磁感应电阻抗断层成像技术初步研究
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摘要
磁感应电阻抗断层成像(Magnetic Induction Impedance Tomography，MIT)技术，是一种利用电磁检测原理测量生物组织电阻(电导)率的成像技术，是生物电阻抗成像研究的一个分支，作为一种新型的非接触电阻抗断层成像方法，MIT在区分不同类型的颅内病变有着十分重要的应用前景。本文主要完成了MIT技术初步研究，为实现脑部战创伤急救图像监护系统打下了基础。
MIT脑阻抗测量中，目标是电导率较小的脑组织，它会感应出强度较弱的涡流磁场，易受外界磁场的干扰，为此我们设计并实现了一个基于物理模型的单通道测量系统，来检测因目标电导率发生改变而引起的涡流磁场相位信息变化，主要工作包括以下内容：
1．激励源的设计与实现，当输出频率10MHz时，带负载线圈的稳定输出特性满足实验要求；
2．检测电路的设计与实现，其灵敏度测试结果符合测量所提出的要求；
3．研制了适合在MIT激励—检测模式下工作的线圈，并给出了
第四军医大学硕士学位论文
优选线圈的原理和方法；
4．设计并制作了单通道的旋转测量平台模型，使用步进电机精确
控制线圈自由转动一定的角度，便于自动获得独立测量数；
5．实现了MIT反投影算法，提出了沿主磁场的直线距离加权法，
对不同位置不同电导率的目标进行了仿真成像，结果验证了算法的适
用性；
6．以接近正常人脑组织电导率的NaCI盐溶液为目标，得到了较
为理想的初步成像结果。
对系统进行了误差分析，提出了可能的改进意见。
Magnetic Induction Impedance Tomography ( MIT ), a kind of imaging technology for measuring the distribution of biological tissue's electrical impedance or conductivity by applying the theory of electrical magnetic field detecting. As a new method of contactless electrical impedance tomography, MIT has some great prospective application in distinguishing different types of encephalic pathological changes. In this paper, we fulfilled the preliminary MIT research that is the basis of the imaging monitor system for the cerebral wound emergency.
When detecting brain's impedance in MIT, the object is the brain tissue with minor conductivity, which can induce some weak eddy current that is easy to be interfered by outside magnetic field. For this reason, we designed and realized a single-channel measuring system based on a physical phantom to detect the phase changes of eddy current induced from the object with conductivity changing. The main content is as follows:
1. designed and fulfilled the exciting source, and its output specifications loaded with a coil met the design requirements.
2. designed and fulfilled the measuring circuit, sensitivity experiment of which met the design requirements.
3. developed the coils that were properly used under the Exciting -Measuring mode of MIT. And we presented the principle and method how to select coils.
4. designed and made the single-channel circumvolving platform with screen and applied stepping motors to control the coils rotating certain angle precisely. Then we automatically obtained independent measuring numbers.
5. realized the back-projection algorithm of MIT. We put forward the weighed method in a straight line along the main magnetic field. The algorithm was proved to be applicable by the images of modeled object with different conductivity in various position.
6. the preliminary and ideal imaging results were given by utilizing NaCl brine as an object in this paper, which approximately had the same conductivity with the normal human brain tissue.
And we made the errors of results analyzed and gave some possible advice on improving them.
MIT脑阻抗测量中，目标是电导率较小的脑组织，它会感应出强度较弱的涡流磁场，易受外界磁场的干扰，为此我们设计并实现了一个基于物理模型的单通道测量系统，来检测因目标电导率发生改变而引起的涡流磁场相位信息变化，主要工作包括以下内容：
1．激励源的设计与实现，当输出频率10MHz时，带负载线圈的稳定输出特性满足实验要求；
2．检测电路的设计与实现，其灵敏度测试结果符合测量所提出的要求；
3．研制了适合在MIT激励—检测模式下工作的线圈，并给出了
第四军医大学硕士学位论文
优选线圈的原理和方法；
4．设计并制作了单通道的旋转测量平台模型，使用步进电机精确
控制线圈自由转动一定的角度，便于自动获得独立测量数；
5．实现了MIT反投影算法，提出了沿主磁场的直线距离加权法，
对不同位置不同电导率的目标进行了仿真成像，结果验证了算法的适
用性；
6．以接近正常人脑组织电导率的NaCI盐溶液为目标，得到了较
为理想的初步成像结果。
对系统进行了误差分析，提出了可能的改进意见。
Magnetic Induction Impedance Tomography ( MIT ), a kind of imaging technology for measuring the distribution of biological tissue's electrical impedance or conductivity by applying the theory of electrical magnetic field detecting. As a new method of contactless electrical impedance tomography, MIT has some great prospective application in distinguishing different types of encephalic pathological changes. In this paper, we fulfilled the preliminary MIT research that is the basis of the imaging monitor system for the cerebral wound emergency.
