Time-shifted multiband construction of wideband pulses

Motivation: Adiabatic pulses are popular for wideband inversion or refocusing, but limited by SAR in high-field. Conventional modulated pulses are limited in bandwidth by peak voltage requirements. Goal(s): Develop an intuitive wideband pulse design method compatible with limited peak voltage for ultra-high field applications. Approach: We construct a “multiband” pulse covering the desired bandwidth. We use time-shifting to reduce the peak voltage. Results: We illustrate by designing a 4.4kHz bandwidth pulse, which has similar peak amplitude but better B1 robustness than a root-flipped SLR pulse. We use this pulse for semi-LASER MRS in a phantom, giving similar spectra to an adiabatic hypersecant pulse. Impact: We introduce a time-shifted multiband method to design wideband pulses that is fast and intuitive to construct and avoids the tradeoff between RF peak amplitude and bandwidth. These pulses are useful for inversion or refocusing in twice-refocused sequences like semi-LASER.