Controllable pulse parameter transcranial magnetic stimulator with enhanced circuit topology and pulse shaping

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 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 10 healthy volunteers. Significance The cTMS3 features could extend the utility of TMS as a research, diagnostic, and therapeutic tool.

Controllable Pulse Parameter TMS and TMS-EEG As Novel Approaches to Improve Neural Targeting with rTMS in Human Cerebral Cortex

“…Commercially-available TMS devices cannot vary pulse width and cannot make use of the different strength-duration behavior of cortical axons to target particular sets of neurons. However, novel devices such as the cTMS (Peterchev et al, 2014) allow flexible control of pulse width, shape (e.g., monophasic/unidirectional or biphasic/bidirectional) and direction, and can be implemented during single pulse and rTMS modes. We recently showed that motor cortical axons recruited by AP and PA currents have different strength-duration behavior (D'Ostilio et al, 2016).…”

“…A separate, but related, issue is that rTMS over a given cortical area is often assumed to affect all neuronal populations equally and thus affect all behaviors involving that area similarly, but this may not be true. Here we argue that advanced technologies and methodologies, such as controllable pulse parameter TMS (cTMS; Peterchev et al, 2014) and combining TMS with electroencephalography (EEG; Ilmoniemi and Kicic, 2010), might facilitate the development of more selective forms of stimulation targeting particular neuronal populations or brain states, and ultimately improve the reliability and behavioral specificity of rTMS protocols.…”

Pulse Width Affects Scalp Sensation of Transcranial Magnetic Stimulation

“…It is possible that the pulse characteristics such as pulse width affect the perception of TMS in different ways for single pulses and for pulse trains. In future studies, the pulse characteristics of repetitive TMS pulse trains could be modified using cTMS devices that allow high-frequency trains [29,30]. Moreover, this study did not explore the differences in sensation between conventional sinusoidal pulses and cTMS near-rectangular pulses.…”

“…As well, some commercial TMS devices allow adjustment, albeit limited, of the pulse width [26,27]. Finally, we have developed a family of TMS devices with controllable pulse parameters (cTMS) that allow adjustment of the pulse width over a substantial range, potentially allowing optimization of this parameter [28–30]. …”

Development of instrumentation for neuronavigation and transcranial magnetic stimulation

“…When the Introduction switch is closed, the capacitor rapidly discharges a current through the wires of the coil and generates the magnetic field. Nowadays, much more complex circuits have been developed to allow full control of current's waveform (Koponen et al, 2017;Peterchev et al, 2014).…”