Modular multilevel TMS device with wide output range and ultrabrief pulse capability for sound reduction

Abstract

Objective: This article presents a novel transcranial magnetic stimulation (TMS) pulse generator with a wide range of pulse shape, amplitude, and width. Approach: Based on a modular multilevel TMS (MM-TMS) topology we had proposed previously, we realized the first such device operating at full TMS energy levels. It consists of ten cascaded H-bridge modules, each implemented with insulated-gate bipolar transistors, enabling both novel high-amplitude ultrabrief pulses as well as pulses with conventional amplitude and duration. The MM-TMS device can output pulses including up to 21 voltage levels with a step size of up to 1100 V, allowing relatively flexible generation of various pulse waveforms and sequences. The circuit further allows charging the energy storage capacitor on each of the ten cascaded modules with a conventional TMS power supply. Main results: The MM-TMS device can output peak coil voltages and currents of 11 kV and 10 kA, respectively, enabling suprathreshold ultrabrief pulses (> 8.25 μs active electric field phase). Further, the MM-TMS device can generate a wide range of near-rectangular monophasic and biphasic pulses, as well as more complex staircase-approximated sinusoidal, polyphasic, and amplitude-modulated pulses. At matched estimated stimulation strength, briefer pulses emit less sound, which could enable quieter TMS. Finally, the MM-TMS device can instantaneously increase or decrease the amplitude from one pulse to the next in discrete steps by adding or removing modules in series, which enables rapid pulse sequences and paired-pulse protocols with variable pulse shapes and amplitudes. Significance: The MM-TMS device allows unprecedented control of the pulse characteristics which could enable novel protocols and quieter pulses.

Closed-loop and automatic tuning of pulse amplitude and width in EMG-guided controllable transcranial magnetic stimulation (cTMS)⋆

“…Finally, Fig. (7) confirms that solving the optimization problem (11) tunes the pulse width to maximize the normalized depolarization factor rp .…”

“…Transcranial magnetic stimulation (TMS) is a therapeutic intervention used in psychiatric and neurological disorders as well as a tool for probing brain function in cognitive neuroscience and neurophysiology [1,2,3,4]. In parallel to the rapid spread of TMS usage, novel technological refinements and developments are emerging, such as TMS devices with adjustable pulse shapes, among them controllable TMS (cTMS), and closed-loop TMS [5,6,7,8,9].…”

A formalism for sequential estimation of neural membrane time constant and input–output curve towards selective and closed-loop transcranial magnetic stimulation⋆

“…In conventional TMS devices, the pulse width is fixed [41, 38]. Thus, the proposed modeling is also applicable to them as a special case just as it is to more advanced TMS technology with more flexible pulse control [42, 43, 44] .…”