Transcranial magnetic stimulation induced fields in different brain models

This paper gives a comparison of the numerical results for the induced electric field, electric current density, and the magnetic flux density inside the adult, 10-years-old, and 5-years-old homogeneous brain models, for three different transcranial magnetic stimulation (TMS) coils. The numerical results are obtained using the TMS model based on the surface integral equation formulation and efficient numerical solution via Method of Moments. The two child brain models are obtained by linearly scaling the adult brain model. The age-dependent parameters of the brain are taken into account as well. The results show that the decrease in the homogeneous brain size results in the increased values of all TMS-induced fields. Implementing the age-related parameters significantly increases the induced current density values while moving the point with half maximum electric field value closer to the surface. The analysis undertaken in this work has underlined the importance of the brain size and the brain tissue conductivity in the modeling of TMS in children. Knowledge about the differences of the TMS-induced fields in adult and child brain models could potentially contribute to development of optimal TMS coils and stimulating parameters, which is especially important when applying TMS on pediatric patients in hospitals.