摘要
神经科很多常见疾病如脑卒中、颅脑外伤、脑炎及颅内肿瘤等，由于在疾病的病程中出现严重的脑水肿以及颅内压增高，若不能得到及时的救治，其致死率及致残率均很高。如果临床上能够早期、及时准确评价各种病因所致脑组织病变的部位、性质及范围或严重程度，以及其发展，和对药物等治疗的反应，无疑直接关系到脑水肿和颅内压的正确处理，这是神经科急危重症患者抢救成败的关键。虽然目前的检测技术如头颅CT、核磁共振（MRI）及磁共振弥散成像（DWI）等，可以准确判定危重疾病的性质、范围和程度,但是还是无法进行床旁连续的成像，对于病情危重、变化较快，但又不宜反复搬动的患者不能监测其病灶的动态变化，因此对病情演变的及时判断及调整治疗方案受到限制。所以急需一种便携，能够对病人进行连续监护的医学影像诊断设备，尤其重要的是能够有效地检测脑水肿与颅内压的状况。
磁感应成像技术（Magnetic Induction Tomography，MIT）是一种新兴的非接触式测量组织电导率的成像技术，也是当今生物医学工程无损检测前沿研究课题之一。磁感应成像技术具有快捷、便携、低成本、无创等特点，这特点在生物医学无创检测成像和连续动态监护领域有很好的应用前景，特别是对颅内疾病的连续监护。
本论文主要的研究目的是颅内病变组织的实时监护。主要研究内容是研制一种基于磁感应成像方式快速的、实时监护的、便携式的功能性成像系统，同时研究其重构算法和测量实验。本论文主要的研究工做和总结如下：
①本论文中提出使用亥姆霍兹线圈作为激励线圈产生一组均匀场，同时分析了激励磁场的均匀度。
②对磁感应成像正问题的研究，用棱边有限元法建立相应的有限元方程，用MATLAB实现有限元方程的生成和计算。计算了在无异物和有异物时的涡流的分布，同时计算了被测物体旋转不同角度对测量电压的影响，为后面的逆问题提供指导和数据来源。
③提出了基于均匀时谐磁场激励磁感应成像的滤波反投影重构算法。同时测试了在不同模型下的重构算法的效果和抗噪声能力。
④硬件研究。设计了高精度的同步检波的相位检测电路，以及为激励线圈提供电流的恒流源，同时设计了高SNR的线圈传感器。测试了单通道的硬件的关键技术指标。
⑤研制了一套旋转磁感应断层成像系统，通过单目标和双目标的琼脂模型实验，测试了成像系统在几种模型下的成像效果。这一系列的物理模型实验将为将来的临床实验提供指导意义，为实现颅内监护提供打下实验基础。
⑥研制了一套16通道的磁感应平面直接投影成像的临床系统。在儿童医院对7例脑膜炎患者和正常人进行初步的检测，其中包括2名脑炎患者和5名脑部正常的患者。比较两种情况的检测数据，脑膜炎病人的检测数据明显高于脑部正常的数据，这比较结果为将来动态监护提供很有价值的参考。
In general, in the course of many common neural diseases, such as stroke, braininjury, encephalitis and intracranial tumors, the serious brain edema and intracranialhypertension are occurred. If there is no prompt treatment, the death rate and disabilityrate are very high undoubtedly. Early, timely and accurate evaluation of, the location,nature and extent or severity, as well as the development and drug response of the tissuelesions, which are caused by various etiologies, is directly related to correct process ofcerebral edema and intracranial pressure.meanwhile, this is the key to the neurologicalemergency rescue.
The traditional detection technology, e.g., head CT, Magnetic Resonance Imaging(MRI) and Diffusion Weighted Imaging and Diffusion Tensor MR Imaging (DWI), canaccurately determine the critical nature, range and degree of the disease, but these aren’tstill available to continuous imaging for monitoring. However in some critical cases,patients need to be moved repeatedly to monitor the dynamic changes of the lesions.Hence, these existing devices are limited to the timely judging disease and adjustingtreatment. Therefore, there is urgent demand for a kind of portable medical imagingequipment, which can continuously monitor the patient, especially for effectivecontinuous monitoring of brain edema and intracranial pressure.
