The Key Technology Of Spectral Domain Optical Coherence Tomography

Spectral-domain Optical Coherence Tomography(SDOCT)is a new kind of optical imaging technology.Because of its high SNR and high speed,SDOCT has great potential for applications in the fields such as ophthalmology and functional imaging.However,there are still some problems including the decrease of the depth resolution with depth,the trade-off between the lateral resolution and focal depth and the decrease of the image qual-ity induced by the motion of the sample that limit the applications of SDOCT.This disser-tation is mainly focused on these problems and the methods were proposed to solve these problems,and the main work in this thesis includes following:1.A 3-D full range SDOCT system with a center wavelength of 840 nm was designed and built.The parameters that describe the pergormance of SDOCT were analyzed in detail.The theoretical axial resolution is about 6.2 ?m with the lateral resolution of 2.1 ?m and imaging depth of 4.2 mm.Acctually the axial resolution measured in experiment is about 6.7 ?m with the imaging depth of 4.4 mm and the resolution target shows that the lateral resolution of our system is about 2.5 pm.The SNR of the system is 105 dB.Finally the cross-sectional images and 3-D images of tissue were presented to demonstrate the capa-bility of the system.2.To overcome the decrease of the axial resolution with depth,a reconstruction me-thod was proposed based on the detected matrix,in which the mirror was used as a sample in the sample arm,and the detected matrix was obtained by scanning the reference mirror.With the help of this matrix the interference signal is reconstructed with the capability of maintaining the axial resolution over the whole imaging depth.Compared with other tech-niques,No external calibration instruments such as standard light source were needed.The results obtained with our method were compared with that of other methods.The experi-ment results showed that the axial resolution obtained by our method is about 9 ?m when the imaging depth is 1 mm and the axial resolution at the same depth obtained by direct FFT and by resampling are 130 ?m and 38 ?m,respectively.Note that even though the axial resolution can be improved by resampling the interference signal,the axial resolution obtained by detected matrix is 4 times higher than that obtained by resampling the interfe-rence signal.3.To solve the problem of decreae of the lateral resolution with depth,a Fresnel lens based SDOCT system was proposed in which the Fresnel lens was used in the sample arm instead of objective lens.Since there are a series of focus points of Fresnel lens,the lateral resolution in these points keeps constant over the focal depth of the SDOCT system.The experimental data show that Fresnel lens based SDOCT had a lateral resolution of?6.2 ?m over a depth of 2 mm which is one order bigger than focal depth in conventional SDOCT.4.To suppress the influence of the axial motion on image quality,an algorithm of axial motion compensation was proposed in which the depth differences of the sample be-tween two adjacent A-scans were used to distinguish the axial motion.By summing the value of axial motion between two adjacent A-scans,the value of compensation can be ob-tained with the help of the axial motion detected,the image quality was improved by shift-ing the pixel number.5.For the application of OCT in esophagus imaging,an endoscopic swept source OCT was designed which was illuminated by a source with the center wavelength of 1310 nm and a bandwidth of 107 nm.The effects of the distance between the fiber and grin lens on system performance and the choice of the grin lens's Pitch were analyzed.According to the simulation of the system performance with Zemax,the theoretical axial resolution is about 7.1 ?m with the lateral resolution of 17 ?gm and imaging depth of 7 mm.The expe-rimental data show that the axial resolution of the system is?9 ?m and the lateral resolu-tion is?19.5 ?m with the imaging depth of 6 mm in air.The initial cross-sectional images of the intestinal tract of pig were presented to demonstrate the capability of the system for endoscopic applications.