3D position estimation of flexible instruments: marker-less and marker-based methods.

Objective: Endoscopic images can be used to allow accurate flexible endoscopic instrument control. This can be implemented using a pose estimation algorithm, which estimates the actual instrument pose from the endoscopic images.

Methods: In this paper, two pose estimation algorithms are compared: a marker-less and a marker-based method. The marker-based method uses the positions of three markers in the endoscopic image to update the state of a kinematic model of the endoscopic instrument. The marker-less method works similarly, but uses the positions of three feature points instead of the positions of markers. The algorithms are evaluated inside a colon model. The endoscopic instrument is manually operated, while an X-ray imager is used to obtain a ground-truth reference position.

Results: The marker-less method achieves an RMS error of 1.5, 1.6, and 1.8 mm in the horizontal, vertical, and away-from-camera directions, respectively. The marker-based method achieves an RMS error of 1.1, 1.7, and 1.5 mm in the horizontal, vertical, and away-from-camera directions, respectively. The differences between the two methods are not found to be statistically significant.

Conclusions: The proposed algorithms are suitable to realize accurate robotic control of flexible endoscopic instruments, enabling the physician to perform advanced procedures in an intuitive way.