Assessing the error between the actual versus ideal STN-DBS electrode location.An example of the fused preoperative MRI and postoperative CT for a single patient with two electrodes implanted in the STN region. The nominated, ideal location to apply DBS in the dorsal STN is marked in red. The location of the electrode trajectory at this axial slice is defined by the electrode artefact occurring on CT (hyperintense voxels). The electrode location error is the straight-line (Euclidean) distance between the actual electrode trajectory versus the nominated, ideal location to apply DBS, as indicated by the blue arrows and measured in millimeters. A = Anterior, P = Posterior, L = Left, R = Right.