携双抗体纳米微泡对卵巢癌细胞增殖活性的影响

背景：免疫治疗可通过多种途径增强抗肿瘤免疫反应，联合免疫治疗是一个更好的选择。超声靶向微泡破坏技术可将药物、基因、抗体和细胞因子直接输送到免疫细胞的细胞质中，进一步增强免疫应答。然而，通过超声靶向微泡破坏技术将携趋化因子受体4抗体和细胞程序性死亡配体1抗体双靶向纳米微泡应用于卵巢癌的治疗尚未见报道。目的：探讨超声辐照携趋化因子受体4抗体和程序性死亡配体1抗体双靶向纳米微泡对卵巢癌细胞增殖、迁移的影响。方法：对IOSE-80正常卵巢上皮细胞及SKOV3、CAOV3卵巢癌细胞进行培养及扩增，采用双标记荧光免疫法对3种细胞中的趋化因子受体4和细胞程序性死亡配体1蛋白进行共定位，蛋白质印迹法检测3种细胞中趋化因子受体4和程序性死亡配体1蛋白相对表达量，并筛选出实验细胞。制备携不同配体的靶向纳米微泡后，即单纯的纳米微泡、携趋化因子受体4抗体的纳米微泡、携趋化因子受体4和程序性死亡配体1抗体的纳米微泡。取对数生长期的SKOV3卵巢癌细胞，分6组处理：A组加入McCoy’s 5A培养基，B组加入含基质细胞衍生因子1的McCoy’s5A培养基，C组加入单纯的纳米微泡溶液与含基质细胞衍生因子1的McCo...     

高分子材料超声对比剂的制备及显影特征

背景：目前所用的超声对比剂均为内含不同气体成分的微气泡,其外壳材料多数为表面活性剂类、人血蛋白质类、脂类等。随着高分子化学的发展,高分子材料对比剂成为超声对比剂研究领域的热点。 目的：探讨各种超声对比剂制备中遇到的困难以及解决方法,从而最终寻找合理的高分子材料超声对比剂。 方法：采用电子检索的方式,在万方数据库(http://www.wanfangdata.com.cn/)中检索2005-01/2010-12有关高分子材料应用于超声造影方面的研究文章,关键词为“高分子材料,超声,对比剂”。排除重复研究、普通综述或Meta分析类文章,筛选纳入26篇文献进行评价。 结果与结论：近年来随着高分子科学与多学科融合的分子医学的兴起和快速发展,显像对比剂受到了越来越广泛的关注。高分子材料超声对比剂由于具有好的生物相容性,粒径大小均匀,良好的抗压性能,较长的显影持续时间等特点,已成为目前研究的热点。其中靶向微泡对比剂经静脉注射可到达特定靶区,低功率超声作用下可提高局部组织显影的分辨率。携带治疗药物或基因的靶向微泡对比剂在低频(1 MHz)超声作用下可以产生瞬态空化效应,迫使细胞膜的通透性增加,从而有效提高了药物或基因的转染率。如今,靶向微泡携抗肿瘤药物联合超声作用正逐渐成为治疗肿瘤的一种新模式,是近期医学研究的一个热点。超声联合靶向微泡技术在临床诊断和治疗中显示出了较大的优势,但其准确的生物学机制目前医学界还未清楚,超声治疗参数需进一步优化。     

超声对比剂的材料学特点及临床应用

背景：目前临床上应用的超声对比剂均是含有不同包膜材料和气体成分的微泡对比剂,微泡对比剂的出现使超声诊断技术得到了较大的发展。 目的：探讨超声对比剂的材料学研究特点,及超声对比剂在临床疾病治疗中的应用。 方法：超声对比剂是由气体微泡和外部包裹的膜物质组成,包膜材料主要分为白蛋白、大分子脂质体、多聚体和各种表面活性剂等。超声造影是通过增强背向散射信号来成像。超声对比剂研究的发展大致分为3个阶段,造影相关技术包括二次谐波、组织特异性显像、反相脉冲谐波成像、相干造影成像技术、对比脉冲序列、能量多普勒谐波成像、间歇谐波成像技术、编码谐波成像和超声造影三维成像。 结果与结论：超声对比剂形式的不同主要是通过改变微泡包膜和气体的性质和设计来实现的。微气泡能够实现超声对比剂的显影作用,还可在药物传输上发挥功能。新型的微泡超声对比剂不仅可以提供血流灌注学信息,还可以通过靶向作用于病变组织,分析病变的发生机制,使微泡对比剂的诊断更准确。随着微泡对比剂材料学研究以及制备工艺完善,使超声对比剂具有良好的生物相容性。不仅可以用于各种状态下的特异性超声造影,还可以利用空化效应携带药物或治疗基因向目标组织转移释放。微泡造影技术具有治疗、诊断和超声成像的功能,是一种安全、高效、无创的诊断和靶向传输治疗手段。     

