Variability of pulse width in transcranial magnetic stimulation

Area of Science:

• Neuroscience
• Biomedical Engineering
• Medical Physics

Background:

• High variability in transcranial magnetic stimulation (TMS) physiological effects limits measurement generalizability.
• Variability is often attributed to individual brain differences, neglecting physical stimulus properties.
• Systematic investigation of TMS pulse width variability is needed.

Purpose of the Study:

• To systematically investigate the variability in pulse width across different TMS pulse sources and stimulation intensities.
• To compare pulse widths between various MagVenture® pulse sources and stimulation levels.
• To assess deviations from manufacturer-specified pulse width values.

Main Methods:

• Measured pulse widths of seven MagVenture® pulse sources using a Near Field Probe and oscilloscope.
• Tested stimulation intensities from 10% to 100% in 10% increments.
• Used a consistent C-B60 coil for biphasic pulse delivery.

Main Results:

• The mean pulse width was 288.11 ± 0.37 µs, differing from the manufacturer's 280 µs.
• Significant differences in average pulse width were found between pulse sources and intensities (p < .001).
• Coefficients of variation within groups were low (0.13%-0.67%).

Conclusions:

• TMS pulse width exhibits deviations from manufacturer specifications and varies between devices and intensities.
• Pulse width variability within a single manufacturer's devices is minimal but differs across models.
• Pilot study suggests pulse width variability may affect motor evoked potential latencies, warranting further investigation.