Magnetic Induction Tomography (MIT), which is one of the current advancedresearches in the nondestructive testing of biomedical engineering, is a novelnon-contacting technology for the tissue conductivity imaging; MIT has severaladvantages, for example, fast, portable, low-cost, and noninvasive. Because of thesefeatures, it has a good application prospect in the biomedical noninvasive imaging andcontinuous dynamic monitoring fields, especially in the continuous monitoring ofintracranial diseases.
This main purpose of this dissertation is to study the real-time monitoring ofintracranial lesion tissue. The main work is to develop a rapid, real-time monitoring,and portable MIT functional imaging system and discuss the reconstruction algorithmand experiments. The main research contents and summarizes as follows:
①This paper proposed the Helmholtz coil which can generate a set of uniformexcitation fields, and analyzed the uniformity of excitation field.
②The forward problem of the magnetic induction tomography. The corresponding finite element equations were established by MATLAB software using the edge finiteelement. The distributions of eddy current with or without perturbation object werecalculated by the finite element equations. In addition, the measuring voltages in thedifferent rotation angles were also calculated to provide guidance and data sources forthe inverse problem.
③Research on the reconstruction algorithm of magnetic induction tomographybased on the uniform magnetic excitation. The effect of reconstruction algorithm in thedifferent models and its noise immunity were tested.
④Hardware research. The high precision phase detection circuit usingsynchronous detection, the constant current source circuit, and the high SNR coil sensorwas developed. The key performance of a single channel experiment platform wastested.
⑤A rotating MIT system was designed. The system was tested for the imagingeffect in the several models, such as a single object, double object agar models. Thesephysical model experiments, which lay a solid foundation for intracranial monitoring,provide the guidance for clinical experiments in the future.
⑥A set of16channels direct projection MIT clinical system was established.Using the MIT measurement system, seven preliminary clinical experiments, including2mumps with meningitis patients, and5brain normal patients were carried out inChildren Hospital. Comparing the results of the two kinds of cases, the values ofmeningitis patients are higher than these of normal patients, which is a very valuablereference for the future dynamic monitoring.
引文
[1] Griffiths H, Stewart W R, Gough W. Magnetic induction tomography: a measuring system forbiological tissues [J]. Ann. NY Acad. Sci.,1999,873:335-345.
[2] H Griffiths. Magnetic induction tomography [J]. Measurement Science and Technology,2001,12:1126-1131.
[3] Thom F. Oostendorp, Jean Delbeke, Dick F. Stegeman. The conductivity of the human skull:results of in vivo and in vitro measurements [J]. IEEE Trans. Biomed. Eng.,2000,47(11):1487-1492.
[4] D. Gursoy, H. Scharfetter. Reconstruction artefacts in magnetic induction tomography due topatient’s movement during data acquisition [J]. Physiol. Meas.,2009(30):165-174.
[5] N. G. Gencer, M. Nejat Tek. Imaging tissue conductivity via contactless measurements: afeasibility study [J]. ELEKTRIK,1998,6(3):183-200.
[6] Xi G., Keep R. F., Hoff J.T. Mechanisms of brain injury after intracerebral haemorrhage [J].Lancet Neurol,2006,5(1):53-63.
[7] Xi G.,Wagner K.R., Keep R.F., et al. Role of blood clot formation on early edemadevelopment following experimental intracerebral hemorrhage [J]. Stroke,1998,29(12):2580-2586.
[8] A.M.Dijkstra, B.H. Brown, A.D. Leathard, et al, Clinical Applications of ElectricalImpedance Tomography, Journal of Medical Engineering&Technology,1993,17(3):89-98.
[9] Y. Kim, H.W. Woo, A.E. Luedtke, Impedance Tomography and its Application in DeepVenous Thrombosis Detection. IEEE Engineering in Medicine and Biology Magazine,1989,March:46-49.
