Development of three-dimensional endoscopic optical coherence tomography and fiber based multiphoton microscopy using miniaturized imaging probe

Probe-based imaging techniques including endoscopes have been primarily used for diagnosing diseases of internal organs. At present, miniaturized imaging probes are used not only for diagnosis, but also for planning and monitoring treatment strategies. Probe-based imaging of existing diagnostic tools such as ultrasound, computed tomography, and magnetic resonance imaging have various functional and practical limits; low resolution, invasive manner or lack of portable implementation. Optical imaging approaches can be an additional means to fulfill requirements of probe based diagnosis, because they offer unique technical characteristics such as high spatial resolution and sensitivity, noninvasive application, non-ionizing radiation, functional imaging capability, as well as compact and portable implementation via fiber optics. The main goal of this thesis is to develop high resolution, non invasive optical imaging techniques using miniaturized probes and investigate their feasibility as diagnostic tools.;Optical coherence tomography (OCT) is a cross-sectional imaging method based on the detection of backscattered near infrared light from tissue. It is capable of noninvasive, high resolution imaging in real time. OCT has already been used for purpose of endoscopic imaging using fiber-optic probes that intrinsically offer easy integration with clinical endoscopes. Currently, most of probe-based images are restricted to 2-D. However, it is difficult for clinicians to find the exact location and extent of a diseased site with 2-D information. 3-D OCT image can provide instant visualization of the size and extent of the diseased tissues to the clinicians thus making the imaging procedures more accurate and faster. The first section of this thesis covers the development and investigation of an advanced 3-D endoscopic OCT system. In particular, the endoscopic probe in this study was designed using 2-axis scanning microelectromechanical system (MEMS) mirror which supports rapid scanning, compact size, high reliability, and flexibility in scanning pattern. Feasibility studies were then performed on various animal and human tissues in vivo.;OCT typically images tissue morphology with contrast derived from tissue scattering, whereas multiphoton microscopy (MPM) provides information of tissue functionality. MPM is based on nonlinear multi-photon excitation of fluorophores generated at the focal point of the microscope objective. It permits high resolution, non-invasive images of cellular and extracellular matrix at depths of several hundred microns within tissues. Currently, studies of probe-based MPM are still under evaluation because of the engineering challenges such as miniaturization of scanning probe. The second section of thesis focuses on the design and implementation of a miniaturized MPM probe. In order to resolve key challenges of such a probe, a MEMS scanning mirror and a double-clad photonic crystal fiber (DCPCF) were utilized. The use of a MEMS mirror and a DCPCF provides many advantages, such as size reduction, rapid and precise scanning, efficient delivery of short pulses, and high collection efficiency of fluorescent signals. The completed probe was integrated into an MPM system and used to image fluorescent beads, paper and biological specimens. Engineering solutions developed in these studies provide knowledge and enable accumulation of experience that will aid in successful transitioning of optical imaging platforms from the laboratory setting to the clinical environment.