Electrical Impedance Imaging Technology And System Design

The technology of Electrical Impedance Tomography is to estimate the conductivity of an object from the boundary voltage or current measurements. A group of electrodes is attached to the surface of the object while the current stimuli are applied via these electrodes. Then the resulting voltages from the boundary are measured. Using the voltage measurements at the surface to estimate the conductivity as a function of space inside the object is called reconstruction.The EIT technology contains two problems that are the Forward Problem and the Inverse Problem. Mathematically the procedure of the EIT reconstruction is a non-linear and morsidity inverse problem, so the stable solution of which requires regularization methods.This thesis is mainly composed by two parts, the basic math-physics theory of EIT and the hardware design of an EIT system. In the part of theory, the forward and inverse problems are discussed. The Finite Elements Method is applied when we solve the forward problem. There are two main reconstruction methods to solve the inverse problem, the dynamic and static reconstruction arithmetic. In this thesis the static arithmetic is mainly introduced, especially the linear Newton iterative arithmetic and the regularization Newton arithmetic, the later can decrease the conditions of Jacobian matrix. At the end of this part, a series of emulational images simulated by MATLAB software are presented.The second part of this thesis is to discuss the way of hardware design of a generalized medical EIT system in the fourth chapter. The EIT system commonly consists of two blocks, the signal stimulation source and the voltage measurement block. This thesis adopts the FPGA as the main logical control and signal processing chip. Different from the routine method of using an analog Phase-Sensitive demodulator for EIT, we designed a digital Phase-Sensitive demodulator using FPGA.