Increased time rate of change of gradient fields: effect on peripheral nerve stimulation at clinical MR imaging

To increase gradient stimulation from 100% to a fixed 120% level and to assess patient acceptance of the degree of peripheral nerve stimulation (PNS) at magnetic resonance (MR) imaging.

Two hundred ten patients underwent MR imaging of various body regions according to clinical indications. An additional three-dimensional fast low-angle shot sequence with the 120% stimulation level was performed. A patient questionnaire was distributed after MR imaging to document the presence, degree, and location of PNS. Degree was measured with an 11-point scale (score range, 0-10). Age was analyzed between the sexes for significant statistical differences. Furthermore, correlation between location of examination and location and degree of stimulation was performed. To determine stimulation discomfort relative to other factors typically present at MR imaging, the degree of discomfort due to room temperature, size of magnet bore, acoustic noise, examination time, and heating sensation was determined for comparison, as well.

Thirty-five (16.7%) patients reported a stimulation sensation during imaging in one or more locations, while six (2.9%) felt very uncomfortable local stimulation (score of 8-10). No significant difference between male and female patients regarding age, sex, and appearance or degree of stimulation sensation could be detected. No significant correlation between location of examination and location and degree of stimulation was recorded. Compared with other side effects, PNS was considered relatively unimportant.

The 120% gradient stimulation level seems acceptable for routine clinical imaging with this gradient system, since only 2.9% of patients experienced very uncomfortable local stimulation.