B1+ Inhomogeneity Compensation using 3D Parallel Excitation is Enhanced by Simultaneous Linear & Nonlinear Gradient Encoding

William A. Grissom¹, Laura Sacolick¹, Mika W. Vogel¹

3D parallel spokes excitation pulses have been proposed for compensating flip angle inhomogeneities induced by inhomogeneous B1+ at high field. While flip angle homogeneity improves with increasing spokes pulse duration and an increasing number of parallel excitation channels, competing desires to limit off-resonance sensitivity and system complexity limit these pulses' effectiveness in practice. We show that nonlinear gradient phase encoding is well-suited to this application and that simultaneous linear and nonlinear phase encoding can significantly improve spokes pulse performance, enabling shorter pulse durations and fewer transmit channels for a desired level of flip angle homogeneity.