Harnessing cavitation using a tubular transducer geometry for catheter based applications

大血管闭塞是导致死亡和残疾的主要原因。这些包括冠状动脉、脑或外周血管中的（软）血凝块的急性滞留以及可能具有刚性上游帽的更复杂的长期闭塞（慢性完全闭塞）。 因此，解决血管闭塞以恢复血流是高度临床优先事项，但在许多情况下，当前方法解决得很差。标准治疗方法包括药物治疗（例如静脉注射药物）、手术（例如冠状动脉搭桥术）和导管手术（例如取出凝块或放置支架）。治疗性超声波也在研究中，以疏通闭塞。这包括一系列方法，其中许多涉及用超声波诱导微米尺寸的循环气泡的振动（空化）。 我们最近提出了一个新的设计概念，并原型向前导向导管为基础的超声，涉及一个管状换能器（超声源）位于其尖端。这提供了许多独特的优点。从本质上讲，它可以通过导丝直接引导到闭塞处，通过导管和换能器孔注入气泡和药物，然后在目标部位精确地暴露超声。对于这种新方法及其几何形状，还存在许多用于将超声输送到闭塞的未探索的物理考虑。本研究计划的目的是调查这种情况下的空化的基本方面，以便为制定暴露方案提供合理的依据。这个程序中有两个流。 首先，我们将研究气泡在管内的行为，超声波如何将它们推出管外，以及如何适当地爆破它们以打破阻塞。这些效应将是波束的空间图案的函数，波束的空间图案又是管的长度和所使用的超声的频率的函数。这将通过计算机模拟、测量压力并使用非常高速的显微镜来观察气泡行为来实现。这项工作与现有临床批准的气泡通过导管头端注入时相关。 在第二个流程中，我们将研究如何使用超声在导管头端内实际生成气泡。这将使用非常小的液滴-尺寸小于一微米，以及将稳定管内产生的任何气泡的简单脂质溶液来完成。然后，所产生的气泡可以用于治疗，而无需外部注入气泡。 这项工作将共同提供知识的基础，使这种新的方法得到优化。优化系统的最终结果将是一种影响大部分慢性完全闭塞（20%）冠心病患者以及其他大血管中有血栓的患者治疗的方法。

The occlusion of large blood vessels is a leading cause of death and disability. These include the acute lodging of (soft) blood clots in coronary, brain or peripheral vessels as well as more complex longer term occlusions (chronic total occlusions) which can have a stiff upstream caps'. Resolving vascular occlusions to restore blood flow is therefore a high clinical priority, but is in many circumstances poorly addressed by current methods. Standard of care approaches include medical therapy (e.g. intravenously injecting drugs), surgery (e.g. coronary bypass) and catheter procedures (e.g. to retrieve clot or place a stent). Therapeutic' ultrasound is also under investigation to unblock occlusions. This encompasses a range of methods, many of which involve inducing vibrations (cavitation') of micron sized circulating bubbles with the ultrasound. We have recently proposed and prototyped a novel design concept for forward directed catheter based ultrasound that involves a tubular transducer (ultrasound source) situated at its tip. This presents a number of unique advantages. Essentially it can be guided over a wire right up to the occlusion, inject the bubbles and drugs through the catheter and transducer hole then expose with ultrasound precisely at the target site. With this new approach and its geometry, there are also many unexplored physical considerations for delivering ultrasound to occlusions. This research program has the objective of investigating basis aspects of cavitation for this situation in order to provide a rational basis for developing exposure protocols. There are two Streams within this program. First, we will examine how bubbles behave within the tube, how the ultrasound can push them out of the tube, and how to burst' them appropriately to break up the occlusion. These effects will be a function of the spatial pattern of the beam, which is in turn a function of the length of the tube and the frequency of ultrasound that is used. This will be approached with computer simulations, measuring the pressures and using a very high speed microscope to look at the bubble behaviour. This work is relevant to when existing clinically approved bubbles are injected through the catheter tip. In the second Stream, we will investigate how to actually generate bubbles within the tip of the catheter with the ultrasound. This will be done using very small droplets'- less than a micron in size, as well as a simple solution of lipids which will stabilize any bubbles generated within the tube. The resulting bubbles can then be used for therapy without externally injected bubbles. Together this work will provide the foundation of knowledge that will enable this new approach to be optimized. The end result of the optimized system will be a method to impact the treatment of a significant portion of patients with coronary disease that have chronic total occlusions (20%), as well as other patients that have blood clots in large vessels.