Title : Electromagnetic - thermal dosimetry of the human brain - Application

1. WM topic and description Transcranial magnetic stimulation (TMS) is a non-invasive and painless technique for stimulation or inhibition of certain brain regions. A stimulating coil placed near the surface of a patient's head is energized by a very short current pulse, generating the time varying magnetic field of high intensity penetrating into nearby tissues such as skull and brain. According to differential form of Faraday's law, the time varying magnetic field gives rise to the electric field, thus depolarizing or hyperpolarizing the neuronal cell membranes located within a few centimeters of the cortex. When membrane depolarization reaches certain threshold, the action potential is generated. Macroscopically, brain activation occurs in the regions with the highest values of the induced electric field [1]-[4]. TMS has become a valuable tool in not only the study of specific cortex areas, but also in diagnostics and for therapeutic purposes. In addition to the treatment of depression, which is so far the most commonly studied application of TMS, this technique is applicable in treating various other neurological and psychiatric disorders. Although TMS is a widely used technique, some more research is still to be done, such as the development of highly sophisticated methods to determine the distribution of the electromagnetic fields induced in the human brain. Modeling of brain stimulation is important for not only to determine the exact location and the level of stimulation, but also to clarify the related underlying mechanisms. Numerical modeling is necessary to provide plausible interpretation of the experimental results and to design efficient stimulation systems, such as multi coil designs for focused and deep brain stimulation [5] –[7]. Also, it is a well established fact that the principal biological effect of high frequency EM radiation is predominantly thermal in nature [8]-[10]. If the total power absorbed by the body is high enough, it may break down the protective thermoregulatory mechanisms. These harmful effects can be quantified by the analysis of the body thermal response or the thermal increase in a particular organ can be considered [11]. In addition to modeling the thermal response of the human brain exposed to undesired electromagnetic radiation, the thermal model of the brain can be used elsewhere, e.g. to investigate the effects of the targeted brain hypothermia [12], [13], the thermal effects due to the deep brain stimulation [53], or can even aid in modeling the temperature regulation in the brain during the functional …