Effect of echo-sampling strategy on the accuracy of out-of-phase and in-phase multiecho gradient-Echo MRI hepatic fat fraction estimation

Purpose To assess the effect of echo-sampling strategy on the accuracy of out-of-phase (OP) and in-phase (IP) multiecho gradient-echo magnetic resonance imaging (MRI) hepatic fat fraction (FF) estimation, using MR spectroscopy (MRS) proton density FF (PDFF) as a reference standard. Materials and Methods In this Institutional Review Board (IRB)-approved, Health Insurance Portability and Accountability Act (HIPAA)-compliant prospective study, 84 subjects underwent proton MRS and non-T-1-weighted gradient-echo imaging of the liver at 3T. Imaging data were collected at 16 nominally OP and IP echo times (TEs). MRI-FF was estimated while varying two echo-sampling parameters (number of consecutive echoes, starting echo number). For each combination of these parameters, MRI-FF estimation accuracy was assessed with slope, intercept, average bias, and R-2 from a linear regression of MRS-PDFF on MRI-FF. The relationship between accuracy metrics and echo-sampling parameters was assessed by Spearman rank correlation. Results For FF calculations using 3-16 echoes and a starting echo number of 1, the intercept ranged from 0.0046 to 0.0124, slope from 0.941 to 0.96, average bias from 0.0034 to 0.0078, and R-2 from 0.968 to 0.976. All four accuracy metrics were the best with the 3- and 4-echo calculations and worsened progressively with an increasing number of echoes. For a given number of echoes, there was an overall trend toward decreasing accuracy as starting echo number increased. Spearman correlation coefficients between starting echo number and intercept, slope, average bias, and R-2 were 0.911, -0.64, -0.889, and -0.954, respectively, indicating progressive loss of accuracy in each case. Conclusion Multiecho OP and IP imaging provided high FF estimation accuracy. Accuracy was highest using the earliest 3 or 4 echoes. Incorporation of additional echoes or delaying the starting echo number progressively reduced accuracy. J. Magn. Reson. Imaging 2014;39:567-575. (c) 2013 Wiley Periodicals, Inc.