比较脂质微泡与聚合物超声造影剂的微循环流变学

目的 探讨脂质微泡与高分子聚合物超声造影剂在大鼠肠系膜微循环中的流变学特征。方法 对10只大鼠经股静脉分别注射DiI标记的脂质微泡和高分子聚合物超声造影剂,通过倒置荧光显微镜观察两种不同造影剂在大鼠肠系膜微循环中的运动情况;比较注射前后小动脉、小静脉及毛细血管内径的变化,测定红细胞与两种造影剂在微循环内的流速。结果 注射后两种造影剂在大鼠肠系膜微循环内均可随血流移动,仅见少量脂质微泡短暂滞留。注射造影剂前后小动脉、小静脉及毛细血管内径无明显改变(P>0.05);两种造影剂在微循环内的流速与红细胞相似,差异无统计学意义(P>0.05)。结论 脂质微泡和高分子聚合物超声造影剂具有与红细胞相似的微循环流变学特征,均可作为红细胞示踪剂。     

Microvascular behavior and effects of sonazoid microbubbles in the cremaster muscle of rats after local administration.

OBJECTIVE: The purpose of this study was to observe Sonazoid perfluorobutane microbubbles (GE Healthcare, Amersham, Buckinghamshire, England) in and their effects on the cremaster capillary microcirculation of rats. METHODS: Sonazoid (0.3 x 10(9) microbubbles in 0.5 mL) was observed by intravital microscopy in the cremaster muscle after retrograde administration into the femoral artery of 6 animals. Microbubble and microvessel diameters and blood flow velocities and the overall mean and SD of the 1-minute volume flow through the microscopic field were calculated from the 2 to 4 capillaries observed in the field of each animal. Fluorescein isothiocyanate-dextran leakage was used to assess extravasation after microbubble passage. RESULTS: seconds, respectively, before they were released and capillary flow normalized. No microbubble size changes, damming, or coalescence of bubbles and no changes in microvessel diameter or microvascular blood flow velocities, volume flow, or perfusion heterogeneity occurred during or after the passage of the Sonazoid suspension or the vehicle. No fluorescein isothiocyanate-dextran leakage was observed. CONCLUSIONS: The passage of Sonazoid bubbles at concentrations higher than those expected after intravenous administration of the Sonazoid did not durably impair microvascular perfusion, structural integrity, or macromolecular retention in the rat cremaster muscle. The duration of discrete capillary obstructions was short and in all cases comparable with that of naturally occurring leukocyte plugging.     

Capillary Hemorrhage Induced by Contrast-Enhanced Diagnostic Ultrasound in Rat Intestine

Contrast-enhanced diagnostic ultrasound (CEDUS) can lead to microvascular injury and petechial hemorrhage by the cavitational mechanism of ultrasonic bioeffects. Capillary hemorrhage has been noted in the heart and kidney, which are common targets of CEDUS examination. CEDUS has also become useful for monitoring intestinal inflammation. In the 1990s, the risk of intestinal microvascular hemorrhage was investigated both for incidental exposure by lithotripter shockwaves and for contrast agent microbubbles acting as cavitation nuclei with laboratory pulsed ultrasound systems. This study was initiated to update the risk assessment for intestine exposed to diagnostic imaging simulating CEDUS. The abdomens of anesthetized rats were scanned by a 1.6 MHz phased array probe during infusion of microbubble suspensions simulating Definity ultrasound contrast agent. Dual image frames were triggered intermittently, and the output power was varied to assess the exposure response. Petechiae counts in small intestine mucosa and muscle layers increased with increasing trigger interval from 2 s to 10 s, indicative of a slow refill after microbubble destruction. The counts increased with increasing output above a threshold of 1.4 MPa peak rarefactional pressure amplitude. Petechiae were also seen in Peyer's patches, and occult blood was detected in many affected segments of intestine. These results are consistent with early laboratory pulsed-ultrasound results.     

