title: Fat fraction bias correction using T1 estimates and flip angle mapping.
abstract: OBJECTIVE
  To develop a new method of reducing T1 bias in proton density fat fraction (PDFF) measured with iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL).
  
  
  METHODS
  PDFF maps reconstructed from high flip angle IDEAL measurements were simulated and acquired from phantoms and volunteer L4 vertebrae. T1 bias was corrected using a priori T1 values for water and fat, both with and without flip angle correction. Signal-to-noise ratio (SNR) maps were used to measure precision of the reconstructed PDFF maps. PDFF measurements acquired using small flip angles were then compared to both sets of corrected large flip angle measurements for accuracy and precision.
  
  
  RESULTS
  Simulations show similar results in PDFF error between small flip angle measurements and corrected large flip angle measurements as long as T1 estimates were within one standard deviation from the true value. Compared to low flip angle measurements, phantom and in vivo measurements demonstrate better precision and accuracy in PDFF measurements if images were acquired at a high flip angle, with T1 bias corrected using T1 estimates and flip angle mapping.
  
  
  CONCLUSIONS
  T1 bias correction of large flip angle acquisitions using estimated T1 values with flip angle mapping yields fat fraction measurements of similar accuracy and superior precision compared to low flip angle acquisitions.
authors.affiliation: Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Issac Y
authors.initials: IY
authors.lastname: Yang
authors.forename: Yifan
authors.initials: Y
authors.lastname: Cui
authors.forename: Curtis N
authors.initials: CN
authors.lastname: Wiens
authors.forename: Trevor P
authors.initials: TP
authors.lastname: Wade
authors.forename: Lanette J
authors.initials: LJ
authors.lastname: Friesen-Waldner
authors.forename: Charles A
authors.initials: CA
authors.lastname: McKenzie
mesh_terms: D000273:Adipose Tissue / Q000502:physiology; D001853:Bone Marrow / Q000502:physiology; D003198:Computer Simulation; D064368:Healthy Volunteers; D006801:Humans; D021621:Imaging, Three-Dimensional; D008159:Lumbar Vertebrae / Q000502:physiology*; D008279:Magnetic Resonance Imaging; D019047:Phantoms, Imaging; D011522:Protons; D015203:Reproducibility of Results; D059629:Signal-To-Noise Ratio; D014867:Water / Q000737:chemistry*
chemical_list: D011522:Protons; D014867:Water
keywords: T1 bias correction; fat quantification; flip angle map