Purpose of Review
The dramatic increase in nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) fostered the development and evaluation of non-invasive, imaging based methods for diagnosing NAFLD, NASH, and its complications. We herein review different radiologic modalities in diagnosing steatosis, fibrosis, and liver cirrhosis.
While routine abdominal ultrasound with hyperechogenic liver structure only detects moderate to severe steatosis, controlled attenuation parameter (CAP), magnetic resonance spectroscopy (MRS), and, especially, MRI-proton density fat fraction (MRI-PDFF) are more sensitive to diagnose and quantify steatosis. MRI-PDFF appears suitable to monitor treatment-related changes in liver fat in clinical trials. Liver fibrosis is related to hepatic and extrahepatic morbidity and mortality in NAFLD. Fibrosis and cirrhosis can be suspected by ultrasound-based elastography techniques (vibration-controlled transient elastography, VCTE; acoustic resonance forced impulse imaging, ARFI; shear wave elastography, SWE), which may be used to screen for fibrosis in high-risk patients. MR elastography (MRE) appears advantageous to quantify and stage fibrosis, while angiographic hepatic venous pressure gradient (HVPG) measurement can confirm portal hypertension in cirrhosis. Screening for hepatocellular carcinoma (HCC) in cirrhotic livers is done by ultrasound; suspicious nodules are followed by multiphasic CT/MRI, contrast-enhanced ultrasound (CEUS), or contrast-enhanced MRI.
Different radiologic modalities exist to screen, diagnose, stage, and monitor steatosis, steatohepatitis, fibrosis, and HCC, thereby complementing liver biopsy and blood biomarkers in the management of patients with NAFLD.