Monte Carlo Simulation Of An Optical Coherence Tomography In High Scattering Tissue

OCT is a typical application of optical coherence tomography technique in biological tissue, it has been successfully used in clinical ophthalmology examination since the 90's in last century, now it receives increased attention in other area, like the skin diagnosis, dental diagnosis and blood vessels imaging. Compared to traditional imaging method, the biggest advantage of OCT is high resolution. Although OCT has a wide application prospect, it's application in high scattering tissue, like skin and teeth, is still hard. The main difficulty of the application of OCT in high scattering medium is that the imaging depth that OCT can get a clear image is shallow. To provide theoretical guidance for OCT imaging in high scattering organizations, an OCT simulation model based on Monte Carlo method is proposed, and the simulation model is mainly used in skin to study the OCT performance in high scattering tissue.The simulation model is mainly composed of a focused Gaussian beam model, Monte Carlo model which simulates the spread of the light in tissue and a probe model. As for the Gaussian beam model, comparison between cone model and hyperboloid model was made, and results verified the effectiveness of hyperboloid model. The Monte Carlo model simulates the scattering, absorption, reflection and transmission process of light in skin. Taking the Rayleigh scattering and Mie scattering characteristics of skin into consideration, a new phase function was presented to suit for the skin model. Probe model was based on the confocal scanning system characteristics of OCT, and the new classification rules for Class I and Class II photon was made.To accelerate the Monte Carlo simulation process, a new combined importance sampling method was used to speed up the convergence. On the basis of the proposed simulation model above, the OCT images and attenuation compensation are simulated according to Extended Huygens-Fresnel model. In addition, single and multiple scattering phenomenon was studied, and the effect of wavelength, coherence length on OCT signal-to-noisc ratio, maximum detection depth and other key parameters of the system were analyzed as well. Experimental results show that the proposed simulation model is an appropriate tool to simulate the OCT system in muti-layerd turbid media.