title: Hadamard-encoding combined with two-dimensional-selective radiofrequency excitations for flexible and efficient acquisitions of multiple voxels in MR spectroscopy.
abstract: OBJECTIVE
  To improve the efficiency and flexibility of acquisitions of multiple voxels in MR spectroscopy by combining two-dimensional-selective radiofrequency (2DRF) excitations and Hadamard encoding.
  
  
  METHODS
  With 2DRF excitations (PROPELLER trajectory, 16 half-Fourier segments, each with five lines) two voxels are defined. By combining the individual 2DRF pulses with Hadamard-like encoded phases, the voxels are acquired simultaneously but the individual contributions can be isolated from the obtained spectra. This is demonstrated on a 3 Tesla whole-body MR system in phantoms and in the human brain in vivo.
  
  
  RESULTS
  Compared with sequential single-voxel acquisitions the signal efficiency increases with the number of voxels covered. Furthermore, in comparison to conventional single-voxel MRS based on cross-sectional RF excitations, 2DRF excitations offer a higher flexibility because they allow for arbitrary voxel sizes, orientations, in-plane positions, and shapes.
  
  
  CONCLUSIONS
  The presented approach improves the flexibility and efficiency of acquisitions of multiple voxels, i.e., can shorten acquisition times accordingly, and can help to reduce partial volume effects.
authors.affiliation: Department of Systems Neuroscience, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
authors.forename: Martin G
authors.initials: MG
authors.lastname: Busch
authors.forename: Jürgen
authors.initials: J
authors.lastname: Finsterbusch
mesh_terms: D000465:Algorithms; D001921:Brain / Q000033:anatomy & histology* / Q000378:metabolism*; D044962:Data Compression / Q000379:methods*; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity