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PubMed2004

Differentiating pyopneumothorax and peripheral lung abscess: chest ultrasonography.

BACKGROUND: Differentiation between pyopneumothorax and lung abscess can be difficult but has important therapeutic consequences. The role of chest ultrasonography in this issue remains undetermined. Sonographic features of hydropneumothorax and/or pyopneumothorax are characteristic and not difficult to recognize. In this study, the authors evaluate the usefulness of a panel of sonographic findings characteristic of hydropneumothorax in distinguishing pyopneumothorax from lung abscess. METHODS: This series included 16 patients with lung abscess and 19 with pyopneumothorax. A diagnosis of lung abscess or pyopneumothorax was based on the following criteria: pus aspiration from the lesion, appropriate clinical setting, thoracic computed tomographic findings, serial follow-up of chest radiograms, and consistent clinical course. The panel of sonographic features suggestive of hydropneumothorax, including the presence of air-fluid level, the curtain sign, loss of gliding sign above the air-fluid level, and the suspended microbubble sign, were recorded and analyzed by a consensus of blinded readers. In addition, sonographic features used to differentiate empyema and lung abscess were also evaluated. RESULTS: The results indicated that the presence of air-fluid level, the curtain sign, loss of gliding sign above the air-fluid level, and the suspended microbubble sign were valuable in distinguishing pyopneumothorax from lung abscess. All four sonographic findings were observed in 17 of 19 patients with pyopneumothorax. In contrast, two or fewer sonographic findings were seen in 16 patients with lung abscess. Our results confirmed that the wall characteristics, shape of the lesion, chest wall angle, and pleural separation were also useful. CONCLUSIONS: The panel of sonographic findings is of considerable value in differentiating pyopneumothorax and lung abscess.

Adult↗

PubMed2004

Retrograde air embolization during routine radial artery catheter flushing in adult cardiac surgical patients: an ultrasound study.

BACKGROUND: Rapid flushing of radial artery catheters may result in retrograde embolization of air into the cerebral circulation. This study examined the incidence of central air embolization during and after flushing of an arterial pressure monitoring system. METHODS: One hundred adult patients undergoing cardiac surgical procedures were enrolled in this study. Ten ml of saline and blood were withdrawn into a syringe in the arterial flushing-sampling pressure system and then readministered to the patient through a 20-gauge radial artery catheter over 3-12 s. The right carotid artery, left carotid artery, and aortic arch were visualized using ultrasound imaging techniques during three manual flushes of the system. The left and right common carotid arteries were examined for the presence of macrobubbles or microbubbles using a linear array ultrasound transducer. The aortic arch was imaged using transesophageal echocardiography to detect retrograde air emboli. The severity of air embolization was quantified using a modification of an established grading system. RESULTS: A total of 298 ultrasound studies in 100 patients were recorded and analyzed after radial artery catheter flushing. Two aortic arch images were not obtained because of an inability to place the probe. Most clinicians (54%) returned flush solution to patients at near-maximal injection rates (2-3 ml per second). No air emboli (macrobubbles or microbubbles) were detected in the carotid arteries or aortic arch of any subject. CONCLUSION: Retrograde air embolization is a rare event after routine radial artery catheter flushing in adult patients with stable hemodynamic conditions.

Aged↗

PubMed2006

Expansion of gas bubbles by nitrous oxide and xenon.

BACKGROUND: Nitrous oxide is well known to expand gas bubbles trapped in enclosed spaces and is contraindicated in situations where this may occur. Xenon, an anesthetic gas with similar physical properties to nitrous oxide, is also likely to expand gas bubbles, and it has been predicted that microbubbles in the circulation may expand dramatically when exposed to xenon. Because of the possibility that xenon will be used during cardiopulmonary bypass surgery, a procedure that is likely to introduce microbubbles into the circulation, the authors reinvestigated the extent to which xenon expands gas bubbles in aqueous solution. METHODS: Gas bubbles of either air or oxygen were formed in an aqueous solution, and their size was monitored using optical microscopy when they were exposed to a rapidly flowing solution of xenon, nitrous oxide, or a xenon-oxygen mixture. RESULTS: Both nitrous oxide and xenon rapidly expanded air bubbles, although nitrous oxide caused a much larger expansion. The observed expansion was not greatly dependent on the initial size of the bubble but was significantly greater at lower temperatures. Under conditions relevant to cardiopulmonary bypass surgery (50% xenon-50% oxygen, 30 degrees C), the increase in diameter was modest (9.7 +/- 0.8%). CONCLUSIONS: Although xenon does expand small air and oxygen bubbles, the extent to which this occurs under clinically relevant conditions of concentration and temperature is modest.

