Electrical impedance tomograph is a system that produces the electrical impedance image of the cross section of the body based on the application of current and measurement of voltage from the periphery. The impedance may be represented as two parameters such as resistivity (conductivity) and permittivity. It provides the electrical property of the tissue inside the body. The hardware design of this system includes (1) oscillator circuit, (2) current generator, (3) digital control circuit, (4) voltage measurement circuit, and (5) electrode array. The design is based on the modularized circuit, multi-current channels, and multi-frequency concept for better system testing and maintenance. The frequency for the carrier signal of proposed system may be set to be 15 kHz, 30 kHz, 80 kHz, and the combined 10 kHz and 80 kHz. The specifications of the whole system may be summarized as that it has 32 electrodes, the maximal current is ± 5 mA (rms), each current generators has 12-bit resolution in current setting, the sampling rate is 312 kHz, the input voltage range is ± 4 V (rms), and the maximal load resistance is 800 Ω. The needed voltage supplies are ± 12 V and 5 V. Finally, it is demonstrated to produce resistivity image for the phantom using one-step Newton-Raphson based image reconstruction algorithm.
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