Research On Key Issues Of Micron Resolution Spectral Domain OCT Imaging System

Optical coherence tomography(OCT)is an emerging biomedical imaging technology characterized by its no damage operation,high sensitivity and high resolution.The short coherent length of broadband light source used in OCT allows high-resolution cross-section imaging of scatting tissue.In this thesis,the related important problems about the development of a micrometer resolution spectral domain OCT imaging system were studied.First of all,the imaging principle of a spectral domain OCT system is analyzed,the methods for calculating the parameters of system were summarized,and the main factors affecting the axial resolution of the system were analyzed.Second,a spectral domain optical coherence tomography system based on a Michelson interferometer was set up.The effects of the spectral calibration,dispersion compensation and spectral shaping on the axial resolution were investigated.A Doppler frequency shift method was then proposed to improve the accuracy of coherent spectrum conversion from wavelength domain to wavenumber domain.The iterative algorithm was used to calculate the optimal phase compensation amount to compensate the phase error caused by dispersion mismatch between the reference arm and the sample arm,and the ultra-wideband light source was shaped by using a Gaussian window function to suppress the sidelobe effect.Finally,the properties of the speckle noises present in the reconstructed OCT image was analyzed and an improved nonlocal filtering method was proposed to reduce the noise of the reconstructed OCT image.A variety of noise reduction algorithms were compared and four evaluation parameters such as structural similarity,peak signal-to-noise ratio,edge preservation index,and contrast-to-noise ratio were used to illustrate the image quality after noise reduction.These parameters demonstrate the superiority of non-local filtering in OCT image noise reduction.