Korean J Radiol.  2004 Dec;5(4):258-265. 10.3348/kjr.2004.5.4.258.

Comparison of Wet Radiofrequency Ablation with Dry Radiofrequency Ablation and Radiofrequency Ablation Using Hypertonic Saline Preinjection: Ex Vivo Bovine Liver

• Lee JM
• Han JK
• Kim SH
• Shin KS
• Lee JY
• Park HS
• Hur H
• Choi BI

• KMID: 1118833
• DOI: http://doi.org/10.3348/kjr.2004.5.4.258

Abstract

OBJECTIVE
We wished to compare the in-vitro efficiency of wet radiofrequency (RF) ablation with the efficiency of dry RF ablation and RF ablation with preinjection of NaCl solutions using excised bovine liver. MATER AND METHODS: Radiofrequency was applied to excised bovine livers in a monopolar mode for 10 minutes using a 200 W generator and a perfused-cooled electrode with or without injection or slow infusion of NaCl solutions. After placing the perfused-cooled electrode in the explanted liver, 50 ablation zones were created with five different regimens: group A; standard dry RF ablation, group B; RF ablation with 11 mL of 5% NaCl solution preinjection, group C; RF ablation with infusion of 11 mL of 5% NaCl solution at a rate of 1 mL/min, group D; RFA with 6 mL of 36% NaCl solution preinjection, group E; RF ablation with infusion of 6 mL of 36% NaCl solution at a rate of 0.5 mL/min. In groups C and E, infusion of the NaCl solutions was started 1 min before RF ablation and then maintained during RF ablation (wet RF ablation). During RF ablation, we measured the tissue temperature at 15 mm from the electrode. The dimensions of the ablation zones and changes in impedance, current and liver temperature during RF ablation were then compared between the groups. RESULTS: With injection or infusion of NaCl solutions, the mean initial tissue impedance prior to RF ablation was significantly less in groups B, C, D, and E (43-75 omega) than for group A (80 omega) (p< 0.05). During RF ablation, the tissue impedance was well controlled in groups C and E, but it was often rapidly increased to more than 200 omega in groups A and B. In group D, the impedance was well controlled in six of ten trials but it was increased in four trials (40%) 7 min after starting RF ablation. As consequences, the mean current was higher for groups C, D, and E than for the other groups: 401+/-145 mA in group A, 287+/-32 mA in group B, 1907+/-96 mA in group C, 1649+/-514 mA in group D, and 1968+/-108 mA in group E (p< 0.05). In addition, the volumes of RF-induced coagulation necrosis were greater in groups C and E than in group D, which was greater than in groups A and B than in group E (p < 0.05) ; 14.3+/-3.0 cm3 in group A; 12.4+/-3.8 cm3 in group B; 80.9+/-9.9 cm3 in group C; 45.3+/-11.3 cm3 in group D and 81.6+/-8.6 cm3 in group E. The tissue temperature measured at 15 mm from the electrode was higher in groups C, D and E than other groups (p< 0.05) : 53+/-12 degreesC in group A, 42+/-2degreesC in group B, 93+/-8 degreesC in group C; 79+/-12 degreesC in group D and 83+/-8 degreesC in group E. CONCLUSION: Wet RF ablation with 5% or 36% NaCl solutions shows better efficiency in creating a large ablation zone than does dry RF ablation or RF ablation with preinjection of NaCl solutions.

Keyword

Experimental study; Interventional procedures; Liver; Radiofrequency ablation

MeSH Terms

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

Figure

• 

  Fig. 1 Photograph of the perfused-cooled electrode which was used for wet RF ablation.

• 

  Fig. 2 Measurement of the ablated area. Photographs of specimen created by dry RF ablation (group A) in the electrode insertion axis (A) and in the transverse axis perpendicular to the electrode shaft (B). Arrows indicate the three directional diameters of the RF-induced coagulation necrosis: V indicates the vertical diameter; T1, the transverse diameter on the plane along the electrode insertion axis; and T2, the transverse diameter on the plane perpendicular to the electrode shaft.

• 

  Fig. 3 Graphic depiction of the changes occurring in tissue impedance, current, and power during radiofrequency ablation. Note that tissue impedance increased markedly and the current decreased during radiofrequency energy instillation in the dry radiofrequency mode. The upper row indicates radiofrequency power (watt), the middle row indicates current (mA) and the lower row indicates impedance (ohm). The horizontal axis indicates ablation time (second). A. Standard dry radiofrequency ablation (group A). B. Wet radiofrequency ablation with 5% NaCl infusion (group C). C. Radiofrequency ablation with 36% NaCl preinjection (group D).

• 

  Fig. 4 Graphs of mean tissue temperatures at 15 mm from the electrode in each group. Note that a higher temperature was achieved in groups C, D, and E than in groups A and B.

• 

  Fig. 5 Comparison of radiofrequency-induced ablation areas in the five groups. Arrow indicates the electrode insertion site and arrowhead indicates the thermocouple insertion site. A. Photograph of specimen from group A (standard dry RF ablation). B. Photograph of specimen from group B (RF ablation with 11 mL of 5% NaCl solution preinjection). C. Photograph of specimen from group C (wet RF ablation with infusion of 11 mL of 5% NaCl solution). D. Photograph of specimen from group D (RF ablation with 6 mL of 36% NaCl solution preinjection). E. Photograph of specimen from group E (wet RF ablation with infusion of 6 mL of 36% NaCl solution).

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