Magnetic coil design considerations for functional magnetic stimulation.

Area of Science:

• Biomedical Engineering
• Neuroscience
• Rehabilitation Technology

Background:

• Functional magnetic stimulation (FMS) shows promise for treating spinal cord injury by stimulating bladder, bowel, and expiratory muscles.
• A key limitation of current magnetic coils (MC) is their inability to precisely target specific tissues, often activating surrounding areas.
• Optimizing MC design is crucial for enhancing FMS efficacy and patient outcomes.

Purpose of the Study:

• To investigate governing parameters in MC design, including coil configuration, diameter, and number of turns.
• To design, construct, and evaluate novel MCs for improved focal nerve excitation.
• To determine how variations in coil parameters affect induced electric field distribution and penetration.

Main Methods:

• Designed and constructed two sets of novel magnetic coils based on a slinky coil configuration.
• Compared the focal nerve excitation capabilities of slinky coils against planar round coils.
• Systematically varied coil diameter and the number of turns per loop to assess field penetration and strength.

Main Results:

• Slinky coil designs demonstrated significantly more focalized stimulation than planar round coils.
• Primary-to-secondary peak ratios for induced electric fields in slinky coils ranged from 1.00 to 3.54.
• Larger coil diameters improved field penetration, while fewer turns per loop resulted in higher initial field strengths and sustained strength at distance.

Conclusions:

• The slinky coil design offers superior focalization for nerve stimulation compared to planar coils.
• Coil diameter and number of turns are critical parameters for optimizing MC performance in FMS.
• These findings provide a foundation for customizing MC designs for specific clinical applications and patient variability.