Gaze Contingent Control for a Robotic Laparoscope Holder

Abstract

One of the main problems existing in minimally invasive surgery (MIS) is the surgeons' lack of control over the laparoscope. Typically, the laparoscope is controlled by an assistant. As the surgeon uses both of his/her hands to manipulate the instruments, he/she must verbally communicate with the assistant whenever a new segment of the surgical field needs to be seen. In light of the fact that the assistant is positioned in a different point of reference in relation to the surgeon and the surgical field is being projected remotely from the patient's body, it can be difficult for the assistant to fully understand which are of the surgical field the surgeon would like to view/focus on.To solve this problem, robotic laparoscope holders were introduced into MIS to substitute the human assistant. Examples of these robotic systems holders include the automated laparoscope system for optimal positioning (AESOP) (Computer Motion, Santa Barbara, CA, USA), EndoAssist (Armstrong Healthcare Ltd.), and freehand (Prosurgics). Their control methods include speech, gestures, and head mounted infrared (IR) emitters.However, each control interface encounters challenges in practice. For example, voice control may distract other surgical staff in the operating room. Moreover, it limits the communication of the surgeon with staff on the surgical team. IR emitter and gestures control would place more workload on the surgeon. Therefore, there is a need to develop new control methods for robotic laparoscope holders.We present a gaze control system that allows the surgeon to control a robotic laparoscope holder with his/her eye gaze. The system as shown in Figure 1 comprises a robotic laparoscope holder that is networked with an eye tracking system by a laptop.CoBRASurge (Compact Bevel-geared Robot for Advanced Surgery) [1] is used as the robotic laparoscope holder. It is based on a spherical bevel geared mechanism consisting of three gear pairs and six turning pairs. CoBRASurge creates a mechanically constrained remote center of motion (RCM) with three rotational degrees of freedom (DOFs) about the rotation center and one translational DOF passing through it. The rotation center would coincide with the surgical entry port during the surgery. A laparoscope can be fitted into the articulated mechanism using a collar. It can produce a cone workspace with 60 vertex angle and its tip locates at the incision port. There are four motors mounted on CoBRASurge, three for orientation about the center of RCM and one for the insertion-extraction of the instrument.S2 Eye Tracker (Mirametrix) is a video-based remote eye tracking system which allows a certain amount of head movement within a working volume of 25 × 11 × 30 cm3. S2 can report the gaze data at 60 Hz with an accuracy of 0.5 deg – 1 deg and draft <0.3 deg. Per-user calibration is needed to build the correlation between eye movements and gaze positions on the screen. The raw gaze data are first filtered (low pass) to reduce noise effects of drift and micro-saccades.The relation between the equipment is shown as Figure 2. A webcam with high resolution 1600 × 896 is mounted on a slender shaft acting as a laparoscope. The video stream from the laparoscope is displayed to the surgeon upon a laptop screen. The surgeon's eye gaze is recorded by the eye tracker and sent to the laptop for analysis in real-time. Any field of view on the screen that is being looked at for 2s is identified, located and assumed to be the potential view of interest (fixation) that the surgeon wants the laparoscope to focus on. An elliptical area at the screen center is defined as the surviving area. When the surgeon's gaze position falls into the elliptical area, CoBRASurge discards this gaze position and holds its position. When the reported fixation locates outside of this area, the deviation from the center of the screen to the fixation indicates the direction and the travel distance that CoBRASurge needs to move. As an additio