Introduction: The accuracy of frameless stereotactic method, with bone fiducials, is 1.26mm in phantom studies and 3.1 mm in the clinical situation. This has been shown to be equivalent to the stereotactic frame. The next steps in the evolution of frameless technology are to eliminate the 3 mm error as well as the need for the application of bone fiducials or the stereotactic frame. The mobile Oarm Imaging System is a multi-dimensional surgical imaging platform developed for spine surgery. This study reports on the accuracy of the Oarm for registration and the reliability of intracranial device locations taken during surgery.

Methods: In this study 40 frameless DBS procedures were completed using intra-operative O-arm scans. The locations of 6 bone fiducials are indicated on the preoperative CT as well as on the intra-operative Oarm images. These locations are matched with the real world fiducials on the patient's head during the registration process. The accuracy of the registration is assessed by using the N drop 1 method. Five fiducials are employed in the registration process and the 6th fiducial is employed as a target. The location of presumed stationary objects on subsequent scans was assessed.

Results: We were able to identify significant deviations of the microelectrode and DBS as it exited a cannula 20 mm above the planned target. The Oarm was able to demonstrate a clinically significant reduction in this deviation when using a 10 mm above cannula. There was a small degree of variability in the location of fixed objects from scan to scan which can be attributed to error in identification of the object, pneumocephalus, and head motion. The ability of enhanced mode images to replace a preoperative CT for registration will be discussed.

Conclusions: The addition of Oarm imaging to DBS surgery was useful and may lead to a more comfortable and accurate procedure

Patient Care: The goals of this research are to improve patient comfort when undergoing DBS surgery and the accuracy of the procedure.

Learning Objectives: By the conclusion of this session, the participant should be able to understand 1) the utility and the 2) limitations of Oarm imaging during DBS surgery.

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