Research On The Focusing Method Of Transcranial Magneto-acousto-electrical Stimulation Based On Time Reversal

Noninvasive regulation of brain function is of great significance in the diagnosis and treatment of neuropsychiatric diseases.Transcranial magneto-acousto-electrical stimulation(TMAES)as a new non-destructive method of brain nerve stimulation,acts on nerve tissue through ultrasound and magnetic field together,and then generates induction current to achieve the regulation of the target brain area,which has the advantages of high spatial resolution and good stimulation depth.At present,in the process of transcranial magneto-acousto-electrical stimulation,ultrasonic unit transducer and collimator are used to focus the acoustic field.The lack of focusing activity limits the controllability of the key stimulation parameter,the induced current,and further affects the overall stimulation effect.In this paper,the time inversion method is used to focus the sound field with phased array transducer,which increases the induced current control mode and improves the flexibility of tmaes stimulation.The main research work includes the following parts:1.The principle of transcranial magneto-acousto-electrical stimulation is discussed.The mechanism of magnetoacoustic coupling effect is studied.According to acoustic wave equation and Helmholtz Kirchhoff integral theorem,the calculation method of sound field in different focusing modes is analyzed.This paper enumerates the common ultrasonic focusing methods at home and abroad,including self focusing of single vibrator,focusing of transducer equipped with acoustic lens and electronic focusing of phased array,compares the advantages and disadvantages of different focusing methods and their respective focusing principles,introduces the basic idea and implementation steps of time inversion focusing method,and provides theoretical basis for later research.2.The focus area evaluation method of transcranial magneto-acousto-electrical stimulation is established,and the focus depth,stimulation intensity,focus width,focus depth and deflection angle are determined as the evaluation indexes of focus characteristics to measure the focus level of acoustic field and induced electric field.The sound field distribution of plane probe,self focusing probe and phased array probe are calculated respectively,and the influence of ultrasonic frequency,transducer size,transducer structure,emission waveform,deflection angle and other factors on the focusing characteristics are explored.3.According to the CT scanning data of rats,the head model of rats with real brain structure and anatomical characteristics was reconstructed.The distribution of intracranial sound field and electromagnetic field was solved by the finite element method.Based on the model,the single point focusing of super sound was carried out by the time inversion method of phased array combined with virtual point source,and the distribution of intracranial sound field was solved according to the acoustic characteristics of real brain It compensates for the shift of focus caused by skull.The results show that the phased array ultrasonic transducer has obvious advantages over the traditional single element transducer,which can greatly improve the flexibility and controllability of stimulation.In the actual stimulation experiment,the appropriate transducer array parameters should be selected according to the stimulation requirements.The distortion and attenuation caused by the skull of the rat can not be ignored,which will lead to the displacement of the target and the actual target.The virtual point source time inversion phased array focusing method based on the real head model of the rat can adaptively compensate for the displacement of the focus,which is helpful to promote the development of the accurate brain control technology of transcranial magneto-acousto-electrical stimulation.