液态氟碳脂质微球靶向损伤心肌细胞的体外实验

采用生物素-亲和素作用实现自制液态氟碳脂质微球与损伤后心肌细胞的靶向结合。先体外培养大鼠原代心肌细胞,将培养出的心肌细胞分为TNF-α处理组和非处理组,TNF-α处理组的心肌细胞给予200ng/ml TNF-α溶液刺激。6h后两组均先后加入等量的生物素化的抗大鼠细胞间黏附分子-1(ICAM-1)单克隆抗体、链酶亲和素和自制生物素化液态氟碳脂质微球,然后用Hoechst液对两组心肌细胞核染色,最后在荧光显微镜下观察。结果显示TNF-α处理组染成蓝色的心肌细胞核周围可见大量绿色荧光微球,但非处理组蓝色的心肌细胞核周围有极少许绿色荧光微球。研究表明心肌细胞在TNF-α刺激下可产生ICAM-1炎症细胞因子,液态氟碳脂质微球联合ICAM-1单克隆抗体可通过生物素-亲和素作用实现与体外培养的大鼠损伤心肌细胞靶向连接。     

超声微泡增效移植间充质干细胞的归巢机制

背景:国内外动物实验已证实超声联合微泡能够显著增强干细胞移植治疗缺血性心血管疾病,但对其作用机制仍不明确目的:通过超声微泡体外作用于细胞,探讨超声联合微泡能够显著增强干细胞移植治疗缺血性心血管疾病的机制。方法:体外分别培养大鼠血管内皮细胞和骨髓间充质干细胞于培养板中,随机各分为对照组、超声组、超声微泡组。对照组不做干预,超声组以频率1 MHz,输出功率1 W/cm2,持续辐照90 s;超声微泡组加入5μL含氟碳气体脂质体超声微泡(约2×1011L-1),以同样超声条件作用90 s。结果与结论:超声微泡组血管内皮细胞上清液的血管内皮生长因子和基质细胞衍生因子1表达水平均比对照组显著增高(P0.05)。超声组血管内皮生长因子表达水平为与对照组无差异;而基质细胞衍生因子1为较对照组明显降低(P0.01)。骨髓间充质干细胞干预后CXCR4基因表达,超声微泡组、超声组较对照组均明显增强(P0.01),但超声微泡组和超声组无统计学差异(P0.05)。说明超声(1 MHz,1 W/cm2)联合微泡作用90 s能够促进血管内皮细胞分泌细胞因子(血管内皮生长因子和基质细胞衍生因子1),同时促进骨髓间充质干细胞CXCR4基因表达,是其增强移植干细胞归巢效应的机制之一。     

归巢因子基质细胞衍生因子1/CXCR4在角膜上的分布

背景：基质细胞衍生因子1/CXCR4在介导骨髓移植等组织器官的干细胞归巢中起着重要的作用。对于角膜干细胞移植的归巢和目前角膜上基质细胞衍生因子1/CXCR4的具体分布及含量较为少见。 目的：荧光定量PCR检测大鼠角膜组织中基质细胞衍生因子1/CXCR4基因mRNA的表达水平。 方法：取完整正常大鼠角膜组织,细分为角膜中央区,角膜旁中央及角膜缘区,用荧光定量PCR法(染料法)检测相应部位基质细胞衍生因子1/CXCR4基因mRNA的表达水平。 结果与结论：角膜中央区基质细胞衍生因子1及CXCR4基因mRNA的表达水平分别为0.213±0.015,0.189± 0.02;角膜旁中央区基质细胞衍生因子1及CXCR4基因mRNA的表达水平分别为0.529±0.077,0.285± 0.015;角膜缘区基质细胞衍生因子1及CXCR4基因mRNA的表达水平分别为0.666±0.069,0.258±0.067。结果表明,在大鼠角膜组织中,角膜中央区,周边区及边缘区相应基质细胞衍生因子1及CXCR4的基因mRNA的表达水平均存在着显著性的差异,这种差异性对于角膜缘干细胞缺乏症干细胞移植治疗中细胞的归巢及移行起着重要的作用。 中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程     

