Design of calibration-free RF pulses for T2-weighted single-slab 3D turbo-spin-echo sequences at 7T utilizing parallel transmission

PurposeT2-weighted turbo-spin-echo (TSE) sequences are a fundamental technique in brain imaging but suffer from field inhomogeneities at ultra-high fields. Several methods have been proposed to mitigate the problem, but were limited so far to non-selective 3D measurements, making short acquisitions difficult to achieve when targeting very high resolution images, or needed additional calibration procedures, thus complicating their application. MethodsSlab-selective excitation pulses were designed for flexible placement utilizing the concept of kT -spokes. Phase-coherent refocusing universal pulses were subsequently optimized with the Gradient Ascent Pulse Engineering algorithm and tested in vivo for improved signal homogeneity. ResultsImplemented within a 3D variable flip angle TSE sequence, these pulses led to a SNR improvement ranging from 10-30% compared to a 2D T2w TSE sequence employing B+1-shimmed pulses. B+1field inhomogeneities could be mitigated and artifacts from B0 deviations reduced.The concept of universal pulses was successfully applied. ConclusionWe present a pulse design method which provides a set of calibration-free universal pulses for slab-selective excitation and phase-coherent refocusing in slab-selective TSE sequences.