A standard hepatic MRE technique uses a 2D gradient-echo (GRE) pulse sequence with an echo time (TE) of ~20 ms¹. This relatively long TE makes the sequence T2*-weighted, and thus sensitive to T2* shortening which can lead to unreliable estimates of liver stiffness. To overcome this problem, a 2D spin-echo echo-planar-imaging (SE-EPI) MRE sequence was developed that uses a shorter TE (11.8 ms) and so is less sensitive to T2 and T2* effects^2,3,4. Some investigators advocate the use of this sequence at 3T instead of the 2D GRE sequence, as it may provide higher signal-to-noise ratio. However, to our knowledge, agreement of liver stiffness estimates obtained using these two sequences has not been fully examined at 3T. Thus, the main purpose of this study was to evaluate agreement between these sequences for estimating liver stiffness at 3T. A secondary purpose was to compare wave-image quality of the two sequences, using the size of the adequate-wave-quality region of interest (ROI) as an objective indicator of wave-image quality.This was an IRB-approved, HIPAA-compliant, secondary analysis of MRE data acquired prospectively in 30 adults with histology-confirmed nonalcoholic fatty liver disease (NAFLD) enrolled in a research registry at our institution. 2D GRE and 2D SE-EPI MRE sequences with superior/inferior motion sensitization were obtained at 3T (GE Signa EXCITE HDxt, GE Healthcare, Waukesha, WI). MRE pulse sequences and hardware were supplied by Resoundant Inc. (Rochester, MN). Images were analyzed using a 2D multimodel direct inversion (MMDI) technique⁵. Parameters common to both sequences included: four 10-mm axial slices with 0 mm gaps, four phase offsets, torso receiver-array surface coil, and 60 Hz mechanical vibration frequency. Additional parameters for 2D GRE/SE sequence included: TR 50/267 ms, TE 20/11.8 ms, and FA 30°/90°. Elastograms depicting the spatial distribution of stiffness were generated automatically with overlain confidence maps demarcating the areas in which wave data was adequate. Trained analysts used a custom software package (MRE/Quant software, Mayo Clinic) to specify the largest possible adequate-wave-quality ROIs in the liver while excluding large blood vessels and liver edges. ROI sizes and mean stiffness values in the ROIs were recorded for both sequences. Stiffness estimates and ROI sizes were compared with Bland-Altman analyses and t-tests as appropriate. Additionally, a multivariate analysis was performed to assess the relationship between ROI size, liver stiffness measurement, and MRE sequence.Mean hepatic stiffness of 3.3 ± 1.6 kPa (range 2.1 kPa to 9.4 kPa) using GRE and 3.1 ± 1.2 kPa (range 2.0 to 6.9 kPa) using SE. As shown in Figure 1, agreement between liver stiffness estimates for the two MRE sequences was good. Bland-Altman bias was small (GRE stiffness > SE stiffness by 0.19 kPa) and not significant (p =0.12). Limits of agreement were tight (-1.092-1.476) overall. However, disagreement increased as stiffness increased: there was a strong correlation between the average of the two sequences’ stiffness estimates and the absolute values of the difference (p<00001). Mean ROI size for the 2D SE-EPI sequence (4,369±2181 pixels) was larger than for the 2D GRE sequence (2,935±1200 pixels)(p<0.01). ROI sizes for the two sequences were correlated (r= 0.65). In the multivariate analysis, there was no significant relationship between ROI size and differences in estimated stiffness by the two sequences (r =0.0045, p=0.44).Although agreement in stiffness values by the two MRE sequences was close overall, it diverged in subjects with higher liver stiffness values. This suggests that while both sequences may be used clinically and in research they may not be interchangeable, especially in patients with more advanced disease. It may be prudent to use the same sequence for longitudinal monitoring in any given individual. Wave-image quality was better for the 2D SE-EPI sequence, as assessed by ROI size, but in multivariate analysis the superior wave-image quality did not account for differences in liver stiffness estimated by the two sequences. The significant correlation in ROI size for the two sequences indicates that common factors affect wave image quality. Further research is needed to identify the causes of stiffness estimation disagreement, to better understand the factors that affect wave image quality, and to compare the accuracy of the two sequences (beyond the scope of this analysis) for fibrosis assessment at 3T.Liver stiffness values obtained from 2D GRE and 2D SE-EPI MRE sequences agree closely across a range of liver stiffness values in adults with NAFLD, although agreement tends to diverge at higher stiffness values. Differences at higher liver stiffness values were not explained by differences in image wave quality.