开放式电阻抗断层成像的测量系统设计与研究
摘要
电阻抗成像技术(Electrical Impedance Tomography, EIT)是是继形态、结构成像之后,于最近三十年才出现的新一代无损伤成像技术。封闭式电阻抗成像(CEIT)主要围绕2维圆形场域,电极均匀分布于被测对象周围,电极围成的整个截面作为成像区域,但CEIT遇到了诸如分辨率较低、电极位置不确定、计算场域模型和应用场域形状不一致、皮肤的接触阻抗等问题。为了克服封闭式电阻抗成像电极位置不确定等问题,开放式电阻抗成像( OEIT)采用排电极阵列,借鉴超声的扫描工作机制,通过排电极的扫描被测体,成像目标仅是排电极下的浅层区域,但通过排电极的反复移动,而获得了整个被测体浅层区域电导率分布,有效解决了封闭式EIT在应用上电极不等间隔、不方便放置等应用问题。
论文以开放式电阻抗成像技术为主要目标开展基础应用研究,研究实现一种实用、快速、具有一定分辨率的开放式电阻抗成像仪,以提供一种能进行自动测量、高精度的测量仪器,为图像重构软件提供精确的测量数据。论文在分析、参考国内外有关电阻抗成像仪器设计及方法上,研制了开放式电阻成像仪CQU2, CQU2采用直接数字频率合成(DDS)产生幅度为0-5mA,频率在10KHz-1MHz的正弦电流信号到电极上,在恒流源电路中采用了负电容补偿电路及校正网络以提高恒流源的输出阻抗。应用数字相敏检波技术对被测电压进行解调以获得准确的幅度与相位信息,获得了高达80dB的测量信噪比,同时为获得快速的测量响应时间设计了高速数据采集器:高达40MHz采样率的ADC、FPGA及数字信号处理器,采用电压可控增益放大器在DSP处理器控制下对于不同测量对象实现自动增益控制。实验测试表明CQU2的电流源在10KHz-1MHz范围内可获6M?-500KΩ的输出阻抗。
通过大量实验表明,开放式电阻成像仪能配合软件算法准确定位水槽和琼脂模型中的异物,较好地区分低差异电导率组织。同时利用仪器对乳腺病癌病人做了初步临床试验,获得了珍贵的临床数据,验证了装置的可用性,为继续深入研究奠定了基础。
Electrical Impedance Tomography (EIT) is an effective noninvasive imaging technique following the techniques of shape imaging and structure imaging, and is developed recently 30-years. Closed Electrical Impedance Tomography (CEIT) mainly centered on a circular 2-dimensional field, the electrode uniformly distributed in the measured object , around the electrode surrounded the entire cross-section as the imaging region, but encountered a CEIT, such as low resolution, the electrode position uncertainty calculate the market domain model and application of inconsistent field shape, skin contact impedance problem. Closed in order to overcome the electrical impedance tomography uncertain issues such as electrode location, open electrical impedance tomography (OEIT) using row electrode arrays, referenced from ultrasound scanning working mechanism, through row electrodes scanning the measured body, imaging goal is only the shallow area under the electrodes. By repeatedly moving row electrodes, get conductivity distribution for the whole measured body. Develop an effective solution to inconvenient placement of electrodes.
The thesis based on Open Electric Impedance Imaging technology, carry out basic application research for OEIT , achieve to design a practicably, rapid, high resolution, high-precision measuring automatic instrument which provide high precise measurement data for image reconstruction software. After studying and analyzing the international design and methodology of Electrical Impedance Tomography instrument , developed CQU2 instrument for Open Electric Impedance Imaging. CQU2 using Direct Digital Synthesis (DDS) method to generate sinusoidal signal inject to the electrode, the sinusoidal current has a a range of 1-5mA, frequency at 10KHz-1MHz, the constant current source circuit used a negative capacitance compensation circuit and calibration network to improve the output impedance of current source. And also applicated Digital Phase-Sensitive Detection(DPSD) technology to obtain accurate amplitude and phase information between electrodes .The measurement Signal-to-Noise Ratioobtained up to 80dB , at the same time in order to obtain a fast measurement response time , design a high-speed data collector: up to 40MHz sampling rate of ADC(AD9228), using high speed FPGA (EP2C20F256C8) and Digital Dignal Processors(TMS320F2812), Voltage control variable gain amplifier used in the board to implement automatic measurement , and DSP processor control the gain for VGA under different measured objects . Experimental shows that range of the current source output impedance at 10KHz-1MHz is 6M-500KΩ.
A large number of experiments show that CQU2 can work well with OEIT image software algorithms , and accurately locate eyewinker in the sink and agar model. Better distinguish low difference conductivity of the Organization. Also carry out a preliminary clinical experimentation for breast cancer patient , get valuable clinical data. It's be true that Open Electric Impedance technology will tend toward to clinical application in the future.
