title: Scan time reduction in ²³Na-Magnetic Resonance Imaging using the chemical shift imaging sequence: Evaluation of an iterative reconstruction method.
abstract: OBJECTIVE
  To evaluate potential scan time reduction in (23)Na-Magnetic Resonance Imaging with the chemical shift imaging sequence (CSI) using undersampled data of high-quality datasets, reconstructed with an iterative constrained reconstruction, compared to reduced resolution or reduced signal-to-noise ratio.
  
  
  METHODS
  CSI (23)Na-images were retrospectively undersampled and reconstructed with a constrained reconstruction scheme. The results were compared to conventional methods of scan time reduction. The constrained reconstruction scheme used a phase constraint and a finite object support, which was extracted from a spatially registered (1)H-image acquired with a double-tuned coil. The methods were evaluated using numerical simulations, phantom images and in-vivo images of a healthy volunteer and a patient who suffered from cerebral ischemic stroke.
  
  
  RESULTS
  The constrained reconstruction scheme showed improved image quality compared to a decreased number of averages, images with decreased resolution or circular undersampling with weighted averaging for any undersampling factor. Brain images of a stroke patient, which were reconstructed from three-fold undersampled k-space data, resulted in only minor differences from the original image (normalized root means square error < 12%) and an almost identical delineation of the stroke region (mismatch < 6%).
  
  
  CONCLUSIONS
  The acquisition of undersampled (23)Na-CSI images enables up to three-fold scan time reduction with improved image quality compared to conventional methods of scan time saving.
authors.affiliation: Computer Assisted Clinical Medicine, University Medical Center Mannheim, Heidelberg University, Mannheim, Germany. Electronic address: sebastian.weingaertner@medma.uni-heidelberg.de.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Weingärtner
authors.affiliation: Computer Assisted Clinical Medicine, University Medical Center Mannheim, Heidelberg University, Mannheim, Germany; Trinity Institute of Neuroscience, Trinity College, Dublin University, Dublin, Republic of Ireland.
authors.forename: Friedrich
authors.initials: F
authors.lastname: Wetterling
authors.affiliation: Computer Assisted Clinical Medicine, University Medical Center Mannheim, Heidelberg University, Mannheim, Germany.
authors.forename: Simon
authors.initials: S
authors.lastname: Konstandin
authors.affiliation: Department of Neurology, University Medical Center Mannheim, Heidelberg University, Mannheim, Germany.
authors.forename: Marc
authors.initials: M
authors.lastname: Fatar
authors.affiliation: Department of Neuroradiology, University Medical Center Mannheim, Heidelberg University, Mannheim, Germany.
authors.forename: Eva
authors.initials: E
authors.lastname: Neumaier-Probst
authors.affiliation: Computer Assisted Clinical Medicine, University Medical Center Mannheim, Heidelberg University, Mannheim, Germany.
authors.forename: Lothar R
authors.initials: LR
authors.lastname: Schad
mesh_terms: D000465:Algorithms; D001921:Brain / Q000378:metabolism* / Q000473:pathology*; D005240:Feasibility Studies; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D057054:Molecular Imaging / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012964:Sodium / Q000493:pharmacokinetics*; D013997:Time Factors
chemical_list: D012964:Sodium
keywords: (23)Na-MRI; (23)Na-Magnetresonanzbildgebung; Compressed Sensing; Unterabtastung; beschränkte Rekonstruktionsverfahren; compressed sensing; constrained reconstruction; undersampling