Acoustic Characterization and Pharmacokinetic Analyses of New Nanobubble Ultrasound Contrast Agents

In contrast to the clinically used microbubble ultrasound contrast agents, nanoscale bubbles (or nanobubbles) may potentially extravasate into tumors that exhibit more permeable vasculature, facilitating targeted molecular imaging and drug delivery. Our group recently presented a simple strategy using the non-ionic surfactant Pluronic as a size control excipient to produce nanobubbles with a mean diameter of 200 nm that exhibited stability and echogenicity on par with microbubbles. The objective of this study was to carry out an in-depth characterization of nanobubble properties as compared with Definity microbubbles, both in vitro and in vivo. Through use of a tissue-mimicking phantom, in vitro experiments measured the echogenicity of the contrast agent solutions and the contrast agent dissolution rate over time. Nanobubbles were found to be more echogenic than Definity microbubbles at three different harmonic frequencies (8, 6.2 and 3.5 MHz). Definity microbubbles also dissolved 1.67 times faster than nanobubbles. Pharmacokinetic studies were then performed in vivo in a subcutaneous human colorectal adenocarcinoma (LS174T) in mice. The peak enhancement and decay rates of contrast agents after bolus injection in the liver, kidney and tumor were analyzed. No significant differences were observed in peak enhancement between the nanobubble and Definity groups in the three tested regions (tumor, liver and kidney). However, the decay rates of nanobubbles in tumor and kidney were significantly slower than those of Definity in the first 200-s fast initial phase. There were no significant differences in the decay rates in the liver in the initial phase or in three regions of interest in the terminal phase. Our results suggest that the stability and acoustic properties of the new nanobubble contrast agents are superior to those of the clinically used Definity microbubbles. The slower washout of nanobubbles in tumors suggests potential entrapment of the bubbles within the tumor parenchyma.     

Quantitative Guidelines for the Prediction of Ultrasound Contrast Agent Destruction During Injection

Experiments and theory were undertaken on the destruction of ultrasound contrast agent microbubbles on needle injection, with the aim of predicting agent loss during in vivo studies. Agents were expelled through a variety of syringe and needle combinations, subjecting the microbubbles to a range of pressure drops. Imaging of the bubbles identified cases where bubbles were destroyed and the extent of destruction. Fluid-dynamic calculations determined the pressure drop for each syringe and needle combination. It was found that agent destruction occurred at a critical pressure drop that depended only on the type of microbubble. Protein-shelled microbubbles (sonicated bovine serum albumin) were virtually all destroyed above their critical pressure drop of 109 ± 7 kPa Two types of lipid-shelled microbubbles were found to have a pressure drop threshold above which more than 50% of the microbubbles were destroyed. The commercial lipid-shelled agent Definity was found to have a critical pressure drop for destruction of 230 ± 10 kPa; for a previously published lipid-shelled agent, this value was 150 ± 40 kPa. It is recommended that attention to the predictions of a simple formula could preclude unnecessary destruction of microbubble contrast agent during in vivo injections. This approach may also preclude undesirable release of drug or gene payloads in targeted microbubble therapies. Example values of appropriate injection rates for various agents and conditions are given.     

微泡声学造影剂气体构成对二次谐波显像的作用

目的探讨二次谐波成像条件下改变微泡造影剂的气体构成是否能够增强经静脉注射后的心肌显像效果。方法对１０条开胸犬经静脉注射含有不同气体的声振右旋糖酐白蛋白微泡造影剂ＲＡ（空气,ｒｏｏｍａｉｒ）、ＳＦ６（六氟化硫,ｓｕｌｆｕｒｈｅｘａｆｌｕｏｒｉｄｅ）、ＦＸ系列（含有氟碳气体Ｃ３Ｆ８、Ｃ４Ｆ１０、Ｃ５Ｆ１２）。二次谐波显像条件下取左心室短轴切面观,观察心肌造影效果。结果含有氟碳气体的微泡造影剂经静脉注射后二次谐波显像下产生强烈的心肌显影,心肌声学密度分别为（１４．７２±２．７）ｄＢ（ＦＸ３３０）、（１４．３±２．４ｄＢ）（ＦＸ４３０）、（１３．７８±２．２４）ｄＢ（ＦＸ５３０）;氟硫气体仅存在轻微的心肌显像［（６．２４±１．５８）ｄＢ］,但心腔显影强烈［（２９．４８±６．０２）ｄＢ］,空气造影剂经静脉注射后几乎不产生心肌显影［（２．５３±０．７８）ｄＢ］,心腔内造影剂亦较弱［（１１．３±４．９６）ｄＢ］。结论不同气体构成的微泡声学造影剂二次谐波显像效果差异显著。氟碳气体声振右旋糖酐白蛋白是较好的经静脉声学造影剂。     

