A Wideband Electrical Impedance Tomography System Based on Sensitive Bioimpedance Spectrum Bandwidth

Abstract

A wideband electrical impedance tomography (EIT) system based on bioimpedance spectrum (BIS) analysis was proposed to image biological objects. The system integrated 16 electrodes to realize driving and measurement over 1 kHz-1.1 MHz. A modified Howland current source and voltage measurement channels were designed to obtain complex impedance. Peripheral component interconnect interface-based serial data acquisition module transferred the measurement data to a host PC. The system has the least signal-to-noise ratio of 40 dB in each channel and good consistency. The system utilized a two-step strategy, based on short-time Fourier transform and Hilbert transform, the wideband chirp excitation signal was employed to analyze the BIS first, from which the sensitive bandwidth, i.e., the frequency range in which the amplitude (and phase angle) of the object changes rapidly, is obtained. Then, the discrete frequency points among the sensitive bandwidth were selected to compose a multisinusoidal signal for impedance tomography with time-difference and frequency-difference (FD) methods. An impedance model was tested to evaluate the performance of BIS analysis. Experiments on phantoms consisting of carrot cylinder and nylon rod were designed to verify the working strategy of the system. The results indicated that the developed system can distinguish the objects and reconstruct medium distribution with high image contrast and frequency resolution. Compared with the traditional multifrequency EIT, the proposed method and system show advantages in imaging the local electrical properties with high-frequency resolution and obtaining the FD images in the sensitive BIS bandwidth.