用于漫射光层析成像的数字锁相检测技术研究
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摘要
DOT(Diffuse Optical Tomography)依靠扩散光在组织中较深的穿透深度实现器官级的诊断层析成像,能提供组织体的解剖和生理功能信息,以其无创性、安全性等优点在乳腺成像、新生儿大脑供氧状况及血氧动力学观测等方面得到了广泛应用。
连续光DOT的图像重建算法需要测量多点分别激励下表面各点的光流输出分布,因此需要对光源进行编码。目前使用最多的是基于光开关的时分复用技术,这种方法需要将光源分时依次导入不同位置的入射光纤,当源的位置较多或使用多波长测量时,测量时间会因此变的很长,且同一测量周期内不同位置的测量间隔也较长,这非常不利于需要捕捉变化信号的动态成像应用,如脑功能成像。频分复用的源编码技术可以解决这个问题,它使用不同频率的正弦波调制多个光源,并将这些光源同时入射到成像腔,在探测端使用数字锁相检测技术可以从混合的信号中将各个光源对应的出射光信息分别求得。这种方法大大加快了DOT系统的测量速度,并且能够同时获取不同源-探测器位置的多个测量值,其成像结果更加真实的反映客观现象。
本文研究了数字锁相检测技术在基于光子计数的稳态DOT系统中的应用,以FPGA为平台实现了用于光子计数测量系统的数字锁相检测装置,初步建立了一个双通道光子计数DOT实验系统,主要包括两个可调制连续激光器、光子计数探测器、数字锁相检测与控制电路,并编写计算机程序进行控制和显示。最后通过一系列测量实验对该实验系统进行评估和分析,总结成果和不足,并对下一步的研究进行展望。
Relying on deeper penetration of light in the tissue,DOT(Diffuse Optical Tomography)achieves organ-level tomography diagnosis, which can provide information on anatomical and physiological features. DOT has been widely used in imaging of breast, neonatal cerebral oxygen status and blood oxygen kinetics observed by its non-invasive, security and other advantages.
Continuous wave DOT image reconstruction algorithms need the measurement of the surface distribution of the output photon flow inspired by more than one driving source, which means that source coding is necessary. Most currently used source coding in DOT is time-division multiplexing technology, which utilizes the optical switch to switch light into optical fiber of different locations. In case of large amounts of the source locations or using the multi-wavelength, the measurement time and the measurement interval between different locations within the same measurement period will therefore become too long to capture the dynamic changes in real-time imaging applications, such as brain imaging. Frequency division multiplexing source coding technology can solve this problem. It uses several light sources modulated by different frequency sine wave incident to the imaging chamber simultaneously. Signal corresponding to the various sources are obtained from the mixed output light using digital phase-locked detection technology in the detection end. This method greatly accelerates the DOT system measurement, and can also obtain the multiple measurements in different source-detector locations. The imaging results reflect the objective phenomenon more accurately.
This paper studies the digital lock-in detection technology in continuous wave DOT imaging system based on photon counting. A digital lock in detection circuit for photon counting measurement system is implemented in a FPGA development platform. A dual-channel DOT photon counting experimental system is preliminary established, including the two continuous lasers, photon counting detectors, digital lock in detection, control circuit, and computer programs to control and display. A series of experimental measurements is taken to validate the feasibility of the system. Finally, the paper summarizes the results and shortcomings, and prospects for future research.
连续光DOT的图像重建算法需要测量多点分别激励下表面各点的光流输出分布,因此需要对光源进行编码。目前使用最多的是基于光开关的时分复用技术,这种方法需要将光源分时依次导入不同位置的入射光纤,当源的位置较多或使用多波长测量时,测量时间会因此变的很长,且同一测量周期内不同位置的测量间隔也较长,这非常不利于需要捕捉变化信号的动态成像应用,如脑功能成像。频分复用的源编码技术可以解决这个问题,它使用不同频率的正弦波调制多个光源,并将这些光源同时入射到成像腔,在探测端使用数字锁相检测技术可以从混合的信号中将各个光源对应的出射光信息分别求得。这种方法大大加快了DOT系统的测量速度,并且能够同时获取不同源-探测器位置的多个测量值,其成像结果更加真实的反映客观现象。
本文研究了数字锁相检测技术在基于光子计数的稳态DOT系统中的应用,以FPGA为平台实现了用于光子计数测量系统的数字锁相检测装置,初步建立了一个双通道光子计数DOT实验系统,主要包括两个可调制连续激光器、光子计数探测器、数字锁相检测与控制电路,并编写计算机程序进行控制和显示。最后通过一系列测量实验对该实验系统进行评估和分析,总结成果和不足,并对下一步的研究进行展望。
Relying on deeper penetration of light in the tissue,DOT(Diffuse Optical Tomography)achieves organ-level tomography diagnosis, which can provide information on anatomical and physiological features. DOT has been widely used in imaging of breast, neonatal cerebral oxygen status and blood oxygen kinetics observed by its non-invasive, security and other advantages.