When detecting brain's impedance in MIT, the object is the brain tissue with minor conductivity, which can induce some weak eddy current that is easy to be interfered by outside magnetic field. For this reason, we designed and realized a single-channel measuring system based on a physical phantom to detect the phase changes of eddy current induced from the object with conductivity changing. The main content is as follows:
1. designed and fulfilled the exciting source, and its output specifications loaded with a coil met the design requirements.
2. designed and fulfilled the measuring circuit, sensitivity experiment of which met the design requirements.
3. developed the coils that were properly used under the Exciting -Measuring mode of MIT. And we presented the principle and method how to select coils.
4. designed and made the single-channel circumvolving platform with screen and applied stepping motors to control the coils rotating certain angle precisely. Then we automatically obtained independent measuring numbers.
5. realized the back-projection algorithm of MIT. We put forward the weighed method in a straight line along the main magnetic field. The algorithm was proved to be applicable by the images of modeled object with different conductivity in various position.
6. the preliminary and ideal imaging results were given by utilizing NaCl brine as an object in this paper, which approximately had the same conductivity with the normal human brain tissue.
And we made the errors of results analyzed and gave some possible advice on improving them.
引文
[1] Griffiths H, Stewart WR and Gough W .Magnetic induction tomography. A measuring sys-tem for biological tissues[J]. Ann N Y Acad Sci,1999,873: 335-345.
[2] Hossmann KA .Cortical steady potential, impedance and excitability changes during and after total ischemia of cat brain Q[J]. Neueurol, 1971, 32: 163-175.
[3] Elazar Z, Kado RT, Adey WR. Impedance changes during epile-ptic seizures [J]. Epilepsia, 1966,7(4):291-307.
[4] Holder PS and Gardner-Medwin AR.Some possible numerical applications of applied potential tomography [J]. Clin. Phys. Physiol. Meas,1988, 9( Supplement A ): 111-119.
[5] Van der Veen PH, Go KG, Zuiderveen F, Buiter D and Van der Mea J. Electrical impedance of at brain with cold-induced edema Exp[J]. Neural, 1973,40: 675-682.
[6] Go KG, van der Veen PH, Ebels EJ, van Woudenberg F. A study of electrical impedance of oedematous cerebral tissue during operations. Correlation of impedance with water and electrolyte content and with histology [J]. Acta Neurochir (Wien), 1972,27(3): 113-24
[7] Tideswell AT, Gibson A, Bayford RH and Holder DS. Electrical
impedance tomography of human brain activity with a two-dimensional ring of scalp electrodes. Physiol. Meas, 2001,22: 167-175.
[8] Netz J, Forner E and Haagemann S. Contactless impedance measurement by magnetic induction-a possible method for investigation of brain impedance[J]. Physiol.Meas, 1993, 14(4):463-471.
[9] Scharfetter H, Lackner HK and Rosell J. Magnetic induction tomography: hardware for multi-frequency measurements in biological tissues[J]. Physiol. Meas,2001,22 (1): 1-16.
[10] 任吉林，林俊明，高春法主编，电磁检测[M]．北京：机械工业出版社，2000，45-48．
[11] Korjenevsky AV and Cherepenin VA. Progress in realisation of magnetic induction tomography Ann[J]. NY Acad. Sci, 1999, 873: 346-352.
[12] Peyton AJ,Yu ZZ,Lyon G, et al.An overview of electromagnetic inductance tomography: description of three different systems[J]. Meas. Sci. Technol, 1996, 7:171-261.
[13] Rosell J, Casanas R and Scharfetter H.Sensitivity maps and system requirements for magnetic induction tomography using a planar gradiometer[J].Physiol Mea,2000,22(1): 121-130.
[14] Tozer JC, Ireland RH, Barber DC, et al. Magnetic impedance tomography [J]. Ann N Y Acad Sci,1999,873: 353-359.
