Research On Key Technology Of Fiber-based Polarization Sensitive Optical Coherence Tomography

Optical coherence tomography is a non-invasive,high-resolution and high-sensitivity imaging technique with capability of generating cross-sectional images of biological tissues in vivo.Polarization sensitive OCT(PS-OCT)is a functional extension of conventional OCT that utilizes the polarization properties of back-reflected light to non-invasively obtain additional physiological information,which is able to diagnose the early diseases and indicates the potential value in clinical application.The PS-OCT systems are available with large volume in free space system,and a great deal of calculations are needed in fiber-optics-based systems.They are also unable to obtain orientation of absolute optics axis of biological tissues in fiber system.In this thesis,an all single-mode fiber(SMF)-based PS-OCT system was proposed to obtain the teeth tomographic images in vivo and the absolute optics axis of tissue samples.The main work and innovations include the following:In order to achieve the teeth images in vivo,a handheld spectral domain OCT system was designed and built.The lateral scanning was realized by using a galvanometer scanner.The handheld probe was characterized by its compact size,low cost and being portable,making it easier for ex vivo and in vivo teeth imaging.The interface between the enamel and the dentin can be clearly observed in the teeth images generated by the system,demonstrating the capibility of the handhled OCT system.In order to eliminate unknown fiber birefringence due to fiber imperfections in a SMF-based PS-OCT system with single input polarization state,a method based on Mueller matrix was proposed.In the arrangement,by empolying polarization controllers in PS-OCT,the phase retardance and relative optic axis orientation of normal and burned biological samples were accurately obtained.In addition,the contribution of the multi-backscattering in tissues to the orthogonal polarization interference signals is readily suppressed by subtracting the unpolarized component of the scattered light,improving the image quality.In order to obtain the absolute optic axis orientation of biological samples,an algorithm was developed with an all SMF-based PS-OCT.The SMF system polarization was adjusted by polarization controllers so that the system retardance was equal to multiple integers of?and the output Stokes vectors at the spectrometer from the sample surface was[0,1,0]~T.The Mueller matrix-based model of the system was developed and the formula for calculating absolute optic axis orientation of the samples was then derived.The proposed algorithm has been validated in the quantification of the optic axis orientation of a quarter-wave plate with the measured error of approximately 3°.In order to non-invasively assess relationship between the caries lesion activity and the thickness of the highly mineralized transparent surface layer,an experiment measurement design was proposed which was based on the combination of the PS-OCT,near-infrared(NIR)reflectance and thermal imaging.The experimental results show that,after mechanical removal of the mineralized surface layer covering the lesion,both the intensity change in NIR reflectance images after drying the lesions and the change in thermal emission measured with a thermal camera increased significantly(P<0.05),indicating the permeability of the lesion to fluids increased.This study provides the evidence for understanding the mechanism of arresting caries lesions and suggests that the transparent surface layer above the subsurface lesion greatly inhibits the diffusion of liquids in the lesion.