An Endoscope With 2 DOFs Steering of Coaxial Nd:YAG Laser Beam for Fetal Surgery

This paper reports a rigid endoscope that provides an endoscopic view and transmits a high-power infrared laser beam coaxially to arbitrary points in the view to photocoagulate body tissue, mainly for treatment of twin-to-twin transfusion syndrome. The endoscope system consists of a hot mirror for coaxial transmission of visible light and a neodymium-doped yttrium aluminum garnet laser beam, and an optical galvano scanner for steering the laser beam from the endoscope tip. The optical system of the endoscope is designed for high-power laser transmission, and achieves a small laser beam. The camera and galvano mirrors are calibrated to control the laser spot automatically by pointing a target on the endoscopic image. We evaluated the laser transmission efficiency, firing angle, positioning accuracy, and feasibility of photocoagulation by in vitro experiment. The laser transmission efficiency was 34%. However, the endoscope provided changeable firing angles of 24° in a horizontal direction and 22° in a vertical direction. Furthermore, the positioning accuracy was sufficiently high because the errors in both air and water were mostly smaller than the diameter of target vessels of 1 mm. As an in vitro experiment, we successfully coagulated rabbit's mesenteric vessels by changing the firing angle.