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Developing highly efficient methane (CH4) hydrate storage methods and understanding the hydrate dissociation kinetics can contribute to advancing CH4 gas storage and transport. The effects of tetrabutylammonium bromide (TBAB) (a thermodynamic promoter) addition on the kinetics of CH4 hydrate were evaluated on the microscopic scale using synchrotron x-ray computed tomography (CT) and powder x-ray diffraction. Microscopic observations showed that a 5 wt. % TBAB solution facilitated the nucleation of CH4 hydrate owing to the initial growth of TBAB semi-clathrate hydrate particles. The CH4 hydrate crystals in the CH4 + TBAB hydrate sample were sponge-like with many internal pores and exhibited slightly enhanced self-preservation compared to the pure CH4 hydrate, both in the bulk and after pulverization to a fine powder. This study demonstrates the feasibility of controlling the rate of CH4 hydrate formation and preservation by using aqueous TBAB solutions in CH4 hydrate formation. [ABSTRACT FROM AUTHOR]

In this study, we observed natural methane (CH4) hydrate sediments, which are a type of unconventional natural gas resources, using x-ray computed tomography (CT). Because CH4 hydrates are formed by hydrogen bonding of water molecules with CH4, material decomposition becomes challenging when CH4 hydrates coexist with liquid or solid water in natural sediments. Tri-contrast (absorption, refraction, and scattering) imaging was performed via diffraction enhanced x-ray CT optics using monochromatic synchrotron x rays. The quantitative characterization of the contrast changes successfully enabled the decomposition of CH4 hydrates coexisting with frozen seawater (ice) in natural sediments obtained from the Okhotsk Sea. This study reveals complementary structural information about the microtexture and spatial relation among CH4 hydrates, ice, and pores by utilizing the distinct physical properties of x rays when passing through the materials. These results highlight the exceptional capabilities of high-resolution multicontrast x-ray tomography in materials science and geoscience applications. [ABSTRACT FROM AUTHOR]

Objective. X-ray microangiography provides detailed information on the internal structure and function of a biological subject. Its ability to evaluate the microvasculature of small animals is useful for acquiring basic and clinical medical knowledge. The following three conditions are necessary to attain detailed knowledge of biological functions: (1) high temporal resolution with sufficient x-ray intensity, (2) high spatial resolution, and (3) a wide field of view. Because synchrotron radiation microangiography systems provide high sapatial resolution and high temporal resolution as a result of their high x-ray intensity, such systems have been developed at various synchrotron radiation facilities, starting with the photon factory, leading to numerous medical discoveries. However, the three aforementioned functions are incompatible with the use of synchrotron radiation because the x-ray intensity decreases when a wide field of view is obtained. To overcome these problems, we developed a new x-ray optical system for microangiography in rats using synchrotron radiation x-rays. Approach. Instead of using monochromatic synchrotron radiation x-rays with a conventional double-crystal monochromator, we used white synchrotron radiation x-rays and an asymmetric Si crystal to simultaneously monochromatize the beam and widen the field of view. Main results. The intensity profile and spatial resolution of the x-ray images were then evaluated. The proposed x-ray optics increased the x-ray intensity and beam width by factors of 1.3 and 2.7, respectively, compared with those of conventional monochromatic x-rays. In addition, in vivo studies on microangiography in rats were performed to confirm that the images had sufficient intensity, spatial resolution, and field of view. One of a series of images taken at 50 ms frame−1 was shown as an example. Significance. This x-ray optics provides sufficient x-ray intensity, high spatial resolution, and a wide field of view. This technique is expected providing new insights into the evaluation of the vascular system. [ABSTRACT FROM AUTHOR]

In x-ray imaging methods, such as synchrotron radiation microangiography, the x-ray intensity has become more important in recent years for real-time dynamic observations to evaluate temporal changes in samples. Many synchrotron radiation facilities use x-rays monochromated by diffraction from perfect Si crystals to improve the spatial resolution of x-ray images and obtain detailed information about a sample. In this paper, monochromatic synchrotron x-ray images were acquired using Si crystals lapped with abrasives to enhance the x-ray intensity using white synchrotron radiation x-rays for observing dynamic changes in samples. The x-ray intensity, spatial resolution, and contrast noise ratio (CNR) in the acquired x-ray images were quantitatively evaluated using a state-of-the-art high-spatial-resolution detector. The x-ray intensity was substantially increased by a factor of ∼8 when a lapped Si crystal was used. When the lapped Si crystal was used, the spatial resolution of x-ray images in the diffraction-plane direction was ∼70% lower than when an etched Si crystal was used at a spatial resolution of 10 lp/mm. By contrast, the CNR in x-ray images, which is important for observing the interior of a sample, increased threefold when a contrast agent containing iodine at a concentration of 38 wt. % was used. It was confirmed that the combination of white synchrotron radiation x-rays and a lapped crystal produces an intense monochromatic x-ray, providing an important evaluation for the use of optics for each research purpose. [ABSTRACT FROM AUTHOR]

