Research On Novel Coil Design And Optimization Algorithm Based On Transcranial Magnetic Stimulation

Transcranial Magnetic Stimulation(TMS)is a new technology for the diagnosis and treatment of mental and neurological diseases,which is safe and non-invasive.As an important part of the TMS system,the stimulation coil indirectly generates an induced electric field at the target point of the brain,thereby changing the excitability of the nervous tissue.Among the main performance evaluation indexes of TMS,the most critical is to improve focality.The coil with high focality can reduce the bad influence on the non-target area.Based on the basic theory of electromagnetic field,a new type of three-layer figure-of-8 coil is designed in this paper,which has stronger focality,achieves a further balance between focus and stimulation depth,and improves the effectiveness and safety of TMS treatment.First of all,this paper proposes a new three-layer figure-of-8 coil based on the principle of magnetic field superposition and cancellation and the structure of the standard figure-of-8 coil.Compared with other coils,three-layer figure-of-8 coil obtains a smaller focusing area and stronger stimulation intensity at the cost of a reduced stimulation depth.In order to improve the balance between the focality and the depth of stimulation,this article has obtained many different types of three-layer figureof-8 coils by changing the rotation angle along the middle tangent and the size of unit coils where in the upper and lower.In this paper,a three-layer figure-of-8-A coil with relatively optimal performance is selected according to the conditions.Compared with the figure-of-eight coil,the stimulation intensity of the coil is increased by 33.92%,the focusing area is reduced by 25.43%,and the stimulation performance is significantly improved.Next,in order to further optimize the focality of the three-layer figure-of-8-A coil quickly and effectively,this paper proposes a new improved PSO algorithm with three improved strategies based on the particle swarm optimization(PSO).The three improvement strategies are: changing the speed update formula,adopting dynamic multi-group-von Neumann structure and increasing mutation strategy.This paper selects 10 test functions as the experimental objects.The results show that the new improved PSO algorithm has higher convergence accuracy and stronger continuous optimization ability.Then the algorithm is used to optimize the input current parameters.Compared with before optimization,the focusing area of the coil after optimization can be reduced by 7.3%,and the stimulation depth can be increased by 3.4%.It shows the optimized three-layer figure-of-8-A coil has further improved the balance of focality and stimulation depth.Finally,in order to further verify the therapeutic effect of the three-layer figure-of-8 coil,this article changes the ball head model to a complex real head model structure which is more in line with the actual situation.By comparing the stimulation performance of different coils in the real head model,the results verify the stimulation advantages of the optimized three-layer figure-of-8-A coil,and also prove the correctness of the simulation based on the ball head model.The new three-layer figure-of-8 coil has strong focality.Its longitudinal multilayer arrangement provides a new idea for the design of coils and promotes the development of TMS.Aiming at the optimization of focality,this paper proposes a new and improved PSO algorithm,which further deepens the application of the algorithm in the TMS field.