Mechanical accuracy of a new stereotactic guide

Abstract

Objective: A new stereotactic guide using a navigational computer is developed for stereotactic procedures. In order to compare the mechanical accuracy of the guide to frame based systems, an error analysis study was designed.

Methods: A biopsy procedure was simulated using a phantom model. Targets with known co-ordinates in a three-dimensional Cartesian co-ordinate system were positioned inside the skull model. A biopsy needle was inserted along computer set trajectories from three different entry points. The position of the biopsy needle in the co-ordinate system was measured. Distance from needle tip to target was calculated and defined as the error of the system for each trial. The results were statistically analyzed for precision and biasedness.

Results: A total of 242 accuracy measurements (182 on two MRI scans, 60 on one CT scan) were carried out. Mean incision length along the trajectories was 59 mm. Mean error using MRI scans was 3.8 mm and for the CT scan 2.9 mm. The error of the stereotactic computer was found to be 1.0 mm with both MR and CT imaging. The main cause of error for the MRI based trials was distortion of the magnetic field.

Conclusion: The results indicate a stereotactic system with high degree of accuracy. This is confirmed by a clinical study of 39 biopsies where all tumours were reached. MRI affected the mechanical accuracy significantly due to distortion of the magnetic field. The accuracy is comparable to other studies performed on both stereotactic computers and frame based systems.