title: Fat quantification in skeletal muscle using multigradient-echo imaging: Comparison of fat and water references.
abstract: OBJECTIVE
  To investigate the precision, accuracy, and repeatability of water/fat imaging-based fat quantification in muscle tissue using a large flip angle (FA) and a fat reference for the calculation of the proton density fat fraction (FF). Comparison is made to a small FA water reference approach.
  
  
  METHODS
  An Intralipid phantom and both forearms of six patients suffering from lymphedema and 10 healthy volunteers were investigated at 1.5T. Two multigradient-echo sequences with eight echo times and FAs of 10° and 85° were acquired. For healthy volunteers, the acquisition of the right arm was performed twice with repositioning. From each set, water reference FF and fat reference FF images were reconstructed and the average FF and the standard deviation were calculated within the subfascial compartment. The small FA water reference was considered the reference standard.
  
  
  RESULTS
  A high agreement was found between the small FA water reference and large FA fat reference methods (FF bias = 0.31%). In this study, the large FA fat reference approach also resulted in higher precision (38% smaller FF standard deviation in homogenous muscle tissue), but no significant difference in repeatability between the various methods was detected (coefficient of repeatability of small FA water reference approach 0.41%).
  
  
  CONCLUSIONS
  The precision of fat quantification in muscle tissue can be increased with maintained accuracy using a larger flip angle, if a fat reference instead of a water reference is used.
authors.affiliation: Department of Medical Radiation Physics, Malmö, Department of Translational Medicine, Lund University, Skåne University Hospital, Malmö, Sweden.
authors.forename: Pernilla
authors.initials: P
authors.lastname: Peterson
authors.affiliation: Center for Medical Image Science and Visualization (CMIV), Linköping University, Linköping, Sweden.|Department of Biomedical Engineering, IMT, Linköping University, Linköping, Sweden.
authors.forename: Thobias
authors.initials: T
authors.lastname: Romu
authors.affiliation: Plastic and Reconstructive Surgery, Department of Clinical Sciences in Malmö, Lund University, Skåne University Hospital, Malmö, Sweden.
authors.forename: Håkan
authors.initials: H
authors.lastname: Brorson
authors.affiliation: Center for Medical Image Science and Visualization (CMIV), Linköping University, Linköping, Sweden.|Department of Medical and Health Sciences, Linköping University, Linköping, Sweden.
authors.forename: Olof
authors.initials: O
authors.lastname: Dahlqvist Leinhard
authors.affiliation: Department of Medical Radiation Physics, Malmö, Department of Translational Medicine, Lund University, Skåne University Hospital, Malmö, Sweden.
authors.forename: Sven
authors.identifier: http://orcid.org/0000-0002-5706-5142
authors.initials: S
authors.lastname: Månsson
mesh_terms: D000273:Adipose Tissue / Q000033:anatomy & histology* / Q000502:physiology*; D050154:Adiposity / Q000502:physiology*; D000465:Algorithms; D001834:Body Water / Q000378:metabolism; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D018482:Muscle, Skeletal / Q000033:anatomy & histology* / Q000502:physiology*; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
keywords: fat quantification; internal fat reference; skeletal muscle; water reference; water/fat imaging