Microbubbles containing gadolinium as contrast agents for both phase contrast and magnetic resonance imaging

Portal vein imaging is an important method for investigating portal venous disorders. However, the diagnostic requirements are not usually satisfied when using single imaging techniques. Diagnostic accuracy can be improved by combining different imaging techniques. Contrast agents that can be used for combined imaging modalities are needed. In this study, the feasibility of using microbubbles containing gadolinium (MCG) as contrast agents for both phase contrast imaging (PCI) and magnetic resonance imaging (MRI) are investigated. MCG were made by encapsulating sulfur hexafluoride (SF₆) gas with gadolinium and lyophilized powder. Absorption contrast imaging (ACI) and PCI of MCG were performed and compared in vitro. MCG were injected into the main portal trunk of living rats. PCI and MRI were performed at 2 min and 10 min after MCG injection, respectively. PCI exploited the differences in the refractive index and visibly showed the MCG, which were not detectable by ACI. PCI could facilitate clear revelation of the MCG‐infused portal veins. The diameter of the portal veins could be determined by the largest MCG in the same portal vein. The minimum diameter of clearly detected portal veins was about 300 µm by MRI. These results indicate that MCG could enhance both PCI and MRI for imaging portal veins. The detection sensitivity of PCI and MRI could compensate for each other when using MCG contrast agents for animals.     

A novel imaging tool for hepatic portal system using phase contrast technique with hydrogen peroxide‐generated O2 gas

The objective of this study was to investigate the potential of hydrogen peroxide‐generated oxygen gas‐based phase contrast imaging (PCI) for visualizing mouse hepatic portal veins. The O₂ gas was made from the reaction between H₂O₂ and catalase. The gas production was imaged by PCI in real time. The H₂O₂ was injected into the enteric cavity of the lower sigmoid colon to produce O₂ in the submucosal venous plexus. The generated O₂ gas could be finally drained into hepatic portal veins. Absorption contrast imaging (ACI) and PCI of O₂‐filled portal veins were performed and compared. PCI offers high resolution and real‐time visualization of the O₂ gas production. Compared with O₂‐based ACI, O₂‐based PCI significantly enhanced the revealing of the portal vein in vivo. It is concluded that O₂‐based PCI is a novel and promising imaging modality for future studies of portal venous disorders in mice models.     

In vivo physiological saline‐infused hepatic vessel imaging using a two‐crystal‐interferometer‐based phase‐contrast X‐ray technique

Using a two‐crystal‐interferometer‐based phase‐contrast X‐ray imaging system, the portal vein, capillary vessel area and hepatic vein of live rats were revealed sequentially by injecting physiological saline via the portal vein. Vessels greater than 0.06 mm in diameter were clearly shown with low levels of X‐rays (552 µGy). This suggests that in vivo vessel imaging of small animals can be performed as conventional angiography without the side effects of the presently used iodine contrast agents.     

Influence of nesting shell size on brightness longevity and resistance to ultrasound-induced dissolution during enhanced B-mode contrast imaging

This study aims to bridge the gap between transport mechanisms of an improved ultrasound contrast agent (UCA) and its resulting behavior in a clinical imaging study. Phospholipid-shelled microbubbles nested within the aqueous core of a polymer microcapsule are examined for their use and feasibility as an improved UCA. The nested formulation provides contrast comparable to traditional formulations, specifically an SF₆ microbubble coated by a DSPC PEG-3000 monolayer, with the advantage that contrast persists at least nine times longer in a mock clinical, in vitro setting. The effectiveness of the sample was measured using a contrast ratio in units of decibels (dB) which compares the brightness of the nested microbubbles to a reference value of a phantom tissue mimic. During a 40 min imaging study, six nesting formulations with average outer capsule diameters of 1.95, 2.53, 5.55, 9.95, 14.95, and 20.51 μm reached final contrast ratio values of 0.25, 2.35, 3.68, 4.51, 5.93, and 8.00 dB, respectively. The starting contrast ratio in each case was approximately 8 dB and accounts for the brightness attributed to the nesting shell. As compared with empty microcapsules (no microbubbles nested within), enhancement of the initial contrast ratio increased systematically with decreasing microcapsule size. The time required to reach a steady state in the temporal contrast ratio profile also varied with microcapsule diameter and was found to be 420 s for each of the four smallest shell diameters and 210 s and 150 s, respectively, for the largest two shell diameters. All nested formulations were longer-lived and gave higher final contrast ratios than a control sample comprising un-nested, but otherwise equivalent, microbubbles. Specifically, the contrast ratio of the un-nested microbubbles decreased to a negative value after 4 min of continuous ultrasound exposure with complete disappearance of the microbubbles after 15 min whereas all nested formulations maintained positive contrast ratio values for the duration of the 40 min trial. The results are consistent with two distinct stages of gas transport: in the first stage, passive diffusion occurs under ambient conditions across the microbubble monolayer within the first few minutes after formulation until the aqueous interior of the microcapsule is saturated with gas; in the second stage ultrasound drives additional gas dissolution even further due to pressure modulation. It is important to understand the chemistry and transport mechanisms of this contrast agent under the influence of ultrasound to attain better perspicacity for enhanced applications in imaging. Results from this study will facilitate future preclinical studies and clinical applications of nested microbubbles for therapeutic and diagnostic imaging.     