Anesthetics, Inhalation↗

PubMed2006

Influence of endothelial glycocalyx degradation and surfactants on air embolism adhesion.

BACKGROUND: Microbubble adherence to endothelial cells is enhanced after damage to the glycocalyx. The authors tested the hypothesis that exogenous surfactants delivered intravascularly have differential effects on the rate of restoration of blood flow after heparinase-induced degradation of the endothelial glycocalyx. METHODS: Air microbubbles were injected into the rat cremaster microcirculation after perfusion with heparinase or saline and intravascular administration of either saline or one of two surfactants. The surfactants were Pluronic F-127 (Molecular Probes, Eugene, OR) and Perftoran (OJSC SPC Perftoran, Moscow, Russia). Embolism dimensions and dynamics were observed using intravital microscopy. RESULTS: Significant results were that bubbles embolized the largest diameter vessels after glycocalyx degradation. Bubbles embolized smaller vessels in the surfactant treatment groups. The incidence of bubble dislodgement and the magnitude of distal displacement were smallest after glycocalyx degradation alone and largest after surfactant alone. The time to bubble clearance and restoration of blood flow was longest with heparinase alone and shortest with Pluronic F-127 alone. CONCLUSIONS: Degradation of the glycocalyx causes air bubbles to adhere to the endothelium more proximally in the arteriolar microcirculation. Surfactants added after glycocalyx degradation and before gas embolization promotes bubble lodging in the distal microcirculation. Surfactants may have a clinical role in reducing embolism bubble adhesion to endothelial cells undergoing glycocalyx disruption.

Animals↗

PubMed2001

Recent advances in myocardial contrast echocardiography.

Myocardial contrast echocardiography (MCE) has undergone many advances in the past several years through remarkable developments in contrast agent and ultrasound equipment technology. Microbubble ultrasound contrast agents can now safely transit the pulmonary circulation to provide opacification of the left ventricular cavity, improved endocardial border definition, and detection of myocardial perfusion. The role of contrast echocardiography in enhancing technically difficult images is now well established in clinical practice, and has proven especially useful in the stress and intensive care unit settings. Major progress has been made in the application of MCE for myocardial perfusion assessment in acute and chronic ischemic heart disease syndromes, and comprises the focus of this review. Advances in novel applications of contrast echocardiography, including targeted delivery of genetic and pharmaceutical materials, have also occurred, but remain in a preclinical phase. In summary, the combination of recent innovations in ultrasound equipment, and microbubble acoustics, allows for exciting exploration of the expanding role of contrast echocardiography in clinical practice.

Coronary Circulation↗

PubMed2002

Myocardial contrast echocardiography in acute coronary syndromes.

Myocardial contrast echocardiography (MCE) is an emerging technique in which microbubble contrast agents are visualized in the coronary microvasculature. MCE is an ideal modality for the noninvasive evaluation of acute coronary syndromes because it provides portable, simultaneous assessment of regional wall motion and myocardial perfusion. Recent advances in microbubble contrast agents and ultrasound imaging technology have allowed new clinical applications of MCE in acute coronary syndromes. Studies suggest a promising role for MCE in the evaluation of chest pain, the diagnosis and prognosis in acute myocardial infarction, the assessment of the success of reperfusion, and the differentiation of myocardial stunning from myocardial necrosis. Potential future applications of MCE in acute coronary syndromes include the detection of inflammation and ultrasound induced thrombolysis. The following serves as a review of the current status of myocardial contrast echocardiography in acute coronary syndromes.

