Figure 3a. Transverse contrast-enhanced CT scans show partial necrosis and regrowth of residual tumor in a large bronchogenic squamous cell carcinoma located in right upper lobe treated with RF ablation in a 66-year old man. (a) Before RF ablation, scan shows a 6.0-cm enhancing heterogeneous mass (mean attenuation value, 92 HU; arrow) abutting the pleura in the right upper lobe. (b) During RF ablation, a 17-gauge cluster electrode with 2.5-cm exposed tips was placed into the tumor. (c) CT scan obtained 1 day after RF therapy shows peripheral thin enhancing rim along the medial portion of the tumor (mean attenuation value, 65 HU; net enhancement value, 26 HU; arrows) and multiple air bubbles within nonenhancing area (mean attenuation value, 39 HU; net enhancement value, 1 HU) of the tumor. (d) CT scan obtained 3 months after RF ablation shows cavitation of the tumor (arrowhead) and growth of focal enhancing area (arrow) along the medial portion of the mass compared with those features on the previous follow-up CT scan (c).