Continuous wave DOT image reconstruction algorithms need the measurement of the surface distribution of the output photon flow inspired by more than one driving source, which means that source coding is necessary. Most currently used source coding in DOT is time-division multiplexing technology, which utilizes the optical switch to switch light into optical fiber of different locations. In case of large amounts of the source locations or using the multi-wavelength, the measurement time and the measurement interval between different locations within the same measurement period will therefore become too long to capture the dynamic changes in real-time imaging applications, such as brain imaging. Frequency division multiplexing source coding technology can solve this problem. It uses several light sources modulated by different frequency sine wave incident to the imaging chamber simultaneously. Signal corresponding to the various sources are obtained from the mixed output light using digital phase-locked detection technology in the detection end. This method greatly accelerates the DOT system measurement, and can also obtain the multiple measurements in different source-detector locations. The imaging results reflect the objective phenomenon more accurately.
This paper studies the digital lock-in detection technology in continuous wave DOT imaging system based on photon counting. A digital lock in detection circuit for photon counting measurement system is implemented in a FPGA development platform. A dual-channel DOT photon counting experimental system is preliminary established, including the two continuous lasers, photon counting detectors, digital lock in detection, control circuit, and computer programs to control and display. A series of experimental measurements is taken to validate the feasibility of the system. Finally, the paper summarizes the results and shortcomings, and prospects for future research.
引文
[1]徐可欣,高峰,赵会娟,生物医学光子学,科学出版社,2007:1-194;
[2]赵会娟,高峰,牛憨笨,光学医学成像实验技术综述II——间接成像法,激光与光电子学进展,1999,10:7-10
[3] Markolf H. Niemz著,张镇西等译,激光与生物组织的相互作用——原理及应用,西安:西安交通大学出版社,1999
[4] D. A. Boas, et al, Imaging the body with diffuse optical tomography, IEEE Signal Process. Mag., 2001, 18: 57-75
[5]李麟荪,医学影像学,南京:东南大学出版社,2002
[6]许振玉,早期乳腺癌的诊断体会,中国全科医学,2006,8(8)
[7]刘维,用于乳腺扩散光层析成像的多通道光子计数系统的设计,[硕士学位论文],天津,天津大学,2007
[8] D. Haensse, P. szabo, D. Brown, A new multichannel near infrared spectro photometry system for functional studies of the brain in adults and neonates, Opt. Express, 2005, 13:4525-4538
[9] YOKO HOSHI. Functional near-infrared optical imaging: Utility and limitations in human brain mapping. Psychophysiology, 2003, 40: 511-520
[10]覃东利,时间分辨组织体光学参数测量及扩散光学成像实验研究:[硕士学位论文],天津,天津大学,2007
[11]唐晓英,宋毅,刘伟峰,近红外光乳腺检测频域方法的研究,北京理工大学学报,2006,26(11):1022-1025
[12] Nicolas Ducros, Anabela da Silva, Jean-Marc Dinten. Continuous Wave and Time-Resolved Fluorescence Diffuse Optical Tomography Comparison for different Lifetimes and Optical Properties. OSA/ BIOMED/DH/LACSEA, 2008
[13] Liping Qian, Defu Cheng, Juntuan Zhang, etal. Design and analysis of digital lock-in sine-wave amplitude detector based on TMS320C6xEVM. ICSP Proceedings, 2004
[14] F. Barone, E. Calloni, L. DiFiore, A. Grado, L. Milano, and G. Russo, High performance modular digital lock-in ampli?er, Rev. Sci. Instrum., 66(6):3697–3702
