High-resolution X-ray Imaging System Research Articles

Synergistic Effects of Aqueous Phase Viscoelasticity and Reduced Interfacial Tension on Nonwetting Phase Displacement Efficiency: An In Situ Experimental Investigation.

This study uses in situ experimental investigation techniques to probe the synergistic effects of aqueous phase viscoelasticity and reduced interfacial tension on nonwetting phase displacement efficiency in natural porous media. Specifically, it examines the efficacy of viscoelastic surfactant (VES) solutions in enhancing oil recovery and investigates the pore-scale displacement mechanisms and VES-oil interactions. To this end, we first performed an extensive rheological characterization to select two VES solutions from multiple CTAB/NaNO3 (CTN) and Cocobetaine/SDS/NaCl (CSN) mixtures. The selected aqueous solutions were then used in unsteady-state imbibition experiments conducted on miniature, water-wet Prairie Shell carbonate core samples. The experiments were performed utilizing a high-pressure, high-temperature two-phase core-flooding apparatus integrated with a high-resolution X-ray imaging system to acquire pore-scale fluid occupancy maps during the displacements. The results indicate that the injection of the selected CSN and CTN solutions into the carbonate samples under capillary-dominated flow regimes boosts the oil recovery by 12 and 2%, respectively, compared to those of the base waterflood. The VES solutions lowered the oil-water interfacial tension and exerted significant shear forces at the entrance of pores. The shear forces could exceed the threshold surface free energy required to deform oil globules, and consequently, large oil clusters were fragmented into smaller blobs and eventually produced from the pore space. The higher oil recovery by CSN flooding was attributed to its stronger viscoelastic properties. The VES injection under the viscous-dominated flow regime intensified the frequency of oil globule fragmentation. As a result, residual oil saturation values were sharply reduced in the rock samples from 44 to 55% during the capillary-dominated flows to approximately 8%. The above-mentioned observations were also verified using morphological analysis of residual oil clusters. The impacts of VES flooding on the pore-scale oil configuration and the fragmentation of large oil clusters were particularly evident at higher VES flow rates.

In-vivo imaging of a mouse by detecting bremsstrahlung X-rays from 14C using a La-GPS imaging system

ABSTRACT Imaging of 14C outside of the subject is considered to be difficult because it is a radionuclide that emits only low-energy beta particles. However, we found that bremsstrahlung X-rays form 14C could be imaged from outside of subjects and is thus applicable to in vivo small animal imaging. We developed a high-resolution low-energy X-ray imaging system using a (Gd, La)2Si2O7:Ce(La-GPS) plate combined with a flat panel photomultiplier tube (FP-PMT) for in vivo imaging of a mouse to detect the X-rays from a 14C solution administered. Without using a parallel hole collimator, accumulated 14C in the mouse’s abdomen was imaged in 1 min and dynamic in vivo imaging was possible although the spatial resolution was moderate. With a parallel hole collimator, 14C in the abdomen was obtained with a higher spatial resolution with a 60-min acquisition time. We conclude that in vivo imaging of 14C is possible by using the developed high-resolution La-GPS imaging system and may be promising for molecular imaging research.

A Transparent Nano-Polycrystalline ZnWO4 Thin-Film Scintillator for High-Resolution X-ray Imaging.

Facile approaches for creating thin-film scintillators with high spatial resolutions and variable shapes are required to broaden the applicability of high-resolution X-ray imaging. In this study, a transparent nano-polycrystalline ZnWO4 thin-film scintillator was fabricated by thermal evaporation for high-resolution X-ray imaging. The scintillator is composed of nano-sized grains smaller than the optical wavelength range to minimize optical scattering. The high transparency of the scintillators affords a sufficiently high spatial resolution to resolve the 2 μm line and space patterns when used in a high-resolution X-ray imaging system with an effective pixel size of 650 nm. The thermal evaporation method is a convenient approach for depositing thin and uniform films on complex substrates. ZnWO4 thin-film scintillators with various shapes, such as pixelated and curved, were fabricated via thermal evaporation. The results show that the transparent nano-polycrystalline ZnWO4 thin-film scintillator deposited through thermal evaporation has a potential for use in various high-resolution X-ray imaging applications.

