A 40-year-old male with a 10-year history of chronic hepatitis B presents with fatigue, weight loss, poor appetite, and occasional discomfort in the liver area. Physical exam: no scleral icterus, no spider angiomas, liver palpable 1.5cm below the costal margin with firm consistency and no tenderness, spleen palpable 2 fingerbreadths below the costal margin with firm consistency, no shifting dullness. Normal liver function tests. HBsAg(+), anti-HBe(+), anti-HBc(+). A diagnosis of hepatitis B cirrhosis is considered. Which of the following is most valuable for diagnosing nodular cirrhosis?