[15] Maximiliano Osvaldo Sonnaillon, Fabian Jose Bonetto. A low-cost high performance digital signal processor-based lock-in amplifier capable of measuring multiple frequency sweeps simultaneously. Review of Scientific Instruments, 2005, 76: 024703
[16] Javier Gaspar, Suei Feng Chen, Alejandro Gordillo, etal. Digital lock in amplifier: study, design and development with a digital signal processor, Microprocessors and Microsystems, 2004, 28:157-162
[17] R. Alonso, F. villuendas, J. Borja. Low-cost digital lock-in module with external reference for coating glass transmission/reflection spectrophotometer. Meas. Sci. Technol, 2003, 14: 551-557
[18] Adrian A. Dorrington, Rainer Kunnemeyer. A simple microcontroller based digital lock-in amplifier for the detection of low level optical signals, Proceedings of the First IEEE, International Workshop on Electronic Design, Test and Applications, 2002
[19] Dieter Braun, Albert Libchaber. Computer-based photon-counting lock-in for phase detection at the shot-noise limit. Optics letters, 2002, 27(16):1418-1420
[20] Steven J. Lascos, Daniel T. Cassidy. Multichannel digital phase sensitive detection using a field programmable gate array development platform. Rev. Sci. Instrum. 2008, 79, 074702
[21] A. Restelli, R. Abbiati, A. Geraci. Digital Field Programmable Gate Array-based Lock-in Amplifier for High-performance Photon Counting Applications ,Rev. Sci. Instrum. 2005, 76, 093112
[22] James M. Masciotti, J. M. lasker, A. H. hielscher. Digital Lock-in Algorithm for biomedical spectroscopy and Imaging instruments with multiple modulated souces. Proceedings of the 28th IEEE, EMBS Annual international conference. 2006
[23] James M. Masciotti, Joseph M. Lasker, Andreas H. Hielscher, Digital Lock-In Detection for Discriminating Multiple Modulation Frequencies With High Accuracy and Computational Efficiency, IEEE Transactions on Instrumentation and Measurement, 2008, 57(1):182-189
[24] Joseph M. Lasker, James M. Masciotti, Yang Li, etal. Dynamic Optical Tomographic Imager with Optimized Digital Lock-In Filtering. Proc. of SPIE-OSA Biomedical Optics, 2007, 6629, 662903-1
[25] Maria Angela Franceschini. Danny K. Joseph, Theodore J. Huppert, Diffuse optical imaging of the whole head, Journal of Biomedical Optics, 2006, 11(5), 054007
[26]李静,基于FPGA的数字锁相放大器设计,[硕士学位论文],武汉,桂林工学院,2008
[27] Maximiliano O.sonnaillon, Raul Urteaga, Fabian Jose Bonetto. Implementation of a high-frequency digital lock-in amplifier. Proceedings of IEEE, CCECE/CCGEI, 2005
[28]王超,徐明,徐真真等,用于混频信号的双通道数字锁相放大器,电子器件,2007,30(4):1321-1324
[29] Danny K. Joseph, Theodore J. Huppert, Maria Angela Franceschini, Diffuse optical tomography system to image brain activation with improved spatial resolution and validation with functional magnetic resonance imaging, APPLIED OPTICS, 2006, 45(31): 8142-8151
[30]北京创毅视讯科技有限公司,一种频率合成器及频率合成方法,中国专利,200810102330,2008-8-13
[31]黄智伟,锁相环与频率合成器电路设计,西安:西安电子科技大学出版社,2008,1-23
[32] Analog Devices, Inc., A Technical Tutorial on Digital Signal Synthesis, Analog Devices, Inc. 1999
[33]盛骤,谢式千,潘承毅,概率论与数理统计,北京:高等教育出版社,2001
[34]阮平巧,组织光学测量中光子计数技术研究——基于CPLD的多通道光子计数器设计,[硕士学位论文],天津,天津大学,2007
[35] Future Technology Device International Ltd, FT_000052, FT245R USB FIFO IC Datasheet Version2.02, 2008
[36] Analog Device, Inc. AD9763/AD9765/AD9767 Datasheet
[37] EDA先锋工作室,吴继华,王诚,Altera FPGA/CPLD设计(高级篇),北京:人民邮电出版社,2005,19-21
[38]崔文,叶信峰,基于查找表和CORDIC算法的数控振荡器的设计,电子科技,2006,7:23-25
[39]张欣,扩频通信数字基带信号处理算法及其VLSI实现,北京:科学出版社,2004,40-100
