数字超声成像关键技术的优化设计与实现
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摘要
B超诊断仪在医疗诊断设备中有着非常重要的地位,研制全数字化的B超诊断仪已成为当前技术发展的主流。实现全数字化B超诊断仪的关键是数字扫描超声成像技术(DSC),它直接决定了B超诊断仪的各项性能指标。在数字化超声成像技术领域,我国与国外先进水平尚有较大的差距,因此对数字超声成像关键技术开展研究具有重要的意义。
设计了以FPGA(EP2C35F484C8)为主控器,以发射放大、接收放大、模数转换、USB2.0接口和其它电路为辅的数字B超采集卡硬件电路;对基于FPGA的超声成像数字化方法进行了研究,重点对数字超声成像的核心部分:波束形成、动态滤波、坐标变换、时间增益补偿进行了优化设计,且对它们的设计结果进行了仿真和分析。
在波束形成方面,细化延时基准时钟,提高了延时叠加的精度;采用分段动态聚焦,提高了成像的分辨率和对比度;采用窗函数实现的幅度变迹,有效的抑制了旁瓣的幅度、提高了图像的对比度;通过在不同聚焦深度采用不同的孔径,达到了减少最大延时量、增加近场区的焦区深度和减少时间增益的控制范围的目的。在动态滤波方面,针对回波信号的频率随探测深度增加而变小的状况,通过改变FIR滤波器系数的方法和采用分布式算法的设计方法,达到了高速、有效的滤除杂波的功能。在坐标变换方面,通过采用双时钟控制坐标旋转数字计算机算法和定时输出的方法,使坐标变换达到了实时性好、速度快、精度高、节约资源的效果。在时间增益补偿方面,采用了在B超采集卡上使用定曲线补偿与在上位机上使用可变、可控数字增益放大相结合的二级补偿方法,实现了高增益、可控性好、实时性好的时间增益补偿。
以本文设计的数字B超采集卡硬件和超声成像软件系统为核心的数字B超诊断仪,在医院试用中表现稳定,成像效果较好,图像内容丰富,证明本文的总体设计正确,采用的优化方法有效。
B-mode ultrasonic apparatus is playing a very important role in the modern clinic. And now, research and manufacturing full-digital B-mode ultrasonic apparatus is becoming the inevitable trend. The key to realize full-digital is DSC, which directly determines the parameters of the apparatus. At present, the level of our country has great disparities compared to the international advanced technology in the field of digital medical imaging technology. Therefore, the research of the digital B-mode ultrasonic imaging has great significance.
A high reliability and signal noise ratio (SNR) digital B-mode ultrasonic gather card based on FPGA (EP2C35F484C8) was designed in this paper, combined with USB2.0 interface and other circuits. The methods of digital ultrasonic imaging were well researched based on FPGA, focusing on the optimized design and implementation of the key technology of the ultrasonic imaging, such as beam forming, dynamic filter, coordinate transformation and time gain compensation (TGC), and the results of their programs were simulated and verified.
In the design of beam forming, the accuracy of delay superposition was improved by refining delay reference clock, the imaging resolution and contrast were improved by segmented dynamic focusing, the side lobe peak was suppressed effectively and the imaging contrast was improved by variable magnitude using window function, and the maximum time delay and the TGC range were decreased, as the same time the focus depth of the near-field was increased by changing the aperture with different focusing depth. During the design of filter, the frequency of the echo signal becomes smaller when the depth of the focus increased, so an effective dynamic filter with changing coefficients was designed and realized by the distributed arithmetic (DA). In the realization of coordinate transformation, the design with better real-time, faster response, higher precision and less source was realized by using dual-clock control of Coordinate Rotation Digital Computer (CORDIC) algorithm and timing output. In the design of TGC, the method of fixed curve compensation on the full-digital B-mode ultrasonic gather card and veriable, controllable compensation on the host computer was designed for TGC, which led to a high gain, easy control and good real-time compensation effect.
During the trial period in hospital, the full-digital B-mode ultrasonic apparatus, which is mainly composed by the hardware of full-digital B-mode ultrasonic gather card and the soft system of the digital ultrasonic image, has showed its superiorities, stability, well imaging effect, rich image content. Therefore, the design of the full-digital B-mode ultrasonic gather card in this paper is correct. The optimized methods of the imaging, which were used in this full-digital B-mode ultrasonic apparatus, are efficient.
