3D-EIT系统电极优化设计

Electrode Optimization Design of 3D Electrical Impedance Tomography System

探究三维电阻抗成像系统电极结构对数据测量及图像重建的影响。考虑到电极形状和电极在边界上的分布状态对成像效果的影响,在构建的3D电阻抗系统模型及层间准对角激励相邻(QBD)测量工作模式下,对方形电极(I型)、圆形电极(II型)、同心圆复合电极(III型)和方圆复合电极(IV型)4种形状电极,就0.2到0.7之间8种不同电极占空比(DR)情况进行对比研究。采用重建图像的相关度R,敏感场的灵敏度均匀性P,测量电压动态范围D进行评价。对比结果表明,在DR为0.4~0.5之间,4种电极结构下的图像相关度R均优于其他DR情况,而且IV型电极的R和P指标略优于I^III型,但复合型电极(III和IV型)在DR为0.3和0.35时边界测量电压动态范围D偏大,稳定性差。对三维场域中5个高度不等(7.5~30 cm之间)、电导率相同的物体,采用共轭梯度算法进行图像重建。数据经归一化处理,截取2个电极层、1个电极间层及2个电极外层共5个等间隔的不同断层图像进行对比,4种电极模型下的成像结果均与真实分布相吻合,IV型电极所成图像伪影略小,效果较好,与指标评价结果一致。本研究为QBD模式的三维电阻抗成像系统确定了电极形状及电极分布,为进一步研究三维空间的电阻抗分布奠定基础。

The aim of this work is to explore influences of electrode structure parameters on data measurement and the image reconstruction of 3D medical electrical impedance tomography （EIT） system. Considering the influences of the shape and distribution of electrodes on image reconstruction, four kinds of electrode structure are designed： square （Ⅰ）, round （Ⅱ）, concentric cylindrical combination electrode （Ⅲ） , and square-round combination electrode （Ⅳ）. Based on QBD （quasi-opposite drive between two layers） working pattern, eight different duty ratios between 0.2 and 0.7 were studied comparatively. By studying the targets as correlation coefficient of the images R, the uniformity of sensitivity field distribution P and the voltage dynamic range D, the measured data and reconstructed images are evaluated under the four electrode structures. Results showed that the four types achieved satisfied R between 0.4 - 0.5 exceed other DR, among them type IV gets better R and P than others types. But when DR 0. 3 and 0. 35, the compound electrodes （Type Ⅲ and Ⅳ） were unstable with higher D than others. Images were reconstructed after regularization for five different layers from the bottom to the top including two electrodes layers, internal layer and external layers. The five targets with same conductivity but in different height （from 7.5 cm to 30 cm with equal intervals） were placed inside the tank. The images are coincident with the real distribution. The images by type Ⅳ appear less artifacts andhigher imaging quality which is fitted with the targets analysis results. This research gives a light in considering the electrode configuration in three dimensional EIT with QBD working pattern and makes a foundation for 3D- EIT further research.