骨髓间充质干细胞定向趋化及骨修复中基质细胞衍生因子1的作用

背景：骨折愈合与聚集在骨折端的骨髓间充质干细胞的数量及功能密切相关,基质细胞衍生因子1可增强骨髓间充质干细胞的趋化功能。 目的：采用携带绿色荧光蛋白转基因骨髓间充质干细胞的骨髓嵌合体小鼠,制作左胫骨骨折模型,观察基质细胞衍生因子1对骨髓间充质细胞定向迁移的影响及其骨折修复中的作用,并初步探讨其作用机制。 方法：利用密度梯度离心法从携带绿色荧光蛋白转基因小鼠C57BL的骨髓内分离培养出携带绿色荧光蛋白的骨髓间充质干细胞;将经X射线照射后携带绿色荧光蛋白转基因的骨髓间充质干细胞与雄性小鼠的骨髓非贴壁细胞联合移植,最后建立起稳定的骨髓嵌合型小鼠模型,再建立左胫骨骨折模型。建模后分别用基质细胞衍生因子1和基质细胞衍生因子1抗体干预,并设置对照组。 结果与结论：建模后第1,3,7,14天各相应时相点骨折端的骨髓间充质干细胞数量,建模后第14,21天各相应时相点的骨痂量,建模后第28天抗折力,均为基质细胞衍生因子1组>对照组>基质细胞衍生因子1抗体组(P < 0.05);在建模后第28天基质细胞衍生因子1组骨痂量减少(P < 0.05),骨小梁融合成片,部分骨髓腔再通,对照组和基质细胞衍生因子1抗体组髓腔未通。证实,基质细胞衍生因子1 可促进骨髓间充质干细胞向骨折端迁移,具有促进骨折愈合的作用。     

加载PEDF的多聚体超声微泡研制及其特性

目的:针对血管新生类疾病,研制与色素上皮源因子（PEDF）具有最大结合率的多聚体超声微泡,并明确其理化特性。方法:首先应用声空化方法制备多聚体超声微泡;然后将PEDF按浓度分为0.4、2.0、10.0和50.0 μg /mL组,应用跨膜按梯度法包裹入脂质体,使其与超声微泡结合,进而置于荧光显微镜下观察。应用流式细胞仪检测PEDF与超声微泡的最大结合率,采用荧光分光光度法测定载药超声微泡的包封率及体外释药特性。结果:成功制备了与PEDF最大结合率为（96.14±1.21）%的多聚体超声微泡。脂质体对PEDF的包封率约为（79.20±2.31）%,体外释放浓度于微泡击破后1 min内达到峰值,持续释放10 min后浓度显著减低。结论:与PEDF具有较高结合率的多聚体超声微泡可以作为合适的药物载体,靶向治疗血管新生类疾病。     

超声微泡造影剂的发展及最新临床应用研究

目的:超声微泡造影剂经历了不同的技术发展阶段,目前靶向微泡造影剂的应用是一个重要的研究领域。方法:超声微泡造影剂可分为普通型和特殊型两类。普通超声造影剂经历了三个发展阶段,第一代为内含空气的气泡,无包膜且尺寸大;第二代内含空气,有膜包被,尺寸小;第三代内含氟碳类气体,有稳定的膜壳。靶向微泡造影剂是一类特殊造影剂,最新研究用于超声-微泡介导的靶向分子成像,如血栓、炎症显影,还可用于溶栓治疗,靶向药物或基因治疗等方面。结果:超声造影剂的稳定性不断提高,靶向微泡造影剂经静脉注射可到达特定靶区,低能超声作用下可提高局部组织显影的分辨率。携带治疗药物或基因的靶向微泡造影剂在低频(1MHz)超声作用下产生瞬态空化效应,细胞膜的通透性增加,因而有效提高了药物或基因的转染率。结论:超声联合靶向微泡技术在临床诊断和治疗中显示出了较大的优势,但其确切的生物学机制还未清楚,超声治疗参数需进一步优化。     

