title: Self-calibrated trajectory estimation and signal correction method for robust radial imaging using GRAPPA operator gridding.
abstract: OBJECTIVE
  In radial imaging, projections may become "miscentered" due to gradient errors such as delays and eddy currents. These errors may result in image artifacts and can disrupt the reliability of direct current (DC) navigation. The proposed parallel imaging-based technique retrospectively estimates trajectory error from miscentered radial data without extra acquisitions, hardware, or sequence modification.
  
  
  METHODS
  After phase correction, self-calibrated GRAPPA operator gridding (GROG) weights are iteratively applied to shift-miscentered projections toward the center of k-space. A search algorithm identifies the shift that aligns the peak k-space signals by maximizing the sum-of-squares DC signal estimate of each projection. The algorithm returns a trajectory estimate and a corrected radial k-space signal.
  
  
  RESULTS
  Data from a spherical phantom, the head, and the heart demonstrate that image reconstruction with the estimated trajectory restores image quality and reduces artifacts such as streaks and signal voids. The DC signal level is increased and variability is reduced.
  
  
  CONCLUSIONS
  Retrospective phase correction and iterative application of GROG can be used to successfully estimate the trajectory error in two-dimensional radial acquisitions for improved image reconstruction without requiring extra data acquisition or sequence modification.
authors.affiliation: Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, USA.
authors.forename: Anagha
authors.initials: A
authors.lastname: Deshmane
authors.affiliation: Research Center Magnetic-Resonance-Bavaria (MRB), Würzburg, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Blaimer
authors.affiliation: Research Center Magnetic-Resonance-Bavaria (MRB), Würzburg, Germany.
authors.forename: Felix
authors.initials: F
authors.lastname: Breuer
authors.affiliation: Research Center Magnetic-Resonance-Bavaria (MRB), Würzburg, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Jakob
authors.affiliation: Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, USA.|Department of Radiology, University Hospitals, Cleveland, Ohio, USA.
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Duerk
authors.affiliation: Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, USA.
authors.forename: Nicole
authors.initials: N
authors.lastname: Seiberlich
authors.affiliation: Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, USA.|Department of Radiology, University Hospitals, Cleveland, Ohio, USA.
authors.forename: Mark
authors.initials: M
authors.lastname: Griswold
mesh_terms: D000465:Algorithms; D016477:Artifacts; D002138:Calibration; D006257:Head / Q000033:anatomy & histology*; D064368:Healthy Volunteers; D006321:Heart / Q000033:anatomy & histology*; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging
keywords: DC signal; parallel imaging; radial; trajectory estimation