Hansjoerg Rempp, Presenter: Nothing to Disclose

Dorothee Mezger, Abstract Co-Author: Nothing to Disclose

Matthias Voigtländer, Abstract Co-Author: Nothing to Disclose

Markus D. Enderle MD, Abstract Co-Author: Nothing to Disclose

Claus Detlef Claussen MD, Abstract Co-Author: Nothing to Disclose

Stephan Clasen MD, Abstract Co-Author: Nothing to Disclose

Philippe Lucien Pereira MD, Abstract Co-Author: Support, Terumo Corporation Support, Celon AG medical instruments Support, Siemens AG Support, CeloNova BioSciences, Inc Support, Bayer AG Support, Bracco Group Support,Sirtex Medical Ltd

To evaluate the size of the ablation zone created in ex vivo bovine liver tissue using mono- and bipolar internally CO2- and water-cooled radiofrequency (RF) applicators.

Ablations were performed at fresh ex vivo bovine liver tissue using single mono- and bipolar 15G RF applicators with a 30 mm active tip. The applicators were either water perfused (with a closed water circuit, perfusion rate = 100 ml/min) or internally CO2 -cooled, using a gas pressure of 600 psi. The application time was limited to 15 minutes. The electric current was varied between 1100 mA and 1300 mA in steps of 50 mA in the monopolar setting and- with a comparable current density at the electric poles - between 500 and 700 mA in the bipolar setting. Six experiments were performed per current setting (6) and applicator type (4), leading to a total number of 6 x 6 x 4 = 144 experiments. The long and short axis diameter of the white ablation zone was measured. A Mann-Whitney-U-Test was used to compare the short axis values. Shape ratio was defined as short axis diameter/long axis diameter.

Within the tested parameter combinations, no spots of untreated tissue were observed close to the cooled needle track. Largest short axis diameter was 4.05±0.4cm achieved with the gas-cooled monopolar applicator at a current level of 1250mA. With the gas-cooled bipolar applicators, maximum short axis diameter was significantly smaller (p=0.0005), reaching 3.02±0.2cm at 650mA. Monopolar water-cooled probes achieved a maximum short axis of 3.18±0.2cm, significantly inferior to gas-cooled monopolar probes (p=0.003). Bipolar water-cooled applicators reached a short axis diameter of 2.72±0.3cm (not significantly smaller than with the gas cooled applicator). Long axis diameters varied between 2.8 and 5.2cm; there was no significant difference between the different applicator types. Shape ratio was largest at gas-cooled monopolar probes with 0.81±0.08 versus 0.68±0.03 at the bipolar probes (p=0.0035), 0.58±0.04 at bipolar water-cooled probes and 0.60±0.04 at monopolar water-cooled probes.

In this ex vivo study, gas-cooled monopolar applicators were superior to water-cooled monopolar applicators and bipolar applicators in terms of creation of a spherical ablation zone and large short axis diameters.

Applicator cooling can be used to increase the ablation zones' critical short axis.

Rempp, H, Mezger, D, Voigtländer, M, Enderle, M, Claussen, C, Clasen, S, Pereira, P, Ex Vivo Comparison of Monopolar and Bipolar Internally Gas- and Water-cooled Radiofrequency Applicators.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9012222.html