核酸适配体W3介导靶向乳腺癌的量子点成像

目的 利用核酸适配体W3对乳腺癌细胞的结合特异性，对乳腺癌细胞以及临床乳腺癌组织石蜡切片标本进行量子点(QDs)成像。方法 利用流式细胞测量术检测核酸适配体W3对乳腺癌细胞系的结合特异性，基于生物素与链霉亲和素的结合反应原理，通过荧光显微镜观察核酸适配体W3对乳腺癌细胞系以及临床乳腺癌患者组织标本的量子点靶向成像，并进一步分析其临床意义。结果 核酸适配体W3能特异性结合恶性程度较高的乳腺癌细胞，偶联量子点QD605形成量子点探针(W3-QDs),能够对恶性程度较高的乳腺癌细胞系以及乳腺癌组织实现靶向成像，并且具有高恶性程度的乳腺癌组织的荧光强度明显高于恶性程度低的乳腺癌组织。结论 核酸适配体W3偶联量子点后能够实现乳腺癌的靶向成像，可用于乳腺癌的早期诊断。     

Selective imaging of adherent targeted ultrasound contrast agents

The goal of ultrasonic molecular imaging is the detection of targeted contrast agents bound to receptors on endothelial cells. We propose imaging methods that can distinguish adherent microbubbles from tissue and from freely circulating microbubbles, each of which would otherwise obscure signal from molecularly targeted adherent agents. The methods are based on a harmonic signal model of the returned echoes over a train of pulses. The first method utilizes an 'image-push-image' pulse sequence where adhesion of contrast agents is rapidly promoted by acoustic radiation force and the presence of adherent agents is detected by the signal change due to targeted microbubble adhesion. The second method rejects tissue echoes using a spectral high-pass filter. Free agent signal is suppressed by a pulse-to-pulse low-pass filter in both methods. An overlay of the adherent and/or flowing contrast agents on B-mode images can be readily created for anatomical reference. Contrast-to-tissue ratios from adherent microbubbles exceeding 30 dB and 20 dB were achieved for the two methods proposed, respectively. The performance of these algorithms is compared, emphasizing the significance and potential applications in ultrasonic molecular imaging.     

In vivo ultrasound visualization of non-occlusive blood clots with thrombin-sensitive contrast agents

The use of microbubbles as ultrasound contrast agents is one of the primary methods to diagnose deep venous thrombosis. However, current microbubble imaging strategies require either a clot sufficiently large to produce a circulation filling defect or a clot with sufficient vascularization to allow for targeted accumulation of contrast agents. Previously, we reported the design of a microbubble formulation that modulated its ability to generate ultrasound contrast from interaction with thrombin through incorporation of aptamer-containing DNA crosslinks in the encapsulating shell, enabling the measurement of a local chemical environment by changes in acoustic activity. However, this contrast agent lacked sufficient stability and lifetime in blood to be used as a diagnostic tool. Here we describe a PEG-stabilized, thrombin-activated microbubble (PSTA-MB) with sufficient stability to be used in vivo in circulation with no change in biomarker sensitivity. In the presence of actively clotting blood, PSTA-MBs showed a 5-fold increase in acoustic activity. Specificity for the presence of thrombin and stability under constant shear flow were demonstrated in a home-built in vitro model. Finally, PSTA-MBs were able to detect the presence of an active clot within the vena cava of a rabbit sufficiently small as to not be visible by current non-specific contrast agents. By activating in non-occlusive environments, these contrast agents will be able to detect clots not diagnosable by current contrast agents.     

Ultrasound molecular imaging of tumor angiogenesis with a neuropilin-1-targeted microbubble

Ultrasound molecular imaging has great potential to impact early disease diagnosis, evaluation of disease progression and the development of target-specific therapy. In this paper, two neuropilin-1 (NRP) targeted peptides, CRPPR and ATWLPPR, were conjugated onto the surface of lipid microbubbles (MBs) to evaluate molecular imaging of tumor angiogenesis in a breast cancer model. Development of a molecular imaging agent using CRPPR has particular importance due to the previously demonstrated internalizing capability of this and similar ligands. In vitro, CRPPR MBs bound to an NRP-expressing cell line 2.6 and 15.6 times more than ATWLPPR MBs and non-targeted (NT) MBs, respectively, and the binding was inhibited by pretreating the cells with an NRP antibody. In vivo, the backscattered intensity within the tumor, relative to nearby vasculature, increased over time during the ∼6 min circulation of the CRPPR-targeted contrast agents providing high contrast images of angiogenic tumors. Approximately 67% of the initial signal from CRPPR MBs remained bound after the majority of circulating MBs had cleared (8 min), 8 and 4.5 times greater than ATWLPPR and NT MBs, respectively. Finally, at 7–21 days after the first injection, we found that CRPPR MBs cleared faster from circulation and tumor accumulation was reduced likely due to a complement-mediated recognition of the targeted microbubble and a decrease in angiogenic vasculature, respectively. In summary, we find that CRPPR MBs specifically bind to NRP-expressing cells and provide an effective new agent for molecular imaging of angiogenesis.     

