title: Nonalcoholic fatty liver disease: diagnostic and fat-grading accuracy of low-flip-angle multiecho gradient-recalled-echo MR imaging at 1.5 T.
abstract: OBJECTIVE
  To assess the accuracy of four fat quantification methods at low-flip-angle multiecho gradient-recalled-echo (GRE) magnetic resonance (MR) imaging in nonalcoholic fatty liver disease (NAFLD) by using MR spectroscopy as the reference standard.
  
  
  METHODS
  In this institutional review board-approved, HIPAA-compliant prospective study, 110 subjects (29 with biopsy-confirmed NAFLD, 50 overweight and at risk for NAFLD, and 31 healthy volunteers) (mean age, 32.6 years +/- 15.6 [standard deviation]; range, 8-66 years) gave informed consent and underwent MR spectroscopy and GRE MR imaging of the liver. Spectroscopy involved a long repetition time (to suppress T1 effects) and multiple echo times (to estimate T2 effects); the reference fat fraction (FF) was calculated from T2-corrected fat and water spectral peak areas. Imaging involved a low flip angle (to suppress T1 effects) and multiple echo times (to estimate T2* effects); imaging FF was calculated by using four analysis methods of progressive complexity: dual echo, triple echo, multiecho, and multiinterference. All methods except dual echo corrected for T2* effects. The multiinterference method corrected for multiple spectral interference effects of fat. For each method, the accuracy for diagnosis of fatty liver, as defined with a spectroscopic threshold, was assessed by estimating sensitivity and specificity; fat-grading accuracy was assessed by comparing imaging and spectroscopic FF values by using linear regression.
  
  
  RESULTS
  Dual-echo, triple-echo, multiecho, and multiinterference methods had a sensitivity of 0.817, 0.967, 0.950, and 0.983 and a specificity of 1.000, 0.880, 1.000, and 0.880, respectively. On the basis of regression slope and intercept, the multiinterference (slope, 0.98; intercept, 0.91%) method had high fat-grading accuracy without statistically significant error (P > .05). Dual-echo (slope, 0.98; intercept, -2.90%), triple-echo (slope, 0.94; intercept, 1.42%), and multiecho (slope, 0.85; intercept, -0.15%) methods had statistically significant error (P < .05).
  
  
  CONCLUSIONS
  Relaxation- and interference-corrected fat quantification at low-flip-angle multiecho GRE MR imaging provides high diagnostic and fat-grading accuracy in NAFLD.
authors.affiliation: Department of Radiology, University of California, San Diego Medical Center, University of California at San Diego, MR3 Laboratory, 408 Dickinson St, San Diego, CA 92103-8226, USA.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Yokoo
authors.forename: Mark
authors.initials: M
authors.lastname: Bydder
authors.forename: Gavin
authors.initials: G
authors.lastname: Hamilton
authors.forename: Michael S
authors.initials: MS
authors.lastname: Middleton
authors.forename: Anthony C
authors.initials: AC
authors.lastname: Gamst
authors.forename: Tanya
authors.initials: T
authors.lastname: Wolfson
authors.forename: Tarek
authors.initials: T
authors.lastname: Hassanein
authors.forename: Heather M
authors.initials: HM
authors.lastname: Patton
authors.forename: Joel E
authors.initials: JE
authors.lastname: Lavine
authors.forename: Jeffrey B
authors.initials: JB
authors.lastname: Schwimmer
authors.forename: Claude B
authors.initials: CB
authors.lastname: Sirlin
mesh_terms: D000273:Adipose Tissue / Q000737:chemistry*; D000328:Adult; D000368:Aged; D000465:Algorithms; D002648:Child; D005234:Fatty Liver / Q000175:diagnosis* / Q000378:metabolism*; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014280:Triglycerides / Q000032:analysis*; D055815:Young Adult
chemical_list: D014280:Triglycerides