  This paper reports a detailed evaluation results of a colonoscope tracking
method. A colonoscope tracking method utilizing electromagnetic sensors and a
CT volume has been proposed. Tracking accuracy of this method was evaluated by
using a colon phantom. In the previously proposed paper, tracking errors were
measured only at six points on the colon phantom for the accuracy evaluation.
The point number is not enough to evaluate relationships between the tracking
errors and positions in the colon. In this paper, we evaluated the colonoscope
tracking method based on more detailed measurement results of the tracking
errors. We measured tracking errors at 52 points on the colon phantom and
visualized magnitudes of the tracking errors. From our experiments, tracking
errors in the ascending and descending colons were enough small to perform
colonoscope navigations. However, tracking errors in the transverse and
descending colons were large due to colon deformations.
