  Peripheral Nerve Stimulation (PNS) constrains the clinical performance of
Magnetic Resonance and Particle Imaging (MRI and MPI) systems. Extensive
magneto-stimulation studies have been carried out recently in the field of MPI,
where typical operation frequencies range from single to tens of kilo-hertz.
PNS literature is scarce for MRI in this regime, where the resonant character
of MPI coils prevents studies of broad-band excitation pulses. We have
constructed an apparatus for PNS threshold determination on a subject's limb,
capable of narrow and broad-band magnetic excitation with pulse characteristic
times down to 40 us. From a first set of measurements on 51 volunteers, we
observe that PNS limits coincide for sinusoidal (biphasic narrow-band) and
triangular (biphasic broad-band) excitations, and are slightly lower for
trapezoidal (monophasic broad-band) pulses. We have also measured statistically
significant correlations of PNS sensitivity with arm size and body weight, and
no correlation with height or gender. As opposed to resonant systems, our setup
allows the execution of arbitrarily short pulse trains. We have confirmed
thresholds increase significantly as trains transition from tens to a few
pulses also in these fast timescales. By changing the polarity of the coils in
our setup, we also looked at the influence of the spatial distribution of
magnetic field strength on PNS effects. We find that thresholds are higher in
an approximately linearly inhomogeneous field (relevant to MRI) than in a
rather homogeneous distribution (as in MPI). Finally, given the large
intersubject variability of PNS sensitivity, we propose employing a versatile
low-cost system (such as presented here) for fast offline determination of a
subject's limits prior to medical scanning, and then using this information to
boost clinical imaging while preserving the patient's safety.
