Magnetic resonance elastography (MRE) is a noninvasive imaging tool for the quantitative measurement of liver stiffness. MRE has a high accuracy for the diagnosis of liver fibrosis, independent of BMI or chronic liver disease etiology . Several studies have characterized the diagnostic performance of MRE for the staging of liver fibrosis in chronic liver disease. These studies report a range of threshold values used for fibrosis staging (Table 1).
For example, the following values are used at the Mayo Clinic .
<2.5 kPa = Normal
2.5 – 2.9 = Normal or Inflammation
2.9 – 3.5 = Stage 1-2
3.5 – 4.0 = Stage 2-3
4.0 – 5.0 = Stage 3-4
>5.0 kPa = Stage 4
Although liver biopsy is considered the standard reference of the diagnosis of liver fibrosis, there are several important limitations including questionable accuracy due to sampling error and inter- and intra-observer variability, invasiveness, expense, and limited application for monitoring treatment response.
Determining liver stiffness thresholds for fibrosis staging may be confounded by these inaccuracies, where misclassification of fibrosis stage can occur in up to 25% of cases . The proposed stiffness thresholds were calculated as the mean reported threshold for each fibrosis stage from the literature.
References:  S. Singh et al., “Magnetic resonance elastography for staging liver fibrosis in non-alcoholic fatty liver disease: a diagnostic accuracy systematic review and individual participant data pooled analysis,” Eur Radiol, 2016; 26:1431–1440.  S.K. Venkatesh and R.L. Ehman “Magnetic Resonance Elastography of Liver,” Magn Reson Imaging Clin N Am, 2014; 22:433–446.  A. Regev et al., “Sampling error and intra-observer variation in liver biopsy in patients with chronic HCV infection.” Am J Gastroenterol. 2002; 97:2614-2618.