title: Effects of intravenous gadolinium administration and flip angle on the assessment of liver fat signal fraction with opposed-phase and in-phase imaging.
abstract: OBJECTIVE
  To assess the effects of intravenous gadolinium (Gd) and flip angle (FA) on liver fat quantification by opposed-phase (OP) and in-phase (IP) imaging.
  
  
  METHODS
  Our Institutional Review Board (IRB) approved this Health Insurance Portability and Accountability Act (HIPAA)-compliant, retrospective, clinical study. We identified 79 patients in whom abdominal OP and IP gradient-echoes were obtained at 1.5T before and after Gd administration. All 79 patients were imaged at high FA (> or =70 degrees ); 57 were also imaged at low FA (< or =20 degrees ). Fat signal fraction (FSF) was calculated from pre- and post-Gd liver images for each subject and FA using the formula, FSF = (S(IP) - S(OP))/2S(IP), where S(IP) and S(OP) are the OP and IP signal intensities, respectively. The dataset pairs (pre-Gd vs. post-Gd; high-FA vs. low-FA) were compared using linear regression analysis.
  
  
  RESULTS
  Before Gd, FSF was significantly greater at high FA than at low FA, with regression parameters (slope/intercept) of 1.27*/0.02*, where * indicates P value <0.01. After Gd, FSF was similar at high and low FA (0.99/-0.00). Gd administration caused an FA-dependent reduction in FSF, larger at high FA (0.68*/-0.03*) than at low FA (0.94, -0.01*).
  
  
  CONCLUSIONS
  FSF by OP-IP imaging is highly dependent on FA before Gd, but this dependency is eliminated after administration of Gd. Gd appears to minimize the effect of T1-weighting and may improve the accuracy of liver fat quantification.
authors.affiliation: Department of Radiology, University of California-San Diego, 408 Dickinson Street, San Diego, CA 92122, USA.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Yokoo
authors.forename: Julie M
authors.initials: JM
authors.lastname: Collins
authors.forename: Robert F
authors.initials: RF
authors.lastname: Hanna
authors.forename: Mark
authors.initials: M
authors.lastname: Bydder
authors.forename: Michael S
authors.initials: MS
authors.lastname: Middleton
authors.forename: Claude B
authors.initials: CB
authors.lastname: Sirlin
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005234:Fatty Liver / Q000175:diagnosis*; D005260:Female; D005682:Gadolinium / Q000008:administration & dosage*; D006801:Humans; D007275:Injections, Intravenous; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies
chemical_list: D005682:Gadolinium