Development and testing of implanted carbon electrodes for electromagnetic field mapping during neuromodulation

Abstract

Purpose Deep brain stimulation electrodes composed of carbon fibers were tested as a means of administering and imaging magnetic resonance electrical impedance tomography (MREIT) currents. Artifacts and heating properties of custom carbon‐fiber deep brain stimulation (DBS) electrodes were compared with those produced with standard DBS electrodes. Methods Electrodes were constructed from multiple strands of 7‐μm carbon‐fiber stock. The insulated carbon electrodes were matched to DBS electrode diameter and contact areas. Images of DBS and carbon electrodes were collected with and without current flow and were compared in terms of artifact and thermal effects in phantoms or tissue samples in 7T imaging conditions. Effects on magnetic flux density and current density distributions were also assessed. Results Carbon electrodes produced magnitude artifacts with smaller FWHM values compared to the magnitude artifacts around DBS electrodes in spin echo and gradient echo imaging protocols. DBS electrodes appeared 269% larger than actual size in gradient echo images, in sharp contrast to the negligible artifact observed in diameter‐matched carbon electrodes. As expected, larger temperature changes were observed near DBS electrodes during extended RF excitations compared with carbon electrodes in the same phantom. Magnitudes and distribution of magnetic flux density and current density reconstructions were comparable for carbon and DBS electrodes. Conclusion Carbon electrodes may offer a safer, MR‐compatible method for administering neuromodulation currents. Use of carbon‐fiber electrodes should allow imaging of structures close to electrodes, potentially allowing better targeting, electrode position revision, and the facilitation of functional imaging near electrodes during neuromodulation.

Neurosurgical Implant Safety in 7 T MRI: A Scoping Review

“…Implantable DBS leads and electrodes were imaged in two studies, and one study reported following ASTM International standards. All components had temperature increases <1 °C when tested in phantom models 28,29 . Ashok Kumar et al imaged carbon electrodes and reported a lower temperature increase of 0.1 °C compared to 0.9 °C when traditional platinum‐iridium electrodes were used 29 …”

“…All components had temperature increases <1 °C when tested in phantom models 28,29 . Ashok Kumar et al imaged carbon electrodes and reported a lower temperature increase of 0.1 °C compared to 0.9 °C when traditional platinum‐iridium electrodes were used 29 …”

Deep brain stimulation: Challenges at the tissue‐electrode interface and current solutions

“…With MREIT, DBS current flow and electric field distributions can be measured, providing information about stimulation through target tissues and around brain structures. This information could then be used to further our understanding of the mechanisms underlying DBS 16 …”

“…Pulse generators that have the ability to modify the pulse width are available in newer models and compatible electrodes 13 . The amplitude is easier to manipulate with most IPGs, and is tuned to the range of 1 V to 5 V 16 . Increased amplitude does not result in higher clinical benefit, but decreased pulse width can increase the therapeutic window.…”

“…Carbon fiber electrodes are promising for neural recording because they demonstrate fewer MRI artifacts, improve magnetic field homogeneity, and induce a smaller temperature change in MR environments than Pt–Ir electrodes. They have been used successfully for treatment of patients with epilepsy 16 . Additionally, carbon fiber electrodes are smaller in diameter, 4–7 microns, compared to Pt–Ir electrodes; thus, they may decrease glial encapsulation while still being electrically conductive.…”