title: Spectroscopic localization by simultaneous acquisition of the double-spin and stimulated echoes.
abstract: OBJECTIVE
  To design a proton MR spectroscopy ((1) H-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.
  
  
  METHODS
  We propose a family of (1)H-MRS sequences comprising three orthogonal spatially selective pulses with flip angles 90° < α, β, γ < 128°. 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 ≈ 90° nutations of α, β, γ provide STEAM-like advantages (lower SAR, in-plane CSD and TE; greater B1+ immunity), but with SNRs comparable with PRESS.
  
  
  RESULTS
  Phantom 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.
  
  
  CONCLUSIONS
  The 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.
authors.affiliation: Department of Radiology, New York University School of Medicine, New York, New York, USA.
authors.forename: Assaf
authors.initials: A
authors.lastname: Tal
authors.affiliation: Department of Radiology, New York University School of Medicine, New York, New York, USA.
authors.forename: Oded
authors.initials: O
authors.lastname: Gonen
mesh_terms: D000328:Adult; D000465:Algorithms; D001224:Aspartic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D001921:Brain / Q000378:metabolism*; D003401:Creatine / Q000378:metabolism*; D005260:Female; D006801:Humans; D066244:Proton Magnetic Resonance Spectroscopy / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D013113:Spin Labels
chemical_list: D013113:Spin Labels; D001224:Aspartic Acid; C000179:N-acetylaspartate; D003401:Creatine
keywords: CPMG; STRESS; chemical shift displacement (CSD); chemical shift displacement artifact (CSDA); coherence pathway; point resolved spectroscopy (PRESS); spin echo; stimulated echo; stimulated echo acquisition mode (STEAM)