Design Of Miniature Objectives For Fluorescence Confocal Microendoscopy

Recently, fluorescence confocal microendoscopy was used as a new diagnostic tool to acquire real-time high-resolution images through the working channel of conventional endoscopy. According to the imaging results, the doctors choose the tissue from suspicious region for biopsy, which could make conventional biopsies more efficient. Miniature objective is one of the important components of fluorescence confocal microendoscopy. The optical probe, composed of the miniature objective and fiber bundle, enters the human body via the biopsy channel of a conventional endoscope. The resolution and field of view of fluorescence confocal microendoscopy are determined by the numerical aperture and magnification of the miniature objective. In order to make sure that the fluorescence confocal microendoscopy could be applied for clinical diagnosis, the miniature objective should meet the requirements of small size, small aberrations and high-resolution-performance, as well as the limitations by common technology of fabrication and assembly.According to the imaging requirements of the fluorescence confocal microendoscope, the design targets and processing limitations of the miniature objectives by conventional fabrication technology were first described in this dissertation, followed by the design methods of the miniature objectives. Then, the testing method and system for the performance of the miniature objectives were presented. The lateral resolution, MTF curves, and the chromatic focal shift of the miniature objectives could be measured by the test system.According to the design targets and processing limitations of the miniature objectives, three miniature objectives of different sizes with five-lens-easy-to-implement-structure were designed in this research. The difficulty of the design increased as the size of the miniature objective decreased. To confirm the design methods of the miniature objectives, the 6 mm diameter miniature objective was first designed and manufactured using all-glass-spherical-lens structure. In order to cooperate with conventional colonoscopy, the 3.5 mm diameter miniature objective was designed by taking advantage of the aspheric lens in aberration correction. Replacing one glass spherical lens with one plastic aspheric lens effectively solved the problem that the difficulty of aberration correction increased as the size of miniature objective decreased. For cooperating with the conventional gastros copy, the 2.6 mm diameter miniature objective was composed of four spherical lenses and one aspheric lens, and optimized by globe optimization methods during optical design. The length of the 2.6 mm miniature objective was 10.3 mm, facilitating access into the human body through the working channel of conventional gastro cope. The working distance of the miniature objective, 150 ?m, was useful for observation of gastric pit in gastric mucosa. The FOV(field of view) of the 2.6 mm miniature objectivewas 360 ?m, allowing the classification of gastric pits to be observed effectively in clinical diagnosis. The performances of the three miniature objectives which were processed by common technology of fabrication and assembly, were measured by the testing system. All the miniature objectives could resolve the group 9, element 3 bars of the resolution target. The MTF values of all the miniature objectives at 167 lp/mm in fiber space are bigger than 0.5. The chromatic focal shifts of all the miniature objectives are small enough for the fluorescence confocal microendoscope. The testing results of the three miniature objectives meet the imaging requirements of the fluorescence confocal microendoscope. The miniature objectives were integrated with the fluorescence confocal microendoscope for imaging experiments of the fresh tissue of mice and typical structures of organs of mice could be resolved. The crypt structures and epithelial cells, which are important for early cancer diagnosis, can be recognized in the imaging results of the fresh colon tissue of mice by the fluorescence confocal microendoscope with the 2.6 mm diameter miniature objective, indicating that the fluorescence confocal microendoscope with the 2.6 mm miniature objective could be applied for clinical research.For imaging with different depths in tissue, adual-focal miniature objective for the fluorescence confocal microendoscope was designed in this dissertation. The dual-focal miniature objective was designed with new lens structure which was composed of a collimating lens and a focusing lens. And the focusing lens was combined by two half lens with different focal length but same thickness. The dual-focal miniature objective has an outer diameter of 2.6 mm and a wavelength range of 488-550 nm. And the dual-focal miniature objective could be easily implemented with the simple structure. The dual-focal imaging ability of the miniature objective was demonstrated by the imaging results.In this dissertation, four miniature objectives were designed for the fluorescence confocal microendoscope after choosing appropriate structure and right types of lenses of different materials for aberration correction. The imaging results acquired by the fluorescence confocal microendoscope integrated with the miniature objectives meet the expectations. The easy-to-implement and high-performance miniature objectives could be integrated with the fluorescence confocal microendoscope and used for clinical research in the future, making a contribution to the early cancer diagnosis.