Research On Image Reconstruction Of Open Electrical Impedance Tomography Based On Particle Swarm Optimization Algorithm

Electrical Impedance Tomography (EIT), which is one of the significant research projects in current biomedicine engineering, is an effective noninvasive imaging technique following the techniques of shape imaging and structure imaging. EIT is a relatively new medical imaging modality that produces images by computing electrical properties within the human body. Sinusoidal electrical currents are applied to a subject's body using electrodes attached to the skin, and the voltages that are developed on the electrodes are measured. Reconstruction algorithms use the applied electrical current and the measured electrode voltages to compute the electrical conductivity (or receptivity) distributions in the body. The reconstructed images can give not only the anatomy structure, but also the functional image. The X-CT, MRI and other imaging techniques can't compare this with EIT.In this paper, with detailed analysis of the limitations and problems in closed EIT, and based on the clinical application, a new model of EIT—the open EIT is used and the open EIT system is constructed to do the research. Described the basic principle and established the model and analysis the electromagnetic mathematical field, compare with three electrode-simulated mode, and then the back-electrode mode is chosen as simulated mode. Based on analyzing the image method of domestic and abroad, the PSO algorithm is proposed to realize the process of image reconstruction calculation, also some improvements in PSO is done to adapt EIT especially on initial population selection and high dimension, and also a lot of simulation and experiment is done to test the performance of algorithm. Establishe and improve electrical impedance tomography system of open software platform.The main work of this dissertation is as follows:(1) Analysis of the limitations and problems of closed EIT in the clinical application, and use a new model of EIT—the open EIT,which has many advantages, such as its adaptability, simple in operation, accurate in electrode positioning and strong anti-jamming capability, which makes it more suitable for clinical application. OEIT domain model was given out and electromagnetic problem was simplified, then get the basic electromagnetic equations. OEIT region model, electrode model and stimulated pattern is analyzed, then complete electrode model and back-electrode simulated pattern is chosen. In the finite element mesh model, we do fine mesh on the shallow area near the electrode while coarse mesh away from the electrode part, which both to improve imaging accuracy also to some extent control the amount of computation.(2) In the study of EIT inverse problem, first its research significance and difficulty is pointed out, and a detailed analysis of the ill-conditioned is carried out. Do a brief introduction on existing image reconstruction algorithm and focus on the static reconstruction algorithm, and then point out the problems in these static algorithms.(3) In the study of image reconstruction algorithms, on the basis of analyzing the tradition image algorithm, the mathematical optimization model of EIT inverse problem is proposed, and particle swarm optimization algorithm is chosen to realize the image reconstruction question. In order to enable the search of PSO to have direction, we use result of NOSER as initial population. At the same time, in order to solve the slow rate of computation and convergence which caused by high dimension, we carries on the classification to the granule according to spatial and the conductivity value's distribution. In brief, some measures was utilized to enhance the algorithm performance, and finally confirmed the algorithm through the simulation result. To further verify the performance of PSO algorithm, a lot of simulations have done in a closed EIT region, and its anti-noise performance were analyzed.(4) The software platform of OEIT system is established and perfected, which has multi-functions including display of FEM, data and image, serial communication, computation of forward and inverse problem, etc.Finally, this paper summarizes the major research achievements, as well as the existing problems and deficiencies. At the end of this paper, the author points out the further researches on this topic.