直接射频采样接收机在磁共振系统中的研究与设计
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摘要
磁共振成像是现代医学影像的重要组成。随着磁共振成像技术的快速发展,它对磁共振谱仪有着新的要求。现有的商用磁共振谱仪由于其昂贵的价格使得磁共振成像系统难以普及。因此,研究低成本的磁共振成像系统对于我国磁共振成像的普及和推广有着重要的意义。
磁共振接收机是磁共振系统的重要组成部分,接收机性能的好坏对磁共振成像质量有着很大的影响。虽然接收机广泛应用于通信以及雷达等各个领域,但由于磁共振成像的特殊性,磁共振成像系统对磁共振接收机在动态范围、噪声以及线性等各项指标有着较高的要求。现有的磁共振接收机为满足磁共振成像的要求,采用了大量高性能但是价格昂贵的器件,使得磁共振接收机成本较高。
直接射频接收机广泛应用于软件无线电当中。通过对信号的直接射频采样,一方面使得模拟电路能得到最大限度的简化,降低接收机成本;另一方面,信号处理的大部分过程将在数字域完成,随着DSP以及FPGA技术的不断成熟,诸如滤波、混频及解调等功能都能在数字域方便地完成,而且其性能也远远优于传统的模拟接收机。基于以上分析,将直接射频接收机应用于磁共振成像,将有利于于接收机构造的简化及成本的降低。
本文将对直接射频采样接收机进行研究与设计,首先分析了时钟稳定度对于接收机性能的影响,在此基础上提出了一种测量相位噪声的方法。对几种模数转换器的实际性能进行测试,并结合具体电路对信号动态范围的改善进行分析。最后提出一种将导频信号与可控增益放大器相结合应用于直接射频磁共振接收机的方法,以此改善接收机动态范围,满足磁共振成像的要求。
Magnetic Resonance Imaging is an important part of modern medical imaging. With the development of MRI technology, there’re new requirements for MR spectrometer. The commercial MR spectrometer has high performance and powerful functionality. However, the price is an important factor that limits the universalization of the MRI system. Therefore, the research of low cost MRI system means a lot to the healthcare business in our country.
MRI receiver plays an important role in MRI system. The performance of receiver may be decisive in the imaging quality. Different from receiver application in other fields, MRI system requires that MRI receiver has very high dynamic range, low noise and good linearity. To achieve the specification of MRI receiver, many devices with high performance but also high price are applied, which pushes up the cost of MRI receiver.
Direct radio frequency sampling receiver is applied in software define radio. There’re benefits with application of direct radio frequency sampling receiver in MRI system. First, the part of analog circuit can be simplified which helps cost down. Second, with the development of DSP and FPGA technologies, the signal processing such as filtering and frequency mixing can be done in digital field. The digital way of signal processing is more flexible and its performance is much better than the analog way. In conclusion, the application of direct RF sampling receiver in MRI system will simplify the structure of system and reduce the cost.
The direct RF sampling receiver is researched in this article. The influence of clock stability to the performance of receiver is analyzed. An improved method of phase noise measurement is introduced. Several ADCs are analyzed and tested. The issue of dynamic range in MRI system is discussed. A method that combines automatic gain control technology with pilot signal in MRI receiver is introduced to improving the dynamic range of MRI receiver.
