Fluoroscopy based accuracy assessment of electromagnetic tracking

Tracking organ motion due to respiration is important to enable precise interventions in the regions of the abdomen and thorax. Respiratory induced motion in these regions may limit the accuracy of interventions which do not employ some type of tracking. One method of tracking organ motion is to use a predictive model based on external tracking that is correlated to internal motion. This approach depends on the accuracy of the model used for correlating the two motions. Ideally, one would track the internal motion directly. We are investigating the use of electromagnetically tracked fiducials to enable real-time tracking of internal organ motion. To investigate the in-vivo accuracy of this approach we propose to use stereo-fluoroscopy. In this paper we show that stereofluoroscopy is accurate enough to serve as a validation method, displaying sub-millimetric accuracy (maximal error of 0.66mm). We study the effect of the bi-plane fluoroscopes on the electromagnetic systems’ accuracy, and show that placing the bi-plane fluoroscopes in a typical intra-operative setup has a negligible effect on the tracking accuracy (maximal error of 1.4mm). Finally, we compare the results of stereo-fluoroscopy tracking and electromagnetic tracking of needles in an animal study, showing a mean (std) difference of 1.4 (1.5)mm between modalities. These results show that stereo-fluoroscopy can be used in conjunction with electromagnetic tracking with minimal effect, and that the electromagnetic system is accurate enough for motion tracking of internal organs.