Crystal-based X-ray interferometry (CXI) detects X-ray phase shifts by using the superposition of waves, and its sensitivity is the highest among the other X-ray phase-detecting methods. Therefore, phase-contrast X-ray imaging (PCXI) using CXI has the highest density resolution among the PCXI methods and enables fine, non-destructive observation with a density resolution below sub-mg/cm3. It has thus been applied in a wide range of fields, including biology, medicine, geology, and industry, such as visualization of the testis and brains of aged rats with tumors, human embryos at each Carnegie stage, air hydrates in old Antarctic ice, and ion distribution in electrolytes. Novel imaging methods have also been developed to take advantage of its high sensitivity, such as visualization of the effective atomic number (Zeff) and the three-dimensional temperature of samples. This article reviews the principles and history of PCXI and crystal-based X-ray interferometers, as well as a CXI system using synchrotron radiation and its potential applications from biomedical to industrial. [ABSTRACT FROM AUTHOR]

The visualization of temperature-controlled crystal growth and dissociation of tetrahydrofuran clathrate hydrates and ice in the interparticle spaces between beads is presented. Phase-contrast X-ray imaging using synchrotron X-ray radiation is a unique technique to study clathrate hydrates coexisting with both ice and liquid water and is used here to observe tetrahydrofuran hydrate and ice formation in situ. The nondestructive images obtained reveal a morphology change of tetrahydrofuran clathrate hydrate grown under isothermal temperature conditions at 253 K, which may be caused by the thermal history of crystallization of the clathrate hydrate. In addition, the water freezing process in the interparticle spaces between is observed using phase-contrast X-ray imaging. This method is useful for understanding the kinetics of clathrate hydrates in interparticle spaces. Key words: gas hydrate, memory effect, X-ray absorption contrast, X-ray CT, X-ray interferometry. Nous presentons la visualisation de la croissance a temperature controlee de cristaux d'hydrate de tetrahydrofurane et de glace et leur dissociation dans les espaces interparticulaires des clathrates. L'imagerie X par contraste de phase a l'aide du rayonnement synchrotron X est une technique privilegiee pour l'etude des hydrates en clathrate en coexistence simultanee avec l'eau et la glace, et est employee dans ces travaux afin d'observer la formation in situ de l'hydrate de tetrahydrofurane et de la glace. Les images non destructives obtenues en conditions isothermes a 253 K revelent un changement de la morphologie de l'hydrate de tetrahydrofurane cristallise en clathrate. Ce changement peut etre attribuable aux antecedents thermiques de la cristallisation du clathrate. En outre, l'imagerie X par contraste de phase a permis d'observer le processus de congelation de l'eau dans les espaces interparticulaires. Cette technique permet de mieux comprendre la cinetique des hydrates de gaz dans les espaces interparticulaires des clathrates. [Traduit par la Redaction] Mots-cles: hydrate de gaz, effet memoire, contraste de l'absorption des rayons X, tomographie a rayons X, interferometrie par rayons X., Introduction Clathrate hydrates (also called gas hydrates) are ice-like crystals comprising water and guest molecules such as methane (C[H.sub.4]) or carbon dioxide. (1) Most gas hydrates exist under conditions of [...]

