Abstract
An optical model of an ultrathin scanning fiber endoscope was constructed using a non-sequential ray tracing program and used to study the relationship between fiber deflection and collection efficiency from tissue. The problem of low collection efficiency of confocal detection through the scanned single-mode optical fiber was compared to non-confocal cladding detection. Collection efficiency is 40x greater in the non-confocal versus the confocal geometry due to the majority of rays incident on the core being outside the numerical aperture. Across scan angles of 0 to 30o, collection efficiency decreases from 14.4% to 6.3% for the non-confocal design compared to 0.34% to 0.10% for the confocal design. Non-confocality provides higher and more uniform collection efficiencies at larger scan angles while sacrificing the confocal spatial filter.
Highlights
Invasive medical procedures will benefit from flexible endoscopes that are extremely thin yet produce wide field of view and high resolution images
Rays were traced and statistics were generated to determine where the backscatter flux was located internally and able to be captured by the endoscope, as well as the general direction and intensity of rays external to the housing
Since the smallest illumination spot is desired at the tissue, single mode operation is required
Summary
Invasive medical procedures will benefit from flexible endoscopes that are extremely thin yet produce wide field of view and high resolution images. Current flexible endoscopes use fiber bundles or silicon image sensors placed in the distal tip to capture imagery while illumination is delivered via a separate fiber bundle. At the University of Washington, a flexible scanning fiber endoscope (SFE) is being developed to provide high resolution images in which the resolution is less dependent on the distal tip diameter [5]. Initial prototype SFEs have been made in the non-confocal geometry and their performance has been demonstrated to have 500 lines of resolution across a 1.5 mm diameter field with better than 10 micron resolution [8] In this preliminary study, the expected performance of using SFEs to image tissue is modeled and the confocal arrangement is compared to non-confocal geometries to provide guidance to future laser-scanning endoscope designs. A function was built which provides the appropriate reflectance value as a function of the scatter direction, including both specular and diffuse behavior, as exhibited by human tissue
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