Key Technologies Research Of Medical Electrical Impedance Tomography Based On Physical Model

Electrical Impedance Tomography (EIT) combined with computer technology, electronic information technology and graphics technology. The greatest advantage of EIT is the no damage and no radiation. Therefore, EIT gradually got the attention of the research groups.This paper is based on the modular thought to EIT system design. The hardware platform includes DDS module, incentive and measurement channel control module, data processing module, data transmission module. The test for DDS module includes voltage controlled current source(VCCS) output impedance, fifth-order Butterworth low-pass filter amplitude-frequency character, the error of output frequency. The signal processing module includes pre-programmed differential amplifier, demodulation, and programmable filter. In front of the differential amplifier circuit design,using more advanced technology,performance is more excellent the PGA281 amplifier, using DIP switches controlled gain adjustment. The data transmission module includes a power supply, A/D protection and correction, data transmission. Choose CJ431chip to produce two lines of reference voltage for correcting gain and offset error of A/D. The type of TMS320F2812 DSP can complete A/D conversion, data transmission. Data processing and transmission software consist of upper computer and lower computer. Upper computer part can complete the data receiving and preservation, lower computer part includes A/D conversion and correction, analog switch control, filter control, etc. The conversion accuracy error below 1.3% by software and hardware adjust. The improved Newton-Raphson(NR) algorithm for image reconstruction,direct regularization method for solving Jacobi matrix instead of NR iterative. Increase the speed of image reconstruction .In the last,Measuring the EIT system consistency of the channel, the electrical change rate under disturbance, tomographic image reconstruction based on physics model, by the parameters of position error, resolution, shape deformation,etc, evaluate the performance of reconstruction image.Through test the EIT hardware system, consistency of the channel electrical change rate under disturbance, image reconstruction and the performance of reconstruction image, EIT system worked stability and had good performance, EIT system with the idea of modular upgrade easily, during debug and experiment can find the lack of specific module.