Research On Image Reconstruction Algorithms And Design Of Software System For Electrical Tomography

Electrical Tomography (ET) is a new detection technique developed in recent years. Due to the advantages of being non-radiant, non-intrusive, rapid response and low cost, ET should have a good application prospect in many fields such as industrial process imaging, medical imaging and so on. Electrical Capacitance Tomography (ECT) and Electrical Resistance Tomography (ERT) based on different principle are two categories of ET.Although great progress has been made in ET technique in the past two decades, satisfactory reconstructed images in terms of good quality haven't been achieved because the reconstruction problem of ET is a nonlinear, underdetermined and ill-conditioned inverse problem. Meanwhile, the development of the software system has lagged behind leading to deficient functions. To solve the problems existed, the principles of some commonly used image reconstruction algorithms were studied, the Tikhonov pre-iteration algorithm and a fast image reconstruction algorithm based on Kalman filtering were proposed, and a software system for ET was developed in this thesis. The main work and results are as follows:1. The inverse problem of ET was analyzed. Five commonly used image reconstruction algorithms were reviewed, including sensitivity coefficient, Landweber iteration, Tikhonov regularization, Newton-Raphson and conjugate gradient method. Based on them, the Tikhonov pre-iteration algorithm which can markedly improve the reconstruction speed of Tikhonov iteration algorithm was proposed.2. The commonly used image reconstruction algorithms were evaluated in terms of the quality of reconstructed images and the reconstruction speed through simulation and experiment respectively.3. A fast image reconstruction algorithm based on Kalman filtering was proposed. And its effectiveness was verified through simulation and experiment. The results show that the proposed algorithm has the characteristic of good quality of reconstructed images, high reconstruction speed and good robustness to noise.4. TJU-ET-IV, a software system for ET which can be used for online testing and offline analysis, was developed using MFC and OpenGL under the programming environment of Visual C++. This software system containing five fast image reconstruction algorithms can carry out the image reconstruction for 12/16 electrode ECT/ERT system on two different cross sections at the same time. Also, it implements the functions of high-speed communication via USB, inspection of the longitudinal section, real-time display of void fraction, measurement of the cross-correlation velocity, history data storage and playback, and the like.5. The principle of cross-correlation velocity measurement was analyzed. A gas-liquid two-phase flow cross-correlation velocity measurement method based on void fraction was proposed. Taking advantage of the history data storage and playback function of TJU-ET-IV software system, the proposed cross-correlation velocity measurement method was evaluated. Experiment results show that the proposed method has good stability and high precision.