Korean J Radiol.  2006 Jun;7(2):106-117. 10.3348/kjr.2006.7.2.106.

Hepatic Radiofrequency Ablation Using Multiple Probes: Ex Vivo and In Vivo Comparative Studies of Monopolar versus Multipolar Modes

• Lee JM
• Han JK
• Lee JY
• Kim SH
• Choi JY
• Lee MW
• Choi SH
• Eo H
• Choi BI

• KMID: 1782183
• DOI: http://doi.org/10.3348/kjr.2006.7.2.106

Abstract

OBJECTIVE
We wanted to compare the efficiency of multipolar radiofrequency ablation (RFA) using three perfused-cooled electrodes with multiple overlapping- and simultaneous monopolar techniques for creating an ablation zone in ex vivo bovine livers and in in vivo porcine livers. MATERIALS AND METHODS: In the ex vivo experiments, we used a 200 W generator (Valleylab, CC-3 model) and three perfused-cooled electrodes or internally cooled electrodes to create 30 coagulation zones by performing consecutive monopolar RFA (group A, n = 10), simultaneous monopolar RFA (group B, n = 10) or multipolar RFA (group C, n = 10) in explanted bovine livers. In the consecutive mode, three ablation spheres were created by sequentially applying 150 watts radiofrequency (RF) energy to the internally cooled electrodes for 12 minutes each for a total of 36 minutes. In the simultaneous monopolar and multipolar modes, RF energy was concurrently applied to the three perfused-cooled electrodes for 20 minutes at 150 watt with instillation of 6% hypertonic saline at 2 mL/min. During RFA, we measured the temperatures of the treated area at its center. The changes in impedance, the current and liver temperature during RFA, as well as the dimensions of the thermal ablation zones, were compared among the three groups. In the in vivo experiments, three coagulations were created by performing multipolar RFA in a pig via laparotomy with using same parameter as the ex vivo study. RESULTS: In the ex vivo experiments, the impedance was gradually decreased during the RFA in groups B and C, but in group A, the impedance was increased during RFA and this induced activation by the pulsed RF technique. In groups A, B and C, the mean final-temperature values were 80 +/- 10 degrees C, 69+/-18 degrees C and 79 +/- 12 degrees C, respectively (p < 0.05). The multipolar mode created a larger volume of ablation than did the other modes: 37.6 +/-4.0 cm3 (group A); 44.9 +/- 12.7 cm3 (group B); and 78.9 +/- 6.9 cm3 (group C) (p < 0.05). In the in vivo experiment, the pig well tolerated the RFA procedure and no major complications occurred during the 4 days of the follow-up period. The mean volume of coagulations produced by multipolar RFA in the pig liver was 60.5+/-17.9 cm3. CONCLUSION: For the multiple probe RFA, the multipolar mode with hypertonic saline instillation was more efficient in generating larger areas of thermal ablation than either the consecutive or simultaneous monopolar modes.

Keyword

Liver, interventional procedures; Radiofrequency ablation; Experimental study

MeSH Terms

Tomography, X-Ray Computed
Swine
Necrosis
Liver Neoplasms/pathology/surgery
Liver/pathology/physiology/radiography/*surgery
Equipment Design
*Electrodes
Cattle
Catheter Ablation/*instrumentation/methods
Body Temperature
Animals

Figure

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  Fig. 1 Photographs of a perfused-cooled electrode and a prototype adaptor.

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  Fig. 2 Photographs of the specimen in the preliminary experiments to find the ideal interelectrode distance.

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  Fig. 3 Comparison of radiofrequency-induced coagulation created by applying radiofrequency in the consecutive, simultaneous and multipolar modes with a 4-cm inter-probe distance. Note that the mean short-axis diameter was largest in the bipolar mode. The arrowheads indicate the electrode insertion sites.

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  Fig. 4 Graphs of mean temperatures at the center portion of the triangle that connected each electrode in each group. Note that higher temperatures occurred with the multipolar mode than with either the consecutive- or simultaneous-monopolar mode.

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  Fig. 5 Contrast-enhanced CT scans and photographs of the liver treated with multipolar RFA for 20 minutes in an in vivo pig model.

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