电阻抗层析成像系统激励电路的设计
|
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。
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.
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。
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.
引文
[1]何为,罗辞勇,徐征.电阻抗成像原理[M]北京;科学出版社,2009
[2] Surowiec AJ, Stuchly SS, Bar JB. Dielectric properties of breast carcinoma and the surrounding tissues,1988(04).
[3] Jossinet. The Variability of Resistivity in Human Breast Tissue. Medical and Biological Engineering and Computing, 1996, Vol(34):346-350.
[4] Prasad SN, Houserkova D, Campbell J. Breast imaging using 3D electrical impedence tomography,2008(01).
[5]廖琪梅,董秀珍,付峰.人体乳腺组织电阻抗特性的研究[ J] .国际生物医学工程杂志, 2006, 29( 4) : 218-221.
[6] E. J. Linkley, B. H. Brown, R. Knowles, Y. Mangnall, F. J. McArdle, and A. J. Wilson,―Development of a portable EIT system for gastric emptying measurements,‖Proc. 13th Ann. Int. Conf. IEEE Eng. Med. & Bio. Soc,Vol. 11, No.4 1993.
[7] D. A. Witsoe, E. Kinnen. Electrical Resistivity of Lung at 100kHz, Med. Biol. Eng., 1967,5:239-248.
[8] M. E. Valentinuzzi, L.A. Geddes, L.E. Baker. The Law of Impedance Pneumography, Med. Biol. Eng., 1971,9:157-163.
[9] Boone K, Barber D, Brown B. Imaging with electricity review of the European concerted action on impedance tomography. Journal of Medical Engineering &Technology,1997,21(6):201.
[10] R.Avill, Y.F.Mangnall, B.H.Brown et al. Applied Potential Tomography: A New Invasive Technique for Measuring Gastric Emptying, Gastroenterol, 1987, 92: 1019 -1026.
[11] S.P.Devane. Application of EIT TO Gastric Emptying in Infants: Validation Against Residual Volume Method, Clinical and Physiological Applications of Electrical Impedance Tomography, D.Holder(ed).UCL Press,London.1993,Chapter 12,113-123.
[12] A.J.Baxter, Y.F.Mangnall et al. Evaluation of Applied Potential Tomography as a New Non-invasive Gastric Secretion Test,Gut 30:1730-1735.
[13] R.H.Smallwood, Y.F.Mangnall et al. Transport of Gastric Contents, Physiol.Meas., 1994, 15(Suppl.2A):175 -188.
[14]费力,季耀东.颅脑损伤性急性病情恶化临床分析(附16例报告)[J].创伤外卡杂志, 2001, 3(3):190-193.
[15]唐秀贞,吴珂,崔群生.慢性持续性脑内出血的CT表现[J].中国医学计算机成像杂志,1999, 5(1):12-14.
[16]孙国成,蔡振杰,刘维永.体外循环心内直视术后脑部并发症的急救处理[J].中国急救医学, 2000, 20(7):395-397.
[17]董秀珍.生物电阻抗技术研究进展[J].中国医学物理学杂志,2004,21(6):311-316.
[18] K.A. Dines and R.J. Lytle. Analysis of Electrical Conductivity Imaging, Geophysics, 1981, 46:1025-1036.
[19] F. Dicken, M. Wang. Electrical Resistance Imaging for Process Applications. Meas. Sci. Technol., 1996, 7:247-260.
[20]徐桂芝,杨硕,李颖等.电阻抗断层成像技术综述[J].河北工业大学学报,2004,33(2)35-40.
[21] Henderson RP and Webster JG.IEEE BME 1978,25:250-254.
[22] L.R. Price. Electrical Impedance Computed Tomography(ICT):A new CT Imaging Technique,IEEE Trans. Nucl. Sci., 1979,26: 2736-2739.
[23] D.C. Holder. Biomedical Applications of Electrical Impedance Tomography[J]. Physiol. Meas., 2002, 23(1):3-5.
[24]Newell JC. An Electric Current Tomograph. IEEE Trans Biomed Eng, 1988;35(10):828-833
[25] Brown BH, Seagar AD. The Sheffield data collection system. Clin Phys Physiol Meas. 1987 91-97
[26]刘锐岗.电阻抗断层成像的激励模式[J].国外医学生物医学工程分册, 1999, 22(1): 20- 24.
[27]Towers C M, McCann H, Wang M, Beatty P C, Poinfrett D J D and Beck M S 2000 3D simulation of EIT for monitoring impedance variations within the human head Physiol. Meas. 21 119-24.
[28] Holder DS.Electrical impedance tomography methods,history and applications [M]. UK:Bristol,Inst Phys Pub,2005.
[29]王妍,任超世.电阻抗断层成像电极系统性能与评价方法研究[D].北京:中国协和医科大学生物医学工程,2009.
[30]尤福生,董秀珍等.电阻抗断层成像中临近和对象激励模式的研究[J].第四军医大学学报,2004,25(1):88-91.
