Patients undergoing computed tomography guided radiofrequency ablation of hepatic tumor under scheduled general anesthesia, and fulfilled one of following inclusion criteria:  diameter of hepatic tumor is larger than 2 cm distance of tumor site is near the hepatic surface < 2cm  Exclusion criteria:  A history of allergic reaction to local anesthetics or iohexol Renal insufficiency, creatinine clearance < 30mL/min Coagulopathy or other bleeding disorder that cannot perform nerve block Under pregnancy or lactation Opioid tolerant patient