title: MAGPI: A framework for maximum likelihood MR phase imaging using multiple receive coils.
abstract: OBJECTIVE
  Combining MR phase images from multiple receive coils is a challenging problem, complicated by ambiguities introduced by phase wrapping, noise, and the unknown phase-offset between the coils. Various techniques have been proposed to mitigate the effect of these ambiguities but most of the existing methods require additional reference scans and/or use ad hoc post-processing techniques that do not guarantee any optimality.
  
  
  METHODS
  Here, the phase estimation problem is formulated rigorously using a maximum-likelihood (ML) approach. The proposed framework jointly designs the acquisition-processing chain: the optimized pulse sequence is a single multiecho gradient echo scan and the corresponding postprocessing algorithm is a voxel-per-voxel ML estimator of the underlying tissue phase.
  
  
  RESULTS
  Our proposed framework (Maximum AmbiGuity distance for Phase Imaging, MAGPI) achieves substantial improvements in the phase estimate, resulting in phase signal-to-noise ratio (SNR) gains by up to an order of magnitude compared to existing methods.
  
  
  CONCLUSIONS
  The advantages of MAGPI are: (1) ML-optimal combination of phase data from multiple receive coils, without a reference scan; (2) voxel-per-voxel ML-optimal estimation of the underlying tissue phase, without the need for phase unwrapping or image smoothing; and (3) robust dynamic estimation of channel-dependent phase-offsets.
authors.affiliation: Department of Medical Imaging, The University of Arizona, Tucson, Arizona, USA.
authors.forename: Joseph
authors.initials: J
authors.lastname: Dagher
authors.affiliation: Department of Medical Imaging, The University of Arizona, Tucson, Arizona, USA.
authors.forename: Kambiz
authors.initials: K
authors.lastname: Nael
mesh_terms: D000465:Algorithms; D001921:Brain / Q000000981:diagnostic imaging; D001931:Brain Mapping / Q000379:methods; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D012815:Signal Processing, Computer-Assisted
keywords: MR phase; coil array; frequency offset; maximum likelihood; phase offset