磁共振接收机是磁共振系统的重要组成部分,接收机性能的好坏对磁共振成像质量有着很大的影响。虽然接收机广泛应用于通信以及雷达等各个领域,但由于磁共振成像的特殊性,磁共振成像系统对磁共振接收机在动态范围、噪声以及线性等各项指标有着较高的要求。现有的磁共振接收机为满足磁共振成像的要求,采用了大量高性能但是价格昂贵的器件,使得磁共振接收机成本较高。
直接射频接收机广泛应用于软件无线电当中。通过对信号的直接射频采样,一方面使得模拟电路能得到最大限度的简化,降低接收机成本;另一方面,信号处理的大部分过程将在数字域完成,随着DSP以及FPGA技术的不断成熟,诸如滤波、混频及解调等功能都能在数字域方便地完成,而且其性能也远远优于传统的模拟接收机。基于以上分析,将直接射频接收机应用于磁共振成像,将有利于于接收机构造的简化及成本的降低。
本文将对直接射频采样接收机进行研究与设计,首先分析了时钟稳定度对于接收机性能的影响,在此基础上提出了一种测量相位噪声的方法。对几种模数转换器的实际性能进行测试,并结合具体电路对信号动态范围的改善进行分析。最后提出一种将导频信号与可控增益放大器相结合应用于直接射频磁共振接收机的方法,以此改善接收机动态范围,满足磁共振成像的要求。
Magnetic Resonance Imaging is an important part of modern medical imaging. With the development of MRI technology, there’re new requirements for MR spectrometer. The commercial MR spectrometer has high performance and powerful functionality. However, the price is an important factor that limits the universalization of the MRI system. Therefore, the research of low cost MRI system means a lot to the healthcare business in our country.
MRI receiver plays an important role in MRI system. The performance of receiver may be decisive in the imaging quality. Different from receiver application in other fields, MRI system requires that MRI receiver has very high dynamic range, low noise and good linearity. To achieve the specification of MRI receiver, many devices with high performance but also high price are applied, which pushes up the cost of MRI receiver.
Direct radio frequency sampling receiver is applied in software define radio. There’re benefits with application of direct radio frequency sampling receiver in MRI system. First, the part of analog circuit can be simplified which helps cost down. Second, with the development of DSP and FPGA technologies, the signal processing such as filtering and frequency mixing can be done in digital field. The digital way of signal processing is more flexible and its performance is much better than the analog way. In conclusion, the application of direct RF sampling receiver in MRI system will simplify the structure of system and reduce the cost.
The direct RF sampling receiver is researched in this article. The influence of clock stability to the performance of receiver is analyzed. An improved method of phase noise measurement is introduced. Several ADCs are analyzed and tested. The issue of dynamic range in MRI system is discussed. A method that combines automatic gain control technology with pilot signal in MRI receiver is introduced to improving the dynamic range of MRI receiver.
引文
1 Lauterbur. PC Imaging Formation by Induced Local Interactions: Examples Employing Nuclear Magnetic Resonance. Nature. 1973, 242:190~191
2 Saleem Zaroubi and Gadi Goelman. Comples Denoising of MR Data via Wavelet Analysis: Application for functional MRI. Magnetic Resonance Imaging. 2000, 18:59~68
3 Yingying Yao, Junpeng Xie, Guangzheng Ni, Guangzhong Hu. The Optimal Design Method of Permanent Magnet Assemblies with Completely Open Architecture for MRI. International Journal of Applied Electromagnetics and Mechanics. 2007, v25:n1~4
4 H.W. Lorenzen, R. Zickermann, D. Schafer. Homogeniazation of the Magnetic Field in the Air-Gap of a Permanent Superconductor Bearing. IEEE Transactions on Applied Superconductivity. 2001, v11, n1Ⅱ: 1793~1796
