Research And Design Of Electrical Impedance Tomography Testing System

Electrical impedance tomography(EIT) is a new medical imaging technique making use of the resistivity distribution in vivo, which has a broad application prospect in biological information detection and imaging. The basic principle is that different biological tissues have different impedance characteristics, and the disease or physiological activity can cause changes in the electrical impedance. By injecting current signal to the organism through excitation electrode system to obtain voltage signal from the electrode, using a specific algorithm to reconstruct the graphics reacting the inside electrical characteristics, it can obtain the structure and function information about the tissue or organ.In this paper, electrical impedance imaging test system has been optimized. The system and each function modules are constructed and completed. By modular method, the excitation current source module, multi-channel switch module, data acquisition module, electrode physical model and processor control module are designed. The main contents are as follows:(1) Design and implement a EIT system, which can be compatible with both the 16 and 32 electrodes, composed of precision signal generator, enhanced Howland current source, 16-channel and 32-channel multiplexer, pre-filter circuit, precision instrumentation amplifier, variable gain amplifier, four-order band-pass filter, phase-sensitive demodulation circuit, 16-bit A/D converter circuit and ARM processor control system. The control program is to achieve accurate and effective control of the system. With the ARM processor as the core controller to construct embedded EIT system and corresponding control program, the system has good performance, high acquisition speed, and simplicity to expand its function. In the phase sensitive demodulation circuit, sine wave signal instead of square wave signal is used as a reference signal for switching demodulation, which has a better detection performance and higher precision.(2) Construction of physical model whose electrode structural parameters are variable. By connecting stainless steel alligator clip to the steel pads fixed to the wall of water tank, the electrode is easy to be disassembled and replaced, which is beneficial to study the influence of the variation of electrode parameters on the measurement data and imaging result. Physical models of 16 electrodes and 32 electrodes are built as the detection objects.(3) Research on the EIT system excitation and measurement mode, and test the performance of each module and the whole system. The imaging data is collected through the salt water tank experiment, and the stability, consistency and validity of the data is tested. The image reconstruction of the physical model of the 16 electrode and the 32 electrode is realized by the Newton Gauss algorithm and the sensitive matrix algorithm respectively. The experimental results show that this system has good imaging effect and high resolution, and can effectively realize the localization and detection of the target area.