Estimation of Induced Eddy Current in the Brain and Characteristics of Nerve Excitation by Magnetic Stimulation

点击翻译按钮获取中文摘要

In recent years, the contactless and non-invasive magnetic stimulation is used to diagnose the function of nerve in the clinical application. In magnetic stimulation, it is important for clarifying the location of nerve excitation to estimate the distributions of induces eddy current in a living body. It is, however, difficult to predict distributions of induced eddy currents in an inhomogeneous medium like as the humanbrain. In order to investigate the characteristics of induced eddy currents in the cranium, the distributions of induced eddy current in the simple cranium model which is filled with the saline solution was measured by the probe made of a thin flexible mini coaxial cable. Moreover, the estimation of the stimulated point in the nerve was performed by using the nerve muscle model of a bull frog's sciatic nerve.The purpose of this study is to find out the distributions of induced eddy current generated in the cranial model filled with the saline solution, when the model was exposed to pulsed magnetic fields. We discussed the relationship between a focality of the induced eddy currents and an excited location in the head due to the orientation of the coil. As a result, the distribution of induced eddy current depends on the structure of boundary of the skull or narrow space. This experiment showed that the highest density of induced eddy currents provided a result when the current flowed in the vicinity of the rear edge of foramen occipitale magnum. The intensity of induced eddy currents at the foramen magnum differs a little due to the direction of current flow. From the results of the nerve muscle model in the internal acoustic meatus by the magnetic stimulation, it is showed that the nerve is easy to be stimulated at where the change of induced eddy current density is very large or the nerve is bent in the finite medium, for example an arm tank model.