Radiofrequency ablation of thoracic lesions: Part I, experiments in the normal porcine thorax

OBJECTIVE. Radiofrequency ablation has been used extensively in the liver for the localized thermal coagulation of tumors. It has been applied more recently percutaneously in the lung under CT imaging guidance. In advance of our own clinical application, we performed experimental percutaneous radiofrequency ablation in normal lung tissues in a large animal model using a U.S. Food and Drug Administration-approved device to assess its use. MATERIALS AND METHODS. Radiofrequency ablation of 22 thoracic sites was performed in vivo in three pigs with an array-style electrode. Tissue impedance and ablation duration were measured for each site. The intact lungs were excised for gross inspection and for imaging with CT and MRI. Representative lesions were evaluated histologically. RESULTS. The mean intraprocedural tissue impedance was 93 Omega (range, 52-184 Omega). Six of 22 ablations exhibited a marked increase in impedance after 5 min of treatment. On gross inspection, parenchymal lesions were generally round and targetlike in appearance. CT showed sites of ablation to be composed of a heterogeneous inner zone surrounded by a high-density outer zone. On MRI, the inner zone was typically hyperintense on T1-weighted fast spin-echo imaging, and the outer zone was hyperintense on T2-weighted fast spin-echo imaging. At histology, the inner zone was characterized by coagulation necrosis, and the outer zone by hyperemia and edema. No acute lung-specific complications were seen. There was one extensive skin burn and one cardiac-related death. CONCLUSION. These results support current seminal clinical evidence that percutaneous radiofrequency ablation in the lung is feasible and can be applied safety. Radiofrequency-induced lesions in the normal porcine lung can be visualized with both CT and MRI; image appearance is concordant with histologic tissue changes.