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Conventional surgical tracking configurations carry a variety of limitations in line-of-sight, geometric accuracy, and
mismatch with the surgeon's perspective (for video augmentation). With increasing utilization of mobile C-arms,
particularly those allowing cone-beam CT (CBCT), there is opportunity to better integrate surgical trackers at bedside to
address such limitations. This paper describes a tracker configuration in which the tracker is mounted directly on the Carm.
To maintain registration within a dynamic coordinate system, a reference marker visible across the full C-arm
rotation is implemented, and the "Tracker-on-C" configuration is shown to provide improved target registration error
(TRE) over a conventional in-room setup - (0.9±0.4) mm vs (1.9±0.7) mm, respectively. The system also can generate
digitally reconstructed radiographs (DRRs) from the perspective of a tracked tool ("x-ray flashlight"), the tracker, or the
C-arm ("virtual fluoroscopy"), with geometric accuracy in virtual fluoroscopy of (0.4±0.2) mm. Using a video-based
tracker, planning data and DRRs can be superimposed on the video scene from a natural perspective over the surgical
field, with geometric accuracy (0.8±0.3) pixels for planning data overlay and (0.6±0.4) pixels for DRR overlay across all
C-arm angles. The field-of-view of fluoroscopy or CBCT can also be overlaid on real-time video ("Virtual Field Light")
to assist C-arm positioning. The fixed transformation between the x-ray image and tracker facilitated quick, accurate
intraoperative registration. The workflow and precision associated with a variety of realistic surgical tasks were
significantly improved using the Tracker-on-C - for example, nearly a factor of 2 reduction in time required for C-arm
positioning, reduction or elimination of dose in "hunting" for a specific fluoroscopic view, and confident placement of
the x-ray FOV on the surgical target. The proposed configuration streamlines the integration of C-arm CBCT with realtime
tracking and demonstrated utility in a spectrum of image-guided interventions (e.g., spine surgery) benefiting from
improved accuracy, enhanced visualization, and reduced radiation exposure.
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