Effects of intravenous gadolinium administration and flip angle on the assessment of liver fat signal fraction with opposed-phase and in-phase imaging

Purpose: 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. Materials and 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 (≥70°); 57 were also imaged at low FA (≤20°). 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*). Conclusion: 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.