Noriaki Yamanaka

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 rabbits mesenteric vessels by changing the firing angle.

MRI-Compatible Rigid and Flexible Outer Sheath Device with Pneumatic Locking Mechanism for Minimally Invasive Surgery

To reduce the invasiveness of surgery, we developed an outer sheath device using a flexible toothed link and pneumatic locking mechanism that works with flexible devices used in minimally invasive surgery. The outer sheath can be switched between flexible and rigid modes, and the angle of its tip can be controlled by a nylon wire. All parts of this device are made of plastic and are MRI-compatible. We manufactured a sheath prototype, 300 mm long, with a 20-mm outer diameter, and an 8-mm inner diameter. Experiment results showed that the outer sheath can protect tissues from high insertion force and secure the path for flexible devices. It can follow a curved path with a reasonable radius.

A Coaxial Laser Endoscope with Arbitrary Spots in Endoscopic View for Fetal Surgery

In this paper, we describe a rigid endoscope that transmits a laser beam coaxially to arbitrary points in the endoscopic view, mainly for treatment of twin-to-twin transfusion syndrome. The endoscope consists of a hotmirror for coaxial transmission of visible light and a Nd:YAG laser beam, and galvanometers for controlling the beam irradiation angle. We evaluated the transmission efficiency of the laser power, the spot size through the endoscope and accuracy in positioning the beam. The maximum laser transmission efficiency was 39% and the spot diameter was 2.2-3.2 mm at a distance of 10-20 mm. The positioning accuracy was mostly within 1.0 mm in the endoscopic view at the distance. The average laser power density on the spot was estimated to be 170-370 W/cm2, and a chicken liver was successfully coagulated by changing the laser beam irradiation angle.

Automatic Tracking Algorithm in Coaxial Near-Infrared Laser Ablation Endoscope for Fetus Surgery

This article reports a stable vessel object tracking method for the treatment of twin-to-twin transfusion syndrome based on our previous 2 DOF endoscope. During the treatment of laser coagulation, it is necessary to focus on the exact position of the target object, however it moves by the mothers respiratory motion and still remains a challenge to obtain and track the position precisely. In this article, an algorithm which uses features from accelerated segment test (FAST) to extract the features and optical flow as the object tracking method, is proposed to deal with above problem. Further, we experimentally simulate the movement due to the mothers respiration, and the results of position errors and similarity verify the effectiveness of the proposed tracking algorithm for laser ablation endoscopy in-vitro and under water considering two influential factors. At average, the errors are about 10 pixels and the similarity over 0.92 are obtained in the experiments.

A Laser Steering Endoscope with High Laser Transmission Efficiency

This paper reports a miniaturized endoscope that transmits a high-power infrared laser beam to arbitrary points in the endoscopic view for the treatment of twin-to-twin transfusion syndrome. The miniaturized endoscope has an external diameter of 3.5 mm expect for illumination and also improved on the laser transmission efficiency by using a GRIN rod lens as a relay lens. The experiment showed the laser transmission efficiency on the unit of the object and relay lens system was 72%. The thermal increase of the endoscope tip during the laser irradiation was 0.5°C. The maximum laser power was almost 30 W at the source power of 50 W. The laser power has the possibility to coagulate vessels. The steerable ranges were a total of 28.7 degrees in horizontal direction and a total of 25.9 degrees in vertical direction. This large range of selecting target provides easier use.

Polarizing Beam Splitter Endoscope for Simultaneously Observing Front and Lateral View

Fetal surgery sometimes requires multiple field-of-views (FOVs). The authors have developed an FOV extended endoscope for simultaneously observing front and lateral view with single lens system. A polarizing beam splitter (PBS) mounted at its distal end guides the rays from the two FOVs to relay lenses in orthogonal linear polarizations, and the other PBS mounted at its base separates them at eye lens systems. However, the images of the two views are superimposed because lenses rotate the direction of linear polarization. To solve the problem, the authors adopt a rectifier to cancel the rotation. Additional approaches consist of polarizing plates, image processing, and light source control. Polarizing plates improve the contrast of image by 13.8%. Light source control unit switches chip LEDs on and off. The cameras synchronized to LEDs get images alternately. Taken endoscopic movie with light source control was 30fps. By using these methods, clearer images are acquired.

Surgical Manipulator with Balloon for Stabilizing Fetus in Utero under Ultrasound Guidance

This paper describes a surgical manipulator to stabilize intrauterine fetus with ultrasound image guidance. The manipulator includes an outline of 4 mm in diameter, a mechanism with 7 joints, and a set of balloons. The manipulator is arranged as straight form and the balloon is fold to be a minimum size before the insertion. Accuracy evaluation of bending performance showed that the standard deviations were ±3.6 degrees on wired-driven mechanism and ±1.6 degrees on linkage-driven mechanism. Experimental results also demonstrated high repeatability of the mechanisms. In feasibility experiments, ultrasound images in 2D and 3D modes were examined for guiding the manipulator. The 2D images provided wide view and easily viewable display of the balloon inflation. The 3D images provided easily viewable display of bending motion of the arm and the relative position of a phantom. It is possible to operate the manipulator in utero under the ultrasound guidance in 2D and 3D by switching them in each procedural stage.

Balloon-based manipulator with multiple linkages for intrauterine surgery

This paper describes a manipulator for controlling position and posture of fetus in uterus and a surgical procedure for supporting the fetus in intrauterine surgery. The manipulator is equipped with multiple linkages and a balloon to support the fetus softly in the uterus. The linkages with two bending mechanisms are designed for inserting the balloon to an optimal position under the fetus. The balloon is fold before the operation and inflated by saline water after arriving at the required position in the uterus. Accuracy evaluation showed that the standard deviations of the bending angle of the wire-driven mechanism and the linkages-driven mechanism were 1.0 degree and 2.5 degree, respectively. Force experiment showed that the balloon-type stabilizer could generate load-bearing power of 500 gf. Furthermore, the manipulator could be well controlled with guidance of ultrasound images. The manipulator could minimize injure to the fetus since the area contacted with the fetus by the balloon could be well controlled.