Spectroscopic Localization by Simultaneous Acquisition of the Double-Spin and Stimulated Echoes

PurposeTo design a proton MR spectroscopy (H-1-MRS) localization sequence that combines the signal-to-noise-ratio (SNR) benefits of point resolved spectroscopy (PRESS) with the high pulse bandwidths, low chemical shift displacements (CSD), low specific absorption rates (SAR), short echo times (TE), and superior radiofrequency transmit field (B1+) immunity of stimulated echo acquisition mode (STEAM), by simultaneously refocusing and acquiring both the double-spin and stimulated echo coherence pathways from the volume of interest. Theory and MethodsWe propose a family of H-1-MRS sequences comprising three orthogonal spatially selective pulses with flip angles 90 degrees<, , <128 degrees. The stimulated and double-spin echo are refocused in-phase simultaneously by altering the pulses' phases, flip angles and timing, as well as the interpulse gradient spoiling moments. The approximate to 90 degrees nutations of , , provide STEAM-like advantages (lower SAR, in-plane CSD and TE; greater B1+ immunity), but with SNRs comparable with PRESS. ResultsPhantom and in vivo brain experiments show that 83-100% of the PRESS SNR (metabolite-dependent) is achieved at under 75% of the SAR and 66% lower in-plane CSD. ConclusionThe advantages of STEAM can be augmented with the higher SNR of PRESS by combining the spin and stimulated echoes. Quantification, especially of J-coupled resonances and intermediate and long TEs, must be carefully considered. Magn Reson Med 73:31-43, 2015. (c) 2014 Wiley Periodicals, Inc.