Nonlinear Bubble Dynamics and Medical Ultrasound

9712179 Szeri高频声波，又称超声波，在医学上越来越多地被用于诊断和治疗模式。当存在微泡时，超声的有益效果往往会增加；这些微泡可能是由声场本身产生的，也可能是注入患者体内的。因此，微泡的非线性动力学和体积振荡的控制在超声的各种医学应用中具有重要的意义。在医学成像中，微泡作为造影剂很有价值。由于气泡相对于周围组织的可压缩性，气泡从入射声场返回更强的回声，可以用来构建对医生有用的图像。通过利用气泡的非线性振荡可以增强来自气泡的回声，该非线性振荡以入射频率的简单分数或倍数返回回声，进一步区分气泡与周围组织。在被称为声动力疗法的第二种应用中，超声波与微泡相互作用，推动化学反应，从注射的试剂中释放自由基，破坏肿瘤组织。限速步骤是通过吸收周围液体中溶解的气体，使微泡缓慢增长到有用的尺寸。当缓慢生长的气泡变得足够大时，剧烈的坍塌就会启动治疗效果。非线性动力学对于这些发展中的应用的重要性是显而易见的，然而，对于在医学相关条件下经历非线性振荡的气泡的物理学，人们还知之甚少。为此，提出了研究超声诱导气泡生长的共振、阻尼、包覆效应和气泡振荡控制的非线性动力学问题。新的控制能力正在开发中，其中包括一种新的技术，通过改变简单正弦波的驱动声波波形来优化气泡动力学。可以将优化构建为S，以增加成像中使用的微泡的回声，或增加用于声动力疗法的超声诱导气泡的生长速度。这些增强不需要更强的超声波，而是声学波形的改变，因此可以在不增加患者风险的情况下获得。***

9712179 Szeri High frequency sound waves, known as ultrasound, are used in an increasing number of diagnostic and therapeutic modes in medicine. The beneficial effects of ultrasound can often be increased when microbubbles are present; these may either be produced by the sound field itself or injected into the patient. Hence, the nonlinear dynamics and control of volume oscillations of microbubbles is of great importance in a variety of medical applications of ultrasound. In medical imaging, microbubbles are valuable as contrast agents. Owing to their compressibility relative to surrounding tissue, bubbles return a stronger echo from an incident sound field that can be used to construct an image useful to physicians. The echo from bubbles can be enhanced by exploiting the nonlinear oscillations of bubbles which return an echo at a simple fraction or multiple of the incident frequency, further differentiating the bubbles from the surrounding tissue. In a second application known as sonodynamic therapy, ultrasound interacting with microbubbles drives chemical reactions that release radicals from injected reagents to destroy tumor tissue. The rate-limiting step is the slow growth of microbubbles to useful size by uptake of dissolved gases from the surrounding liquid. When the slowly growing bubbles become large enough, violent collapses initiate the therapeutic effect. The importance of nonlinear dynamics to these developing applications is clear, yet much is unknown about the physics of bubbles undergoing nonlinear oscillations at medically-relevant conditions. Therefore, research is proposed into nonlinear dynamics of resonances, damping, ultrasound-induced bubble growth, effects of encapsulation, and control of bubble oscillations. New control capabilities are under development that involve a novel technique for optimizing bubble dynamics by alteration of the driving acoustic waveform from a simple sine wave. The optimization can be constructed so a s to increase the echo from microbubbles used in imaging, or to increase the rate of ultrasound-induced growth of bubbles used in sonodynamic therapy. These enhancements do not require more intense ultrasound, but rather alterations in the acoustic waveform, and so can be obtained without additional risk to the patient. ***