Production of Membrane-Filtered Phase-Shift Decafluorobutane Nanodroplets from Preformed Microbubbles.

There are many methods that can be used for the production of vaporizable phase-shift droplets for imaging and therapy. Each method utilizes different techniques and varies in price, materials, and purpose. Many of these fabrication methods result in polydisperse populations with non-uniform activation thresholds. Additionally, controlling the droplet sizes typically requires stable perfluorocarbon liquids with high activation thresholds that are not practical in vivo. Producing uniform droplet sizes using low-boiling point gases would be beneficial for in vivo imaging and therapy experiments. This article describes a simple and economical method for the formation of size-filtered lipid-stabilized phase-shift nanodroplets with low-boiling point decafluorobutane (DFB). A common method of generating lipid microbubbles is described, in addition to a novel method of condensing them with high-pressure extrusion in a single step. This method is designed to save time, maximize efficiency, and generate larger volumes of microbubble and nanodroplet solutions for a wide variety of applications using common laboratory equipment found in many biological laboratories.

Selecting the optimal parameters for sonoporation of pancreatic cancer in a pre-clinical model.

Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest cancers in the modern world, in part due to poor delivery of chemotherapeutics. Sonoporation can be used to enhance the efficacy of standard of care therapies for PDAC. Using xenograft models of PDAC we investigate sonoporation using four ifferent ultrasound contrast agents (UCAs) and two ultrasound regimens to identify the ideal parameters to increase therapeutic efficacy. MIA-PaCa2 xenografts in over 175 immunodeficient mice were treated with gemcitabine and paclitaxel and subjected to low or high power ultrasound (60 and 200 mW/cm2 respectively) in conjunction with one of four different UCAs. The UCAs investigated were Definity®, SonoVue®, Optison™ or Sonazoid™. Tumor volumes, vascularity, hemoglobin, and oxygenation were measured and compared to controls. High power treatment in conjunction with Sonazoid sonoporation led to significantly smaller tumors when started early (tumors ~50mm3; p = .0105), while no UCAs significantly increased efficacy in the low power cohort. This trend was also found in larger tumors (~250mm3) where all four UCA agents significantly increased therapeutic efficacy in the high power group (p < .01), while only Definity and SonoVue increased efficacy in the low power cohort (p < .03). Overall, the higher power ultrasound treatment modality was more consistently effective at decreasing tumor volume and increasing vascularity characteristics. In conclusion, Sonazoid was the most consistently effective UCA at decreasing tumor volume and increasing vascularity. Thus, we are pursuing a larger phase II clinical trial to validate the increased efficacy of sonoporation in conjunction with chemotherapy in PDAC patients.

Characterization of different bubble formulations for blood-brain barrier opening using a focused ultrasound system with acoustic feedback control.

Focused ultrasound combined with bubble-based agents serves as a non-invasive way to open the blood-brain barrier (BBB). Passive acoustic detection was well studied recently to monitor the acoustic emissions induced by the bubbles under ultrasound energy, but the ability to perform reliable BBB opening with a real-time feedback control algorithm has not been fully evaluated. This study focuses on characterizing the acoustic emissions of different types of bubbles: Optison, Definity, and a custom-made nanobubble. Their performance on reliable BBB opening under real-time feedback control based on acoustic detection was evaluated both in-vitro and in-vivo. The experiments were conducted using a 0.5 MHz focused ultrasound transducer with in-vivo focal pressure ranges from 0.1-0.7 MPa. Successful feedback control was achieved with all three agents when combining with infusion injection. Localized opening was confirmed with Evans blue dye leakage. Microscopic images were acquired to review the opening effects. Under similar total gas volume, nanobubble showed a more reliable opening effect compared to Optison and Definity (p < 0.05). The conclusions obtained from this study confirm the possibilities of performing stable opening using a feedback control algorithm combined with infusion injection. It also opens another potential research area of BBB opening using sub-micron bubbles.

Ultrasound microbubble-carried PNA targeting to c-myc mRNA inhibits the proliferation of rabbit iliac arterious smooth muscle cells and intimal hyperplasia.

OBJECTIVE: To elucidate the transfected effect of albumin ultrasound microbubbles carrying peptide nucleic acids (PNAs) against c-myc gene to the vascular walls and their effect on the intimal proliferation induced by vascular denudation. METHODS: A rabbit iliac artery intimal proliferation model was constructed and PNA against c-myc mRNA was designed and synthesized and was added to albumin solution before ultrasound microbubbles were prepared and encapsulated in matrix of albumin. The ultrasound microbubbles carrying PNA were transfected to intima under ultrasound exposure. The transfected effect was identified by a histochemical method and the expression of c-myc was detected by in situ hybridization. The proliferation of intimal smooth muscle cells was estimated by the expression of proliferative cell nuclear antigen (PCNA) of them. The intimal area and thickness were judged morphologically for intimal hyperplasia. RESULTS: The ultrasound microbubbles with PNA were successfully prepared and c-myc PNA was transfected to vascular intimal cells. The expression of c-myc and PCNA by intimal vascular smooth muscle cells (vSMCs) was inhibited significantly and the intimal thickness and area were reduced remarkably. CONCLUSION: Transfection of c-myc PNA could inhibit proliferartion of vSMCs and intima in the rabbit iliac artery intimal proliferation model and the targeted transfection of albumin ultrasound microbubbles carrying PNA offers a feasible way to facilitate its access to specific cells in vivo and produce bioavailability.

