Investigations of Ultrasound Propagation and Image Processing

超声波被广泛用于医学诊断和治疗以及许多工业应用。它对医学诊断的重要性来自于它的非侵入性，以及它使用比笔记本电脑大不了多少的系统以相对经济的方式提供图像和定量信息的能力。诊断系统利用发射超声波的换能器并收集反射信号，以创建结构图像或成像血流。它们有一些局限性，在信号和图像处理方面的新想法和改进的帮助下，应该能够进一步提高它们的性能。在这项赠款申请中，提出了几个子主题，其中一些涉及当前的限制，另一些则考虑与诊断应用直接相关的问题。在下面的内容中，只详细介绍了其中的两个主题。 美国诊断系统的复杂性以及接受检查的患者中存在的各种异常，使得开发用于培训放射科医生和超声师的模拟系统非常重要，就像用于实时航空公司飞行员培训的系统一样。到目前为止，一个主要的问题是难以实时模拟换能器的场特性。最近，我们已经展示了如何将其作为可并行化问题而不是脉冲响应来解决。我们将进一步发展这一想法。 我们计划进一步研究的第二个主题是使用声子超材料(一类工程材料)来实现更清晰的超声图像，景深更大，可能还会达到亚波长分辨率。这种材料具有以周期性方式排列的两种或两种以上组成材料。声波在这种介质中的传播可以表现出负折射，从而能够开发出独特的场操纵特性。可能存在纵波和横波，波模转换发生在界面上。为了更好地了解波的传播，我们正在开发分析这种介质的新方法，希望这能改善成像系统。

Ultrasound is widely used both for medical diagnostic and therapeutics as well as for many industrial applications. Its importance for medical diagnosis arises from its non-invasive nature and its ability to provide images and quantitative information in a relatively economical manner using systems that are not much larger than a lap-top computer. Diagnostic systems make use of transducers that emit the ultrasound and gather the reflected signal so as to create structural images or to image blood flow. They have a number of limitations which, with the help of new ideas and improvements in signal and image processing, should enable their performance to be further enhanced. In this grant application several sub-topics are proposed, some of which address current limitations and some consider issues directly related to diagnostic applications. In what follows below, just two of the topics are detailed. The complexity of US diagnostic systems and the wide variety of abnormalities that are present in the patients being examined make it important to develop simulation systems for training radiologists and sonographers, much like that used for real-time airline pilot training. Up to now a major problem has been the difficulty of simulating the transducer field properties in real-time. Recently, we have shown how this can be addressed as a parallelizable problem rather than as an impulse response. We will further develop this idea. The second topic that we plan to further investigate is the use of phononic metamaterials (a class of engineered materials) for achieving sharper ultrasound images with a greater depth of field, and possibly, sub-wavelength resolution. Such materials have two or more constituent materials arranged in a periodic manner. Acoustic wave propagation in such a medium can exhibit negative refraction, enabling unique field manipulation properties to be developed. Compressional and shear waves may be present with wave-mode conversion occurring at the interfaces. To better understand wave propagation we are developing new methods for analyzing such media with the expectation that this could lead to improved imaging systems.