开放式电阻抗断层成像测量系统设计与成像试验研究

Study on Opening Electrical Impedance Tomography Principles and Imaging Experiment

目的:研制一种基于开放式电阻成像的高精度测量系统,用于物理模型试验研究,为临床试验奠定基础。方法:开放式电阻抗成像(OEIT)采用固定电极阵列,克服了封闭式电阻抗成像(CEIT)在应用上电极间隔不等、放置不方便等问题;测量系统采用直接数字频率合成(DDS)产生激励信号,采用FPGA与ADC实现数字相敏检波,检测出电极间的正弦电压幅值与相位,经成像算法得到试验图像。结果:该测量系统的信噪比达104dB,在300mS/m背景电导率情况下,可区分电导率分别为400mS/m和200mS/m的双目标。结论:该测量系统满足开放式电阻抗成像对测量信噪比的要求,水槽和琼脂物理模型的双目标成像试验结果表明,OEIT具有较好的分辨率和定位准确度,可以应用于区分低电导率差异的组织。

Objective To develop a high-precision measuring system based on opening electrical impedance tomography （OEIT） for the survey of physical model and clinical application. Methods The fixed electrode array that can conquer the problem of unequal distance and inconvenient arrangement of the electrode in CElT was used in the OEIT. The direct digit synthesis（DDS） was employed by measuring system to produce the exciting signal, and FPGA and ADC were developed to realize digital phase-sensitive wave detecting and obtain the voltage amplitude and phase of the electrodes. Finally, the conductivity image distribution was given by computation according to numerical algorithm. Results The signal to noise ratio（SNR） of the measurement system was up to 104 dB, and can distinguish two objects with conductivity of 400 mS/m and 200 mS/m respectively under 300 mS/m electric conductivity. Conclusion The measurement system can satisfy with the requirement of SNR to OEIT. The two objects experiment in water-tank and agar model shows that OEIT has good resolution and positioning accuracy, can be applied to distinguish the small difference in hypo-conductivity structure.