Mapping microbubble viscosity using fluorescence lifetime imaging of molecular rotors.

Encapsulated microbubbles are well established as highly effective contrast agents for ultrasound imaging. There remain, however, some significant challenges to fully realize the potential of microbubbles in advanced applications such as perfusion mapping, targeted drug delivery, and gene therapy. A key requirement is accurate characterization of the viscoelastic surface properties of the microbubbles, but methods for independent, nondestructive quantification and mapping of these properties are currently lacking. We present here a strategy for performing these measurements that uses a small fluorophore termed a "molecular rotor" embedded in the microbubble surface, whose fluorescence lifetime is directly related to the viscosity of its surroundings. We apply fluorescence lifetime imaging to show that shell viscosities vary widely across the population of the microbubbles and are influenced by the shell composition and the manufacturing process. We also demonstrate that heterogeneous viscosity distributions exist within individual microbubble shells even with a single surfactant component.

Novel preparation techniques for controlling microbubble uniformity: a comparison.

In recent years, there has been increasing interest in the use of coated microbubbles as vehicles for ultrasound mediated targeted drug delivery. This application requires a high degree of control over the size and uniformity of microbubbles, in order to ensure accurate dosing of a given drug and to maximise delivery efficiency. Similarly, as more advanced imaging techniques are developed which exploit the complex nonlinear features of the microbubble signal and/or enable quantification of tissue perfusion, the ability to predetermine the acoustic response of a microbubble suspension is becoming increasingly important. Consequently, a number of new preparation technologies have been developed to meet the demand for improved control over microbubble characteristics. The aim of the work described in this paper was to compare a conventional microbubble preparation technique, sonication, with two more recent methods: coaxial electrohydrodynamic atomisation and microfluidic (T-junction) processing, in terms of their ability to produce bubbles which are sufficiently small and stable for in vivo use, microbubble uniformity, relative production rates and other practical and economic considerations.

Tratamento de trombose intravascular com ultra-som de baixa frequencia e microbolhas / low frequency ultrasound and intravenous microbubbles for the treatment of acute intravascular thrombi

Introdução: Estudos experimentais têm demonstrado que ultra-som terapêutico(UST) de baixa frequencia e microbolhas(MB) podem ser utilizados para dissolver trombos intravasculares. Recentemente novas modalidades de imagem de ultra-som diagnóstico(USD) que utilizam baixo índice mecânico foram desenvolvidas e permitem a detecção de pequenas quantidades de MB, sem causar sua destruição. Assim, a monitoração das MB dentro do trombo com USD tem o potencial de otimizar o processo de trombólise com UST. Objetivo: Estudar o valor do UST mais MB na recanalização de trombos arteriais e o papel do USD na otimização do tratamento em modelo experimental. Métodos: Em modelo canino de trombose de enxerto arteriovenoso agudo, foram aplicados três tipos randomizados de tratamentos: MB injetadas por via endovenosa com aplicação de UST (1 MHz) guiada pelo USD para determinar o momento de maior concentração de MB no trombo (n igual 12), MB injetadas por via endovenosa com aplicação de UST não guiada (n igual 6), e aplicação de UST sem MB (controle, n igual 6). O sucesso do tratamento foi definido como fluxo escore 3 no enxerto pela angiografia. Resultados: Sucesso do tratamento foi maior no grupo MB mais UST mais USD que nos demais grupos..

Imaging technologies and techniques.

Equipment manufacturers provide contrast-specific detection techniques that have excellent sensitivity and excellent agent-to-tissue specificity along with helpful tools that improve workflow efficiency dramatically. Excellent contrast agents have been approved for LV opacification and are available worldwide. Techniques designed for low-MI imaging offer real-time acquisition capabilities and lead to faster examinations. Techniques designed for medium-MI imaging offer better sensitivity than low-MI techniques while maintaining the benefit of rapid image acquisition. Techniques designed for high-MI imaging offer the best sensitivity with longer acquisition times. These techniques are viable means for imaging contrast agents tailored to clinical needs. Progress by contrast agent manufacturers, equipment manufacturers, and physicians will continue to drive improvements in the areas of detection and clinical workflow for improved patient care.

Implementing contrast echocardiography in the laboratory.

Contrast echocardiography is an important and a significant addition to a modern echocardiography laboratory. Its successful implementation is dependent on a team approach between sonographers, nurses, and physicians. A practical plan is one that includes a proper understanding of indications, logistical matters, technical and performance standards, and reimbursement issues.