Accelerated Clearance of Ultrasound Contrast Agents Containing Polyethylene Glycol is Associated with the Generation of Anti-Polyethylene Glycol Antibodies

Emerging evidence suggests that the immune system can recognize polyethylene glycol (PEG), leading to the accelerated blood clearance (ABC) of PEGylated particles. Our aim here was to study the generation of anti-PEG immunity and changes in PEGylated microbubble pharmacokinetics during repeated contrast-enhanced ultrasound imaging in rats. We administered homemade PEGylated microbubbles multiple times over a 28-d period and observed dramatically accelerated clearance (4.2?×?reduction in half-life), which was associated with robust anti-PEG IgM and anti-PEG IgG antibody production. Dosing animals with free PEG as a competition agent before homemade PEGylated microbubble administration significantly prolonged microbubble circulation, suggesting that ABC was largely driven by circulating anti-PEG antibodies. Experiments with U.S. Food and Drug Administration-approved Definity microbubbles similarly resulted in ABC and the generation of anti-PEG antibodies. Experiments repeated with non-PEGylated Optison microbubbles revealed a slight shift in clearance, indicating that immunologic factors beyond anti-PEG immunity may play a role in ABC, especially of non-PEGylated agents.     

载诺帝脂质微泡的制备及特性的实验研究

目的 制备载诺帝(去甲二氢愈创木酸)脂质微泡并测定其包封率、载药量及观察其体内超声显像效果.方法 采用机械振荡法制备载诺帝脂质微泡,测定其粒径大小、分布和Zeta电位、包封率、载药量;超声造影观察其在兔肝内的显像效果.结果 载药脂质微泡的浓度为(2.53±0.52)×109个/ml,粒径为(2.61±0.32)μm,Zeta电位为+(17.52±2.04)mV;脂质微泡诺帝的包封率(27.1±2.01)%,载药量为(10.9±0.90)%;微泡经外周静脉注射后,兔肝可见良好、持续的增强显像效果.结论 采用机械振荡法可以成功制备携带诺帝的脂质微泡,微泡可以通过肺血管床,符合静脉注射要求,在家兔体内获得了良好的显像效果.     

Microbubble Type and Distribution Dependence of Focused Ultrasound-Induced Blood–Brain Barrier Opening

Focused ultrasound, in the presence of microbubbles, has been used non-invasively to induce reversible blood–brain barrier (BBB) opening in both rodents and non-human primates. This study was aimed at identifying the dependence of BBB opening properties on polydisperse microbubble (all clinically approved microbubbles are polydisperse) type and distribution by using a clinically approved ultrasound contrast agent (Definity microbubbles) and in-house prepared polydisperse (IHP) microbubbles in mice. A total of 18 C57 BL/6 mice (n = 3) were used in this study, and each mouse was injected with either Definity or IHP microbubbles via the tail vein. The concentration and size distribution of activated Definity and IHP microbubbles were measured, and the microbubbles were diluted to 6 × 10⁸/mL before injection. Immediately after microbubble administration, mice were subjected to focused ultrasound with the following parameters: frequency = 1.5 MHz, pulse repetition frequency = 10 Hz, 1000 cycles, in situ peak rarefactional acoustic pressures = 0.3, 0.45 and 0.6 MPa for a sonication duration of 60 s. Contrast-enhanced magnetic resonance imaging was used to confirm BBB opening and allowed for image-based analysis. Permeability of the treated region and volume of BBB opening did not significantly differ between the two types of microbubbles (p > 0.05) at peak rarefractional acoustic pressures of 0.45 and 0.6 MPa, whereas IHP microbubbles had significantly higher permeability and opening volume (p < 0.05) at the relatively lower pressure of 0.3 MPa. The results from this study indicate that microbubble type and distribution could have significant effects on focused ultrasound-induced BBB opening at lower pressures, but less important effects at higher pressures, possibly because of the stable cavitation that governs the former. This difference may have become less significant at higher pressures, where inertial cavitation typically occurs.     

