0601
Diagnostic performance of magnetic resonance elastography in mice with NASH and significant metabolic liver disease.1Université de Paris, Laboratory of Imaging Biomarkers, Center of Research on Inflammation, UMR 1149, Inserm, F-75018 Paris, France, Paris, France, 2Université de Paris, Institut Cochin, CNRS, INSERM, Paris, France., Paris, France, 3Service d’hépatologie et UMR1149, Hôpital Beaujon, Clichy-la-Garenne ; APHP, Université de Paris et Inserm, Clichy-la-Garenne, France, 4Diderot, CNRS, Centre de Recherche sur l'Inflammation (CRI), Paris, F-75890, France., Paris, France, 5Department of Radiology, AP-HP, Beaujon University Hospital Paris Nord, F-92110 Clichy, France, Clichy, France
Synopsis
Nonalcoholic steatohepatitis (NASH) and significant metabolic liver disease (MLD) are progressive forms of nonalcoholic fatty liver disease (NAFLD). MR elastography parameters have been shown to be useful for assessing NAFLD/NASH and liver inflammation. To assess the role of viscoelastic parameters in diagnosing NASH and significant MLD, MRE hepatic examinations were performed in mice with NAFLD. Our results showed that the diagnostic performance of MR elastography was higher in significant MLD than in NASH. This may be explained by inflammation and fibrosis occurring in indeterminate NASH cases included in MLD, and by poor performance of MR elastography to detect hepatocyte ballooning.
Introduction
Nonalcoholic fatty liver disease (NAFLD) includes simple steatosis and more progressive forms of the disease, namely nonalcoholic steatohepatitis (NASH) and significant metabolic liver disease (MLD)[1-4]. At histology, NASH is defined by the combination of three histological features: steatosis, hepatocyte ballooning, and lobular inflammation[1, 2, 5]. Significant MLD is defined histologically by fibrosis stage ≥ 2 and/or activity (sum of inflammation and ballooning) grade ≥ 2[1-4]. Significant MLD represents several histological subtypes including NASH, but also indeterminate NASH (in which inflammation and hepatocyte injury are present but atypical of definite steatohepatitis) and steatofibrosis (non-NASH with fibrosis)[6]. MR elastography has been shown to be useful for assessing NAFLD. Indeed, mechanical parameters including shear, storage and loss modulus, damping ratio and frequency dispersion coefficient have been proposed to assess the severity of NASH and liver inflammation[7-9]. However, the value of these parameters to diagnose NASH and significant MLD in NAFLD remains to be determined. Here, we assessed the value of MR elastography to diagnose NASH and significant MLD in mice with NAFLD.Methods
After local ethics committee approval, three groups of male C57BL/6 mice fed with normal diet, high fat diet or high fat, choline-deficient diet were examined with MRI (7T, 300mT/m Bruker system) at 4, 10 and 16 weeks (n = 12/time point and group). 3D MRE hepatic examinations were performed at 200 Hz, 400 Hz and 600 Hz. Monofrequency mechanical parameters (storage modulus G’, loss modulus G″, and damping ratio ζ) at 400 Hz and frequency dispersion coefficient (power law of shear stiffness (|G*|) frequency dispersion: γG*) were calculated using regions of interest covering the whole liver avoiding fat and vessels. Following MRI, mice were euthanized and their livers were analyzed by an expert liver pathologist blinded to the dietary conditions and the MRI results. Using the SAF scoring system and FLIP algorithm[1, 2], steatosis was graded from 0 to 3, inflammation from 0 to 2, ballooning from 0 to 2 and fibrosis was staged from 0 to 4. Livers with at least grade 1 for steatosis, lobular inflammation and ballooning were classified as NASH. Significant MLD was defined in the livers with fibrosis ≥ 2 and/or activity ≥ 2. To study the effect of NASH/significant MLD on hepatic mechanical parameters and assess the relationship between the MR elastography parameters and histological features, rank correlations and ROC curve analysis were used. Statistical analysis was performed only in mice with steatosis. Mice with healthy liver at histology were not included in the MR elastography evaluation.Results
Among the 59 mice with NAFLD, 21 (36%) had NASH, whereas 38 mice (64%) had significant MLD. The 38 mice with significant MLD included the 21 NASH mice and 17 mice with activity ≥ 2 without hepatocellular ballooning. Moreover, the 17 mice all had some fibrosis, including 8 mice with fibrosis ≥ 2. The results of diagnostic performance with ROC analysis showed that the storage and loss modulus and the frequency dispersion coefficient had similar moderate accuracy for diagnosing NASH (AUC 067 – 068) (Table 1). The accuracy for diagnosing significant MLD was higher (AUC 0.71 – 0.77). In contrast, the diagnostic performance of the damping ratio was low (0.51 for NASH and 0.65 for significant MLD). The correlations between the mechanical parameters showed high correlation between the storage and loss modulus (r = 89) and mild correlation between the frequency dispersion coefficient and the storage and loss modulus (r = -0.53 and r = -0.58). The damping ratio was only moderately correlated with the loss modulus (r = 39) (Table 2). Evaluation of the relationship between viscoelastic parameters and histological features showed that storage modulus G’, loss modulus G″ and frequency dispersion coefficient γG* were correlated with fibrosis and to a lesser degree with inflammation and none of them was correlated with ballooning (Table 3). Damping ratio was only correlated with fibrosis.Discussion
Our results showed that the hepatic mechanical parameters had better performance for diagnosing significant MLD than for diagnosing NASH. This may be explained by two reasons. First, significant MLD included mice with indeterminate NASH in addition to definite NASH . These mice with indeterminate NASH had substantial inflammation and fibrosis that alter the viscoelastic parameters at MR elastography. Second, the histological feature that differentiated between indeterminate and definite NASH in our study was hepatocyte ballooning. However, no correlation between the mechanical parameters and hepatocyte ballooning was observed, suggesting that MR elastography has poor performance to detect hepatocyte ballooning characteristic of NASH.Conclusion
In mice with NAFLD, the diagnostic performance of MR elastography is higher in significant MLD than in NASH. This may be explained by the fact that significant MLD includes indeterminate NASH cases with substantial inflammation and fibrosis without hepatocyte ballooning. Hepatocyte ballooning is mandatory for NASH diagnosis but does not appear to substantially alter the mechanical parameters at MR elastography in this study.Acknowledgements
This work was funded by the "Agence Nationale de la Recherche" : grants ANR-17-RHUS-0009 and ANR-11-INBS-0006.
Authors wish to thank the Inserm UMS34 platform FRIM (Federation of Research on Imaging and Multimodality).
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