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Tanskanen, Adrian Sakari

University of British Columbia

This thesis explores multipath artifacts in multimodal endoscopic optical coherence tomography (OCT). In non-multimodal systems, endoscopic OCT is generated using single-mode fibers (SMF) to ensure that the backscattered light is collected by the fundamental mode. To add a secondary type of imaging without increasing endoscope size, multimodal OCT systems use double-clad fiber (DCF). DCF has a single-mode core for OCT, and a high numerical aperture inner-cladding for the secondary modality. Unfortunately, multimodal systems come at the cost of multipath artifacts. Multipath artifacts are blurred ghost images inherent to the use of DCF which degrade OCT image quality. The initial goal of this thesis was to develop a method to mitigate multipath artifacts and improve the image quality of multimodal OCT systems to the same as SMF-based OCT. First, using experimental methods such as spatially and spectrally resolved imaging, I discovered that multipath artifacts are generated by LP11-like inner-cladding modes. Leveraging this research, I demonstrated that catheters fabricated with a triple-clad W-Type fiber in place of DCF can be used to remove multipath artifacts without degrading the quality of the secondary modality (autofluorescence imaging). However, in the process of studying multipath artifacts, I discovered that they could be projected from blurred images in 3D, to high-quality en face images. These images contain different features than an equivalent projection of the OCT image carried by the DCFs fundamental mode. Using modelling and experimentation, I revealed that the higher-order modes of the multipath artifact couple off-axis backscattering. This discovery essentially changed a bug into a feature, providing the basis for multipath contract imaging (MCI). MCI is a ratiometric measure of the total power coupled into the fundamental mode divided by the higher-order modes: providing a visualization of tissues angular diversity. As multipath artifacts are inherent to multimodal OCT devices, MCI can be generated from old datasets meaning that a wealth of clinical data could be retrospectively analyzed.

Text

2024-10-17

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/89428

Biomedical Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/