A Real-Time Endoscope Motion Tracker

Abstract

Objective: In colonoscopy, it is desirable to accurately localize the position of the endoscope's distal tip. Current tip localization techniques are not sufficient for recording the position and movement of the tip, nor is its rotation measured. We hypothesize that integration of multiple tracking modalities can effectively record the endoscope's motion in real time and continuously corrects cumulative errors.

Methods: A dual modality tracking method is developed to measure the motion of the endoscope's insertion tube in real time, including insertion length, rotation angle, and their velocities. Optical trackballs were used to measure the endoscope insertion tube's motion and cameras were used to correct cumulative errors.

Results: The accuracy of insertion length and rotational angle were measured. For speeds ≤ 10 mm/s, the median and 90th percentile insertion position errors were 0.88 mm and 2.2 mm, respectively. The insertion position error increases with the speed, reaching a maximum of 10 mm for speeds < 40 mm/s. 11° and 21° were the median and 90th percentile rotation angle errors for angular speeds < 40°/s. Cumulative errors are sufficiently reduced by the imaging modality.

Conclusion: The prototype device can precisely measure an unmodified endoscope's position, rotation, and motion in real time without significant accumulative error. The prototype device is small and compatible with existing commercial endoscopes as an add-on accessory, which could be used for reporting, localizing the lesions in follow up procedures, operational guidance, quality assurance, and training. Clinical and Translational Impact Statement-This preclinical research develops an endoscope tracker that can be integrated into colonoscopy training, automatically record endoscope motion, and be further developed to improve polyp and tumor localization during colonoscopy.

Keywords: Colonoscopy; endoscopes; medical devices; motion measurement; real-time systems.

FIGURE 1.

Side view schematic of the sensor cuff and endoscope. Positive position is directed into the page and positive rotation is clockwise.

FIGURE 2.

Photograph of the endoscope motion tracker prototype with a gastroscope inserted. The endoscope’s position (insertion length) increases when it is moved towards the right as it passes through the sensor cuff.

FIGURE 3.

Interior photograph of the sensor cuff with the top housing appearing above the bottom housing. The color-coded circles show how the corners correspond to each other and to Fig. 2. The positive position axis for the bottom trackball is upwards in this figure.

FIGURE 4.

Still images taken by the leader and follower cameras. Both images show the white line (green box) marking the 50 cm position. The black gap in the 50 cm line (orange box) is also shown. The gap is located at a positive (CW) angle relative to the center of the leader image. The images also partially show the two ‘50’ number markings on the gastroscope.

FIGURE 5.

Positional error (blue line) and average velocity (orange x) results. The arrows show the direction of insertion or withdrawal in each plot. Zero white line features were missed during these trials.

FIGURE 6.

Positional error is plotted versus average velocity for each translation in Groups 1–3. The piecewise trend line is shown in purple.

FIGURE 7.

Rotational error and average rotational velocity are plotted versus the rotational ground truth. The arrows show the direction of CW or CCW rotation in each plot. In (a), zero black line gap features were missed. Whereas in (b), three black line gap features were not correctly detected when they crossed the center (vertically) of the leader or follower images.