Angina Pectoris↗

PubMedDate not supplied

A bovine model for detecting high intensity transient signals originating from mechanical heart valves.

In patients with mechanical heart valves (MHVs), transcranial Doppler methods commonly detect high intensity transient signals (HITS) representing microemboli. These microemboli, which are presumably gaseous, may cause stroke and cognitive deterioration. A bovine model was therefore developed for studying the relationship between mitral MHV induced HITS and potential etiogenic factors. We placed an 18 mm, 4 MHz Doppler probe in the brachiocephalic artery to detect MHV induced microbubbles at baseline (rest) and under 9 other conditions. To elucidate the gas composition (CO2 or N2) of the microbubbles, we administered 1%, 3%, and 5% CO2, and 100% O2. To determine effect of the heart rate, we paced the heart at 120, 160, and 180 bpm. To alter the myocardial contractility, we gave dobutamine and esmolol. Two independent, blinded observers counted the HITS from recorded doppler spectra. HITS were defined by an initial unidirectional spectral deviation, a signal power of >8 dB relative to the background power, and lack of a cyclic appearance. The electrocardiogram, aortic and LV pressures, and LV dP/dt were obtained telemetrically. The calves were studied 4 to 6, 8 to 10, and 12 to 14 weeks postoperatively, after which the animals were sacrificed at an approximate 4 month study duration, and a postmortem evaluation of the heart and the main viscera was performed. In all, 27 HITS recordings were made in 10 calves. Myocardial contractility was the only factor to significantly affect HITS frequency; the heart rate and blood gas concentrations had minimal effect on HITS frequency. Our bovine model will be useful for assessing valve designs, as well as the mechanism of HITS, the composition of the microemboli, and their possible pathophysiologic effects on the kidneys and brain.

Adrenal Glands↗

PubMed1997

Phase I clinical trials of MRX-115. A new ultrasound contrast agent.

RATIONALE AND OBJECTIVES: Stabilized microbubbles are under development as contrast agents for medical ultrasound. The authors report the results of Phase I clinical trials of a new ultrasound contrast agent based on lipidencapsulated perfluorocarbon gas microbubbles. METHODS: Lipids encapsulating perfluoropropane gas (Aerosomes MRX-115, ImaRx Pharmaceutical Corp., Tucson, AZ) were evaluated in Phase I clinical trials. Two separate studies were performed. The first was a single escalating-dose study (n = 30 subjects), and the second was a multiple-dose study (n = 18 subjects) with rechallenge in several subjects (n = 4) after 21 days. Echocardiographic examinations were performed before and after contrast agent for each test drug administration for both studies, with the exception of the rechallenge group. Doses tested in the single-dose study ranged from 0.005 mL/kg to 0.100 mL/kg body weight. In the multiple-dose study, five doses of 0.005 mL/ kg to 0.030 mL/kg (0.025-0.150 mL/kg total dose) were evaluated. Studies were single-masked, placebo-controlled, and safety assessment and adverse events were monitored. RESULTS: All doses in both studies were well tolerated with no treatment-related changes in safety measures for either study. Left ventricular cavity and myocardial enhancement were seen with all doses of MRX-115. CONCLUSIONS: MRX-115 is a promising new intravascular ultrasound contrast agent that was safe and well tolerated at the doses evaluated in these studies.

Adult↗

PubMed2001

Comparison of contrast-enhanced fundamental imaging, second-harmonic imaging, and pulse-inversion harmonic imaging.

RATIONALE AND OBJECTIVES: To investigate the feasibility of recent contrast-specific ultrasound techniques in depicting vascular flow and the effects of changing the output power of the transducer and insonation mode on contrast enhancement, the authors performed an experimental study with a flow phantom. METHODS: While changing the mechanical index and the sound insonation mode (continuous and intermittent), images were obtained with three contrast-enhanced ultrasound techniques: fundamental, second-harmonic, and pulse-inversion harmonic imaging (PIHI) after a bolus injection of microbubble contrast agent. The images were compared on a time-intensity curve. RESULTS: In assessing fixed flow (10 cm/s), PIHI showed the best depiction of flow signal. In intermittent scanning, increases in the mechanical index caused stronger flow signals and longer enhancement duration in all techniques. However, continuous scanning revealed poor depiction of flow signal regardless of the technique or changes in the mechanical index because of significant bubble destruction. CONCLUSIONS: Microbubble-enhanced PIHI with intermittent scanning at a high mechanical index can depict vascular flow highly effectively without shortening the duration of enhancement.