[40] Neil Eklund. CORDIC: Elementary Function Computation Using Recursive Sequences. Electronic, Proceedings of the Eleventh Annual International Conference on Technology in Collegiate Mathematics, 1998
[41]雷元武,周杰,葛颖增,并行CORDIC算法的研究及FPGA实现,计算机工程与科学,2008,30(8):75-78
[42] Ray Andraka. A survey of CORDIC algorithms for FPGA based computers, Proceedings of the ACM/SIGDA sixth international symposium on Field programmable gate arrays,. 1998
[43]李全,陈石平,付佃华,基于CORDIC算法的32位浮点三角超越函数之正余弦函数的FPGA实现,电子产品世界,2006(10):150-151
[44]孙健,汪彦彦,基于CORDIC算法的高速高精度NCO的FPGA设计,火控雷达技术,2007,12(30):68-72
[45]李刚,张丽君,林凌,一种新型数字锁相放大器的设计及其优化算法,天津大学学报,2008,41(4):429-432
[46]朱虹,林君,吴衷杰,近红外光谱仪中的数字锁相技术研究,仪器仪表学报,2006,27(10):1258-1261
[47]陈跃,田书林,刘科,非理想DDS输出信号分析及滤波处理,测试测量技术,2008,9:4-7
[48] Daniele Contini, Fabrizio Martelli, Giovanni Zaccanti, Photon migration through a turbid slab described by a model based on diffusion approximation, I. Theory, Applied Optics, 1997, 36(19): 4587-4594
[49]谢琼,李建平,高晓光等,动态多频数字锁相算法及其应用,电子与信息学报,2009,31(8):2006-2009
[2]赵会娟,高峰,牛憨笨,光学医学成像实验技术综述II——间接成像法,激光与光电子学进展,1999,10:7-10
[3] Markolf H. Niemz著,张镇西等译,激光与生物组织的相互作用——原理及应用,西安:西安交通大学出版社,1999
[4] D. A. Boas, et al, Imaging the body with diffuse optical tomography, IEEE Signal Process. Mag., 2001, 18: 57-75
[5]李麟荪,医学影像学,南京:东南大学出版社,2002
[6]许振玉,早期乳腺癌的诊断体会,中国全科医学,2006,8(8)
[7]刘维,用于乳腺扩散光层析成像的多通道光子计数系统的设计,[硕士学位论文],天津,天津大学,2007
[8] D. Haensse, P. szabo, D. Brown, A new multichannel near infrared spectro photometry system for functional studies of the brain in adults and neonates, Opt. Express, 2005, 13:4525-4538
[9] YOKO HOSHI. Functional near-infrared optical imaging: Utility and limitations in human brain mapping. Psychophysiology, 2003, 40: 511-520
[10]覃东利,时间分辨组织体光学参数测量及扩散光学成像实验研究:[硕士学位论文],天津,天津大学,2007
[11]唐晓英,宋毅,刘伟峰,近红外光乳腺检测频域方法的研究,北京理工大学学报,2006,26(11):1022-1025
[12] Nicolas Ducros, Anabela da Silva, Jean-Marc Dinten. Continuous Wave and Time-Resolved Fluorescence Diffuse Optical Tomography Comparison for different Lifetimes and Optical Properties. OSA/ BIOMED/DH/LACSEA, 2008
[13] Liping Qian, Defu Cheng, Juntuan Zhang, etal. Design and analysis of digital lock-in sine-wave amplitude detector based on TMS320C6xEVM. ICSP Proceedings, 2004
[14] F. Barone, E. Calloni, L. DiFiore, A. Grado, L. Milano, and G. Russo, High performance modular digital lock-in ampli?er, Rev. Sci. Instrum., 66(6):3697–3702
[15] Maximiliano Osvaldo Sonnaillon, Fabian Jose Bonetto. A low-cost high performance digital signal processor-based lock-in amplifier capable of measuring multiple frequency sweeps simultaneously. Review of Scientific Instruments, 2005, 76: 024703
[16] Javier Gaspar, Suei Feng Chen, Alejandro Gordillo, etal. Digital lock in amplifier: study, design and development with a digital signal processor, Microprocessors and Microsystems, 2004, 28:157-162
[17] R. Alonso, F. villuendas, J. Borja. Low-cost digital lock-in module with external reference for coating glass transmission/reflection spectrophotometer. Meas. Sci. Technol, 2003, 14: 551-557
[18] Adrian A. Dorrington, Rainer Kunnemeyer. A simple microcontroller based digital lock-in amplifier for the detection of low level optical signals, Proceedings of the First IEEE, International Workshop on Electronic Design, Test and Applications, 2002
[19] Dieter Braun, Albert Libchaber. Computer-based photon-counting lock-in for phase detection at the shot-noise limit. Optics letters, 2002, 27(16):1418-1420
