Wet radio-frequency ablation using multiple electrodes: comparative study of bipolar versus monopolar modes in the bovine liver.
OBJECTIVE
To determine whether hypertonic saline (HS)-mediated bipolar radio-frequency (rf) application as advantages over monopolar simultaneous and alternating rf applications for creating larger areas of coagulation necrosis.


METHODS
A total of 60 rf ablations using double perfused-cooled electrodes and a 200 W generator (CC-3 model, Radionics) were performed in three different modes in explanted bovine livers: simultaneous monopolar mode (groups A and A'); alternating monopolar mode (groups B and B'); or bipolar mode (groups C and C'). Electrodes were placed at inter-electrode distances of 3 and 5 cm, and HS (6% NaCl solution) was instilled into tissue at a rate of 1 mL/min through the electrodes. rf was applied for 10 (3 cm distance) or 15 min (5 cm distance). During rf application, we measured the tissue temperature at the mid-point between the two electrodes. Dimensions of the thermal ablation zones, and temperatures were compared between the 3 groups using analysis of variance or the Kruskal-Wallis test. To compare configurations of the ablation zones in each group, the ratio of longitudinal diameter (Dl) to vertical diameter (D(v)) was calculated.


RESULTS
With a 3-cm inter-electrode spacing, the D(v) between the electrodes of ablated lesions was 2.4 +/- 1.2 cm in group A, 4.5 +/- 1.0 cm in group B, and 6.1 +/- 0.9 cm in group C (P < 0.05), and at a 5-cm spacing, groups B' and C' produced a single ablation area, but group A' produced two separated ablation spheres: the D(v)s were 1.4 +/- 0.2 in group A, 2.9 +/- 1.0 mm in group B, and 6.6 +/- 0.4 cm in group C (P < 0.05). For both 5- and 3-cm spacings, the temperatures at the mid-point were higher in bipolar mode than in either monopolar simultaneous or alternating modes. The ratios of Dl/D(v) of groups A, B, and C were 2.5 +/- 0.2, 1.4 +/- 0.1, and 1.1 +/- 0.1, respectively, and the corresponding figures of groups A', B' and C' were 4.5 +/- 0.2, 2.7 +/- 0.1, and 1.1 +/- 0.1, respectively (P < 0.05).


CONCLUSIONS
HS-enhanced bipolar rf ablation creates larger, more regular coagulation necrosis than either monopolar simultaneous or alternating rf ablation.
Lee
Jeong Min
JM
Department of Radiology, Seoul National University Hospital, 28 Yongon-Dong, Chongno-Gu, Seoul 110744, Republic of Korea. leejm@radcom.snu.ac.kr
Han
Joon Koo
JK
Kim
Se Hyung
SH
Han
Chang Jin
CJ
An
Su Kyung
SK
Lee
Jae Young
JY
Choi
Byung In
BI
D000704:Analysis of Variance; D000818:Animals; D017115:Catheter Ablation / Q000295:instrumentation*; D002417:Cattle; D004566:Electrodes; D008099:Liver / Q000601:surgery*; D009336:Necrosis; D012462:Saline Solution, Hypertonic / Q000008:administration & dosage*; D018709:Statistics, Nonparametric
D012462:Saline Solution, Hypertonic