Magnetic Stimulation with Arbitrary Waveform Shapes

Goetz, Stefan M.; Singer, Matthias; Huber, Jonas; Pfaeffl, M.; Marquardt, Rainer; Weyh, Thomas

doi:10.1007/978-3-642-29305-4_589

Cited by 4 publications

(11 citation statements)

References 14 publications

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“…Neither conventional TMS nor conventional power electronic inverter circuits could achieve such pulse-shape control as the combination of power and bandwidth overwhelms transistors while standard inverter circuits fur- thermore generate poor electric field output quality with large high-frequency components. MPS TMS leveraged power electronics solutions we have developed over the past decade [133][134][135][136]. The technology combines a modular circuit that breaks the requisite high power and fast switching dynamics with latest unipolar wide-bandgap semiconductors to achieve an exceptionally high power-bandwidth product.…”

Section: Discussionmentioning

confidence: 99%

“…Notably, the modular pulse synthesizer principle generates pulses through electronic control, without any intentional resistance or damping. In consequence, all pulses, including monophasic ones, are generated with energy recycling [133,134]. Conventional TMS circuits, in contrast, can recover some of the pulse energy only for biphasic pulses.…”

Section: Discussionmentioning

confidence: 99%

“…We previously argued that a conventional inverter circuit cannot provide at the same time the quality, power, and bandwidth necessary for flexible TMS pulse synthesis, and introduced alternative circuits; these circuits split the high voltage, current, and switching frequency into smaller, manageable portions distributed over many faster, lower-power semiconductor devices [133][134][135][136][137][138][139]. We developed as well as tested the principle in various stages and recently used a simplified implementation with older semiconductor technology to reduce the sound of TMS pulses through different coil structures and pulses with dominant frequency contents above the hearing range [76,80,140].…”

Section: Limitations For Generating Any User-defined Pulsementioning

confidence: 99%

“…We combined two ingredients to solve this problem. First, we designed a circuit class that splits power and switching into smaller, manageable portions [133][134][135][136]. Figure 1D depicts the circuit topology as a string of modules, which jointly generate the output.…”

Section: Modular Circuit Topologymentioning

confidence: 99%

“…Naturally, the device can generate other conventional pulse shapes, such as just half a period of a sinusoidal current and cosinusoidal voltage, sometimes called half-wave pulses (see Figure 13), and monophasic pulses (see Figure 14). As was already pointed out in our previous descriptions of the technology, the circuit does not contain any resistors for shaping a pulse [133,134]. The abandonment of any resistance for pulse shaping, which is essential in conventional monophasic TMS devices and responsible for most of the problems of the pulse shape, has substantial impact: As a consequence of the energy recovery and the low energy loss even in monophasic pulses, the technology can generate monophasic pulses at repetition rates of 50 Hz and higher.…”

Section: Synthesis Of All Conventional Pulses With Energy Recoverymentioning

confidence: 99%

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Transcranial Magnetic Stimulation Tech-nology with Freely Adjustable Pulse Shape and Sequence

Li¹,

Zhang²,

Peterchev³

et al. 2023

Preprint

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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 ~ 4,000 V, ~ 8,000 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, MPS TMS 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 (EEG). 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.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Limitations For Generating Any User-defined Pulsementioning

confidence: 99%

Section: Modular Circuit Topologymentioning

confidence: 99%

Section: Synthesis Of All Conventional Pulses With Energy Recoverymentioning

confidence: 99%

See 3 more Smart Citations

Transcranial Magnetic Stimulation Tech-nology with Freely Adjustable Pulse Shape and Sequence

Li¹,

Zhang²,

Peterchev³

et al. 2023

Preprint

View full text Add to dashboard Cite

show abstract

Modular pulse synthesizer for transcranial magnetic stimulation with fully adjustable pulse shape and sequence

Zhang

Peterchev

et al. 2022

J. Neural Eng.

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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: Existing 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 (~ 4,000 V, ~ 8,000 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, MPS TMS 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. 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 (EEG). 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.

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Optimized monophasic pulses with equivalent electric field for rapid-rate transcranial magnetic stimulation

Wang

Zhang

et al. 2023

J. Neural Eng.

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Objective. Transcranial magnetic stimulation (TMS) with monophasic pulses achieves greater changes in neuronal excitability but requires higher energy and generates more coil heating than TMS with biphasic pulses, and this limits the use of monophasic pulses in rapid-rate protocols. We sought to design a stimulation waveform that retains the characteristics of monophasic TMS but significantly reduces coil heating, thereby enabling higher pulse rates and increased neuromodulation effectiveness.Approach. A two-step optimization method was developed that uses the temporal relationship between the electric field (E-field) and coil current waveforms. The model-free optimization step reduced the ohmic losses of the coil current and constrained the error of the E-field waveform compared to a template monophasic pulse, with pulse duration as a second constraint. The second, amplitude adjustment step scaled the candidate waveforms based on simulated neural activation to account for differences in stimulation thresholds. The optimized waveforms were implemented to validate the changes in coil heating.Main results. Depending on the pulse duration and E-field matching constraints, the optimized waveforms produced 12% to 75% less heating than the original monophasic pulse. The reduction in coil heating was robust across a range of neural models. The changes in the measured ohmic losses of the optimized pulses compared to the original pulse agreed with numeric predictions.Significance. The first step of the optimization approach was independent of any potentially inaccurate or incorrect model and exhibited robust performance by avoiding the highly nonlinear behavior of neural responses, whereas neural simulations were only run once for amplitude scaling in the second step. This significantly reduced computational cost compared to iterative methods using large populations of candidate solutions and more importantly reduced the sensitivity to the choice of neural model. The reduced coil heating and power losses of the optimized pulses can enable rapid-rate monophasic TMS protocols.

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Magnetic Stimulation with Arbitrary Waveform Shapes

Cited by 4 publications

References 14 publications

Transcranial Magnetic Stimulation Tech-nology with Freely Adjustable Pulse Shape and Sequence

Transcranial Magnetic Stimulation Tech-nology with Freely Adjustable Pulse Shape and Sequence

Modular pulse synthesizer for transcranial magnetic stimulation with fully adjustable pulse shape and sequence

Optimized monophasic pulses with equivalent electric field for rapid-rate transcranial magnetic stimulation

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