Monodisperse versus Polydisperse Ultrasound Contrast Agents: In Vivo Sensitivity and safety in Rat and Pig

Recent advances in the field of monodisperse microbubble synthesis by flow focusing allow for the production of foam-free, highly concentrated and monodisperse lipid-coated microbubble suspensions. It has been found that in vitro, such monodisperse ultrasound contrast agents (UCAs) improve the sensitivity of contrast-enhanced ultrasound imaging. Here, we present the first in vivo study in the left ventricle of rat and pig with this new monodisperse bubble agent. We systematically characterize the acoustic sensitivity and safety of the agent at an imaging frequency of 2.5 MHz as compared with three commercial polydisperse UCAs (SonoVue/Lumason, Definity/Luminity and Optison) and one research-grade polydisperse agent with the same shell composition as the monodisperse bubbles. The monodisperse microbubbles, which had a diameter of 4.2 μm, crossed the pulmonary vasculature, and their echo signal could be measured at least as long as that of the polydisperse UCAs, indicating that microfluidically formed monodisperse microbubbles are stable in vivo. Furthermore, it was found that the sensitivity of the monodisperse agent, expressed as the mean echo power per injected bubble, was at least 10 times higher than that of the polydisperse UCAs. Finally, the safety profile of the monodisperse microbubble suspension was evaluated by injecting 400 and 2000 times the imaging dose, and neither physiologic nor pathologic changes were found, which is a first indication that monodisperse lipid-coated microbubbles formed by flow focusing are safe for in vivo use. The more uniform acoustic response and corresponding increased imaging sensitivity of the monodisperse agent may boost emerging applications of microbubbles and ultrasound such as molecular imaging and therapy.     

Correlation between estimates of tumor perfusion from microbubble contrast-enhanced sonography and dynamic contrast-enhanced magnetic resonance imaging.

OBJECTIVE: We compared measurements of tumor perfusion from microbubble contrast-enhanced sonography (MCES) and dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) in an animal tumor model. METHODS: Seven mice were implanted with Lewis lung carcinoma cells on their hind limbs and imaged 14 days later with a Philips 5- to 7-MHz sonography system (Philips Medical Systems, Andover, MA) and a Varian 7.0-T MRI system (Varian, Inc, Palo Alto, CA). For sonographic imaging 100 microL of a perfluoropropane microbubble contrast agent (Definity; Bristol-Myers Squibb Medical Imaging, Billerica, MA) was injected and allowed to reach a pseudo steady state, after which a high-mechanical index pulse was delivered to destroy the microbubbles within the field of view, and the replenishment of the microbubbles was imaged for 30 to 60 seconds. The MRI included acquisition of a T(10) map and 35 serial T(1)-weighted images (repetition time, 100 milliseconds; echo time, 3.1 milliseconds; alpha, 30 degrees ) after the injection of 100 microL of 0.2-mmol/kg gadopentetate dimeglumine (Magnevist; Berlex, Wayne, NJ). Region-of-interest and voxel-by-voxel analyses of both data sets were performed; microbubble contrast-enhanced sonography returned estimates of microvessel cross-sectional area, microbubble velocity, and mean blood flow, whereas DCE-MRI returned estimates of a perfusion-permeability index and the extravascular extracellular volume fraction. RESULTS: Comparing similar regions of tumor tissue seen on sonography and MRI, region-of-interest analyses revealed a strong (r(2) = 0.57) and significant relationship (P < .002) between the estimates of perfusion obtained by the two modalities. CONCLUSIONS: Microbubble contrast-enhanced sonography can effectively depict intratumoral heterogeneity in preclinical xenograft models when voxel-by-voxel analysis is performed, and this analysis correlates with similar DCE-MRI measurements.     

