热声效应对磁声信号的频率影响分析

Influence of thermoacoustic effect for frequency of magnetoacoustic signals

目的 :探究在磁声成像(magnetoacoustic tomography,MAT)中待测样本中的热声效应对磁声信号频率的影响。方法:选取铜、石墨、琼脂仿体及猪肉组织作为待测样本,其中铜及石墨属于高电导率材料,而琼脂及猪肉组织为低电导率的类生物组织及生物组织。通过设计实验,获得上述材料在不同条件下的磁声信号与热声信号,并对其进行时频对比分析。结果:分析获得不同材料磁声信号与热声信号的特点,高电导率材料的声信号频率相对激励频率向低频偏移程度很小,而类生物及生物组织声信号频率向低频偏移程度显著。且材料的热声信号并不与激励信号同频,相对激励频率显著降低。结论:热声效应是引起类生物组织及生物组织磁声信号频率显著下降的原因,热声信号成分引起了MAT声信号的频率偏移现象。该研究为进一步提高MAT重建质量、优化MAT理论及实验方法提供了新思路。

Objective To research the influence of the thermoacoustic effect for the frequency of the magnetoacoustic signals in the magnetoacoustic tomography(MAT).Methods Some experiments were designed,and the magnetoacoustic signals and the thermoacoustic signals of several materials with different conductivities were analyzed and compared in the time domain and the frequency domain respectively,of which,copper and graphite were high-conductivity materials,and agar and pork were used as low-conductivity biological or similar tissue.Results The characteristics of the magnetoacoustic signals and the thermoacoustic signals of different materials were acquired.The results illustrated that there was a little drop in frequencies of acoustic signals of the materials with high conductivities while a big drop in frequencies of signals of the tissue-like materials comparing with the stimulant pulse.Furthermore,the main frequencies of acoustic signals were not accordant but much lower than the stimulant ones.Conclusion It is found that the thermoacoustic effect is related to the frequency of the acoustic signals.The drop in the center frequencies of the acoustic signals could be explained by the thermoacoustic effect of materials.The acoustic signals with lower main frequencies have the higher proportion of thermoacoustic signals.The studies could contributing to optimizing MAT method and improving MAT imaging quality.