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PubMed2005

Contrast-enhanced intraoperative ultrasonography during hepatectomies for colorectal cancer liver metastases.

Preliminary reports showed that contrast-enhanced intraoperative ultrasonography (CEIOUS) provides information on primary or metastatic tumors of the liver that is not obtainable with conventional intraoperative ultrasonography (IOUS). This study validates the impact of CEIOUS, focusing on resective surgery for colorectal cancer (CRC) liver metastases. Twenty-four consecutive patients underwent liver resection using IOUS and CEIOUS for CRC liver metastases. CEIOUS was accomplished with intravenous injection of 4.8 mL of sulphur-hexafluoride microbubbles. CEIOUS found lesions missed at preoperative imaging and at IOUS in four patients and confirmed all of the new findings of IOUS in four patients. In addition, CEIOUS helped to define the tumor margins of the main lesion in 29% of patients with CRC liver metastases. No adverse effects were observed in relation with CEIOUS. In conclusion, CEIOUS improves IOUS accuracy with a significant impact on surgical strategy and radicality in patients who undergo surgery for CRC liver metastases.

Adult↗

PubMed2006

An insight into the mechanism of protein separation by colloidal gas aphrons (CGA) generated from ionic surfactants.

Colloidal gas aphrons (CGA), which are surfactant stabilised microbubbles, have been previously applied for the recovery of proteins from model mixtures and a few studies have demonstrated the potential of these dispersions for the selective recovery of proteins from complex mixtures. However there is a lack of understanding of the mechanism of separation and forces governing the selectivity of the separation. In this paper a mechanistic study is carried out to determine the main factors and forces influencing the selectivity of separation of whey proteins with CGA generated from ionic surfactants. Two different separation strategies were followed: (i) separation of lactoferrin and lactoperoxidase by anionic CGA generated from a solution of sodium bis-(2-ethyl hexyl) sulfosuccinate (AOT); (ii) separation of beta-lactoglobulin by cationic CGA generated from a solution of cetyltrimethylammonium bromide (CTAB). Separation results indicate that electrostatic interactions are the main forces determining the selectivity however these could not completely explain the selectivities obtained following both strategies. Protein-surfactant interactions were studied by measuring the zeta potential changes on individual proteins upon addition of surfactant and at varying pH. Interestingly strongest electrostatic interactions were measured at those pH and surfactant to protein mass ratios which were optimum for protein separation. Effect of surfactant on protein conformation was determined by measuring the change in fluorescence intensity upon addition of surfactant at varying pH. Differences in the fluorescence patterns were detected among proteins which were correlated to differences in their conformational features which could in turn explain their different separation behaviour. The effect of conformation on selectivity was further proven by experiments in which conformational changes were induced by pre-treatment of whey (heating) and by storage at 4 degrees C. Overall it can be concluded that separation of proteins by ionic CGA is driven mainly by electrostatic interactions however conformational features will finally determine the selectivity of the separation with competitive adsorption having also an effect.

Colloids↗

PubMed2006

Application of high intensity air-borne ultrasound for debubbling liquid coating layers.

In the coating processes, the formation of bubbles and microbubbles is relatively frequent inside the coating layer. Such bubbles, which are formed as a consequence of air retention, are difficult to remove and specifically in high-speed (quick-drying) industrial application where they cause permanent imperfections in the homogeneity of the layer. High-intensity air-borne ultrasound may represent a clean means to improve homogenization by quickly breaking the bubbles just when they are formed inside the coating film. This paper deals with the direct application of air-borne high-intensity ultrasonic radiation at a frequency of about 21 kHz over coating layers just immediately they have been deposited over wood substrates. Such novel process has been implemented and experimentally studied at laboratory and semi-industrial stages.

Coated Materials, Biocompatible↗

PubMed2006

High frequency attenuation measurements of lipid encapsulated contrast agents.

