为了提高频域OCT成像系统的性能, 提出一种复谱频域OCT成像方法。给出了系统结构及核心模块设计, 从理论上论证了系统的设计原理。提出一种复振幅干涉光谱重构算法, 并对该重构算法进行了理论分析。总结了该复谱频域OCT成像方法的实施步骤。利用复谱频域OCT的成像方法, 进行了仿真试验。理论分析和仿真试验结果表明, 利用该复谱频域OCT成像方法, 无须使用参考相位移动或调制装置, 所生成的被测样品OCT层析图, 清除了复共轭镜像和寄生像的影响, 能够反映被测样品的真实结构。

Spectral domain optical coherence tomography (SDOCT) is a noninvasive, cross-sectional imaging technique that measures depth resolved reflectance of tissue by Fourier transforming the spectral interferogram with the scanning of the reference avoided. Interferometric synthetic aperture microscopy (ISAM) is an optical microscopy computed-imaging technique for measuring the optical properties of biological tissues, which can overcome the compromise between depth of focus and transverse resolution. This paper describes the principle of SDOCT and ISAM, which multiplexes raw acquisitions to provide quantitatively meaningful data with reliable spatially invariant resolution at all depths. A mathematical model for a coherent microscope with a planar scanning geometry and spectral detection was described. The two-dimensional fast Fourier transform (FFT) of spectral data in the transverse directions was calculated. Then the nonuniform ISAM resampling and filtering was implemented to yield the scattering potential within the scalar model. Inverse FFT was used to obtain the ISAM reconstruction. One scatterer, multiple scatterers, and noisy simulations were implemented by use of ISAM to catch spatially invariant resolution. ISAM images were compared to those obtained using standard optical coherence tomography (OCT) methods. The high quality of the results validates the rationality of the founded model and that diffraction limited resolution can be achieved outside the focal plane.

针对频域光学相干层析(SD-OCT)系统特有硬件(线阵CCD及分光光栅)参数对成像质量造成的影响, 展开了对基于光纤的频域OCT系统中硬件参量的模拟和优化工作, 分析了分光计中CCD线列阵像素数及数字化深度、CCD安装偏差等因素对OCT成像质量的影响, 并对光谱像素图定位进行了修正。研究表明：纵向分辨率不受CCD线列阵像素数的影响, CCD线列阵像素数的增多将线性地增大最大测量深度; CCD数字化深度小于6bit将直接导致系统纵向分辨率的锐减; 线阵CCD偏离聚焦透镜焦面将导致点扩展函数的强度减弱、系统分辨率降低; 在较小角度内转动CCD, 将使纵向分辨率得到提高; 采用氖灯光谱进行像素图定位校正之后, 可以相应地提高系统分辨率。部分模拟结论得到实验验证。采用此模拟优化结果, 可根据OCT成像的具体要求对系统硬件参量进行优化选择。

在频谱光学相干析成像(频谱OCT)系统中普遍使用的CCD采样的数据是波长的函数。CCD对不同波长的信号具有不同的响应,而且图像重建进行的傅里叶逆变换所需要的数据是波数的函数,忽略这两个问题对频谱OCT成像质量的影响比较大。基于以上分析,提出了响应度补偿法和波长数据-波数数据转换线性补偿法,并对样品进行了实验验证。实验结果表明,该方法能够将OCT图像的信噪比(SNR)提高约30%,明显改善了图像质量。