Korean J Radiol.  2003 Sep;4(3):163-169. 10.3348/kjr.2003.4.3.163.

A Comparative Experimental Study of the, In-vitro Efficiency of Hypertonic, Saline-Enhanced Hepatic Bipolar and, Monopolar Radiofrequency Ablation

• Lee JM
• Han JK
• Kim SH
• Sohn KL
• Lee KH
• Ah SK
• Choi BI

• KMID: 754020
• DOI: http://doi.org/10.3348/kjr.2003.4.3.163

Abstract

OBJECTIVE
To compare the in-vitro efficiency of a hypertonic saline (HS) -enhanced bipolar radiofrequency (RF) system with monopolar RF applications by assessing the temperature profile and dimensions of RF-created coagulation necrosis in bovine liver. MATERIALS AND METHODS: A total of 27 ablations were performed in explanted bovine livers. After placement of two 16-gauge open-perfused electrodes at an interelectrode distance of 3 cm, 5% HS was instilled into tissue at a rate of 1 mL/min through the electrode. Seventeen thermal ablation zones were created in the monopolar mode (groups A, B), and ten more were created using the two open-perfused electrodes in the bipolar mode (group C). RF was applied to each electrode for 5 mins (for a total of 10 mins, group A) or 10 mins (for a total of 20 mins, group B) at 50W in the sequential monopolar mode, or to both electrodes for 10 min in the bipolar mode (group C). During RF instillation, we measured tissue temperature at the midpoint between the two electrodes. The dimensions of the thermal ablation zones and changes in impedance and wattage during RFA were compared between the groups. RESULTS: With open-perfusion electrodes, the mean accumulated energy output value was lower in the bipolar mode (group C: 26675+/-3047 Watt's) than in the monopolar mode (group A: 28778+/-1300 Watt's) but the difference was not statistically significant (p > 0.05). In the bipolar mode, there were impedance rises of more than 700 omega during RF energy application, but in the monopolar modes, impedance did not changed markedly. In the bipolar mode, however, the temperature at the mid-point between the two probes was higher (85degrees C) than in the monopolar modes (65degrees C, 80degrees C for group A, B, respectively) (p < 0.05). In addition, in HS-enhanced bipolar RFA (group C), the shortest diameter at the midpoint between the two electrodes was greater than in either of the monopolar modes: 5.4+/-5.6 mm (group A) ; 28.8+/-8.2 mm (group B) ; 31.2+/-7.6 mm (group C) (p < 0.05) CONCLUSION: Using an open perfusion system, HS-enhanced bipolar RFA more efficiently created larger areas of thermal ablation and higher tissue temperatures than monopolar RFA.

Keyword

Liver, interventional procedures; Radiofrequency ablation; Experimental study

Figure

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  Fig. 1 General setting in monopolar and bipolar radiofrequency ablation in an in-vitro bovine liver model. A. Berchtold® radio-frequency system in monopolar mode (groups A and B). An open perfused electrode and injector were used for the continuous injection of hypertonic saline. Impedance, accumulated energy and power were continuously monitored by a generator. A thermocouple was inserted 15 mm from an electrode. B. Berchtold® radio-frequency system in bipolar mode (group C). Two pumps were employed to infuse hypertonic saline solution into the tissue. Note that a thermocouple was inserted midway between the two electrodes.

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  Fig. 2 Measurements of the ablated lesions: 1- overlapping width, 2- and 3- the longest diameters along the electrode, 4- the shortest diameter midway between the two electrodes.

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  Fig. 3 Graphs of mean temperatures at the midpoint between the two electrodes in each group. Note that the highest temperatures occurred in the bipolar mode.

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  Fig. 4 Comparison of radiofrequency-induced coagulation created by applying radiofrequency in the three groups. Note that the mean shortest coagulation diameters midway between the two electrodes were largest in group C. Arrows indicate electrode tracks. A. Photograph of specimen from group A B. Photograph of specimen from group B C. Photograph of specimen from group C

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