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Abstract：
As a noninvasive neuromodulation technique, transcranial magnetic stimulation (TMS) has important applications both in the exploration of mental disorder causes and the treatment of mental disorders. During the stimulation, the TMS system generates the intracranial time-varying induced E-field (E-field), which alters the membrane potential of neurons and subsequently exerts neural regulatory effects. The temporal waveform of the induced E-fields is directly related to the stimulation effect. To meet the needs of scientific research on diversified stimulation waveforms and flexible adjustable stimulation parameters, a novel efficient pulse magnetic stimulation circuit (the EPMS circuit) design based on asymmetric cascaded multilevel technology is proposed in this paper. Based on the transient analysis of the discharge circuit, this circuit makes it possible to convert the physical quantity (the intracranial induced E-field) that needs to be measured after magnetic stimulation into easily analyzable electrical signals (the discharge voltage at both ends of the stimulation coil in the TMS circuit). This EPMS circuit can not only realize monophasic and biphasic cosine-shaped intracranial induced E-fields, which are widely used in the market, but also realize three types of new intracranial induced E-field stimulation waveform with optional amplitude and adjustable pulse width, including monophasic near-rectangular, biphasic near-rectangular and monophasic/biphasic ladder-shaped stimulation waveform, which breaks through the limitation of the stimulation waveform of traditional TMS systems. Among the new waveforms produced by the EPMS circuit, further research was conducted on the dynamic response characteristics of neurons under the stimulation of the biphasic four-level waveform (the BFL waveform) with controllable parameters. The relationship between TMS circuit parameters (discharge voltage level and duration) and corresponding neural response characteristics (neuron membrane potential change and neuronal polarizability ratio) was explained from a microscopic perspective. Accordingly, the biological physical quantities (neuronal membrane potential) that are difficult to measure can be transformed into easily analyzable electrical signals (the discharge voltage level and duration). Results showed that compared with monophasic and biphasic cosine induced E-fields with the same energy loss, the neuron polarization ratio is decreased by 54.5% and 87.5%, respectively, under the stimulation of BFL waveform, which could effectively enhance the neuromodulation effect and improve the stimulation selectivity.
摘要：
作为一种非侵入性神经调节技术，经颅磁刺激(TMS)在探讨精神障碍的病因和治疗中都有重要的应用。在刺激过程中,TMS系统产生颅内随时间变化的诱发电场（E场），改变神经元的膜电位，随后发挥神经调节作用。诱导的电场的时间波形与刺激效果直接相关。满足科学研究对多样化的刺激波形和灵活可调的刺激参数的需求，本文提出了一种基于非对称级联多电平技术的新型高效脉冲磁刺激电路(EPMS电路)设计方案。基于放电电路的瞬态分析，该电路可以将磁刺激后需要测量的物理量(颅内感应电场)转换为易于分析的电信号(TMS电路中刺激线圈两端的放电电压)。该EPMS电路不仅可以实现单相和双相余弦型颅内诱导电场,在市场上广泛使用，而且还实现了三种类型的新型颅内诱导电场刺激波形，具有可选的幅度和可调的脉冲宽度，包括单相近矩形，双相近矩形和单相/双相梯形刺激波形，突破了传统TMS系统刺激波形的局限性。在EPMS电路产生的新波形中，进一步研究了参数可控的双相四电平波形(BFL波形)刺激下神经元的动态响应特性。从微观角度解释了TMS电路参数（放电电压水平和持续时间）与相应的神经响应特征（神经元膜电位变化和神经元极化率）之间的关系。因此，难以测量的生物物理量（神经元膜电位）可以转化为易于分析的电信号（放电电压水平和持续时间）。结果表明，与单相和双相余弦诱导的E场相比，具有相同的能量损失，神经元极化率分别下降54.5%和87.5%,分别,在BFL波形的刺激下，能有效增强神经调节效果,提高刺激选择性。
