Research On The Space Model And Algorithm In Electrical Impedance Tomography For Gastric Motility

Abnormal gastric motility is one of the most important sources of gastrointestinal diseases.However,due to the lack of understanding of the pathophysiological mechanisms of gastric motility abnormalities and a detection method that can fully reflect the gastric motility,currently the prevention and treatment of gastrointestinal diseases are not very satisfactory.According to the functional changes of human tissues prior to the characteristics of organic lesions,this article uses an electrical Impedance Tomography(EIT)technology that can be used for early detection of diseases and to perform functional studies on gastric motility,extract the electrical properties of gastric motility.The main work is as follows:1.The mathematical model of EIT positive problem is established by combining the boundary conditions.Based on the anatomical characteristics of gastric organs and abdominal cavity,a finite element subdivision model of human abdominal cavity was established.A three-layer electrode model was constructed and three kinds of electrode excitation models were established: the same-layer adjacent electrode excitation model,the same-layer opposite electrode excitation model,and cross-layer upper and lower electrode excitation models.This thesis put forward two evaluation parameters: the measured boundary voltage sensitivity,boundary voltage measurement dynamic range.Using the Comsol Multiphysics software platform to carry on the simulation,we can know the simulation results by analyzing the simulation results: the sensitivity and stability of the boundary measurement voltage of the same-layer electrode excitation model is better than that of the cross-layer electrode excitation model,and the same-layer electrode model is better than the cross-layer electrode excitation model in distinguishing gastric contents.The sensitivity of adjacent excitation model is better,but the dynamic range of boundary voltage is smaller,the smaller the dynamic range of boundary voltage is,the better the imaging quality of the model is.In the case of different gastric contents,the relative electrode excitation model has the largest difference in parameter values,so the relative electrode excitation model requires more complex image reconstruction.2.The open electrode model was introduced to compare with the three-layer closed electrode model.Through comparison,the open electrode model has higher measurement voltage sensitivity,but has poorer distinguishability for different conductivity,and the voltage dynamic range larger than the closed three-layer electrode model stability.Therefore,considering comprehensively,the closed three-layer electrode model combined with the relative electrode excitation model is more in line with the requirements of image reconstruction.3.The conjugate gradient algorithm was used to reconstruct the image of gastric impedance imaging.The equal potential line back projection algorithm,the fastest descent method and the Newton-Raphson algorithm are analyzed,and the conjugate gradient method is proposed for the image reconstruction in this study.The principle of the conjugate gradient method and the proof of its convergence are expounded,and the best convergent times of the 10 times are obtained.The image reconstruction is calculated by MATLAB,the first construction of intraperitoneal model,simulated gastric organ using a sphere,the sphere size change of simulated gastric emptying,and then through the iterative algorithm has been reconstructed image,the reconstructed image,using the image correlation coefficient a,structure parameter deviation function SSIM(X,Y)of the reconstructed image is evaluated.Results: the same-layer opposite electrode excitation model is obtained by calculating the electrode image a value and SSIM(X,Y)are the largest value,that it's the best imaging quality.Through the research of positive problem and inverse problem,it is proved that EIT technology can be used to detect gastric motility function,and the advantage of the same layer electrode excitation model in the study of gastric motility and the applicability of conjugate gradient algorithm in inverse problem solving are clarified.