Coil Efficiency for Inductive Peripheral Nerve Stimulation

Abstract

Magnetic stimulation of peripheral nerves is evoked by electric field gradients caused by high-intensity, pulsed magnetic fields created from a coil. Currents required for stimulation are very high, therefore devices are large, expensive, and often too complex for many applications like rehabilitation therapy. For repetitive stimulation, coil heating due to power loss poses a further limitation. The geometry of the magnetic coil determines field depth and focality, making it the most important factor that determines the current required for neuronal excitation. However, the comparison between different coil geometries is difficult and depends on the specific application. Especially the distance between nerve and coil plays a crucial role. In this investigation, the electric field distribution of 14 different coil geometries was calculated for a typical peripheral nerve stimulation with a 27 mm distance between axon and coil. Coil parameters like field strength and focality were determined with electromagnetic field simulations. In a second analysis, the activating function along the axon was calculated, which quantifies the efficiency of neuronal stimulation. Moreover, coil designs were evaluated concerning power efficacy based on ohmic losses. Our results indicate that power efficacy of magnetic neurostimulation can be improved significantly by up to 40 % with optimized coil designs.

Multi-objective optimization method for coil current waveform of transcranial magnetic stimulation

“…It can be found that the Joule heating is less than the reference full-sine, but the vibration energy is much larger. However, one peak of the optimized waveform might be obviously larger than the opposite peak if the Joule heating is taken as the optimization objective only [ 19 ].…”

“…To deal with the problem of coil heat, some scholars have improved the efficiency of stimulation by changing the coil structure such as modifying the geometry [ 19 ] or adding iron-core to reduce the heat generation [ 20 , 21 ]. In addition, Ref.…”

Helical Hyperbolic Magnetic Field in Nerves, when they Act as Current Conductors

“…Axon polarization is dependent on the properties of the magnetic field (i.e., orientation to the axon, magnitude, and frequency), its geometry (i.e., axon radius, membrane thickness), and its electrical properties (i.e., conductivity, dielectric permittivity) [7]. The distance between the nerve and the coil plays a crucial role [8]. All of the above also depends on the characteristics of the magnetic field of the nerve itself, knowledge of which is the objective of this work.…”

“…A nerve has a electromagnetic field, which can be modified when another external electromagnetic field is applied in therapy. Numerous studies have been done to see if an electromagnetic pulse could regenerate injured peripheral nerves [1][2][3][4][5][6][7][8][9][10][11]. The results indicate that electromagnetic therapy increases the number of motor neurons to restore proper connections in the injured peripheral nerve [1,10].…”

Parameters for magnetic stimulation of the phrenic nerve

“…In order to simulate under the most realistic conditions possible, we conducted previous experiments with wires leading in and out of the coil [73]. However, we found that this approach leads to almost identical E-fields in the region of interest, and thus only increases the computation time unnecessarily.…”