永磁型磁共振系统中匀场线圈设计的研究
|
摘要
在我国,因造价低廉,维护方便,目前应用最为广泛的是永磁型磁共振成像系统,其中磁场均匀性是决定设备好坏的极为关键的技术参数,但是,由于受采用的铁磁质原料和加工工艺的影响,永磁型核磁共振成像系统常常会存在磁场不均匀性等设备缺陷,这会极大地降低成像质量,最终妨碍了病情的诊断。为了解决这一问题,研究人员做了大量的研究,其中,利用外部的设备对主磁场进行校正,即均匀主磁场被认为是最为简单有效的方式。
本文主要针对磁共振成像系统中直径为20cm的球域设计匀场线圈,通过在磁场上另外使用一套辅助设备,在磁极中间设计一定形状的匀场线圈,并调整线圈中的通电电流,通过控制线圈中的电流产生不同方向的磁场分量叠加到主磁场上,针对磁体磁场变化进行实时再校正,从而使成像区域内的主磁场变得更加均匀。本文首先介绍了核磁共振成像理论,了解了磁共振成像的三个必要条件,简要介绍了磁共振成像设备的一般结构组成。然后根据电磁场理论得出Z轴上磁场强度的级数表达式,通过分析通电载流圆弧产生的磁场强度泰勒级数展开式的分布规律,系统阐述了径向和轴向匀场线圈设计的思路和方法,通过设计通电圆弧的不同半径、对称方式、通电方向等达到设计不同阶线圈的目的。考虑到分布匀场线圈的设计不仅需要分析永磁体产生的不均匀磁场的特点,而且还需要结合匀场线圈的工程实践应用。本文运用Matlab仿真软件,通过设计具体的参数,对比分析了设计匀场线圈的半径和极板间隔、线性度之间的关系,进而优化匀场线圈设计。最后在低阶线圈的基础上分析了高阶线圈的设计方向。
In our country, due to low cost and convenient maintenance, the magnetic resonance imaging system of permanent magnet type have been most widely used. Magnetic field uniformity is the crucial technical parameters that affect the equipment's quality.However, with the influence of raw ferromagnetic material and processing technology, magnetic fields is often inhomogeneous.The equipment defects greatly reduce image quality and finally hinder illness diagnoses. In order to solve this problem, the researchers have done lots of research. Among of all works, using external equipment to correct the main field is considered the most simple and effective way.
In this paper, we will pay attention to designing shim coils in the 20cm diameter spherical volume field for magnetic resonance imaging system.We can use a set of auxiliary equipment and design a certain shape shimming coils in the magnetic field.Then adjust the current of the coil to generate the magnetic field components in different directions. Finally the main magnetic field in the region becomes more uniform. This paper introduces the theory about magnetic resonance imaging.Three conditions must be needed for magnetic resonance imaging.Then the paper gives a brief introduction to the general structure of magnetic resonance imaging system.Learning from the electromagnetic theory, we can get the series expression of magnetic field intensity of Z axis.With discussing Taylor series expansion of magnetic field generated through the arc, the methods of the design of radial and axial shimming coils can be found. Designing shimming coils not only need pay attention to analyzing the characteristics of the non-uniform magnetic field produced by permanent magnet, but also require a combination of shim coils for engineering application. In order to optimize the design, we use the Matlab simulation software, through the design of specific parameters, find the relationship among the radius of shim coils,the plate spacing and the magnet field linear. Finally, on the basis of the coils in the low-level,the paper analyzes the design direction of the high-level coils.
本文主要针对磁共振成像系统中直径为20cm的球域设计匀场线圈,通过在磁场上另外使用一套辅助设备,在磁极中间设计一定形状的匀场线圈,并调整线圈中的通电电流,通过控制线圈中的电流产生不同方向的磁场分量叠加到主磁场上,针对磁体磁场变化进行实时再校正,从而使成像区域内的主磁场变得更加均匀。本文首先介绍了核磁共振成像理论,了解了磁共振成像的三个必要条件,简要介绍了磁共振成像设备的一般结构组成。然后根据电磁场理论得出Z轴上磁场强度的级数表达式,通过分析通电载流圆弧产生的磁场强度泰勒级数展开式的分布规律,系统阐述了径向和轴向匀场线圈设计的思路和方法,通过设计通电圆弧的不同半径、对称方式、通电方向等达到设计不同阶线圈的目的。考虑到分布匀场线圈的设计不仅需要分析永磁体产生的不均匀磁场的特点,而且还需要结合匀场线圈的工程实践应用。本文运用Matlab仿真软件,通过设计具体的参数,对比分析了设计匀场线圈的半径和极板间隔、线性度之间的关系,进而优化匀场线圈设计。最后在低阶线圈的基础上分析了高阶线圈的设计方向。
In our country, due to low cost and convenient maintenance, the magnetic resonance imaging system of permanent magnet type have been most widely used. Magnetic field uniformity is the crucial technical parameters that affect the equipment's quality.However, with the influence of raw ferromagnetic material and processing technology, magnetic fields is often inhomogeneous.The equipment defects greatly reduce image quality and finally hinder illness diagnoses. In order to solve this problem, the researchers have done lots of research. Among of all works, using external equipment to correct the main field is considered the most simple and effective way.
