Department of Electrical and Computer Engineering, Duke University, Durham, NC 27708, United States of America.
Department of Psychiatry and Behavioral Sciences, Duke University, Durham, NC 27710, United States of America.
J Neural Eng. 2022 Nov 23;19(6). doi: 10.1088/1741-2552/ac9d65.
The temporal shape of a pulse in transcranial magnetic stimulation (TMS) influences which neuron populations are activated preferentially as well as the strength and even direction of neuromodulation effects. Furthermore, various pulse shapes differ in their efficiency, coil heating, sensory perception, and clicking sound. However, the available TMS pulse shape repertoire is still very limited to a few biphasic, monophasic, and polyphasic pulses with sinusoidal or near-rectangular shapes. Monophasic pulses, though found to be more selective and stronger in neuromodulation, are generated inefficiently and therefore only available in simple low-frequency repetitive protocols. Despite a strong interest to exploit the temporal effects of TMS pulse shapes and pulse sequences, waveform control is relatively inflexible and only possible parametrically within certain limits. Previously proposed approaches for flexible pulse shape control, such as through power electronic inverters, have significant limitations: The semiconductor switches can fail under the immense electrical stress associated with free pulse shaping, and most conventional power inverter topologies are incapable of generating smooth electric fields or existing pulse shapes. Leveraging intensive preliminary work on modular power electronics, we present a modular pulse synthesizer (MPS) technology that can, for the first time, flexibly generate high-power TMS pulses (one-side peak ∼4000 V, ∼8000 A) with user-defined electric field shape as well as rapid sequences of pulses with high output quality. The circuit topology breaks the problem of simultaneous high power and switching speed into smaller, manageable portions, distributed across several identical modules. In consequence, the MPS TMS techology can use semiconductor devices with voltage and current ratings lower than the overall pulse voltage and distribute the overall switching of several hundred kilohertz among multiple transistors. MPS TMS can synthesize practically any pulse shape, including conventional ones, with fine quantization of the induced electric field (⩽17% granularity without modulation and ∼300 kHz bandwidth). Moreover, the technology allows optional symmetric differential coil driving so that the average electric potential of the coil, in contrast to conventional TMS devices, stays constant to prevent capacitive artifacts in sensitive recording amplifiers, such as electroencephalography. MPS TMS can enable the optimization of stimulation paradigms for more sophisticated probing of brain function as well as stronger and more selective neuromodulation, further expanding the parameter space available to users.
经颅磁刺激（TMS）中脉冲的时间形状会影响优先激活哪些神经元群体，以及神经调节效应的强度甚至方向。此外，各种脉冲形状在效率、线圈加热、感觉感知和咔嗒声方面存在差异。然而，可用的 TMS 脉冲形状库仍然非常有限，只有几种双相、单相和多相脉冲，具有正弦或近似矩形形状。单相脉冲虽然在神经调节方面被发现更具选择性和更强，但产生效率低下，因此仅可用于简单的低频重复方案。尽管人们对利用 TMS 脉冲形状和脉冲序列的时间效应有浓厚的兴趣，但波形控制相对不灵活，只能在某些限制内进行参数控制。以前提出的灵活脉冲形状控制方法，例如通过电力电子逆变器，具有显著的局限性：半导体开关在与自由脉冲成形相关的巨大电应力下可能会失效，并且大多数传统的电力逆变器拓扑无法产生平滑的电场或现有的脉冲形状。利用在模块化电力电子学方面的大量初步工作，我们提出了一种模块化脉冲合成器（MPS）技术，该技术首次能够灵活地生成具有用户定义电场形状的高功率 TMS 脉冲（单边峰值约为 4000V，约为 8000A）以及具有高质量输出的快速脉冲序列。该电路拓扑将同时实现高功率和开关速度的问题分解为更小、更易于管理的部分，分布在几个相同的模块中。因此，MPS TMS 技术可以使用电压和电流额定值低于总脉冲电压的半导体器件，并在多个晶体管之间分配几百千赫兹的总开关。MPS TMS 可以合成几乎任何脉冲形状，包括常规脉冲，并且可以对感应电场进行精细量化（无调制时的粒度 ⩽17%，带宽约为 300kHz）。此外，该技术允许可选的对称差分线圈驱动，从而与传统的 TMS 设备相比，线圈的平均电势保持恒定，以防止在敏感记录放大器（例如脑电图）中产生电容伪影。MPS TMS 可以优化刺激范式，以更深入地探测大脑功能，并实现更强和更具选择性的神经调节，从而进一步扩大用户可用的参数空间。