5 E. Postrekhin, Chong Wang, Ki-Bui Ma, Quark Chen, Wei-Kan Chu. Axial Force in a Superconductor Magnet Journal Bearing. Physica C: Superconductivity and its Applications. 2000, 341-348(Ⅳ): 2617~2618
6 David A. Molyneaux and A. Haq Qureshi. Flexible Quadrature Coil System for Simultaneous Reception of Magnetic Resonance Signals. IEEE Transactions on Magnetics. 1995, v31, n6: 3590~3592
7 Fa-Hsuan Lin, Wei-Peng Kuan, Shyh-Kang Kuan, Jyh-Hong Chen. Quantitative Spectral/Spatial Analysis of Phased Array Coil in Magnetic Resonance Imaging Based on Method of Moment. IEEE Transactions on Medical Imaging. 1999, v18, n12: 1129~1137
8 Charles A. McKenzie, Ernest N. Yeh, Daniel K. Sodickson. Improved Spatial Harmonic Selection For SMASH Image Reconstructions. Magnetic Resonance in Medicine. 2001, 46: 831~836
9谢南柱.医学磁共振在中国临床应用的发展.世界医疗器械. 1998: 4~72
10 Y Shao, SR Cherry, K Farahani, R Slates, RW Silverman, K Meadors, A Bowery, S Siegel, PK Marsden, PB Garlick. Development of a PET Detector System Compatible with MRI/NMR Systems. IEEE Trans Nucl Sci. 1997, 44: 1167~1171
11 Yun Jiang, Yu Jiang, Hongyan Tao, Gengying Li. A Complete Digital Radio-Frequency Source for Nuclear Magnetic Resonance Spectroscopy. Rev Sci Instrum. 2002, Vol 73:3328~3331
12 Carl A. Michal, Kesten Broughton, Elsa Hansen. A High Performance Digital Receiver for Home-Built Nuclear Magnetic Resonance Spectrometers. Rec Sci Instrum. 2002, Vol 73:453~458
13姚澄.软件无线电中的关键接收技术研究.苏州大学,硕士学位论文, 2005: 17~26
14张建军.软件无线电数字化中频接收机设计与实现.南京信息工程大学,硕士学位论文. 2007: 5~14
15蒋勇,龙晓波.数字接收机自动增益控制工程实现方法.信息与电子工程. 2009, Vol 7, No.3: 173~176
16李玉泊,彭启琮.软件数字下变频的实现与算法分析.通信学报. 2000, Vol 21, No.10: 44~49
17盖鹏翱,赵笛. CIC滤波器的原理及FPGA实现.无线通信技术. 2005年第4期: 52~55
18 John C. Hoenninger, Lawrence E. Crooks, Mitusaki Arakawa. A Floating-Point Digital Receiver for MRI. IEEE Transactions On Biomedical Engineering. 2002, Vol. 49, No. 7: 689~692
19 Zhengmin Liu, Cong Zhao, Heqin Zhou, Huangqing Feng. A Novel Digital Magnetic Resonance Imaging Spectrometer Proceedings of the 28th IEEE EMBS Annual International Conference New York City, USA, Aug 30~Sept 3, 2006: 280~283
20 AF Mehlkof and JH Boe. Abstract VII SMRM Meeting SanFrancisco, 1989,192
21 RS Stormont, JP Noonan, NJ Pelc. Abstracit VIII SMRM Meeting, 1989
22徐勤.数字化磁共振成像谱仪.华东师范大学,研究生博士学位论文. 2006: 25~47
23 E. Mark Haacke, Robert W. Brown, Michael R. Thompson, Ramesh Venkatesan. Magnetic Resonance Imaging-Physical Principles and Sequence Design. John Wiley & Sons, Inc. 1999: 11~38
24赵喜平.磁共振成像.科学出版社, 2004: 123~307
25吴祈耀.现代数字医疗核心装备与关键技术.中国医药科技出版社. 2008: 69~93.
26 Waukesha. Current and Future MRI Systems. Microwave Symposium Digest. 2006. IEEE MTT-S International, 2006: 221~224
27 Jens Anders and Giovanni Boero. A Low-Noise CMOS Receiver Frontend for MRI. Biomedical Circuits and Systems Conference, 2008. BioCAS 2008. IEEE, Nov. 2008: 165~168
28 Namgoong Won, H. Meng Teresa. Direct-Conversion RF Receiver Design. IEEETransactions on Communications. March 2001, Vol.49, NO.3: 518~528