论文以开放式电阻抗成像技术为主要目标开展基础应用研究,研究实现一种实用、快速、具有一定分辨率的开放式电阻抗成像仪,以提供一种能进行自动测量、高精度的测量仪器,为图像重构软件提供精确的测量数据。论文在分析、参考国内外有关电阻抗成像仪器设计及方法上,研制了开放式电阻成像仪CQU2, CQU2采用直接数字频率合成(DDS)产生幅度为0-5mA,频率在10KHz-1MHz的正弦电流信号到电极上,在恒流源电路中采用了负电容补偿电路及校正网络以提高恒流源的输出阻抗。应用数字相敏检波技术对被测电压进行解调以获得准确的幅度与相位信息,获得了高达80dB的测量信噪比,同时为获得快速的测量响应时间设计了高速数据采集器:高达40MHz采样率的ADC、FPGA及数字信号处理器,采用电压可控增益放大器在DSP处理器控制下对于不同测量对象实现自动增益控制。实验测试表明CQU2的电流源在10KHz-1MHz范围内可获6M?-500KΩ的输出阻抗。
通过大量实验表明,开放式电阻成像仪能配合软件算法准确定位水槽和琼脂模型中的异物,较好地区分低差异电导率组织。同时利用仪器对乳腺病癌病人做了初步临床试验,获得了珍贵的临床数据,验证了装置的可用性,为继续深入研究奠定了基础。
Electrical Impedance Tomography (EIT) is an effective noninvasive imaging technique following the techniques of shape imaging and structure imaging, and is developed recently 30-years. Closed Electrical Impedance Tomography (CEIT) mainly centered on a circular 2-dimensional field, the electrode uniformly distributed in the measured object , around the electrode surrounded the entire cross-section as the imaging region, but encountered a CEIT, such as low resolution, the electrode position uncertainty calculate the market domain model and application of inconsistent field shape, skin contact impedance problem. Closed in order to overcome the electrical impedance tomography uncertain issues such as electrode location, open electrical impedance tomography (OEIT) using row electrode arrays, referenced from ultrasound scanning working mechanism, through row electrodes scanning the measured body, imaging goal is only the shallow area under the electrodes. By repeatedly moving row electrodes, get conductivity distribution for the whole measured body. Develop an effective solution to inconvenient placement of electrodes.
The thesis based on Open Electric Impedance Imaging technology, carry out basic application research for OEIT , achieve to design a practicably, rapid, high resolution, high-precision measuring automatic instrument which provide high precise measurement data for image reconstruction software. After studying and analyzing the international design and methodology of Electrical Impedance Tomography instrument , developed CQU2 instrument for Open Electric Impedance Imaging. CQU2 using Direct Digital Synthesis (DDS) method to generate sinusoidal signal inject to the electrode, the sinusoidal current has a a range of 1-5mA, frequency at 10KHz-1MHz, the constant current source circuit used a negative capacitance compensation circuit and calibration network to improve the output impedance of current source. And also applicated Digital Phase-Sensitive Detection(DPSD) technology to obtain accurate amplitude and phase information between electrodes .The measurement Signal-to-Noise Ratioobtained up to 80dB , at the same time in order to obtain a fast measurement response time , design a high-speed data collector: up to 40MHz sampling rate of ADC(AD9228), using high speed FPGA (EP2C20F256C8) and Digital Dignal Processors(TMS320F2812), Voltage control variable gain amplifier used in the board to implement automatic measurement , and DSP processor control the gain for VGA under different measured objects . Experimental shows that range of the current source output impedance at 10KHz-1MHz is 6M-500KΩ.
A large number of experiments show that CQU2 can work well with OEIT image software algorithms , and accurately locate eyewinker in the sink and agar model. Better distinguish low difference conductivity of the Organization. Also carry out a preliminary clinical experimentation for breast cancer patient , get valuable clinical data. It's be true that Open Electric Impedance technology will tend toward to clinical application in the future.
引文
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[3]刘国强.医学电阻抗成像[M].北京:科学出版社, 2006.
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[8] Geeraerts B, Van Petegem W·Voltage versus current driven high frequency EIT systems[J]. IEEE Trans Biomed Eng, 1992 45(10):170-179.
[9] H. T. Nicholas and H. Samueli,.An analysis of the output spectrum of direct digital frequency synthesizers in the presence of phaseaccumulator truncation[J]. in Proc. 41st Annu. Frequency Contr. Symp.1987:495–502..
[10] Yuichiro Orino, Minoru Kuribayashi Kurosawa.Direct-Digital Synthesis Using Delta-Sigma Modulated Signals[J].
