Practical Utilization of Nonlinear Spatial Encoding: Fast Field Mapping and FRONSAC-wave

Motivation: Nonlinear gradient imaging is impeded by time-consuming field mapping and the encoding ability is yet to be unleashed. Goal(s): To accelerate nonlinear field mapping and make use of nonlinear encoding. Approach: We report a fast and robust estimation method for nonlinear field mapping and studied the utility of simultaneously applying nonlinear and linear gradients, referred to as FRONSAC-wave, where the high-frequency nonlinear field waveform is complementary to a lower frequency linear field waveform. Results: The fast field mapping decreases the field mapping time from 10 hours to <0.5 hour. FRONSAC-wave demonstrates better imaging ability compared to wave at various acquisition settings. Impact: This study demonstrates the advantage of combined sinusoidal waveforms on linear and nonlinear gradients and proves the feasibility of fast mapping for nonlinear fields. It opens prospects for utilization of nonlinear field encoding in clinical scenarios.