Increasing the accuracy of 3D EEG implantations

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OBJECTIVE

The accuracy of stereoelectroencephalography (SEEG) electrode implantation is an important factor in maximizing its safety. The authors established a quality assurance (QA) process to aid advances in implantation accuracy.

METHODS

The accuracy of three consecutive modifications of a frameless implantation technique was quantified in three cohorts comprising 22, 8, and 23 consecutive patients. The modifications of the technique aimed to increase accuracy of the bolt placement.

RESULTS

The lateral shift of the axis of the implanted bolt at the level of the planned entry point was reduced from a mean of 3.0 ± 1.6 mm to 1.4 ± 0.8 mm. The lateral shift of the axis of the implanted bolt at the level of the planned target point was reduced from a mean of 3.8 ± 2.5 mm to 1.6 ± 0.9 mm.

CONCLUSIONS

This QA framework helped to isolate and quantify the factors introducing inaccuracy in SEEG implantation, and to monitor ongoing accuracy and the effect of technique modifications.

ABBREVIATIONS EP = entry point; iEP = implemented EP; IQR = interquartile range; iTP = distal contact of the implanted electrode; M1, M2, M3 = method 1, method 2, method 3; NHNN = National Hospital for Neurology and Neurosurgery; pTP = planned TP; QA = quality assurance; SEEG = stereoelectroencephalography; TP = target point.

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  • Supplementary Material (PDF 448 KB)

Article Information

Correspondence Roman Rodionov: UCL Queen Square Institute of Neurology, University College London, United Kingdom. roman.rodionov@gmail.com.

INCLUDE WHEN CITING Published online May 17, 2019; DOI: 10.3171/2019.2.JNS183313.

Disclosures Collaborative support was received from Medtronic Ltd in the form of an S7 StealthStation planning computer (on loan).

© AANS, except where prohibited by US copyright law.

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Figures

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    The geometric model of implantation accuracy (parameters P1 to P5; see details in the text) shown using the projections of the planned trajectory and the implanted bolt. Figure is available in color online only.

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    Summary statistics (median, IQR, minimum/maximum, and outliers) for 6 parameters describing the M2 (red bars) and M3 (blue bars) techniques: P1 (lateral shift of iEP from planned trajectory), P2 (lateral shift of pTP from bolt axis), P3 (angle between planned trajectory and bolt axis), P4 (lateral shift of iTP from bolt axis assessing the amount of bending), P5 (deviation to the depth along the planned trajectory), and integral parameter (distance between iTP and pTP). Vertical axis = mm, except for P3 (degrees). + = outliers. * Statistical significance (unpaired Wilcoxon rank-sum test) of the difference for the corresponding pair. Whiskers = either minimum/maximum value in the corresponding sample if there are no outliers, or limits of the range at Q3 + 1.5 × IQR or Q1 – 1.5 × IQR when there are values beyond these limits. IQR = Q3 (75th percentile) − Q1 (25th percentile). The limits marked by whiskers are analogous to approximately ± 2.7 (SD) and 99.3% coverage if the data were normally distributed. Figure is available in color online only.

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    Graph showing the relationship between bending of the electrodes (parameter P4, vertical axis, mm) and distance that the inserted stylet was short of the pTP (horizontal axis, mm), based on 129 recorded values. Red dots = electrodes sampling lateral and middle orbitofrontal cortex (R = 0.91, p < 0.01); blue dots = all other electrodes. Figure is available in color online only.

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    Graph showing the relationship between the intracranial length of the implanted electrode (horizontal axis, mm) and the electrode bending measured at its distal contact (parameter P4, vertical axis, mm) for 63 electrodes when the stylet was advanced close to the TP (less than 6 mm; green rhomboids) and 46 electrodes when the stylet was more than 10 mm from the TP (blue squares) in the M3 cohort. Red line = maximal possible contribution of the stylet deviating from the bolt axis due to wobble of the stylet within the bolt. Figure is available in color online only.

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    Relationship between the bolt axis and the planes’ trajectory (vertical axis) and between the bolt axis and the skull surface (horizontal axis) in the M3 cohort. Orange dots = anterior temporal lobe electrodes; blue dots = all other electrodes. Figure is available in color online only.

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