A comparison of internally water-perfused and cryogenically cooled monopolar and bipolar radiofrequency applicators in ex vivo liver samples.
OBJECTIVE
To evaluate the ex vivo ablation zones created in hepatic tissue using monopolar and bipolar gas- and water-cooled radiofrequency (RF) applicators.


METHODS
RF ablations were performed on ex vivo bovine liver tissue using closed circuit water-cooled and closed circuit cryogenically cooled (via CO₂ enthalpy) 15-ga linear-needle applicators. Both monopolar and bipolar electrode applicators were used, with the electric current administered ranging in 50-mA increments from 1100 to 1300 mA for the monopolar case, and from 500 to 700 mA for the bipolar case. Total ablation time was 15 minutes. Six tissue samples were ablated per setting. The ablated volumes were assumed to have a three-dimensional ellipsoid shape, with one long major axis and two smaller minor axes. Gross histology was used to measure the dimensions of the ablated regions to quantify the ablated volume, the dimensions of the axis, and the ratio between the long axis and the smallest minor axis, which was termed the ellipticity index.


RESULTS
The gas-cooled monopolar applicator achieved the largest short-axis ablation diameter (4.05 ± 0.4 cm), followed by the water-cooled monopolar applicator (3.18 ± 0.29 cm). With the bipolar applicator, the gas-cooled applicators also achieved larger short-axis ablation diameters (3.02 ± 0.15 cm) than the water-cooled applicators (2.72 ± 0.29 cm). The gas-cooled monopolar applicator also provided the largest ablation volume (42.7 ± 10.7 mL) and the most spherically shaped lesions (ellipticity index: 1.21 ± 0.10). Lesion size increased with injected current up to a threshold current of 1200/1250 mA (monopolar water-/gas-cooled) and 600/650 mA (bipolar water-/gas-cooled), but dropped at greater values.


CONCLUSIONS
Gas-cooled monopolar applicators were superior to the other tested applicators in terms of both volume and sphericity of the ablation zone.
Department on Diagnostic and Interventional Radiology, Eberhard Karls University of Tübingen, Hoppe-Seyler-Straße 3, 72076 Tübingen, Germany. Electronic address: Hansjoerg.rempp@med.uni-tuebingen.de.
Hansjörg
H
Rempp
Department on Diagnostic and Interventional Radiology, Eberhard Karls University of Tübingen, Hoppe-Seyler-Straße 3, 72076 Tübingen, Germany.
Dorothee
D
Mezger
ERBE Elektromedizin GmbH, Tübingen, Germany.
Matthias
M
Voigtlaender
Department on General Pathology and Pathological Anatomy, Institute of Pathology, Eberhard Karls University of Tübingen, Tübingen, Germany.
Marcus
M
Scharpf
Department on Diagnostic and Interventional Radiology, Eberhard Karls University of Tübingen, Hoppe-Seyler-Straße 3, 72076 Tübingen, Germany.
Rüdiger
R
Hoffmann
Clinic for Radiology, Nuclear Medicine and Minimal Invasive Therapies, SLK-Clinics, Heilbronn, Germany.
Philippe L
PL
Pereira
ERBE Elektromedizin GmbH, Tübingen, Germany.
Markus D
MD
Enderle
Department on Diagnostic and Interventional Radiology, Eberhard Karls University of Tübingen, Hoppe-Seyler-Straße 3, 72076 Tübingen, Germany.
Claus D
CD
Claussen
Department on Diagnostic and Interventional Radiology, Eberhard Karls University of Tübingen, Hoppe-Seyler-Straße 3, 72076 Tübingen, Germany.
Stephan
S
Clasen
D000818:Animals; D017115:Catheter Ablation / Q000295:instrumentation*; D002417:Cattle; D003080:Cold Temperature; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006498:Hepatectomy / Q000295:instrumentation*; D066298:In Vitro Techniques; D008099:Liver / Q000033:anatomy & histology / Q000601:surgery*; D014159:Transducers; D014867:Water
D014867:Water
Radiofrequency ablation; minimally invasive tumor therapy; monopolar and bipolar RF ablation