New ablation procedure for a radiofrequency liver tissue coagulation system using an expandable needle.

Objective: The stepwise hook extension technique for an expandable needle, which we reported previously, allowed roll-off in short time with low power. The aim of this study was to investigate experimentally the efficacy of a modified extension procedure.
Methods: Three pigs underwent 10 radiofrequency ablation (RFA) procedures using the 10-hook electrode of LeVeen needle. The conventional technique was used in five RFA (group 1; the electrode was deployed in four steps to full extension), while the new technique was used in the other five RFA (group 2; the electrode was closed after the same three steps as group 1 and then fully extended).
Results: The shape of the RFA-induced zone was cone-like or irregular in group 1 and oval-like in group 2. The diameter vertical to the shaft was larger in group 2 (37, range 33-42 mm) than in group 1 (23, range 20-29 mm). The median ablation time was longer in group 2 (10 min 13 s) than in group 1 (3 min 56 s). Although the required energy was higher in group 2 than in group 1, that per volume was comparable between the groups (median 0.9 vs. 1.4 kJ/mm(3)).
Conclusions: Our new procedure requires a longer session but produces larger necrosis of a uniform ellipsoid volume, making it potentially suitable for tumours more than 3 cm in diameter.