Electrical Impedance Imaging System Research Of Digital Phase Sensitive Demodulator

Electrical impedance tomography(EIT) is one of the new biomedical imaging technology which rose in nearly30years in the world.The technology is achieved by placing the electrode on the surface of living organism and injecting the current which creates current field in the living organism, then measuring the voltage of the electrode in accordance with the specific drive mode. The injected AC signal and several voltage values is set as the parameter values of the electrical impedance tomography software algorithms which can be used to obtain the distribution of electrical impedance of the living body. At last, analysing the electrical impedance tomographic image reflect the internal organization characteristics of biological object. As the technology has no radiation, it can achieve the protection for human body continuously and low cost, and these advantages can not be achieved by the traditional medical imaging techniques, which makes it become one of the most ideal and promising topics.This paper describes the basic theories of the electrical impedance tomography technology and its development situation; offers the principle of electrical impedance data acquisition system, and the electrode drive mode and phase-sensitive demodulation technology in detail. In addition, this paper achieves a suitable non-uniform sampling technique for digital phase sensitive demodulation. Based on FPGA, the paper completes the digital phase-sensitive demodulator via VHDL, module schematics and timing simulation of the digital system. Finally, according to the digital system, design the PCB hardware circuit. The circuit hardware tests results show that the system is able to use the low-rate ADC to achieve a high sampling rate, reduces the ADC quantization error and improves the SNR (signal to noise ratio) of electrical impedance tomography system phase-sensitive demodulator.