【作者】 李镐炜；

【导师】 王跃科； 董秀珍；

【作者基本信息】 国防科学技术大学 ， 仪器科学与技术， 2007， 博士

【摘要】 本文围绕生物组织多频电阻抗断层参数成像系统,对EIT理论前提、Cole-Cole模型、多频数据采集策略、图像重构影响因素、参数成像方法等基础问题展开了研究。主要内容如下:1.介绍了EIT基本原理与算法,论述了通常的单频EIT理论模型由于忽略了阻抗频率特性参数,不适宜直接推广用于阻抗断层参数成像。若考虑到频率特性模型又将使问题更复杂难解,这些因素在一定程度上制约了多频阻抗断层参数成像系统在理论上的完善。2.论证了生物组织欧姆电阻和容抗间的非线性谱变换关系,并进一步给出二者在Cole-Cole模型中散射系数α不同时的联系。分析了生物组织欧姆电阻和容抗与Cole-Cole模型参数的关系,进行了实验数据验证。提出以低频段多点测量欧姆电阻为基础的数据采集策略以及相应的Cole-Cole模型参数解析方法,有效避免了宽频段高精度测量电抗的问题。3.介绍了多频采集系统,阐述了数据解调的算法,将MMX技术引入多频采样数据解调,提高了数据解调的速度。4.分析了实验系统影响图像重构的因素。对电极极化及其频率特性对成像的影响进行了仿真和实验验证,提出一种多频系统测试数据预处理方法,实验结果表明预处理后的数据有效削弱了电极频率特性影响,同时理论分析表明预处理有助于减弱多频电流源输出摆动对重构数据的影响。5.建立了一种适于工作频率点较少的阻抗断层参数成像方法,描述了4频采集系统重构部分Cole-Cole模型参数的阻抗断层参数成像算法,采用基于物理模型的测试数据,得到形状和定位准确的初步成像结果。推导出适合对人体主要脏器进行阻抗断层参数成像的系统工作频率。更多还原

【Abstract】 This dissertation centers on the system of muli-frequency and electrical impedance parametric tomography. Theory predictions, Cole-Cole model, strategy of muli-frequency data acquisition, influencing factors on image reconstruction, method of electrical impedance parametric tomography are studied respectively. The main contents of the thesis are as follows:1. The principle and algorithm of EIT are introduced. A discussion is put forward that the method of the single frequency EIT is not conformable for directly transplant to EIPT since the frequency characteristic parameters of the impedance is neglected in the theoretically model. However, the problem is too complicated to solve if the frequency characteristic is taken into account. These theory predictions restrict the perfect description of EIPT come into being.2. Nonlinear transform relationship between the conductance and capacitivity of the bioelectrical impedance is demonstrated, and the relation between them when different dispersion factors exist in the Cole-Cole model is presented in addition. The connection of the Cole-Cole model parameters to the ohm resistance and capactive reactance of biologic tissue is analyzed, and validation experiment is conducted. A strategy of muli-frequency data acquisition avoiding of high precision measurement of reactance within wide frequency range is advanced as well as the corresponding parse method for the Cole-Cole model parameters is brought forward.3. The muli-frequency data acquisition system and the algorithm of data demodulation are introduced. MMX technology is introduced to the demodulation of muli-frequency data acquisition system and data demodulation is accelerated in the test.4. Influencing factors on image reconstruction are analyzed. The effects of the electrode polarization and the electrode frequency characteristics on reconstructed image are simulated and validation experiments are devised as well. A pretreating method for muli-frequency data is proposed. The preliminary experiment result shows the effect of the electrode frequency characteristics is reduced. It is also found in theoretical analysis that the method is helpful to release the influence of the excitation source output swing on the reconstruction data.5. An EIPT reconstruction method for muli-frequency system with fewer frequencies is described. The algorithm for the tomography of the partial Cole-Cole model parameters with a 4-frequecnies system is depicted. Reconstruction result with good location and shape is yielded utilizing the data acquired from a phantom. The working frequencies suitable for EIPT of main human organs are reckoned.更多还原