Magnetohydrodynamics-induced internal crash near density limit in ohmic discharge on experimental advanced superconducting tokamak

The magnetohydrodynamics (MHD)-induced internal crash (IC) is one of the most fundamental dynamics of a tokamak discharge. Study of IC and the consequent formation of seed island (for neo-classical tearing modes) are still attractive in both experimental and numerical studies. In this work, a set of MHD-induced sawtooth like crashes (SLCs) have been observed in experimental advanced superconducting tokamak (EAST) ohmic discharge near density limit. With the tomography of high-resolution upgraded soft x-ray imaging system, it is observed that m/n = 2/1 tearing mode converts to a m/n = 1/1 instability, and it then triggers crash in the plasma core, here, m is the poloidal mode number and n is the toroidal mode number. Similar to sawtooth crash (SC), the crash of SLC here is due to m/n = 1/1 mode nonlinear dynamic. An extended MHD simulation code M3D is used to understand of the dynamics of m/n = 1/1 internal kink mode in SC in torus. A complex SC is reproduced from M3D nonlinear simulation under EAST realistic magnetic flux equilibrium and experimental resistivity. The rapid growth of unstable m/n = 1/1 kink and interaction with its higher harmonics, are responsible for SC. The simulation results show an existence of annular chaos belt outside q = 1 surface during SC. Furthermore, magnetic islands with higher poloidal mode number are found after SC. The formation of island after SC make plasma current profile flat in the core.

Nano-scale experimental investigation of in-situ wettability and spontaneous imbibition in ultra-tight reservoir rocks

We investigated spontaneous imbibition behavior, three-dimensional fluid occupancy maps, and in-situ wettability at the nano scale in five ultra-tight and shale reservoir rock samples. For this purpose, we developed a novel technique by integrating a custom-built in-situ miniature fluid-injection module with a non-destructive high-resolution X-ray imaging system. Small cylindrical core samples (15–60 µm in diameter) were prepared from reservoir rocks using Focused-Ion Beam (FIB) milling technique. The pore network inside the samples were first characterized using ultra-high resolution three-dimensional images obtained at initial state by X-ray nano-tomography (Nano-CT) and FIB-Scanning Electron Microscopy (FIB-SEM) techniques at the nano scale. The petrophysical parameters, including porosity, permeability, pore-size distribution, and organic content were computed for each sample using image analysis. We then performed series of imbibition experiments using brine, oil, and surfactant solutions on each core sample. We observed that both oil and brine phases spontaneously imbibe into the pore network of the rock samples at various quantities. We also, for the first time, examined fluid distribution in individual pores and found a complex wettability behavior at the pore scale in the reservoir rock samples. Three pore types were identified with water-wet, oil-wet, and fractionally-wet behaviors. This work opens a new path to developing an improved understanding of the pore-level physics involved in multi-phase flow and transport not only in tight rock samples but also in other nanoporous material used in different science and engineering applications.

Erratum to: A method of extending the depth of focus of the high-resolution X-ray imaging system employing optical lens and scintillator: a phantom study

Background: The high-resolution X-ray imaging system employing synchrotron radiation source, thin scintillator, optical lens and advanced CCD camera can achieve a resolution in the range of tens of nanometers to sub-micrometer. Based on this advantage, it can effectively image tissues, cells and many other small samples, especially the calcification in the vascular or in the glomerulus. In general, the thickness of the scintillator should be several micrometers or even within nanometers because it has a big relationship with the resolution. However, it is difficult to make the scintillator so thin, and additionally thin scintillator may greatly reduce the efficiency of collecting photons. Methods: In this paper, we propose an approach to extend the depth of focus (DOF) to solve these problems. We develop equation sets by deducing the relationship between the high-resolution image generated by the scintillator and the degraded blur image due to defect of focus first, and then we adopt projection onto convex sets (POCS) and total variation algorithm to get the solution of the equation sets and to recover the blur image. Results: By using a 20 μm thick unmatching scintillator to replace the 1 μm thick matching one, we simulated a high-resolution X-ray imaging system and got a degraded blur image. Based on the algorithm proposed, we recovered the blur image and the result in the experiment showed that the proposed algorithm has good performance on the recovery of image blur caused by unmatching thickness of scintillator. Conclusions: The method proposed is testified to be able to efficiently recover the degraded image due to defect of focus. But, the quality of the recovery image especially of the low contrast image depends on the noise level of the degraded blur image, so there is room for improving and the corresponding denoising algorithm is worthy for further study and discussion.

A method of extending the depth of focus of the high-resolution X-ray imaging system employing optical lens and scintillator: a phantom study.

