Figure 3d. (a) Unenhanced CT scan obtained in a 74-year-old woman with RCC during cryoablation shows a low-attenuation ice ball (arrow) surrounding the cryoprobe (arrowhead). (b) Immediate post-cryoablation unenhanced CT scan obtained following thawing and cryoprobe removal shows residual low attenuation in the tumor ablation zone (arrow). (c) Unenhanced CT scan obtained 5 months later during retreatment of the same kidney with RF ablation for recurrent tumor shows fat stranding (arrow) but no appreciable change in attenuation of the ablation zone. Arrowhead indicates the electrode. (d) On an unenhanced CT scan obtained immediately after RF ablation, the ablation zone (arrow) is mildly hyperattenuating relative to the renal parenchyma.