Molecular imaging with contrast ultrasound and targeted microbubbles

There is growing interest in the development of methods for imaging cellular and molecular mediators of cardiovascular diseases. Techniques for imaging molecular and cellular alterations have been explored for essentially all noninvasive cardiac imaging modalities. Molecular imaging with contrast-enhanced ultrasound relies on the detection of novel site-targeted microbubble contrast agents. These microbubbles are retained within regions of a specific disease process, thereby allowing phenotypic characterization of tissue. As microbubbles are pure intravascular tracers, the disease processes assessed must be characterized by antigens that are expressed within the vascular compartment. Accordingly, the pathologic states that have been targeted include inflammation, neoplasms, angiogenesis, and thrombus formation, all of which are mediated in part by molecular events within the vascular space. This review describes (1) different strategies that have been used to target microbubbles to regions of disease, (2) the unique challenges for imaging targeted ultrasound contrast agents, and (3) some of the early experience imaging molecular events in animal models of disease.     

Microbubble contrast agents: targeted ultrasound imaging and ultrasound-assisted drug-delivery applications

The use of microbubble contrast agents for general tissue delineation and perfusion enjoys steady interest in ultrasound imaging. Microbubbles as contrast materials require a small dosage and show excellent detection sensitivity. Targeting ligands on the surface of microbubbles permit the selective accumulation of these particles in the areas of interest, which show an up-regulated level of receptor molecules on vascular endothelium. Selective contrast imaging of inflammation, ischemia-reperfusion injury, angiogenesis, and thrombosis has been achieved in animal models. Ultrasound-assisted drug delivery and activation, performed by combining microbubble agent containing drug substances or coadministered with pharmaceutical agents (including plasmid DNA for transfection), has been achieved in multiple model systems in vitro and in vivo. Ultrasound and microbubbles-based targeted acceleration of the thrombolytic enzyme action already have reached clinical trials. Overall, microbubble targeting and ultrasound-assisted microbubble-based drug-delivery systems will offer a step toward the application of targeted personalized diagnostics and therapy.     

Ultrasound molecular imaging with targeted microbubble contrast agents

Conclusions  Microbubbles have shown significant promise as molecular imaging agents for ultrasound contrast imaging in the detection of intravascular targets, such as inflammation, ischemia-reperfusion injury, ischemic memory, atherosclerotic plaque detection, and angiogenic vasculature (currently all in the animal-model setting). Combining these preparations with the widespread use of ultrasound imaging equipment and the increasing popularity of circulating nontargeted contrast agents, the success of targeted ultrasound contrast material could be achieved. This research was supported in part by grants 5R01EB002185 and 1R21CA102880 from the National Institutes of Health, Bethesda, Maryland, by a grant from Philips Research, Briarcliff Manor, NY, and by a donation of laboratory equipment to A.K.’s laboratory at the University of Virginia by Mallinckrodt, Inc, Hazelwood, Mo.     

Microbubbles as ultrasound contrast agents for molecular imaging: preparation and application

OBJECTIVE: The purpose of this review is to describe trends in microbubble application in molecular imaging. CONCLUSION: Microbubbles are used for contrast ultrasound imaging as blood-pool agents in cardiology and radiology. Their promise as targeted agents for molecular imaging is now being recognized. Microbubbles can be functionalized with ligand molecules that bind to molecular markers of disease. Potential clinical applications of molecular imaging with microbubble-based ultrasound contrast agents are in the monitoring of the biomarker status of vascular endothelium, visualizing tumor vasculature, and imaging inflammation and ischemia-reperfusion injury zones and thrombi.     

