Bronchoscope tracking without fiducial markers using ultra-tiny electromagnetic tracking system and its evaluation in different environments

This paper presents a method for bronchoscope tracking without any fiducial markers using an ultra-tiny electromagnetic tracker (UEMT) for a bronchoscopy guidance system. The proposed method calculates the transformation matrix, which shows the relationship between the coordinates systems of the pre-operative CT images and the UEMT, by registering bronchial branches segmented from CT images and points measured by the UEMT attached at the tip of a bronchoscope. We dynamically compute the transformation matrix for every pre-defined number of measurements. We applied the proposed method to a bronchial phantom in several experimental environments. The experimental results showed the proposed method can track a bronchoscope camera with about 3.3mm of target registration error (TRE) for wood table environment and 4.0mm of TRE for examination table environment.