Binary phase shaping for selective single‐beam CARS spectroscopy and imaging of gas‐phase molecules

We report on mode‐selective single‐beam coherent anti‐Stokes Raman scattering spectroscopy of gas‐phase molecules. Binary phase shaping (BPS) is used to produce single‐mode excitation of O₂, N₂, and CO₂ vibrational modes in ambient air and gas‐phase mixtures, with high‐contrast rejection of off‐resonant Raman modes and efficient nonresonant‐background suppression. In particular, we demonstrate independent excitation of CO₂ Fermi dyads at ∼1280 and ∼1380 cm⁻¹ and apply BPS for high‐contrast imaging of CO₂ jet in ambient air. Copyright © 2010 John Wiley & Sons, Ltd.     

Electrical behaviour of catalytic nanostructured CeO2/CuOx composites under air-methane gas impulses

Nanostructured composites based on copper oxide and cerium dioxide phases [CuO-CeO₂] were elaborated from sol-gel route, with weight fractions of CuO phase ranging between 0 and 0.4. They are interesting potential catalysts allowing conversion of CH₄ and CO into CO₂ and H₂O and might be used in miniaturized gas sensors. An electrical study of this nanostructured system was carried out to determine catalytic behaviours under air-methane impulses at 350 °C. The electrical analysis was based on a specific homemade electronic device. Time dependent interactions between gas pulses and solid catalyst (CuO/CeO₂) were analyzed from a frequency modification of the electronic device. Kinetic parameters were determined from a model describing adsorption and desorption of gases adapted to short interaction time between gas and solid. These time dependent electrical behaviours were then correlated with infrared spectroscopy analyses allowing time dependent analysis of methane conversion into CO₂ gas, for long interaction time between gas and solid.     

Visualization of mouse spinal cord intramedullary arteries using phase‐ and attenuation‐contrast tomographic imaging

Many spinal cord circulatory disorders present the substantial involvement of small vessel lesions. The central sulcus arteries supply nutrition to a large part of the spinal cord, and, if not detected early, lesions in the spinal cord will cause irreversible damage to the function of this organ. Thus, early detection of these small vessel lesions could potentially facilitate the effective diagnosis and treatment of these diseases. However, the detection of such small vessels is beyond the capability of current imaging techniques. In this study, an imaging method is proposed and the potential of phase‐contrast imaging (PCI)‐ and attenuation‐contrast imaging (ACI)‐based synchrotron radiation for high‐resolution tomography of intramedullary arteries in mouse spinal cord is validated. The three‐dimensional vessel morphology, particularly that of the central sulcus arteries (CSA), detected with these two imaging models was quantitatively analyzed and compared. It was determined that both PCI‐ and ACI‐based synchrotron radiation can be used to visualize the physiological arrangement of the entire intramedullary artery network in the mouse spinal cord in both two dimensions and three dimensions at a high‐resolution scale. Additionally, the two‐dimensional and three‐dimensional vessel morphometric parameter measurements obtained with PCI are similar to the ACI data. Furthermore, PCI allows efficient and direct discrimination of the same branch level of the CSA without contrast agent injection and is expected to provide reliable biological information regarding the intramedullary artery. Compared with ACI, PCI might be a novel imaging method that offers a powerful imaging platform for evaluating pathological changes in small vessels and may also allow better clarification of their role in neurovascular disorders.     

Pressure-broadened iodine-laser-amplifier kinetics and a comparison of diluent effectiveness

An iodine laser kinetic model is used to investigate inversion parameters in highly pressure-broadened amplifier systems using i-C₃F₇I as the parent compound and CO₂, N₂, He, Ne, Ar, Kr, and Xe as the diluent gas. These data are used to calculate a diluent merit function for diluent pressures P_d = 1–100 atm. The most effective choices for buffer gases are as follows: P_d ? 1 atm, CO₂; 1 atm ? P_d ? 10 atm, Ar; and P_d ? 10 atm, Ne.     