基于聚合物微泡的超声/荧光双模态造影剂的制备及成像研究

目的 基于模块化思想,通过将具有荧光成像特性的量子点复合到具有超声响应特性的高分子微泡中,制备超声/荧光双模态医学造影剂.方法 将500 mg聚乳酸、50 mg樟脑、0.5ml油酸修饰的硒化镉/硫化锌量子点(CdSe/ZnS,2.3 μmol/L)溶解分散于10 ml二氯甲烷形成有机相,用碳酸铵溶液构成内水相,用聚乙烯醇溶液构成外水相,采用双乳溶剂挥发法和冷冻干燥技术相结合的方法制备兼具超声/荧光双模态成像功能的荧光微泡.用扫描电子显微镜观察荧光微泡形貌,以荧光分光光度计对其发光性能进行表征.搭建体外超声/荧光成像装置,以推注生理盐水的声像图为对照,观察装置中硅胶管注入荧光微泡后的超声对比增强情况和荧光增强情况及两者同步成像效果.评价荧光微泡在体内超声/荧光双模式下对新西兰大白兔肾脏的成像效果.结果 荧光微泡呈规则的球形,具有中空结构,平均粒径为(1.62±1.47) μm,超过99％的微泡直径小于8μm,能够满足超声造影剂大小的基本要求;荧光微泡的荧光发射峰位于632 nm,并能维持量子点良好的发光特性.体外超声/荧光成像结果示:管腔充满生理盐水时,声像图呈完全无回声;推注荧光微泡后,有造影剂的部分回声增强;紫外灯照射下,有造影剂的液柱见明亮红色荧光.推注荧光微泡后,兔肾脏在声像图上清晰显影.结论 成功制备基于聚合物微泡的超声/荧光双模态造影剂,该造影剂具有良好的回声特性和荧光成像能力,可以弥补单一造影剂的缺陷与不足.     

Safety of ultrasound contrast agents

The use of ultrasound contrast agents has increased over recent years. The Contrast Media Safety Committee (CMSC) of the European Society of Urogenital Radiology (ESUR) decided to review the safety of ultrasound contrast agents in humans and to draw up guidelines. A comprehensive literature search and review was carried out. The resulting report was discussed by the CMSC of ESUR and at the 11th European Symposium on Urogenital Radiology in Santiago de Compostela, Spain, in 2004. Ultrasound contrast agents approved for clinical use are well tolerated, and serious adverse reactions are rarely observed. Adverse events are usually minor (e.g. headache, nausea, altered taste, sensation of heat) and self-resolving. These symptoms may not be related to the ultrasound contrast materials as they have also been observed in placebo–control groups. Intolerance to some components may occur. Generalized allergy-like reactions occur rarely. Ultrasound contrast agents are generally safe. The ultrasound scanning time and the acoustic output should be kept to the lowest level consistent with obtaining diagnostic information. Adverse reactions should be treated symptomatically.Members of the Committee: H.S. Thomsen (Chairman, Denmark), S.K. Morcos (Secretary, UK), T. Almén (Sweden), P. Aspelin (Sweden), M.F. Bellin (France), H. Flaten (Amersham Health, Norway), J.Å. Jakobsen (Norway), A. Löwe (Schering, Germany), R. Oyen (Belgium), A. Spinazzi (Bracco, Italy), F. Stacul (Italy), A.J. van der Molen (The Netherlands), J.A.W. Webb (UK).     

Microbubble ultrasound contrast agents: an update

Microbubble contrast agents for ultrasound (US) have gained increasing interest in recent years, and contrast-enhanced US (CEUS) is a rapidly evolving field with applications now extending far beyond the initial improvements achieved in Doppler US. This has been achieved as a result of the safe profile and the increased stability of microbubbles persisting in the bloodstream for several minutes, and also by the availability of specialized contrast-specific US techniques, which allow a definite improvement in the contrast resolution and suppression of signal from stationary tissues. CEUS with low transmit power allows real-time scanning with the possibility of prolonged organ insonation. Several reports have described the effectiveness of microbubble contrast agents in many clinical applications and particularly in the liver, spleen, and kidneys. CEUS allows the assessment of the macrovasculature and microvasculature in different parenchymas, the identification and characterization of hepatic and splenic lesions, the depiction of septal enhancement in cystic renal masses, and the quantification of organ perfusion by the quantitative analysis of the echo-signal intensity. Other fields of application include the assessment of abdominal organs after traumas and the assessment of vesico-ureteral reflux in children. Finally, tumor-targeted microbubbles make possible the depiction of specific biologic processes.     

MRA contrast bolus timing with ultrasound bubbles.

The purpose of this study was to determine the feasibility of using an ultrasound contrast agent test bolus to determine optimum bolus timing for three-dimensional (3D) gadolinium (Gd)-enhanced magnetic resonance angiography (MRA). Small test doses of ultrasound contrast agent (0.3 ml Optison) were injected intravenously followed immediately by a 20 ml saline flush. Arrival of the contrast agent was detected by spectral Doppler ultrasound (US). This technique was implemented in patients undergoing peripheral vascular MRA and carotid MRA. Arrival of the US contrast agent test bolus was readily detected by the change in amplitude of the Doppler spectrum and by a huge increase in the audio signal amplitude. This contrast travel time measurement accurately guided bolus timing for 3D Gd MRA. Bolus timing for 3D contrast-enhanced MRA can be performed using US, thereby eliminating the problems and MR scanner time required for injecting a test bolus of Gd contrast.     

