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MAGPI: A framework for maximum likelihood MR phase imaging using multiple receive coils
Author(s) -
Dagher Joseph,
Nael Kambiz
Publication year - 2016
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.25756
Subject(s) - voxel , phase (matter) , computer science , estimator , algorithm , offset (computer science) , signal to noise ratio (imaging) , smoothing , mathematics , artificial intelligence , computer vision , physics , statistics , telecommunications , quantum mechanics , programming language
Purpose 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. Theory and 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. Conclusion 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. Magn Reson Med 75:1218–1231, 2016. © 2015 Wiley Periodicals, Inc.