The Design Of Electrical Impedance Tomography System

The Electrical Impedance Tomography(EIT),which has been developed since twenty yearsago,is a new and hot topic,which has a very broad application prospects. It is based on biomedicalimaging techniques. Because the different biological tissues have different electrical impedance,when Organism occurs disease or physiological activity, it can cause electrical impedance changes.By injecting a small alternating current in the human body, collectioning voltage signal from thesurface is used to reconstruct the body’s internal electrical impedance distribution image.The main work contents are as follows:(1) Design a DDS frequency synthesizer module to generate a sine wave voltage signal,using alow-pass filter to filter out the noise component and harmonics. This sinusoidal voltage signalthrough a voltage-controlled current source to get a stable and secure, high output impedance aconstant current source.(2) This paper completes design of data acquisition hardware system, which includes pre-amplifiermodule, phase-sensitive demodulation module, A/D converter module, the measurement model,select electrodes. Design software algorithms part and send the collected signal to the hostcomputer.(3) Do research on EIT system excitation drive mode and measurement mode,using the multiplexercircuit to complete inject motivation and measure voltage. the control terminal of the analogswitch is connected to the latch, which can save the control of the microcontroller IO port.(4) Completed a physical model of16composite electrodes, using multi-core shielded cable as atransmission signal wire, which can effectively shield other external interference.(5) Finally, having the test of the stability of the measurement data and the consistency of eachchannel. Experimental results show that the measurement data has a good stability and gooduniformity of the channels. Putting objects of different resistivity into measurement model andusing the data acquisition system to collect the voltage data, making using of the EIT imagereconstruction algorithm based on Newton-Raphson method to obtain the imaging graphics,imaging results can verify the accuracy of the data and reflect the internal distribution ofelectrical impedance.