摘要
OCT(Optical Coherence Tomography,光学相干层析技术)是一种基于白光干涉的光学成像技术,可以对生物组织内部微观结构进行横断面层析成像。OCT技术以其无损伤、非介入、分辨率高等优点,在科学研究和生物医学等领域具有广泛的应用前景。
本文针对OCT中图像分辨率和清晰成像范围相互矛盾的缺点,深入分析光谱OCT系统的扫描模型和高斯光束自身的影响,借鉴合成孔径雷达(Synthetic Aperture Radar, SAR)的数据处理方法,在课题组近似波数域算法研究的基础上,利用合成孔径算法实现了图像重构,获得了分辨率一致的图像。
论文主要完成了以下工作:
1.详细分析了光谱OCT的基本成像原理和系统扫描模型,借鉴合成孔径雷达的数据处理方法,提出了用于横向扫描和旋转扫描的合成孔径算法来实现图像重构,提高了图像的分辨率。
2.根据光谱OCT系统的横向扫描结构,研究了OCT的衍射物理模型,分析了高斯光束的宽度和波前对图像质量的影响,在此基础上推导出散射的前向模型和图像重构步骤,得到参考光、样品光以及干涉光谱数据的表达式。
3.比较了SAR的距离多普勒(Range Doppler, RD)算法和波数域算法,提出了改进的RD算法,将光谱数据的二维处理分解成两个一维处理:利用波数域的变量替换进行横向距离徙动校正,利用匹配滤波器进行纵向压缩,分别提高了图像的横向和纵向分辨率。为了将OCT技术应用于内窥成像,提出了基于旋转扫描的合成孔径算法,改善了图像质量。
4.针对影响图像质量的主要参数,利用MATLAB进行了横向扫描和旋转扫描的仿真模拟,并搭建光纤型光谱OCT系统,选取新鲜猪肝作为样品进行实验。实验结果与仿真结论相一致,由此验证了算法的正确性。
Optical coherence tomography (OCT) is a latest optical imaging technology based on the white-light interferometry, which can acquire cross image for interior microscopic view of biological system. OCT has many advantages such as non-traumatic detection and high resolution, thus it possesses a wide prospect in scientific research and clinic application.
In this paper, the scanning model of spectral domain optical coherence tomography (SDOCT) system and effects produced by Gaussian beam itself are discussed. Referring to the data processing methods of synthetic aperture radar (SAR) and the approximate wavenumber domain algorithm which our group has researched, we propose the synthetic aperture algorithm to abate the compromise between resolutions and depth of focus in SDOCT, and achieve image reconstruction with spatially invariant resolution.
The researches mainly focus on the following aspects:
1. The paper analyzes the fundamental principle and scanning model of SDOCT in detail. Referring to the data processing methods of SAR, the synthetic aperture algorithms for transverse scanning and rotary scanning respectively are proposed to implement image reconstruction with high resolution.
2. According to the structure of transverse scanning, the physical model of diffraction is presented, along with the finite beam width and the shape of wavefronts produced by Gaussian beam taken into account. On the basis of scattering forward model, the equations of reference light, sample light and interference spectrum are deduced, as well as the procedure of image reconstruction.
3. This paper compares the range Doppler (RD) algorithm and wavenumber domain algorithm. The improved RD algorithm is applied to improve the resolutions in the axial and lateral directions, where the two-dimensional processing of the spectrum data is decomposed into two one-dimensional processings of variable exchange and matched filter. The synthetic aperture algorithm is demonstrated to improve the image quality in the rotary scanning, which makes it possible that OCT can be used in the endoscopic system.
4. The simulations are implemented in terms of the key parameters that influence the image quality. Properly selecting optical devices, the fibre-based interference system is built, and images of fresh pig liver are gained, which effectively shows that the algorithm will be competent for imaging.
