基于电流激励磁声成像的锁相放大检测系统设计

Design of detection system of phase lock-in amplifier based on magnetoacoustic tomography with current excitation

目的:针对磁声信号强度微弱、易受噪声干扰的问题,设计一种锁相放大检测系统。方法:该系统基于电流激励磁声成像设计,由空间定位模块、信号测量处理模块和电磁声屏蔽装置3个部分组成。在不同激励电流下,采用该系统对圆柱形仿体样本进行检测,验证该系统的总体性能;采用该系统对圆柱形仿体样本和新鲜离体猪肉组织样本上的一维和二维磁声信号进行测量,并使用平行双通道电极获得样本表面的电流密度分布和电场分布,验证该系统测量结果的可靠性。结果:实验结果表明,该系统可实现0.01 A量级激励电流下的微弱磁声信号检测,测量磁声信号的精度达到10-7 Pa,成像分辨力达到5 mm,而且该系统测得的声压分布与平行双通道电极测得的电流密度分布趋势基本一致。结论:该系统可实现组织内电流分布与电特性的无创检测,能够提高磁声信号检测的灵敏度,对于推进医用磁声成像设备的临床应用研究具有积极意义。

Objective To design a phase lock-in amplifier detection system to solve the problems of weak magnetoacoustic signals and high susceptibility to noise interferences.Methods A phase lock-in amplifier detection system was designed based on magnetoacoustic tomography with current excitation,which was composed of a spatial positioning module,a signal measurement and processing module and an electromagnetic acoustic shielding module.The overall performances of the system were verified by involving it into the examination of cylindrical mimic samples under different excitation currents;the system was used to measure the one-and two-dimensional magnetoacoustic signals on cylindrical mimic samples and fresh ex vivo pork tissue samples,and the electric field distribution on the sample surface was obtained using parallel bipolar electrodes to verify the reliability of the measurement results of the system.Results The system realized the amplitude detection of low-frequency sound sources under the order of 0.01 A excitation current,with the accuracy of magnetoacoustic signal detection being 10-7 Pa and the imaging resolution being 5 mm.The sound pressure distribution measured by this system was in general agreement with the trend of current density distribution obtained by parallel bipolar electrodes.Conclusion The system developed implements noninvasive detection of current distribution and conductivity in tissue,and improves the sensitivity of magneto-acoustic signal detection,which is of significance to promoting the research and application of medical magnetoacoustic imaging equipment.