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Transcranial MEP threshold voltages and current densities simulated with finite element modelling
Lanjun Guo1, Enock Boakye2, Rosalind J Sadleir2
1Department of Surgical Neurophysiology, University of California - San Francisco, San Francisco, CA, USA.
Summary
The linked quadripolar (LQP) montage requires the lowest stimulation threshold for transcranial motor evoked potentials (tcMEPs). Finite element modeling shows cortical geometry primarily influences current distribution, not electrode montage.
Area of Science:
- Neuroscience
- Biomedical Engineering
- Neurosurgery
Background:
- Transcranial motor evoked potentials (tcMEPs) are crucial for monitoring motor pathways during neurosurgery.
- Optimizing tcMEP stimulation requires understanding electrode montage effects on current delivery and thresholds.
Purpose of the Study:
- To compare stimulation thresholds and brain current densities for tcMEPs using linked quadripolar (LQP), M3-M4, and C1-C2 electrode montages.
- To investigate the influence of electrode montage on current distribution in the motor cortex.
Main Methods:
- Twenty-five patients undergoing cerebral vascular surgery with tcMEP monitoring were studied.
- tcMEP voltage thresholds were compared across LQP, M3-M4, and C1-C2 montages.
- Finite element models (FEM) simulated current densities in hand, arm, and leg regions of interest (ROIs) at tcMEP thresholds.
Main Results:
- LQP montage showed the lowest tcMEP voltage thresholds for both hand (61.5 V) and foot (95.2 V) stimulation.
- M3-M4 and C1-C2 montages required significantly higher thresholds.
- FEM simulations indicated that cortical geometry, rather than electrode montage, predominantly determined local current density distribution in the motor cortex.
Conclusions:
- The LQP montage is most efficient for tcMEP stimulation, requiring lower voltage thresholds.
- FEM simulations suggest that the inherent resistance to current flow in specific cortical regions, influenced by geometry, plays a key role in determining tcMEP thresholds across different montages.
