title: On the confounding effect of temperature on chemical shift-encoded fat quantification.
abstract: OBJECTIVE
  To characterize the confounding effect of temperature on chemical shift-encoded (CSE) fat quantification.
  
  
  METHODS
  The proton resonance frequency of water, unlike triglycerides, depends on temperature. This leads to a temperature dependence of the spectral models of fat (relative to water) that are commonly used by CSE-MRI methods. Simulation analysis was performed for 1.5 Tesla CSE fat-water signals at various temperatures and echo time combinations. Oil-water phantoms were constructed and scanned at temperatures between 0 and 40°C using spectroscopy and CSE imaging at three echo time combinations. An explanted human liver, rejected for transplantation due to steatosis, was scanned using spectroscopy and CSE imaging. Fat-water reconstructions were performed using four different techniques: magnitude and complex fitting, with standard or temperature-corrected signal modeling.
  
  
  RESULTS
  In all experiments, magnitude fitting with standard signal modeling resulted in large fat quantification errors. Errors were largest for echo time combinations near TEinit ≈ 1.3 ms, ΔTE ≈ 2.2 ms. Errors in fat quantification caused by temperature-related frequency shifts were smaller with complex fitting, and were avoided using a temperature-corrected signal model.
  
  
  CONCLUSIONS
  Temperature is a confounding factor for fat quantification. If not accounted for, it can result in large errors in fat quantifications in phantom and ex vivo acquisitions.
authors.affiliation: Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA.
authors.forename: Diego
authors.initials: D
authors.lastname: Hernando
authors.forename: Samir D
authors.initials: SD
authors.lastname: Sharma
authors.forename: Harald
authors.initials: H
authors.lastname: Kramer
authors.forename: Scott B
authors.initials: SB
authors.lastname: Reeder
mesh_terms: D000273:Adipose Tissue / Q000473:pathology / Q000503:physiopathology*; D050154:Adiposity; D016477:Artifacts; D005234:Fatty Liver / Q000473:pathology / Q000503:physiopathology*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013696:Temperature
keywords: confounding factors; fat; fat quantification; liver imaging; proton-density fat-fraction; temperature; water imaging