Study On Open Electrical Impedance Tomography:Theory And Technology

Electrical impedance tomography (EIT) is a kind of new imaging technology which is mainly used in clinical diagnose. EIT uses electrode matrix placed on human surface to inject excitation currents into human body and measures the electrical response signal, and then gets the electrical characters of human tissues that are related to human body's physiological and pathological situation. The imaging result of EIT can reflect not only the human tissue's anatomical construction, but particularly its functional situation, which is an advanced feature for EIT compared with the traditional medicine imaging technologies. EIT doesn't use the nuclide and radial, so it is noninvasive to human body and can be repeatedly used in short time. Meanwhile, the EIT equipment is relatively affordable, and can be operated just in normal environment, so it has a huge market. With these advanced characters, as a new technology in imaging, EIT is considered very attractive and competitive in the world of biomedicine engineering.EIT technology has been researched for about thirty years. However, because EIT is weak in resolving rate, this technology is still in the stage of lab experiment, and the few researches about it are limited in the clinical application domain. It is not realistic for EIT to become the main imaging technology in clinical application in a short time, but as such a new technology with many advanced features, EIT is valuable to be an assistant detecting tool in some particular clinical applications. Beside the low resolving rate, the closed working mode which is widely used in recent years is also a main factor in the marketing of EIT in clinical application. This paper is mainly about this issue.In this paper, with detailed analysis of the limitations and problems in closed EIT, and based on the clinical application, we proposed a new thought of EIT—the open EIT, and constructed the open EIT system to do the theoretical and practical research.In theoretical research, we established the electrode model and the electromagnetic mathematical mode and created its solution based on the finite element method. Then, from the prospective of the forward problem, we used the FEM simulating software to analyze the influence of boundary approximation to the measurement of electrical potential value on boundary and the influence of various excitations to the measuring depth.In imaging reconstruction research, by comparing different reconstruction algorithms of EIT, we focused on the one-step Newton method which has better performance in quality and speed. Based on the future clinical application of open EIT, we developed a frequency difference fast Newton's one-step error reconstruction (FDFNOSER) method and validated its effect through simulation.In the design of hardware system, based on the deep research on the key problem of EIT measurement, and according to the actual structure of open EIT, some advanced signal measurement techniques were employed, such as DDS, DPSD, high-speed DA/AD models. With the help of the high-performance analog and digital integrate chips, the measurement sensor was minimized. The open EIT software studio was constructed with MATLAB. The experiment prototype was built and the basic performance had been tested.To test the validity of the principle and the method of the open EIT and the performance of the corresponding measurement system, the physical model and primary clinical experiments were operated. The physical model experiments include the water-tank and agar model experiments. A rectangle water tank is specially developed for open EIT, and the results show that the open EIT method can clearly reconstruct the conductivity distribution of organic sample in a shallow level. The agar model experiment is more like the clinical application and the result shows that it can differentiate the targets under surface. Based on these physical model experiments, the primary clinical experiments were operated, 37 samples were tested, including breast cancer patients, mammary gland diseases outpatient, and normal individuals. The clinical experiments results reveal that the open EIT method can basically locate the massive tumor in the right position, and its result is consistent with the X-ray and Ultra-sound pictures. However, there is still a rather long way for the final application in the clinical field, so a further research and development on open EIT is required.In the primary study of 3D EIT, concerning with the lack of effective data in 2D EIT, with the construction of open EIT, the 3D model was built, and the FEM simulation was employed in studying the forward problem to find the way to improve the system performance.The final part is the summary description, the main research work and achievements were listed. Meanwhile, the current disadvantages and the correlative research prospect were indicated.