title: Evaluation of 2D spatially selective MR spectroscopy using parallel excitation at 7 T.
abstract: BACKGROUND
  In this work, two-dimensional (2D) spatially selective magnetic resonance spectroscopy (MRS) was evaluated in both phantom and human brain using 8-channel parallel excitation (pTX) at 7 T and compared to standard STEAM.
  
  
  METHODS
  A 2D spiral excitation k-space trajectory was segmented into multiple individual segments to increase the bandwidth. pTX was used to decrease the number of segments by accelerating the trajectory. Different radio frequency (RF) shim settings were used for refocusing, water suppression and fat saturation pulses.
  
  
  RESULTS
  Phantom experiments demonstrate that, although segmented 2D excitation provided excellent spatial selectivity and spectral quality, STEAM outperformed it in terms of outer volume suppression with 0.6% RMSD compared to 1.7%, 2.5%, 3.9% and 5.5% RMSDs for acceleration factors of R=1, 2, 3 and 4, respectively. Seven major metabolites [choline (Cho), creatine (Cr), phosphocreatine (PCr), glutamate (Glu), glutamine (Gln), glutathione (GSH) and N-acetylaspartate (NAA)] were detected with sufficient accuracy [Cramér-Rao lower bounds (CRLBs) <20%] from the in vivo spectra of both methods. Conservative RF power limits resulted in reduced SNR for 2D selective MR spectra (SNR 131 and 82 for R=1 and 2, respectively) compared to the reference STEAM spectrum (SNR 199).
  
  
  CONCLUSIONS
  Single voxel spectra acquired using 2D selective MRS with and without pTX showed very good agreement with the reference STEAM spectrum. Efficient SAR management of the 2D selective MRS sequence would potentially improve the SNR of spectra.
authors.affiliation: 1 Department of Biomedical Magnetic Resonance, Institute for Experimental Physics, Otto-von Guericke University Magdeburg, Leipzigerstr. 44, 39120 Magdeburg, Germany ; 2 Medical Physics, Department of Radiology, University Medical Center Freiburg, Breisacherstr. 60a, 79106 Freiburg, Germany ; 3 German Center for Neurodegenerative Diseases (DZNE), Site Magdeburg, Leipzigerstr. 44, 39120 Magdeburg, Germany ; 4 Leibniz Institute for Neurobiology, Brenneckestr. 6, 39118 Magdeburg, Germany ; 5 Center for Behavioral Brain Sciences, Universitaetsplatz 2, 39106 Magdeburg, Germany.
authors.forename: Gopesh
authors.initials: G
authors.lastname: Patel
authors.affiliation: 1 Department of Biomedical Magnetic Resonance, Institute for Experimental Physics, Otto-von Guericke University Magdeburg, Leipzigerstr. 44, 39120 Magdeburg, Germany ; 2 Medical Physics, Department of Radiology, University Medical Center Freiburg, Breisacherstr. 60a, 79106 Freiburg, Germany ; 3 German Center for Neurodegenerative Diseases (DZNE), Site Magdeburg, Leipzigerstr. 44, 39120 Magdeburg, Germany ; 4 Leibniz Institute for Neurobiology, Brenneckestr. 6, 39118 Magdeburg, Germany ; 5 Center for Behavioral Brain Sciences, Universitaetsplatz 2, 39106 Magdeburg, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Haas
authors.affiliation: 1 Department of Biomedical Magnetic Resonance, Institute for Experimental Physics, Otto-von Guericke University Magdeburg, Leipzigerstr. 44, 39120 Magdeburg, Germany ; 2 Medical Physics, Department of Radiology, University Medical Center Freiburg, Breisacherstr. 60a, 79106 Freiburg, Germany ; 3 German Center for Neurodegenerative Diseases (DZNE), Site Magdeburg, Leipzigerstr. 44, 39120 Magdeburg, Germany ; 4 Leibniz Institute for Neurobiology, Brenneckestr. 6, 39118 Magdeburg, Germany ; 5 Center for Behavioral Brain Sciences, Universitaetsplatz 2, 39106 Magdeburg, Germany.
authors.forename: Niravkumar
authors.initials: N
authors.lastname: Darji
authors.affiliation: 1 Department of Biomedical Magnetic Resonance, Institute for Experimental Physics, Otto-von Guericke University Magdeburg, Leipzigerstr. 44, 39120 Magdeburg, Germany ; 2 Medical Physics, Department of Radiology, University Medical Center Freiburg, Breisacherstr. 60a, 79106 Freiburg, Germany ; 3 German Center for Neurodegenerative Diseases (DZNE), Site Magdeburg, Leipzigerstr. 44, 39120 Magdeburg, Germany ; 4 Leibniz Institute for Neurobiology, Brenneckestr. 6, 39118 Magdeburg, Germany ; 5 Center for Behavioral Brain Sciences, Universitaetsplatz 2, 39106 Magdeburg, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Speck
keywords: Parallel excitation (pTX); radio frequency (RF) shimming; segmented two-dimensional (2D) excitation; single voxel spectroscopy