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Reprinted by permission of Laryngoscope. 2014; 124(4):853-859.

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Augmented Real-Time Navigation With Critical Structure Proximity Alerts for Endoscopic Skull Base Surgery

Benjamin J. Dixon, MBBS; Michael J. Daly, MSc; Harley Chan, PhD; Allan Vescan, MD; Ian J. Witterick, MD; Jonathan C. Irish, MD

Objectives/Hypothesis: Image-guided surgery (IGS) systems are frequently utilized during cranial base surgery to aid in orientation and facilitate targeted surgery. We wished to assess the performance of our recently developed localized intrao- perative virtual endoscopy (LIVE)-IGS prototype in a preclinical setting prior to deployment in the operating room. This sys- tem combines real-time ablative instrument tracking, critical structure proximity alerts, three-dimensional virtual endoscopic views, and intraoperative cone-beam computed tomographic image updates. Study Design: Randomized-controlled trial plus qualitative analysis. Methods: Skull base procedures were performed on 14 cadaver specimens by seven fellowship-trained skull base sur- geons. Each subject performed two endoscopic transclival approaches; one with LIVE-IGS and one using a conventional IGS system in random order. National Aeronautics and Space Administration Task Load Index (NASA-TLX) scores were docu- mented for each dissection, and a semistructured interview was recorded for qualitative assessment. Results: The NASA-TLX scores for mental demand, effort, and frustration were significantly reduced with the LIVE-IGS system in comparison to conventional navigation ( P < .05). The system interface was judged to be intuitive and most useful when there was a combination of high spatial demand, reduced or absent surface landmarks, and proximity to critical struc- tures. The development of auditory icons for proximity alerts during the trial better informed the surgeon while limiting distraction. Conclusions: The LIVE-IGS system provided accurate, intuitive, and dynamic feedback to the operating surgeon. Further refinements to proximity alerts and visualization settings will enhance orientation while limiting distraction. The system is currently being deployed in a prospective clinical trial in skull base surgery. Key Words: Image-guided surgery, endoscopic surgery, surgical navigation, virtual endoscopy, skull base surgery, pituitary surgery. Laryngoscope , 124:853–859, 2014

INTRODUCTION Endoscopic skull base surgery can be technically demanding and requires a continuous appreciation of the surrounding critical structures. 1 Individual anatomic variations, pathologic processes, and tissue ablation for

surgical access can distort or remove landmarks, making navigation in this complex three-dimensional (3D) envi- ronment more difficult. Image-guided surgery (IGS) sys- tems are routinely used in many institutions to aid in orientation and facilitate precise, targeted surgery. 2 The cranial base is relatively rigid due to its bony composi- tion, and limited soft tissue deformation occurs during surgery. This allows image registration to be accurate and reliable, especially around the bone–soft-tissue junction. Various advanced display and feedback options have been developed for IGS systems, but routine clini- cal implementation of these features is rarely accom- plished. Enhanced visualization through virtual views and augmented reality, as well as novel auditory alerts, are among the advancements under investigation. 3–6 Improved computer processing speeds allow these fea- tures to be presented effectively in real time with mini- mal temporal delay. 7 One of the main barriers to clinical implementation is the lack of human factors research focusing on the human–computer interface. 8 The Guided Therapeutics program at the University Health Network, Toronto has developed a localized intra- operative virtual endoscopy IGS system (LIVE-IGS), which incorporates dynamic 3D virtual views, live tool tracking, and critical structure proximity alert zones. 7

From the Department of Otolaryngology–Head and Neck Surgery, University of Toronto ( B . J . D ., I . J . W ., J . C . I .); Department of Surgery, Univer- sity of Melbourne, St. Vincent’s Hospital and Peter MacCallum Cancer Institute, Melbourne, Australia ( B . J . D .); Ontario Cancer Institure ( M . J . D ., H . C .); Institure of Medical Science, Princess Margaret Hospital, Univer- sity of Health Network ( M . J . D .); Department of Otolaryngology–Head and Neck Surgery, Mount Sinai Hospital ( A . V ., I . J . W .); Department of Surgical Oncology ( I . J . W ., J . C . I .), Toronto, Canada Editor’s Note: This Manuscript was accepted for publication August 12, 2013. Presented at the North American Skull Base Society Meeting, Las Vegas, Nevada, U.S.A., February 18, 2012. This work was supported by the Guided Therapeutics Program at the University Health Network, including the Kevin and Sandra Sulli- van Chair in Surgical Oncology, Hatch Engineering Fellowship Fund, RACH Fund, and Princess Margaret Hospital Foundation. Wet laboratory instruments and devices were supplied by Karl Storz Endoscopy Canada and Medtronic of Canada. The authors have no other funding, financial relationships, or con- flicts of interest to disclose. Send correspondence to Jonathan C. Irish, MD, 610 University Avenue, 3–954, Toronto, ON M5G 2M9, Canada. E-mail: jonathan.irish@uhn.on.ca

DOI: 10.1002/lary.24385

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