Short delay time UV preionized TEA CO2 laser operating with binary CO2/H2 and CO2/He gas mixtures

In order to obtain short tail-free output laser pulses from a TEA CO₂ laser, parametric study of the laser operation with CO₂/H₂ and CO₂/He binary gas mixtures containing high CO₂ concentrations was carried out. A small scale UV preionized short delay time TEA CO₂ laser was employed. In terms of the maximum extractable output pulse energy and power, the more conventional CO₂/He gas mixture was found to be inferior in comparison with the CO₂/H₂ mixture proposed here.     

In-situ synchrotron X-ray imaging of ultrasound (US)-generated bubbles: Influence of US frequency on microbubble cavitation for membrane fouling remediation

Gaining an in-depth understanding of the characteristics and dynamics of ultrasound (US)--generated bubbles is crucial to effectively remediate membrane fouling. The goal of present study is to conduct in-situ visualization of US-generated microbubbles in water to examine the influence of US frequency on the dynamics of microbubbles. This study utilized synchrotron in-line phase contrast imaging (In-line PCI) available at the biomedical imaging and therapy (BMIT) beamlines at the Canadian Light Source (CLS) to enhance the contrast of liquid/air interfaces at different US frequencies of 20, 28 and 40 KHz at 60 Watts. A high-speed camera was used to capture 2,000 frames per second of the bubble cavitation generated in water under the ultrasound influence. Key parameters at the polychromatic beamlines were optimized to maximize the phase contrast of gas/liquid of the microbubbles with a minimum size of 5.5 µm. ImageJ software was used to analyze the bubble characteristics and their behavior under the US exposure including the microbubble number, size, and fraction of the total area occupied by the bubbles at each US frequency. Furthermore, the bubble characteristics over the US exposure time and at different distances from the transducer were studied. The qualitative and quantitative data analyses showed that the microbubble number or size did not change over time; however, it was observed that most bubbles were created at the middle of the frames and close to the US field. The number of bubbles created under the US exposure increased with the frequency from 20 kHz to 40 kHz (about 4.6 times). However, larger bubbles were generated at 20 kHz such that the average bubble radius at 20 kHz was about 6.8 times of that at 40 kHz. Microbubble movement/traveling through water was monitored, and it was observed that the bubble velocity increased as the frequency was increased from 20 kHz to 40 kHz. The small bubbles moved faster, and the majority of them traveled upward towards the US transducer location. The growth pattern (a correlation between the mean growth ratio and the exposure time) of bubbles at 20 kHz and 60 W was obtained by tracking the oscillation of 22 representative microbubbles over the 700 ms of imaging. The mean growth ratio model was also obtained.     

Numerical solution of Boltzmann tranport equation for TEA CO2 laser having nitrogen-lean gas mixtures to predict laser characteristics and gas lifetime

Selective laser isotope separation by TEA CO₂ laser often needs short tail-free pulses. Using laser mixtures having very little nitrogen almost tail free laser pulses can be generated. The laser pulse characteristics and its gas lifetime is an important issue for long-term laser operation. Boltzmann transport equation is therefore solved numerically for TEA CO₂ laser gas mixtures having very little nitrogen to predict electron energy distribution function (EEDF). The distribution function is used to calculate various excitation and dissociation rate of CO₂ to predict laser pulse characteristics and laser gas lifetime, respectively.Laser rate equations have been solved with the calculated excitation rates for numerically evaluated discharge current and voltage profiles to calculate laser pulse shape. The calculated laser pulse shape and duration are in good agreement with the measured laser characteristics. The gas lifetime is estimated by integrating the equation governing the dissociation of CO₂. An experimental study of gas lifetime was carried out using quadrapole mass analyzer for such mixtures to estimate the O₂ being produced due to dissociation of CO₂ in the pulse discharge. The theoretically calculated O₂ concentration in the laser gas mixture matches with experimentally observed value. In the present TEA CO₂ laser system, for stable discharge the O₂ concentration should be below 0.2%.     

