Nonlinear Bubble Dynamics and Medical Ultrasound

9712179 Szeri高频声波，即超声波，越来越多地用于医学诊断和治疗模式。当微泡存在时，超声的有益作用往往会增加；这些声音可以由声场本身产生，也可以注射到病人体内。因此，微泡体积振荡的非线性动力学和控制在超声的各种医学应用中具有重要意义。在医学成像中，微泡是有价值的造影剂。由于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，可用于构建对医生有用的图像。气泡的回波可以通过利用气泡的非线性振荡来增强，气泡以入射频率的简单分数或倍数返回回波，从而进一步将气泡与周围组织区分开来。第二种应用被称为声动力疗法，超声与微泡相互作用驱动化学反应，释放注射试剂中的自由基，破坏肿瘤组织。速率限制步骤是微泡通过从周围液体中吸收溶解气体而缓慢增长到有用的尺寸。当缓慢增长的气泡变得足够大时，剧烈的破裂开始产生治疗效果。非线性动力学对这些发展中的应用的重要性是显而易见的，然而，在医学相关条件下，气泡经历非线性振荡的物理特性尚不清楚。因此，提出了共振非线性动力学、阻尼、超声诱导气泡生长、封装效应和气泡振荡控制等方面的研究。新的控制能力正在开发中，涉及一种通过改变简单正弦波的驱动声波波形来优化气泡动力学的新技术。优化后的结构可以增加成像中使用的微气泡的回声，或者增加超声诱导的超声气泡生长的速度，用于声动力治疗。这些增强不需要更强的超声，而是改变声波波形，因此可以在不给患者带来额外风险的情况下获得。＊＊＊

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. ***