Evaluation of the tip-bending response in clinically used endoscopes

Abstract

Background and study aims: Endoscopic interventions require accurate and precise control of the endoscope tip. The endoscope tip response depends on a cable pulling system, which is known to deliver a significantly nonlinear response that eventually reduces control. It is unknown whether the current technique of endoscope tip control is adequate for a future of high precision procedures, steerable accessories, and add-on robotics. The aim of this study was to determine the status of the tip response of endoscopes used in clinical practice.

Materials and methods: We evaluated 20 flexible colonoscopes and five gastroscopes, used in the endoscopy departments of a Dutch university hospital and two Dutch teaching hospitals, in a bench top setup. First, maximal tip bending was determined manually. Next, the endoscope navigation wheels were rotated individually in a motor setup. Tip angulation was recorded with a USB camera. Cable slackness was derived from the resulting hysteresis plot.

Results: Only two of the 20 colonoscopes (10 %) and none of the five gastroscopes reached the maximal tip angulation specified by the manufacturer. Four colonoscopes (20 %) and none of the gastroscopes demonstrated the recommended cable tension. Eight colonoscopes (40 %) had undergone a maintenance check 1 month before the measurements were made. The tip responses of these eight colonoscopies did not differ significantly from the tip responses of the other colonoscopes.

Conclusion: This study suggests that the majority of clinically used endoscopes are not optimally tuned to reach maximal bending angles and demonstrate adequate tip responses. We suggest a brief check before procedures to predict difficulties with bending angles and tip responses.

Fig. 1

A set of antagonist cables running from the navigation wheel (left) to the bent tip (right).

Fig. 2

In-hospital example of setup for hysteresis measurement: 1, motor module; 2, computer; 3, remote drive unit connected to the navigation wheels of a conventional endoscope; 4, camera capturing images of the endoscope tip; 5, light studio to prevent shadow formation from the hovering tip.

Fig. 3

Nonlinearity in the endoscope tip response. The tip is angulated in alternating up-and-down directions, with increasing bending angles. I. Cable pulling starts in neutral position. II. Tip starts bending. III. Tensed cable is released. IV. Tip starts to relax and return to straight position. V. Pulling the antagonist cable. VI. Tip follows the antagonist cable.

Fig. 4

Parameters describing nonlinearity: A, virtual play up/right cables; B, cable slackness; C, virtual play down/left cables.

Fig. 5

Hysteresis plot of a gastroscope with well-tensed (dotted lines) and loose (solid lines) cables. The maximal width is increased with loose cables.