VHF脉冲热声成像技术研究

Microwave thermo-acoustic imaging and photoacoustic imaging have many advantages, such as high contrast, high resolution, non-ionizing radiation, etc., which have attracted lots of attentions in recent years. However, photoacoustic imaging has the drawback of low detection depth. And microwave thermo-acoustic imaging cannot well distinguish tumors and normal biological tissues with high water content. The technique of VHF pulse induced thermo-acoustic imaging which will be studied in this project utilizes VHF band electromagnetic pulse to illuminate on biological tissue, collects stimulated thermo-acoustic signal and carries on image processing. This technique can make up the shortage of low penetration depth for photoacoustic imaging technique and the shortage of low contrast between tumors and biological tissues with high water content for thermo-acoustic imaging technique. This project will build a multi physical field integration simulation platform based on thermo-acoustic effects modeling with two physical processes, i.e., electromagnetic modeling and acoustic modeling. An experimental platform for VHF pulse thermo-acoustic imaging will be developed, based on which, thermo-acoustic effects for tissues with high water content and different ion concentrations will be compared and analyzed. Based on the conductivity model and the relationship between thermo-acoustic signal and image, model based electromagnetics-acoustics inversion algorithm will be researched, which has high accuracy and efficiency. Finally, in order to demonstrate the feasibility of the technique of VHF pulse thermo-acoustic imaging, experiments with imitating tissues and real in vitro biological tissues will be conducted. The research of this project will provide the supports in theory and experimental data for the development of the technique of VHF pulse thermo-acoustic imaging.

微波热声成像和光声成像技术具有高对比度、高分辨率、无电离辐射等优点，近年来受到了广泛的关注。但通常光声成像技术的探测深度浅，微波热声成像不能较好地区分高含水量的正常组织和肿瘤组织。本项目拟开展的VHF脉冲热声成像技术利用VHF频段电磁脉冲对生物组织进行激励，并采集所激发的热声信号进行成像，该技术可弥补光声成像穿透深度不够和微波热声成像对于高含水量生物组织和肿瘤对比度不足的问题。本项目从电磁仿真和声学仿真两个物理过程对热声效应进行建模，构建多物理场一体化仿真平台；研制VHF脉冲热声成像实验平台，对高含水量、多种离子浓度的组织的热声响应进行比对分析；根据电导率模型及VHF频段的热声信号和成像之间的关系，开展基于模型的电磁-声学高效精确反演方法研究；最后，对仿体组织及真实的离体生物组织进行成像实验研究，验证VHF热声成像技术的可行性。项目的研究可为VHF脉冲热声技术的发展提供理论和实验数据支持。

热声成像技术（Thermo-Acoustic Tomography，TAT）是一种近年来新兴的非侵入式医学成像技术，由于同时具有微波成像的高对比度和超声成像的高分辨率，使其在商业应用上具有良好的前景。本项目主要研究VHF波段热声成像的关键技术，重点开展VHF一体化仿真技术、系统设计、热声响应、基于模型的热声反演算法、基于电磁场和声场的联合反演算法等方面的研究。.针对一体化仿真技术，实现了热声成像多物理过程的一体化仿真，分析并研究了电磁频率与极化特性对成像的影响。采用圆极化激励和线极化天线与旋转平台整合的改进措施，改善了激励信号能量分布的均匀性。.针对热声成像系统设计，分析并研究了系统各部分的性能要求，设计了两款高性能辐射天线，并对耦合介质等进行了分析比较和选择。针对系统的电磁兼容问题，设计了实用的屏蔽层隔离方法，显著提高了热声信号的信噪比。.研究了不同样本的热声信号的时频域特性并分析了系统的成像能力。在不同样本种类、结构、传感器阵列的情况下，通过反演算法对目标实现快速成像，并对结果进行了分析。.针对弱非均匀介质中目标成像的难题，提出了基于基追踪的非均匀声速估计算法、基于高斯混合模型的声速自聚焦热声成像算法以及基于电磁场和声场的联合反演算法，显著提高了非均匀介质中热声成像技术的成像质量，大幅增加了热声成像技术的鲁棒性，并通过仿真和实验验证了这些方法的有效性。.针对强散射目标导致逆散射问题的非线性增加，从而使电磁散射难以重构目标的问题。利用电磁反演具有较高对比度，声波反演具有高分辨率的特点，结合两种反演的优势，提出了多种策略下的电磁场-声场联合反演算法。.本项目针对VHF热声成像的前沿问题和关键技术进行了深入研究，研究了VHF热声成像关键技术与成像方法，同时研发了适于成像实验研究的平台，进行了大量成像实验验证。项目的研究成果可被应用于早期肿瘤检测等实际问题中。并且项目提出的针对弱非均匀介质的目标反演算法还可应用于其它复杂环境中的目标探测与成像中。