Theoretic And Applied Research Of Electrical Impedance Tomography

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 resistivity) 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. EIT is a noninvasive imaging technique as it doesn't use nuclide and radial. It can be used to image repeatedly and monitor the patient without any damnification and discomfort for a long time. The EIT device is cheap and can work in any environment. EIT is an ideal and seductive noninvasive imaging technique in biomedical engineering.This dissertation aims at EIT to study its basic application and realize a practical, fast EIT algorithm with better resolution. It provides the imaging monitoring device with the basic theory featuring real-time monitoring and cheapness. Based on the study and analysis of the domestic and overseas EIT algorithms, simulations and experiments on EIT was studied from the aspects of the forward problem, dynamic EIT, static EIT and three-dimensional (3-D) EIT.In the study on forward problem of EIT, the effect of the position and area of electrical conductivity change in the field on the boundary potential was studied. Based on the study results, the noninvasive monitoring instrument for cerebral hematoma and edema was developed. Now the instrument has been applied in the first affiliated hospital of Chongqing university of Medical and Daping hospital, third military medical university in Chongqing. The instrument has got five certificates of Chinese patents.In the study on dynamic EIT, The theory of the equi-potential back-projection algorithm was described based on the principle of X-CT. The algorithm was studied from the aspects of sensitivity, current injection modality, number of electrodes, number of elements of FEM model, anti-noise, and so on. A good formula to calculate theweight coefficient W was brought up. The static EIT has been studied detailedly by using of One Step Newton Method (OSNM). A good method to initialize the initial conductivity in Newton-Raphson algorithm was given.Two dimensional FEM model can be modeled according to patient's CT slices. The model is more close to the real human brain dissection structure. Simulation study on dynamic imaging for cerebral hemorrhage has been done based on the model.The experimental platform of real-time EIT system with 16 electrodes has been developed. The experiment on real-time EIT has been done in a slain filled tank with different objects and also tested on the human thorax. The results show that the real-time imaging system has the feature of high precise location, fast imaging (reconstructed one image per four seconds), and high space resolution. From the reconstructed image on the human thorax, we can distinguish the left from right lung, heart of human thorax. Images are reconstructed according to the practical data of human obtained from foreign EIT. The results show that the equi-potential back-projection and OSNM algorithms can distinguish the physiological characteristics of heart and cms. These prove that the algorithms are valid.The dissertation also analyzed the experimental data. The results of analysis show that the position and relative volume of targets in the tank can be reflect from the change of measurement data. The stability of the hardware system is good. The system's precision is enough to the experiment on slain filled tank, but not eno...