BackgroundThe high-resolution X-ray imaging system employing synchrotron radiation source, thin scintillator, optical lens and advanced CCD camera can achieve a resolution in the range of tens of nanometers to sub-micrometer. Based on this advantage, it can effectively image tissues, cells and many other small samples, especially the calcification in the vascular or in the glomerulus. In general, the thickness of the scintillator should be several micrometers or even within nanometers because it has a big relationship with the resolution. However, it is difficult to make the scintillator so thin, and additionally thin scintillator may greatly reduce the efficiency of collecting photons.MethodsIn this paper, we propose an approach to extend the depth of focus (DOF) to solve these problems. We develop equation sets by deducing the relationship between the high-resolution image generated by the scintillator and the degraded blur image due to defect of focus first, and then we adopt projection onto convex sets (POCS) and total variation algorithm to get the solution of the equation sets and to recover the blur image.ResultsBy using a 20 μm thick unmatching scintillator to replace the 1 μm thick matching one, we simulated a high-resolution X-ray imaging system and got a degraded blur image. Based on the algorithm proposed, we recovered the blur image and the result in the experiment showed that the proposed algorithm has good performance on the recovery of image blur caused by unmatching thickness of scintillator.ConclusionsThe method proposed is testified to be able to efficiently recover the degraded image due to defect of focus. But, the quality of the recovery image especially of the low contrast image depends on the noise level of the degraded blur image, so there is room for improving and the corresponding denoising algorithm is worthy for further study and discussion.

Design of the high-resolution soft X-ray imaging system on the Joint Texas Experimental Tokamak.

A new soft X-ray diagnostic system has been designed on the Joint Texas Experimental Tokamak (J-TEXT) aiming to observe and survey the magnetohydrodynamic (MHD) activities. The system consists of five cameras located at the same toroidal position. Each camera has 16 photodiode elements. Three imaging cameras view the internal plasma region (r/a < 0.7) with a spatial resolution about 2 cm. By tomographic method, heat transport outside from the 1/1 mode X-point during the sawtooth collapse is found. The other two cameras with a higher spatial resolution 1 cm are designed for monitoring local MHD activities respectively in plasma core and boundary.

Design, Characterization, and Modeling for a Modular High-Resolution Solid-State X-Ray Image Intensifier (SSXII)

A high resolution x-ray imaging system designated the solid state x-ray image intensifier (SSXII) is being developed as a potential replacement of conventional lower-resolution x-ray detectors for neurovascular interventions. The SSXII consists of a CsI(Tl) phosphor to convert x-rays to light, a fiber optic taper to extend the field-of-view and to couple the phosphor to an Electron-Multiplying CCD (EMCCD) which has a built-in gain to boost the signal above the read-out noise floor. A parallel cascade linear-system model is explored and applied to quantitatively analyze the signal and noise transfer at each stage, and optimize the detector performance. The modulation transfer function (MTF), detective quantum efficiency (DQE) and frequency dependent instrumentation noise equivalent exposure (INEE) can be obtained from the theoretical model and experimental measurement. Agreement of these results validates the effectiveness of the model. Finally, compared with the traditional flat-panel detector (FPD), the SSXII exhibits better performance with higher spatial resolution, higher DQE and lower INEE.

High-resolution high-efficiency X-ray imaging system based on the in-line Bragg magnifier and the Medipix detector

The performance of a recently developed full-field X-ray micro-imaging system based on an in-line Bragg magnifier is reported. The system is composed of quasi-channel-cut crystals in combination with a Medipix single-photon-counting detector. A theoretical and experimental study of the imaging performance of the crystals-detector combination and a comparison with a standard indirect detector typically used in high-resolution X-ray imaging schemes are reported. The spatial resolution attained by our system is about 0.75 µm, limited only by the current magnification. Compared with an indirect detector system, this system features a better efficiency, signal-to-noise ratio and spatial resolution. The optimal working resolution range of this system is between ∼0.4 µm and 1 µm, filling the gap between transmission X-ray microscopes and indirect detectors. Applications for coherent full-field imaging of weakly absorbing samples are shown and discussed.

On the limitations and optimisation of high-resolution 3D medical X-ray imaging systems

Based on a quantitative analysis of both attenuation and refractive properties of X-ray propagation in human body tissues and the introduction of a mathematical model for image quality analysis, some limitations and optimisation of high-resolution three-dimensional (3D) medical X-ray imaging techniques are studied. A comparison is made of conventional attenuation-based X-ray imaging methods with the phase-contrast X-ray imaging modalities that have been developed recently. The results indicate that it is theoretically possible through optimal design of the X-ray imaging system to achieve high spatial resolution (<100 μm) in 3D medical X-ray imaging of the human body at a clinically acceptable dose level (<10 mGy) by introducing a phase-contrast X-ray imaging technique.

