低场磁共振成像系统中相控阵线圈的研制
摘要
核磁共振成像技术已经成为医学临床诊断和研究的重要工具之一，具有非侵入性、无电离、辐射等特点，其中的射频线圈是成像系统的一个重要元件，接收线圈作为接收链的最前端，对成像质量有着举足轻重的作用，直接影响图像信噪比。多通道相控阵射频接收线圈与其他种类线圈相比较具有高信噪比，高图像空间分辨率，快速成像的特点。然而目前大多数多通道线圈的设计都是针对超导高场MRI系统的[1]。本论文主要开展了低场系统里多通道的八字型脊椎表面线圈的研制，并在永磁0.3T磁共振成像系统上进行了水膜和人体实验。
本论文主要内容如下
第一：首先介绍了核磁共振的原理，然后介绍了核磁共振成像(MRI)扫描仪的基本结构。原理部分介绍了核磁共振基本原理和成像原理；MRI扫描仪组成部分包括磁体部分，谱仪部分和计算机部分。
第二：介绍了射频线圈的基本知识，包括调谐匹配，发射线圈和接收线圈之间的去耦，线圈的信噪比，常见的线圈分类，线圈的接口电路，线圈设计考虑要点。
第三：研制了低场系统里两通道的脊椎相控阵线圈，采用空间位置去耦方法，通过调整两个线圈之间的相对空间位置，使它们重叠合适部分，达到使两个线圈接收信号的耦合最小。并将此脊椎线圈与成像系统集成以后，在0.3T的系统里进行了水膜和人体试验，证明此两通道的脊椎线圈在低场系统里达到了很好的隔离度和比较好的成像结果。接下去进行了三通道的脊椎线圈研制，并与成像系统集成以后，进行了水膜试验和人体试验。
Magnetic Resonance imaging (MRI) is one of the key tools in medical treatment and research, which has no invasion, ionization and radiation characteristic. RF (radio-frequency) coil is one of the important components of MRI system. Receiving coil has a very important influence on the image quality because it is placed at the start of the receiving chain. Multi-channel phased array coils have much higher SNR, higher spatial resolution, faster imaging speed compared with other kinds of coils. However the design of multi-channel phased array coil is generally aimed at super-conduct high-field system at present time[1]. In this paper, the design of a multi-channel phased array RF receiving coil based on the figure-eight surface coil structure is discussed and implemented specially for vertebral imaging in low-field MRI system. In addition, experimental results obtained with both phantom and human vertebral images in a home-built 0.3T MRI system are presented.
The main contents of the paper include:
First, the theory of NMR ( nuclear magnetic resonance ) is introduced briefly, including the theory of NMR and MRI. The hardware structure of MRI scanner is described, which consists of magnet, spectrometer and computer subsystems.
Second, the basis of RF coil is introduced, including tuning and matching interface, decoupling between receiving coil and transmitting coil, SNR (signal and noise ratio) of coil, types of coil, coil interface circuit and essential points of designing an RF coil.
Third, the design of a two-channel RF receiving coil which is implemented specially for vertebral imaging in low-field MRI system is presented. The coupling of the two coils is resolved by adjusting the spatial location of the two coils, overlapping partially so that the coupling problem is minimized. The two-channel RF coil is integrated into the MRI scanner, and the experimental results obtained with both phantom and human vertebral images in a home-built 0.3T MRI system are given. The experiments proved that the two-channel RF coil has good isolation and good image quality. Moreover, a three-channel RF coil is designed and integrated into MRI scanner, and phantom as well as human vertebral experiment is also performed.
