Magnetic resonance elastography (MRE) is more accurate than transient elastography (TE) in identifying liver fibrosis of stage 1 or more, researchers report in the February issue of Gastroenterology, using biopsy analysis as the standard. They also show that MRI-based proton density fat fraction (MRI-PDFF) analysis is more accurate than TE-based controlled attenuation parameter (CAP) assessment in detecting all grades of steatosis in patients with non-alcoholic fatty liver disease (NAFLD).
It is important to accurately measure the level of fibrosis in livers of patients with NAFLD, as it associates with long-term outcomes. Steatosis quantification is also important. Nonalcoholic steatohepatitis (NASH) is a strong indicator of disease progression, but until recently, only liver biopsies have been sufficient to identify inflammation.
TE is an ultrasound-based imaging technique that allows rapid, bedside measurements of tissue stiffness. Addition of CAP allows TE to simultaneously assess steatosis. MRI−based techniques, such as MRE and PDFF, have been shown to accurately diagnose fibrosis and steatosis, respectively, in patients with NAFLD.
Charlie C. Park et al performed a prospective, cross-sectional study to compare the performance of MRE vs TE for diagnosis of fibrosis, and MRI-PDFF analysis vs TE-based CAP for diagnosis of steatosis in 104 adult patients undergoing biopsy analysis for NAFLD.
The authors found that MRE detected any fibrosis (stage 1 or more) with an area under the receiver operating characteristic curve (AUROC) values of 0.82 — significantly higher than that the TE value of 0.67 (see figure).
MRI-PDFF detected any steatosis with an AUROC of 0.99 — significantly higher than the CAP AUROC value of 0.85.
MRE detected fibrosis of stages 2, 3, or 4 with AUROC values of 0.89, 0.87, and 0.87, respectively, whereas TE detected fibrosis of stages 2, 3, or 4 with AUROC values of 0.86, 0.80, and 0.69.
MRI-PDFF identified steatosis of grades 2 or 3 with AUROC values of 0.90 and 0.92, whereas CAP identified steatosis of grades 2 or 3 with AUROC values of 0.70 and 0.73.
Park et al state that although there have been previous direct comparisons between MRE vs TE, and MRI-PDFF vs CAP, in patients with NAFLD, this study was the first to use the XL probe. Furthermore, the findings of Park et al provide estimates of differences in diagnostic accuracy of these techniques in a Western population, with higher body mass indices than the previous studies of Asian patients. Park et al state that their results can therefore be applied to Western cohorts.
Park et al also conclude that MRI-PDFF is significantly more accurate than CAP for diagnosing all dichotomized grades of hepatic steatosis. Other advantages of MRI-based techniques over TE include larger area of the liver measured, which may reduce sampling variability, and the utility of MRI-PDFF for assessing longitudinal changes in steatosis.
The authors explain that although TE has excellent inter- and intra-operator reproducibility and is accurate for diagnosing cirrhosis, its applicability is limited by high failure rates in patients with narrow intercostal space and ascites, interference of liver stiffness measurements by extrahepatic cholestasis and acute liver injury, and low reproducibility in patients with early-stage fibrosis and in the presence of steatosis.
In an editorial that accompanies the article, Thomas Karlas et al state that it is important to remember that histologic assessment, MRE vs PDFF, and TE vs CAP evaluate distinct aspects of steatosis and fibrosis—percentages of affected hepatocytes and distribution of extracellular matrix proteins on the one hand, and physical properties like fat molecule resonance spectra, tissue stiffness, and the attenuation of an ultrasound signal, on the other. The clinical relevance of each needs to be determined. Karlas et al write that we still need a combination of biopsy and noninvasive techniques to study NASH and NAFLD.
Park et al propose that the clinical utility of MRI and TE for diagnosis of fibrosis and steatosis be tested in a multi-center, longitudinal, observational and intervention studies. The cost-effectiveness of MRE vs TE and/or biopsy must also be evaluated to develop optimal strategies for detection of NAFLD-associated fibrosis and steatosis.