A number of recent studies have indicated the potential of ultrasound contrast agent imaging at high ultrasound frequencies. However, the acoustic properties of microbubbles at frequencies above 10 MHz remain poorly understood at present. In this study we characterize the high frequency attenuation properties of (1) BR14, (2) BR14 that has been mechanically filtered (1 and 2 microm pore sizes) to exclude larger bubbles, and (3) the micron to submicron agent BG2423. A narrowband pulse-echo substitution method is employed with a series of four transducers covering the frequency range from 2 to 50 MHz. For BR14, attenuation decreases rapidly from 2 to 10 MHz and then more gradually from 10 to 50 MHz. For 2 microm filtration, the attenuation peaks between 10 and 15 MHz. For 1 microm filtration, attenuation continues to rise until 50 MHz. The agent BG2423 exhibits a diffuse attenuation peak in the range of 15-25 MHz and remains high until 50 MHz. These results demonstrate a strong influence of bubble size on high frequency attenuation curves, with bubble diameters of 1-2 microm and below having more pronounced acoustic activity at frequencies above 10 MHz.

Capsules↗

PubMed2004

Contrast echocardiography: new agents.

In this report, we review the history, rationale, current status and future directions of contrast agents in echocardiography. First, we discuss the historic development of contrast agents through a review of important physical principles of microbubbles in ultrasonography. Second, we identify attributes of an ideal contrast agent and review those that are currently available or in the "pipeline" for clinical use. Third, we review indications for contrast echocardiography, including endocardial border detection, perfusion quantification and reperfusion assessment, and validate these observations by comparisons with other imaging modalities. Then, we briefly review different methodologies of performing a contrast study, including interrupted, real-time and a hybrid modality. Finally, we identify novel future applications of the newest contrast agents. These newer concepts in contrast echocardiography should form a foundation for nearly limitless application of echocardiography in improved anatomical assessment, perfusion imaging and even special applications, such as detection of vascular inflammation and site-specific drug delivery.

Contrast Media↗

PubMed2005

Comparison of different mathematical models to analyze diminution kinetics of ultrasound contrast enhancement in a flow phantom.

Ultrasound (US) energy leads to intensity- and frequency-dependent destruction of US contrast agent (UCA) microbubbles. When applying repeated US pulses, this phenomenon can be detected as contrast diminution over time. Contrast diminution kinetics depend on the replenishment of UCA into the sample volume. Thus, it is related to organ perfusion. To analyze the contrast diminution kinetics following pulsed harmonic US application (SONOS 5500, 1.8-3.6 MHz, MI: 1.6, frame rates: 2, 4, and 6.67 Hz), we performed an in vitro study using SonoVue continuous infusion. Seven flow rates (4.5, 9, 13.5, 18, 22.5, 27 and 36 mL/min) were tested. Based on our results, three mathematical models (linear intensity decrease, exponential decay, and an exponential destruction/reperfusion model) describing diminution kinetics were compared. In 113 (89.7%) of 126 trials, a signal decrease was observed after US application. At higher flow rates (18 to 36 mL/min), curve fitting was not possible for the exponential models. For the linear model, intensity decrease depended significantly on the flow rate (p < or = 0.005, n = 7). A logistic model was fitted to the data, defining the slope in the dynamic range of quasilinear dependence for the different frame rates, as well as the inflection point: The higher the frame rate, the higher the flow rate at the point of inflection. For the exponential model, the contrast half-life was dependent on the flow rate (r = 0.95, p = 0.03, n = 6) only at the highest frame rate (6.67 Hz). The perfusion coefficient derived from the destruction/reperfusion model was not significantly related to the flow rate. In conclusion, the linear intensity decrease correlates well with the flow rate (i.e., flow velocity) and defines optimum frame rates for diminution imaging at different flow velocities. The exponential models, which required curve-fitting procedures, were determined to be inappropriate to describe flow in our phantom.

Contrast Media↗

PubMed2005

The effect of size on the acoustic response of polymer-shelled contrast agents.

In this technical note, we study three polymer-shelled microbubble contrast agents manufactured by POINT Biomedical Corporation that have identical shell composition and mean volumetric diameters of 0.74 microm, 0.91 microm and 1.33 microm. We investigate the effect of agent size on the amplitude, frequency and probability of acoustic echoes received in response to five-cycle, 2.25-MHz pulses of varying pressure. We find that the amplitude and frequency response from the three agents is not significantly different. However, significant differences among the agents do exist in the probability of response to acoustic interrogation: at a pressure of 1.06 MPa, an echo from the 1.33 microm agent is 5 times as likely as an echo from the 0.91 microm agent and 18 times as likely as an echo from the 0.74 microm agent. We hypothesize that there exists an effective pressure-dependent threshold diameter above which single polymer-shelled agents respond to acoustic interrogation.