本论文主要内容如下
第一：首先介绍了核磁共振的原理，然后介绍了核磁共振成像(MRI)扫描仪的基本结构。原理部分介绍了核磁共振基本原理和成像原理；MRI扫描仪组成部分包括磁体部分，谱仪部分和计算机部分。
第二：介绍了射频线圈的基本知识，包括调谐匹配，发射线圈和接收线圈之间的去耦，线圈的信噪比，常见的线圈分类，线圈的接口电路，线圈设计考虑要点。
第三：研制了低场系统里两通道的脊椎相控阵线圈，采用空间位置去耦方法，通过调整两个线圈之间的相对空间位置，使它们重叠合适部分，达到使两个线圈接收信号的耦合最小。并将此脊椎线圈与成像系统集成以后，在0.3T的系统里进行了水膜和人体试验，证明此两通道的脊椎线圈在低场系统里达到了很好的隔离度和比较好的成像结果。接下去进行了三通道的脊椎线圈研制，并与成像系统集成以后，进行了水膜试验和人体试验。
Magnetic Resonance imaging (MRI) is one of the key tools in medical treatment and research, which has no invasion, ionization and radiation characteristic. RF (radio-frequency) coil is one of the important components of MRI system. Receiving coil has a very important influence on the image quality because it is placed at the start of the receiving chain. Multi-channel phased array coils have much higher SNR, higher spatial resolution, faster imaging speed compared with other kinds of coils. However the design of multi-channel phased array coil is generally aimed at super-conduct high-field system at present time[1]. In this paper, the design of a multi-channel phased array RF receiving coil based on the figure-eight surface coil structure is discussed and implemented specially for vertebral imaging in low-field MRI system. In addition, experimental results obtained with both phantom and human vertebral images in a home-built 0.3T MRI system are presented.
The main contents of the paper include:
First, the theory of NMR ( nuclear magnetic resonance ) is introduced briefly, including the theory of NMR and MRI. The hardware structure of MRI scanner is described, which consists of magnet, spectrometer and computer subsystems.
Second, the basis of RF coil is introduced, including tuning and matching interface, decoupling between receiving coil and transmitting coil, SNR (signal and noise ratio) of coil, types of coil, coil interface circuit and essential points of designing an RF coil.
Third, the design of a two-channel RF receiving coil which is implemented specially for vertebral imaging in low-field MRI system is presented. The coupling of the two coils is resolved by adjusting the spatial location of the two coils, overlapping partially so that the coupling problem is minimized. The two-channel RF coil is integrated into the MRI scanner, and the experimental results obtained with both phantom and human vertebral images in a home-built 0.3T MRI system are given. The experiments proved that the two-channel RF coil has good isolation and good image quality. Moreover, a three-channel RF coil is designed and integrated into MRI scanner, and phantom as well as human vertebral experiment is also performed.
引文
1 Michael A Ohliger, Daniel K Sodickson. An introduction to coil array design for parallel MRI[J].NMR Biomed.2006 May, 19 (3):300-315.
2 俎栋林 《核磁共振成像学》 高等教育出版社 2004年
3 詹松华，吴沛宏，杨振燕 《MRI临床医生必读》科学出版社 2003年
4 Mansfield, P. Multi-planar image formation using NMR spin echoes .J Phys C. 10:L55-L58.1977
5 J. Frahm, A. Haase, D.Matthaei, et al. FLASH MR Imaging: From Images to Movies. Radiology 157 (P), 156. 1985