[11] Fujisaka H,Sakamoato M. and Morisue M,”Bit-stream signal processing circuits and their application[J]. IEICE Trans. Fundamental. 2002(4):853–860.
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[13]刘惠敏,刘志伟.直接数字频率合成器频谱性能分析[J].华中科技大学学报(自然科学版) 2005 33(2) :73-75.
[14]远坂俊昭著彭军译.测量电子电路设计-滤波器篇[M].北京,科学出版社. 2006.
[15]王超,王湘嵛,孙宏军等.用于生物阻抗测量的双反馈电流源研究[J].生物医学工程学杂志.2006; 23 (4)∶704～707.
[16] Alexander S Ross1, G J Saulnier, J C Newell.Current source design for electrical impedanceomography[J].Physiol. Meas. 2003 (24): 509–516.
[17] Gary J Saulnier, Alexander S Ross and Ning Liu. A high-precision voltage source for EIT[J]. PHYSIOLOGICAL MEASUREMENT. 2006(27) :221–236.
[18] Steven M. K.统计信号处理基础:估计与检测理论[M].北京:电子工业出版社. 2003: 46-679.
[19]张海风. HyperLynx仿真与PCB设计[M].北京.机械工业出版社. 2005.
[20]任爱锋等.基于FPGA的嵌入式系统设计[M].西安.西安电子科技大学出版社.2004.
[21]唐杉.数字IC设计方法[M].北京.机械工业出版社.2006.
[22]冯杰.高速数字电路设计与安装技巧.北京.科学出版社.2006.
[23] Jan M. Rabaey Anantha Chandrakasan著.周润德译.数字集成电--电路、系统与设计(第二版)[M].北京.电子工业出版社.2005.
[24] John G. Ackenhusen著,李玉柏等译.实时信号处理-信号处理系统的设计与实现[M].北京.电子工业出版. 2002.
[25]王冠,俞一鸣.面向CPLD/FPGA的Verilog设计[M].北京.机械工业出版社. 2007.
[26] TI. LVDS Application and Data Handbook. www. focus.ti.com.cn /cn/lit/ug/slld009 /slld009.pdf. 2006.
[27]尤富生,董秀珍,秦明新等.一个32电极电阻抗断层成像硬件系统[J].第四军医大学学报. 1998. 19 (l): 7-9.
[28]夏晨,莫玉龙.32电极的电阻抗成像系统的设计与实现[J].计算机工程. 2003 29(18) 69-71.
[29] Tzu-Jen Kao, G J Saulnier etc. A compensated radiolucent electrode array for combined EIT and mammography[J]. PHYSIOLOGICAL MEASUREMENT. 2007(28) 291-299.
[30] A McEwan, G Cusick and D S Holder. A review of errors in multi-frequency EIT instrumentation. PHYSIOLOGICAL MEASUREMENT. 2007(28) : 197–215.
[31] Tong In Oh, Eung Je Woo and David Holder.Multi-frequency EIT system with radially symm-etric architecture[J]: KHU Mark1. PHYSIOLOGICAL MEASUREMENT. 2007 (28): 183–196.
[32] Scott Dunlop, Judy Hough etc. Electrical impedance tomography in extremely prematurely born infants and during high frequency oscillatory ventilation analyzed in the frequency domain[J]. PHYSIOLOGICAL MEASUREMENT. 2006 (27): 1151–1165.
[33] S Armstrong and D Jennings. Current injection electrodes for electrical impedance tomography. PHYSIOLOGICAL MEASUREMENT. 2004(25):797–802.
[34]童诗白.模拟电子技术基础.高等教育出版社. 1988.
[35]阎石.数字电子技术基础.高等教育出版社. 1985.
[36]房磊,张焕春,胡银彪.FPGA的配置及接口电路.电子质量,2004,(1):2~3.
[37]丁新宇,朱红莉.基于单片机的cyclone系列FPGA配置方法.今日电子,2003(8):37-38.
[2] Kao Tzu Jen. A 3-D reconstruction algorithm for electrical impedance tomography using planar electrode arrays [D]. New York: The Rensselaer Polytechnic Institute, US, 2005.
[3]刘国强.医学电阻抗成像[M].北京:科学出版社, 2006.
[4] COOK R D. ACT3:A high speed , high precision electrical impedance tomography[D]. Rensselaer Polytechnic Institute.1992.
[5] DAVID H. Electrical Impendance Tomography Methods, History and Applications[M]. London: IOP publishing Ltd, 2005: 3-22.
[6] Hua Ping, Woo JE, Webster JG·Iterative Reconstruction Methods Using Regularization and Optimal Current Patterns in Electrical Impedance Tomography[J]. IEEE Trans on Med Imag·1991 , 10(4): 621-628.
