Finite Element Modeling And TMS Electromagnetic Field Analysis For Real Head Model

As a noninvasive,painless,safe and reliable new medical technology,transcranial magnetic stimulation(TMS)has been widely used in many medical fields and clinical research.Using TMS,the time-varying low-frequency pulsed magnetic field is stimulated to central nervous tissue,an induced electric field is generated,and the current is caused to conduct in the biological tissue,which change the action potential of cerebral cortex neurons and affect brain metabolism and neural electrical activity.The construction of the real brain finite element model is a key step of TMS simulation,and it is also an important prerequisite for the computation of TMS electromagnetic field and energy field distribution.In TMS the main work of this thesis is as follows.Firstly,the simple TMS model of 8-shaped coil and single layer sphere head model are simulated by COMSOL Multiphysics 5.3 software.The corresponding electrophysiological parameters of the model are set up to verify the feasibility of the conventional finite element method for the TMS stimulation model.Then,according to our group’s research on the classification of magnetic resonance imaging(MRI)images,three-dimensional brain model is established on the basis of the segmentation of scalp,skull,cerebrospinal fluid,gray matter and white matter tissue images.Especially for the gray matter,about 150 matrices are drawn into two-dimensional pictures using programming software.After introducing them into the medical image processing software and using image segmentation and image smoothing methods,a gray matter three-dimensional visualization model is obtained which lay a foundation for mesh generation.Finally,the above geometry is imported into the multi-physics modeling software COMSOL Multiphysics 5.3,and the geometric structure parameter of the 8-shaped stimulation coil is added to construct the real brain finite element model.The information of the magnetic field and the stimulated coil is added,and the electromagnetic field of the TMS model is analyzed.In this thesis,a simple head model and a real brain model are constructed respectively as the TMS simulation model.It can be seen that the different current magnitudes and different distances between the brain and the coil have different effects on the brain.In addition,the coils are stimulated on different positions(prefrontal and parietal)of the brain model,and the similar magnetic field effects are obtained.The work of this thesis is conducive to the clinical application of TMS.