A 52-year-old man with a 10-year history of alcohol use presents with jaundice, hepatomegaly, and ascites. Serum bilirubin is 4.2 mg/dL (conjugated 3.1 mg/dL), ALT 58 U/L, AST 95 U/L, ALP 120 U/L. Prothrombin time is prolonged. Which investigation is most appropriate to confirm the suspected diagnosis of cirrhosis and assess its severity?