In this paper, we will pay attention to designing shim coils in the 20cm diameter spherical volume field for magnetic resonance imaging system.We can use a set of auxiliary equipment and design a certain shape shimming coils in the magnetic field.Then adjust the current of the coil to generate the magnetic field components in different directions. Finally the main magnetic field in the region becomes more uniform. This paper introduces the theory about magnetic resonance imaging.Three conditions must be needed for magnetic resonance imaging.Then the paper gives a brief introduction to the general structure of magnetic resonance imaging system.Learning from the electromagnetic theory, we can get the series expression of magnetic field intensity of Z axis.With discussing Taylor series expansion of magnetic field generated through the arc, the methods of the design of radial and axial shimming coils can be found. Designing shimming coils not only need pay attention to analyzing the characteristics of the non-uniform magnetic field produced by permanent magnet, but also require a combination of shim coils for engineering application. In order to optimize the design, we use the Matlab simulation software, through the design of specific parameters, find the relationship among the radius of shim coils,the plate spacing and the magnet field linear. Finally, on the basis of the coils in the low-level,the paper analyzes the design direction of the high-level coils.
引文
[1]武海澄,刘正敏,周荷琴.磁共振成像系统中低阶平板匀场线圈的设计[J].中国电机工程学报,2005,25(24)：154-159.
[2]陈历明,彭承琳,朱学武.0.2T开放式永磁型医用核磁共振成像仪有源匀场系统的研制[J].生物医学工程学杂志,2004,21(2)：288-291.
[3]储越森,黄放.磁共振成像中磁体的匀场线圈设计与磁场计算[J].上海交通大学学报,1996,30(12)：103-109.
[4]Abele M.G.Structures of Permanent Magnets [M].New York:Wiley press,1993.
[5]贺强,俎栋林,宋枭禹,包尚联.磁共振成像(MRI)纵向梯度线圈的研究[J].中国物理学杂志,2002,19(1)：9-11.
[6]Dorri B,Vermilyea M E.Passive shiming of MR magnets:algorithm,hardware,and results [J]. IEEE transactions on applied superconductivity,1993(01):76-78.
[7]赵喜平.磁共振成像系统原理及其应用[M].北京：科学出版社,2005.
[8]徐立勤,曹伟.电磁场与电磁波理论[M].北京：科学出版社,2006.
[9]郭辉萍,刘学观.电磁场与电磁波[M].西安：西安电子科技大学出版社,2002.
[10]冯慈璋,电磁场[M].北京：高等教育出版社,1979.
[11]谢处方,饶克谨.电磁场与电磁波(第4版)[M].北京：高等教育出版社,2006.
[12]贾秀敏.圆形线电流的磁场分布[J].河北科技大学学报,2006,27(1)：25-27.
[13]邱关源.电路[M].北京：高等教育出版社,1978.
[14]王进喜.永磁MRI系统快速动态自动匀场技术研究[D].泰安：泰山医学院硕士学位论文,2006.
[15]Qi Feng,Tang Xin,Wang Weimin,Shen Yifei,Liu Shaopo,Jiang Zhongde. A new simulated annealing method of designing NMR biplanar shim coils[J].Progress atural Science,July 2006,16(7):747-752.
[16]储越森.核磁共振成像磁体的有源匀场技术[J].电工技术学报,1996,11(5)：40-44.
[17]武海澄,周荷琴,刘正敏.有源匀场电流优化算法研究[J].北京生物医学工程,2007,26(5)：465-469.
[18]王清源.核磁共振成像用永磁体不均匀场的调整[J].电工电能新技术,1989, (4)：42-28.
[19]赵薇,刘志文,刘勇.开放式低场永磁MRI磁体的匀场方法研究[J].电工电能新技术,2007,26(3)：29-32.
[20]Forbes Larry K,Brideson Michael A,Crozier Stuart. A target-field method to design circular biplanar coils for asymmetric shim and gradient fields [J].IEEE Transactions on Magnetics,2005(06):213-217.
[21]励庆孚,李益丰.高匀场磁体校正线圈的设计方法[J].电工技术学报,1992,(4)：25-30.
[22]郑敦良.磁共振用超导磁体的磁场均匀性研究[D].济南：山东大学硕士学位论文,2004.
[23]A. Trequattrini, G. Coscia, S. Pittaluga Double-Cavity Open Permanent Magnet for Dedicated MRI. IEEE Applied Superconductivity,2000,10(1):756-758.
[24]Prammer MJ, Haselgrove JC. Device and method for automatic shimming of NMR insmtment:U.S,4761614[P]. (1988).
[25]Turner R.A target field approach to optimal coil design. [J]. Journal of physics D:Applied physics,1986(01):99-102.
[26]Ying ying Yao, You tong Fang, Chang Seop Koh. A new design method for completely open architecture permanent magnet for MRI. IEEE transactions on magnetic,2005(05):282-284.
[27]刘若茜,黄常纲.永磁磁共振成像系统中磁体极板尺寸和梯度线圈的关系[J].电工电能新技术,2000,19(1)：14-18.
