Characterizing close-focus lenses for microendoscopy

Abstract

Microendoscopes are commonly used in small lumens in the body for which a focus near to the distal tip and ability to operate in an aqueous environment are paramount for navigation and disease detection. Commercially available distal optic systems below 1 mm in diameter are severely limited, and custom micro lenses are generally very expensive. Gradient index of refraction (GRIN) singlets are available in small diameters but have limited optical performance adjustability. Three-dimensional (3D)-printed monolithic optical systems are an emerging option that may be suitable for enabling high performance, close-focus imaging. In this manuscript, we compared the optical performance of three custom distal optic systems; a custom-pitch GRIN singlet, 3D-printed monolithic doublet, and 3D-printed monolithic triplet, with a nominal working distance (WD) of 1.5, 0.5, and 0.4 mm in 0.9% saline. These short WDs are ideal for microendoscopy in collapsed or flushed lumens such as pancreatic duct or fallopian tube. The GRIN singlet had performance limited only by the fiber bundle relay over 0.9-to 1.6-mm depth of field (DOF). The 3D-printed doublet was able to achieve a comparable DOF of 0.71 mm, whereas the 3D-printed triplet suffered the most limited DOF of 0.55 mm. 3D printing enables flexible design of monolithic multielement systems with aspheric surfaces of very short WDs and relative ease of integration.

Comparison of micro-optic systems for close-focus microendoscopic applications

“…Additionally, the 3D-printed design can utilize aspheric surfaces that are unachievable by conventional grinding and polishing processes for miniature lenses. We explored the use of 3D-printed lenses created through 2-photonpolymerization (2PP) for our fallopian tube endoscope application in a previous work 35 . We attempted to design two 2PP multi-element lenses to compete against the gold standard: a custom pitch GRIN rod singlet 35 .…”

“…We explored the use of 3D-printed lenses created through 2-photonpolymerization (2PP) for our fallopian tube endoscope application in a previous work 35 . We attempted to design two 2PP multi-element lenses to compete against the gold standard: a custom pitch GRIN rod singlet 35 . Table 2 displays the goal specifications and the as-built results of the GRIN singlet, 3D-printed doublet, and 3D-printed triplet.…”

Design of multiphoton microendoscope system for minimally invasive detection of cancer

“…Additive manufacturing (3D Printing) has opened new doors to creating small complex optical systems. 9,10,11,12,13 Recently our lab has collaborated with the precision freeform optics design, fabrication, and testing facility at the University of Arizona to create 0.5 mm diameter multielement monolithic distal end lens systems suitable for microendoscopes. 13 We intend to extend this collaboration for this project.…”

“…9,10,11,12,13 Recently our lab has collaborated with the precision freeform optics design, fabrication, and testing facility at the University of Arizona to create 0.5 mm diameter multielement monolithic distal end lens systems suitable for microendoscopes. 13 We intend to extend this collaboration for this project. We have created a HNA conceptual design intended to utilize these 3D printing techniques to meet our optical design requirements.…”

Cell-acquiring fallopian endoscope for detection of ovarian cancer via reflectance imaging, fluorescence imaging, and cell collection

“…To determine the performance of the new imaging system, a previously described test setup was used. 33 The 10k element fiber bundle and GRIN singlet system were connected to the detection system in the rack. At the distal end, in front of the tip of the fiber bundle and GRIN singlet, a 3" x 1" positive variable line grating (R1L3S6P, Thorlabs) or a 3" x 3" 1951 USAF Resolution Test Target (DA004, MaxLevy/II-VI) was positioned, and translated by motorized linear actuator (T-NA08A25, Zaber).…”