title: Accelerated five-dimensional echo planar J-resolved spectroscopic imaging: Implementation and pilot validation in human brain.
abstract: OBJECTIVE
  To implement an accelerated five-dimensional (5D) echo-planar J-resolved spectroscopic imaging sequence combining 3 spatial and 2 spectral encoding dimensions and to apply the sequence in human brain.
  
  
  METHODS
  An echo planar readout was used to acquire a single spatial and a single spectral dimension during one readout. Nonuniform sampling was applied to the two phase-encoded spatial directions and the indirect spectral dimension. Nonlinear reconstruction was used to minimize the ℓ1-norm or the total variation and included a spectral mask to enhance sparsity. Retrospective reconstructions at multiple undersamplings were performed in phantom. Ten healthy volunteers were scanned with 8× undersampling and compared to a fully sampled single slice scan.
  
  
  RESULTS
  Retrospective reconstruction of fully sampled phantom data showed excellent quality at 4×, 8×, 12×, and 16× undersampling using either reconstruction method. Reconstruction of prospectively acquired in vivo scans with 8× undersampling showed excellent quality in the occipito-parietal lobes and good quality in the frontal lobe, consistent with the fully sampled single slice scan.
  
  
  CONCLUSIONS
  By utilizing nonuniform sampling with nonlinear reconstruction, 2D J-resolved spectra can be acquired over a 3D spatial volume with a total scan time of 20 min, which is reasonable for in vivo studies.
authors.affiliation: Department of Radiological Sciences, University of California, Los Angeles, California, USA.
authors.forename: Neil E
authors.initials: NE
authors.lastname: Wilson
authors.affiliation: Department of Radiological Sciences, University of California, Los Angeles, California, USA.
authors.forename: Zohaib
authors.initials: Z
authors.lastname: Iqbal
authors.affiliation: Department of Radiological Sciences, University of California, Los Angeles, California, USA.
authors.forename: Brian L
authors.initials: BL
authors.lastname: Burns
authors.affiliation: Department of Pediatrics, University of California, Los Angeles, California, USA.
authors.forename: Margaret
authors.initials: M
authors.lastname: Keller
authors.affiliation: Department of Radiological Sciences, University of California, Los Angeles, California, USA.
authors.forename: M Albert
authors.initials: MA
authors.lastname: Thomas
mesh_terms: D000328:Adult; D000465:Algorithms; D001921:Brain / Q000033:anatomy & histology / Q000378:metabolism*; D017352:Echo-Planar Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008297:Male; D057054:Molecular Imaging / Q000379:methods*; D010865:Pilot Projects; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
keywords: 3D spectroscopic imaging; J-resolved spectroscopic imaging; compressed sensing; echo-planar J-resolved spectroscopic imaging; human brain; nonuniform sampling