Miniature bending manipulator for fetoscopic intrauterine laser therapy to treat twin-to-twin transfusion syndrome.
BACKGROUND
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.


METHODS
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 degrees to 90 degrees . 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.


RESULTS
In performance evaluations of the manipulator, the bending characteristics with a glass fiber were examined. The bending range was -52.6 degrees to 80 degrees, with a very small hysteresis error, and the bending repeatability error was 0.5 degrees +/- 0.2 degrees, 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 degrees, enabled a flexible approach from various directions with a high irradiation efficiency of no less than 96.6%.


CONCLUSIONS
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.
Department of Mechano-Informatics, Graduate School of Information Science and Technology, The Univercity of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan. hiromasa@atre.t.u-tokyo.ac.jp
H
H
Yamashita
K
K
Matsumiya
K
K
Masamune
H
H
Liao
T
T
Chiba
T
T
Dohi
D004867:Equipment Design; D005260:Female; D005330:Fetofetal Transfusion / Q000601:surgery*; D020669:Fetoscopes; D006801:Humans; D053685:Laser Therapy / Q000295:instrumentation*; D008904:Miniaturization; D011247:Pregnancy; D012371:Robotics