[20] Steven J. Lascos, Daniel T. Cassidy. Multichannel digital phase sensitive detection using a field programmable gate array development platform. Rev. Sci. Instrum. 2008, 79, 074702
[21] A. Restelli, R. Abbiati, A. Geraci. Digital Field Programmable Gate Array-based Lock-in Amplifier for High-performance Photon Counting Applications ,Rev. Sci. Instrum. 2005, 76, 093112
[22] James M. Masciotti, J. M. lasker, A. H. hielscher. Digital Lock-in Algorithm for biomedical spectroscopy and Imaging instruments with multiple modulated souces. Proceedings of the 28th IEEE, EMBS Annual international conference. 2006
[23] James M. Masciotti, Joseph M. Lasker, Andreas H. Hielscher, Digital Lock-In Detection for Discriminating Multiple Modulation Frequencies With High Accuracy and Computational Efficiency, IEEE Transactions on Instrumentation and Measurement, 2008, 57(1):182-189
[24] Joseph M. Lasker, James M. Masciotti, Yang Li, etal. Dynamic Optical Tomographic Imager with Optimized Digital Lock-In Filtering. Proc. of SPIE-OSA Biomedical Optics, 2007, 6629, 662903-1
[25] Maria Angela Franceschini. Danny K. Joseph, Theodore J. Huppert, Diffuse optical imaging of the whole head, Journal of Biomedical Optics, 2006, 11(5), 054007
[26]李静,基于FPGA的数字锁相放大器设计,[硕士学位论文],武汉,桂林工学院,2008
[27] Maximiliano O.sonnaillon, Raul Urteaga, Fabian Jose Bonetto. Implementation of a high-frequency digital lock-in amplifier. Proceedings of IEEE, CCECE/CCGEI, 2005
[28]王超,徐明,徐真真等,用于混频信号的双通道数字锁相放大器,电子器件,2007,30(4):1321-1324
[29] Danny K. Joseph, Theodore J. Huppert, Maria Angela Franceschini, Diffuse optical tomography system to image brain activation with improved spatial resolution and validation with functional magnetic resonance imaging, APPLIED OPTICS, 2006, 45(31): 8142-8151
[30]北京创毅视讯科技有限公司,一种频率合成器及频率合成方法,中国专利,200810102330,2008-8-13
[31]黄智伟,锁相环与频率合成器电路设计,西安:西安电子科技大学出版社,2008,1-23
[32] Analog Devices, Inc., A Technical Tutorial on Digital Signal Synthesis, Analog Devices, Inc. 1999
[33]盛骤,谢式千,潘承毅,概率论与数理统计,北京:高等教育出版社,2001
[34]阮平巧,组织光学测量中光子计数技术研究——基于CPLD的多通道光子计数器设计,[硕士学位论文],天津,天津大学,2007
[35] Future Technology Device International Ltd, FT_000052, FT245R USB FIFO IC Datasheet Version2.02, 2008
[36] Analog Device, Inc. AD9763/AD9765/AD9767 Datasheet
[37] EDA先锋工作室,吴继华,王诚,Altera FPGA/CPLD设计(高级篇),北京:人民邮电出版社,2005,19-21
[38]崔文,叶信峰,基于查找表和CORDIC算法的数控振荡器的设计,电子科技,2006,7:23-25
[39]张欣,扩频通信数字基带信号处理算法及其VLSI实现,北京:科学出版社,2004,40-100
[40] Neil Eklund. CORDIC: Elementary Function Computation Using Recursive Sequences. Electronic, Proceedings of the Eleventh Annual International Conference on Technology in Collegiate Mathematics, 1998
[41]雷元武,周杰,葛颖增,并行CORDIC算法的研究及FPGA实现,计算机工程与科学,2008,30(8):75-78
[42] Ray Andraka. A survey of CORDIC algorithms for FPGA based computers, Proceedings of the ACM/SIGDA sixth international symposium on Field programmable gate arrays,. 1998
[43]李全,陈石平,付佃华,基于CORDIC算法的32位浮点三角超越函数之正余弦函数的FPGA实现,电子产品世界,2006(10):150-151
[44]孙健,汪彦彦,基于CORDIC算法的高速高精度NCO的FPGA设计,火控雷达技术,2007,12(30):68-72
[45]李刚,张丽君,林凌,一种新型数字锁相放大器的设计及其优化算法,天津大学学报,2008,41(4):429-432
[46]朱虹,林君,吴衷杰,近红外光谱仪中的数字锁相技术研究,仪器仪表学报,2006,27(10):1258-1261
[47]陈跃,田书林,刘科,非理想DDS输出信号分析及滤波处理,测试测量技术,2008,9:4-7
[48] Daniele Contini, Fabrizio Martelli, Giovanni Zaccanti, Photon migration through a turbid slab described by a model based on diffusion approximation, I. Theory, Applied Optics, 1997, 36(19): 4587-4594
[49]谢琼,李建平,高晓光等,动态多频数字锁相算法及其应用,电子与信息学报,2009,31(8):2006-2009