A Low Power Radiofrequency Pulse for Simultaneous Multislice Excitation and Refocusing

Purpose: Simultaneous multislice (SMS) acquisition enables increased temporal efficiency of MRI. Nonetheless, MultiBand (MB) radiofrequency (RF) pulses used for SMS can cause large energy deposition. Power independent of number of slices (PINS) pulses reduce RF power at cost of reduced bandwidth and increased off-resonance dependency. This work improves PINS design to further reduce energy deposition, off-resonance dependency and peak power.

Theory And Methods: Modifying the shape of MB RF-pulses allows for mixing with PINS excitation, creating a new pulse type with reduced energy deposition and SMS excitation characteristics. Bloch Simulations were used to evaluate excitation and off-resonance behavior of this "MultiPINS" pulse. In this work, MultiPINS was used for whole-brain MB = 3 acquisition of high angular and spatial resolution diffusion MRI at 7 Tesla in 3 min.

Results: By using MultiPINS, energy transmission and peak power for SMS imaging can be significantly reduced compared with PINS and MB pulses. For MB = 3 acquisition in this work, MultiPINS reduces energy transmission by up to ∼50% compared with PINS pulses. The energy reduction was traded off to shorten the MultiPINS pulse, yielding higher signal at off-resonances for spin-echo acquisitions.

Conclusion: MB and PINS pulses can be combined to enable low energy and peak power SMS acquisition.