29 Hongjiang Song, Syed Roomi Naqvi, Bertan Bakkaloglu. I/Q-Channel Mismatch Transfer and Amplification Effects and Applications to the Measurement and Calibration of Integrated VLIF RF Receivers. SOC Conference, 2006 IEEE International: 35~ 38
30 Holly Pekau, James W. Haslett. A Comparison of Analog Front End Architectures for Digital Receivers. Electrical and Computer Engineering, 2005. Canadian Conference on, 2005: 1073~1077
31 Xueqin Jia, Xu Wang, Qiang Li, Jinghong Li. Improved Radio Frequency Receiver Front-end for Magnetic Resonance Imaging. Proceedings of the 2005 IEEE Engineering in Medicine and Biology 27th Annual Conference. Shanghai, China, September 1-4, 2005:1328~1330
32 Alper Demir. Phase Noise and Timing Jitter in Oscillators with Colored-Noise Sources. IEEE Transactions On Circuits And Systems– I: Fundamental Theory And Applications. December 2002, Vol.49, No.12: 1782~1791
33 Young Wan Kim and Jae Du Yu. Phase Noise Model of Single Loop Frequency Synthesizer. IEEE Transactions On Broadcasting. March 2008, Vol.54, No.1:112~119
34 Maxim. Clock(CLK) Jitter and Phase Noise Conversion (Application Note 3359). Maxim. Dec 10, 2004. http://www.maxim-ic.com/app-notes/index.mvp/id/3359
35 Alper Demir. Computing Timing Jitter from Phase Noise Spectra for Oscillators and Phase-Locked Loops With White and 1/f Noise. IEEE Transactions On Circuits And Systems- I: Regular Papers. September 2006, Vol.53, No.9:1869~1884
36 Brad Brannon and Allen Barlow. Aperture Uncertainty and ADC System Performance (Application Note 501). Analog Devices. 2006. http://www.analog.com/static/imported-files/application_notes/AN501_a.pdf
37张志刚.常用A/D、D/A器件手册.电子工业出版社. 2008年9月: 3~18
38 Maxim. Three Methods of Noise Figure Measurement (Application Note 2875). Nov.21, 2003. http://www.maxim-ic.com/app-notes/index.mvp/id/2875
39 Walter Kester. ADC Noise Figure-An Often Misunderstood and Misinterpreted Specification (MT006 Tutorial). Analog Devices. http://www.analog.com/static/imported-files/tutorials/MT-006.pdf
40 Yu-Chung Huang and Wei-Shinn Wey. Second-Order Delta-Sigma Modulation with Interfered Reference. IEEE Transactions On Circuits And Systems-Ⅱ:Analog And Digital Signal Processing. February 2001, Vol.48, No.2: 192~197
41 Akira Yasuda and Hiroshi Tanimoto. A Third-OrderΔ-ΣModulator Using Second-Order Noise-Shaping Dynamic Element Matching. IEEE Journal of Solid-State Circuits. December 1998, Vol.33, No.12: 1879~1886
42 Yanping Liu, Xin Liu, Jing Nan, Jia Yang. Design and Implementation of AGC in Gas Ultrasonic Flowmeter. The Eighth International Conference on Electronic Measurement and Instruments, ICEMI’2007: 534~537
43 Wenzhao Wang, Yaqin Chen, Qi Zhou. Implementation of Mixed Feedback/Feedforward Analog and Digital AGC. 2004 4th International Conference on Microwave and Millimeter Wave Technology Proceedings: 377~381
44 Jeon Okjune, M. Fox Robert, A. Myers Brent. Analog AGC Circuitry for a CMOS WLAN Receiver. IEEE Journal of Solid-State Circuits. October 2006, Vol. 41, No.10: 2291~2300
45曹鹏,费元春.大动态宽带数字中频AGC系统的设计.北京理工大学学报. October 2003, Vol 23, No.5: 613~616
46 A. J. Dunlop. AGC response and target glint. IEEPROC. April 1981, Vol.128, No.2: 83~90
