Background: Intraoperative navigated ultrasonography has reached clinical acceptance, while published data for the accuracy of some systems are missing. We technically quantified and optimised the accuracy of the integration of an external ultrasonography system into a BrainLab navigation system.
Methods: A high-end ultrasonography system (Elegra; Siemens, Erlangen, Germany) was linked to a navigation system (Vector Vision; BrainLab, Munich, Germany). In vitro accuracy and precision was calculated from differences between a real world target (high-precision crosshair phantom) and the ultrasonography image of this target in the navigation coordinate system. The influence of the intrinsic component of the calibration phantom (for ultrasonography probe registration), type of target definition (manual versus automatic) and orientation of the ultrasound probe in relation to the navigation tracking device on accuracy and precision were analysed in different settings (100 measurements for each setting) resembling clinically relevant scenarios in the neurosurgical operating theatre.
Results: Line-of-sight angles of 45°, 62° and 90° for the optical tracking of the navigated ultrasonography probe and a distance of 1.8 m revealed best accuracy and precision. Technical accuracy of the integration of ultrasonography into a standard navigation system is high [Euclidean error: median, 0.79 mm; mean, 0.89 ± 0.42 mm for 62° angle; median range: 1.16-1.46 mm; mean range (±SD): 1.22 ± 0.32 mm to 1.46 ± 0.55 mm for grouped analysis of all angles tested]. Software-based automatic target definition improved precision significantly (p < 0.001).
Conclusions: Integration of an external ultrasonography system into the BrainLab navigation is accurate and precise. By modifying registration (and measurement conditions) via software modification, the in vitro accuracy and precision is improved and requirements for a clinical application are fully met.
Keywords: Accuracy; Brain; Intraoperative; Navigation; Ultrasonography.