Head-Only Z-gradient Array Coil: Induced Electric Field Analysis of 2- and 3-layer Designs

Motivation: High-performance gradient coils are markedly restricted by peripheral nerve stimulation rather than hardware limitations. Goal(s): We aimed to reduce the gradient-induced electric fields on the body and consequently increase peripheral nerve stimulation thresholds. Approach: We introduce a head-only Z-gradient array coil and optimize current weightings of the array configuration to minimize induced electric fields while generating the target gradient within a customizable region with flexible linearity levels. Results: Utilizing the array configuration reduces the maximum electric field up to 50%, 61%, and 78% compared to a conventional mode for a 22cm spherical region, the disk-shape region at the center, and off-center disks, respectively. Impact: Peripheral nerve stimulation thresholds of head gradient coils can be increased using array technology; thus, higher gradient strengths and slew rates can be achieved without causing PNS.