Quantification of microbubble destruction of three fluorocarbon-filled ultrasonic contrast agents

The assessment of myocardial blood velocity using ultrasonic contrast agents is based on the premise that the vast majority of contrast microbubbles within a myocardial region can be destroyed by an acoustic pulse of sufficient magnitude. Determination of the period of time after destruction that a region of myocardium needs to reperfuse may be used to assess myocardial blood velocity. In this study, we investigated the acoustic pressure sensitivity of three solutions of intravenous fluorocarbon-filled contrast agents and the magnitude of acoustic pulse required to destroy the contrast agent microbubbles. A novel tissue-mimicking phantom was designed and manufactured to investigate the relationships between mean integrated backscatter, incident acoustic pressure and number of frames of insonation for three fluorocarbon-filled contrast agents (Definity(R), Optison(R), and Sonazoid(R), formerly NC100100). Using a routine clinical ultrasound (US) scanner (Acuson XP-10), modified to allow access to the unprocessed US data, the contrast agents were scanned at the four acoustic output powers. All three agents initially demonstrated a linear relationship between mean integrated backscatter and number of frames of insonation. For all three agents, mean integrated backscatter decreased more rapidly at higher acoustic pressures, suggesting a more rapid destruction of the microbubbles. In spite of the fact that there was no movement of microbubbles into or out of the beam, only the results from Definity(R) suggested that a complete destruction of the contrast agent microbubbles had occurred within the total duration of insonation in this study.     

Differences in definity and optison microbubble destruction rates at a similar mechanical index with different real-time perfusion systems.

The purpose of this study was to determine microbubble responses to different pulse sequence schemes that exist on low mechanical index (MI) real-time perfusion imaging systems using either intravenous albumin-coated (Optison) or lipid-encapsulated (Definity) microbubbles. A tissue-mimicking phantom was created that permitted insonation of microbubbles at 3 cm (near field) and 9 cm (far field) from the diagnostic transducer face. Differences in effluent microbubble concentration were measured after they passed through vessels being insonified with pulse sequence schemes that transmitted alternating polarity (pulse inversion Doppler), alternating amplitude (power modulation), or both (contrast pulse sequencing) at a similar MI, frame rate, and transmit frequency. Normalized contrast signal intensity within a recirculating chamber was also measured in the near and far field. Pulse inversion Doppler produced less initial normalized contrast signal intensity and greater destruction rates than amplitude varying pulse sequence schemes like power modulation or contrast pulse sequencing at both the 0.1- and 0.2-MI settings. These differences indicate that the same MI setting on different real-time perfusion imaging techniques will produce different microbubble responses.     

Subpleural microvascular flow velocities and shear rates in normal and septic mechanically ventilated rats

Changes in pulmonary microhemodynamics are important variables in a large variety of pathological processes. We used in vivo fluorescent videomicroscopy of the subpleural microvasculature in mechanically ventilated rats to directly monitor microvascular flow velocity (FV) and shear rate in pulmonary arterioles, capillaries, and venules in healthy rats and in septic rats 20 h after cecal ligation and puncture (CLP). Observations were made through a small thoracotomy after injection of fluorescent microspheres (D = 1 microm) into the systemic circulation. The FVs were calculated off-line by frame-by-frame measurements of the distance covered by individual microspheres per unit of time. In healthy rats, inspiratory FV were 1322 +/- 142 microm/s in subpleural arterioles and 599 +/- 25 microm/s in capillaries. The highest FV was found in venules (1552 +/- 132 microm/s). The calculated shear rates were 547 +/- 62/s in arterioles and 619 +/- 19/s in capillaries. The highest shear rates were detected in venules (677 +/- 59/s). No significant changes in FV and shear rates were observed throughout the 1-h observation period in any of the microvascular compartments. Pulmonary microvascular FV and shear rates found in sham-operated rats in the CLP experiments were not significantly different from values of healthy rats. The CLP caused a significant increase in leukocyte sequestration in the lungs and a mean of 27% to 34% decrease in FV in all sections of the pulmonary microvasculature (P < 0.001 in capillaries and P < 0.05 in venules). Also, CLP caused a 23% decrease in capillary shear rate that reached only borderline statistical significance (P < 0.06) and a significant 35% decrease in mean shear rate in venules (P < 0.05). Fluorescent videomicroscopy is offered as a stable and reproducible method for in vivo determinations of pulmonary microhemodynamics in clinically relevant models of sepsis.     

