Position-based adjustment of landmark-based correspondence finding in electromagnetic sensor-based colonoscope tracking method

This paper presents detailed evaluations of a colonoscope tracking method in order to clarify relationships between landmark correspondence parameters used in the method and tracking errors. Based on these evaluations, we implement a colonoscope tracking method whose correspondence finding conditions are adjusted for each position in the colon. An electromagnetic sensor-based colonoscope tracking method has been proposed. This method performs a landmark-based coarse correspondence finding and a length-based fine correspondence finding processes to find the colonoscope tip position. The landmark-based coarse correspondence finding finds corresponding landmark pairs by using distance thresholds. The distance thresholds used in the landmark-based coarse correspondence finding affects tracking errors. However relationships between the landmark-based coarse correspondence finding and tracking errors are not clarified. In this paper, we investigate the relationships between the distance threshold and tracking errors. To evaluate the tracking errors, we measure tracking errors at 52 points in the colon phantom. Based on the measurement results, we change the distance thresholds for each position in the colon phantom. The experimental results showed small distance threshold values caused smaller tracking errors. However, colonoscope tracking using small distance threshold was unstable. Large tracking errors were caused in some colon segments in the colonoscope tracking using small distance threshold.