磁声成像中不同样本声信号的时频特征研究

发布时间：2018-06-07 20:25

本文选题：磁声信号 + 特征分析　；参考：《北京协和医学院》2017年硕士论文

【摘要】：磁声成像(Magnetoacoustictomography,MAT)是一项结合了电磁成像高对比度与超声成像高空间分辨率的新型组织电特性功能成像技术。MAT通过检测组织基于洛伦兹力产生的磁声信号重建电导率分布。分析磁声信号的特性具有重要意义。本文基于优化的MAT系统,针对不同材料不同实验条件下的磁声信号进行了时频特征分析,主要从激励源特性、静磁场条件、声换能器特性、样本特性等方面对磁声信号进行了研究。首先,针对MAT的实验系统平台进行了优化和测试,提高了系统的信噪比,确保了实验的准确性、可靠性和稳定性。其次,通过对不同样本磁声信号的特征分析和研究,发现生物组织和类生物组织在静磁场为零的条件下,仍有与磁声理论不符的声信号产生,说明该类组织信号中包含大量非磁声信号。再次,设计实验对该非磁声信号特性进行了系统的分析,实验得出产生该信号的非洛伦兹力声源为矢量源、且与激励强度二次正相关,与组织电导率和硬度参数线性正相关,结合实验条件及理论模型,推断该非磁声信号为热声信号。基于MAT与TAT(Thermoacoustictomography,TAT)理论,分别对不同材料的磁声信号及热声信号进行了仿真研究及对比分析,仿真结果进一步验证了实验结论。本文通过分析不同材料不同实验条件下声信号的特性,发现了不同类材料样本磁声信号的特点,探究了在生物组织与类生物组织中占优的非洛伦兹力声源特性,为进一步提高MAT重建质量,优化MAT理论及实验方法提供了新思路。
[Abstract]:Magnetoacoustic tomography (MAA) is a new functional imaging technique combining high contrast of electromagnetic imaging and high spatial resolution of ultrasonic imaging. Mat reconstructs conductivity distribution by detecting the magnetoacoustic signal generated by Lorentz force. It is of great significance to analyze the characteristics of magnetoacoustic signals. Based on the optimized mat system, the time-frequency characteristics of magnetoacoustic signals under different experimental conditions are analyzed. The characteristics of excitation source, static magnetic field and acoustic transducer are analyzed. The magnetoacoustic signals are studied in the aspects of sample characteristics. Firstly, the experiment platform of mat is optimized and tested to improve the signal-to-noise ratio of the system and ensure the accuracy, reliability and stability of the experiment. Secondly, by analyzing and studying the characteristics of magnetoacoustic signals from different samples, it is found that under the condition of zero static magnetic field, there are still acoustic signals which are inconsistent with the magnetoacoustic theory. It shows that this kind of tissue signal contains a large number of non-magnetoacoustic signals. Thirdly, the characteristics of the non-magnetoacoustic signal are systematically analyzed. The non-Lorentz force source is a vector source, which is positively correlated with the excitation intensity, and has a linear positive correlation with the structure conductivity and hardness parameters. According to the experimental conditions and theoretical model, the nonmagnetoacoustic signal is deduced to be thermoacoustic signal. Based on the theory of mat and tat, the magnetoacoustic signals and thermoacoustic signals of different materials are simulated and analyzed respectively. The simulation results further verify the experimental results. By analyzing the characteristics of acoustic signals under different experimental conditions of different materials, the characteristics of magnetoacoustic signals in different material samples are found, and the characteristics of non-Lorentz force sources which are dominant in biological and biomedical tissues are explored. It provides a new idea for improving the quality of mat reconstruction and optimizing the theory and experimental method of mat.
【学位授予单位】：北京协和医学院
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：R318;TN911.6

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