Study On Several Key Technologies Of High-speed Imaging Spectral Domain Optical Coherence Tomography

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.