A method for bronchoscope tracking using position sensor without fiducial markers

This paper proposes a method for tracking a bronchoscope using a position sensor without fiducial markers. Recently, a very small electromagnetic position sensor has become available that can be inserted into the bronchoscope's working channel to obtain bronchoscope camera motion. To develop a navigation or guidance system using position sensor, it is necessary to obtain an alignment between the coordinate systems of an actual patient's body and the reference image. Most tracking methods compute the alignment using the positions of fiducial markers attached to an actual patient's body. However, it requires measurement of fiducial marker positions on both the actual patient's body and the reference image. To solve such time consuming task, this paper proposes a method for bronchoscope tracking without fiducial markers that estimates a transformation matrix between the actual patient's body and the CT image. We employ ICP-based approach for this estimation. The alignment is calculated using the correspondences between the sensor outputs and the bronchial region extracted from the CT image. We applied the proposed method to a rubber bronchial phantom. Experimental results showed that average target registration error was about 3.0 mm at minimum. Also, the proposed method could track a bronchoscope camera in real-time.