2 Saleem Zaroubi and Gadi Goelman. Comples Denoising of MR Data via Wavelet Analysis: Application for functional MRI. Magnetic Resonance Imaging. 2000, 18:59~68
3 Yingying Yao, Junpeng Xie, Guangzheng Ni, Guangzhong Hu. The Optimal Design Method of Permanent Magnet Assemblies with Completely Open Architecture for MRI. International Journal of Applied Electromagnetics and Mechanics. 2007, v25:n1~4
4 H.W. Lorenzen, R. Zickermann, D. Schafer. Homogeniazation of the Magnetic Field in the Air-Gap of a Permanent Superconductor Bearing. IEEE Transactions on Applied Superconductivity. 2001, v11, n1Ⅱ: 1793~1796
5 E. Postrekhin, Chong Wang, Ki-Bui Ma, Quark Chen, Wei-Kan Chu. Axial Force in a Superconductor Magnet Journal Bearing. Physica C: Superconductivity and its Applications. 2000, 341-348(Ⅳ): 2617~2618
6 David A. Molyneaux and A. Haq Qureshi. Flexible Quadrature Coil System for Simultaneous Reception of Magnetic Resonance Signals. IEEE Transactions on Magnetics. 1995, v31, n6: 3590~3592
7 Fa-Hsuan Lin, Wei-Peng Kuan, Shyh-Kang Kuan, Jyh-Hong Chen. Quantitative Spectral/Spatial Analysis of Phased Array Coil in Magnetic Resonance Imaging Based on Method of Moment. IEEE Transactions on Medical Imaging. 1999, v18, n12: 1129~1137
8 Charles A. McKenzie, Ernest N. Yeh, Daniel K. Sodickson. Improved Spatial Harmonic Selection For SMASH Image Reconstructions. Magnetic Resonance in Medicine. 2001, 46: 831~836
9谢南柱.医学磁共振在中国临床应用的发展.世界医疗器械. 1998: 4~72
10 Y Shao, SR Cherry, K Farahani, R Slates, RW Silverman, K Meadors, A Bowery, S Siegel, PK Marsden, PB Garlick. Development of a PET Detector System Compatible with MRI/NMR Systems. IEEE Trans Nucl Sci. 1997, 44: 1167~1171
11 Yun Jiang, Yu Jiang, Hongyan Tao, Gengying Li. A Complete Digital Radio-Frequency Source for Nuclear Magnetic Resonance Spectroscopy. Rev Sci Instrum. 2002, Vol 73:3328~3331
12 Carl A. Michal, Kesten Broughton, Elsa Hansen. A High Performance Digital Receiver for Home-Built Nuclear Magnetic Resonance Spectrometers. Rec Sci Instrum. 2002, Vol 73:453~458
13姚澄.软件无线电中的关键接收技术研究.苏州大学,硕士学位论文, 2005: 17~26
14张建军.软件无线电数字化中频接收机设计与实现.南京信息工程大学,硕士学位论文. 2007: 5~14
15蒋勇,龙晓波.数字接收机自动增益控制工程实现方法.信息与电子工程. 2009, Vol 7, No.3: 173~176
16李玉泊,彭启琮.软件数字下变频的实现与算法分析.通信学报. 2000, Vol 21, No.10: 44~49
17盖鹏翱,赵笛. CIC滤波器的原理及FPGA实现.无线通信技术. 2005年第4期: 52~55
18 John C. Hoenninger, Lawrence E. Crooks, Mitusaki Arakawa. A Floating-Point Digital Receiver for MRI. IEEE Transactions On Biomedical Engineering. 2002, Vol. 49, No. 7: 689~692
19 Zhengmin Liu, Cong Zhao, Heqin Zhou, Huangqing Feng. A Novel Digital Magnetic Resonance Imaging Spectrometer Proceedings of the 28th IEEE EMBS Annual International Conference New York City, USA, Aug 30~Sept 3, 2006: 280~283
20 AF Mehlkof and JH Boe. Abstract VII SMRM Meeting SanFrancisco, 1989,192
21 RS Stormont, JP Noonan, NJ Pelc. Abstracit VIII SMRM Meeting, 1989
22徐勤.数字化磁共振成像谱仪.华东师范大学,研究生博士学位论文. 2006: 25~47
23 E. Mark Haacke, Robert W. Brown, Michael R. Thompson, Ramesh Venkatesan. Magnetic Resonance Imaging-Physical Principles and Sequence Design. John Wiley & Sons, Inc. 1999: 11~38
24赵喜平.磁共振成像.科学出版社, 2004: 123~307
25吴祈耀.现代数字医疗核心装备与关键技术.中国医药科技出版社. 2008: 69~93.