靶向超声造影诊疗前列腺癌的实验研究进展

前列腺癌是我国男性常见的恶性肿瘤,近年来其发病率呈现逐渐增高趋势。目前,对于前列腺癌的早期诊断,临床上迫切需要一种高灵敏度、高特异性的方法。由于前列腺癌的早期症状不明显,就诊时多数患者已失去根治切除机会,导致最终疗效差。随着靶向超声分子成像的发展,靶向微泡造影在前列腺癌诊疗中起着越来越重要的作用,现对靶向超声造影诊疗前列腺癌的实验研究方法及进展近况予以综述。     

液态氟碳纳米脂质微粒与全氟丙烷纳米脂质微泡的物理特性及体外显影效果比较

目的 制备液态氟碳(PFOB)纳米脂质微粒与全氟丙烷气体(C3F8)纳米脂质微泡,比较两者一般理化性质及体外显影效果.方法 分别制备PFOB纳米脂质微粒与C3F8纳米脂质微泡,检测2种造影剂形态、粒径、表面电位、浓度及稳定性,并进行比较.制备生物素化(外膜标记生物素)及空白(外膜未标记生物素)的PFOB脂质微粒及C3F8微泡造影剂.以高频探头观察各组造影剂加入亲和素前后的显影效果,并运用Matlab软件获得图像平均灰度值,再进行统计分析.2组间比较采用两样本t检验,同一样本多个时间点观察比较采用重复测量方差分析,组内不同时间点间两两比较采用Bonferroni法,同一样本加入亲和素前后的显影强度比较采用配对t检验.结果 (1)PFOB脂质微粒与C3F8脂质微泡粒径分别为(152.30±35.99) nm和(774.59±108.59)nm,前者明显小于后者(t=-24.327,P＜0.001);表面电位分别为(-40.90±6.51)mV和(-14.80±3.97)mV,前者明显大于后者(t=-15.308,P＜0.001).(2)PFOB脂质微粒造影剂的浓度及粒径在整个观察期间内无明显改变[C0h:(2.28 ±0.64) ×1011/ml,C1周:(2.06 ±0.53)×1011/ml; D0 h:(152.30±35.99) nm,D1周:(178.80±63.07)nm].C3F8脂质微泡造影剂制备后放置12 h,浓度[C0h:(4.08±0.96) ×1010/ml,C12 h:(3.25±1.02)×1010/ml]尚未发生明显改变,而放置24 h、2d、4d及1周后浓度明显减低[C24h:(2.28 ±0.73)×1010/ml,C2d:(1.56±0.54)×1010/ml,C4d:(1.03±0.37) ×1010/ml,C1周:(0.74±0.24)×1010/ml;F=78.515,P＜0.01];C3F8微泡造影剂放置2d内粒径[D0h:(774.59±108.59) nm,D2d:(1020.68 ±223.64) nm]未见明显变化,放置4d及1周后粒径明显增大[D4d:(1391.67 ±268.65) nm,D1周:(1532.41±326.25) nm,F=50.772,P＜0.01].(3)加入亲和素前,空白及生物素化PFOB脂质微粒均未见明显显影,而空白及生物素化C3F8脂质微泡均有较高的显影强度(31.34 ±7.03与28.75±7.18);加入亲和素之后,生物素化PFOB脂质微粒造影剂显影明显增强(2.18 ±0.71和82.19±15.68,t=-15.698,P＜0.001),而空白PFOB脂质微粒及2组脂质C3F8微泡显影情况无明显改变.结论 与C3F8脂质微泡造影剂相比,以PFOB为核心的纳米脂质微粒造影剂在粒径优化和稳定性方面具有更好的可控性,且具有独特的显影特性,有利于制备靶向功能的超声造影剂.     

