Enhanced contrast in OCT imaging of tissues using birefringence, scattering and speckle signatures

The three objectives listed here are the main aim presented in each of the chapters of this thesis. The research work carried out with respect to fulfilling these objectives is one step closer towards extending the possibility of non-invasive imaging modality of OCT and PS-OCT in the field of orthopaedics and tissue engineering. - Non-invasive technique to understand the depth-dependent 3D collagen framework of articular cartilage. - Non-invasive technique to discriminate between different types of connective tissue based on angle-resolved backscattering profiles - Computer based tissue discrimination based on the speckle textural analysis of the OCT images obtained Articular cartilage was imaged using two different schemes of implementation of PS-OCT: time domain PS-OCT and swept source based continuous polarisation modulation PS-OCT system. Detailed analysis is presented for time-domain PS-OCT data obtained from bovine articular cartilage sample over multi-angle measurements and a comparative study of the phase retardance profiles obtained from experimental data is done with those obtained from a layered model of articular cartilage using extended Jones matrix calculus. This includes a noise model chosen for the time domain PS-OCT system to add noise bias to the simulated results. Optimiser algorithms are developed based on this model. This study shows the possibility of using PS-OCT imaging towards non-invasive technique to study the microstructure of articular cartilage. The technique of multi-angle imaging in PS-OCT has also been used in the study of angleresolved backscattering, with the information regarding the reflectivity profiles as obtained from a normal OCT system used for the study. The two connective tissues under study are bovine tendon sample and bovine articular cartilage sample. Articular cartilage is predominantly made of Type II collagen fibrils which are finer and more uniform in nature compared to that in tendon tissue which is predominantly Type I collagen fibrils of larger diameters and coarser packing arrangements. Single scattering model of OCT is used to obtain the angle-resolved backscattering curves and Rayleigh Gans scattering approximation based simulation is carried out to elucidate and understand the results obtained. Speckle texture analysis is carried out to extract sub-resolution based information from OCT towards computer-based classification of different types of OCT images. This has been carried out first on tissue phantoms made of agar-intralipid solutions of different concentrations. Statistical features are extracted and grouped into 3-set features to obtain scatter-plots and receiver operating characteristic curves that determine the correctness of the classification obtained of a particular group of OCT images from the total sample set. With initial success from tissue phantom based speckle textural analysis, this has been extended to study the data classification ability of normal skin from tissue engineered skin with different types of melanoma cell-lines invasion as well as discriminate different types of melanoma invasion of tissue-engineered skin from each other