Contrast-enhanced MRI of murine myocardial infarction - part I

The use of contrast agents has added considerable value to the existing cardiac MRI toolbox that can be used to study murine myocardial infarction, as it enables detailed in vivo visualization of the molecular and cellular processes that occur in the infarcted and remote tissue. A variety of non-targeted and targeted contrast agents to study myocardial infarction are available and under development. Manganese, which acts as a calcium analogue, can be used to assess cell viability. Traditionally, low-molecular-weight Gd-containing contrast agents are employed to measure infarct size in a late gadolinium enhancement experiment. Gd-based blood-pool agents are used to study the vascular status of the myocardium. The use of targeted contrast agents facilitates more detailed imaging of pathophysiological processes in the acute and chronic infarct. Cell death was visualized by contrast agents functionalized with annexin A5 that binds specifically to phosphatidylserine accessible on dying cells and with an agent that binds to the exposed DNA of dead cells. Inflammation in the myocardium was depicted by contrast agents that target cell adhesion molecules expressed on activated endothelium, by contrast agents that are phagocytosed by inflammatory cells, and by using a probe that targets enzymes excreted by inflammatory cells. Cardiac remodeling processes were visualized with a contrast agent that binds to angiogenic vasculature and with an MR probe that specifically binds to collagen in the fibrotic myocardium. These recent advances in murine contrast-enhanced cardiac MRI have made a substantial contribution to the visualization of the pathophysiology of myocardial infarction, cardiac remodeling processes and the progression to heart failure, which helps to design new treatments. This review discusses the advances and challenges in the development and application of MRI contrast agents to study murine myocardial infarction.     

Characterization of individual ultrasound microbubble dynamics with a light-scattering system

Ultrasound microbubbles are contrast agents used for diagnostic ultrasound imaging and as carriers for noninvasive payload delivery. Understanding the acoustic properties of individual microbubble formulations is important for optimizing the ultrasound imaging parameters for improved image contrast and efficient payload delivery. We report here a practical and simple optical tool for direct real-time characterization of ultrasound contrast microbubble dynamics based on light scattering. Fourier transforms of raw linear and nonlinear acoustic oscillations, and microbubble cavitations are directly recorded. Further, the power of this tool is demonstrated by comparing clinically relevant microbubble cycle-to-cycle dynamics and their corresponding Fourier transforms.     

Superparamagnetic iron oxide nanoparticle-embedded encapsulated microbubbles as dual contrast agents of magnetic resonance and ultrasound imaging

An encapsulated microbubble (EMB) of a novel construct is proposed to enhance the magnetic resonance imaging contrast by introducing superparamagnetic iron oxide (SPIO) nanoparticles (mean diameter is 12 nm) into the polymer shell of the microbubble. Such microbubble vesicle has nitrogen gas in the core and its mean diameter is 3.98 μm. An in vitro MR susceptibility experiment using a phantom consisting EMBs has shown that the relationship between the transverse relaxation rate R₂ and the Fe₃O₄ nanoparticle concentration in the shell (the volume fraction of EMBs is kept constant) can be fitted to a linear function and an exponentially growth function is observed between R₂ and the SPIO-inclusion microbubble concentration. The in vivo MRI experiments also show that the SPIO-inclusion microbubbles have longer contrast-enhancement duration time in rat liver than non-SPIO-inclusion microbubbles. An in vitro ultrasound imaging experiment of SPIO-inclusion microbubbles also shows that they can enhance the ultrasound contrast significantly. Additionally, the interaction between the SPIO-inclusion microbubbles and cells indicates that such microbubble construct can retain the acoustic property under the ultrasound exposure by controlling the SPIO concentration in the shell. Therefore, the proposed SPIO nanoparticle-embedded EMBs potentially can become effective MR susceptibility contrast agents while also can be good US contrast agents.     

