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EM vs optical tracking based neuronavigation
During neuronavigation, the 3D positions and angles of the TMS coil, a digitizing stylus and the head of the patient typically must be known at all times. Position tracking of coil, head and stylus can be performed either using optical position tracking with large cameras on a stand, or electromagnetic (EM) position tracking based on a DC pulsed magnetic field emitted by a small box. In the field of Neurosurgery, where the principle of frameless stereotactic neuronavigation was invented decades ago, both optical and EM tracking techniques are around for a long time, and have proven their worth. They are found to be equally accurate in larger studies (Koivukangas T, Katisko JP, Koivukangas JP, 2013 & Ricci WM, Russell TA, Kahler DM, Terrill-Grisoni L, Culley P, 2008). Especially EM tracking offers several advantages, and is currently popular in neurosurgical navigation applications requiring high precision and reliability. One of the main advantages of EM navigation is the lack of so called ‘line-of-sight occlusion’, or the inability to track and navigate when the cameras view is blocked, for example by the arms of a person using the equipment. This is known to be a real nuisance for optical navigation. Another advantage is the compact nature of EM position tracking, no big camera stand is needed, and sensors are much smaller as well. The DC pulsed EM navigation that neurosurgeons use often, and is also used in our navigation system for TMS, is very robust, as it does not induce so called ‘Eddy currents’ in metals that otherwise would cause distortions. The material used inside a TMS coil does not pose any problem for EM position tracking based on DC pulses.
We therefore opted to use reliable DC pulsed EM tracking for TMS neuronavigation as well, and many users around the globe have been successfully using our navigation system since 2011. The system was originally developed and rigorously tested at Utrecht University Medical Center in the Netherlands.
Of course a magnetic pulse generated by a TMS coil very briefly interferes with EM position tracking nearby the TMS coil, for about 1 millisecond. This brief distortion is detected in real time and removed by the Neural Navigator proprietary and well tested algorithms. This allows seamless position tracking of coil and head even during high frequency rTMS and even theta burst TMS protocols.
Hence, you can rest assured that our reliable and proven EM tracking based neuronavigation technology for TMS will serve all your needs. You cannot block its view as for optical tracking based neuronavigation, and you save a lot of space in your treatment rooms.
- Koivukangas T, Katisko JP, Koivukangas JP. Technical accuracy of optical and the electromagnetic tracking systems. Springerplus. 2013, 2(1):90.
- Ricci WM, Russell TA, Kahler DM, Terrill-Grisoni L, Culley P. A comparison of optical and electromagnetic computer-assisted navigation systems for fluoroscopic targeting. Journal of Orthopaedic Trauma. 2008; 22(3):190-4.