Adherence of albunex to an apical left ventricular thrombus.

A previously unrecognized left ventricular thrombus developed a distinct echogenic rim after intravenous injection of albumin microbubbles despite no visible opacification of the left-sided chambers. Absence of visible left ventricular opacification suggests a low density of microbubbles crossing the pulmonary vasculature and a high affinity of the microbubbles for the thrombus or its endothelial surface. These findings support previous observations that albumin microbubbles demonstrate transient adherence to abnormal endothelium.     

Therapeutic Uses of Contrast Microbubbles

Purpose of Review

The potential for non-invasive targeted delivery of therapeutic agents and targeted thrombus dissolution using diagnostic ultrasound (DUS) and intravenous microbubbles or droplets is an emerging technology that will change diagnostic ultrasound systems into therapeutic devices.

Recent Findings

Targeted ultrasound destruction of microbubbles which carry either DNA or inhibitor RNA sequences have been utilized to both promote microvascular regeneration in ischemic myocardium and skeletal muscle and inhibit vascular growth in murine models of carcinoma. Targeted ultrasound microbubble cavitation has been utilized to improve ischemic limb blood flow via nitric oxide pathways and to induce targeted coronary and microvascular recanalization in large animal models of acute ST segment elevation myocardial infarction (STEMI).

Summary

Initial clinical trials utilizing DUS and commercially available microbubbles in acute STEMI patients prior to, and after, emergent percutaneous coronary intervention have demonstrated the feasibility and efficacy of this approach in preserving microvascular flow.

     

Assessment of the Superharmonic Response of Microbubble Contrast Agents for Acoustic Angiography as a Function of Microbubble Parameters

Acoustic angiography is a superharmonic contrast-enhanced ultrasound imaging technique that enables 3-D high-resolution microvascular visualization. This technique utilizes a dual-frequency imaging strategy, transmitting at a low frequency and receiving at a higher frequency, to detect high-frequency contrast agent signatures and separate them from tissue background. Prior studies have illustrated differences in microbubble scatter dependent on microbubble size and composition; however, most previously reported data have utilized a relatively narrow frequency bandwidth centered around the excitation frequency. To date, a comprehensive study of isolated microbubble superharmonic responses with a broadband dual-frequency system has not been performed. Here, the superharmonic signal production of 14 contrast agents with various gas cores, shell compositions, and bubble diameters at mechanical indices of 0.2 to 1.2 was evaluated using a transmit 4 MHz, receive 25 MHz configuration. Results indicate that perfluorocarbon cores or lipid shells with 18- or 20-carbon acyl chains produce more superharmonic signal than sulfur hexafluoride cores or lipid shells with 16-carbon acyl chains, respectively. As microbubble diameter increases from 1 to 4 µm, superharmonic generation decreases. In a comparison of two clinical agents, Definity and Optison, and one preclinical agent, Micromarker, Optison produced the least superharmonic signal. Overall, this work suggests that microbubbles around 1 μm in diameter with perfluorocarbon cores and longer-chained lipid shells perform best for superharmonic imaging at 4 MHz. Studies have found that microbubble superharmonic response follows trends different from those described in prior studies using a narrower frequency bandwidth centered around the excitation frequency. Future work will apply these results in vivo to optimize the sensitivity of acoustic angiography.     

Effects of transcranial ultrasound and intravenous microbubbles on blood brain barrier permeability in a large animal model