UV-laser-light-controlled photoluminescence of metal oxide nanoparticles in different gas atmospheres: BaTiO3, SrTiO3 and HfO2

The photoluminescence (PL) enhancement has been studied at room temperature using various specimen atmospheres (O₂ gas, CO₂ gas, CO₂–H₂ mixture gas, Ar–H₂ mixture gas and vacuum) under 325 nm laser light irradiation on various metal oxides. Of them, the results obtained for BaTiO₃ nanocrystals, SrTiO₃ ones and HfO₂ powder crystal are given in the present paper. Their PL were considerably increased in intensity by irradiation of 325 nm laser light in CO₂ gas and CO₂–H₂ mixture gas. The cause of the PL intensity enhancements is discussed in the light of the exciton theory, the defect chemistry and the photocatalytic theory. The results may be applied for the utilization of greenhouse gas (CO₂) and the optical sensor for CO₂ gas.     

Particle imaging of ignition and devolatilization of pulverized coal during oxy-fuel combustion

Oxy-fuel combustion of coal is a promising technology for cost-effective power production with carbon capture and sequestration that has ancillary benefits of emission reductions and lower flue gas cleanup costs. To fully understand the results of pilot-scale tests of oxy-fuel combustion and to accurately predict scale-up performance through CFD modeling, fundamental data are needed concerning coal and coal char combustion properties under these unconventional conditions. In the work reported here, the ignition and devolatilization characteristics of both a high-volatile bituminous coal and a Powder River Basin subbituminous coal were analyzed in detail through single-particle imaging at a gas temperature of 1700 K over a range of 12–36 vol % O₂ in both N₂ and CO₂ diluent gases. The bituminous coal images show large, hot soot cloud radiation whose size and shape vary with oxygen concentration and, to a lesser extent, with the use of N₂ versus CO₂ diluent gas. Subbituminous coal images show cooler, smaller emission signals during devolatilization that have the same characteristic size as the coal particles introduced into the flow (nominally 100 μm). The measurements also demonstrate that the use of CO₂ diluent retards the onset of ignition and increases the duration of devolatilization, once initiated. For a given diluent gas, a higher oxygen concentration yields shorter ignition delay and devolatilization times. The effect of CO₂ on coal particle ignition is explained by its higher molar specific heat and its tendency to reduce the local radical pool. The effect of O₂ on coal particle ignition results from its effect on the local mixture reactivity. CO₂ decreases the rate of devolatilization because of the lower mass diffusivity of volatiles in CO₂ mixtures, whereas higher O₂ concentrations increase the mass flux of oxygen to the volatiles flame and thereby increase the rate of devolatilization.     

Application of Notched Long-Period Fiber Grating Based Sensor for CO2 Gas Sensing

An inductively coupled plasma etching process to fabricate notched long-period fiber gratings for CO₂ gas sensing is proposed in this article. In the gas sensing test, the 15% mixed CO₂ gas was used for characterization of CO₂ adsorption by the amine-modified nanoporous silica foams of the notched long-period fiber grating sensor. The results shows the spectra were changed with the CO₂ gas flow within 13 min. During the absorption process, the transmission of the resonant dip was decreased by 2.884?dB. Therefore, the proposed notched long-period fiber grating gas sensor shows good performance and is suitable as a gas sensor for monitoring the CO₂ adsorption process.     

Photoacoustic analysis of CO2 content in annual tree rings

We have used laser photoacoustic gas analysis to study the CO₂ content sorbed by the capillary porous system of annual rings in cross-sectional disks of some conifers. The measurement results showed that in most cases, the CO₂ content in gas samples extracted by the vacuum method from annual rings in the disks is higher than the CO₂ content in atmospheric air. In the disks, we observe an annual trend in the CO₂ concentration, correlating in a number of cases with a rise in atmospheric CO₂. The annual trend in the average value of the CO₂ concentration change sign from positive to negative. We hypothesize that the observed pattern for the annual distribution of CO₂ in the disks is connected with a rise in atmospheric CO₂ and a change in the concentration gradient between stem and atmospheric CO₂. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 477–480, May–June, 2009.     

Experimental evaluation of strategies for quantitative laser-induced-fluorescence imaging of nitric oxide in high-pressure flames (1-60 bar)

Nitric oxide laser-induced-fluorescence (NO-LIF) 2-D imaging measurements using a new multi-spectral detection strategy are reported for high-pressure flames (1-60 bar). This work builds on previous research that identified interference LIF from O₂ and CO₂ in high-pressure flames and optimized the choice of excitation strategies as a function of application conditions. In this study, design rules are presented to optimize the LIF detection wavelengths for quantitative 2-D NO-LIF measurements over a wide range of pressures (1-60 bar) and temperatures. Simultaneous detection of LIF in multiple wavelength regions enables correction of the NO signal for interference from O₂ and CO₂ and allows simultaneous imaging of all three species. New experiments of wavelength-resolved 1-D LIF in slightly lean (? = 0.9) and slightly rich (? = 1.1) methane/air flames are used to evaluate the design rules and estimate the NO detection limits for a wide range of flame conditions. The quantitative 2-D measurements of NO in the burnt gas are compared with model calculations (using GRI-Mech 3.0) versus pressure for slightly lean and slightly rich flames. The discussions and demonstrations reported in this study provide a practical guideline for application of instantaneous 1-D or 2-D NO-LIF imaging strategies in high-pressure combustion systems.     

