# Validation of an RF Image System for Real-Time Tracking Neurosurgical Tools
###### Abstract  
A radio frequency (RF)-based system for surgical navigation is presented. Surgical navigation technologies are widely used nowadays for aiding the surgical team with many interventions. However, the currently available options still pose considerable limitations, such as line-of-sight occlusion prevention or restricted materials and equipment allowance. In this work, we suggest a different approach based on a microwave broadband antenna system. We combine techniques from microwave medical imaging, which can overcome the current limitations in surgical navigation technologies, and we propose methods to develop RF-based systems for real-time tracking neurosurgical tools. The design of the RF system to perform the measurements is shown and discussed, and two methods (Multiply and Sum and Delay Multiply and Sum) for building the medical images are analyzed. From these measurements, a surgical tool's position tracking system is developed and experimentally assessed in an emulated surgical scenario. The reported results are coherent with other approaches found in the literature, while overcoming their main practical limitations. The discussion of the results discloses some hints on the validity of the system, the optimal configurations depending on the requirements, and the possibilities for future enhancements. microwave-based medical image; real-time tracking; RF antenna system; surgical navigation 20222223845 2022223845 2022223845 2022223845 2022223845 2022223845 2022223845 2022223845 2022223845 202223845 2022223845 202223845 202223845 20222 cameras placed at a convenient position (usually attached to the ceiling of the room). By triangulation calculations, the camera system can compute the spatial coordinates of the detected markers, associated to the tool's coordinates. The markers may be either passive (e.g., near-infrared reflectors) or active (e.g., LEDs). In recent years, these systems have been combined with augmented reality (AR) tools to provide more immersive handling during surgical navigation and training of medical procedures [2], and even for marker-less surgical guiding approaches [3]. Despite the progresses, challenges such as misalignments between the physical and the virtual objects are still to be faced [4], as well as inaccuracies during the intra-operative AR-based navigation [5]. These systems can provide highly accurate surgical tool tracking [6; 7], but they have the drawback of requiring direct line-of-sight contact with the markers [8]. If a body (someone from the staff) or an object (another tool, a piece of equipment, etc.) hinders this contact, the track is lost, in addition to other specific limitations associated to intra-operative imaging resolution [9] and misalignments between pre-operative and intra-operative images and tracking [10]. A couple of examples of these systems currently available in the market are the Polaris(r) system from NDI [11] or the custom systems based on OptiTrack Motion Capture [12]. The electromagnetic trackers provide a solution for the direct line-of-sight requirement. In this case, the markers are made of ensembles of small sensor coils usually housed in a small case, again attached to the point to be tracked. The tracker is available to detect the spatial location of these markers due to the variations in the electromagnetic field caused by their interaction with the field. This detection can be made even when there is no direct line-of-sight between the tracker and the marker [13], thereby allowing free movements of the surgical team, and making them suitable for operations with minimal incision. However, these systems show two main drawbacks. Firstly, their effective action field is considerably reduced in comparison with the optical ones [14], and their application is limited to operations involving small areas, such as otorhinolaryngological ones.