# In Vivo Evaluation of a Novel Radiofrequency Ablation Electrode in Pig Layers
## 3 Results  
### Outcomes of RFA  
Gross necropsy findings showed a well-demarcated ablated lesion that could be distinguished from surrounding liver parenchyma by a whitish peripheral rim (Figure 2). Figure 1: Endoscopic radiofrequency electrode and power generator (STARmed, Seoul, Korea). (**A**) 19-gauge endoscopic radiofrequency ablation electrode. (**B**) A VIVA radiofrequency power generator. In test one, at 0.5, 0.7, 1, and 1.5 cm probe tip lengths, the mean maximal injury widths were 0.46 \(\pm\) 0.07, 0.54 \(\pm\) 0.05, 0.65 \(\pm\) 0.05, and 0.77 \(\pm\) 0.02 cm, respectively, while the mean maximal injury depths were 0.65 \(\pm\) 0.07, 0.92 \(\pm\) 0.08, 1.26 \(\pm\) 0.14, and 1.80 \(\pm\) 0.11 cm, respectively (Table 1, Figures 2 and 3). Therefore, injury width and depth increased with electrode length and RFA power. The roll-off phenomenon occurred between 7 s and  
In test two, in groups A (1 cm, 30 W, 10 s), B (1 cm, 30 W, 15 s), and C (1 cm, 50 W, 10 s), the mean maximal injury widths were 0.56 \(\pm\) 0.05, 0.65 \(\pm\) 0.06, and 0.65 \(\pm\) 0.05 cm, respectively, while the mean maximal injury depths were 1.06 \(\pm\) 0.29, 1.14 \(\pm\) 0.05, and 1.26 \(\pm\) 0.09 cm, respectively (Table 2, Figures 4 and 5). Therefore, the maximal injury width and depth were similar between groups B and C (Table 2). The roll-off phenomenon occurred between 12 and 15 s in group B.  
lesions are located in the left lobe and in the caudate lobe, however, percutaneous RFA may be difficult. Furthermore, the subcapsular/subdiaphragmatic location may have an intrinsic risk of thermal injury, resulting in pleural effusion or hemothorax and a higher risk of tumor seeding/tumor recurrence [12]. EUS-RFA could be beneficial when percutaneous RFA is not applicable in patients with hepatic tumors. However, overall clinical experience with EUS-RFA is limited, therefore, there is uncertainties of clinical efficacy and concerns about EUS-RFA related adverse events. Therefore, preclinical validation is mandatory for the application of EUS-RFA. Ex vivo experiments are easy to perform, however, these may produce different ablation results than in vivo studies since blood flow is absent. Proximity to large blood vessels also plays a significant role in heat transmission. Blood flow acts as a \"heat sink\" and cools nearby tissue, thereby limiting the ablation effect [13, 14]. Although it is more difficult to perform in vivo tests, they do produce more realistic data. In the present study, therefore, we evaluated the effects of a novel RFA electrode using pig livers in vivo as a virtual mass to correctly measure the effects probe and procedure variables have on the width and depth of ablation. Our results showed that the ablation effects correlate with the length of electrode. There is a possibility that the shortest probe length (0.5 cm) at the weakest power (10 W) may lead to insufficient ablation. In contrast, when treating with the longest probe length (1.5 cm) at the strongest power (75 W), the ablation effect can be increased for ablation of hepatic lesions. Furthermore, we also compared ablation effects based on ablation power and time, including the settings currently used for EUA-RFA for pancreatic tumors (1 cm, 50 W, 10 s) [1, 3, 6]. Ablation effects increased with ablation power (50 W) and time (15 s), unpredictable roll-off phenomena occurred at extended ablation time. This might decrease the ablation effect in target lesions. Unlike pancreatic lesions, hepatic lesions are surrounded by a large parenchyma, safety margins in the liver are larger than in the pancreas. In terms of optimal settings for EUS-RFA, its efficacy for ablation of hepatic tumors, therefore, longer probe with stronger power will be effective for treating hepatic tumors. A major limitation of this study is that RFA was conducted only in a small number of pigs. Secondly, we could not evaluate possible late adverse events, such as bleeding, or perforation.