MEMS based optical coherence tomography imaging

Optical coherence tomography (OCT) can provide subsurface cross-sectional information of tissue samples with high resolutions of 1-15 µm. Microelectromechanical system (MEMS) mirrors are small and can perform fast optical scans; they are suitable for realizing lateral optical scans in OCT systems. In this thesis, MEMS technology is applied to enable endoscopic OCT imaging. Two generations of MEMS mirrors have been used. The MEMS mirrors are 2 mm x 2 mm and 1.7 mm x 1.55 mm respectively in size. Four generations of MEMS-OCT endoscopic probes have been developed; the diameters of the probes are reduced from 5 mm in the first generation down to 2.5 mm in the fourth generation. The effects of the positions of the optical components and the protective tubing on OCT imaging performance have been studied through simulation and verified experimentally. In vivo imaging experiments were done on mouse tongue, mouse ear and injected tumor; layered structures of mouse tongue and ear, and accurate shape of tumor regions were clearly detected.;The same MEMS-OCT system has also been used to measure localized refractive index of acute rat brain tissue slices; regions including cerebral cortex, thalamus, corpus callosum, hippocampus and putamen were measured; refractive index in the corpus callosum was found to be ∼ 4% higher than the RIs in other regions. Changes in refractive index with tissue deformation were also measured in the cerebral cortex and corpus callosum under uniform compression (20-80% strain). For 80% strain, measured RIs increased nonlinearly by up to 70% and 90% in the cerebral cortex and corpus callosum respectively. Further, two types of functional OCT have been realized: polarization sensitive (PS) OCT and Doppler OCT. PS OCT has been successfully applied on canine meniscus, and tissue birefringence were detected and represented by their Stokes parameters shown by 2D and 3D images. Rat blood vessels were identified by Doppler OCT. In addition, MEMS based OCT combined with photoacoustic imaging was demonstrated.;This is the first detailed study on applying MEMS technology to realize endoscopic OCT imaging. This work opens up many promising opportunities in early cancer detection and real-time imaging guided surgery.