Computer emulation of the method for comparing the isotopic composition of CO<Subscript>2</Subscript> in gas mixtures based on laser spectral analysis at the 2.05-<Emphasis Type="Italic">µ</Emphasis>m line

An algorithm for processing spectral data in order to determine the isotopic composition of gas mixtures is proposed and simulated using emulated transmission spectra of CO₂ in exhaled air tests. It is shown that the ratio of the optical-density spectra of the analyzed and reference gas mixtures is a contrast spectrum with resonant features and a fixed depth of their amplitude modulation. Based on the simulation results several spectral ranges are found to be optimal for analyzing the relative ¹²CO₂ and ¹³CO₂ contents in exhaled air. The effect of random noise on the isotopic analysis result is estimated, and the correlation between the optical density of analyzed gas media, level of random noise, and sensitivity of isotopic analysis is determined. The use of the algorithm proposed reduces the effect of such noises as interference at optical elements, absorption in open atmosphere, drift of the laser pulse envelope, and disbalance of spectral channels. This algorithm is valid for comparative isotopic analysis of any other gas molecules with similar spectral properties.     

CO2 gas resonance absorption at CO2 laser wavelength in?multiple laser coating

Multiple laser beams demonstrate many advantages as energy sources in diamond synthesis. In a reported amazingly-fast multiple laser coating technique, CO₂ gas is claimed as the sole precursor or secondary precursor for forming a diamond or diamond-like carbon, which remains poorly understood. The absorption coefficient changes under the irradiation of multiple lasers are one of the keys to resolve the mysteries of multiple laser beam coating processes. This study investigates the optical absorption in CO₂ gas at the CO₂ laser wavelength. The resonance absorption process is modeled as an inverse process of the lasing transitions of CO₂ lasers. The well-established CO₂ vibrational-rotational energy structures are used as the basis for the calculations with the Boltzmann distribution for equilibrium states and the three-temperature model for non-equilibrium states. Based on the population distribution, our predictions of the CO₂ absorption coefficient changes as a function of temperature are in agreement with the published data.     

Determination of binary diffusion coefficients of gases using photothermal deflection technique

A photothermal deflection (PD) technique was applied to measure the binary diffusion coefficients of various gases (CO₂–N₂, CO₂–O₂, N₂–He, O₂–He, and CO₂–He). With an in-house-made Loschmidt diffusion cell, a transverse PD system was employed to measure the time-resolved PD signal associated with the variation of the thermal diffusivity and the temperature coefficient of the refractive index of the gas mixture during the diffusion. The concentration evolution of the gas mixture was deduced from the PD amplitude and phase signals based on our diffraction PD model and was processed using two mass-diffusion models explored in this work for both short- and long-time diffusions to find the diffusion coefficient. An optical fiber oxygen sensor was also used to measure the concentration changes of the mixtures with oxygen. Experimental results demonstrated that the binary diffusion coefficients precisely measured with the PD technique were in agreement with the literature values. Moreover, the PD technique can measure the diffusion coefficients of various gas mixtures with both short- and long-time diffusions. In contrast, the oxygen sensor is only suitable for the long-time diffusion measurements of the gas mixtures with oxygen. PACS 78.20.Nv; 51.20.+d     

Bifunctional Au-nanorod@Fe3O4 nanocomposites: synthesis, characterization, and their use as bioprobes

Membrane gas separation technology has been rapidly growing for industrial applications such as air separation, carbon dioxide (CO₂) separation from natural gas production, hydrogen separation, etc. Needs for CO₂ separation are increasing as carbon capture technology has been recognized as an essential part when combating the global warming issue. Membrane gas separation technology deals with mass transport phenomena through the membrane engineered on a sub-nanoscale controlling transport properties of small gas molecules such as CO₂, N₂, O₂, H₂, etc. In this review, we will report on the recent developments in capture technologies utilizing various membranes including nano-engineered thermally rearranged (TR) polymers. TR polymer membranes show high gas permeability as well as good separation properties, especially in CO₂ separation processes such as from post-combustion flue gas and natural gas sweetening.