrated along the beam direction is obtained by photography using the CCD camera, which enables fast and easy data acquisition. The light intensity is converted to the range of the proton beam using a light-to-range conversion table made beforehand, and a pCT image is reconstructed. An experiment for demonstration of the pCT system was performed using a 70 MeV proton beam provided by the AVF930 cyclotron at the National Institute of Radiological Sciences. Three-dimensional pCT images were reconstructed from the experimental data. A thin structure of approximately 1 mm was clearly observed, with spatial resolution of pCT images at the same level as that of xCT images. The pCT images of various substances were reconstructed to evaluate the pixel value of pCT images. The image quality was investigated with regard to deterioration including multiple Coulomb scattering.

Quantifying fracture geometry with X-ray tomography: Technique of Iterative Local Thresholding (TILT) for 3D image segmentation

This paper presents a new method—the Technique of Iterative Local Thresholding (TILT)—for processing 3D X-ray computed tomography (xCT) images for visualization and quantification of rock fractures. The TILT method includes the following advancements. First, custom masks are generated by a fracture-dilation procedure, which significantly amplifies the fracture signal on the intensity histogram used for local thresholding. Second, TILT is particularly well suited for fracture characterization in granular rocks because the multi-scale Hessian fracture (MHF) filter has been incorporated to distinguish fractures from pores in the rock matrix. Third, TILT wraps the thresholding and fracture isolation steps in an optimized iterative routine for binary segmentation, minimizing human intervention and enabling automated processing of large 3D datasets. As an illustrative example, we applied TILT to 3D xCT images of reacted and unreacted fractured limestone cores. Other segmentation methods were also applied to provide insights regarding variability in image processing. The results show that TILT significantly enhanced separability of grayscale intensities, outperformed the other methods in automation, and was successful in isolating fractures from the porous rock matrix. Because the other methods are more likely to misclassify fracture edges as void and/or have limited capacity in distinguishing fractures from pores, those methods estimated larger fracture volumes (up to 80 %), surface areas (up to 60 %), and roughness (up to a factor of 2). These differences in fracture geometry would lead to significant disparities in hydraulic permeability predictions, as determined by 2D flow simulations.

Alterations of Fractures in Carbonate Rocks by CO2-Acidified Brines.

Fractures in geological formations may enable migration of environmentally relevant fluids, as in leakage of CO2 through caprocks in geologic carbon sequestration. We investigated geochemically induced alterations of fracture geometry in Indiana Limestone specimens. Experiments were the first of their kind, with periodic high-resolution imaging using X-ray computed tomography (xCT) scanning while maintaining high pore pressure (100 bar). We studied two CO2-acidified brines having the same pH (3.3) and comparable thermodynamic disequilibrium but different equilibrated pressures of CO2 (PCO2 values of 12 and 77 bar). High-PCO2 brine has a faster calcite dissolution kinetic rate because of the accelerating effect of carbonic acid. Contrary to expectations, dissolution extents were comparable in the two experiments. However, progressive xCT images revealed extensive channelization for high PCO2, explained by strong positive feedback between ongoing flow and reaction. The pronounced channel increasingly directed flow to a small region of the fracture, which explains why the overall dissolution was lower than expected. Despite this, flow simulations revealed large increases in permeability in the high-PCO2 experiment. This study shows that the permeability evolution of dissolving fractures will be larger for faster-reacting fluids. The overall mechanism is not because more rock dissolves, as would be commonly assumed, but because of accelerated fracture channelization.

The Long-term Corrosion Behavior of Abandoned Wells Under CO2 Geological Storage Conditions: (1) Experimental Results for Cement Alteration