[10] B.M. Eyuboglu, A.F. Oner, U. Baysal, etal, Application of Electrical Impedance Tomographyin Diagnosis of Emphysema-a Clinical Study, Physiol. Meas.,1995,16(Suppl.3A):1991-212.
[11] L.E. Baker Applications of the Impedance Technique to the Respiratory System. IEEEEngineering in Medicine and Biology Magazine,1989, March:50-52.
[12]何为,罗辞勇,徐征,等.电阻抗成像原理[M].北京：科学出版社.2009:251.
[13]刘国强.医学电磁成像[M].北京:科学出版社,2006:103.
[14] Gerhard Mook, Rolf Lange, Ole Koeser. Non-destructive characterisation of carbon fibrereinforced plastics by means of eddy-currents [J]. Composites Science and Technology,2001,61(6):865-873.
[15] Raimond Grimberg, Lalita Udpa, Adriana Savin.2D Eddy current sensor array [J]. NDT&EInternational,2006,39:264-271.
[16] Williams R A, Beck M S. Process Tomography Principles, Techniques and Applications [M].Oxford: Butterworth Heinmann.1995:581.
[17] Peyton A J, Yu Z Z, Lyon G, et al. An overview of electromagnetic inductance tomography:description of three different systems [J]. Meas. Sci. Technol.1996,7:261-271.
[18] Pham M H, Hua Y, Gray N G. Eddy current tomography for metal solidification imaging [C].Proc.1st World congress on industrial process Tomography, Buxton, UK.1999, April14:451-458.
[19] Tarjan P P, McFee R, Electrodeless measurements of the effective resistivity of the humantorso and head by magnetic induction [J]. IEEE Trans. Biomed. Eng.1968:266-278.
[20] Al-Zeibak S, Saunders N H. A feasibility study of in vivo electromagnetic imaging [J]. Phys.Med. Biol.1993,38:151-160.
[21] N.G. Gencer, Y. Z. Ider, S. J. Williamson. Electrical Impedance Tomography:Induced-Current Imaging Achieved with a Multiple Coil System. IEEE Transactions onbiomedical imaging,1996,43(2):139-149.
[22] Ulker B, Gencer N G. Electrical Conductivity Imaging via Contactless Measurements [J].IEEE Transactions on medical imaging,1999,18(7):617-627.
[23] Ulker B, Gencer N G. Implementation of data acquisition system for contactless conductivityimaging [J]. IEEE Engineering in Medicine and Biology Magazine.2002,21(5):152-155.
[24] Korjenevsky A, Cherepenin V, Sapetsky S. Magnetic induction tomography: experimentalrealization [J]. Physiol. Meas.2000,21(1):89-94.
[25] H. Griffiths, W. Gough, S. Watson,et al. Residual capacitive coupling and the measurement ofpermittivity in magnetic induction tomography [J]. Physiol. Meas.2007,28:301-311.
[26] Watson S, Williams R J, Gough W, et al. Phase measurement in biological magneticinduction tomography[C]. Proc.2nd World congress on industrial process Tomography,Hannover, Germany,2001, Aug29-31:517-524.
[27] J. Rosell-Ferrer, R. Merwa, P. Brunner, et al. A multifrequency magnetic inductiontomography system using planar gradiometers: data collection and calibration [J]. Physiol.Meas.,2006,27:271-280.
[28] Ulker B, Gencer N G. Electrical Conductivity Imaging via Contactless Measurements: AnExperimental Study [J].IEEE Transactions on medical imaging,2003,22(5):627-635.
[29] Riedel CH, Dossel O. Planar system for magnetic induction impedance measurement [C].Abstracts of4th Conference on Biomedical Applications of Electrical ImpedanceTomography. UMIST, Manchester,2003, April23-25:32.
[30] Liu Ruigang, Li Ye, You Fusheng, et al. Preliminary imaging results of magnetic inductiontomography based on physical phantom[C]. Proceedings of the30th Annual InternationalConference of the IEEE Engineering in Medicine and Biology Society, EMBS'08,2008:4559-4562.
[31]王聪,董秀珍,刘锐岗,等.在简单头模型上的磁感应断层成像仿真图像重建[J].系统仿真学报,2009,21(1):50-57.
