Peripheral nerve stimulation characteristics of an asymmetric head-only gradient coil compatible with a high-channel-count receiver array.

Purpose: To characterize peripheral nerve stimulation (PNS) of an asymmetric head-only gradient coil that is compatible with a commercial high-channel-count receive-only array. Methods: Two prototypes of an asymmetric head-only gradient coil set with a 42-cm inner diameter were constructed for brain imaging at 3T with maximum performance specifications of up to 85 mT/m and 708 T/m/s. Tests were performed in 24 volunteers to measure PNS thresholds with the transverse (x = left-right; y = anterior-posterior [A/P]) gradient coils of both prototypes. Fourteen of these 24 volunteers were also tested for the z-gradient PNS in the second prototype and were scanned with high-slew-rate echo planar imaging (EPI) immediately after the PNS tests. Results: For both prototypes, the y-gradient PNS threshold was markedly higher than the x-gradient threshold. The z-gradient threshold was intermediate between those for the x-and y-coils. Of the 24 volunteers, only two experienced y-gradient PNS at 80 mT/m and 500 T/m/s. All volunteers underwent the EPI scan without PNS when the readout direction was set to A/P. Conclusion: Measured PNS characteristics of asymmetric head-only gradient coil prototypes indicate that such coils, especially in the A/P direction, can be used for fast EPI readout in high-performance neuroimaging scans with substantially reduced PNS concerns compared with conventional whole body gradient coils. (C) 2015 International Society for Magnetic Resonance in Medicine