节点文献
生物医学超声中若干非线性问题的研究
【作者】 杜宏伟；
【作者基本信息】 中国科学技术大学 ， 生物医学工程， 2007， 博士
【摘要】 在生物医学超声理论和应用中，非线性现象的研究是近年来的一个热点和难点。非线性原理应用于超声成像可以获得更高的分辨率和对比度，从而得到高质量的超声图像，更清晰、更真实地反映成像对象，在实际应用中已经表现出显著的优势和诱人的前景。本文的研究遵循严密、可行和有效的原则，对非线性超声的原理与应用中所需解决的若干重点问题在理论推理、建模、数值计算和仿真等层面上进行了较为深入的探讨。取得了如下几个方面的研究成果：1．提出了一种基于Fourier-Bessel级数的新方法，用于计算吸收媒质中非线性超声场的高次谐波分量，得到其级数形式的解析解，由此推导出吸收媒质中零阶Bessel超声场、Gauss聚焦超声场高次谐波的封闭解析解，进而对其声场特性尤其是近场特性进行了研究。2．通过频域有限差分方法求解KZK方程，对吸收媒质中的零阶Bessel超声场、Gauss聚焦超声场进行计算，得到基波和高次谐波声场的数值解和仿真图，计算仿真结果验证了上述的理论结论。3．对于高次谐波超声成像原理及模型进行了初步研究，提出了一个高次谐波成像计算仿真模型的框架。本文的研究工作得到了国家自然科学基金项目“高分辨率高帧率超声成像系统的研究”(No．60471057)和中国科学技术大学青年科学基金“非线性非衍射波的特性研究及其在医学超声中的应用”(No．KA2100230001)的资助。
【Abstract】 In theory and application of biomedical ultrasound, the study of nonlinear phenomena is one of the highlights and difficulties during the last several years. Better resolution and contrast can be obtained by employing nonlinear principles in ultrasonic imaging. Ultrasound images with higher quality then can be constructed to describe the imaging objects more clearly and truly. It has shown us remarkable advantages and an attractive future.All research work introduced in this thesis follows the rigorous、feasible and effective principle, and offers systematic theory、modeling、numerical computation and simulation methods in solving some important problems in the principle and application of nonlinear ulteasound. The research achievements presented in this doctoral dissertation has following features:1. A new method based on the Fourier-Bessel series is proposed to calculate the higher-order harmonic components of a nonlinear ultrasound field in absorbing medium and an analytical solution of a series form is obtained. A closed analytical solution of the higher-order harmonics in the zeroth-order Bessel ultrasound field and the focused Gaussian ultrasound field is deduced to study the field property, especially the near-field property.2. The fundamental and higher-order harmonic ultrasound fields of a zeroth-order Bessel ultrasound field and focused Gaussian field in absorbing medium are computed and simulated by solving the KZK equation using a frequency domain finite difference method. The computation and simulation results verified the theoretical conclusion.3. A preliminary study of the harmonic imaging theory and model is introduced, and a simple computation model frame is proposed.This research is sponsored by the National Science Foundation of China project "Study on high resolution and high frame rate ultrasonic imaging system" (No. 60471057) and the Youth Foundation of the University of Science and Technology of China "Study of the property of nonlinear non-diffraction beam and its application in medical ultrasound" (No. KA2100230001).