Tracking endoscopic instruments without a localizer: a shape-analysis-based approach.

We present an approach to localizing endoscopic instruments with respect to the camera position, based purely on processing of the endoscope image. No localizers are needed; the only requirement is a colored strip at the distal part of the instrument shaft to facilitate image segmentation. The method exploits perspective image analysis applied to the cylindrical shape of the instrument shaft, allowing measurement of the instrument position and orientation with five degrees of freedom. We describe the method theoretically, and experimentally derive calibration curves for tuning the parameters of the algorithm. Results show that the method can be used for applications where accuracy is not critical, such as workspace measurement, gesture analysis, augmented-reality guidance, telementoring, etc. If this method is used in combination with an endoscope tracker or a robotic camera holder, full localization with respect to the patient reference frame can be achieved.