Intracranial image-guided neurosurgery: Experience with a new electromagnetic navigation system

Background. The aim of image-guided neurosurgery is to accurately project c omputed tomography (CT) or magnetic resonance imaging (MRI) data into the o perative field for defining anatomical landmarks, pathological structures a nd tumour margins. To achieve this end, different image-guided and computer -assisted, so-called "neuronavigation" systems have been developed in order to offer the neurosurgeon precise spatial information. Method. The present study reports on the experience gained with a prototype of the NEN-NeuroGuard (TM) neuronavigation system (Nicolet Biomedical, Mad ison, WI, USA). It utilises a pulsed DC electromagnetic field for determini ng the location in space of surgical instruments to which miniaturised sens ors are attached. The system was evaluated in respect to its usefulness, ea se of integration into standard neurosurgical procedures, reliability and a ccuracy. Findings. The NEN-system was used with success in 24 intracranial procedure s for lesions including both gliomas and cerebral metastases. It allowed re al-time display of surgical manoeuvres on pre-operative CT or MR images wit hout a stereotactic frame or a robotic arm. The mean registration error ass ociated with MR was 1.3 mm (RMS error) and 1.5 mm (RMS error) with CT-data. The average intra-operative target-localising error was 3.2 mm (+/-1.5 mm SD). Thus, the equipment was of great help in planning and performing skin incisions and craniotomies as well as in reaching deep-seated lesions with a minimum of trauma. Interpretation. The NEN-NeuroGuard (TM) system is a very user-friendly and reliable tool for image-guided neurosurgery. It does not have the limitatio ns of a conventional stereotactic frame. Due to its electromagnetic technol ogy it avoids the "line-of-sight" problem often met by optical navigation s ystems since its sensors remain active even when situated deep inside the s kull or hidden, for example, by drapes or by the surgical microscope.