[15] Hart LW, Ko HW, Meyer JH,et al.. A noninvasive electromagnetic conductivity sensor for biomedical application [J]. IEEE Trans. Biomed.
Eng, 1988, 35: 1011-1121.
[16] Scharfetter H, Ninaus W, Puswald B,et al.Inductively coupled wideband transceiver for bioimpedance spectroscopy (IBIS)[J].Ann. NY Acad.Sc,1999, 873: 322-334.
[17] Tarjan PP and McFee R. Electrodeless measurements of the effective resistivity of the human torso and head by magnetic induction [J]. IEEE Trans Biomed Eng, 1968, 15(4):266-78.
[18] Kittel H and Wach P. Theoretical investigation to the non-contacting conductometry for biological materials [J]. Biomed Tech (Berl) 1981, 26(6):153-7.
[19] Al-Zeibak S and Saunders HN.A feasibility study of in vivo electromagnetic imaging.Phys Med Biol 1993, 38(1): 151-60.
[20] DELisa JA, Gans BM. Rehabilitation Medicine Principles and Practice.[M]. New York. Third Edition Lippioncott-Raven Publishers.1998:78-104.
[21] 冯恩信编著，电磁场与波[M]．西安：西安交通大学出版社出版，1999，82-105．
[22] 雷银照编著，轴对称线圈磁场计算[M]．北京：中国计量出版社出版，1991，1-23．
[23] Cao XW. Gaopin Dianlu Yuanli Yu Fenxi (The Principle and Analyzing of High Frequency Circuit ) [M]. Xi'an: Dian Zi Ke Ji Daxue Chubanshe ( Xi'an: Xidian University), 2001:109-112.
[24] Morris A,Griffiths H,Gough W. A numerical model for magnetic induction tomographic measurements in biological tissues [J]. Physio Meas, 2001,22(1):113-119.
[25] Miu HS. Dianliao Yu Guangliao(Electrotherapeutics and Phototherapy) [M].Shanghai Kexue Jishu Chubanshe (Shanghai: Science and Technology Publishing House ), 1990: 269-271.
[26] 童诗白主编，模拟电子技术基础[M]．北京：高等教育出版社出版，1991，533-541．
[27] 张唯真主编，生物医学电子学[M]．北京：清华大学出版社出版，1990，243-255．
[28] Brooks RA, Chiro GDI.Theory of image reconstruction in computed tomography[J]. Radiology, 1975, 117:561-572.
[29] 孙尧 编著，现代成像技术原理[M]．黑龙江：黑龙江科学技术出版社出版，1993，145-165．
[30] 石明国 主编，实用CT影像技术学[M]．陕西：陕西科学技术出版社出版，1995，24-35．
[31] 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(Suppl)：7-9．
[32] 汤孟兴，董秀珍，秦明新等．一种用于电阻抗断层成像的图像重建新方法[J]，第四军医大学学报，1998，19(Suppl)：1-3．
[33] 董秀珍，刘锐岗，秦明新等．电阻抗断层成像软件实验系统设计[J]，第四军医大学学报，2000，21(11)：1381-1383．
[2] Hossmann KA .Cortical steady potential, impedance and excitability changes during and after total ischemia of cat brain Q[J]. Neueurol, 1971, 32: 163-175.
[3] Elazar Z, Kado RT, Adey WR. Impedance changes during epile-ptic seizures [J]. Epilepsia, 1966,7(4):291-307.
[4] Holder PS and Gardner-Medwin AR.Some possible numerical applications of applied potential tomography [J]. Clin. Phys. Physiol. Meas,1988, 9( Supplement A ): 111-119.
[5] Van der Veen PH, Go KG, Zuiderveen F, Buiter D and Van der Mea J. Electrical impedance of at brain with cold-induced edema Exp[J]. Neural, 1973,40: 675-682.
[6] Go KG, van der Veen PH, Ebels EJ, van Woudenberg F. A study of electrical impedance of oedematous cerebral tissue during operations. Correlation of impedance with water and electrolyte content and with histology [J]. Acta Neurochir (Wien), 1972,27(3): 113-24
[7] Tideswell AT, Gibson A, Bayford RH and Holder DS. Electrical
impedance tomography of human brain activity with a two-dimensional ring of scalp electrodes. Physiol. Meas, 2001,22: 167-175.
