Orientation of Directional Deep Brain Stimulation Leads on CT: Resolving the Ambiguity

While directional deep brain stimulation (DBS) shows promising clinical effects by providing a new degree of freedom in programming, precise knowledge of the lead position and orientation is necessary to mitigate the resulting increased complexity. Two methods for orientation assessment based on postoperative CT imaging have become available, but neither of them is currently able to resolve the respective 180{degrees} artifact symmetry. Both rely on information about the intended orientation and assume that a deviation of more than {+/-} 90{degrees} is very unlikely. Our aim was to develop an enhanced algorithm capable of detecting asymmetries in the CT data and to thus eliminate the need for user interaction. Two different approaches are presented: one based on the lead markers center of mass (COM) and one based on asymmetric sampling of the markers intensity profile (ASM). Both were tested on a total of 98 scans of 2 lead phantoms, resulting in 165 measurements with a large variety of lead implantation and orientation angles. The 180{degrees} ambiguity was correctly resolved in 99.4% of cases by COM and in 96.4% of cases by ASM. These results demonstrate the substantial and currently unused asymmetry in CT and the potential for a truly automated workflow.