Polarization-sensitive optical coherence tomography imaging of articular cartilage

Articular cartilage is the connective tissue protecting the joints, which can be divided into four structural zones from shallow to deep: superficial zone, transitional zone, deep zone and calcified zone. Osteoarthritis, a common joint disease, is associated with the progressive degeneration of the cartilage structure. The destruction progressively develops from the superficial zone towards the deep zone as the disease progresses. Thus, visualization of articular cartilage structural zones would significantly facilitate cartilage disease diagnosis, repair, regeneration, and transplantation. Polarization sensitive optical coherence tomography (PS-OCT) is a powerful non-invasive imaging modality capable of evaluating the birefringent properties in biological tissue such as collagen. The second harmonic generation (SHG) imaging in multiphoton microscopy (MPM) can provide complementary high-resolution imaging of the microscopic structure of collagen fibers. In this thesis, we apply both PS-OCT and SHG imaging on articular cartilage. An automated 3-D segmentation method based on PS-OCT phase retardation measurement is developed to differentiate the structural zones of articular cartilage. Since the collagen fiber organization varies from the tissue surface to deep regions, the depth-resolved phase retardation measured by PS-OCT is utilized to distinguish and segment the depth-related structural zones of cartilage tissue. The segmentation results are validated by the high-resolution SHG imaging. This method offers a novel quantification and tissue segmentation approach based on the phase retardation measurement by PS-OCT. A comparison between PS-OCT and SHG imaging on articular cartilage is also carried out. Based on the multilayer architecture of articular cartilage, various features extracted from PS-OCT and SHG are compared along the tissue depth. The segmentation method is implemented to distinguish the tissue layers based on the birefringence property. The segmentation results match well with the different quantification results achieved from the top-view and side-view illumination PS-OCT, and some features extracted from SHG, such as the SHG intensity and the collagen fiber orientation. The results show reasonable association between the tissue birefringence detected by PS-OCT and the fiber organization detected by SHG microscopy. PS-OCT and SHG are capable to analyze both the macro and micro characteristics of collagen fibers in articular cartilage, showing great potential in detecting related disease progression.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofGraduat