| With the accelerating pace of modern social life,the incidence rate of psychiatric disorders has increased sharply.As a surgical-free and noninvasive neuromodulation technology,transcranial magnetic stimulation(TMS)has important applications in the exploration of mental disorder causes and the treatment of mental diseases.The performance of TMS system influences the effect of neural regulation.However,there are still contradictions between the existing TMS system performance level and the performance requirements of clinical application and scientific research,which are mainly reflected in: The contradiction between the realization of intracranial induced electric field the spatial distribution improvement on multiple characteristics and the inadequate optimization of the geometry of stimulation coil;The contradiction between the realization of diversied stimulation waveform,flexible stimulation parameters and the limited performance of existing TMS circuit;The contradiction between the demand of continuously workable TMS system and the intermittent mode of TMS system caused by stimulation coil temperature exceeding safety limit.Therefore,how to further improve the performance of TMS system through the research of key technologies of TMS system has important scientific research significance and clinical value.Based on extensive reading of relative literature,the key technologies of TMS system is further studied in this paper aiming to improve the performance of TMS system.The research covers following major contents: the modeling and analysis of TMS system,the study of high-performance stimulation coil,the study of diversified transcranial magnetic stimulation waveform generating circuit and the optimization design of the continuous workable TMS system.In research on TMS system modeling and analysis,for the difficulties of TMS system modeling caused by the complexity of multi physical field coupling characteristics of TMS system regarding electromagnetic,thermal,stress properties and electrophysiological characteristics of neurons,the mathematical model of the TMS stimulation coil is established with electromagnetic,thermal and stress properties,the monophasic and biphasic TMS pulse discharge circuit model are established,the dynamic neuron response model under TMS is established,which can accurately accounts for the influence of TMS system parameters on the temporal and spatial distribution characteristics of intracranial induced E-field and the change of neuron membrane potential.Considering the variability of neuron threshold,TMS closedloop control model based on neuron dynamic response is proposed,which can realize dynamic tracking of neuron membrane potential,and solve the problem that it is difficult to adjust the stimulation parameters according to neuron response in open-loop stimulation.the TMS closedloop control model is proposed based on neuron dynamic threshold prediction,which realizes dynamic tracking of neuron membrane potential and solves the problem of stimulation failure in open-loop TMS with fixed pulse width.In research on the high-performance stimulation coil: Firstly,aiming to solve the problem of insufficient stimulation intensity and unsatisfied focalization caused by traditional TMS coils,the semi-ellipse coil pair(SEP)is proposed.Under the same Joule loss,compared with the figure of eight(FOE),which is widely used in the market at present,the optimized SEP can improve the stimulation intensity and focalization in the intracranial target area by 44% and 6%,respectively.Secondly,the U-Shaped stimulation coil pair(USP)is further proposed to improve the spatial distribution characteristics of intracranial induced E-field on multi aspects.Based on the establishment of the mapping relationship between USP geometric parameters and the spatial distribution characteristics of the intracranial induced E-field,the establishment of comprehensive evaluation model of the spatial distribution characteristics of the intracranial induced E-field,the global particle swarm optimization algorithm is used to optimize the geometric parameters of USP.Under the same Joule loss,compared with FOE,the optimized USP can increase the stimulation intensity by 8.0%,the focalization by 30%,the positive and negative peak ratio(RPN)by 49%,the longitudinal attenuation performance by 8.3%,and the comprehensive performance of the intracranial induced E-field by 28%.In research on diversified transcranial magnetic stimulation waveform generating circuit,the hybrid multi waveform transcranial magnetic stimulation circuit(h TMS)based on multi module IGBT full bridge structure is proposed to meet the needs of scientific research for diversified stimulation waveform and adjustable stimulation parameters.Besides the monophasic and biphasic cosine intracranial induced E-field waveform,three new stimulation waveforms including the monophasic near rectangular,biphasic near rectangular and monophasic/biphasic ladder shape induced E-field waveform with optional amplitude and adjustable pulse width can be generated by h TMS,which breaks through the limitation of stimulation waveform types in traditional TMS system.Among the obtainable waveforms of h TMS,the biphasic four-level induced E-field(BFE)with controllable parameters is further studied as an example.The relationship between the BFE waveform parameters and the dynamic response of neurons is deeply analyzed.Results showed that under constant energy loss,compared with the commonly used monophasic and biphasic cosine intracranial induced E-field waveform,the neuron polarizability under the stimulation of BFE waveform is decreased by 54.5% and 87.5%,respectively,which could effectively enhance the neuromodulation effect and increase the stimulation selectivity.In research on the continuously workable TMS system with internal cooling,aiming to solve the problems that the stimulation coil temperature exceeds safety limit resulting in intermittent work and traditional cooling methods,such as liquid nitrogen cooling and oil immersed cooling,cause the system to be bulky and affect the flexible positioning of coils,the intercooling transcranial magnetic stimulator with low power loss(i TMS)is proposed.The optimal low power loss intercooling stimulation coil(OIC)is obtained after the establishment of the medical effect evaluation model,Joule heat model and comprehensive evaluation model.When the same medical effect is obtained,the Joule power caused by OIC is reduced by 30%.On this basis,the cooling parameters of i TMS system are optimized.Results show that when3000 effective stimulation pulses are applied continuously: the cooling performance of i TMS system is better than the TMS system with internal cooling design on the market at present(Medtronics,Cool-B65)and it proves that the i TMS can realize continuous work on the premise of ensuring medical effect. |
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