Electrode System Property And The Evaluation Method Of Electrical Impedance Tomography

Electrical impedance tomography (EIT) is one of the most important research topics in today's biomedical engineering. It has the following outstanding advantages: noninvasive, harmless, functional imaging and medical image monitoring. EIT is an attractive medical imaging technology with potential clinical application.Electrode system lies in the front of the whole EIT system and contacts with human body directly. It is one of the most pivotal parts of EIT system. There are a lot of problems should be studied and improved in the electrode system of EIT. The useless information from electrode system, such as noise, contact impedance and polarization voltage etc, goes into the following circuits as useful signals. They are amplified, transferred and participate in signal processing process, and therefore influence the result of reconstruction finally. The uncertainty made by the change of boundary shape and electrode movement, as well as the arrange function of electrode system, are also affect the quality of reconstruction image greatly. These problems are even serious, as EIT is stepping from experimental study into clinical study currently. The study of both the property of electrode system and optimizing the electrode system is very important.In this paper, firstly, the research history of EIT has been reviewed. Then the problems of current electrode systems have been presented. The principle of EIT, hardware system and image reconstruction method have been introduced. Several criteria functions used to evaluate the quality of reconstructed image have been proposed. The software, hardware and test platform have developed. Saveral reconstruction algorithms have been compared.We studied the influence of electrode type, electrode structure parameter, electrode count and the exitation function on the quality of image reconstruction, based on the coercive equipotential node finite element model. Some optimizing design suggestion has been proposed. A new electrode install method with simple structure has been designed, which is convenient to remove and install the electrode slices. And the electrode parameter can be changed freely.The impedance characteristic of EIT electrode, especially the amplitude and the stability of the alternating current impedance, is very important. Since the one-off ECG electrode has been widely used in clinical EIT measurement, we studied and compared more than ten ECG electrodes. Some suggestions need attention have been proposed. To minish the image error made by electrode movement and boundary deform in EIT pulmonary function measurement, we used a modified regularization algorithm and an elliptical model based algorithm to improve the image quality.An EIT method with planar electrode array has been proposed and a hand-held planar electrode system has been designed. Based on a 3-dimentional finite element model, a modified weighted backprojection algorithm, which is back-projected along equipotential surfaces of the 3D electric filed, is used to reconstruct slice images of 3D conductivity distribution, which is parallel to the electrode array. The method using planar electrode array establishs the foundation for EIT breast mesurement.