6 Wesbey. G, Moon K, Crooks L, et al. Magn Reson Med 1:273 1984
7 裴奉奎，裘祖文 《核磁共振波谱》 科学出版社 1986年
8 杨福家 《原子物理学》 第三版 高等教育出版社 2000年
9 曾谨言 《量子力学》 第三版 科学出版社 2000年
10 赵喜平 《磁共振成像学》 科学出版社 2004年
11 赵喜平 《磁共振成像系统的原理及应用》 科学出版社 2000年
12 M. T Vlaardingerbroek, J. A den Boer, Magnetic Resonance Imaging: Theory and Practice. Springer 1999
13 Cynthia B. Paschal, H. Douglas Morris. K-Space in the Clinic. JMRI 19:145-159 2004
14 晏小龙，谢海滨，边明华，李鲠颖，一种通用的核磁共振微成像系统。波谱学杂志 Vol．3，No．4．1998
15 乔勇 2006届研究生学位论文 300MHz数字化核磁共振频率源
16 徐勤，沈杰，蒋瑜，李鲠颖，一体化核磁共振数字接收机的设计波谱学杂志，Vol．22 No．4，2005 357-365
17 辛立静，王鹤，徐勤，李鲠颖，一种用于核磁共振脉冲场梯度单元。波谱学杂志，20(4)，349-355，2003。
18 辛立静 2005届研究生硕士学位论文 用于磁共振成像系统的梯度波形发生器
沈杰，徐勤，陶红艳，蒋瑜，李鲠颖，基于PC机的脉冲序列发生器。波谱学杂志，20(2)，150-154，2003。
19 Boesch C, Gruetter R, Martin E. (1991) Temporal and spatial analysis of fields generated by eddy currents in superconducting magnets: optimization of corrections and quantitative characterization of magnet/gradient systems. Magn Reson Med, 20:268-284
20 Van Vaals J J, Bergman A H. Optimization of Eddy-Current Compensation. J Magn Reson, 1990, 90:52-70
21 Robertson S, Hughes, D G, Liu, Q, Allen P S. (1992) Analysis of the temporal and spatial dependence of the Eddy current fields in a 40-cm bore magnet. Magn Reson Med, 25:158-166
22 Bean C P, Deblois R W, Nesbitt L B. (1959) Eddy-Current method for measuring the resistivity of metals. J Appl Phys 30:1976-1980
23 陶红艳(2003)核磁共振成像仪器技术研究，硕士学位论文
24 zhang Hong-jie(张宏杰)，Bai Guo-gang(白国刚)，et al(等等)．An Endorectal RF Coil for MRI of the Prostate(磁共振成像前列腺射频线圈的研制)[J]．Chinese Journal of Medicial instrumentation(中国医疗器械杂志)，2006，30(2)
25 Zeng xiaozhuang(曾晓庄)．医用磁共振成像设备的市场分析(Market analysis of MRI)[J]．中国医疗器械信息(china Medical Devices Information)，2001，7(5)：32-37．
26 Roemer PB, Edelstein WA, Hayes CE, et al. The NMR phased array [J]. Magn Reson.Med, 1990 Nov, 16(2):192-225.
27 Jevtic J. Pikelja V. Menon A. Seeber D. Tatum N. Design Guidelines for the Capacitive Decoupling Networks. in Proc.11th Annual Meeting of the International Society for Magnetic Resonance in Medicine.Toronto,2003, 428.
28 Wang J-X, Plewes DB. Decoupling of strongly coupled MRI surface coils using virtual-shield method. In Proc.12th Annual Meeting of the International Society for Magnetic Resonance in Medicine.Kyoto.2004, 1584.
29 Roemer PB, Edelstein WA, Hayes CE, Souza SP, Mueller OM. The NMR phased array [J]. Magn Reson Med 1990,16(2): 192-225.
30 Ledden P. Inati S. Four channel preamplifier decoupled phased array for brain imaging at 1.5T. In Proc.9th Annual Meeting of the International Society for Magnetic Resonance in Medicine,Glasgow,2001, 1117.
31 Jovan Jevtic. West Allis. Phased array local coil for MRI imaging having non-overlapping regions of sensitivity [p]. United States: US 7,091,721 B2,2006 Au .
32 Lee RF,.Randy.Christopher J. Coupling and decoupling theory and its application to the MRI phased array [J].Magn.Reson.Med. 2002, 48(1): 203-213.
