Technique for the localization of intracranially implanted electrodes

Clinical article

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Object

The anatomical localization of electrodes in the human brain is important for the interpretation of pathophysiological (epileptifom spikes, seizures) and functional data (stimulation mapping, evoked potentials). Electroencephalography and evoked potentials are volume-conducted field effects that are most easily interpreted with knowledge of the location and topology of adjacent structures, and brain stimulation techniques produce current fields whose effects are highly dependent on the geometry of electrode assemblies in relation to adjacent structures. In this paper, the authors describe a straightforward method for implanted electrode localization, and detail their experience to date with the technique.

Methods

The described method is based on the coregistration of preoperative MR imaging studies with postimplant CT scans by using standard mutual information optimization of rigid body transformation of the CT to the MR image. Fused images of the MR and thresholded CT images are derived, and electrodes are visualized using various standard computer projections, renderings, and measurement tools.

Results

The authors have successfully used the described method over an extended period to localize electrode contacts in intracranial implants for seizure localization, and in long-term implants for movement disorders and seizure control. The accuracy of localization is very good, although it is dependent on image quality and possible brain shift between acquisition of the CT and MR images.

Conclusions

This method is easily implemented and is useful for a wide variety of clinical and research applications. It is a straightforward process to extend it to additional image modalities that are emerging for surgical planning and image guidance.

Abbreviation used in this paper: EEG = electroencephalography.

Article Information

Address correspondence to: Terrance M. Darcey, Ph.D., Sections of Neurology and Neurosurgery, Dartmouth-Hitchcock Medical Center, 1 Medical Center Drive, Lebanon, New Hampshire 03756. email: tdarcey@dartmouth.edu.

Please include this information when citing this paper: published online January 29, 2010; DOI: 10.3171/2009.12.JNS091678.

© AANS, except where prohibited by US copyright law.

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Figures

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    Illustrations of fused MR/CT images and visualization. Panels A and B show maximum intensity projections of postimplant CT scans, in which the platinum electrode contacts are clearly seen and in high contrast to other elements of the image. The remaining panels show the visualized electrodes as typically seen for neocortical grids and strips (D), interhemispheric grids (E), and depth electrodes (C and F).

References

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    Darcey TMJobst BCThadani VMManem SWilliamson PDRoberts DW: Motor cortex mapping at the bedside in patients with implanted electrodes using high-frequency pulse train stimulation and EMG pickup. Epilepsia 45:Suppl 759602004. (Abstract)

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    Studholme CHill DLGHawkes DJ: Automated three-dimensional registration of magnetic resonance and positron emission tomography brain images by multiresolution optimization of voxel similarity measures. Med Phys 24:25351997

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    Studholme CNovotny EZubal IGDuncan JS: Estimating tissue deformation between functional images induced by intracranial electrode implantation using anatomical MRI. Neuroimage 13:5615762001

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