[32]王聪,董秀珍,刘锐岗,等.磁感应断层成像技术中涡流问题的有限元法仿真研究[J].航天医学与医学工程,2007,20(3):220-221.
[33]李烨,董秀珍,刘锐岗,等.医用磁感应阻抗成像敏感性基础研究[J],医疗卫生装备2006,27(3):1-2.
[34] Hu Xiaoyan, Qin Mingxin, Liang Wenwen, et al. Study on technique of phase detection inmagnetic induction tomography [C],1st International Conference on Bioinformatics andBiomedical Engineering, ICBBE2007,2007,770-773.
[35] Qin Mingxin,Wang Yun, Hu Xiaoyan, et al. Study of MIT phase sensitivity for detecting abrain edema based on FDTD method [C]，1st International Conference on Bioinformatics andBiomedical Engineering, ICBBE2007,2007,660-663.
[36]胡晓彦,秦明新,焦明克,等.磁感应成像系统中相位检测方法研究[J],医疗卫生装备,2007,28(4):11-13.
[37]秦明新,王海彬,焦李成,等.磁感应方法检测脑组织电导率的FDTD仿真研究[J],中国医学物理学杂志,2006,23(2):104-107.
[38]傅林,于进强,肖宏,等.磁聚焦电导率成像系统的阵列线圈驱动电路设计实现[J].四川大学学报,2008,45(6):1405-1409.
[39]傅林,黄卡玛.磁聚焦电导率成像系统信号源与信号提取的实现[J].四川大学学报,2006,38(2):155-158.
[40]刘国强,霍小林.层状生物组织磁感应成像[J].中国医学物理学杂志,2003,20(1):59-61.
[41] Zheng Xu, Haijun Luo, Wei He, et al. A Multi-channel Magnetic Induction TomographyMeasurement System for Human Brain Model Imaging [J]. Physiol. Meas.,2009,30:175–186.
[42]徐征,何为,何传红,等.开放式磁感应成像原理及成像试验研究[J].仪器仪表学报,2008,29(9):1878-1882.
[43]徐征,何为,何传红,等.生物组织电导率磁感应测量原理及系统研究[J].中国生物医学工程学报,2009,28(1):141-144.
[44]何为,李倩,徐征,等.头部分层球模型磁感应成像正问题的解析解[J].计算物理,2010,27(6):912-918.
[45] Li Ke, Qiang Du. Reconstruction Method of Magnetic Induction Tomography based on FilterBack-Projection[C].ICBBE2009,3rd International Conference on Bioinformatics andBiomedical Engineering,2009:1-4.
[46]吕轶，王旭，金晶晶，等.正则化一步动态重建算法在磁感应成像中的应用[J].电子学报,2011,39(12):2801-2806.
[47] Chi Tang, Fusheng You, Guang Cheng, et al. Modeling the frequency dependence of theelectrical properties of the live human skull [J]. Physiol. Meas.,2009,30:1293-1301.
[48]王健,董为伟,张占龙,等.无创性阻抗法检测脑水肿的可行性研究[J].中华物理医学与康复杂志2005,27(8):510-511.
[49] S. Watson, R. J. Williams, H. Griffiths,et al. A transceiver for direct phase measurementmagnetic induction tomography [C].2001Proceeding of the23rd annual EMBS internationalconference, October25-28, Istanbul, Turkey:3182-3184.
[50] H. Scharfetter, A. Kostinger, S. Issa. Hardware for quasi-single-shot multifrequency magneticinduction tomography (MIT): the Graz Mk2system [J]. Physiol. Meas.,2008,29:431-443.
[51] M. Vauhkonen, M. Hamsch, et al. A measurement system and image reconstruction inmagnetic induction tomography [J]. Physiol. Meas.,2008,29:445-454.
[52] C. H. Igney,S. Watson,R. J. Williams,et al. Design and performance of a planar-array MITsystem with normal sensor alignment[J]. Physiol. Meas.,2005,26:263-278
[53] M. Soleimani, M. Vauhkonen, W. Q. Yang, et al. Dynamic imaging in electrical capacitancetomography and electromagnetic induction tomography using a Kalman filter [J]. Meas. Sci.Technol,2007,18:3287–3294.
