IMPROVING CARDIAC IMAGING WITH NONLINEAR ULTRASOUND

描述(由申请人提供)： 这项拟议研究的长期目标是通过阐明使用非线性成像的物理原理来促进超声诊断的扩展和增强。超声心动图在极短的时间内从线性(基波)成像发展到非线性(谐波)成像。促进这一快速发展的仪器进展最初是为了利用造影剂的特性而开发的。然而，人们很快发现，仅组织的非线性特性就足够强，可以在接近2-f的频率下从以1-f传输的超声束中形成图像。对于许多患者来说，产生的谐波图像的质量明显高于相应的基本图像。支持我们提出的研究的基本原理是，更好地理解产生(随距离传播的)非线性信号的物理原因，这些非线性信号产生于成像换能器表面形成的(线性产生的)基本超声场，将为图像质量的更显著改善奠定基础。我们建议在实验室条件下，通过类似于胸壁或腹壁的位相畸变介质，以及在衰减、后向散射和声速得到很好控制的组织模拟介质中，研究非线性超声在切除的心脏和其他组织中的传播。我们建议将我们的测量结果与基于Burgers方程增强的非线性角谱模拟方法的预测结果进行比较。利用这些实验和模拟的结果，我们建议评估“有效变迹”概念的优点和局限性，以表征在患者体内传播的衍射场和衰减场的中心特征。这项拟议的研究旨在通过对一系列明确提出的问题提供明确的答案来加强超声在临床环境中的作用。

DESCRIPTION (provided by applicant): The long range objective of the proposed research is to contribute to extending and enhancing diagnostic ultrasound by elucidating the physical principles underlying the use of nonlinear imaging. Echocardiography evolved from linear (fundamental) imaging to nonlinear (harmonic) imaging in a remarkably short period of time. The instrumental advances that facilitated this rapid evolution were initially developed to capitalize on the properties of contrast agents. However, it soon became clear that the nonlinear properties of tissue alone were sufficiently strong that images could be formed at frequencies near 2-f from an ultrasonic beam transmitted at 1-f. For many patients, the resulting harmonic images are of notably higher quality than the corresponding fundamental images. The rationale that underpins our proposed research is that a better understanding of the physics responsible for the generation (with distance traveled) and the propagation of the nonlinear signals, which arise from the (linearly generated) fundamental ultrasonic field developed at the face of the imaging transducer, will lay the foundation for even more significant improvements in image quality. We propose experimental studies under laboratory conditions of nonlinear ultrasonic propagation in excised hearts and other tissues interrogated through phase-aberrating media analogous to chest or abdominal wall, and in tissue-mimicking media with well-controlled attenuation, backscatter, and speed of sound. We propose to compare the results of our measurements with predictions based on a Burgers equation enhanced, nonlinear angular spectrum simulation approach. Using the results of these experiments and simulations, we propose to evaluate the strengths and limitations of the concept of "effective apodization" to characterize the central features of the diffracting and attenuating nonlinearly generated field as it propagates in the patient. The proposed research is designed to enhance the role of ultrasound in the clinical environment by providing definitive answers to a detailed series of explicitly posed questions.