Research On Optimization Theory And Method Of Transcranial Magnetic Stimulation System

With the rapid development of global economy and society,the stress of people's life is increasing,and the incidence of organic/functional brain diseases is also rising,which leads to more and more serious social problems.As a non-invasive neuromodulation technique,transcranial magnetic stimulation(TMS)generates alternative induction electromagnetic fields that can directly interfere with the electrical properties of the subject's intracranial stimulation target area,thereby activating or inhibiting brain tissue.TMS is also widely applied in the treatment of various psychiatric and neurological disorders caused by intracranial lesions.In recent years,with the rapid advancement of TMS in medical field,the performance of TMS systems has also been subject to higher requirements.In this paper,in order to improve the overall performance of TMS system,the optimization theory and method of TMS system are explore to investigate how to optimize the temporal distribution characteristics of intracranial electrical signals,improve the spatial distribution characteristics of intracranial induced electric field,extend the continuous operation time and enhance the treatment effects.The main works are summarized as follows.In terms of improving the TMS waveform characteristics,the TMS stimulation waveform optimization and regulation method is proposed from the perspective of improving the energy utilization efficiency of the TMS system and optimizing the intracranial electrical signal time distribution characteristics.On the one hand,a coupling model of neuronal cell membrane potential-stimulation waveform-coil vibration energy/heat loss is established based on the TMS stimulation waveform characteristics,and the preferred TMS stimulation waveform is solved on the basis of waveform parametric modeling and optimization algorithm to reduce the coil's vibration energy and heat loss.On the other hand,a tunable TMS pulse generation circuit topology is designed,and the corresponding circuit topology parameters and control strategy are derived for the desired stimulation waveform using a nonlinear least squares trust domain algorithm,which provides a theoretical basis for meeting diverse stimulation requirements.As for the optimization of the TMS core coil design,the TMS thin core coil structure and optimization design method is put forward from the point of improving the spatial distribution characteristics of the intracranial induced electric field of conventional TMS coils.First,the effects of the length,width and thickness of the thin core on the spatial intensity of the intracranial induced electric field Emax,the focality performance of the coil S1/2 and the heating ratio of the core coil Hratio are qualitatively analyzed,after which a multi-objective optimization model for the design of the thin core coil is established,and the heat loss of the core coil is reduced.In addition,an experimental test platform for TMS thin core coils is built and an induction field detection method based on circular detection coils is designed as well,which provides the correctness of the optimized TMS thin core coil design method and verifies the improvement of the coil performance.For the synergistic optimization of TMS system,considering the coupling effects between the spatial distribution characteristics of the intracranial induced electric field generated by the TMS coil and the temporal distribution characteristics of the intracranial electric signal generated by the stimulation waveform on the final stimulation effect,a synergistic optimization method that integrates the TMS stimulation waveform and the core coil structure is adopted.First,the relationship among the stimulation waveform,the thin core coil and the energy loss and time/space distribution characteristics of the system is investigated,and an optimization model is established to take both the spatial and temporal distribution characteristics of TMS into consideration.Furthermore,in terms of the clinical application characteristics of TMS,a posteriori TMS system decision scheme based on the improvement of hierarchical analysis is developed,which can combine the advantages of subjective human judgment and objective judgment to filter and decide on the solution sets of multiple optimization objectives,and finally obtain the optimal TMS system co-design under different TMS application scenarios.In terms of the reduction of the impulse noise of TMS,the noise suppression method of TMS system is applied to address the problem of subject discomfort caused by impulse noise.Firstly,the association between pulsed electromagnetic force and noise is analyzed according to the working mechanism of TMS,the mechanism of TMS pulsed noise generation is elaborated,a TMS noise propagation model is established,and the propagation law of TMS pulsed noise is derived.What's more,by profiling the actual acquired TMS pulse noise signal and combining the clinical treatment law of repetitive transcranial magnetic stimulation,an active noise reduction method that is applicable to TMS is formed,and it can ensure the accuracy and synchronization of the secondary acoustic wave output and realize the adaptive matching of noise,so as to achieve a good noise reduction effects and improve the system stability.Most importantly,the optimal allocation scheme of secondary acoustic sources to achieve spatial range noise reduction is established,and the construction of spatial active quiet zone is formed as well.