Magnetic resonance elastography: Better, but still the same!
Authors: Wuttiporn Manatsathit, Hrishikesh Samant, Marco A. Olivera‐Martinez
Journal: Hepatology (2016)

Potential conflict of interest: Nothing to report. Author names in bold designate shared co‐first authorship. To the Editor: The article published in Hepatology by Cui et al.1 is the first study comparing magnetic resonance elastography (MRE) with acoustic radiation force impulse (ARFI) in patients with nonalcoholic steatohepatitis (NASH), a population becoming more important in the modern world. Staging of fibrosis in this population, however, remains challenging without liver biopsy. The study concluded that MRE is superior to ARFI in diagnosing fibrosis (stage 0 vs. stages 1‐4) in patients with NASH based on the area under an receiver operating characteristic curve (AUROC) (MRE 0.7999 vs. ARFI 0.664; P = 0.012). This remains true in the obese population (MRE 0.85 vs. ARFI 0.603; P < 0.001). However, the most important implication of noninvasive fibrosis tests is not only in their ability to identify any fibrosis (stages 1‐4), but also in their ability to accurately identify patients with advanced fibrosis (stages 3‐4), given that this could minimize liver biopsy. However, the group of patients with stage 4 fibrosis in this study had wide variability of stiffness by MRE as compared with ARFI. This finding is also consistent with a pilot study by Loomba et al.2 demonstrating a significant amount of patients with stage 4 fibrosis with low stiffness by MRE. As expected, there are noticeable drops in the AUROCs of MRE in patients with stage 4 (0.882) compared with stage 3 (0.934). Surprisingly, the AUROCs of MRE were not significantly lower than ARFI in determining patients with stage 4 fibrosis (0.882 vs. 0.862; P = 0.418), mainly because of the small population with stage 4 fibrosis (7.5% of studied population). Therefore, although the researchers concluded that MRE is superior to ARFI, there is significant concern whether MRE can be utilized to accurately classify patients with advanced fibrosis (stages 3‐4) given that these patients are at risk of disease progression. Interestingly, a recent study by Imajo et al.3 also demonstrated that MRE is superior to ARFI in patients with NASH. This study, on the other hand, showed low variability of liver stiffness by MRE among patients with stage 4 fibrosis. This can be explained by a remarkable difference between the study by Imajo and the studies by Cui and Loomba. To be specific, the average body mass index (BMI) in the study by Imajo was 28.1 kg/m2 whereas the average BMI in the studies by Loomba and Cui were 32.4 and 31.8 kg/m2, respectively. This suggests that MRE may be superior to ARFI in the obese population, but only to a certain level of BMI. In summary, although MRE appears to be superior to ARFI, according to this study, this superiority is questionable in patients with a very high BMI. More studies are required to address this specific problem. Moreover, MRE still shares the same limitations with other noninvasive tests, including ARFI, especially in patients with stages 1‐3, because the AUROCs in this population remain unsatisfactory.