Design and development of an endoscopic optical coherence tomography (OCT) imaging system

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Reyes, Carlos
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University College Cork
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Optical coherence tomography (OCT) has been established as a noninvasive medical optical imaging modality that is capable of generating cross sectional images with a high axial resolution (1-10 μm) and a penetration depth of 2 mm in tissue. OCT imaging can be combined with conventional white-light endoscopes through an imaging probe capable of providing micro structural information of tissue samples based on backscattered light. This allows the study in internal hollow organs including the gastrointestinal (GI) tract. In this thesis a novel swept-source OCT endoscopy using a fibre-cantilever piezotube (PZT) scanner has been developed with a linear field-of-view of 0.5 mm and axial resolution of 10 μm at 1300 nm. The achieved A-scan rate is 200 kHz as defined by the swept source, and a B-scan rate of 1.4 kHz given by the fibre resonance frequency. The tradeoff between faster scanning speed and fewer A-scans/B-scan was compensated by an interleaving algorithm where three consecutive B-scans are acquired and then interleaved, increasing the sampling density hence improving image quality. This process emulates a resonance frequency of 460 Hz without having to add extra-weight to the fibre. The imaging probe can be integrated into the working channel of a commercial endoscope and has a diameter ∅ = 2.5 mm, rigid length of 25 mm and a total length of 2.2 meter to allow mobility for in-vivo imaging. OCT images of ex-vivo rat colon samples and human finger are presented. The main target users of the developed endoscope OCT probe are gastroenterologists since the presented OCT system provides value in cancer tissue analysis for applications where imaging of ex-vivo resected tissue samples is required to provide immediate structural diagnosis and can be made compatible with in-vivo measurement. Finally, this thesis presents a new heterodyne method to characterize akinetic all- semiconductor sampled-grating distributed Bragg reflector lasers that can be the core of a swept source. This method provides opto-electronic characterization in the form of DC and AC tuning maps that represents the current combinations needed to obtain the desired linear tuning profile as needed by swept-source applications.
Biophotonics , Interferometry , Optical coherence tomography , Biomedical optics , Optical fibres
Reyes, C. 2021. Design and development of an endoscopic optical coherence tomography (OCT) imaging system. PhD Thesis, University College Cork.