Objective: The aim of this study was to design a novel radiofrequency (RF) electrode for larger and more round ablation volumes and its ability to achieve the complete ablation of liver tumors (> 3 cm in diameter) using finite element method. Methods: A new RF expandable electrode comprising three parts (i.e., insulated shaft, changing shaft, and hooks) was designed. Two modes of this new electrode (i.e., monopolar expandable electrode (MEE) and hybrid expandable electrode (HEE)) and a commercial expandable electrode (CEE) were investigated using liver tissue with and without liver tumor. A temperature-controlled radiofrequency ablation (RFA) protocol with a target temperature of 95 °C and an ablation time of 15 minutes was used in this study. Both the volume and shape of the ablation zone were studied for all RF electrodes. A large liver tumor with the diameter of 3.5 cm was used to evaluate the effectiveness on the complete ablation of the new designed electrode. Results: In the first scenario (without liver tumor), the ablation volumes of CEE, HEE, and MEE were 9.96 cm3, 41.0 cm3, and 46.14 cm3, respectively. The values of sphericity index (SI) of CEE, HEE, and MEE were 0.36, 0.94, and 0.98, respectively. The best performance was achieved by the MEE electrode. In the second scenario (with liver tumor), the ablation volumes of MEE and CEE were 67.56 cm3 and 20.62 cm3, respectively. Also, a rounder ablation volume was generated by MEE compared to CEE (SI: 0.98 vs 0.55). Conclusion: This study concludes that compared with CEE, both MEE and HEE are able to get larger and more round ablation volumes due to the larger electrode-tissue interface and more round shape of hooks; compared with HEE, MEE is better to get a larger and rounder ablation volume; MEE is able to ablate a large liver tumor (i.e., 3.5 cm in diameter) completely.

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