Improved flip-angle uniformity in 0.35-mm slices using asymmetric pTx spoke pulses

Motivation: Parallel transmit allows efficient radiofrequency pulse designs that produce uniform excitations. However, for 2D acquisitions with thin slices, long sub-pulse durations are needed to satisfy gradient system limitations which increases sensitivity to off-resonance. Goal(s): To improve flip-angle uniformity in thin slices using asymmetric pTx spoke pulses. Approach: Symmetric and asymmetric pTx spoke pulses were designed with B0 correction. Bloch simulations were performed to evaluate excitation fidelity targeting 0.5-mm and 0.35-mm slice thickness. Results: Tailored asymmetric pTx spokes can achieve uniform slice excitation particularly in regions where off-resonance effects are prominent when targeting thin imaging slices down to 0.35-mm thick. Impact: Parallel transmit is well known for efficient radiofrequency pulse designs that produce uniform excitations. We show that asymmetric spokes can mitigate off-resonance effects and generate uniform excitation for 0.5-mm and 0.35-mm thick slices.