A Multi-frequency Electrical Impedance Tomography System Working in Four Frequencies Simultaneously.

Objective To establish a data acquisition system for multi-frequency electrical impedance tomography(EIT) that can diminish the effect of the dynamic change of tissue impedance. Method A driving signal with four frequency components was produced based on digital synthesis technique. The driving signals were injected into the imaging object, and impedance information at each frequency was extracted by orthogonal sequential digital demodulation method. Result The established system could work at a wide range of frequencies from 1. 6 kHz to 380 kHz. Its common mode rejection ratio(CMRR) was 65 dB at 100 kHz. Measuring precision on a 100 Ω, resistor was better than -80 dB in full bandwidth. The images based on physical phantom could reflect the impedance parameter(such as real part and imaging part) changes inside the phantom clearly. Conclusion This multi-frequency EIT system has a high measuring precision, and meets the need of multi-frequency EIT research.