title: Single acquisition quantitative single-point electron paramagnetic resonance imaging.
abstract: OBJECTIVE
  Electron paramagnetic resonance imaging has emerged as a promising noninvasive technology to dynamically image tissue oxygenation. Owing to its extremely short spin-spin relaxation times, electron paramagnetic resonance imaging benefits from a single-point imaging scheme where the entire free induction decay signal is captured using pure phase encoding. However, direct T2 (*)/pO2 quantification is inhibited owing to constant magnitude gradients which result in time-decreasing field of view. Therefore, conventional acquisition techniques require repeated imaging experiments with differing gradient amplitudes (typically 3), which results in long acquisition time.
  
  
  METHODS
  In this study, gridding was evaluated as a method to reconstruct images with equal field of view to enable direct T2 (*)/pO2 quantification within a single imaging experiment. Additionally, an enhanced reconstruction technique that shares high spatial k-space regions throughout different phase-encoding time delays was investigated (k-space extrapolation).
  
  
  RESULTS
  The combined application of gridding and k-space extrapolation enables pixelwise quantification of T2 (*) from a single acquisition with improved image quality across a wide range of phase-encoding time delays. The calculated T2 (*)/pO2 does not vary across this time range.
  
  
  CONCLUSIONS
  By utilizing gridding and k-space extrapolation, accurate T2 (*)/pO2 quantification can be achieved within a single data set to allow enhanced temporal resolution (by a factor of 3).
authors.affiliation: Department of Radiology, Wisconsin Institute for Medical Research, University of Wisconsin, Madison, Wisconsin, USA.
authors.forename: Hyungseok
authors.initials: H
authors.lastname: Jang
authors.forename: Sankaran
authors.initials: S
authors.lastname: Subramanian
authors.forename: Nallathamby
authors.initials: N
authors.lastname: Devasahayam
authors.forename: Keita
authors.initials: K
authors.lastname: Saito
authors.forename: Shingo
authors.initials: S
authors.lastname: Matsumoto
authors.forename: Murali C
authors.initials: MC
authors.lastname: Krishna
authors.forename: Alan B
authors.initials: AB
authors.lastname: McMillan
mesh_terms: D000465:Algorithms; D016477:Artifacts; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D057054:Molecular Imaging / Q000295:instrumentation / Q000379:methods*; D010092:Oximetry / Q000379:methods*; D010100:Oxygen / Q000032:analysis*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D010100:Oxygen
keywords: EPR imaging; gridding; hypoxia; quantitative imaging; single point imaging; tissue oxygenation
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