Ultrahigh-speed X-ray imaging of hypervelocity projectiles

High-speed X-ray imaging is an extremely important modality for healthcare, industrial, military and research applications such as medical computed tomography, non-destructive testing, imaging in-flight projectiles, characterizing exploding ordnance, and analyzing ballistic impacts. We report on the development of a modular, ultrahigh-speed, high-resolution digital X-ray imaging system with large active imaging area and microsecond time resolution, capable of acquiring at a rate of up to 150,000 frames per second. The system is based on a high-resolution, high-efficiency, and fast-decay scintillator screen optically coupled to an ultra-fast image-intensified CCD camera designed for ballistic impact studies and hypervelocity projectile imaging. A specially designed multi-anode, high-fluence X-ray source with 50 ns pulse duration provides a sequence of blur-free images of hypervelocity projectiles traveling at speeds exceeding 8 km/s (18,000 miles/h). This paper will discuss the design, performance, and high frame rate imaging capability of the system.

GaAs Medipix2 hybrid pixel detector

A GaAs Medipix2 hybrid pixel detector based on high purity epitaxial GaAs material was successfully fabricated. The mesa type GaAs sensor with 256×256 pixels and total area of 1.4×1.4 cm 2 was made of a 140-μm-thick epitaxial p–i–n structure utilizing reactive ion etching. A final thickness of approximately 110 μm for the all-epitaxial sensor element is achieved by back-thinning procedure. The sensor element is bump bonded to a Medipix2 read-out ASIC. The detector is capable of room temperature spectroscopic operation and it demonstrates the potential of GaAs for high resolution X-ray imaging systems operating at room temperature. This work describes the manufacturing process and electrical properties of the GaAs Medipix2 hybrid detector.

Fabrication of Double Shell Targets with a Glass Inner Capsule Supported by SiO2 Aerogel for Shots on the Omega Laser in 2006

Indirectly driven double shell implosions are being investigated as a possible noncryogenic path to ignition on the National Ignition Facility. Lawrence Livermore National Laboratory has made several technological advances that have produced double shell targets that represent a significant improvement to previously fielded targets. The inner capsule is supported inside the ablator shell by SiO2 aerogel with a nominal density of 50 mg/cm3. The aerogel is cast around the inner capsule and then machined concentric to it. The seamless sphere of aerogel containing the embedded capsule is then assembled between the two halves of the ablator shell. The concentricity between the two shells has been improved to less than 1.5 μm. The ablator shell consists of two hemispherical shells that mate at a step joint that incorporates a gap with a nominal thickness of 0.1 μm. Using a new flexure-based tool holder that precisely positions the diamond cutting tool on the diamond turning machine, step discontinuities on the inner surface of the ablator of less than 0.5 μm have been achieved. New methods have been used to comprehensively characterize each of the targets using high-resolution x-ray imaging systems.

Investigation of the imaging characteristics of the Gd 2O 3:Eu nanophosphor for high-resolution digital X-ray imaging system

For possible applications in high-resolution medical image systems, we manufactured a Eu 3+-doped Gd 2O 3 nanophosphor using the low-temperature solution combustion method, and evaluated its performance as an image sensor. The structural and optical characteristics of the fabricated nanophosphor were investigated using field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), photoluminescence spectrum (PL), and luminescence decay time measurements. From the FE-SEM and XRD results, we established that the fabricated nanophosphor was formed of spherical particles of about 30–40 nm, and confirmed that the particles agglomerated as the sintering temperature increases. From PL spectra, a strong peak appeared near 611 nm, and the luminescent intensity was seen to be affected by the doping concentration of Eu. Gd 2O 3:Eu nanophosphor particles have shown the highest luminescent efficiency at a Eu concentration of 5 wt%. In the luminescent decay time measurements, the mean decay time was about 2.3–2.6 ms, about two times longer than that of the general bulk phosphor, and affected by the of Eu-doping concentration. For the investigation of the imaging characteristics of the fabricated nanophosphor, we connected the Gd 2O 3:Eu nanophosphor film to a commercial CMOS image sensor, obtained the X-ray images and evaluated the modulation transfer function (MTF) as a function of the Eu concentration. We were able to obtain high-resolution X-ray images and found that the Eu concentration also influenced the imaging characteristics.

An airport cargo inspection system based on X-ray and thermal neutron analysis (TNA)

A cargo inspection system incorporating a high-resolution X-ray imaging system with a material-specific detection system based on Ancore Corporation's patented thermal neutron analysis (TNA) technology can detect bulk quantities of explosives and drugs concealed in trucks or cargo containers. The TNA process utilises a 252Cf neutron source surrounded by a moderator. The neutron interactions with the inspected object result in strong and unique gamma-ray signals from nitrogen, which is a key ingredient in modern high explosives, and from chlorinated drugs. The TNA computer analyses the gamma-ray signals and automatically determines the presence of explosives or drugs. The radiation source terms and shielding design of the facility are described. For the X-ray generator, the primary beam, leakage radiation, and scattered primary and leakage radiation were considered. For the TNA, the primary neutrons and tunnel scattered neutrons as well as the neutron-capture gamma rays were considered.

