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 nearzero
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.