[28]高国灿.开放式C型磁共振成像系统永磁体匀场研究[D].沈阳：东北大学硕士学位论文,2003.
[29]Rastislav Vadovic.Magnetic field correction using magnetized shims[J]. IEEE Transactions on Magnetics,1989(04):435-436.
[30]J.E.C Williams,E.S.Bobrov,Y.Iwasa.NMR Magnet Technology at MIT[J]. IEEE Transactions on Magnetics,1992,28(1):627-630.
[31]Anatoly podolskii. Design Procedure for Permanent Magnet Assemblies with Uniform Magnetic Fields for MRI Devices [J]. IEEE Transactions on Magnetics, 2000,36(2):484-490.
[2]陈历明,彭承琳,朱学武.0.2T开放式永磁型医用核磁共振成像仪有源匀场系统的研制[J].生物医学工程学杂志,2004,21(2)：288-291.
[3]储越森,黄放.磁共振成像中磁体的匀场线圈设计与磁场计算[J].上海交通大学学报,1996,30(12)：103-109.
[4]Abele M.G.Structures of Permanent Magnets [M].New York:Wiley press,1993.
[5]贺强,俎栋林,宋枭禹,包尚联.磁共振成像(MRI)纵向梯度线圈的研究[J].中国物理学杂志,2002,19(1)：9-11.
[6]Dorri B,Vermilyea M E.Passive shiming of MR magnets:algorithm,hardware,and results [J]. IEEE transactions on applied superconductivity,1993(01):76-78.
[7]赵喜平.磁共振成像系统原理及其应用[M].北京：科学出版社,2005.
[8]徐立勤,曹伟.电磁场与电磁波理论[M].北京：科学出版社,2006.
[9]郭辉萍,刘学观.电磁场与电磁波[M].西安：西安电子科技大学出版社,2002.
[10]冯慈璋,电磁场[M].北京：高等教育出版社,1979.
[11]谢处方,饶克谨.电磁场与电磁波(第4版)[M].北京：高等教育出版社,2006.
[12]贾秀敏.圆形线电流的磁场分布[J].河北科技大学学报,2006,27(1)：25-27.
[13]邱关源.电路[M].北京：高等教育出版社,1978.
[14]王进喜.永磁MRI系统快速动态自动匀场技术研究[D].泰安：泰山医学院硕士学位论文,2006.
[15]Qi Feng,Tang Xin,Wang Weimin,Shen Yifei,Liu Shaopo,Jiang Zhongde. A new simulated annealing method of designing NMR biplanar shim coils[J].Progress atural Science,July 2006,16(7):747-752.
[16]储越森.核磁共振成像磁体的有源匀场技术[J].电工技术学报,1996,11(5)：40-44.
[17]武海澄,周荷琴,刘正敏.有源匀场电流优化算法研究[J].北京生物医学工程,2007,26(5)：465-469.
[18]王清源.核磁共振成像用永磁体不均匀场的调整[J].电工电能新技术,1989, (4)：42-28.
[19]赵薇,刘志文,刘勇.开放式低场永磁MRI磁体的匀场方法研究[J].电工电能新技术,2007,26(3)：29-32.
[20]Forbes Larry K,Brideson Michael A,Crozier Stuart. A target-field method to design circular biplanar coils for asymmetric shim and gradient fields [J].IEEE Transactions on Magnetics,2005(06):213-217.
[21]励庆孚,李益丰.高匀场磁体校正线圈的设计方法[J].电工技术学报,1992,(4)：25-30.
[22]郑敦良.磁共振用超导磁体的磁场均匀性研究[D].济南：山东大学硕士学位论文,2004.
[23]A. Trequattrini, G. Coscia, S. Pittaluga Double-Cavity Open Permanent Magnet for Dedicated MRI. IEEE Applied Superconductivity,2000,10(1):756-758.
[24]Prammer MJ, Haselgrove JC. Device and method for automatic shimming of NMR insmtment:U.S,4761614[P]. (1988).
[25]Turner R.A target field approach to optimal coil design. [J]. Journal of physics D:Applied physics,1986(01):99-102.
[26]Ying ying Yao, You tong Fang, Chang Seop Koh. A new design method for completely open architecture permanent magnet for MRI. IEEE transactions on magnetic,2005(05):282-284.
[27]刘若茜,黄常纲.永磁磁共振成像系统中磁体极板尺寸和梯度线圈的关系[J].电工电能新技术,2000,19(1)：14-18.
[28]高国灿.开放式C型磁共振成像系统永磁体匀场研究[D].沈阳：东北大学硕士学位论文,2003.
[29]Rastislav Vadovic.Magnetic field correction using magnetized shims[J]. IEEE Transactions on Magnetics,1989(04):435-436.
[30]J.E.C Williams,E.S.Bobrov,Y.Iwasa.NMR Magnet Technology at MIT[J]. IEEE Transactions on Magnetics,1992,28(1):627-630.
[31]Anatoly podolskii. Design Procedure for Permanent Magnet Assemblies with Uniform Magnetic Fields for MRI Devices [J]. IEEE Transactions on Magnetics, 2000,36(2):484-490.