Korean J Radiol.  2004 Dec;5(4):250-257. 10.3348/kjr.2004.5.4.250.

Optimization of Wet Radiofrequency Ablation Using a Perfused-Cooled Electrode: A Comparative Study in Ex Vivo Bovine Livers

• Lee JM
• Han JK
• Kim SH
• Lee JY
• Shin KS
• Han CJ
• Lee MW
• Choi JI
• Choi BI

• KMID: 1118832
• DOI: http://doi.org/10.3348/kjr.2004.5.4.250

Abstract

OBJECTIVE
To determine the optimized protocol for wet monopolar radiofrequency ablation (RFA) using a perfused-cooled electrode to induce coagulation necrosis in the ex vivo bovine liver. MATER AND METHODS: Radiofrequency was applied to excised bovine livers in a monopolar mode using a 200W generator with an internally cooled electrode (groups A and B) or a perfused-cooled electrode (groups C, D, E, and F) at maximum power (150-200 W) for 10 minutes. A total of 60 ablation zones were created with six different regimens: group A - dry RFA using intra-electrode cooling; group B - dry RFA using intra-electrode cooling and a pulsing algorithm; group C - wet RFA using only interstitial hypertonic saline (HS) infusion; group D - wet RFA using interstitial HS infusion and a pulsing algorithm; group E - wet RFA using interstitial HS infusion and intra-electrode cooling; and group F - wet RFA using interstitial HS infusion, intra-electrode cooling and a pulsing algorithm. In groups C, D, E, and F, RFA was performed with the infusion of 6% HS through the perfused cooled electrode at a rate of 2 mL/minute. During RFA, we measured the tissue temperature at a distance of 15 mm from the electrode. The dimensions of the ablation zones and the changes in impedance, currents, and liver temperature during RFA were compared between these six groups. RESULTS: During RFA, the mean tissue impedances in groups A (243+/-88 omega) and C (252.5+/-108 omega) were significantly higher than those in groups B (85+/-18.7 omega), D (108.2+/-85 omega), E (70.0+/-16.3 omega), and F (66.5+/-7 omega) (p < 0.05). The mean currents in groups E and F were significantly higher than those in groups B and D, which were significantly higher than those in groups A and C (p < 0.05) : 520+/-425 mA in group A, 1163+/-34 mA in group B, 652.5+/-418 mA in group C, 842.5+/-773 mA in group D, 1665+/-295 mA in group E, and 1830+/-109 mA in group F. The mean volumes of the ablation regions in groups E and F were significantly larger than those in the other groups (p < 0.05) : 17.7+/-5.6 cm3 in group A, 34.5+/-3.0 cm3 in group B, 20.2+/-15.6 cm3 in group C, 36.1+/-19.5 cm3 in group D, 68.1+/-12.4 cm3 in group E, and 79.5+/-31 cm3 in group F. The final tissue temperatures at a distance of 15 mm from the electrode were higher in groups E and F than those in groups A, C, and D (p < 0.05) : 50+/-7.5 degreesC in group A, 66+/-13.6 degreesC in group B, 60+/-13.4 degreesC in group C, 61+/-12.7 degreesC in group D, 78+/-14.2 degreesC in group E, and 79+/-12.0 degreesC in group F. CONCLUSION: Wet monopolar RFA, using intra-electrode cooling and interstitial saline infusion, showed better performance in creating a large ablation zone than either dry RFA or wet RFA without intra-electrode cooling.

Keyword

Experimental study; Interventional procedures; Liver; Radiofrequency ablation

MeSH Terms

Animals
Body Temperature
Catheter Ablation/*instrumentation
Cattle
Disease Models, Animal
Electric Impedance
Electrodes, Implanted
Equipment Design
Liver/pathology/*surgery
Necrosis
Perfusion
Saline Solution, Hypertonic/administration & dosage

Figure

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  Fig. 1 Photograph of a perfused-cooled electrode equipped for saline interstitial infusion on one side.

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  Fig. 2 Comparison of radiofrequency-induced coagulation between the four groups. Note that the shot-axis coagulation diameters were larger in groups E and F than in the other groups. Arrows indicate the short-axis diameter of the ablation zone. A. Photograph of specimen from group A (Standard dry RFA using intra-electrode cooling). B. Photograph of specimen from group B (Standard dry RFA using intra-electrode cooling and a pulsed algorithm). C. Photograph of specimen from group C (Wet RFA using interstitial saline infusion). D. Photograph of specimen from group D (Wet RFA using interstitial saline infusion and a pulsed algorithm). E. Photograph of specimen from group E (Wet RFA using interstitial saline infusion and intra-electrode cooling). F. Photograph of specimen from group F (Wet RFA using interstitial saline infusion, intra-electrode cooling and a pulsed algorithm).

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