Neuronavigation and surgery of intracerebral tumours.

Approximately four decades after the successful clinical introduction of framebased stereotactic neurosurgery by Spiegel and Wycis, frameless stereotaxy emerged to enable more elaborate image guidance in open neurosurgical procedures. Frameless stereotaxy, or neuronavigation, relies on one of several different localizing techniques to determine the position of an operative instrument relative to the surgical field, without the need for a coordinate frame rigidly fixed to the patients' skull. Currently, most systems are based on the optical triangulation of infrared light sources fixed to the surgical instrument. In its essence, a navigation system is a three-dimensional digitiser that correlates its measurements to a reference data set, i.e. a preoperatively acquired CT or MRI image stack. This correlation is achieved through a patient-to-image registration procedure resulting in a mathematical transformation matrix mapping each position in 'world space' onto 'image space'. Thus, throughout the remainder of the surgical procedure, the position of the surgical instrument can be demonstrated on a computer screen, relative to the CT or MRI images. Though neuronavigation has become a routinely used addition to the neurosurgical armamentarium, its impact on surgical results has not yet been examined sufficiently. Therefore, the surgeon is left to decide on a case-by-case basis whether to perform surgery with or without neuronavigation. Future challenges lie in improvement of the interface between the surgeon and the neuronavigator and in reducing the brainshift error, i.e. inaccuracy introduced by changes in tissue positions after image acquisition.

The analysis of intraoperative neurosurgical instrument movement using a navigation log-file.

BACKGROUND: The purpose of this study was to define the technical requirements of future (tele)robotic neurosurgical systems. We aimed to analyse the movements of surgical instruments during neurosurgical procedures. METHODS: A commercially available neuronavigation system (StealthStation TREON(plus), Medtronic, USA) was used to determine the position and orientation of the surgical instrument. A custom-made log-mode was implemented in the software to file instrument coordinates intraoperatively. Data was collected during the debulking of malignant primary brain tumours, temporal epilepsy surgery and skull base tumour surgery. RESULTS: Maximum tip displacement velocity varied, per procedure, in the range 6.6-12.7 cm/s and maximum rotational speed 21-40 degrees/s. Maximum instrument orientation differences within the volume of movement varied. The largest differences were detected during temporal epilepsy surgery (73 degrees and 52 degrees in the coronal and axial planes, respectively), while the smallest differences were detected in the debulking of an intraventricular tumour. CONCLUSIONS: In this study, we have demonstrated the feasibility of motion analysis in image-guided neurosurgery. To mimic ordinary open neurosurgery, future neurosurgical (tele)robotic systems should at least support translational speeds up to 12.7 cm/s, rotational speeds up to 40 degrees/s and differences in instrument orientation of up to 73 degrees.