【作者】 张泰石；

【导师】 李刚；

【作者基本信息】 天津大学 ， 精密仪器及机械， 2007， 博士

【摘要】 光学相干层析成像技术(Optical Coherence Tomography,简称OCT)作为一种全新的光学断层成像技术,以其无辐射、非侵入、高分辨率及高探测灵敏度等特点,在临床医学领域具有巨大的发展潜力。频域OCT(Spectral Domain OCT,简称SDOCT)无需样品深度扫描,就能实现高速实时成像的特点,引起了许多研究者的关注。使频域OCT成为一种快速、实时成像的医疗诊断系统,其关键是提高系统的轴向分辨率和信噪比。因此,本文主要针对这两个方面,进行了频域OCT高速成像若干关键技术的研究。本文完成的主要工作为:1.为了分析频域OCT成像机理及图像结构,还有找出对信噪比与轴向分辨率影响的因子,根据一阶Born近似傅里叶衍射定理,构建了频域OCT系统的数学模型,推出了频域OCT图像函数。频域OCT图像函数中g函数决定样品每层析面的真实图像及寄生图像的位置与其轴向分辨率,它的系数决定图像的灰度。2.干涉光谱的傅里叶逆变换得到了样品所有层析面的深度信息,为了标定深度方向上的图像坐标,提出了一种频域OCT图像的深度坐标标定方法。3.为了解决CCD对不同波长的响应不一样,并且图像重建进行的傅里叶逆变换所需要的数据与CCD检测的数据所依赖的变量不同的问题,提出了CCD响应度补偿法和波长数据-波数数据转换线性补偿法,该方法将信噪比约提高了30%,改善了OCT图像质量。4.为了解决样品每层析面的图像灰度随深度递减的问题,根据频域OCT图像函数,提出了图像灰度补偿法。该方法通过补偿样品每层析面的入射光功率与背向功率散射率,来得到样品每层析面图像的真实灰度,提高了OCT图像质量。5.为了消除频域OCT图像中的寄生图像信息,提出了一种频域OCT光学相移器标定方法——差分光谱法。该方法是一种直接相位测量法,标定精度提高约6%。实验结果表明该方法能够将频域OCT图像的信噪比提高约10%。6.为了提高频域OCT系统的轴向分辨率和信噪比,根据频域OCT图像函数,提出了光源的相干长度及频域OCT图像的轴向分辨率测量方法,此基础上,建立了一种基于子光谱分析的白光频域OCT系统。该系统通过选择所需的白光光源及其接收频段,既能保证最大探测深度和高轴向分辨率,又能提高信噪比。以上工作为频域OCT系统的高速实时成像和实用化应用奠定了一定的基础。工作中的主要创新之处为:1.提出了频域OCT图像函数。利用该函数分析了频域OCT成像机理及图像结构,找出了对信噪比与图像轴向分辨率影响的因子,提出了图像灰度补偿法与频域OCT图像的轴向分辨率测量方法。2.提出了CCD响应补偿法和波长数据-波数据转换线性补偿法。该方法能够将OCT图像的信噪比提高约30%,明显改善了图像质量。3.提出了图像灰度补偿法。该方法解决了样品每层析面的图像灰度随深度递减的问题,提高了频域OCT的图像质量。4.提出了一种频域OCT光学相移器标定法——差分光谱法。该方法将标定精度提高约6%,将OCT图像的信噪比提高约10%。5.提出了光源的相干长度和频域OCT图像的轴向分辨率测量方法,此基础上,建立了一种基于子光谱分析的白光频域OCT系统。该系统通过选择所需的白光光源及其接收频段,既能保证最大探测深度和高轴向分辨率,又能提高信噪比。更多还原

【Abstract】 Optical coherence tomography (OCT) is a novel optical tomography technique which has many advantages, such as non-contact and non-invasion detection, high resolution, high sensitivity for the imaging of living biological tissue. It has been possessed of great development potential application in clinical medicine. Many researchers focus their attention on Spectral Domain OCT(SDOCT),which has the advantage that no moving parts are required to obtain axial scans, and gives the potential to high speed imaging.In order to make SDOCT become a kind of high-speed imaging, practical medical diagnosis system, the key techniques are enhancing longitudinal resolution and SNR. The study of high-speed imaging of SDOCT system is carried out on both these sides.The mainly completed work is:1. In order to make a detailed analysis of the imaging-mechanism of SDOCT and find out the influential factors on SNR and longitudinal resolution, the mathematical model of SDOCT system is constructed based on first order Born approximation. Then the imaging function (IF) is deduced. The depth position and the longitudinal resolution of true images and parasitic images of each layer along the depth of the sample depend on the function g in IF, and the image grey levels are governed by its coefficients.2. The inverse Fourier Transformation of interference spectrum at one time reaches the depth information of each layer of the sample. Then a method of depth-coordinate calibration of SDOCT image is introduced.3. In order to solve the problem of wavelength-depended response of CCD, and the difference between data used in inverse Fourier Transformation and those sampled by CCD, methods of CCD response compensation and an algorithm of linear interpolation are suggested. Results show that SNR is increased by 30%, the OCT image quality is greatly improved.4. In order to solve the problem of attenuating image gray level along along depth direction,according to the IF of SDOCT, the method for image gray level compensation is suggested. Through compensating the incident power and scattering coefficient of back-scattered light in each layer of the samlpe, the real gray level of the image is obtained by then. The experimental results show that OCT image quality is greatly improved.5. In order to remove the parasitic part of SDOCT image, a calibration method for SDOCT optical phase shifter--difference spectrum method is developed. It is a direct phase measurement with precision increase of 6%. The experimental results show that SNR is increased by 10%.6. In order to enhance the longitudinal resolution and SNR of SDOCT, a method of measuring coherence length of light source and longitudinal resolution is practiced here. A white-light source SDOCT based on partial spectrum analysis is developed and introduced. Proper white light source and band width have been selected. It ensures to acquire high maximum detecting depth, axial resolution and SNR.The main innovative point can be summarized as follows:1. IF of SDOCT is conducted for the first time. Make a detailed analysis of the imaging-mechanism of SDOCT, find out the influential factors of SNR and axial resolution and bring out the method of gray level compensation and the measurement method of axial resolution of SDOCT image.2. A noble method of CCD response compensation and algorithm of linear interpolation are put forward in this thesis. SNR is increased by 30%, the OCT image quality is greatly improved.3. A method for image gray level compensation is proposed for the first time in this thesis. The method solves the problem of attenuating image gray level along axial coordiate, and greatly improves OCT image quality.4. A calibration method for for SDOCT optical phase shifter--difference spectrum method is brought forward for the first time in this thesis. The precision of calibration is increased by 6%, and SNR is increased by10%.5. A method of measuring coherence length of light source and axial resolution is realized for the first time in this thesis. A white-light source SDOCT based on partial spectrum analysis is developed and introduced. Proper white light source and band width have been selected. It ensures to acquire high maximum detecting depth, axial resolution and SNR.更多还原