Theories And Experiments On Optical Coherence Tomography

Optical coherence tomography (OCT) is a fundamentally new type of optical imaging modality, which performs non-invasive, high-resolution, high sensitivity, high speed, cross-sectional tomographic imaging, and enables "optical biopsy". The work is focused on the design of OCT system, the analysis of its performance, and the exploration of OCT application in biomedical areas.First of all, an experimental OCT system was designed. The fundamental laws governing the resolution, imaging time, sensitivity, and imaging depth of OCT were analyzed in detail, and the related design notes were given out. Finally,16μm axial resolution and-90 dB detection sensitivity was obtained. With the OCT system, we investigated the morphologic structure of in vivo skin in several locations. Structures of the stratum corneum (plamoplantar), the epidermis, and the upper dermis can be distinguished from the obtained cross-sectional images. Therefore, it was demonstrated that OCT is a feasible method for investigation of morphologic structure of superficial layers of human skin.Second, it was shown that the optical properties of biological tissue can be determined with OCT by fitting a model to the OCT signal from a region of interest. The validity of the single-scattering and multiple-scattering model for both the highly scattering and weakly scattering media was studied using calibrated samples in the fixed focus geometry. According to the experiment results, a proper correction for the confocal properties of the sample arm was presented. Finally, scattering properties of in vitro rat liver and in vivo human skin were obtained.Third, it was proposed that the statistics properties of the speckle can be discussed theoretically for the OCT signals in the logarithmic scale with the random phasor sum theorem. In the experiments, OCT signals of tissue phantoms with different scattering properties were analyzed under two different focusing conditions. It was found that the effect of the speckle noise can be suppressed by displaying OCT images in the logarithmic scale and using the objective lens with higher numerical aperture. It was also demonstrated that the speckle properties is correlated with the scattering properties of the tested sample, which may provide a new way to characterize the scattering properties of biological tissue.Finally, it was found that a method based on the Fourier transform and the polynomial fit can be used to extract the information about the structure and function of bio-tissues from the dispersion signal in OCT. The interferogram envelope in OCT was Fourier transformed to the frequency domain, and then the second order dispersion information was obtained by performing a polynomial fit to the phase spectrum. Theoretical simulation and experimental data validated the method. The obtained results in this work not only can be used for the dynamical dispersion compensation, but also provide a way to characterize different tissues, and different physiological conditions.