Whole‐body gradient coils with longer linear regions expose larger areas of the body to rapidly switching magnetic fields, inducing higher E‐fields. The primary determinant of the PNS threshold for a given gradient coil is its linear region length along the z‐axis. Require that scanners operate at or below population‐average PNS thresholds and well below cardiac stimulation thresholds. Widely adopted regulatory guidelines such as those found in International Electrotechnical Commission 60601‐2‐33 In theory, as these amplitudes or switching rates increase, there is a risk of cardiac stimulation, although cardiac thresholds are typically much higher than PNS thresholds. Because of PNS, present‐day high‐performance body gradients often operate below their hardware limits for sequences that require high amplitudes and/or switching rates. Low‐level PNS is considered safe, but uncomfortable levels must be avoided. The rapid switching of strong gradients, required for high‐speed and high‐resolution imaging, gives rise to electric fields (E‐fields) in the human body that can depolarize nerves, with peripheral nerves typically being much more sensitive than central nerves. Gradient coil and amplifier technologies have developed rapidly over the past few decades, such that MRI gradient performance is now more limited by peripheral nerve stimulation (PNS) than by hardware capabilities.
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