Background: Phase-contrast X-ray computed tomography imaging (PCI) based on crystal X-ray interferometry can detect minute density differences within biological soft tissues without contrast agents. Ethanol fixation yields increased tissue-background density differences due to the dehydrating and delipidifying effects of ethanol. Purpose: To obtain high image contrast of cerebral white matter structures in PCI, tissue fixation using ethanol and routinely used formalin have been examined. Material and Methods: Ethanol-fixed (EF) (n = 4) and formalin-fixed (FF) (n = 4) rat brains were imaged by crystal X-ray interferometry-based PCI. Tissue staining/microscopy was also performed for histological comparison and myelin density evaluation. Three-dimensional white matter tract images were reconstructed. Results: Superior image contrast was obtained in the images of EF brains (EF images) compared to those of formalin-fixed brains (FF images), particularly for white matter structures. Significant density differences between the white matter structures and hippocampus (P < 0.01)/thalamus (P < 0.001) were observed in the EF, but not FF, images. Ethanol fixation enhanced the image contrast of white matter tracts by approximately sixfold compared to formalin fixation, and close agreement (r2 = 0.97; P < 0.05) between the density values on the CT images and the myelin density values in histological images was observed for the EF brains. Three-dimensional reconstruction of the white matter tracts was possible from the EF images, but not FF images. Conclusion: Ethanol fixation resulted in marked contrast enhancement of cerebral white matter structures in PCI. Thus, high-resolution PCI using ethanol for tissue fixation could be valuable for experimental neurological studies and postmortem neuropathology evaluation. [ABSTRACT FROM AUTHOR]

Coherence-contrast x-ray imaging--which detects changes in the degree of coherence caused by the placement of a sample in an x-ray interferometer--was developed for biomedical applications. Because the technique's sensitivity depends on the density gradient in the sample, it is particularly suitable for observing biomedical samples with large density differences, such as samples that include both biological soft tissue and bone. A measurement principle and method of this technique are described, and a fine coherence-contrast image of a mouse leg is given as an example result. OCIS codes: 120.5050, 170.7440, 340.7440, 340.7450.

Research was conducted to examine the characteristics of branching patterns of the intramural coronary artery (IMCA) with those of the epicardial coronary artery (EPCA) and with those of the distal ileal artery in the intestinal organ. Digital processing for high-definition microangiography, which permits the quantification of small vessel diameters with high accuracy and reproducibility with a public domain program and a personal computer, was used. Results indicate that the self-similar branching pattern of coronary arteries was discrete at the connection between the EPCA and IMCA.

Intramyocardial vessels in eight dogs were examined via synchrotron microangiography. It was observed that myocardial contraction reduced the vascular short-axial diameters of the end-diastolic values and increased the longitudinal dimension. To-and-fro blood flow was observed in penetrating transmural arteries with visual identification of capacitive backflow, resistive forward flow during ischemia on coronary arteriography, and even under baseline conditions in coronary venography.

We describe a new system of incoherent scatter computed tomography (ISCT) using monochromatic synchrotron X rays, and we discuss its potential to be used in in vivo imaging for medical use. The system operates on the basis of computed tomography (CT) of the first generation. The reconstruction method for ISCT uses the least squares method with singular value decomposition. The research was carried out at the BLNE5A bending magnet beam line of the Tristan Accumulation Ring in KEK, Japan. An acrylic cylindrical phantom of 20mm diameter containing a cross-shaped channel was imaged. The channel was filled with a diluted iodine solution with a concentration of 200 [[micro]gram]I/ml. Spectra obtained with the system's high purity germanium (HPGe) detector separated the incoherent X-ray line from the other notable peaks, i.e., the [K.sub.[Alpha]] and [K.sub.[[Beta].sub.1] X-ray fluorescent lines and the coherent scattering peak. CT images were reconstructed from projections generated by integrating the counts in the energy window centering around the incoherent scattering peak and whose width was approximately 2 keV. The reconstruction routine employed an X-ray attenuation correction algorithm. The resulting image showed more homogeneity than one without the attenuation correction. Index Terms - Computed tomography, incoherent scatter, least squares method, Monte Carlo simulation, singular value decomposition, synchrotron radiation.

We describe a new attenuation correction method for fluorescent X-ray computed tomography (FXCT) applied to image nonradioactive contrast materials in vivo. The principle of the FXCT imaging is that of computed tomography of the first generation. Using monochromatized synchrotron radiation from the BLNE-5A bending-magnet beam line of Tristan Accumulation Ring in KEK, Japan, we studied phantoms with the FXCT method, and we succeeded in delineating a 4-mm-diameter channel filled with a 500 [[micro]gram] I/ml iodine solution in a 20-mm-diameter acrylic cylindrical phantom. However, to detect smaller iodine concentrations, attenuation correction is needed. We present a correction method based on the equation representing the measurement process. The discretized equation system is solved by the least-squares method using the singular value decomposition. The attenuation correction method is applied to the projections by the Monte Carlo simulation and the experiment to confirm its effectiveness. Index Terms - Computed tomography, fluorescent X-ray, least-squares method, Monte Carlo simulation, singular value decomposition, synchrotron radiation.