引文
[1] D. Huang, E. A. Swanson, J. G. Fujimoto, et al., Optical coherence tomography, Science, 1991, 254(5053): 1178~1181
[2] J. M.Schmitt, Optical Coherence Tomography (OCT): A Review, IEEE Journal of Selected Topics in Quantum Electronics, 1999, 5(4): 1205~1215
[3]冯若,超声诊断设备原理与设计,北京:中国医学科技出版社,1993
[4]赵喜平,核磁共振成像,北京:科学出版社,2004
[5]吉永星,俎栋林,包尚联,CT机和核磁共振成像(MRI)机之间的比较研究,CT理论与应用研究,2000,9(3): 1~8
[6] R. C. Youngquist, S. Carr, D. E. N. Davies, et al., Optical coherence-domain reflectometry: a new optical evaluation technique, Optics Letters, 1987, 12(3): 158~160
[7] K. Takada, I. Yokohama, K. Chida, et al., New measurement system for fault location in optical wavegukde devices based on an interfereometric technique, App. Lett., 1987, 26(3): 1603~1606
[8] H. H. Gilgen, R. P. Salsthe, W. Hodel, Submillimeter optical reflectometry, IEEE J Lightwave Technol, 1989, 7(3): 1225~1233
[9] A. F. Fercher, K. Mengednot, W. Werner, Eye-length measurement by interferometry with partially coherence light, Optics Letters, 1988, 13(3): 186~188
[10] W. Jung, D. T. McCoormick, Y. C. Ahn, et al., In vivo three-dimensional spectral domain endoscopic optical coherence tomography using a microelectromechanical system mirror, Optics Letters, 2007, 32(22): 3239~3241
[11] D. C. Adler, Chao Zhou, T. H. Tsai, et al., Three-dimensional endomicroscopy of the human colon using optical coherence tomography, Optics Express, 2009, 17(2): 784~796
[12] Xiaojing Mu, Winston Sun, Hanhua Feng, et al., MEMS micromirror integrated endoscopic probe for optical coherence tomography bioimaging, Sensors and Actuators A, 2011, 168: 202~212
[13]李乔,光谱OCT内窥镜成像系统的研究:[博士学位论文],天津:天津大学,2010
[14]高长磊,嵌入式光谱OCT内窥成像系统的研究:[硕士学位论文],天津:天津大学,2009
[15]卢萍,新型全光纤OCT实验系统的控制和数据采集:[硕士学位论文],天津:天津大学,2007
[16]顾宁,偏振OCT信号提取与处理:[硕士学位论文],天津:天津大学,2009
[17] Shuichi Makita, Yoshiaki Yasuno, Takashi Endo, et al.,Polarization contrast imaging of biological tissues by polarization-sensitive Fourier-domain optical coherence tomography,Applied Optics, 2006, 45(6): 1142~1147
[18]申小丽,黄丽娜,光学相干断层成像技术的临床应用新进展,国际眼科杂志,2000, 9(12): 2395~2398
[19] A. M. Sergeev, V. M. Gelikonov, G. V. Gelikonov, et al., In vivo optical coherence tomography of human skin microstructure, Proc. SPIE, 1994, 2328: 144~150
[20] S. Yazdanfar, M. D. Kulkarni, J. A. Lzatt, High resolution imaging of in vivo cardiac dynamics using color Doppler optical coherence tomography, Optics Express, 1997, 1(13): 424~431
[21] B. W. Colston, L. B. DaSilva , M. J. Everett, Dental OCT, Optics Express, 1998, 3(6): 230~238
[22] Yueli Chen, Linda Otis, Daqing Piao, et al., Characterization of dentin, enamel, and carious lesions by a polarization-sensitive optical coherence tomography system, Applied Optics, 2005, 44(11): 2041~2048
[23] G. J. Tearney, B. E. Bourma, S. A. Boppart, et al., In Vivo Endoscopic Optical Coherence Tomography, Science, 1997, 276: 2037~2039
[24]王治乐,周彦平,张伟等,合成孔径技术对比研究,哈尔滨工业大学学报,2004, 36(3): 384~387
[25]尤素萍,蔡本晓,吴跃丽等,合成孔径技术和光的衍射理论,中国现代教育装备,2010, 11: 82~84
[26]皮亦鸣,杨建宇,付毓生等,合成孔径雷达成像原理,成都:电子科技大学出版社,2007
