Development of a Fiducial System for Registration of Stereotactic Head Frames: Process and Outcomes.

Background and objectives: It is critical to have fast and accurate intraoperative navigation coregistration between neuroimaging studies and the patient's cranial anatomy for functional neurosurgery procedures. Scalp-based laser or skull fiducial-based coregistration approaches have notable limitations. We have overcome these challenges by developing and manufacturing novel, noninvasive metal fiducial markers that attach directly to stereotactic head frames. We describe our development of fiducials, delineate our operative technique, and compare initial outcomes in targeting stereoelectroencephalography cases using fiducials for registration vs historical controls using a standard laser-based approach.

Methods: A system of 6 aluminum fiducial markers ("Felducials," named after one of the senior authors) that are hollowed out on the apex to match the robotic registration pointer probe of the ROSA robot were developed for the Cosman-Roberts-Wells® stereotactic frame and adapted to the Leksell Vantage™ frame. The operative approach involved placement of the stereotactic head frame, acquisition of intraoperative computed tomography, merging of preoperative MRI with intraoperative computed tomography, and navigation of the registration probe to each fiducial site. Root mean square coregistration accuracy and registration time were compared between patients who underwent registration with fiducials and laser.

Results: In our pilot comparison study, 32 patients underwent coregistration with our fiducials and 21 with standard ROSA laser-based methodology. Root mean square error was significantly lower in the fiducial group (0.38 ± 0.15) relative to the laser group (0.46 ± 0.12) ( P = .012). Registration time was also significantly lower in the fiducial group (6.28 ± 3.70 minutes) compared with the laser group (17.81 ± 8.99 minutes) ( P < .001).

Conclusion: Our novel noninvasive aluminum fiducial system ("Felducials") is compatible with common stereotactic head frame systems and readily adaptable to other stereotactic systems as they are developed. Registration of the ROSA ONE® Brain system using Felducials provided superior accuracy and registration time in comparison with the standard laser approach.