title: Reproducibility of MR-based liver fat quantification across field strength: Same-day comparison between 1.5T and 3T in obese subjects.
abstract: OBJECTIVE
  To examine the reproducibility of quantitative magnetic resonance (MR) methods to estimate hepatic proton density fat-fraction (PDFF) at different magnetic field strengths.
  
  
  METHODS
  This Health Insurance Portability and Accountability Act (HIPAA)-compliant study was approved by the Institutional Review Board. Following informed consent, 25 severely obese subjects (mean body mass index [BMI]: 45 ± 4, range: 38-53 kg/m(2) ) were scanned at 1.5T and 3T on the same day. Two confounder-corrected multiecho chemical shift-encoded gradient-echo-based imaging methods were acquired to estimate PDFF over the entire liver: 3D complex-based (MRI-C) and 2D magnitude-based (MRI-M) MRI. Single-voxel MR spectroscopy (MRS) was performed in the right liver lobe. Using linear regression, pairwise comparisons of estimated PDFF were made between methods (MRI-C, MRI-M, MRS) at each field strength and for each method across field strengths.
  
  
  RESULTS
  1.5T vs. 3T regression analyses for MRI-C, MRI-M, and MRS PDFF measurements yielded R(2) values of 0.99, 0.97, and 0.90, respectively. The best-fit line was near unity (slope(m) = 1, intercept(b) = 0), indicating excellent agreement for each case: MRI-C (m = 0.92 [0.87, 0.99], b = 1.4 [0.7, 1.8]); MRI-M (m = 1.0 [0.90, 1.08], b = -1.4 [-2.4, -0.5]); MRS (m = 0.98 [0.82, 1.15], b = 1.2 [-0.2, 3.0]). Comparing MRI-C and MRI-M yielded an R(2)  = 0.98 (m = 1.1 [1.02, 1.16], b = -1.8 [-2.8, -1.1]) at 1.5T, and R(2)  = 0.99 (m = 0.98 [0.93, 1.03], b = 1.2 [0.7, 1.7]) at 3T.
  
  
  CONCLUSIONS
  This study demonstrates that PDFF estimation is reproducible across field strengths and across two confounder-corrected MR-based methods.
authors.affiliation: Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA.
authors.forename: Nathan S
authors.initials: NS
authors.lastname: Artz
authors.affiliation: Department of Radiology, University of California, San Diego, California, USA.
authors.forename: William M
authors.initials: WM
authors.lastname: Haufe
authors.affiliation: Department of Radiology, University of California, San Diego, California, USA.
authors.forename: Catherine A
authors.initials: CA
authors.lastname: Hooker
authors.affiliation: Department of Radiology, University of California, San Diego, California, USA.
authors.forename: Gavin
authors.initials: G
authors.lastname: Hamilton
authors.affiliation: Department of Computational and Applied Statistics Laboratory, University of California, San Diego, California, USA.
authors.forename: Tanya
authors.initials: T
authors.lastname: Wolfson
authors.affiliation: Department of Surgery, University of Wisconsin, Madison, Wisconsin, USA.
authors.forename: Guilherme M
authors.initials: GM
authors.lastname: Campos
authors.affiliation: Department of Computational and Applied Statistics Laboratory, University of California, San Diego, California, USA.
authors.forename: Anthony C
authors.initials: AC
authors.lastname: Gamst
authors.affiliation: Department of Radiology, University of California, San Diego, California, USA.|Department of Pediatrics, University of California, San Diego, California, USA.|Department of Gastroenterology, Rady Children's Hospital, San Diego, California, USA.
authors.forename: Jeffrey B
authors.initials: JB
authors.lastname: Schwimmer
authors.affiliation: Department of Radiology, University of California, San Diego, California, USA.
authors.forename: Claude B
authors.initials: CB
authors.lastname: Sirlin
authors.affiliation: Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA.|Department of Medical Physics, University of Wisconsin, Madison, Wisconsin, USA.|Department of Biomedical Engineering, University of Wisconsin, Madison, Wisconsin, USA.|Department of Medicine, University of Wisconsin, Madison, Wisconsin, USA.|Department of Emergency Medicine, University of Wisconsin, Madison, Wisconsin, USA.
authors.forename: Scott B
authors.initials: SB
authors.lastname: Reeder
mesh_terms: D000273:Adipose Tissue / Q000473:pathology*; D000328:Adult; D015992:Body Mass Index; D017352:Echo-Planar Imaging; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D008099:Liver / Q000473:pathology; D008279:Magnetic Resonance Imaging; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008875:Middle Aged; D065626:Non-alcoholic Fatty Liver Disease / Q000473:pathology; D009765:Obesity / Q000503:physiopathology*; D011522:Protons; D012044:Regression Analysis; D015203:Reproducibility of Results
chemical_list: D011522:Protons
keywords: chemical shift; fat quantification; liver; magnetic resonance imaging; obesity; proton density fat-fraction; reproducibility