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.     

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.     

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.     

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.