A 38-year-old woman with a history of alcohol use disorder presents with jaundice, hepatomegaly, and mild ascites. Liver function tests show ALT 85 U/L, AST 120 U/L, alkaline phosphatase 95 U/L, and bilirubin 3.2 mg/dL. Ultrasound abdomen shows hepatic steatosis with normal echotexture otherwise. Which investigation would be most appropriate to determine whether the hepatic injury is reversible (fatty change) or has progressed to irreversible cirrhosis?