Comparison of three techniques for calculation of target coordinates in functional stereotactic procedures

We compared three techniques of target coordinate determination for various functional stereotactic procedures. All procedures were based on preoperative MRI with contiguous 3-mm cuts. The first technique involved determination of anatomical landmarks and fiducial markers of the stereotactic frame on the monitor screen of an MRI scanner and calculation of the target point using a series of formulas; the second technique used a Leksell tabletop localizer, and the third technique is a part of 'Stealth' stereotactic navigation software. Final coordinates for the procedure were derived from all three techniques and subsequently adjusted using intraoperative electrical macrostimulation. We found that difference between techniques was on average 0.9 +/- 0.4 mm in each of three directions, and 1.8 +/- 0.9 mm in absolute distance. There were 7 cases in which one of the techniques had a discrepancy of more than 3 mm (more than 1 MRI slice thickness) compared with the other two, indicating a potential error in coordinate determination. This difference could potentially result in inappropriate placement of the electrode, thus affecting the procedure outcome. In 6 cases, such an error apparently occurred with the first or second technique of calculation. The average number of mapping trajectories decreased from 1.8 to 1.4 since this stereotactic software became a part of operative planning. We conclude that use of computerized planning software increases the precision of target coordinate calculation and improves the accuracy of functional stereotactic procedures.