For a feasible risk assessment of CO2-leakage through wells of the carbon dioxide storage sites at abandoned wells of aquifers and depleted gas fields, the CO2 reactivity and permeability of casing steel, pseudo formation and cement- plug need to be evaluated experimentally as functions of temperature, pressure and formation water chemistry to provide fundamental information for the assessment.Two types of laboratory experiments were conducted. These experiments are shown below:(1) Conventional batch-reaction experiments of cement cores in the system of CO2 and simulated formation water as 0.5 M NaCl, at 50 and 70 C, 5, 8, 18 MPa for 100-1600hr. In this experiment, individual cement cores are allowed to react with wet CO2 and NaCl solution charged in titanium reaction vessels with PTFE separators.(2) CO2-injection reaction involving casing (API Grade J-55)-cement (API class A) and cement (API class A)-shale composites which were saturated with 0.5 M NaCl solution.As a counter experiment for batch experiments, zero CO2 runs for these cements were additionally carried out at 50 and 70 C at 5 MPa for 100 and 400 hr. The CO2-injection runs were carried out at 50 C and 8.5 MPa with a constant differential pressure of 5 kPa. The resultant products were used to analyze alteration depth via micro-focused X-ray computed tomography (-XCT) and electron probe micro analyzer (EPMA). For observation and determination of alteration phases, field mission scanning electron microscopy with energy dispersive spectroscopy (FESEM-EDS) and micro X-ray diffractometry (-XRD) were also performed.The alteration zones identified in the both cement cores of A and G in wet CO2 showed spatial developments of zones appearing in -XCT images as a function of square root of time (t1/2), which can be interpreted as a diffusion-limited reaction. However, in the NaCl solution, these cement cores developed little alteration zones and poorly displayed time-dependency after 100 h.

TU‐G‐BRB‐06: Conversion of X‐Ray Sinogram to Proton Sinogram to Address the Limited‐Range Issue in Proton Computed Tomography

Purpose: To investigate a novel methodology of converting x‐ray sinograms into proton sinogram, which can be used to replace the missing part of an actual proton sinogram due to the limited‐range problem. Methods: Modeling has shown that there exist correlations between proton projection and multispectral x‐ray projection for materials in the human body. Based on these correlations, materials can be categorized into: A) adipose tissue, B) non‐adipose soft tissue, C) bone. These three categories can be identified on a regular x‐ray computed tomography (xCT) image without much effort. With an xCT image and its sinogram available, the x‐ray sinogram can be converted to the corresponding proton sinogram by: 1) converting the x‐ray raysum through adipose and non‐adipose soft tissues using the predetermined relationships and the relative portions of two types of material along the ray; and 2) by correcting for bone if the ray passes through it. In a proof‐of‐principle study, numerical simulations were done. The converted proton sinogram was compared to the simulated one. The converted proton sinogram is used to make up the 200 MeV proton projections through water‐equivalent depth (WED) larger than 20 cm, which are then combined with simulated proton projections through WED &lt; 20 cm for pCT stopping power reconstruction. Results: A sinogram profile for view angle = 0 showed the converted projections had a mean error of −0.13% (standard deviation 1.7%), RMS error of 0.20%, compared to the simulated one. The pCT stopping power image reconstructed using the sinogram with converted part (13.5% of total projections) showed a mean error of only +0.3% (standard deviation 4.6%). Conclusions: The proposed methodology allows one to convert x‐ray sinograms into proton sinograms with a reasonable accuracy, and is particularly useful to address the limited‐range problem of pCT scanning.

7.医用ディジタル画像の総合表示(総合医用画像について)

For the purpose of improving diagnostic efficacy integrated evaluation of various medical images is very important. We attempted to display the digital images of different modalities, such as nuclear image and X-ray CT image, simultaneously and the usefulness of this method is reported. LFOV gamma camera and scintillation scanner (Elscint ) were used for nuclear imaging and CT/T 8800 (G.E.) was used for XCT imaging. Nuclear images stored by Scintipac 200 (Shimadzu) were transfered using magnetic tape to the mini-computer attached to CT system. Our computer programs include (1) composite display of scintigram and XCT image, (2) reconstruction and display of RCT image associated with coronal and sagittal images, (3) superimpcsing display of RCT image and XCT contour image and (4) cine mode display of multi-view original images for RCT reconstruction. Composite display of nuclear image and XCT image made it easier to evaluate each image complementarily, as regional function image and morphological image respectively. Superimposing display of RCT image and XCT contour image was useful for identification of functioning tissues in relation to the adjacent organ structures. Cine mode display of ratating original images for RCT was helpful for three dimentional observation of nuclear image.