【作者】 罗辞勇；

【导师】 何为；

【作者基本信息】 重庆大学 ， 电气工程， 2005， 博士

【摘要】 生物电阻抗是反映生物组织、器官、细胞或整个生物机体电学性质的物理量。生物电阻抗技术是利用生物组织与器官的电特性及其变化提取与人体生理、病理状况相关的生物医学信息的一种无损伤检测技术,具有快速、简捷、成本低廉、安全等特点。本论文在分析、研究国内外有关电阻抗成像重建算法及其研究状况的基础上,研究实现了一种实用、快速、具有一定分辨率的电阻抗成像算法——快速牛顿一步误差重构(FNOSER)动态算法,对成像算法进行了大量的实验研究和数据分析,对成像系统所采用的硬件测量装置的性能进行了研究。本文主要工作如下: (1)研究了目前常用的相邻、相对、交叉等驱动模式。利用开发的电阻抗仿真软件,在有限元模型中所有单元电导率为1 均匀背景下,比较了相邻、相对、交叉驱动模式下的数据和曲线。从三种驱动模式存在着共性出发,提出了统一驱动模式和驱动角的概念。数据分析表明在相同的硬件测量装置下,驱动角在不断加大的过程中数据测量的稳定性不断提高。(2)基于牛顿法的一步误差重构算法对静态电阻抗成像技术进行了详细研究,推导出FNOSER 静态算法,快速牛顿一步误差重构算法其雅可比矩阵等可以事先计算好,从而可以获得和反投影算法类似的成像速度。仿真研究表明:FNOSER 算法可以实现静态电阻抗成像,且具有图像分辨率高、定位精确、成像速度快等特点。(3)在FNOSER 静态算法基础上,提出了FNOSER 动态算法。针对FNOSER算法和反投影算法,研究了静态算法和动态算法之间的转换关系。在FNOSER 算法和反投影算法中,动静态算法是统一的,可以相互转换的。如果参考电压数据是利用有限元正向计算单位电阻率均匀分布下的“测量电压”拟合出来的理想参考电压就是静态算法,而如果参考电压数据采用初始的测量值(或者称前次测量值)就是动态算法。(4)对反投影算法和FNOSER 算法进行了仿真比较。反投影算法没有经过严密的数学推导,是借鉴CT 反投影理论而形成的电阻抗成像算法。由于其投影路径不仅是曲线,而且比较宽,是“宽投影”,并且投影面积大小不一,因此成像的分辨率差。而FNOSER 算法经过严密的数学推导,其公式中的很多量具有很强的物理含义,仿真研究表明FNOSER 算法定位准确,相比反投影算法,FNOSER 算法可以分离多个目标。(5)提出了消除伪迹均值算法。伪迹的产生主要来自于测量数据中所包含的噪声和误差,对于反投影算法还有反投影理论本身所固有的星状伪迹。针对反投影和FNOSER 两种不同的成像算法,在仿真和实验条件下,分别验证了均值算法具有消更多还原

【Abstract】 Biology electrical impedance is a kind of physics quantum reflecting biology tissue、apparatus、cell or the electrics character of whole biology economy. The biology electric impedance technology, which is a kind of check technique without trauma, is to distill biomedicine information related to physiology or pathology of God’s image according to the electricity characteristic or the change of biology tissue and apparatus. Based on the analysis and research of the domestic and overseas EIT algorithms, a practical and fast EIT algorithm with better resolution---Fast Newton’s One-Step Error Reconstructor (FNOSER) dynamic algorithm is studied and realized in this dissertation. Based on a great deal of experiment researches, the EIT algorithm and performance of hardware-measuring device needed by imaging system are analyzed. The main work is described as follows: (1). The primary drive patterns such as adjacent, polar and cross drive are studied. With all elements’conductivity being considered as one, the data and curve from adjacent, polar and cross drive patterns are compared with EIT simulating software. Based on the commonness of the three drive patterns, the concept of uniform drive pattern and drive angle is put forward. Data analysis result indicated that with the same hardware, the stability of data-measuring is improved continuously when the drive angle kept on increasing. (2). FNOSER static algorithm has been brought forward based on the detail study on One-Step Error Reconstructor algorithm of the static EIT. As the Jacobi Matrix of Fast One-Step Newton Error Reconstructor algorithm can be calculated previously t, the same imaging speed as back-projection algorithm can be made. The study results show that the FNOSER algorithm can obtain static image with a character of high space resolution, accurate orientation, fast imaging, and so on. (3). The FNOSER dynamic algorithm has been put forward based on the FNOSER static algorithm, and the relationship between static and dynamic algorithm has also been studied aiming at FNOSER and back-projection. In the FNOSER and back-projection algorithm, the dynamic and static algorithm are uniform and can be transformed each other. If the reference voltage data is the ideal reference voltage obtained from “measure voltage”considering symmetrical distribution of unit resistance in finite element forward calculation, it’s a static algorithm. If reference voltage data is obtained from the first value (or called former value), it’s a dynamic algorithm. (4). The back-projection and FNOSER algorithm have been simulated to make a compare. Without strong mathematical theory basis, the back-projection algorithm is a kind of electrical impedance imaging algorithm using the CT back-projection theory for reference, and it has a bad imaging resolution because its projection and path are not only curve, but also very wide, called “Wide Projection”with different area sizes. FNOSER algorithm has strong mathematical theory basis. Research show that FNOSER algorithm can distinguish targets well than back-projection algorithm (5). Eliminating spurious loci algorithm is put forward. The spurious loci mainly come from noise and error included in measure data. For star false trace is indigenous to back-projection algorithm and theory, aiming at two different imaging algorithm back-projection and FNOSER, the simulation and experiments results show apart that mean algorithm has a better capability of avoiding spurious loci to make imaging target more clear. (6). EIT imaging software system has been developed. The system is an integrated whole including simulation and real-time data gathering imaging, whose finite element model can be analyzed automatically and size can be adjusted. The isoline and nephogram drawing algorithm in finite element after-management have been realized. It supports uniform drive pattern and its drive angle can be adjusted at will. (7). Many experimental researches have been carried out with the hardware and imaging software. Experiment results show that definition of imaging using FNOSER dynamic algorithm is better than that of back-projection dynamic algorithm. A lot of experiments have been done to study different objects, such as perspex bar, aluminum bar, pencil and 2mm lead, etc. Studies show that by using FNOSER dynamic algorithm in EIT system, these objects in the flume can be accurately displayed, and the resolution is very high. Relative size and position can also be reflected. Clear reconstructed images can be obtained through experimental data based on plaster cast perspex. (8). Experiments have been done on a grown rabbit. Objects have been put into thorax and skull of a rabbit, and clear dynamic re-construction images have been obtained by using FNOSER dynamic algorithm. (9). Drive angle experiments show that small objects, such as pencil, can not be imaged when there is only one electrode for drive angle in EIT device II, but when there are 3 electrodes or more than that for drive angle, these small objects can be imaged. So,increase on drive angle helps to improve imaging effect of single target. When there are 2 or 3 electrodes for drive angle, the limit between two targets is obvious and the images are very clear. In course of increasing electrodes for drive angle from 4, the re-construction image of central target becomes weaker and darker. When there are 8 electrodes for drive angle, the central image becomes so dark that two targets with the same size can not be distinguished from image. (10). FNOSER static algorithm has been studied. Collectivity of realizing on experimental device in existence is unsuccessful, which results from great system error. So there is a need for improving hardware-measuring device and imaging algorithm to make static algorithm better applied.更多还原