title: A g-factor metric for k-t-GRAPPA- and PEAK-GRAPPA-based parallel imaging.
abstract: OBJECTIVE
  The aim of this work is to derive a theoretical framework for quantitative noise and temporal fidelity analysis of time-resolved k-space-based parallel imaging methods.
  
  
  BACKGROUND
  An analytical formalism of noise distribution is derived extending the existing g-factor formulation for nontime-resolved generalized autocalibrating partially parallel acquisition (GRAPPA) to time-resolved k-space-based methods. The noise analysis considers temporal noise correlations and is further accompanied by a temporal filtering analysis.
  
  
  METHODS
  All methods are derived and presented for k-t-GRAPPA and PEAK-GRAPPA. A sliding window reconstruction and nontime-resolved GRAPPA are taken as a reference. Statistical validation is based on series of pseudoreplica images. The analysis is demonstrated on a short-axis cardiac CINE dataset.
  
  
  RESULTS
  The superior signal-to-noise performance of time-resolved over nontime-resolved parallel imaging methods at the expense of temporal frequency filtering is analytically confirmed. Further, different temporal frequency filter characteristics of k-t-GRAPPA, PEAK-GRAPPA, and sliding window are revealed.
  
  
  CONCLUSIONS
  The proposed analysis of noise behavior and temporal fidelity establishes a theoretical basis for a quantitative evaluation of time-resolved reconstruction methods. Therefore, the presented theory allows for comparison between time-resolved parallel imaging methods and also nontime-resolved methods. Magn Reson Med 74:125-135, 2015. © 2014 Wiley Periodicals, Inc.
authors.affiliation: Department of Diagnostic Radiology, Medical Physics, University Medical Center, University of Freiburg, Freiburg, Germany.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Ramb
authors.affiliation: Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland.
authors.forename: Christian
authors.initials: C
authors.lastname: Binter
authors.affiliation: Department of Diagnostic Radiology, Medical Physics, University Medical Center, University of Freiburg, Freiburg, Germany.
authors.forename: Gerrit
authors.initials: G
authors.lastname: Schultz
authors.affiliation: Department of Diagnostic Radiology, Medical Physics, University Medical Center, University of Freiburg, Freiburg, Germany.
authors.forename: Jakob
authors.initials: J
authors.lastname: Assländer
authors.affiliation: Research Center Magnetic Resonance Bavaria, Diagnostic Imaging, Wuerzburg, Germany.
authors.forename: Felix
authors.initials: F
authors.lastname: Breuer
authors.affiliation: Department of Diagnostic Radiology, Medical Physics, University Medical Center, University of Freiburg, Freiburg, Germany.
authors.forename: Maxim
authors.initials: M
authors.lastname: Zaitsev
authors.affiliation: Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland.|Imaging Sciences and Biomedical Engineering, King's College London, London, UK.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Kozerke
authors.affiliation: Department of Diagnostic Radiology, Medical Physics, University Medical Center, University of Freiburg, Freiburg, Germany.|Institute of Diagnostic, Interventional and Pediatric Radiology, University Hospital Bern, Bern, Switzerland.
authors.forename: Bernd
authors.initials: B
authors.lastname: Jung
keywords: PEAK-GRAPPA; g-factor; k-t-GRAPPA; noise enhancement; pseudoreplica