The application accuracy of a skull-mounted trajectory guide system for image-guided functional neurosurgery

Objective: Frameless image guided systems have traditionally been perceived as being less accurate than stereotactic frames, limiting their adoption for trajectory-based procedures such as deep brain stimulator placement which require submillimetric accuracy. However, some studies have suggested that high degrees of accuracy are attainable with optical localization systems. We evaluated the application accuracy of a skull-mounted trajectory guide coupled to an optical image-guided surgery system in a laboratory setting. Materials and Methods: A plastic skull phantom was fitted with five fiducial markers rigidly attached via self-drilling bone screws. Varying MRI and CT imaging protocols were obtained at 25 different centers. A metal disc marked in 1-mm increments was placed at the expected target point. Following registration and alignment of the trajectory guide, radial and depth localization errors were measured. A total of 560 measurements were obtained and detailed statistical analyses were performed. Results: Mean localization error was 1.25 mm with a 95% confidence interval of 2.1 mm and a 99.9% confidence interval of 4.0 mm. These values were significantly lower than those published for the two most widely used frame systems (p < 0.001). Conclusions: Accuracy of image-guided localization using a rigid trajectory guide can meet or exceed that achievable with a stereotactic frame.