26 Waukesha. Current and Future MRI Systems. Microwave Symposium Digest. 2006. IEEE MTT-S International, 2006: 221~224
27 Jens Anders and Giovanni Boero. A Low-Noise CMOS Receiver Frontend for MRI. Biomedical Circuits and Systems Conference, 2008. BioCAS 2008. IEEE, Nov. 2008: 165~168
28 Namgoong Won, H. Meng Teresa. Direct-Conversion RF Receiver Design. IEEETransactions on Communications. March 2001, Vol.49, NO.3: 518~528
29 Hongjiang Song, Syed Roomi Naqvi, Bertan Bakkaloglu. I/Q-Channel Mismatch Transfer and Amplification Effects and Applications to the Measurement and Calibration of Integrated VLIF RF Receivers. SOC Conference, 2006 IEEE International: 35~ 38
30 Holly Pekau, James W. Haslett. A Comparison of Analog Front End Architectures for Digital Receivers. Electrical and Computer Engineering, 2005. Canadian Conference on, 2005: 1073~1077
31 Xueqin Jia, Xu Wang, Qiang Li, Jinghong Li. Improved Radio Frequency Receiver Front-end for Magnetic Resonance Imaging. Proceedings of the 2005 IEEE Engineering in Medicine and Biology 27th Annual Conference. Shanghai, China, September 1-4, 2005:1328~1330
32 Alper Demir. Phase Noise and Timing Jitter in Oscillators with Colored-Noise Sources. IEEE Transactions On Circuits And Systems– I: Fundamental Theory And Applications. December 2002, Vol.49, No.12: 1782~1791
33 Young Wan Kim and Jae Du Yu. Phase Noise Model of Single Loop Frequency Synthesizer. IEEE Transactions On Broadcasting. March 2008, Vol.54, No.1:112~119
34 Maxim. Clock(CLK) Jitter and Phase Noise Conversion (Application Note 3359). Maxim. Dec 10, 2004. http://www.maxim-ic.com/app-notes/index.mvp/id/3359
35 Alper Demir. Computing Timing Jitter from Phase Noise Spectra for Oscillators and Phase-Locked Loops With White and 1/f Noise. IEEE Transactions On Circuits And Systems- I: Regular Papers. September 2006, Vol.53, No.9:1869~1884
36 Brad Brannon and Allen Barlow. Aperture Uncertainty and ADC System Performance (Application Note 501). Analog Devices. 2006. http://www.analog.com/static/imported-files/application_notes/AN501_a.pdf
37张志刚.常用A/D、D/A器件手册.电子工业出版社. 2008年9月: 3~18
38 Maxim. Three Methods of Noise Figure Measurement (Application Note 2875). Nov.21, 2003. http://www.maxim-ic.com/app-notes/index.mvp/id/2875
39 Walter Kester. ADC Noise Figure-An Often Misunderstood and Misinterpreted Specification (MT006 Tutorial). Analog Devices. http://www.analog.com/static/imported-files/tutorials/MT-006.pdf
40 Yu-Chung Huang and Wei-Shinn Wey. Second-Order Delta-Sigma Modulation with Interfered Reference. IEEE Transactions On Circuits And Systems-Ⅱ:Analog And Digital Signal Processing. February 2001, Vol.48, No.2: 192~197
41 Akira Yasuda and Hiroshi Tanimoto. A Third-OrderΔ-ΣModulator Using Second-Order Noise-Shaping Dynamic Element Matching. IEEE Journal of Solid-State Circuits. December 1998, Vol.33, No.12: 1879~1886
42 Yanping Liu, Xin Liu, Jing Nan, Jia Yang. Design and Implementation of AGC in Gas Ultrasonic Flowmeter. The Eighth International Conference on Electronic Measurement and Instruments, ICEMI’2007: 534~537
43 Wenzhao Wang, Yaqin Chen, Qi Zhou. Implementation of Mixed Feedback/Feedforward Analog and Digital AGC. 2004 4th International Conference on Microwave and Millimeter Wave Technology Proceedings: 377~381
44 Jeon Okjune, M. Fox Robert, A. Myers Brent. Analog AGC Circuitry for a CMOS WLAN Receiver. IEEE Journal of Solid-State Circuits. October 2006, Vol. 41, No.10: 2291~2300
45曹鹏,费元春.大动态宽带数字中频AGC系统的设计.北京理工大学学报. October 2003, Vol 23, No.5: 613~616
46 A. J. Dunlop. AGC response and target glint. IEEPROC. April 1981, Vol.128, No.2: 83~90