An FPGA-Based Multifrequency EIT System With Reference Signal Measurement

Abstract

Multifrequency electrical impedance tomography (MFEIT) has been rapidly developed and has shown great potential for biomedical analysis and imaging. This article presents the design and evaluation of a wideband and high-precision MFEIT system which incorporates novel features to fit biomedical application. First, a high-accuracy multifrequency current source with adjustable output frequency and amplitude as well as high-output impedance is designed based on the combination of the classic current mirror and a differential topology, which demonstrates stable performance in high frequencies. Second, a reference measurement circuit is developed for the calibration of phase measurement data through which precise measurements of both amplitude data and phase data can be obtained. Furthermore, the low-pass filters utilized in the system have been designed based on the Butterworth filter theory to realize the flattest frequency response in the passband. The MFEIT system is systematically tested and evaluated in terms of filter performance, signal to noise ratio (SNR), channel consistency and measurement repeatability, flatness analysis and load dependence as well as imaging experiments. Experimental results showed that the maximum amplitude SNR and phase SNR of the boundary measurements are 71.55 and 64.12 dB, respectively. The evaluation results indicate that the system has good performance over a wide frequency band (100 Hz–1 MHz) and achieves a relatively high SNR.