Development and application of a novel nanophosphor scintillator for a low-dose, high-resolution digital X-ray imaging system

The recent development of a novel nanophosphor screen technology by Bhargava RN and associates (Nanocrystal technology, Briarcliff Manor, NY) started the exciting new phase of digital nanocrystal X-ray technology and its applications to the continually changing field of digital radiology. Charge-Coupled Devices (CCD) and Complimentary Metal Oxide Semiconductors (CMOS) traditionally use scintillators for conversion of X-ray photons to visible light, and these, in turn expose the sensitive digital image receptors in the process of recording images. During the conversion process, light gets scattered, resulting in loss of utilization efficiency and indirectly contributing to the loss of image resolution. The newly developed and patented nanophosphor screen converts the X-ray photons to light, and captures the light by way of reflection and microchanneling to light collecting devices and or electronic detectors. This concept of increased resolution while capturing images of teeth and associated structures via digital X-ray sensors, although theoretically accepted; requires in-vitro and in-vivo testing. The prototype of the sensor is in the design phase, and once the benefits of this new X-ray imaging system are completely proven, successful large-scale application of nano-scintillators to enhance the image resolution combined with a dose reduction can be achieved. Application of this technology will revolutionize the way digital radiographic images are acquired in dentistry along with possible applications in the near future in the fields of Medicine and Veterinary Medicine.

REAL-TIME X-RAY INSPECTION OF WHEAT FOR INFESTATION BY THE GRANARY WEEVIL, SITOPHILUS GRANARIUS (L.)

A high-resolution real-time x-ray imaging system was assembled using a low-energy, high-current x-ray source,a low-energy x-ray image intensifier, and a CCD camera interfaced to a PC. Overall system resolution was measured at 5 linepairs per mm (100 .m), sufficient for identifying infestations of the granary weevil, Sitophilus granarius (L.) in kernels of wheat.The field of view for imaging of the system was 6 cm2, large enough to image approximately 350 kernels of grain in a single frame.The exposure time for a single frame was 149 ms, yielding a maximum potential throughput rate of around 2500 kernels persecond. For this study, 1500 wheat kernels were x-rayed, both on film and with the system described above. Of the imagedkernels, 682 contained infestations ranging in maturity from the egg to the adult life stage of the granary weevil, while 818 wereuninfested. Both film and digital images were presented to human subjects to compare recognition of the infested kernels.Overall recognition results averaged 84.4% for the images from the intensifier system vs. 90.2% for the film observations.However, when considering only infestations more advanced than the 3rd larval instar, errors for both sets of images fell below2% and were not significantly different.

放射光マイクロイメージングによる腫ように伴う微小血管の観察

A tumor stimulates the growth of small blood vessels for feeding itself. Tumor-derived small blood vessels are an intrinsic part of the tumor's development and progression. Radiographic depiction of tumor-derived small vessels is a useful tool for a basic medical study of malignant tumors. A high-resolution X-ray imaging system with a spatial resolution in the micrometer range was developed at SPring-8 for the depiction of newly formed blood vessels in animal models of cancer. The imaging system is composed of two types of detectors. One is an X-ray indirect-conversion type detector, which is a fluorescent-screen optical-lens coupling system using a high-sensitivity HARPICON pickup tube. The other type is an X-ray direct-conversion type detector, which incorporates an X-ray direct-sensing SATICON pickup tube. Small tumor blood vessels with diameters of around 15μm were observed after injecting a contrast material to the artery in experiments using small animals.

Optical properties of europium-doped Gd2O3 waveguiding thin films prepared by the sol–gel method

Abstract Recently, there has been a growth of interest in the preparation of new phosphor films for high-resolution X-ray imaging systems. Europium activated gadolinium oxide is very interesting because of its scintillation properties especially as a red component. The sol–gel method has been used to synthesize europium-doped gadolinium oxide films. The films present waveguiding properties and this special feature is used to study their microstructure by Raman spectroscopy in waveguiding configuration. Structural results, confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) observations, show that the crystallization in the cubic phase occurs at 700 °C. Opto-geometrical parameters were determined with respect to the annealing temperature. After annealing at 1000 °C, very dense europium-doped gadolinium oxide films are obtained with a thickness of 390 nm and a refractive index of 1.88 at 632.8 nm. Spectroscopic results constituted by emission spectra (UV and X-ray excitation) and decay measurements are presented.