Abstract
In recent years, magnetic stimulation has emerged as a useful method for stimulating nerves in clinical site, because magnetic stimulation is noninvasive and less painful than electric stimulation. In magnetic stimulation, it is important to estimate induced currents produced in a volume conductor. It is, however, difficult to predict distributions of induced currents in an inhomogeneous medium like as the human brain. There is no paper has shown the accurate distributions of induced currents in such that medium. In this paper, we measured spatial distributions of currents generated in the tank model of an assumed human brain filled with saline solution, when the tank model was exposed to pulsed magnetic fields. We used a commercial magnetic stimulator. The induced currents were measured with a current probe which is made of ultra-mini coaxial cable. We discussed the focality of the induced current and an effect of dura on the induced current in the vicinity. In the half-spherical tank, the part of the cross section of figure-of-8 coil becomes the point of highest current density, while the part corresponding to an edge of a coil also becomes the point of higher current density. In the tank with skull, the distribution of the current is also compressed near the bone and the current flows along the surface of inside skull. The value of current density perpendicular to the skull decreases about 20%. On the other hand, the current density perpendicular to the dura decreases about 15% rather than without dura.
