| Optical coherence tomography (OCT) is based on the optical coherence interferometry and has the ability to produce the optical sectioning images with high axial resolution. Color Doppler optical coherence tomography ( CDOCT; also called Optical Doppler tomography, ODT ) is a recent invention which permits spatially localized flow velocity mapping simultaneous with micro-structural imaging. CDOCT is an extension of OCT and is based on the use of Doppler phenomenon. Using inexpensive fiber-optic and semiconductor components, CDOCT provides the capability for non-invasiveimaging of sub-surface microstrutures simultaneously with velocity.First the OCT signal expression is derived by using the theory of partially optical coherence, and the CDOCT signal is analyzed according to the principle of the optical Doppler phenomena. Then, based on the structures and the optical parameters of human blood, a model of human blood stream is described. The light is scattered mainly by red cells; the numerical simulation of the CDOCT signal with the MATLAB tool is realized. Finaly, by using the time-frequency analysis method, the fringe of the simulated CDOCT signal is calculates and its phase information is derived to re-construct the static image and the dynamic velocity image of the blood vessel. The images are consistent with predicted conclusion of the theoretical analyses.Based on the theoretical analyses of the CDOCT signal, a Monte Carlo Simulation model is described, which is derived from the real CDOCT experiment. According to the object-oriented programming theory, the MCML program is rewitten , which describes the light transport in multi-layered tissues, and the improved CDOCT monte carlo simulation in four-layer skin tissue with blood vessel is done, which is irradiated by gaussian beam. The result of the simulation is also consistent with the theoretical analysis.At the end, our homemade instrumentation of the CDOCT system is descibed. |
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