Microwave ablation: results in ex vivo and in vivo porcine livers with 2450-MHz cooled-shaft antenna.

Background Imaging-guided thermal ablation using different energy sources continues to gain favor as a minimally invasive technique for the treatment of primary and metastatic hepatic malignant tumors. This study aimed to evaluate the performance of microwave ablation with 2450-MHz internally cooled-shaft antenna in ex vivo and in vivo porcine livers. Methods All studies were animal care and ethics committee approved. Microwave ablation was performed using a noncooled or cooled-shaft antenna in 23 ex vivo (92 ablations) and eight in vivo (36 ablations) porcine livers. Diameters of the coagulation zone were observed on gross specimens. The coagulation diameters achieved in different microwave ablation parameter groups were compared. Curve estimation analysis was performed to characterize the relationship between applied power and treatment duration and coagulation diameter (including short-axis and long-axis diameter). Results Coagulation zones were elliptical and an arrowed-shaped carbonization zone around the shaft was observed in all groups. But the antenna track was also coagulated in the noncooled-shaft antenna groups. In ex vivo livers, the short-axis diameter correlated with the power output in a quadratic curve fashion (R-2=0.95) by fixing ablation duration to 10 minutes, and correlated with the ablation duration in a logarithmic curve fashion (R-2=0.98) by fixing power output to 80 W. The short-axis reached a relative plateau within 25 minutes. In in vivo livers, short-axis diameter correlated with the coagulation duration in a sigmoidal curve fashion (60 W group R-2=0.76, 80 W group R-2=0.87), with a relative plateau achieved within 10 minutes for power settings of 60 W and 80 W. Conclusions The internally cooled microwave antenna may be advantageous to minimize collateral damage. The short-axis diameter enlargement has a plateau by fixing power output. Chin Med J 2011;124(20):3386-3393