title: Parameter estimation approach to banding artifact reduction in balanced steady-state free precession.
abstract: OBJECTIVE
  The balanced steady-state free precession (bSSFP) pulse sequence has shown to be of great interest due to its high signal-to-noise ratio efficiency. However, bSSFP images often suffer from banding artifacts due to off-resonance effects, which we aim to minimize in this article.
  
  
  METHODS
  We present a general and fast two-step algorithm for 1) estimating the unknowns in the bSSFP signal model from multiple phase-cycled acquisitions, and 2) reconstructing band-free images. The first step, linearization for off-resonance estimation (LORE), solves the nonlinear problem approximately by a robust linear approach. The second step applies a Gauss-Newton algorithm, initialized by LORE, to minimize the nonlinear least squares criterion. We name the full algorithm LORE-GN.
  
  
  RESULTS
  We derive the Cramér-Rao bound, a theoretical lower bound of the variance for any unbiased estimator, and show that LORE-GN is statistically efficient. Furthermore, we show that simultaneous estimation of T1 and T2 from phase-cycled bSSFP is difficult, since the Cramér-Rao bound is high at common signal-to-noise ratio. Using simulated, phantom, and in vivo data, we illustrate the band-reduction capabilities of LORE-GN compared to other techniques, such as sum-of-squares.
  
  
  CONCLUSIONS
  Using LORE-GN we can successfully minimize banding artifacts in bSSFP.
authors.affiliation: Department of Information Technology, Uppsala University, Uppsala, Sweden.
authors.forename: Marcus
authors.initials: M
authors.lastname: Björk
authors.forename: R Reeve
authors.initials: RR
authors.lastname: Ingle
authors.forename: Erik
authors.initials: E
authors.lastname: Gudmundson
authors.forename: Petre
authors.initials: P
authors.lastname: Stoica
authors.forename: Dwight G
authors.initials: DG
authors.lastname: Nishimura
authors.forename: Joëlle K
authors.initials: JK
authors.lastname: Barral
mesh_terms: D000465:Algorithms; D016477:Artifacts; D001931:Brain Mapping / Q000379:methods*; D003198:Computer Simulation; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009010:Monte Carlo Method; D019047:Phantoms, Imaging
keywords: LORE; bSSFP; banding artifacts; off-resonance; parameter estimation