Nano/microparticles and ultrasound contrast agents

Microbubbles have been used for many years now in clinical practice as contrast agents in ultrasound imaging. Recently, their therapeutic applications have also attracted more attention. However, the short circulation time (minutes) and relatively large size (two to ten micrometers) of currently used commercial microbubbles do not allow effective extravasation into tumor tissue, preventing efficient tumor targeting. Fortunately, more multifunctional and theranostic nanoparticles with some special advantages over the traditional microbubbles have been widely investigated and explored for biomedical applications. The way to synthesize an ideal ultrasound contrast agent based on nanoparticles in order to achieve an expected effect on contrast imaging is a key technique. Currently a number of nanomaterials, including liposomes, polymers, micelles, dendrimers, emulsions, quantum dots, solid nanoparticles etc., have already been applied to pre or clinical trials. Multifunctional and theranostic nanoparticles with some special advantages, such as the tumor-targeted (passive or active), multi-mode contrast agents (magnetic resonance imaging, ultrasonography or fluorescence), carrier or enhancer of drug delivery, and combined chemo or thermal therapy etc., are rapidly gaining popularity and have shown a promising application in the field of cancer treatment. In this mini review, the trends and the advances of multifunctional and theranostic nanoparticles are briefly discussed.     

运用2种新型超声对比剂(BR55和BR38)对不同侵袭性乳腺癌异种移植的分子和功能显像

目的探讨长循环(BR38)微泡和血管内皮生长因子2(VEGFR2)靶向(BR55)微泡临床运用的可行性并评价这两种微泡对不同侵袭性乳腺癌小鼠模型的鉴别能力。方法研究BR38和BR55在健康小鼠体内的循环特性。实验通过     

Wideband harmonic imaging: a novel contrast ultrasound imaging technique

A novel ultrasonic imaging method, wideband harmonic imaging, for nonlinear imaging of microbubble contrast agents is evaluated. In wideband harmonic mode, two pulses of alternate phase are send out. The image is then processed from the sum of both pulses, resulting in an image of nonlinear scatterers such as microbubbles. A prototype ultrasound system, Siemens Elegra, was evaluated with in vitro investigations and animal trials, using conventional, harmonic and wideband harmonic settings with the galactose based ultrasound contrast agent Levovist. Wideband harmonic imaging offers superior sensitivity for ultrasound contrast agents compared to conventional imaging and harmonic imaging. At low transmit power settings (MI 0. 1-0.5) the nonlinear response is already sufficient to generate a image of the blood pool distribution of Levovist in the rabbit kidney including the microvasculature, with clear delineation of vessels and perfused parenchyma. At high transmit amplitudes, nonlinear tissue response reduced the apparent image contrast between contrast agent and tissue. The results suggest that wideband harmonic imaging is currently the most sensitive contrast imaging technique, maintaining highest spatial resolution. This may add to image quality and offer new clinical potential for the use of ultrasound contrast agents such as Levovist.     

Magnetic resonance imaging contrast agents: Overview and perspectives

Magnetic resonance imaging (MRI) is a non-invasive clinical imaging modality, which has become widely used in the diagnosis and/or staging of human diseases around the world. Some MRI examinations include the use of contrast agents. The categorizations of currently available contrast agents have been described according to their effect on the image, magnetic behavior and biodistribution in the body, respectively. In this field, superparamagnetic iron oxide particles and soluble paramagnetic metal chelates are two main classes of contrast agents for MRI. This review outlines the research and development of MRI contrast agents. In future, the ideal MRI contrast agent will be focused on the neutral tissue- or organ-targeting materials with high relaxivity and specificity, low toxicity and side effects, suitable long intravascular duration and excretion time, high contrast enhancement with low dose in vivo, and with minimal cost.     

Renal imaging with ultrasound contrast: current status

The application of UCAs to the kidney is still in its infancy; however, there are several areas of great promise. UCAs may replace CT in complex renal cyst evaluation and follow-up, eliminating the need for costly CT scans with their attendant potential contrast nephrotoxicity. This approach may decrease patient and physician uncertainty and improve diagnostic confidence. The use of UCAs is likely to be clinically useful in the evaluation of the indeterminate small renal mass on CT or MR imaging. Another probable useful application will be in renal artery stenosis. Routine application of UCAs may increase the percentage of diagnostic examinations, increase diagnostic confidence, and decrease examination times. It also will likely become the first line of evaluation in pyelonephritis, and be useful in immediate assessment of residual tumor after radiofrequency ablation. Of course, substantial additional work needs to be performed in large groups of patients to prove this currently optimistic outlook.