title: Phase-uncertainty quality map for two-point Dixon fat-water separation.
abstract: This work investigates and compares two different phase-correction algorithms for Dixon fat-water separation and two different quality maps (QM) for region-growing: the original QM, based on phase gradients, and a QM based on phase uncertainty, proposed in this article. A spoiled dual-gradient-echo sequence was employed at 1.5 T to acquire in-phase and out-of-phase images of joints, parotid glands, abdomen and test objects. All 97 datasets were processed eight times each: with two different phase correction algorithms (original and hierarchical phase correction), with two different QM, and with/without removing linear component of the phase drifts associated with dual-echo acquisitions and bipolar readout gradient waveforms. The linear component of the phase drift along the readout direction was found to reach 4.1° pixel(-1), depending on the geometric parameters. Pre-processing to remove linear phase shifts has little impact on outcome. The hierarchic phase-correction algorithm outperformed the original phase-correction algorithm in all applications. The proposed phase-uncertainty QM provides a small performance improvement in clinical images, but can be vulnerable to flow-related phase shifts in bright vessels. Overall the most successful phase-correction technique employed phase-uncertainty QMs and hierarchic algorithms, with pre-processing to correct the linear phase drift associated with dual-echo acquisitions and bipolar readout gradient waveform.
authors.affiliation: Cancer Research UK and EPSRC Cancer Imaging Centre, Royal Marsden NHS Foundation Trust and Institute of Cancer Research, Sutton SM2 5PT, UK. maria.schmidt@icr.ac.uk
authors.forename: Maria A
authors.initials: MA
authors.lastname: Schmidt
mesh_terms: D000005:Abdomen / Q000473:pathology*; D000273:Adipose Tissue / Q000378:metabolism*; D000465:Algorithms; D000818:Animals; D016477:Artifacts; D001834:Body Water / Q000378:metabolism*; D017352:Echo-Planar Imaging / Q000379:methods*; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007596:Joints / Q000473:pathology; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D010306:Parotid Gland / Q000473:pathology; D035501:Uncertainty