[7] Woo HW, and Kim Y·A Medical System With Electrical Impedance[J]. IEEE/Eighth Annu Conf of the Eng in Med and Bio Soc . 1986: 343-346.
[8] Geeraerts B, Van Petegem W·Voltage versus current driven high frequency EIT systems[J]. IEEE Trans Biomed Eng, 1992 45(10):170-179.
[9] H. T. Nicholas and H. Samueli,.An analysis of the output spectrum of direct digital frequency synthesizers in the presence of phaseaccumulator truncation[J]. in Proc. 41st Annu. Frequency Contr. Symp.1987:495–502..
[10] Yuichiro Orino, Minoru Kuribayashi Kurosawa.Direct-Digital Synthesis Using Delta-Sigma Modulated Signals[J].
[11] Fujisaka H,Sakamoato M. and Morisue M,”Bit-stream signal processing circuits and their application[J]. IEICE Trans. Fundamental. 2002(4):853–860.
[12] DAVID H. Electrical Impendance Tomography Methods, History and Applications[M]. London: IOP 2005: 35-220.
[13]刘惠敏,刘志伟.直接数字频率合成器频谱性能分析[J].华中科技大学学报(自然科学版) 2005 33(2) :73-75.
[14]远坂俊昭著彭军译.测量电子电路设计-滤波器篇[M].北京,科学出版社. 2006.
[15]王超,王湘嵛,孙宏军等.用于生物阻抗测量的双反馈电流源研究[J].生物医学工程学杂志.2006; 23 (4)∶704～707.
[16] Alexander S Ross1, G J Saulnier, J C Newell.Current source design for electrical impedanceomography[J].Physiol. Meas. 2003 (24): 509–516.
[17] Gary J Saulnier, Alexander S Ross and Ning Liu. A high-precision voltage source for EIT[J]. PHYSIOLOGICAL MEASUREMENT. 2006(27) :221–236.
[18] Steven M. K.统计信号处理基础:估计与检测理论[M].北京:电子工业出版社. 2003: 46-679.
[19]张海风. HyperLynx仿真与PCB设计[M].北京.机械工业出版社. 2005.
[20]任爱锋等.基于FPGA的嵌入式系统设计[M].西安.西安电子科技大学出版社.2004.
[21]唐杉.数字IC设计方法[M].北京.机械工业出版社.2006.
[22]冯杰.高速数字电路设计与安装技巧.北京.科学出版社.2006.
[23] Jan M. Rabaey Anantha Chandrakasan著.周润德译.数字集成电--电路、系统与设计(第二版)[M].北京.电子工业出版社.2005.
[24] John G. Ackenhusen著,李玉柏等译.实时信号处理-信号处理系统的设计与实现[M].北京.电子工业出版. 2002.
[25]王冠,俞一鸣.面向CPLD/FPGA的Verilog设计[M].北京.机械工业出版社. 2007.
[26] TI. LVDS Application and Data Handbook. www. focus.ti.com.cn /cn/lit/ug/slld009 /slld009.pdf. 2006.
[27]尤富生,董秀珍,秦明新等.一个32电极电阻抗断层成像硬件系统[J].第四军医大学学报. 1998. 19 (l): 7-9.
[28]夏晨,莫玉龙.32电极的电阻抗成像系统的设计与实现[J].计算机工程. 2003 29(18) 69-71.
[29] Tzu-Jen Kao, G J Saulnier etc. A compensated radiolucent electrode array for combined EIT and mammography[J]. PHYSIOLOGICAL MEASUREMENT. 2007(28) 291-299.
[30] A McEwan, G Cusick and D S Holder. A review of errors in multi-frequency EIT instrumentation. PHYSIOLOGICAL MEASUREMENT. 2007(28) : 197–215.
[31] Tong In Oh, Eung Je Woo and David Holder.Multi-frequency EIT system with radially symm-etric architecture[J]: KHU Mark1. PHYSIOLOGICAL MEASUREMENT. 2007 (28): 183–196.
[32] Scott Dunlop, Judy Hough etc. Electrical impedance tomography in extremely prematurely born infants and during high frequency oscillatory ventilation analyzed in the frequency domain[J]. PHYSIOLOGICAL MEASUREMENT. 2006 (27): 1151–1165.
[33] S Armstrong and D Jennings. Current injection electrodes for electrical impedance tomography. PHYSIOLOGICAL MEASUREMENT. 2004(25):797–802.
[34]童诗白.模拟电子技术基础.高等教育出版社. 1988.
[35]阎石.数字电子技术基础.高等教育出版社. 1985.
[36]房磊,张焕春,胡银彪.FPGA的配置及接口电路.电子质量,2004,(1):2~3.
[37]丁新宇,朱红莉.基于单片机的cyclone系列FPGA配置方法.今日电子,2003(8):37-38.