Research On Annular Tissue Impedance Imaging Based On Conjugate Gradient Method

For the existing diagnosis of colorectal cancer has a greater subjectivity,for the depth of the invasion of the intestinal wall and the lesion diffusion boundary can not be accurately determined,according to its functional changes before the characteristics of organic disease,this paper put forward a Electrical Impedance Tomography(EIT),which can be used in the early detection of disease,uses this technique to study the electrical properties of the disease by studying the annular tissue(eg,esophageal tissue,intestinal tissue,etc.).The main contents of this paper are as follows:(1)The mathematical model of EIT positive problem is established by combining boundary conditions.According to the special geometry of the ring organization and the direction of the power line,the ring finite element method is established,and the triangular element is subdivided on the basis of it.The effects of four kinds of splitting densities on the boundary voltage are analyzed,and the appropriate simulation model is selected to save the computation time and get better results.The imaging model of three kinds of EIT positive problems is established and simulated.Finally,the correctness of the positive problem is verified by physical experiments.The feasibility of the model was obtained by comparing the boundary voltage with the relative model and the simulation of the three kinds of common diseases.(2)Using the Agilent4294 A precision impedance analyzer to measure the resistance of the in vitro animal ring tissue at different frequencies,the optimal current excitation frequency range is 3k Hz-400 k Hz.An agar model 1 with an electrical conductivity of0.2 S/m was prepared to simulate the normal annular structure.The conductivity at 10S/m was used to simulate the agar model 2 of the diseased tissue.Select the frequency range of 100 k Hz as a stimulus,with a multi-channel impedance tester measured two agar models at the same location voltage,the voltage difference of 0.29 V,and the voltage difference can be reconstructed through the algorithm,indicating that the ring organization The EIT positive problem model is set correctly.(3)The conjugate gradient method is used to image reconstruct in the EIT inverse problem of ring organization.This paper analyzes the isometric line backprojection algorithm,the steepest descent method and the Landweber iterative algorithm,and proposes a conjugate gradient method for image reconstruction in this study.The principle and convergence of the conjugate gradient method are proved,and the optimal convergence times are obtained.The reconstructed images were evaluated by parametric image correlation coefficient r and structural deviation function SSIM(X,Y).The reconstructed images were evaluated by conjugate gradient method,equipotential line backprojection algorithm and Landweber iterative method respectively.The results show that the value of r and the SSIM(X,Y)value of the reconstructed image are the largest by the conjugate gradient method,which proves that the image quality is the best.The study of positive and inverse problems proves that EIT can be used for early disease detection.