Thanks to recent advances in medical technology, functional endoscopic sinus surgery (FESS) can now be performed more precisely using ENT (Ears Nose Throat) surgical navigation systems. During such operations, instruments such as endoscopes, debriders and other surgical instruments are inserted through the nose to remove nasal polyps, restore drainage of paranasal sinuses and treat sinusitis.
Even with a surgeon's detailed knowledge of anatomy, however, the anatomical complications of individual patients can make performing endoscopic surgery effectively a demanding process. Needless to say, avoiding entering the brain or injuring the eye are all paramount concerns during such surgical procedures.
Hence it is vitally important that surgeons are able to visualize the location of the instruments they are deploying in the operating theater. Fortunately, several image-guided surgery systems are now available that are able to do so, providing surgeons with real time location of the tip of the surgical instruments mapped to a corresponding location in a CT image, enabling them to remove diseased tissue while avoiding critical areas.
In the past, systems used to track instruments through electromagnetic means have been complex and expensive. Now, however, engineers at Toronto-based ClaroNav Kolahi Inc. have developed a simpler form of tracking system called NaviENT that relies on optical tracking instead. The system could provide surgeons in emerging and cost sensitive markets with a new, less expensive, way to guide them during both sinus and trans-nasal skull base endoscopic surgery procedures.
According to Ahmad Kolahi, the CEO of ClaroNav Kolahi, the NaviENT system itself comprises four key components - an integrated illumination and a 3D stereo camera, a Mac Book Pro laptop for processing the data, a set of instruments with black and white checkered markers and a compact and foldable cart to position the tracking box and laptop conveniently next to endoscope monitor in the operating room. Its small footprint enables it to be deployed in any environment, including a cramped office (Figure 1).
The NaviENT system dynamically determines the position of the tip of any surgical instrument in three dimensions using an optical triangulation technique. The position of the instrument is then mapped to a corresponding location in a pre-acquired computerized tomographic (CT) scan of the patient's head. The result is that a surgeon can easily visualize the position of the instrument in the skull during surgery.
To ascertain the location of the instrument tip, the system employs a Bumblebee XB3 three-sensor multi-baseline IEEE-1394b (FireWire) stereo camera. The stereo camera features three 1.3 Mpixel progressive scan CCDs, two of which are used for acquiring left and right monochrome images with a 1280 x 960 resolution at 16 frames/sec, while the third captures an overview of the scene. The camera itself has two stereo baselines available for stereo processing - one 12 cm and one 24 cm. In the NaviENT system, the extended 24 cm baseline of the XB3 stereo camera was chosen to provide more precision at longer ranges.
In use, the XB3 camera on the system detects the location of black and white checkered patterns affixed to both the surgical instrument and on a patient tracker that is attached to the patient's forehead prior to surgery (Figure 2). The FlyCapture Software Development Kit (SDK) 2.5 running on a 64-bit version of Windows 10 is then used to acquire the images. The position of the instrument relative to the patient tracker is calculated by ClaroNav's own "Micron Tracker" proprietary optical tracking software to small fraction of a millimeter.
During typical sinus and skull base procedures, surgery is performed under low light conditions. Hence it was important to create an imaging tracking system that would be completely unobtrusive to the surgeon. To illuminate the scene, the NaviENT system uses an array of infrared LEDs mounted inside its tracking box together with the Bumblebee XB3 stereo camera. IR light projected onto the scene is then returned to the cameras which filter the light using infrared pass-band filters prior to processing.
To overlay this information on the CT image, however, it is necessary to first register the patient to the CT image. To do so, the surgeon marks a few landmark points on the CT image and then identifies the corresponding landmarks on the physical patient using NaviENT's registration pointer captured by the tracking camera. Having done so, the system can automatically generate a registration map which correlates the position of the instruments in physical space with their location in the virtual space of the CT scan.
While the stereoscopic camera in the XB3 is used to help determine the position of the instruments, the third center camera in the unit captures and displays live video to the surgery. According to Ahmad Kolahi, providing such a live image has great advantages. Notably, if the field of view of the stereoscopic camera becomes obstructed, the system will be unable to detect the position of the instruments. If this should occur, a surgeon can immediately refer to the live video feed to remove the obstruction prior to proceeding further with the surgery.
Optical tracking advantages
Uniquely, the NaviENT system can be set up for each operation in minutes while the patient undergoes anesthesia, or even in the middle of the surgery. The display used in the NaviENT system can also be used in concert with a display from an endoscope - without the need for any physical and electronic integration with the endoscope and its cart.
Unlike electromagnetic sensors, the Micron Tracker proprietary optical tracking technology used in the NaviENT system does not require wired sensors and is not affected by the presence of metallic objects and electromagnetic fields in the environment. Furthermore, unlike other existing optical tracking systems, its accuracy does not degrade when targets are partly occluded or soiled. Lastly, because the system tracks steam sterilizable permanent markers, the markers themselves do not require any maintenance or replacement.
There are other benefits too. "NaviENT has the shortest and easiest set up of any navigation device," said Kolahi. "There are no cables to connect, no spherical optical targets to mount, no head straps to wrap and no field generator to place near or below the patient's head. NaviENT's user interface is streamlined and very simple to learn, and it enables the surgeon to control the system during surgery by gesture based commands, with no assistance."
The NaviENT system itself has been in clinical trials since 2013 and has evolved significantly since then. Early in 2016, NaviENT received all technical certificates required for Health Canada and CE submission (such as 60601-1, EMC, 62471 photobiological and biocompatibility) and in April 2016 the device was approved by Health Canada for sale and marketing in Canada.
About ClaroNav Inc.
ClaroNav Inc. is dedicated to the development of surgical navigation hardware and software. Founded in 2001, as Claron Technology Inc., it has been actively involved in the development of surgical guidance technology since 2002. The ClaroNav team has developed and commercialized a range of surgical navigation systems. ClaroNav invented the MicronTracker, a unique position sensor based on visible light. MicronTracker is now utilized in Navident and other navigation systems to provide sub-millimeter accuracy in positioning surgical tools.