[27] P. T. Gough, D. W. Hawkins, United framework for modern synthetic aperture imaging algorithm, 1997, John Wiley & Sons, Inc., 8: 343~358
[28]姜男,孙大军,田坦,合成孔径声纳中RD算法和? ?k成像算法的比较,2002, 14(2): 58~62
[29] T. S. Ralston, S. G. Adie, D. L. Marks, et al., Cross-validation of interferometric synthetic aperture microscopy and optical coherence tomography, Optics Letters, 2010, 35(10): 1683~1685
[30] T. S. Ralston, D. L. Marks, P. S. Carney, et al., Inverse scattering for optical coherence tomography, J. Opt. Soc. Am. A, 2006, 23: 1027~1037
[31] Lingfeng Yu, Bin Rao, Jun Zhang, et al., Improved transverse resolution in optical coherence tomography by digital focusing using two dimensional numerical diffraction method, Optics Express, 2007, 15(12): 7634~7641
[32] Yoshiaki Yasuno, Jun-ichiro Sugisaka, Yusuke Sando, et al., Non-iterative numerical method for laterally superresolving Fourier domain optical coherence tomography, Optics Express, 2006, 14(3): 1006~1020
[33]李乔,陈晓冬,雷湧，汪毅，郁道银，基于近似波数域算法的干涉合成孔径显微技术的研究,中国激光,2010,37(11): 2725~2729
[34] D. L. Marks, A. L. Oldenburg, J. J. Reynolds, et al., Study of an ultrahigh-numerical-aperture fiber continuum generation source for optical coherence tomography, Optics Letters, 2002, 27(22): 2010~2012
[35] B. W. Graf, S. G. Adie, S. A. Boppart, Correction of coherence gate curvature in high numerical aperture optical coherence imaging, Optics Letters, 2010, 35(18): 3120~3122
[36] T. S. Ralston, D. L. Marks, P. S. Carney, et al., Interferometric synthetic aperture microscopy, USA, 0140341 A1, 2007-06-10
[37] T. S. Ralston, D. L. Marks, P. S. Carney, et al., Interferometric synthetic aperture microscopy, Nature Physics, 2007, 5: 129~134
[38] B. J. Davis, D. L. Marks, T. S. Ralston, et al., Interferometric Synthetic Aperture Microscopy: Computed Imaging for Scanned Coherent Microscopy Boppart, Sensors, 2008, 8: 3903~3931
[39] M. Wojtkowski, V. Srinivasan, T. Ko, et al., Ultrahigh-resolution, high-speed, Fourier domain optical coherence tomography and methods for dispersion compensation, Optics Express, 2004, 12(11): 2404~2422
[40] I. G. Cumming, F. H. Wong, Digital Processing Of Synthetic Aperture Radar Data: Algorithms and Implementation, Artech House Inc, Massachusetts, 2004
[41] J. C. Curlander, R. N. Mcdonough, Synthetic Aperture Radar: Systems and Signal Processing, John Wiley & Sons, New York, 1991
[42]俞宽新,江铁良,赵启大,激光原理与激光技术,北京:北京工业大学出版社,2003
[43] B. J. Davis, S. C. Schlachter, D. L. Marks, et al., Nonparaxial vector-field modeling of optical coherence tomography and interferometric synthetic aperture microscopy, J. Opt. Soc. Am. A, 2007, 24(9): 2527~2542
[44] Hao-Chung Yang, Jiechen Yin, Changhong Hu, et al., A dual-modality probe utilizing intravascular ultrasound and ptical coherence tomography for intravascular imaging applications, 2010, 57(12): 2839~2843
[45] T. S. Ralston, D. L. Marks, P. S. Carney, et al., Inverse scattering for rotationally scanned optical coherence tomography, Opt. Soc. Am. A, 2006, 23(10): 2443~2439