title: Two-point Dixon fat-water separation: improving reliability and accuracy in phase correction algorithms.
abstract: OBJECTIVE
  To propose an advanced phase-correction region-growing algorithm for two-point fat-water separation suitable for parotid assessment, and to evaluate the general performance of phase-correction algorithms.
  
  
  METHODS
  Two region-growing algorithms were evaluated in test objects and in head images: the original phase-correction algorithm (OPC) and the advanced phase-correction algorithm with voxel size manipulation (VSM) which includes: 1) starting the region-growing process from images of lower resolution and subsequently stepping toward the original matrix size, and 2) limiting the use of low-pass filters to fat-water interfaces with partial volume effects
  
  
  RESULTS
  Fundamental problems relate to biological tissue spectrum being poorly approximated by two discrete peaks for fat and water. The VSM algorithm was shown to be less noise-sensitive, faster, and to produce a better approximation for the field inhomogeneity map. In head images (6 volunteers, 10 slices each) 43 errors were found with the OPC algorithm and only 6 errors with the VSM algorithm. Only the OPC algorithm produced errors surrounding the parotids (10 errors).
  
  
  CONCLUSIONS
  The VSM algorithm provides a more accurate and less noise-sensitive fat-water separation. This highly significant performance improvement allows the application of phase-correction algorithms to a wider range of clinical applications.
authors.affiliation: Department of Medical Physics, St George's Hospital, London, UK. maria.schmidt@icr.ac.uk
authors.forename: Maria A
authors.initials: MA
authors.lastname: Schmidt
authors.forename: Karlene M
authors.initials: KM
authors.lastname: Fraser
mesh_terms: D000273:Adipose Tissue; D000465:Algorithms; D001834:Body Water; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D010306:Parotid Gland / Q000473:pathology*; D015203:Reproducibility of Results