Iron oxide nanoparticle-containing microbubble composites as contrast agents for MR and ultrasound dual-modality imaging

Magnetic resonance (MR) and ultrasound (US) imaging are widely used diagnostic modalities for various experimental and clinical applications. In this study, iron oxide nanoparticle-embedded polymeric microbubbles were designed as multi-modal contrast agents for hybrid MR-US imaging. These magnetic nano-in-micro imaging probes were prepared via a one-pot emulsion polymerization to form poly(butyl cyanoacrylate) microbubbles, along with the oil-in-water (O/W) encapsulation of iron oxide nanoparticles in the bubble shell. The nano-in-micro embedding strategy was validated using NMR and electron microscopy. These hybrid imaging agents exhibited strong contrast in US and an increased transversal relaxation rate in MR. Moreover, a significant increase in longitudinal and transversal relaxivities was observed after US-induced bubble destruction, which demonstrated triggerable MR imaging properties. Proof-of-principle in?vivo experiments confirmed that these nanoparticle-embedded microbubble composites are suitable contrast agents for both MR and US imaging. In summary, these magnetic nano-in-micro hybrid materials are highly interesting systems for bimodal MR-US imaging, and their enhanced relaxivities upon US-induced destruction recommend them as potential vehicles for MR-guided US-mediated drug and gene delivery.     

Preparation and evaluation of poly(L-lactide-co-glycolide) (PLGA) microbubbles as a contrast agent for myocardial contrast echocardiography

A kind of absorbable PLGA microbubble-based contrast agent (PLGA microspheres with porous or hollow inner structure) was fabricated by an improved double emulsion-solvent evaporation method. The contrast efficiency was evaluated and proved both in vitro and in vivo. By adjusting the polymer concentration and volume of the inner aqueous phase during the fabrication of microbubbles, the inner structure of the microbubbles could be controlled. Both air-filled and perfluoropropane-filled microbubbles can opacify the left ventricle. However, when compared with air-filled microbubbles, perfluoropropane-filled microbubbles can produce significantly longer enhancement in left ventricle in the dog model due to the lower diffusivity and lower solubility of perfluoropropane in blood. A suspension of perfluoropropane-filled PLGA microbubbles (1.8 microm average microbubbles size, 2 x 10(8) microbubbles/mL concentration) has successfully and safely achieved myocardial opacification in closed-chest dogs. A perfusion defect was observed in both of the two dogs with acute myocardial infarction with Power Contrast Imaging (PCI) triggered technology. In the examination of contrast in both ventricular and myocardial opacification, the high mechanical index (MI) was found to have superior contrast sensitivity over the low MI for PLGA-based contrast agents.     

Real-time targeted molecular imaging using singular value spectra properties to isolate the adherent microbubble signal

Ultrasound-based real-time molecular imaging in large blood vessels holds promise for early detection and diagnosis of various important and significant diseases, such as stroke, atherosclerosis, and cancer. Central to the success of this imaging technique is the isolation of ligand-receptor bound adherent microbubbles from free microbubbles and tissue structures. In this paper, we present a new approach, termed singular spectrum-based targeted molecular (SiSTM) imaging, which separates signal components using singular value spectra content over local regions of complex echo data. Simulations were performed to illustrate the effects of acoustic target motion and harmonic energy on SiSTM imaging-derived measurements of statistical dimensionality. In vitro flow phantom experiments were performed under physiologically realistic conditions (2.7?cm s(-1)?flow velocity and 4?mm diameter) with targeted and non-targeted phantom channels. Both simulation and experimental results demonstrated that the relative motion and harmonic characteristics of adherent microbubbles (i.e. low motion and large harmonics) yields echo data with a dimensionality that is distinct from free microbubbles (i.e. large motion and large harmonics) and tissue (i.e. low motion and low harmonics). Experimental SiSTM images produced the expected trend of a greater adherent microbubble signal in targeted versus non-targeted microbubble experiments (P < 0.05, n = 4). The location of adherent microbubbles was qualitatively confirmed via optical imaging of the fluorescent DiI signal along the phantom channel walls after SiSTM imaging. In comparison with two frequency-based real-time molecular imaging strategies, SiSTM imaging provided significantly higher image contrast (P < 0.001, n = 4) and a larger area under the receiver operating characteristic curve (P < 0.05, n = 4).     

Preparation of targeted microbubbles: ultrasound contrast agents for molecular imaging

Targeted ultrasound contrast agents can be prepared by attaching targeting ligands to the lipid, protein or polymer shell coating of gas-filled microbubbles. These materials are stable on storage, fully biocompatible and can be administered parenterally. Detection of microbubble contrast agents by ultrasound is very efficient (single particles with picogram mass can be visualized). Covalent or noncovalent binding techniques can be used to attach targeting ligands. Ligand-carrying microbubbles adhere to the respective molecular targets in vitro and in vivo. Several biomechanical methods are available to improve targeting efficacy, such as the use of a flexible tether spacer arm between the ligand and the bubble, and the use of folds on the microbubble shell, that project out, enhancing the contact area and increasing the length of the lever arm.