【作者】 童倜；

【导师】 马艺馨；

【作者基本信息】 上海交通大学 ， 仪器仪表工程， 2011， 硕士

【摘要】 电阻抗层析成像技术(Electrical Impedance Tomography, EIT)是一种基于电学敏感原理的功能成像技术。它依据人体内不同组织具有不同的电阻抗、同一组织在不同的生理条件下具有不同的电阻抗这一物理现象,在体表施加弱的安全电流,并从体表测量电压,然后根据一定反问题算法来重建人体内部的电阻抗分布图像,用于疾病诊断和临床监测。相对于现有的常规医学影像技术,EIT具有快速、无创、无放射性危害、便携、经济、检测灵敏度高、可长期用于床边观测等优点,吸引着国内外众多研究者的关注。本论文的主要内容是在现有理论的基础上,开发并实现高频宽高输出阻抗的用于生物电阻抗成像数据采集系统的激励电路。首先研究比较了包括文氏桥振荡电路、DDS技术在内的正弦波发生器实现方案,选用商业化的高性能DDS芯片用于EIT系统的正弦波发生器;其次研究采用双路1:2的模拟开关TS3USB221与1:16的模拟开关CD74HCT4067-Q1构建模拟开关阵列的方案,满足了64电极EIT系统对选通功能的需求;然后研究了电压控制电流源性能的测量方法,给出了频率升高时消除测量误差的方法;通过电路仿真实验、实际电路测试,研究比较了现有的基于独立元件实现的电压控制电流源电路的性能;重点研究了改进的Howland电路的特性,通过电路仿真与实验测试,实现了基于AD8610的改进的Howland电路,其输出电流幅值误差小于0.5%,在200KHz以下频率时输出阻抗大于80KΩ,表现出了比其他电压控制电流源方案更高的输出阻抗以及幅值稳定性的性能。改进的Howland电路的输出阻抗在大于200KHz时受寄生电容耦合电容等影响而下降,为克服电容的影响,本研究进一步提出采用GIC并联提高电流源输出阻抗的方法。基于PSPICE的仿真结果表明,当Howland电路并联GIC以后可以得到1MHz频率范围内高于1MΩ的输出阻抗,且保持了良好的线性度,能很好地满足医用EIT系统的需要。最后对本论文的研究工作进行了总结并对今后的研究工作给出建议。更多还原

【Abstract】 Electrical Impedance Tomography (EIT) is a new functional imaging technology. EIT bases on the physical principles that the human body’s different organizations have different electrical impedance. EIT apply weak current at the surface of human body, and measurement voltage. Then according to certain algorithms, EIT reconstruct the impedance distribution image within the body. Compare with the existing conventional medical imaging techniques, EIT’s advantages include non-invasive, non-radioactive, portable, affordable, long-term observation for bed, etc., Recently, EIT is attracting the attention of many researchers at home and abroad.The main content of this paper is based on the existing theory to develop and implement high-bandwidth high-output impedance excitation circuit for electrical impedance tomography system.The paper first studies on the theories of sine wave generator, including the Wilson Circuit and DDS technology. Use commercial DDS chip for high-performance EIT system sine wave generator. The paper uses dual 1:2 analog switch TS3USB221 and 1:16 analog switch CD74HCT4067-Q1 to build analog switch array to meet the gating function of 64 electrode EIT system. Then studies the measurement methods of voltage-controlled current source’performance. Study the method to eliminate errors with the frequency increases. Compared the performance of existing voltage-controlled current source based on independent components by circuit simulation and actual circuit testing. Study on the characteristics of the enhanced Howland circuit. Improve Howland circuit to achieve high output impedance voltage controlled current source. Achieved an enhanced Howland circuit based on AD8610, the output current amplitude error is less than 0.5%, when frequency is less than 200 KHz, the output impedance is greater than 80KΩ. This circuit’output impedance and amplitude stability performance is better than other voltage-controlled current sources. The coupling capacitance by parasitic capacitance effects of decreased the output impedance performance of enhanced Howland circuit when the frequency is greater than 200 KHz. To overcome the effects of capacitor, propose a further improvement of the VCCS by using generalized impedance converter circuit. Based on PSPICE simulation results, this improvement could get output impedance of 1MΩat 1MHz. Also maintain a good linearity, could meet the needs of medical EIT system.Finally, this paper summarizes the research work carried out and recommendations for future research are given.更多还原