[8] Netz J, Forner E and Haagemann S. Contactless impedance measurement by magnetic induction-a possible method for investigation of brain impedance[J]. Physiol.Meas, 1993, 14(4):463-471.
[9] Scharfetter H, Lackner HK and Rosell J. Magnetic induction tomography: hardware for multi-frequency measurements in biological tissues[J]. Physiol. Meas,2001,22 (1): 1-16.
[10] 任吉林，林俊明，高春法主编，电磁检测[M]．北京：机械工业出版社，2000，45-48．
[11] Korjenevsky AV and Cherepenin VA. Progress in realisation of magnetic induction tomography Ann[J]. NY Acad. Sci, 1999, 873: 346-352.
[12] Peyton AJ,Yu ZZ,Lyon G, et al.An overview of electromagnetic inductance tomography: description of three different systems[J]. Meas. Sci. Technol, 1996, 7:171-261.
[13] Rosell J, Casanas R and Scharfetter H.Sensitivity maps and system requirements for magnetic induction tomography using a planar gradiometer[J].Physiol Mea,2000,22(1): 121-130.
[14] Tozer JC, Ireland RH, Barber DC, et al. Magnetic impedance tomography [J]. Ann N Y Acad Sci,1999,873: 353-359.
[15] Hart LW, Ko HW, Meyer JH,et al.. A noninvasive electromagnetic conductivity sensor for biomedical application [J]. IEEE Trans. Biomed.
Eng, 1988, 35: 1011-1121.
[16] Scharfetter H, Ninaus W, Puswald B,et al.Inductively coupled wideband transceiver for bioimpedance spectroscopy (IBIS)[J].Ann. NY Acad.Sc,1999, 873: 322-334.
[17] Tarjan PP and McFee R. Electrodeless measurements of the effective resistivity of the human torso and head by magnetic induction [J]. IEEE Trans Biomed Eng, 1968, 15(4):266-78.
[18] Kittel H and Wach P. Theoretical investigation to the non-contacting conductometry for biological materials [J]. Biomed Tech (Berl) 1981, 26(6):153-7.
[19] Al-Zeibak S and Saunders HN.A feasibility study of in vivo electromagnetic imaging.Phys Med Biol 1993, 38(1): 151-60.
[20] DELisa JA, Gans BM. Rehabilitation Medicine Principles and Practice.[M]. New York. Third Edition Lippioncott-Raven Publishers.1998:78-104.
[21] 冯恩信编著，电磁场与波[M]．西安：西安交通大学出版社出版，1999，82-105．
[22] 雷银照编著，轴对称线圈磁场计算[M]．北京：中国计量出版社出版，1991，1-23．
[23] Cao XW. Gaopin Dianlu Yuanli Yu Fenxi (The Principle and Analyzing of High Frequency Circuit ) [M]. Xi'an: Dian Zi Ke Ji Daxue Chubanshe ( Xi'an: Xidian University), 2001:109-112.
[24] Morris A,Griffiths H,Gough W. A numerical model for magnetic induction tomographic measurements in biological tissues [J]. Physio Meas, 2001,22(1):113-119.
[25] Miu HS. Dianliao Yu Guangliao(Electrotherapeutics and Phototherapy) [M].Shanghai Kexue Jishu Chubanshe (Shanghai: Science and Technology Publishing House ), 1990: 269-271.
[26] 童诗白主编，模拟电子技术基础[M]．北京：高等教育出版社出版，1991，533-541．
[27] 张唯真主编，生物医学电子学[M]．北京：清华大学出版社出版，1990，243-255．
[28] Brooks RA, Chiro GDI.Theory of image reconstruction in computed tomography[J]. Radiology, 1975, 117:561-572.
[29] 孙尧 编著，现代成像技术原理[M]．黑龙江：黑龙江科学技术出版社出版，1993，145-165．
[30] 石明国 主编，实用CT影像技术学[M]．陕西：陕西科学技术出版社出版，1995，24-35．
[31] 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(Suppl)：7-9．
[32] 汤孟兴，董秀珍，秦明新等．一种用于电阻抗断层成像的图像重建新方法[J]，第四军医大学学报，1998，19(Suppl)：1-3．
[33] 董秀珍，刘锐岗，秦明新等．电阻抗断层成像软件实验系统设计[J]，第四军医大学学报，2000，21(11)：1381-1383．