设计了以FPGA(EP2C35F484C8)为主控器,以发射放大、接收放大、模数转换、USB2.0接口和其它电路为辅的数字B超采集卡硬件电路;对基于FPGA的超声成像数字化方法进行了研究,重点对数字超声成像的核心部分:波束形成、动态滤波、坐标变换、时间增益补偿进行了优化设计,且对它们的设计结果进行了仿真和分析。
在波束形成方面,细化延时基准时钟,提高了延时叠加的精度;采用分段动态聚焦,提高了成像的分辨率和对比度;采用窗函数实现的幅度变迹,有效的抑制了旁瓣的幅度、提高了图像的对比度;通过在不同聚焦深度采用不同的孔径,达到了减少最大延时量、增加近场区的焦区深度和减少时间增益的控制范围的目的。在动态滤波方面,针对回波信号的频率随探测深度增加而变小的状况,通过改变FIR滤波器系数的方法和采用分布式算法的设计方法,达到了高速、有效的滤除杂波的功能。在坐标变换方面,通过采用双时钟控制坐标旋转数字计算机算法和定时输出的方法,使坐标变换达到了实时性好、速度快、精度高、节约资源的效果。在时间增益补偿方面,采用了在B超采集卡上使用定曲线补偿与在上位机上使用可变、可控数字增益放大相结合的二级补偿方法,实现了高增益、可控性好、实时性好的时间增益补偿。
以本文设计的数字B超采集卡硬件和超声成像软件系统为核心的数字B超诊断仪,在医院试用中表现稳定,成像效果较好,图像内容丰富,证明本文的总体设计正确,采用的优化方法有效。
B-mode ultrasonic apparatus is playing a very important role in the modern clinic. And now, research and manufacturing full-digital B-mode ultrasonic apparatus is becoming the inevitable trend. The key to realize full-digital is DSC, which directly determines the parameters of the apparatus. At present, the level of our country has great disparities compared to the international advanced technology in the field of digital medical imaging technology. Therefore, the research of the digital B-mode ultrasonic imaging has great significance.
A high reliability and signal noise ratio (SNR) digital B-mode ultrasonic gather card based on FPGA (EP2C35F484C8) was designed in this paper, combined with USB2.0 interface and other circuits. The methods of digital ultrasonic imaging were well researched based on FPGA, focusing on the optimized design and implementation of the key technology of the ultrasonic imaging, such as beam forming, dynamic filter, coordinate transformation and time gain compensation (TGC), and the results of their programs were simulated and verified.
In the design of beam forming, the accuracy of delay superposition was improved by refining delay reference clock, the imaging resolution and contrast were improved by segmented dynamic focusing, the side lobe peak was suppressed effectively and the imaging contrast was improved by variable magnitude using window function, and the maximum time delay and the TGC range were decreased, as the same time the focus depth of the near-field was increased by changing the aperture with different focusing depth. During the design of filter, the frequency of the echo signal becomes smaller when the depth of the focus increased, so an effective dynamic filter with changing coefficients was designed and realized by the distributed arithmetic (DA). In the realization of coordinate transformation, the design with better real-time, faster response, higher precision and less source was realized by using dual-clock control of Coordinate Rotation Digital Computer (CORDIC) algorithm and timing output. In the design of TGC, the method of fixed curve compensation on the full-digital B-mode ultrasonic gather card and veriable, controllable compensation on the host computer was designed for TGC, which led to a high gain, easy control and good real-time compensation effect.
During the trial period in hospital, the full-digital B-mode ultrasonic apparatus, which is mainly composed by the hardware of full-digital B-mode ultrasonic gather card and the soft system of the digital ultrasonic image, has showed its superiorities, stability, well imaging effect, rich image content. Therefore, the design of the full-digital B-mode ultrasonic gather card in this paper is correct. The optimized methods of the imaging, which were used in this full-digital B-mode ultrasonic apparatus, are efficient.
引文
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[33]刘波.精通Verilog HDL语言编程.北京:电子工业出版社,2007,5:476-491
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[36]卢智远,丁华,孙文权,石频频,王文芳.CORDIC算法在B超数字扫描变换器中的应用.中国生物工程报,2005,12,24(6):80-83
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[41]彭龙飞,李辉,赵军旗,李俊.一种高效实现B超坐标变换的方法.声学技术,2009,28(4):260-263
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[2]中电网.新医改8500亿蛋糕的角逐元器件因势得利. http://finance.qq.com/a/20090506/004469.htm,2009,5,6
[3]上海医疗器械信息网.2012年中国超声诊断设备市场将达到6.2亿美元. http://www.39kf.com/medicine/news/yiliaoqixie/2008-11-25-531909.shtml,2008,11,25
[4]陈智文,张旦松.B型超诊断仪原理调试与维修.湖北:湖北科学技术出版社,2000,8,6-21
[5]彭虎.超声成像算法导论.安徽:中国科学技术大学出版社,2008,10:2-122
[6] Hu Peng. A New Model of Ultrasonic Imaging System Based on Plane Wave Transmission and Angular Spectrum Propagation Principle. Proceedings of the 2007 IEEE International Conference on Integration Technology March 20-24, 2007, 307-310