Contrast Media↗

PubMed2005

On the relationship between encapsulated ultrasound contrast agent and pressure.

Noninvasive measurement of pressure within the heart cavities and other internal organs (e.g., kidney, liver) has significant clinical value, but currently is not feasible. Noninvasive pressure estimation using encapsulated ultrasound (US) contrast agents (UCA) as sensors is a challenge because they supposedly respond to their ambient pressure, but they are more rigid and less sensitive to pressure than gas microbubbles. Here, Optison sensitivity was studied (f(resonance) = approximately 2 MHz) to varying pressures, when excited at 2 times and also at 0.5 times f(resonance). Cyclic momentary increases in ambient pressure of 0 to 5, 0 to 10, 0 to 15 or 0 to 20 kPa at 1.0 Hz, mimicking left ventricular (LV) pressure changes, caused amplitude decrease of echoes at 0.5, 1 and 2 times the transmitted frequency and decrease of attenuation. Changes at 0.5 times the transmitted frequency correlated best, but only after 70 to 150 s. The correlations (mean +/- SD) during 150 to 300 s were 0.706 +/- 0.072 for 0 to 10 kPa, 0.844 +/- 0.042 for 0 to 15 kPa and 0.859 +/- 0.031 for 0 to 20 kPa. Attenuation presented less correlation. For 1.0 Hz, 10 to 15 kPa or 15 to 20 kPa pressures, mimicking systemic pressures, the attenuation decayed fast and even faster for slow (0.05 Hz) cyclic varying pressures, or elevated steady-state pressures (of 10 kPa and 20 kPa). Thus, cyclic pressure effects on UCA are demonstrated to be reversible, but elevated static pressures cause UCA destruction. This allows cyclic pressure variations to be detected, using the subharmonics of the transmitted frequency, down to 10 kPa.

Albumins↗

PubMed2006

Therapeutic effects of paclitaxel-containing ultrasound contrast agents.

Drug delivery vehicles that combine ultrasonic and molecular targeting are shown to locally concentrate a drug in a region-of-interest. The drug delivery vehicles, referred to as acoustically active lipospheres (AALs), are microbubbles surrounded by a shell of oil and lipid. In a region limited to the focal area of ultrasound application, circulating AALs are deflected by radiation force to a vessel wall and can subsequently be fragmented. Ligands targeting the alphavbeta3 integrin are conjugated to the AAL shell and increase in vitro binding by 26.5-fold over nontargeted agents. Toxicity assays demonstrate that paclitaxel-containing AALs exert a greater antiproliferative effect after insonation than free paclitaxel at an equivalent concentration. Lastly, ultrasound and molecular targeting are combined to deliver a model drug to the endothelium and interstitium of chorioallantoic membrane vasculature in vivo.

Animals↗

PubMed2006

Quantification of hepatic parenchymal blood flow by contrast ultrasonography with flash-replenishment imaging.

Flash-replenishment (FR) utilizes destruction of microbubbles in the scan volume by high-power ultrasound and enables to observe reperfusion at a low acoustic power. In this paper, we introduced theoretic equation between probability density function (PDF) of the transit time in the scan volume and time intensity curve (TIC) measured by FR method. From the equations, it was explained that the mean transit time (MTT) through the scan volume was calculated from the plateau level and tangent of the initial slope. Animal experiments were also performed to measure TIC in the parenchymal region of the liver using FR method. From the result of the TIC, the variant of the PDF for the transit time was found to be small and the average MTT was 11.1 s. Hepatic blood flow by an ultrasonic transit time flowmeter was also measured in the same experiment, and adequate correlation was obtained from between the two methods. The results suggested that the FR method, which is a noninvasive measurement, can predict the blood flow of the liver.

Animals↗

PubMed2006

The potential of a new stable ultrasound contrast agent for site-specific targeting. An in vitro experiment.