[54] Ma, L., Wei, H. Y., Soleimani M., Pipelines inspection using Magnetic InductionTomography based on a narrowband pass filtering method [J]. Progress In ElectromagneticsResearch M,2007,23,65-78.
[55] S. Watson, A. Morris, R. J. Williams,et al. A Primary Field Compensation Scheme for PlanarArray Magnetic Induction Tomography [J]. Physiol. Meas.,2004,1:271-279.
[56] T. C. Hsieh, C. N. Huang, F. M. Yu,et al. The Primary Field Compensation for ContactlessImpedance Measurement [C].2005Biomedical Engineering Society Annual Symposium,Taiwan,2005:78.
[57] H.Scharfetter, H. K. Lackner, J. Rosel. Magnetic induction tomography: hardware formulti-frequency measurements in biological tissues [J]. Physiol. Meas.,2001,22:131–146.
[58] C. H. Riedel, M. Keppelen, S. Nani, et al. System for magnetic induction conductivitymeasurement using a sensor matrix [J]. Physiol. Meas.,2004,25:403–411.
[59] H. J. Luo, W. He, Z. Xu, et al. Preliminary results on brain monitoring of Meningitis using16channels Magnetic Induction Tomography Measurement System [J]. Progress InElectromagnetics Research M,2012,24:57-68.
[60] K. Stawicki, S. Gratkowski, M. Komorowski, et al. A New Transducer for MagneticInduction Tomography [J]. IEEE Transactions on Magnetics.2009,45(3):1832-1835.
[61]刘国强.医学电磁成像[M].北京:科学出版社,2006:104.
[62] Korzhenevskii A V, Cherepenin V A. Magnetic induction tomography [J]. Comm. Tech.Electronics.,1997,42(4):469-474.
[63] Watson S, Williams RJ, Griffiths H, et al. Magnetic induction tomography: phase vs. vectorvoltmeter measurement techniques [J]. Physiol. Meas.2003,24:555-564.
[64] S. Watson, R. J. Williams, H. Griffiths, et al. Frequency downconversion and phase noise inMIT [J]. Physiological Measurement,2002,23:189–194.
[65]李烨,董秀珍,刘锐岗,等.磁感应断层成像中的一种高精度同步相位测量方法[J].仪器仪表学报,2009,30(4):796-801.
[66] W.Gough. Circuit for measurement of small phase delays in MIT [J]. PhysiologicalMeasurement.2003,24:501-507.
[67] A. Morris, H. Griffiths, W. Gough. A numerical model for magnetic induction tomographicmeasurements in biological tissues, Physiological measurement,2001,22:113-119.
[68] Karl Hollaus, Christian Magele, Robert Merwa,et al. Numerical Simulation of the eddycurrent problem in magnetic induction tomography for biomedical application by edgeelements, IEEE Transactions on Magnetics,2004,40(2):623-626.
[69] M Zolgharni, P D Ledger, D W Armitage, et al. Imaging cerebral haemorrhage with magneticinduction tomography: numerical modeling[J]. Physiol. Meas.,2009,30:187-200.
[70]刘国强,王涛,蒙萌等.用棱单元方法求解磁感应成像的正问题[J].中国生物医学工程学报，2006,25(2):163-165.
[71]殷朝庆,董秀珍,刘锐岗等.脑磁感应成像的数学模型及仿真结果[J].第四军医大学学报，2006,27(20):1913-1915.
[72]刘阳,闫丹丹,朱善安,等.电流磁共振电阻抗成像仿真研究[J].中国生物医学工程学报,2009,28(2):244-250.
[73]柯丽,杜强,王旭.基于滤波反投影的磁感应图像重建算法研究[J].仪器仪表学报，2009，30(6)增刊:5-7.
[74] D. B. Geselowitz. An Application of Electrocardiographic Lead Theory to ImpedancePlethysmography. IEEE Trans. Biomed. Eng.,1971,18(1):38-41.
