title: Comparison of optimized long echo time STEAM and PRESS proton MR spectroscopy of lipid olefinic protons at 3 Tesla.
abstract: OBJECTIVE
  To investigate the response of lipid olefinic protons (≈ 5.35 ppm) as a function of STEAM (Stimulated Echo Acquisition Mode) mixing time (TM), and echo time (TE), to find values that resolve the olefinic resonance from water in vivo while retaining sufficient olefinic signal.
  
  
  METHODS
  PRESS (Point RESolved Spectroscopy) and STEAM experiments with varying timing parameters (TE and also TM for STEAM) were conducted on nine oils (almond, canola, cod liver, corn, linseed, peanut, sesame, sunflower, and walnut oil), and on vertebral bone marrow in vivo at 3 Tesla (T). Olefinic and methylene (methyl + methylene in vivo) peak areas were measured.
  
  
  RESULTS
  Optimal STEAM parameters were found to be TM = 20 ms and TE = 100 ms. The STEAM olefinic/methylene area ratios (ranging between 0.1 and 0.4) calculated for each oil correlated well with ratios deduced from oil compositions in the literature (R(2)  = 0.975). The optimized STEAM sequence resolved the olefinic peak from water in vivo and yielded on average 1.91 times more olefinic signal compared with a previously optimized PRESS (TE = 200 ms) sequence tailored for the same purpose. Olefinic/(methyl + methylene) area ratios obtained with optimized STEAM and PRESS in vivo were linearly correlated (R(2)  = 0.972).
  
  
  CONCLUSIONS
  A STEAM sequence with TE = 100 ms and TM = 20 ms provides an alternative to the previously optimized PRESS (TE = 200 ms) sequence for determining relative amounts of lipid unsaturation at 3T.
authors: Department of Oncology, University of Alberta, Edmonton, Alberta, Canada; Department of Bioengineering, Yıldız Technical University, Istanbul, Turkey.
authors: Ayhan
authors: A
authors: Bingölbali
authors: B Gino
authors: BG
authors: Fallone
authors: Atiyah
authors: A
authors: Yahya
mesh_terms: D000328:Adult; D000475:Alkenes / Q000737:chemistry*; D001853:Bone Marrow / Q000737:chemistry*; D003060:Cod Liver Oil / Q000737:chemistry*; D064368:Healthy Volunteers; D006801:Humans; D008055:Lipids / Q000737:chemistry*; D008297:Male; D019047:Phantoms, Imaging; D010938:Plant Oils / Q000737:chemistry*; D066244:Proton Magnetic Resonance Spectroscopy / Q000379:methods*
chemical_list: D000475:Alkenes; D008055:Lipids; D010938:Plant Oils; D003060:Cod Liver Oil
keywords: PRESS; STEAM; lipid unsaturation; magnetic resonance spectroscopy; olefinic protons; spinal bone marrow