Microbubble-based ultrasound contrast agents can be used for specific site targeting, but demonstrate time-limited opacification. We have previously demonstrated the potential of gold-bound microtubules to provide a stable ultrasound contrast effect. Aim of the present study was to test the feasibility of gold-bound microtubules specifically to bind to human thrombi and to inflammatory activated human umbilical vein endothelial cells (HUVEC) in vitro. HUVEC were incubated with tumor necrosis factor, to induce expression of adhesion molecules. Human clots and HUVEC were incubated with biotinylated monoclonal antifibrin and anti-E-selectin antibodies, respectively. Probes were incubated with excess avidin followed by biotinylated gold-bound microtubules and by secondary Cy3-anti-beta-tubulin antibody and processed for immune fluorescence microscopy. Clots were transferred in copolymer foils filled with buffer and were ultrasonographically imaged before and after their treatment with the antifibrin antibody and with biotinylated microtubules, using a broadband harmonic transducer, transmitting and receiving at a mean frequency of 1.7 MHz and 3.2 MHz. The feasibility of specific gold-bound microtubules conjugation to antibody treated clots and HUVEC was confirmed using immune fluorescence analysis. Contrast intensities of the clots significantly increased after their treatment with antifibrin antibody and incubation with gold-bound microtubules (39 +/- 2 dB versus 26 +/- 2 dB, p < 0.001) and remained high after 20 min of ultrasound exposure (37 +/- 2 dB versus 39 +/- 2 dB, p = NS). Thus, gold-bound microtubules can specifically bind to human thrombi and to endothelial cells, providing a significant contrast effect which remains stable in the ultrasound field. This may be a promising approach to target thrombi and inflammatory active atherosclerotic plaques.

Antibodies, Monoclonal↗

PubMed2006

Microdroplet dissolution into a second-phase solvent using a micropipet technique: test of the Epstein-Plesset model for an aniline-water system.

The Epstein-Plesset model was originally derived for the dissolution of a single gas bubble in an infinite aqueous solution (Epstein, P. S.; Plesset, M. S. J. Chem. Phys. 1950, 18, 1505-1509). The micropipet manipulation technique was previously shown to test this theory on air microbubbles and air-filled lipid-coated microparticles accurately and appropriately (Duncan, P. B.; Needham, D. Langmuir 2004, 20, 2567-2578). This same theory is now tested to model liquid microdroplet dissolution in a well-defined solution environment. As presented previously for the gas-bubble system, holding a single microparticle at the end of a micropipet was not shown to affect the dissolution profile and allowed isotropic diffusion significantly, a necessary condition for the validation of the theory. Here, an aniline-water system with an initial droplet diameter of 50 microm was used as a model liquid-liquid system. A microdroplet of aniline in an aqueous solution presatureated with aniline at distinct levels was tested, as was the reverse system of a water droplet in an aniline solution. The dissolution lifetime was shown to increase with increasing medium saturation fraction according to the Epstein-Plesset time-dependent theory (including the time required to establish the stationary layer) neglecting interfacial tension. The droplet lifetime can be increased by an order of magnitude (from about 10 to 100 s) by increasing the saturation fraction from 0 to 0.9 and by another order of magnitude by increasing from 0.9 to 0.99. The technique proved to be an accurate and appropriate method to test the dissolution of single liquid microdroplets in a second liquid solution and establishes a systematic experimental and theoretical approach to the investigation of the formation of polymer and other microparticles.

Aniline Compounds↗

PubMed2006

Polymeric nano/microcapsules of liquid perfluorocarbons for ultrasonic imaging: physical characterization.

Ultrasonic imaging is a widely available, noninvasive, and cost-effective diagnostic modality, but vessels smaller than 200 mum in diameter are impossible to visualize. Commercial ultrasound contrast agents (UCAs), consisting of encapsulated gas microbubbles injected intravenously, enable only a qualitative visualization of the microvascularization for a short period of time since they are rather unstable. In a strategy to develop more stable UCAs, we designed a process to obtain nano/microcapsules with a single core of liquid perfluorocarbons within a biodegradable polymeric shell of homogeneous thickness. The polymer shell should improve the stability of the capsules as compared to UCAs stabilized by a monomolecular layer, while the acoustic impedance of the perfluorocarbons should ensure their echogenicity. These capsules have been optimized to encapsulate several liquid perfluorocarbons: perfluorohexane, perfluorodecalin, and perfluorooctyl bromide. The system is rather versatile: the mean size of the capsules can be adjusted between 70 nm and 25 microm and the thickness-to-radius ratio (T/R) can be easily modulated by simply modifying the polymer-to-perfluorocarbon ratio. T/R does not depend on the size of the capsules and is between 0.2 and 0.6. The dependence of the echogenic properties of the capsules with their size and their T/R has yet to be studied experimentally before this system can be evaluated in vivo.