Blood Flow Velocity↗

PubMed2000

Contrast agent specific imaging modes for the ultrasonic assessment of parenchymal cerebral echo contrast enhancement.

Previous work has demonstrated that cerebral echo contrast enhancement can be assessed by means of transcranial ultrasound using transient response second harmonic imaging (HI). The current study was designed to explore possible advantages of two new contrast agent specific imaging modes, contrast burst imaging (CBI) and time variance imaging (TVI), that are based on the detection of destruction or splitting of microbubbles caused by ultrasound in comparison with contrast harmonic imaging (CHI), which is a broadband phase-inversion-based implementation of HI. Nine healthy individuals with adequate acoustic temporal bone windows were included in the study. Contrast harmonic imaging, CBI, and TVI examinations were performed in an axial diencephalic plane of section after an intravenous bolus injection of 4 g galactose-based microbubble suspension in a concentration of 400 mg/mL. Using time-intensity curves, peak intensities and times-to peak-intensity (TPIs) were calculated off-line in anterior and posterior parts of the thalamus, in the region of the lentiform nucleus, and in the white matter. The potential of the different techniques to visualize cerebral contrast enhancement in different brain areas was compared. All techniques produced accurate cerebral contrast enhancement in the majority of investigated brain areas. Contrast harmonic imaging visualized signal increase in 28 of 36 regions of interest (ROIs). In comparison, TVI and CBI examinations were successful in 32 and 35 investigations, respectively. In CHI examinations, contrast enhancement was most difficult to visualize in posterior parts of the thalamus (6 of 9) and the lentiform nucleus (6 of 9). In TVI examinations, anterior parts of the thalamus showed signal increase in only 6 of 9 examinations. For all investigated imaging modes, PIs and TPIs in different ROIs did not differ significantly, except that TVI demonstrated significantly higher PIs in the lentiform nucleus as compared with the thalamus and the white matter (P < 0.05). The current study demonstrates for the first time that CBI and TVI represent new ultrasonic tools that allow noninvasive assessment of focal cerebral contrast enhancement and that CBI and TVI improve diagnostic sensitivity as compared with CHI.

Adult↗

PubMed2002

Advances in ultrasound for the detection of prostate cancer.

The introduction of ultrasound (US) microbubble contrast agents has dramatically expanded the possibilities for US detection of prostate cancer. Recent advances in US technology have increased the value of US contrast agents. Many newer US techniques, which are quite sensitive for detection of microbubbles, are yet to be explored for prostate applications. A critical evaluation of the current status of transrectal US imaging for the detection of prostate cancer and background information for US contrast agents and imaging techniques are presented. Early results have demonstrated the feasibility of US contrast agents to enhance US imaging of prostatic disease. The application of US contrast agents for the detection and clinical staging of prostate cancer is promising. Future clinical trials are needed to determine whether the promise of contrast-enhanced US of the prostate will evolve into widespread clinical application.

Journal Article↗

PubMed1995

Assessment of myocardial perfusion in coronary artery disease using myocardial contrast echocardiography.

MCE has evolved over the past decade as a clinically useful technique for the assessment of myocardial perfusion in patients with coronary artery disease. At present, its applications are limited because of the necessity of injecting microbubbles directly into the arterial circulation. Newer contrast agents, capable of producing myocardial opacification from a venous injection, are likely to broaden significantly the application of this technique in patients with coronary artery disease. Advances in ultrasound technology, such as second-harmonic imaging will make MCE a valuable non-invasive method, capable of simultaneously assessing regional perfusion and function. The advent of ultrasound systems that provide a linear relationship between the tissue concentration of microbubbles and the video intensity will make the method truly quantitative. It is likely that MCE will replace nuclear cardiology for the assessment of myocardial dysfunction by the turn of the century in many patients with coronary artery disease.