[31]杜岩,柳重堪,程吉宽.电阻抗成像的加权Newton-Raphson算法[J].北京航空航天大学学报,1998,24(2):161-165.
[32] Mi Wang.F J Dickin.M S Beck Improved electrical impedance tomography and collection system and measurement protocols 1992
[33] Tierney J, Rader C, Gold B. A Digital Frequency Synthesizer[J].IEEE Transaction on audio and Electroacoustics, 1971, 19(1): 48-57.
[34]华成英.模拟电子技术基本教程[M]北京:清华大学出版社, 2006.
[35]H Eisellslon. Frequency synthesis using DDS/NCO technology [J].Electro International, 1991,(4):400-418.
[36]Thomas J Endres, Robert B Hall, Alan M Lopez, Design and analysis methods ofDDS-based synthesis for military space-borne applications [A]. proceedings of 1994 IEEE International Frequency Control Symposium[C]. Boston, US:IEEE Press,1994. 624-632.
[37]吴秋兰.现代数字系统设计方法研究及其在AWG中的应用[D].济南:山东大学,2001.
[38]P Bertemes–Filho, B H Brown and A J Wilson. A Comparsion of modified Howland circuits as current generators with current mirror type circuits [J]. Physiol. Meas. 2000,21 1-6.
[39]幸新鹏,李冬梅,王志华.一个电压接近1 V/ ppm/℃带曲率补偿的CMOS带隙基准源[ J ] .半导体学报, 2008 , 29(1) :24228.
[40]周玮,吴贵能,李儒章.一种二阶补偿的CMOS带隙基准电压源[J] .重庆邮电大学学报,2009,21(1) :78282.
[41] Paul R, Patra A. A Temperature2compensated Bandgap Voltage Reference Circuit for High Precision Applications[A] . Proceedings of the IEEE India Annual Conference[C] .2004 :5532556.
[42]秦世才,贾香鸾.模拟集成电子学.天津:天津科技出版社,1996.
[43]赵玉山,周跃庆,王萍一电流模式电路.天津:天津大学出版社,2001.
[44]王超,王化祥.用于医学电阻抗成像的电压控制电流源(VCCS) [J] .电子测量技术,2001,3:18-20.
[45]Saulnier G J 2005 EIT instrumentation Electrical Impedance Tomography: Methods, History and Applications(Bristol: Institute of Physics Publishing) pp 67–104.
[46]Van Valkenburg M E 1982 Analog Filter Design (New York: Holt, Rinehart and Winston).
[47]Sedra A S and Brackett P O 1978 Filter Theory and Design: Active and Passive (Portland, OR: Matrix).
[2] Surowiec AJ, Stuchly SS, Bar JB. Dielectric properties of breast carcinoma and the surrounding tissues,1988(04).
[3] Jossinet. The Variability of Resistivity in Human Breast Tissue. Medical and Biological Engineering and Computing, 1996, Vol(34):346-350.
[4] Prasad SN, Houserkova D, Campbell J. Breast imaging using 3D electrical impedence tomography,2008(01).
[5]廖琪梅,董秀珍,付峰.人体乳腺组织电阻抗特性的研究[ J] .国际生物医学工程杂志, 2006, 29( 4) : 218-221.
[6] E. J. Linkley, B. H. Brown, R. Knowles, Y. Mangnall, F. J. McArdle, and A. J. Wilson,―Development of a portable EIT system for gastric emptying measurements,‖Proc. 13th Ann. Int. Conf. IEEE Eng. Med. & Bio. Soc,Vol. 11, No.4 1993.
[7] D. A. Witsoe, E. Kinnen. Electrical Resistivity of Lung at 100kHz, Med. Biol. Eng., 1967,5:239-248.
[8] M. E. Valentinuzzi, L.A. Geddes, L.E. Baker. The Law of Impedance Pneumography, Med. Biol. Eng., 1971,9:157-163.
[9] Boone K, Barber D, Brown B. Imaging with electricity review of the European concerted action on impedance tomography. Journal of Medical Engineering &Technology,1997,21(6):201.
[10] R.Avill, Y.F.Mangnall, B.H.Brown et al. Applied Potential Tomography: A New Invasive Technique for Measuring Gastric Emptying, Gastroenterol, 1987, 92: 1019 -1026.
[11] S.P.Devane. Application of EIT TO Gastric Emptying in Infants: Validation Against Residual Volume Method, Clinical and Physiological Applications of Electrical Impedance Tomography, D.Holder(ed).UCL Press,London.1993,Chapter 12,113-123.
[12] A.J.Baxter, Y.F.Mangnall et al. Evaluation of Applied Potential Tomography as a New Non-invasive Gastric Secretion Test,Gut 30:1730-1735.
[13] R.H.Smallwood, Y.F.Mangnall et al. Transport of Gastric Contents, Physiol.Meas., 1994, 15(Suppl.2A):175 -188.
[14]费力,季耀东.颅脑损伤性急性病情恶化临床分析(附16例报告)[J].创伤外卡杂志, 2001, 3(3):190-193.
