title: 3D sensitivity encoded ellipsoidal MR spectroscopic imaging of gliomas at 3T.
abstract: OBJECTIVE
  The goal of this study was to implement time efficient data acquisition and reconstruction methods for 3D magnetic resonance spectroscopic imaging (MRSI) of gliomas at a field strength of 3T using parallel imaging techniques.
  
  
  METHODS
  The point spread functions, signal to noise ratio (SNR), spatial resolution, metabolite intensity distributions and Cho:NAA ratio of 3D ellipsoidal, 3D sensitivity encoding (SENSE) and 3D combined ellipsoidal and SENSE (e-SENSE) k-space sampling schemes were compared with conventional k-space data acquisition methods.
  
  
  RESULTS
  The 3D SENSE and e-SENSE methods resulted in similar spectral patterns as the conventional MRSI methods. The Cho:NAA ratios were highly correlated (P<.05 for SENSE and P<.001 for e-SENSE) with the ellipsoidal method and all methods exhibited significantly different spectral patterns in tumor regions compared to normal appearing white matter. The geometry factors ranged between 1.2 and 1.3 for both the SENSE and e-SENSE spectra. When corrected for these factors and for differences in data acquisition times, the empirical SNRs were similar to values expected based upon theoretical grounds. The effective spatial resolution of the SENSE spectra was estimated to be same as the corresponding fully sampled k-space data, while the spectra acquired with ellipsoidal and e-SENSE k-space samplings were estimated to have a 2.36-2.47-fold loss in spatial resolution due to the differences in their point spread functions.
  
  
  CONCLUSIONS
  The 3D SENSE method retained the same spatial resolution as full k-space sampling but with a 4-fold reduction in scan time and an acquisition time of 9.28 min. The 3D e-SENSE method had a similar spatial resolution as the corresponding ellipsoidal sampling with a scan time of 4:36 min. Both parallel imaging methods provided clinically interpretable spectra with volumetric coverage and adequate SNR for evaluating Cho, Cr and NAA.
authors.affiliation: Margaret Hart Surbeck Laboratory of Advanced Imaging, Department of Radiology and Biomedical Imaging, University of California, San Francisco, CA 94158, USA. esin.ozturk@mrsc.ucsf.edu
authors.forename: Esin
authors.initials: E
authors.lastname: Ozturk-Isik
authors.forename: Albert P
authors.initials: AP
authors.lastname: Chen
authors.forename: Jason C
authors.initials: JC
authors.lastname: Crane
authors.forename: Wei
authors.initials: W
authors.lastname: Bian
authors.forename: Duan
authors.initials: D
authors.lastname: Xu
authors.forename: Eric T
authors.initials: ET
authors.lastname: Han
authors.forename: Susan M
authors.initials: SM
authors.lastname: Chang
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Vigneron
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Nelson
mesh_terms: D000328:Adult; D000368:Aged; D001932:Brain Neoplasms / Q000175:diagnosis* / Q000473:pathology; D005260:Female; D005910:Glioma / Q000175:diagnosis* / Q000473:pathology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008055:Lipids / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D051598:Whole Body Imaging
chemical_list: D008055:Lipids