Contrast Media↗

PubMed2003

Detection of resting myocardial perfusion defects by SonoVue myocardial contrast echocardiography.

BACKGROUND: SonoVue is a new microbubble contrast agent containing sulfur hexafluoride. We assessed the efficacy of SonoVue myocardial contrast echocardiography (MCE) to detect resting perfusion abnormalities. METHODS: Nineteen adult patients with a wall motion abnormality in a screening echocardiogram were studied. Each patient received up to four bolus injections of 2.0 mL SonoVue (Bracco Diagnostics, Inc.) during echocardiographic examination using either B-mode(n = 12)or power Doppler(n = 7)imaging. Each patient also had SPECT nuclear perfusion imaging performed. Segmental assessment of myocardial perfusion from SonoVue MCE images were compared with corresponding SPECT nuclear images. RESULTS: Using B-mode imaging, the mean number of views obtained with a single SonoVue injection ranged from 1.4 to 1.9, with 2 or 3 injections required for a complete examination. Ninety-four percent of segments were scored as diagnostic. Agreement between B-mode and SPECT images was 72% for segments with a perfusion defect, 86% for normal perfusion, and 80% for segments with either perfusion defect or normal perfusion (all views combined). Using power Doppler imaging, the mean number of views obtained with a single SonoVue injection ranged from 1.0 to 1.3, with 2 to 4 injections required for a complete examination. Sixty-eight percent of segments were scored as diagnostic. Agreement between power Doppler and SPECT images was 67% for perfusion defects, 53% for segments with normal perfusion, and 59% for segments with either perfusion defect or normal perfusion (all views combined). CONCLUSIONS: SonoVue MCE has the potential to assess myocardial perfusion at rest. B-mode imaging was more accurate than power Doppler imaging when compared with SPECT nuclear imaging.

Aged↗

PubMed2006

Targeting mucosal addressin cellular adhesion molecule (MAdCAM)-1 to noninvasively image experimental Crohn's disease.

BACKGROUND & AIMS: Inflammatory bowel disease (IBD) is the second most common chronic inflammatory disorder worldwide; however, a noninvasive means of accurately assessing the severity and extent of intestinal inflammation is currently not available. The aim of the present study was to develop a noninvasive imaging modality to detect and evaluate ileitis in SAMP1/YitFc (SAMP) mice. METHODS: An image-enhancing ultrasound (US) contrast agent, consisting of encapsulated gaseous microbubbles (MB), was developed specifically to bind mucosal addressin cellular adhesion molecule-1 (MAdCAM-1), a mucosal-restricted addressin up-regulated during gut inflammation. MAdCAM-1-targeted MB (MB(M)) were tested for binding specificity on MAdCAM-1 protein and tumor necrosis factor (TNF)-stimulated SVEC4-10 endothelial cells using an in vitro flow chamber assay and for their ability to detect and quantify ileitis by intravital microscopy and transabdominal US. RESULTS: Under in vitro flow conditions, a 100-fold increase in MB(M) binding was observed on MAdCAM-1 protein compared with nonspecific MB (P < .001). TNF-stimulated endothelial cells bound significantly more MB(M) vs nonspecific MB (P < .001), which was abrogated after preincubation with anti-MAdCAM-1 antibodies (P < .001). In vivo, MB(M) specifically accumulated in focal areas of ileal inflammation and produced stronger acoustic echoes, measured by average video intensity, in SAMP vs uninflamed AKR mice (P < .001) or SAMP given nonspecific MB (P < .001). MB(M)-specific video intensity showed a strong positive correlation with total ileal inflammatory scores (R2 = 0.92). CONCLUSIONS: We have developed a novel intravascular US contrast agent targeting MAdCAM-1 that specifically detects and quantifies intestinal inflammation in experimental ileitis, providing the potential for a reliable, noninvasive means to diagnose and monitor disease in patients with IBD.

