Lung Ventilation Functional Imaging Based On Electrical Impedance Tomography

Bioelectrical impedance is one of the electrical characteristics of biological tissue, organs and cells when injected a safety current under threshold value. Electrical impedance tomography (EIT) is an imaging technique which aims at estimating the interior conductivity or resistivity distribution within a region of interest (ROI). In EIT, a sensing electrode array is attached on the boundary of an object, safe alternating currents are injected through these electrodes, and the resulting voltages are measured which reflecting the electrical characteristics of the biological tissue and organs. After data collection and processing, the conductivity or resistivity distribution is imaged by reconstructed algorithms.Compared to the conventional medical imaging techniques, such as X-ray computerized tomography (CT) or Magnetic resonance imaging (MRI), EIT has the advantages of reasonable cost, harmlessness, and portability, etc. Furthermore,it is of advantage, such as non-invasion functional imaging technique through mining a wealth of physiological and pathological information by means of bioelectrical impedance. EIT makes bedside continuous monitoring achievable. The research work of lung ventilation functional imaging by EIT is illustrated briefly as following:1. EIT_TJU_III system is researched based on Field Programmable Array (FPGA);2. Reconstruction algorithms are researched. Firstly, a dual-model reconstruction algorithm is put forward, which reconstructs two dimension images based on a sensitivity matrix calculated from three dimension model. The dynamic ventilation is imaged by Matlab. Secondly, adaptive multigrid (AMG) reconstruction algorithm considering posterior estimate and adaptive refinement in the forward problem is researched, and the imaging results using regularized gauss-Newton algorithm are achieved. Finally, the conjugate gradient least squares (CGLS) algorithm is also researched and the some performance indexes are given out.3. The impedance frequency characters of pig's lung, heart, muscle and fat are measured with small current injecting under different frequencies, the human health lung tissue and the soakage lung cancer tissues are also measured and analyzed by frequency dispersion theory. The Cole-Cole parameters are calculated.4. An approach to producing an accurate reconstruction image of the object regarding the physical geometry and prior conductivities information within thorax is proposed and simulated. The sensitivity distributions of traditional circular platform and the proposed physical platform are compared. The lung ventilation experiments are undertaken. A software kit is developed using Visual C++ and the math library of Matlab C++, it can realize the real-time dynamic imaging with prior information.5. The experiments for testing the spatial resolution and the resistivity resolution of EIT_TJU_II are undertaken. The thesis gives out some performance indexes.6. An idea of characteristic pixels is put forward in medical electrical impedance tomography, which can mine more useful biological information for clinic application.At the end of the thesis, the research work is summarized briefly and further research work is suggested.