Optimized Extremity Coil System for Gradient-Free Low-Field MRI using the Bloch-Siegert Shift for RF Spatial Encoding

Traditional B0 gradients have several drawbacks including high acoustic noise, PNS, bulkiness, and high cost. To address this, we present a coil system for Bloch-Siegert (BS) RF encoding comprising an optimized square root solenoid with a bucking coil for high efficiency encoding and a nested uniform saddle coil for the imaging Tx/Rx coil at 47.5mT (2MHz), a field strength that is especially attractive due to its low SAR and accessibility. The coil designed for in-vivo imaging was evaluated in simulation including SAR measurements and experimentally on a resolution phantom using a 3D BS phase-encoded imaging and optimized ‘U’ shaped pulses.