Fig. 7.

Expected treatment response after percutaneous ethanol ablation (PEA), radiofrequency ablation (RFA) and microwave ablation (MWA). Axial contrast-enhanced CT images of the liver obtained in late arterial phase are illustrated: a Pretreatment: RFA is used with curative intent of early-stage hepatocellular carcinoma (≤ 3 cm) in non-surgical patients. PEA is typically used when RFA is unsafe or contraindicated. MWA may target larger tumor with curative intent but additional studies are needed. Larger tumor (> 3 cm) may be targeted for downstaging purpose or as a bridging therapy prior to transplantation alone or in combination with other treatments. b 1–3 months posttreatment: Diameter of ablation zone at the time of treatment is usually 5 to 10 mm greater than the treated lesion. The following features may be seen: intratumoral gas foci up to 1 month posttreatment, thin linear peripheral enhancement along ablation zone, smooth rind or wedge-shaped parenchymal enhancement around ablation zone, intralesional hyperdensity/intensity on unenhanced CT or on T1-weighted MRI (reflecting coagulation necrosis), and hypodense liver parenchyma may be seen along needle trajectory. c ≥ 6 months posttreatment: ablation zone involutes over time. Thin linear peripheral enhancement along ablation zone decreases. Parenchymal enhancement resolves. At any point posttreatment, presence of nodular arterial phase hyperenhancement, washout appearance, or enhancement similar to pretreatment indicates recurrence or residual viable tumor