Computational Optimization of Notch Spacing for a Transnasal Ear Endoscopy Continuum Robot

Benefits of Side-Firing Optical Fibers in Endoscopic Laser Treatment of the Larynx

OBJECTIVE

To elucidate potential tissue coverage of side-firing optical fibers in office-based endoscopic laser treatment of larynx, as well as to demonstrate their enhanced ability to address challenging anatomic areas.

METHOD

We performed a comparative study of four different fiber designs: a traditional forward-facing fiber, and three side-firing fibers that emit light at an angle of 45°, 70°, and 90°, respectively. The study was conducted in simulation, using eight three-dimensional models of the human larynx generated from microtomography x-ray scans. A computer program simulated the insertion of the endoscope into the larynx, and the Möller-Trumbore algorithm was used to simulate the application of laser light.

RESULTS

Side-firing laser fibers increased potential tissue coverage by a mean of 50.2 (standard deviation [SD] 25.8), 73.8 (SD 41.3), and 84.0 (SD 47.6) percent for angles of 45°, 70°, and 90°, respectively, compared to forward-facing fibers. Angled fibers provided access to areas of the larynx considered difficult to address by traditional methods, including the infraglottis, laryngeal ventricle, and right vocal fold.

CONCLUSION

Simulation results suggest that side-firing optical fibers have the potential to enhance anatomical access during in-office endoscopic laser procedures in the larynx. Further research is needed to better understand the benefits and any potential risks or contraindications of side-firing optical fibers.

LEVEL OF EVIDENCE

NA Laryngoscope, 133:1205-1210, 2023.

Beyond Constant Curvature: A New Mechanics Model for Unidirectional Notched-Tube Continuum Wrists

This paper presents a new mechanics model for unidirectional notched-tube continuum wrists, a class of mechanisms frequently used to implement distal steering in needle-sized surgical robotic instruments. Existing kinematic models available for these devices are based on the simplifying assumption that, during actuation, all the notches undergo the same amount of deflection, so that the shape of a wrist can be approximated by an arc of constant curvature. This approach is analytically attractive, but, as we show in this paper, it can sometimes fail to provide good tracking accuracy. In this article, we provide a new model that relaxes the assumption above, and we report experimental evidence showing its superior accuracy. We model wrist deflection using Castigliano's second theorem, with the addition of a capstan friction term that accounts for frictional losses on the actuation tendon. Because notched-tube wrists are typically made of Nickel-Titanium (Nitinol), which has nonlinear stress-strain characteristics, we use a technique to obtain a local linearized approximation of the material modulus, suitable for use in the deflection model. The result of our modeling is a system of nonlinear equations that can be solved numerically to predict the wrist configuration based on the applied actuation force. Experimental results on physical specimens show that this improved model provides a more accurate estimate of wrist kinematics than prior models assuming constant curvature bending.