Evaluating the efficiency of stimulators used in magnetic stimulation of the spinal cord

This paper aims in evaluating the efficiency of magnetic stimulators capable of stimulating neural tracts of the spinal cord in healthy subjects. Our previous preliminary tests had shown that the commercial clinical magnetic stimulator Magstim Rapid2 was unable to activate nerve structures located in the spinal cord, with its maximum deliverable energy. In this study we evaluate the characteristics of magnetic stimulators designed and tested (by modelling) for this specific application and we show that the circular commercial coil is the most efficient applicable shape, and no improvements could be gained by changing the distribution of the windings of the magnetic coils. The main conclusion of the study was that a much higher initial voltage should be loaded by the stimulator's capacitor in order to achieve activation of neural tracts within the spinal cord.