Albumins↗

PubMed2005

Intravenous myocardial contrast echocardiography for the diagnosis of coronary artery disease.

PURPOSE OF REVIEW: Myocardial contrast echocardiography is a recently developed technique that permits the noninvasive assessment of myocardial perfusion. Myocardial contrast enhancement from microbubbles characteristically reflects the myocardial blood volume. The analysis of microbubble kinetics using quantitative myocardial contrast echocardiography permits the evaluation of myocardial blood flow both at rest and during pharmacological stress. RECENT FINDINGS: Myocardial contrast echocardiography has been shown to have good concordance with single photon emission computed tomography for the localization of perfusion abnormalities. As a result of its better spatial resolution and the fact that it tracks myocardial blood flow changes, it seems to have higher sensitivity for the detection of angiographically significant coronary artery disease, while maintaining similar specificity to single photon emission computed tomography. Low mechanical index imaging techniques (real-time myocardial contrast echocardiography) have the advantage of permitting simultaneous analysis of wall motion and perfusion, which is particularly important during dobutamine stress. Myocardial perfusion analysis using real-time myocardial contrast echocardiography has been shown to have higher sensitivity and diagnostic accuracy than wall motion analysis for the detection of coronary artery disease. Quantitative myocardial contrast echocardiography seems to overcome the expertise requirements for appropriate interpretation of myocardial perfusion images, and may have been demonstrated to be an accurate supplemental technique for estimating the severity of coronary artery disease. SUMMARY: Recent technological advances have positioned myocardial contrast echocardiography as a safe and feasible technique for the evaluation of myocardial perfusion. The analysis of myocardial perfusion using myocardial contrast echocardiography has higher diagnostic accuracy than wall motion analysis for detecting coronary artery disease.

Contrast Media↗

PubMedDate not supplied

Aqueous oxygen near the homogeneous nucleation limit of water: stabilization with submicron capillaries.

Previous studies have demonstrated that the metastability threshold of aqueous oxygen (AO) is inversely dependent on the internal diameter of capillary tubes used to deliver it into blood. The hypothesis was tested herein that significantly higher thresholds are attainable with capillaries having markedly smaller dimensions (submicron) than those previously studied. Water was equilibrated with oxygen over a 0.3- to 0.7-k bar range. Inert gases (argon, helium) facilitated studies at pressures to 2.5 k bar. An argon-ion laser was used to visualize fluorescein in the liquid effluent from silica capillaries that were tapered at the distal end to a submicron internal diameter (0.5 +/- 0.3 microns). During infusion of the fluorescent effluent into host water at 21 degrees C and atmospheric pressure, integrity of the effluent and lack of microbubbles were monitored by videomicroscopy. No microbubbles were noted at AO concentrations ranging from 7.5 to 12.8 ml O2/g (0.34 to 0.68 k bar, respectively) or in the aqueous argon effluent at concentrations to 14 ml Ar/g (0.75 k bar). For aqueous helium, effluent nucleation was not observed at a mean concentration of 13 +/- 3 ml He/g (2.0 +/- 0.5 k bar), with an upper value of 15.2 ml He/g (2.4 k bar). The data represent the highest values of the tensile strength of water ever observed and approximate its theoretical homogeneous nucleation limit. Thus, remarkably high metastable concentrations of AO and other gases are attainable with the use of submicron capillaries.

Argon↗

PubMed2000

Anechoic aquarium for ultrasonic neural telemetry.

An acoustic neural telemetry tag has been developed for recording from free-swimming aquatic animals. Microwire electrodes were implanted into the VIIIth nerve of the toadfish, Opsanus tau, and interfaced to the subdermally implanted tag. The telemetry tag frequency modulates the neural signal, converting it into a varying frequency, which is amplified and transmitted acoustically (centre frequency of 90 kHz and a 20 kHz bandwidth). This acoustic signal is detected by a receiver hydrophone, and the receiver reconstructs the full neural waveform from the acoustic signal. However, due to the multipath environment in the experimental aquarium, the acoustic signal is quickly degraded as the hydrophone is moved away from the source. In order to receive the signal independent of fish position, an anechoic aquarium was designed. Streams of microbubbles (ca. 70 microm diameter) were generated to produce a curtain of sound-absorptive material along the walls and water surface of the aquarium. Microbubble generation significantly reduced the multipath artefacts, and allowed signal discrimination independent of fish and hydrophone position. The anechoic aquarium will allow the recording of neural activity from free-swimming fishes in quasi-natural habitats, thus allowing better understanding of the neural mechanisms of behaviour.