[15]唐秀贞,吴珂,崔群生.慢性持续性脑内出血的CT表现[J].中国医学计算机成像杂志,1999, 5(1):12-14.
[16]孙国成,蔡振杰,刘维永.体外循环心内直视术后脑部并发症的急救处理[J].中国急救医学, 2000, 20(7):395-397.
[17]董秀珍.生物电阻抗技术研究进展[J].中国医学物理学杂志,2004,21(6):311-316.
[18] K.A. Dines and R.J. Lytle. Analysis of Electrical Conductivity Imaging, Geophysics, 1981, 46:1025-1036.
[19] F. Dicken, M. Wang. Electrical Resistance Imaging for Process Applications. Meas. Sci. Technol., 1996, 7:247-260.
[20]徐桂芝,杨硕,李颖等.电阻抗断层成像技术综述[J].河北工业大学学报,2004,33(2)35-40.
[21] Henderson RP and Webster JG.IEEE BME 1978,25:250-254.
[22] L.R. Price. Electrical Impedance Computed Tomography(ICT):A new CT Imaging Technique,IEEE Trans. Nucl. Sci., 1979,26: 2736-2739.
[23] D.C. Holder. Biomedical Applications of Electrical Impedance Tomography[J]. Physiol. Meas., 2002, 23(1):3-5.
[24]Newell JC. An Electric Current Tomograph. IEEE Trans Biomed Eng, 1988;35(10):828-833
[25] Brown BH, Seagar AD. The Sheffield data collection system. Clin Phys Physiol Meas. 1987 91-97
[26]刘锐岗.电阻抗断层成像的激励模式[J].国外医学生物医学工程分册, 1999, 22(1): 20- 24.
[27]Towers C M, McCann H, Wang M, Beatty P C, Poinfrett D J D and Beck M S 2000 3D simulation of EIT for monitoring impedance variations within the human head Physiol. Meas. 21 119-24.
[28] Holder DS.Electrical impedance tomography methods,history and applications [M]. UK:Bristol,Inst Phys Pub,2005.
[29]王妍,任超世.电阻抗断层成像电极系统性能与评价方法研究[D].北京:中国协和医科大学生物医学工程,2009.
[30]尤福生,董秀珍等.电阻抗断层成像中临近和对象激励模式的研究[J].第四军医大学学报,2004,25(1):88-91.
[31]杜岩,柳重堪,程吉宽.电阻抗成像的加权Newton-Raphson算法[J].北京航空航天大学学报,1998,24(2):161-165.
[32] Mi Wang.F J Dickin.M S Beck Improved electrical impedance tomography and collection system and measurement protocols 1992
[33] Tierney J, Rader C, Gold B. A Digital Frequency Synthesizer[J].IEEE Transaction on audio and Electroacoustics, 1971, 19(1): 48-57.
[34]华成英.模拟电子技术基本教程[M]北京:清华大学出版社, 2006.
[35]H Eisellslon. Frequency synthesis using DDS/NCO technology [J].Electro International, 1991,(4):400-418.
[36]Thomas J Endres, Robert B Hall, Alan M Lopez, Design and analysis methods ofDDS-based synthesis for military space-borne applications [A]. proceedings of 1994 IEEE International Frequency Control Symposium[C]. Boston, US:IEEE Press,1994. 624-632.
[37]吴秋兰.现代数字系统设计方法研究及其在AWG中的应用[D].济南:山东大学,2001.
[38]P Bertemes–Filho, B H Brown and A J Wilson. A Comparsion of modified Howland circuits as current generators with current mirror type circuits [J]. Physiol. Meas. 2000,21 1-6.
[39]幸新鹏,李冬梅,王志华.一个电压接近1 V/ ppm/℃带曲率补偿的CMOS带隙基准源[ J ] .半导体学报, 2008 , 29(1) :24228.
[40]周玮,吴贵能,李儒章.一种二阶补偿的CMOS带隙基准电压源[J] .重庆邮电大学学报,2009,21(1) :78282.
[41] Paul R, Patra A. A Temperature2compensated Bandgap Voltage Reference Circuit for High Precision Applications[A] . Proceedings of the IEEE India Annual Conference[C] .2004 :5532556.
[42]秦世才,贾香鸾.模拟集成电子学.天津:天津科技出版社,1996.
[43]赵玉山,周跃庆,王萍一电流模式电路.天津:天津大学出版社,2001.
[44]王超,王化祥.用于医学电阻抗成像的电压控制电流源(VCCS) [J] .电子测量技术,2001,3:18-20.
[45]Saulnier G J 2005 EIT instrumentation Electrical Impedance Tomography: Methods, History and Applications(Bristol: Institute of Physics Publishing) pp 67–104.
[46]Van Valkenburg M E 1982 Analog Filter Design (New York: Holt, Rinehart and Winston).
[47]Sedra A S and Brackett P O 1978 Filter Theory and Design: Active and Passive (Portland, OR: Matrix).