| Optical coherence tomography (OCT) is a non-invasive, non-contact imaging modality with micrometer resolution, which uses coherent gating to obtain cross-sectional images of tissue microstructure. As the second generation of OCT technology, spectral domain OCT (SD-OCT) offers significant advantages in imaging speed, detection sensitivity and signal noise ratio (SNR) in contrast to time domain OCT. Therefore, it plays an important role in the field of ophthalmology and functional imaging. This dissertation is mainly focused on SD-OCT technology, the main work and innovations are summarized as following:1. The SD-OCT system at 835nm wavelength is developed, which is consisted of a fiber based Michelson interferometer and a line-scan CCD based high speed spectrometer. The spectral resolution of the spectrometer is about 0.0674nm, corresponding to an axial imaging range of 2.56mm. With the A-scan rate of 29 KHz, the axial resolution and maximum SNR of the system are 7.5μm and 115dB, respectively, which is capable for real time in vivo imaging of biomedical samples.2. A spectral calibration method for spectrometer is proposed, which is directly based on the SD-OCT system itself without the utilization of additional calibration source. With two measurements of interference spectra from two reference mirror position, the corresponding phase differences can be calculated after Hilbert transform and phase unwrapping. Then, with the wavelength value of specific CCD pixel, the wavelength distribution on CCD plane can be determined. Furthermore, this method is not sensitive to system unmatched dispersion.3. The relationship between system sensitivity fall-off and diffraction spot size is studied. According to the spot diagrams on CCD plane obtained by Zemax, system sensitivity fall-off with different spot size of typical spectral components is calculated. When the spot size of typical spectral components are comparable to the size of CCD pixel, improved depth dependent sensitivity fall-off can be achieved, and sensitivity drops by 16.1dB over 2mm imaging depth range.4. Non-uniform discrete Fourier transform (NDFT) is introduced into SD-OCT system for image reconstruction. The spectral data is considered as irregular sampling in wavenumber space, then the depth information can be reconstructed by NDFT directly without interpolation. Real time in vivo imaging of human finger confirms that compared with conventional DFT and interpolation method, reconstruction method based on NDFT indeed improves sensitivity fall-off especially at larger depth.5. A spatial sinusoidal phase modulation for the elimination of complex-conjugate artifact is proposed, where sinusoidal phase modulation of reference arm (M scan) and transverse scanning of sample arm (B scan) are performed simultaneously (sinusoidal B-M method). The complex interference spectra are reconstructed by harmonic analysis, its Fourier transform is free of mirror image and coherent noises. Compared with the linear B-M method, the proposed sinusoidal B-M method relaxes the requirements on the phase-shifting mechanical system and avoids sensitivity fall-off along the transverse direction. Double imaging depth range on shrimp with complex conjugate rejection ratio up to 45dB is achieved.6. Deconvolution method in SD-OCT system is proposed. In SD-OCT system, the spectral data acquired by CCD is the convolution of the original interference spectral signal and the transfer function of spectrometer, which results in the degradation of axial point spread function (PSF) along the depth direction. Herein, the axial modulation function of the PSF is retrieved firstly. Then after compensating the A-scan signal with the modulation function, devolution method is performed in spatial domain by Lucy-Richardson algorithm. In vivo OCT imaging of a fresh shrimp demonstrates that compared with original image, image enhancement is achieved by the proposed deconvolution method.
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