gms | German Medical Science

Objective: Goal of this study was to evaluate and optimize the technical accuracy for integration of a commercially available ultrasonography system into a navigation platform including specific technical settings relevant in the surgical situation.

Method: A phased array probe (7.5 PL 13; Sonoline Elegra, Siemens) was rigidly fixed to a position tracker (PT) of a neuronavigation platform (NP) (Vector Vision, BrainLab). Registration was performed using BrainLab’s standard reference phantom (RP) (Phantom A) or a modified RP (Phantom B). Distances (1.8m) and line-of-sight angles (45°, 62°, 90°) between the Infra-Red navigation camera (IR) (Polaris, Northern Digital) and the ultrasonography (US) PT were modified in different settings for comparison. The accuracy of the integration of the US probe was defined as the spatial difference (x, y, z axes, Euclidean distance) between the real world target and its US images within the NP using a high-precision multiple cross-wire test phantom. Moreover, the influence of software modifications on test accuracy was analyzed. Each group of tests comprised 100 measures.

Results: Testing the Euclidian distance (ED) as a degree of correctness of the combined settings 45°, 1.8m and 62°, 1.8m revealed no significant differences (p=0.07; VV cranial 7.5). Software-based target identification within the US image (VV cranial 7.81) significantly enhanced precision of the test procedure. The highest accuracy was determined as 0.82mm ± 0.1mm (ED) at 62° angle and 1.8m distance to the IR camera. A recalibration procedure significantly reduced accuracy to 1.58mm ± 0.15mm (p < 0.01, ED). Modification of the RP (Phantom B) revealed reduced accuracy for the setting 62°, 1.8m (Phantom A: 0.82mm ± 0.1mm, Phantom B: 1.79mm ± 0.43mm, p < 0.01) but improved accuracy for the setting 45°, 1.8m (Phantom A: 1.42mm ± 0.18mm, Phantom B: 0.96mm ± 0.33mm, p < 0.001).

Conclusions: The optimal distance and angle between IR and PT is 1.8m and 62° to 45°. Integration of the US probe into the tested navigation platform could be realized with submillimeter accuracy (as low as 0.82mm ± 0.1mm). This result supports the concept of integration of an external US platform into neuronavigation. Furthermore, it gives way for studies on the clinical intraoperative accuracy. Together with the improvements of US imaging, this high accuracy allows for the correction of brain shift by morphing preoperative images on intraoperative US imaging. The clinical accuracy of this technical support awaits evaluation.