Animals↗

PubMed2002

Cavitation of Langmuir monolayers.

Cavitation in liquid expanded and liquid condensed Langmuir monolayers induced by laser heating or microbubble coalescence is studied experimentally using fluorescence and Brewster angle microscopy. The kinetics of hole closure of two-dimensional (2D) gaseous cavitation bubbles exhibits a decelerated dynamics for cavities surrounded by a liquid expanded phase and an accelerated dynamics for cavities in a liquid condensed phase. Most of the cavities in liquid condensed phases possess a nonconvex shape and do not close. The results are compared with theoretical predictions derived for 2D cavitation of liquid monolayers of different surface shear viscosities, and for solid monolayers with diffusive flux of vacancies and interstitials. While part of the theory is in qualitative agreement with the experiment, the experimentally observed hole persistence within the liquid condensed phases and the hole closure within liquid expanded phases remains to be explained. The technique of microbubble coalescence might be particularly useful for the study of the rheological properties of hexatic phases.

Journal Article↗

PubMed2006

Acoustic estimation of thermal distribution in the vicinity of femtosecond laser-induced optical breakdown.

Laser-induced optical breakdown (LIOB), or photo-disruption, can generate individual microbubbles in tissues for biomedical applications. We have previously developed a co-localized high-frequency ultrasound system to detect and characterize these laser-induced microbubbles. Because ultrasound speed varies with temperature, this system can also be used to directly estimate thermal effects in the vicinity of photodisruption. In this study, individual bubbles (sizes 60-100 microm) were created at the bottom of a water tank using a 793-nm, 100-fs Ti:Sapphire laser pulsed at 250 kHz. During and after breakdown, pulse-echoes from the tank bottom in the region surrounding a bubble were recorded with a single-element 85-MHz ultrasonic transducer, and temperature-dependent pulse-echo displacements were calculated using phase-sensitive correlation tracking. These displacements were then fit to a finite-element heat transfer model to estimate the effective thermal distribution. Estimates were calculated for laser exposure times ranging from 6.25 to 312.5 ms (1600 to 78 000 laser pulses), at 1.5 and 4 J/cm2 fluences. Results suggest a minimal temperature increase (<1 degrees C) within 100 microm of a bubble created with <1600 laser pulses at 1.5 J/cm2 fluence. This implies that LIOB can be controlled to be thermally noninvasive in the bubble vicinity.

Acoustics↗

PubMed2002

Nondestructive subharmonic imaging.

Ultrasound contrast agent microbubbles are intravascular agents that can be used to estimate blood perfusion. Blood perfusion may be estimated by destroying the bubbles in a vascular bed and observing the refresh of contrast agents back into the vascular bed. Contrast agents can be readily destroyed by traditional imaging techniques. The design of a nondestructive imaging technique is necessary for the accurate quantification of contrast agent refresh. In this work, subharmonic imaging is investigated as a method for nondestructive imaging with the contrast agent microbubble MP1950 (Mallinckrodt, Inc., St. Louis, MO). Optical observation during insonation, in conjunction with a modified Rayleigh-Plesset (R-P) analysis, provides insight into the mechanisms of and parameters required for subharmonic frequency generation. Subharmonic imaging with a transmission frequency that is the same as the resonant frequency of the bubble is shown to require a minimum pressure of insonation that is greater than the experimentally-observed bubble destruction threshold. Subharmonic imaging with a transmission frequency that is twice the resonant frequency of the bubble produces a subharmonic frequency response while minimizing bubble instability. Optimization is performed using optical experimental analysis and R-P analysis.

Blood Vessels↗