Accelerating spin-echo EPI through combined patterned multislice excitation and simultaneous multislice acquisition

Purpose: To demonstrate further acceleration of spin echo MRI by combining the simultaneous multi-slice approach with the recently introduced patterned multislice excitation (PME) technique and evaluate application for rapid diffusion-weighted MRI. Theory and Methods: Implementation at 3T involved the design of RF pulses simultaneously acting on four separate slices within hardware limits on peak amplitude. This was accomplished by time-shifted sub-pulses and a dedicated switching scheme of the slice-select gradient. The new technique was evaluated on two clinical MRI systems with differing maximum gradient strength. Results: Four-fold acceleration was successfully achieved by combining PME with rate-2 SMS. Within fixed measurement time, the proposed approach allows increased averaging or more elaborate sampling of diffusion tensor space. Depending on implementation, gains in SNR per unit time were modest or small, which is attributed to out-of-slice saturation effects of the RF pulses. Conclusion: Combination of PME with SMS-2 for further acceleration of diffusion imaging is feasible at 3T.