IMPROVING CARDIAC IMAGING WITH NONLINEAR ULTRASOUND

描述（由申请人提供）： 拟议的研究的长期目标是通过阐明非线性成像的物理原理来扩展和增强诊断超声。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。促进这种快速发展的仪器进步最初是为了利用造影剂的特性而开发的。然而，很快就清楚了，组织本身的非线性特性就足够强，以至于可以从以1-f发射的超声波束中以接近2-f的频率形成图像。对于许多患者，所得到的谐波图像的质量明显高于对应的基波图像。支持我们提出的研究的基本原理是，更好地理解负责生成（与传播距离）和非线性信号的传播的物理学，这些信号来自于在成像换能器的表面处开发的（线性生成的）基本超声场，将为图像质量的更显着改善奠定基础。我们建议在实验室条件下的非线性超声传播的切除心脏和其他组织的询问，通过相位畸变介质类似于胸或腹壁，并在组织模仿媒体良好控制的衰减，后向散射，和声速的实验研究。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进行比较。使用这些实验和模拟的结果，我们建议评估的优势和局限性的概念“有效切趾”的衍射和衰减的非线性产生的字段，因为它在患者中传播的中心特征的特征。拟议的研究旨在通过为一系列明确提出的问题提供明确的答案来增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.