Animals↗

PubMed2006

[Renal transplant: color duplex ultrasound and contrast-enhanced ultrasound in the evaluation of the early postoperative phase and surgical complications].

Contrast ultrasound is a promising and straightforward method that is superior to established sonographic techniques such as conventional B-mode scanning which is used for volume measurement and hematoma demonstration. Color Doppler is important for the evaluation of rejection, the detection of perfusion defects, and complete vascularization in the diagnostic evaluation of kidney grafts. Moreover, contrast US has the potential for tumor characterization in transplanted kidneys. A single examination by contrast ultrasound can answer a variety of questions with respect to the early postoperative phase and chronic damage. New applications of contrast US will arise from the further technical development of ultrasound equipment. The rapid technical advances seen in recent years have been followed by the introduction of new software tools for the analysis of raw datasets or the improved visualization of microbubbles at very low energy. Initial studies show that efficient and early diagnosis of rejection is possible. Surgical complications like perfusion defects or hematoma can also be identified.

Animals↗

PubMed2005

Ultrasound enhances gene delivery of human factor IX plasmid.

Delivery of plasmid DNA can be enhanced by treatment with ultrasound (US); acoustic cavitation appears to play an important role in the process. Ultrasound contrast agents (UCAs; stabilized microbubbles) nucleate acoustic cavitation, and lower the acoustic pressure threshold for inertial cavitation occurrence. Fifty micrograms of a liver-specific, high-expressing human factor IX plasmid, pBS-HCRHP-FIXIA, mixed with UCA or phosphate-buffered saline was delivered to mouse livers by intrahepatic injection, with simultaneous exposure to 1 MHz-pulsed US using various acoustic protocols. Variable pulse duration (PD) at constant treatment time, pulse repetition frequency, and an acoustic peak negative pressure amplitude of 1.8 MPa produced 2- to 13-fold enhancements in hFIX gene expression, but PD was not a strong determinant. In contrast, a dose-response relationship was demonstrated for the peak negative pressure (P-), with significant enhancement of gene transduction at P- >/= 2 MPa. Up to 63 ng/ml (approaching the therapeutic range for treating hemophilia patients) could be achieved by transducing one liver lobe at 4-MPa P-, corresponding to a 66- fold increment relative to treatment with naked DNA alone. Under the same conditions, mouse livers could also be transduced with a GFP plasmid. Histology showed transient liver damage caused by intrahepatic injection and US exposure at 4-MPa P-; however, the damage was repaired in a few days. We conclude that therapeutic US in combination with UCA has the potential to promote safe and efficient nonviral gene transfer of hFIX for the treatment of hemophilia.

Alanine Transaminase↗

PubMed2006

Contrast echocardiography for the assessment of myocardial viability.

PURPOSE OF REVIEW: The availability of an accurate, non-invasive method for distinguishing viable from irreversibly damaged myocardium, after acute myocardial infarction or in chronic coronary artery disease, is important in clinical decision making. Such a tool would enable physicians to identify patients most likely to benefit from revascularization strategies in patients with coronary artery disease and left ventricular dysfunction. Myocardial contrast echocardiography is a new technique that utilizes acoustically active gas-filled microspheres (microbubbles), which remain exclusively in the intravascular space and allow the simultaneous assessment of global and regional myocardial structure, function, and perfusion. An increasing body of data supports its role in assessing myocardial viability and predicting the recovery of function. RECENT FINDINGS: Myocardial contrast echocardiography accurately differentiates 'stunning' from necrosis, delineates transmural extent of infarction, predicts recovery of regional and global left ventricular systolic function in the recuperative phase, identifies patients at high risk of left ventricular remodelling, and provides incremental viability data when performed in conjunction with low-dose dobutamine echocardiography. SUMMARY: Technological advances have positioned myocardial contrast echocardiography as a safe, practical bedside technique for the evaluation of myocardial viability. It has comparable accuracy with other non-invasive imaging techniques, such as dobutamine stress echocardiography, radionuclide scintigraphy and cardiac magnetic resonance imaging.

Coronary Artery Disease↗