Navigated Bronchoscopy With Electromagnetic Tracking — Cone Beam Computed Tomography Influence on Tracking and Registration Accuracy

Current image guidance systems for bronchoscopy are limited to the diagnosis of small tumors and placing fiducials for radiation therapy and surgery. Ideally, a navigation system should be useable for the range of bronchoscopic procedures, including therapy with concurrent radiology imaging for control. As most guidance systems rely on electromagnetic (EM) fields, it is advised to leave the C-arm mounted fluoroscopy unit outside the operating field during navigation. We have assessed the accuracy of our research navigation platform, containing an EM field generator and a C-arm fluoroscopy unit. We have simulated a regular bronchoscopy session with an initial image-to-patient registration procedure, and a subsequent bronchoscopy with the C-arm inside the EM field. The registration accuracy was significantly influenced, introducing an error that may be carried through to the bronchoscopy procedure. During the bronchoscopy session, the C-arm caused a wave drift in the tracking positions and distorted the EM field, causing a translation error up to 22 mm. Even by averaging out the drift, there was a systematic shift in the x, y, and z positions. The errors were more evident in some C-arm positions and seem to be linked more to the electrical current in the fluoroscopy unit than the metallic C-arm itself. A fluoroscopy unit may be used during a navigation procedure, but care must be taken. To enable real-time navigation, the C-arm could be removed sufficiently from the EM tracking field or correction schemes must be implemented to compensate for the distortions.