Objective: The precision in implantation of deep brain stimulation (DBS) electrodes based on pre-operative MRI planning is of utmost importance for the success of this therapy. By fusion of preoperative MRI and postoperative CT the deviation of the implanted electrode compared to the planning should be identified.

Methods: Out of a consecutive series of 72 patients operated by DBS for movement disorders between April 2013 and February 2015, bilateral electrode placement was investigated in 46 patients. Target and trajectory planning was executed on MRI scans based on anatomical landmarks. For surgical implantation a contrast enhanced stereotactic CT was fused with the MRI. As micro-recording and -stimulation with up to 5 micro-electrodes per side was performed first and could lead to deviation from the anatomically planned path on physiological grounds, only those 43 electrodes at 31 different patients were selected for evaluation where the central trajectory was selected for final electrode placement. Post-operative CT was performed at identical stereotactic principles as before surgery, but without any stereotactic frame and was fused to the pre-operative stereotactic CT and MRI. In the stereotactic planning programme, distances of electrode trajectories and tips to planned trajectories and targets could be measured in all planes.

Results: The average deviation of the centre of the final electrode to the planned position was 0.94 mm in anterior-posterior and medio-lateral direction (SD 0.85 mm). There was a significant difference of deviation data between the first and the second implanted side (Wilcoxon-Test: level of significance of 0.002). On the left side (implanted first) the mean deviation was 0.64 mm and on the right side 1.29 mm.

Conclusions: Image fusion methods applied in this analysis were identical to those for the stereotactic procedure. The mean deviation of 0.94 mm is below the diameter of a DBS electrode and below the distance to the surrounding micro-electrodes speaking in favour of adequate precision of the established stereotactic implantation procedure. The significant difference between first and second implantation side is important when choosing the surgical sequence and is most likely reflecting the progressive intra-operative brain shift during the procedure.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/evaluation-of-the-accuracy-of-stereotactic-dbs-electrode-implantation-by-post-operative-image-fusion/