2 俎栋林 《核磁共振成像学》 高等教育出版社 2004年
3 詹松华，吴沛宏，杨振燕 《MRI临床医生必读》科学出版社 2003年
4 Mansfield, P. Multi-planar image formation using NMR spin echoes .J Phys C. 10:L55-L58.1977
5 J. Frahm, A. Haase, D.Matthaei, et al. FLASH MR Imaging: From Images to Movies. Radiology 157 (P), 156. 1985
6 Wesbey. G, Moon K, Crooks L, et al. Magn Reson Med 1:273 1984
7 裴奉奎，裘祖文 《核磁共振波谱》 科学出版社 1986年
8 杨福家 《原子物理学》 第三版 高等教育出版社 2000年
9 曾谨言 《量子力学》 第三版 科学出版社 2000年
10 赵喜平 《磁共振成像学》 科学出版社 2004年
11 赵喜平 《磁共振成像系统的原理及应用》 科学出版社 2000年
12 M. T Vlaardingerbroek, J. A den Boer, Magnetic Resonance Imaging: Theory and Practice. Springer 1999
13 Cynthia B. Paschal, H. Douglas Morris. K-Space in the Clinic. JMRI 19:145-159 2004
14 晏小龙，谢海滨，边明华，李鲠颖，一种通用的核磁共振微成像系统。波谱学杂志 Vol．3，No．4．1998
15 乔勇 2006届研究生学位论文 300MHz数字化核磁共振频率源
16 徐勤，沈杰，蒋瑜，李鲠颖，一体化核磁共振数字接收机的设计波谱学杂志，Vol．22 No．4，2005 357-365
17 辛立静，王鹤，徐勤，李鲠颖，一种用于核磁共振脉冲场梯度单元。波谱学杂志，20(4)，349-355，2003。
18 辛立静 2005届研究生硕士学位论文 用于磁共振成像系统的梯度波形发生器
沈杰，徐勤，陶红艳，蒋瑜，李鲠颖，基于PC机的脉冲序列发生器。波谱学杂志，20(2)，150-154，2003。
19 Boesch C, Gruetter R, Martin E. (1991) Temporal and spatial analysis of fields generated by eddy currents in superconducting magnets: optimization of corrections and quantitative characterization of magnet/gradient systems. Magn Reson Med, 20:268-284
20 Van Vaals J J, Bergman A H. Optimization of Eddy-Current Compensation. J Magn Reson, 1990, 90:52-70
21 Robertson S, Hughes, D G, Liu, Q, Allen P S. (1992) Analysis of the temporal and spatial dependence of the Eddy current fields in a 40-cm bore magnet. Magn Reson Med, 25:158-166
22 Bean C P, Deblois R W, Nesbitt L B. (1959) Eddy-Current method for measuring the resistivity of metals. J Appl Phys 30:1976-1980
23 陶红艳(2003)核磁共振成像仪器技术研究，硕士学位论文
24 zhang Hong-jie(张宏杰)，Bai Guo-gang(白国刚)，et al(等等)．An Endorectal RF Coil for MRI of the Prostate(磁共振成像前列腺射频线圈的研制)[J]．Chinese Journal of Medicial instrumentation(中国医疗器械杂志)，2006，30(2)
25 Zeng xiaozhuang(曾晓庄)．医用磁共振成像设备的市场分析(Market analysis of MRI)[J]．中国医疗器械信息(china Medical Devices Information)，2001，7(5)：32-37．
26 Roemer PB, Edelstein WA, Hayes CE, et al. The NMR phased array [J]. Magn Reson.Med, 1990 Nov, 16(2):192-225.
27 Jevtic J. Pikelja V. Menon A. Seeber D. Tatum N. Design Guidelines for the Capacitive Decoupling Networks. in Proc.11th Annual Meeting of the International Society for Magnetic Resonance in Medicine.Toronto,2003, 428.
28 Wang J-X, Plewes DB. Decoupling of strongly coupled MRI surface coils using virtual-shield method. In Proc.12th Annual Meeting of the International Society for Magnetic Resonance in Medicine.Kyoto.2004, 1584.
29 Roemer PB, Edelstein WA, Hayes CE, Souza SP, Mueller OM. The NMR phased array [J]. Magn Reson Med 1990,16(2): 192-225.
30 Ledden P. Inati S. Four channel preamplifier decoupled phased array for brain imaging at 1.5T. In Proc.9th Annual Meeting of the International Society for Magnetic Resonance in Medicine,Glasgow,2001, 1117.
31 Jovan Jevtic. West Allis. Phased array local coil for MRI imaging having non-overlapping regions of sensitivity [p]. United States: US 7,091,721 B2,2006 Au .
32 Lee RF,.Randy.Christopher J. Coupling and decoupling theory and its application to the MRI phased array [J].Magn.Reson.Med. 2002, 48(1): 203-213.