Frequency and Causes of Line of Sight Issues During Neurosurgical Procedures Using Optical Image-Guided Systems Amir H. Mehbodniya 1 , Mahmoud Moghavvemi 1,3 , Vairavan Narayanan 2 , Vicknes Waran 2 - BACKGROUND: Navigation (image guidance) is an essential tool in modern neurosurgery, and most surgeons use an optical tracking system. Although the technology is accurate and reliable, one often is confronted by line of sight issues that interrupt the flow of an operation. There has been feedback on the matter, but the actual problem has not been accurately quantified, therefore making this the primary aim of this study. It is particularly important given that robotic technology is gradually making its way into neurosurgery and most of these devices depend on optical navigation when procedures are being conducted. - METHODS: In this study, the frequency and causes of line of sight issues is assessed using recordings of Navigation probe locations and its synchronised video recordings. - RESULTS: The mentioned experiment conducted for a series of 15 neurosurgical operations. This issue occured in all these surgeries except one. Maximum duration of issue presisting reached up to 56% of the navigation usage time. - CONCLUSIONS: The arrangment of staff and equipment is a key factor in avoiding this issue. INTRODUCTION T he use of image guidance in today’s modern neurosurgery is essential as a component that increases accuracy and safety of surgical procedures. Image guidance is used from the most basic neurosurgical procedures (e.g., ventricular can- nulation) to complex cranial base and vascular neurosurgeries. 1-5 Image guidance today is based on either an optical or elec- tromagnetic system. 6 Optical systems are the most commonly used systems because of their earlier introduction, ease of use, and cost factor. Electromagnetic systems (despite the fact that they are more useful in some cases 7,8 ) are usually costlier and require more steps in setting up. They also encounter interference when used with or in proximity of other ferro- magnetic devices. Optical systems too encounter interference in the form of line of sight issues. 9 This can occur when the camera system loses sight of either the reference array (reference star) or the tracking array attached to instruments. In practice, this is a common problem given the presence of various other surgical tools and equipment scattered around the surgical field and surgical personnel who can get in the way. 10 Image guidanceebased neurosurgical procedures can typically be divided into 3 phases: patient registration phase, preoperative image guidance phase, and intraoperative image guidance phase. The image guidance system works by registering the preexisting radiologic images to the patients’ facial structures. During this first phase, the image guidance system is setup in the most ergonomically convenient way to ensure efficiency and safety. The optical camera must be directed to look at both the patient’s face and reference array to allow for optimal registration. In the preoperative phase, the surgeon uses image guidance to plan the surgery, including the initial incision and size of potential craniotomy. The adequacy of the position of the patient is also checked at this point. The patient is subsequently cleaned and draped for surgery. The next phase of image guidance utilization occurs intraoperatively, with drapes and surgical instruments in place, within a sterile surgical field. The line of sight issues can occur during any of these phases, but the impact of it during each phase is different. During the registration and preoperative phase, the surgeon tries to find the Key words - Line of sight issue - Optical image-guided surgery - Surgical navigation Abbreviations and Acronyms IGS: Image-guided surgery From the 1 Centre for Research in Applied Electronics, Department of Electrical Engineering, Faculty of Engineering, and 2 Department of Surgery, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia; and 3 University of Science and Culture, Tehran, Iran To whom correspondence should be addressed: Vicknes Waran, M.D. [E-mail: cmvwaran@gmail.com] Citation: World Neurosurg. (2018). https://doi.org/10.1016/j.wneu.2018.10.069 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2018 Elsevier Inc. All rights reserved. WORLD NEUROSURGERY -: e1-e6, - 2018 www.WORLDNEUROSURGERY.org e1 Original Article