Table 1. A Summary of Studies Approaching DBS Lead Location and Outcome.

Author	n	Target	Objective	Findings
Walter U, et. al 2011	34	GPi, STN, Vim	To determine if transcranial B-mode sonography (TCS) is a more reliable method than MRI for locating postoperative DBS leads	TCS was not as sensitive in the antero-posterior direction and may not be as accurate as MRI or CT or MR-CT fusion [40].
Schlaier JR, et. al 2012	22	STN	To determine if the use of MER in addition to anatomical targeting would improve clinical outcomes	Intra-operative testing leads physicians to a more favorable final stimulation site than anatomic targeting alone [41].
Lalys F, et.al 2012	30	STN	To identify optimum sites for STN DBS by studying symptomatic motor improvement along with neuropsychological side effects	Suggested a more complete DBS modeling system including lead location, stimulation parameters, and clinical ratings
				Reported good motor improvement from leads located in the STN postero-superior region [42]
Paek SH, et. al 2008	53	STN	To correlate surgical outcome with STN lead position	Reported improvements in all parkinsonian symptoms in all regions of the STN [43]
Connolly PJ, et. al 2012	50	STN	To identify the active contacts and their postoperative location within the STN	Contacts 1 or 2 located in the dorsolateral STN region were active in 90% of patients who underwent DBS one-year prior.
				Stimulating at contact 1 or 2 can decrease initial programming time in the clinic [44]
Thani NB, et. al 2011	8	STN, GPi	To compare measuring lead locations on post-op CT images co-registered to intraoperative MRI versus using an MRI-directed guide tube technique	Concluded that the use of the guided tube technique is accurate in documenting the DBS lead location
				Co-registration of CT images to preoperative MRIs was also considered acceptable [38]
Shahlaie K, Larson PS, Starr PA 2011	15	STN	To study measuring lead location on intraoperative CT (iCT) fused with pre-op MRI in comparison to postoperative MRIs	Lead tip measurements were statistically indistinguishable. iCT can reduce the need for postoperative MRI and avoid the possible complications involved with it [45].
York MK, et. al 2009	18	STN	To correlate lead tip locations, surgery trajectories, and location of active contact with mental status	Declines in mental status score were found in lead locations in the frontal quadrant of both hemispheres.
				Declines in verbal learning were associated with leads that were superiorly located in the left hemisphere but were closer to the STN [46]
Gorgulho AA, et. al 2009	18	STN	To determine the coordinates of the location most likely associated with facial contraction during macrostimulation	Mean x, y, and z coordinates associated with facial contraction were found to be in close proximity to the internal capsule [47].
Pilitsis JG, et. al 2008	27	Vim	To assess if suboptimal lead location leads to loss of benefit from stimulation in patients with Vim DBS	No significant difference in lead location of those that experienced failure
				Variations in the final lead locations from targets could lead to eventual loss of stimulation efficacy
				Patients with more laterally placed leads experienced worse outcomes [48]
McClelland S 3rd, et. al 2005	26	STN	To measure variations in final lead location from target locations and how these variations impacted clinical efficacy	DBS electrodes placed within a 6 mm diameter cylinder in the predicted center of the STN were associated with similar clinical efficacy [49].
Hamid NA, et. al 2005	27	STN	To define the roles of MRI and intraoperative electrophysiological recording in targeting optimum stimulation sites	Because of anatomical variations, fixed pre-determined coordinate targets cannot be applied to all DBS cases [50].
Starr PA, et. al 2006	23	GPi	To identify electrode locations with optimal benefits in patients with dystonia	Mean lead tip and active electrode coordinates did not differ between the group with the best outcomes and the group with the worst outcomes.
				Electrodes with good outcome were near the intercommissural plane [51].

Legend: STN- subthalamic nucleus, GPi- globus pallidus internus, VIM- ventralis intermedius nucleus, MER- microelectrode location.