Percutaneous radiofrequency tissue ablation: Optimization of pulsed radiofrequency technique to increase coagulation necrosis

PURPOSE: To develop a computerized algorithm for pulsed, high-current percutaneous radiofrequency (RF) ablation, which maximally increases the extent of induced coagulation necrosis. MATERIALS AND METHODS: An automated, Programmable algorithm for pulsed-RF deposition was designed to permit high-current deposition by periodically reducing current for 5-30 seconds during RF application. Two strategies for pulsed-RF deposition were evaluated: (i) constant peak current (900-1,800 mA) of variable duration and (ii) variable peak current (1,200-2,000 mA) for a specified minimum duration. The extent of induced coagulation was compared to results obtained with continuous (lower current) RF application. Trials were performed in ex vivo calf liver (n = 115) and in vivo porcine liver (n = 30) and muscle (n = 18) with use of 2-4-cm tip, internally cooled electrodes. RESULTS: For 3-cm electrodes in ex vivo liver, applying pulsed-RF with constant peak current for 12 minutes produced 3.5 cm +/- 0.2 of necrosis, Greater necrosis was produced with use of the variable current strategy, in which 4.5 cm +/- 0.2 of coagulation was achieved with use of an initial current greater than or equal to 1,500 mA (minimum peak-RF duration of 10 sec, with 15 sec of reduced current to 100 mA between peaks; P < .01). This variable peak current algorithm also produced 3.7 cm +/- 0.6 of necrosis in in vivo liver, and 6.5 cm +/- 0.9 in in vivo muscle. Without pulsing, a maximum of 750 mA, 1,100 mA, and 1,500 mA could be applied in ex vivo liver, in vivo liver, and in vivo muscle, respectively, which resulted in 2.9 cm +/- 0.2, 2.4 cm +/- 0.2, and 5.1 cm +/- 0.4 of coagulation (P < .05, all comparisons). CONCLUSIONS: A variable peak current algorithm for pulsed-RF deposition can increase coagulation necrosis diameter over other ablation strategies. This innovation may ultimately enable the percutaneous treatment of larger tumors.