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Fig. 2. (a) Three-dimensional virtual view displaying wall-down view of critical structures behind a white mesh overlay of surface contours. The tracked drill is shown. The virtual view updates in real time to provide a view perceptually matched to the endoscopic view. (b) Wet labo- ratory setup showing the virtual view parallel to the endoscopic monitor in addition to the triplanar views. All images update dynamically as the endoscope and drill are tracked by an image-guided surgery camera located above the display. (c) Cone-beam computed tomography used to update imaging after the initial surgical approach and before clivus ablation. This allowed refinement of the display to show more realistic surface contours. (d) Optical tracking registration markers placed on the head, endoscope, and drill. Orientation of markers was adjusted to limit line-of-sight interference.

questions on specific elements, their potential uses, and recom- mendations. A seven-point Likert questionnaire pertaining to aspects of the trial was also administered. The recorded interviews were scrutinized by three investiga- tors. Feedback was categorized, and comments on these features were documented then communicated to an independent observer. Agreement in regard to statements was reached, and these data were entered into a consensus document in subcategories. Statistical Analysis Likert questionnaire responses are displayed as medians and interquartile range (IQR). The Wilcoxon signed rank test was used to compare the paired NASA-TLX responses, with P < .05 deemed significant. RESULTS All seven participants completed the two clivus ablation exercises. A significant amount of time was allo- cated to become familiar with the navigation system and to explore its capabilities. Fiducial registration errors were consistent with current clinical practice (between 1 mm and 1.8 mm for all cases).

registration errors were calculated using a standardized paired- point algorithm. Custom navigation software, developed by our group, provided a real-time 3D virtual view that was displayed on a submonitor adjacent to the endoscopic monitor (Fig. 2a, b). 7 Surface contours were displayed as a mesh and based on intraoperative CBCT imaging (Fig. 2c). A traditional triplanar representation of the updated CT images was placed on the sub- monitor. The drill was tracked live, and its position was shown on both the virtual and cross-sectional views (Fig. 2d). Auditory feedback was provided through alarms when the tracked instru- ment (drill) entered a contoured volume representing a critical structure or a proximity alert zone. Sixteen heads were dissected in total. Two heads were dis- sected as a pilot by the investigators to establish initial labora- tory setup and fine-tune alarm and visualization settings. The seven subjects then performed an endoscopic transclival approach on two heads each; one with the LIVE-IGS system and one in a conventional manner (standard IGS involving a tracked probe and preoperative CT) in random order. The extent of dissec- tion was to each carotid artery laterally and to the dura posteri- orly. Ablation extended from the pituitary fossa down to below the level of the petrous segment of the carotid arteries. The National Aeronautics and Space Administration Task Load Index (NASA-TLX) questionnaire was administered mid- way through the exercise and again at completion. 12 Open feed- back was encouraged during the trial. After completing both dissections, a semistructured interview was carried out and recorded on video. Open responses on general use of the system and each feature were acquired prior to more in-depth

Initial Open Feedback All subjects were generally impressed by the fea- tures displayed, particularly the ability for real-time

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