Abstract
Objective. This work aims at flexible and practical pulse parameter control in transcranial magnetic stimulation (TMS), which is currently very limited in commercial devices. Approach. We present a third generation controllable pulse parameter device (cTMS3) that uses a novel circuit topology with two energy-storage capacitors. It incorporates several implementation and functionality advantages over conventional TMS devices and other devices with advanced pulse shape control. cTMS3 generates lower internal voltage differences and is implemented with transistors with a lower voltage rating than prior cTMS devices. Main results. cTMS3 provides more flexible pulse shaping since the circuit topology allows four coil-voltage levels during a pulse, including approximately zero voltage. The near-zero coil voltage enables snubbing of the ringing at the end of the pulse without the need for a separate active snubber circuit. cTMS3 can generate powerful rapid pulse sequences ( 10 ms inter pulse interval) by increasing the width of each subsequent pulse and utilizing the large capacitor energy storage, allowing the implementation of paradigms such as paired-pulse and quadripulse TMS with a single pulse generation circuit. cTMS3 can also generate theta (50 Hz) burst stimulation with predominantly unidirectional electric field pulses. The cTMS3 device functionality and output strength are illustrated with electrical output measurements as well as a study of the effect of pulse width and polarity on the active motor threshold in ten healthy volunteers. Significance. The cTMS3 features could extend the utility of TMS as a research, diagnostic, and therapeutic tool.
Highlights
Transcranial magnetic stimulation (TMS) involves the delivery of brief, high-strength magnetic pulses to the brain to induce an electric field that modulates neural activity
Addressing this need, we have developed a family of TMS devices with controllable pulse parameters including low repetition rate TMS [13] and high rate repetitive TMS (rTMS) [14]. cTMS1 uses a large energy storage capacitor and a single insulated gate bipolar transistor (IGBT) switch to enable pulse width control. cTMS2 deploys two capacitors and two IGBTs to extend the controllable coil voltage levels from one to two, and to provide efficient high rate rTMS operation; it requires an active snubbing circuit to suppress ringing at the end of each pulse
In this paper we present the design of a novel cTMS device and demonstrate its functionality with electrical measurements of its output and with a first-in-human study. cTMS3 uses a novel circuit topology that incorporates several implementation and functionality advantages over previous cTMS and other TMS devices, including lower transistor voltages, more flexible pulse shaping, and intrinsic pulse snubbing capabilities
Summary
Transcranial magnetic stimulation (TMS) involves the delivery of brief, high-strength magnetic pulses to the brain to induce an electric field that modulates neural activity. Available TMS devices induce damped cosine electric field pulses, with nonexistent or very limited control over the pulse shape parameters [9, 10, 11]. These conventional devices deploy a pulse generator circuit consisting essentially of an energy storage capacitor and a thyristor switch that can be triggered to discharge the capacitor into the stimulation coil but cannot be controllably turned off to shape the pulse. More flexible control of the pulse shape could potentially enable a host of research and clinical applications that are not feasible with available TMS devices, including expanded characterization of neural properties, more selective targeting of neural populations, enhanced neuromodulation effectiveness and reproducibility, reduced energy use and coil heating, as well as mitigation of pulse sensation and sound [12, 13, 11, 14, 15, 16] (see Sec. 5)
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