[75] J. R. Mortarelli. A Generalization of the Geselowitz Relationship Useful in ImpedancePlethysmographic Field Calculations [J]. IEEE Trans. Biomed. Eng.,1980,27(11):665-667.
[76] H. Scharfetter, P. Riu, M. Populo, et al. Sensitivity maps for low-contrast perturbations withinconducting background in magnetic induction tomography [J]. Physiol. Meas.,2002,23:195-202.
[77] D. Gursoy, H. Scharfetter.The effect of receiver coil orientations on the imaging performanceof magnetic induction tomography [J]. Meas. Sci. Technol.,2009,20:1-9.
[78]吕轶,王旭,杨丹,等.一种用于磁感应成像中灵敏度矩阵的计算方法[J].东北大学学报,2011,32(5):618-621.
[79] R. Merwa, K. Hollaus, P. Brunner, et al. Solution of the inverse problem of magneticinduction tomography (MIT)[J]. Physiol. Meas.,2005,26:241-250.
[80]王聪,刘锐岗,李烨,等.一种用于磁感应断层成像的图像重建算法[J].仪器仪表学报,2008,29(10):2052-2057.
[81] Casanova R, da Silva A F, Borges A R, et al. Magnetic induction tomography using Tikhonovregularization [C]. Abstracts of Workshop on Inverse obstacle problems, Lisbon, Portugal.2002.
[82] Casanova R, da Silva A F, Borges A R, et al. MIT image reconstruction based on edgepreserving regularization [J]. Physiol. Meas.2004,25:195-207.
[83] Woo E J, Seo J K. Magnetic resonance electrical impedance tomography (MREIT) forhigh-resolution conductivity imaging [J]. Physiol. Meas.2008,29:1-26.
[84] Birgul O, Eyuboglu B M and Ider Y Z. Experimental results for2D magnetic resonanceelectrical impedance tomography (MR-EIT) using magnetic flux density in one direction [J].Phys. Med. Biol.2003,48:3485-3504.
[85] Yuan Xu, Bin He. Magnetoacoustic tomography with magnetic induction [J]. Phys. Med.Biol.,2005,50:5175–5187.
[86]蒙萌,江凌彤,李士强,等.三维磁共振磁感应成像重建方法研究[J].中国生物医学工程学报,2008,27(5):650-653.
[87]刘国强.医学电磁成像[M].北京:科学出版社,2006:125-126.
[88] N. G. Gencer, M. Nejat Tek. Forward problem solution for electrical conductivity imaging viacontactless measurements [J]. Phys. Med. Biol.,1999,44:927-940.
[89] N. G. Gencer, M. Kuzuoglu, Y. Z. Ider. Electrical impedance tomography using inducedcurrents [J]. IEEE Transactions on medical imaging,1994,13(2):338-350.
[90]雷银照.轴对称线圈磁场计算[M].北京:中国计量出版社,1991.136-138.
[91]朱业俊,陶小平,孙腊珍.亥姆霍兹线圈磁场的探究[J].物理实验,2010,30(5):43-46.
[92]曾晓英.亥姆霍兹线圈磁场的均匀性分析及误差估算[J].物理实验,2000,20(5):38-39.
[93]谢德馨,等.三维涡流场的有限元分析[M].北京:机械工业出版社,2007:8-15.
[94]饶明忠.棱边有限元法及其在电磁场计算中的应用[D].重庆大学博士学位论文.1993:59-61.
[95]曾余庚，徐国华等.电磁场有限单元法[M].北京:科学出版社.1982:245-248.
[96]谢德馨,等.三维涡流场的有限元分析[M].北京:机械工业出版社,2007:59-61.
[97]徐管鑫，电阻抗成像技术理论及基础应用研究[D].重庆大学博士学位论文.2004:44-45.
[98]曾更生.医学图像重建入门[M].北京:高教出版社.2010:4-5.
[99]曾更生.医学图像重建入门[M].北京:高教出版社.2010:22-23.
[100]高晋占.微弱信号检测[M].北京:清华大学出版社.2004:154-157.
[101]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，2006:226.
