时间反演聚焦经颅磁声电刺激仿真与实验研究*

无创脑神经调控技术是生物医学领域的研究热点,经颅磁声电刺激是利用静磁场和声场的耦合而产生的感应电场作用于神经组织,对大脑的目标位置进行刺激和调控的一项技术。颅骨的存在使超声在传播过程中发生相位畸变和幅值衰减,聚焦区域偏离,难以实现精准聚焦。该文基于时间反演法,模拟颅内点声源发射脉冲以及超声传播过程,计算各个阵元接收到的时间差,按照后到先发的原则发射脉冲进行聚焦刺激。与传统相控阵聚焦相比,焦点偏移现象基本得到解决,焦域横向、纵向分辨率均有所提高,提高了声束聚焦精度和感应电场峰值。通过搭建实验平台,将两种聚焦方法所测得的声场归一化处理,验证了时间反演法能补偿焦点偏移,并通过实验证实了超声换能器声场和产生感应电场分布存在较高的一致性。基于真实颅脑结构的虚拟点源时间反演聚焦可以实现无创、精准、灵活的经颅磁声电刺激,有助于推动精准神经调控技术的发展。

Time-reversal focused transcranial magnetic acoustic electrical stimulation simulation and experimental research

Non-invasive brain nerve regulation technology has become a research hotspot in the field of biomedicine. Transcranial magnetic acoustic electrical stimulation uses the induction electric field generated by the coupling of static magnetic field and sound field to act on the nerve tissue to stimulate and control the target area of the brain. The presence of the skull causes phase distortion and amplitude attenuation of ultrasound in the propagation process, and the focus area deviates, making it difficult to achieve precise focusing. Based on the time reversal method, this paper simulates the intracranial point sound source emission pulse and the ultrasonic propagation process, calculates the time difference received by each array element, and emits pulses for focus stimulation according to the principle of last come first. Compared with the traditional phased array focusing, the focus shift phenomenon is basically solved, the focus horizontal and vertical resolution are improved, and the sound beam focusing accuracy and sound pressure intensity are also enhanced. By setting up an experimental platform and normalizing the sound fields measured by the two focusing methods, it is verified that the time reversal method can compensate for the focus shift, it demonstrates through experiments that there is a high consistency between the acoustic field of the ultrasonic transducer and the distribution of the induced electric field. The virtual point source time reversal focusing based on the real brain structure can achieve non-invasive, accurate and flexible TMAES, which promotes the development of precision neuromodulation technology.