Miniature bending manipulator for fetoscopic intrauterine laser therapy to treat twin-to-twin transfusion syndrome
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Recent typical therapy for twin-to-twin transfusion syndrome (TTTS) is selective laser photocoagulation of anastomotic communicating vessels on the placenta using the fetoscopic approach. The difficulty of a conventional laser device approach for this procedure depends significantly on the placental location, so a new robotized device is required to bend the direction of laser irradiation flexibly within the narrow uterus.
The authors designed a miniature bending mechanism impelled by a wire-guided linkage driving method that provides a stable procedure for bending laser irradiation from −90° to 90°. Using this bending mechanism, the authors developed a bending manipulator with a diameter of 3.5 mm and a hollow central channel with a diameter of 0.8 mm for passing a glass fiber for neodymium:yttrium–aluminum-garnet (Nd:YAG) laser photocoagulation. The bending mechanism is motorized by an electrical actuator and controlled by a grip-type interface with a small joystick. The robotized tip’s part and the actuator’s part are easily separable for cleaning and sterilization.
In performance evaluations of the manipulator, the bending characteristics with a glass fiber were examined. The bending range was −52.6° to 80°, with a very small hysteresis error, and the bending repeatability error was 0.5° ± 0.2°, which corresponds with the high accuracy of 0.2 ± 0.1-mm positioning error at the glass fiber’s tip. In the evaluation of Nd:YAG laser photocoagulation, the study confirmed that the manipulator performed effective laser photocoagulation of the placental phantom surface (underwater chicken liver). The large bending range, reaching 80°, enabled a flexible approach from various directions with a high irradiation efficiency of no less than 96.6%.
The authors’ original miniature bending manipulator can change the laser irradiating direction with highly repeatable positioning accuracy for speedy, safe, and effective vessel occlusion in clinical practice.
KeywordsMiniature bending manipulator Selective laser photocoagulation Twin-to-twin transfusion syndrome
A part of this work was supported by Health and Labour Sciences Research Grants in 2005 (research on medical devices for analyzing, supporting, and substituting the function of human body; H17-Physi-006), by FY2005 JSPS Grants-in-Aid for Scientific Research Development of Next Generation End Effecter and Navigation System for Computer Aided Surgery (17100008), and by Research Fellowships of the Japan Society for the Promotion of Science for Young Scientists (041400000227).
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