Common path optical coherence tomography based on fiber bundle imager.

摘要

Optical coherence tomography (OCT) has emerged as a promising medical imaging modality that can provide non-invasive high-resolution tomographic imaging in real-time. Generating high-resolution OCT images in real-time requires a complicated and costly system design. Therefore, there has been an interest in the development of a common-path (CP) approach to OCT which utilizes a simple interferometer where the sample and reference arms share a common optical path. This configuration allows a much simpler system design, lower associated costs, and the ability to use interchangeable probes as well as the freedom to use any arbitrary probe arm length.In this thesis, novel CP optic probes and image processing methods that could make the CP-OCT a practical system for a high-resolution endoscopic imaging have been developed and investigated.Despite the advantages of CP based OCT configurations, CP-OCT have had limited applications since the reference signal is usually obtained from the Fresnel reflection from the distal end of the optical fiber probe. Thus, when the probe is submerged in an aqueous medium or in contact with a target, the magnitude of the reflected power decreases due to the reduced index difference at the fiber probe reference plane. To solve this problem, gold-plated fiber probes were investigated for in situ imaging of retina and surrounding tissues. The probe operating in an aqueous medium was able to provide OCT images that can differentiate various retinal layers.To obtain 2D images, OCT requires a series of axial scans performed by mechanical spatial translation of the probe or the beam. Most current OCT systems use various miniaturized scanning probes in order to obtain lateral scanning. Alternatively, fiber bundle imagers have recently been suggested. However, the results so far have not been promising due to the inefficient coupling of light into the cores and the non-uniformity of the fiber array. Since CP-OCT obtains the reference at the distal end of the probe, it can overcome the difference between the optical properties between the fiber bundle pixels. In this work, the feasibility of pseudo-scanningless probe has been explored based on fiber bundle imager in the CP-OCT. The mechanical lateral scans are accomplished outside the specimen at the proximal entrance of the fiber bundle. This eliminated the need for moving parts in the distal end of the probe.Finally, to enhance the quality of OCT images obtained using a fiber bundle imager. An image processing method that can remove the fiber bundle's pixelation artifact due to the inherent arrangement of the fiber core arrays is proposed and studied. This method of eliminating pixelization effect from en face OCT image is based on applying a histogram equalization process followed by a weighted-averaged Gaussian smoothing filtering to not only remove the structural artifact of the bundle but also to enhances the image quality with minimum blurring of object's image features.