[7]周润景,袁伟亭.Cadence高速电路板设计与仿真.北京:电子工业出版社,2006.9:35-714
[8]黄豪佑,董辉,卢建刚,肖潇.Cadence高速PCB设计与仿真分析.北京:北京航空航天大学出版社,2006,7:1-221
[9] Altera Corporation. Cyclone FPGA Device Handbook. Altera Technology Inc, 2004, 6
[10] Paul Chen, Mike Butts, Brad Budlong Ambric. Medical Ultrasound Digital Beamforming on a Massively Parallel Processor Array Platform. Progress in Biomedical Optics and Imaging Proceedings of SPIE, v 6920, 2008, Medical Imaging 2008: Ultrasonic Imaging and Signal Processing.2008: 6920-6928
[11] Ming Li, Hao Zhou, Shijie Wen, Xiaodong Chen, Daoyin YUDaoyin Yu. Design of embedded endoscopic ultrasonic imaging system. 2008 International Conference on Optical Instruments and Technology: Optical Systems and Optoelectronic Instruments. 2008: 7156-7165
[12] Cypress Semiconductor. CY7C68013 EZ-USB FX2 USB Microcontroller High-Speed USB Peripheral Controller. Cypress Technology Inc, 2002,6: 17-21
[13]钱峰.EZ-USB FX2单片机原理、编程及应用.北京:北京航空航天大学出版社,2006,22-24,94-97
[14] Altera Corporation. MAX II Device Handbook. Altera Technology Inc, 2005, 6
[15] Roy T, Meenna D, Prakasam L G M. FPGA based Digital Beam Forming for Radars. Radars conference, 2009 IEEE, 2009, 5: 1-5
[16] PaiChi Li, JingJung Huang. Efficient dynamic focus control for three-dimensional imaging using two-dimensional arrays. Ultrasonics, Ferroelectrics and Frequency Control, IEEE Transactions on, 2002, 49(3): 1191-1202
[17] Minardo A, Cusano A, BerniniR, Zeni L, Giordano M. Response of fiber Bragg gratings to longitudinal ultrasonic waves. Ultrasonics, Ferroelectrics and Frequency Control, IEEE Transactions on, 2005, 52(2), 304-312
[18]戴文战,蒋明峰,王秀萍.数字信号处理.浙江:浙江教育出版社,2008,2:168-178
[19]夏宇闻.Verilog数字系统设计教程.北京:北京航空航天出版社,2007,1:45-70
[20] ALTERA Corporation. QuartusII Introduction for Verilog Users. Altera Technology Inc, 2005, 6
[21]王静,鱼云岐.基于FPGA的FIR数字滤波器设计与仿真.国外电子元器件,2008,11: 90-92
[22]胡广书.现代信号处理教程[M].北京:清华大学出版社,2007,12:52-60
[23] Li Xiaoying, Liu Dong C. Ultrasound image enhancement using dynamic filtering. Proceedings of the 4th International Conference on Image and Graphics, ICIG 2007. 2007:106-109
[24]胡广书.数字信号处理.北京:清华大学出版社,2007,4:218-385
[25] Xiaohong Huang, Jinsheng Sun. Zhaohua Wang, FIR filter design based on all phase symmetric frequency sampling method. 2006 1st IEEE Conference on Industrial Electronics and Applications, 2006,
[26] Suyama Kenji, Takada Ken'ichi, Hirabayashi Ryuichi, Iwakura Hiroshi. Complex Chebyshev approximation for FIR filters using linear semi-infinite programming method. Electronics and Communications in Japan, Part III: Fundamental Electronic Science, 2004, 3, 87(3): 49-57
[27] Yunlong Wang. A new form of frequency response expression of FIR digital filters for directly obtaining window functions. 2009 International Conference on Signal Processing Systems, ICSPS 2009, 2009: 313-317
[28] Mutapcic, Almir Kim, Seung-Jean, Boyd Stephen. Robust chebyshev FIR equalization. IEEE GLOBECOM 2007 - 2007 IEEE Global Telecommunications Conference. 2007:3074-3079
[29]薛年喜.MATLAB在数字信号处理中的应用.北京:清华大学出版社,2008,1:256-264
[30]丁玉美,高西全.数字信号处理.西安:西安电子科技大学出版社.2005,5:195-225
[31] Uwe Meyer-Baese.Digital Signal Processing With Field Programmable Gate Arrays=数字信号处理的FPGA实现(刘凌,胡永生译).北京:清华大学出版社,2003,1:49-98
[32] Eshtawie Mohamed Al Mahdi, Othman Masuri. On-line DA-LUT architecture for high-speed high-order digital FIR filters. 2006 IEEE Singapore International Conference on Communication Systems, 2006
[33]刘波.精通Verilog HDL语言编程.北京:电子工业出版社,2007,5:476-491
[34]雷元武,周杰,葛颖增,窦勇.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
[35] Abche Antoine B, Maalouf Aldo, Ayoubi Rqfic, Karam Elie, Alameddine A.M. An FPGA implementation of a high resolution phase shift beamformer. ICSPC 2007 Proceedings - 2007 IEEE International Conference on Signal Processing and Communications,2007: 1319-1322
[36]卢智远,丁华,孙文权,石频频,王文芳.CORDIC算法在B超数字扫描变换器中的应用.中国生物工程报,2005,12,24(6):80-83
[37]姚博,张笑微,刘薇.一种并行CORDIC算法在B超扫描转换器中的应用.自动测量与控制,2008,27(4):75-82
[38]李杰明,郑学仁.基于CORDIC算法的数字图像旋转实现.电子技术应用,2009,6:72-74
[39] Wu C-S, Wu A.-Y. Modified vector rotational CORDIC (MVR-CORDIC) algorithm and architecture. IEEE Transactions on Circuits and Systems II: Analog and Digital Signal Processing, 2001,6,48(6):548-561
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