We sought to determine whether transtemporal-applied 1-MHz ultrasound-induced microbubble destruction may be a safe method of transiently altering blood brain barrier (BBB) permeability for drug delivery in a large animal model. Endothelial cells are an integral component of the BBB but also prevent passage of potentially therapeutic drugs. Ultrasound-mediated destruction (UMD) of microbubbles has been shown to disrupt this barrier in small animals when ultrasound is delivered through bone windows. However, the effects of temporal bone attenuation and scattering in a large animal may limit the clinical application of such a technique. Twenty-four pigs were studied. One-MHz pulsed-wave ultrasound at 2.0 W/cm(2) (20% duty cycle) across the temporal bone was applied for 30 min after intravenous injections of either albumin-coated perfluorocarbon microbubble (PESDA, 8 pigs), lipid-encapsulated perfluorocarbon microbubbles (LEMB, 8 pigs) or ultrasound alone (8 pigs). BBB leak was quantified at 30 and 120 min after insonation using Evans blue. Serial magnetic resonance imaging (MRI) was performed in nine of the pigs (3 for each group) to quantify Gadolinium leak within the parenchyma. Peak negative pressures decreased ten-fold when ultrasound was transmitted across the pig temporal bone. Despite this, spectrophotometric analysis showed that both IV LEMB and PESDA combined with transtemporal ultrasound resulted in a significant increase in Evans blue extravasation across BBB of the treated side at 30 min after insonation (p < 0.001; compared with ultrasound alone) but not at 120 min. There was significant retention of Gadolinium within the insonified parenchyma at 60 and 90 min after insonation, but not at 120 min. Oxygen saturation and arterial pressures were not changed after any microbubble injection. Intravenous microbubbles, combined with transtemporal ultrasound, can transiently increase BBB permeability in a large animal. This induced opening of BBB is reversible and may be a safe noninvasive method of achieving drug or gene delivery across the BBB.     

低能量脉冲式超声联合微泡对兔VX2肿瘤微循环的阻断作用

目的探讨低能量脉冲式超声联合微泡对兔VX2肿瘤微循环的阻断作用及其病理机制。方法将36只皮下VX2荷瘤兔随机平均分成3组:超声微泡组注入0.2ml/kg体质量微泡5ml,并辅以超声辐照10min;单纯超声组注入生理盐水5ml,辐照10min;单纯微泡组仅注入0.2ml/kg体质量微泡5ml,不进行超声辐照。CEUS观察各组治疗前、治疗后0、30min、60min时血流灌注情况,比较各时间点的灌注面积。治疗后即刻随机选取各组6只荷瘤兔处死,完整切取肿瘤,行病理学检查。结果超声微泡组治疗后即刻肿瘤血流灌注完全消失,灌注面积为0,但30min及60min后灌注有所恢复,各时间点治疗后灌注面积显著大于治疗前(均P<0.05);大体病理检查见肿瘤微血管扩张、管壁结构崩解,弥漫性充血、出血和肿瘤组织水肿,局部血肿,形成血栓等。单纯超声组及单纯微泡组治疗前、后造影剂灌注面积无差异,肿瘤内部未见出血、水肿等。结论低能量超声联合微泡能够阻断肿瘤微循环,可能是由于空化效应导致血管壁损伤,组织水肿对局部肿瘤血液循环产生阻力,从而阻断肿瘤血液循环。     

Efficacy of Sonothrombolysis Using Acoustically Activated Perflutren Nanodroplets versus Perflutren Microbubbles

Nanoscale-diameter liquid droplets from commercially available microbubbles may optimize thrombus permeation and subsequent thrombus dissolution (TD). Thrombi were made using fresh porcine arterial whole blood and placed in an in vitro vascular simulation. A diagnostic ultrasound probe in contact with a tissue-mimicking phantom tested intermittent high-mechanical-index (HMI) fundamental multipulse (focused ultrasound [FUS], 1.8 MHz) versus harmonic single-pulse (HUS, 1.3 MHz) modes during a 10-min infusion of Definity nanodroplets (DNDs), Definity microbubbles (DMBs) or saline. The ability of FUS and intravenous DNDs to improve epicardial and microvascular flow was then tested in four pigs with left anterior descending thrombotic occlusion. Sixty in vitro thrombi were tested, 20 in each group. Percentage TD was significantly higher for DND-treated thrombi than DMB-treated thrombi and controls (DNDs: 42.4%, DMBs: 26.7%, saline: 15.0%; p < 0.0001 vs. control). The highest %TD was seen in the HMI FUS-treated DND group (51 ± 17% TD). HMI FUS detected droplet activation within the risk area in three of four pigs with left anterior descending thrombotic occlusion and re-canalized the epicardial vessel in two. DNDs with intermittent diagnostic HMI ultrasound resulted in significantly more intravascular TD than DMBs and have potential for coronary and risk area thrombolysis.