Fluid-modulated bipolar radiofrequency ablation: an ex-vivo evaluation study.
BACKGROUND
The effect of radiofrequency ablation (RFA) can be modulated by fluid injection.


OBJECTIVE
To evaluate the potential of different fluids to modulate the effect of bipolar RFA in an ex-vivo liver model.


METHODS
A bipolar RFA system with an internally cooled needle-shaped applicator (20-mm active tip) was used to induce coagulation lesions in ex-vivo porcine liver. Prior to the ablation procedure, 1-ml samples of seven different fluids were injected (0.9% saline, gadopentetate dimeglumine, ioxithalamate, 10% hydroxyethyl starch, 5% glucose, 95% ethanol, distilled water). Each fluid was used for five RF ablations. During the procedure, applied energy, impedance, and time were recorded. Additionally, temperature was measured at a fixed distance of 0.5 and 1.0 cm from the RF probe. Generator output was set to 20 W, as recommended by the vendor. Five ablation procedures without fluid injection served as the reference standard. The lesion diameters were measured, and volume and an efficiency index (coagulation volume/procedure duration) calculated and compared (ANOVA, Student-Newman-Keuls test).


RESULTS
In comparison to the reference standard, fluid injection resulted in an enlargement of mean coagulation volume for all fluids. In comparison to RF ablation alone (1.42+/-0.33 cm(3)), significant increase (P<0.001) of lesion size was found using gadopentetate dimeglumine, hydroxyethyl starch, glucose, and ethanol. The largest lesions were generated using preinjection of hydroxyethyl starch. Most energy could be applied after injection of glucose. Comparing the efficiency index, no statistically significant differences were found.


CONCLUSIONS
Besides the modulation of the electrical conductivity, the increase in thermal conductivity also contributes to the enhancement of RFA by the injection of the tested fluids. Further studies are needed to evaluate this effect for larger injection volumes under in-vivo conditions.
Bruners
P
P
Applied Medical Engineering and Department for Diagnostic Radiology, Helmholtz Institute for Biomedical Engineering, RWTH Aachen University Hospital, Aachen, Germany. bruners@hia.rwth-aachen.de
Müller
H
H
Günther
R W
RW
Schmitz-Rode
T
T
Mahnken
A H
AH
D000704:Analysis of Variance; D000818:Animals; D001777:Blood Coagulation; D017115:Catheter Ablation / Q000295:instrumentation / Q000379:methods*; D003287:Contrast Media / Q000008:administration & dosage*; D017097:Electric Impedance; D004566:Electrodes; D004867:Equipment Design; D000431:Ethanol / Q000008:administration & dosage*; D005240:Feasibility Studies; D019786:Gadolinium DTPA / Q000008:administration & dosage; D005947:Glucose / Q000008:administration & dosage*; D006895:Hydroxyethyl Starch Derivatives / Q000008:administration & dosage*; D007483:Iothalamic Acid / Q000008:administration & dosage / Q000031:analogs & derivatives; D008099:Liver / Q000601:surgery; D010952:Plasma Substitutes / Q000008:administration & dosage; D012965:Sodium Chloride / Q000008:administration & dosage*; D012997:Solvents / Q000008:administration & dosage; D013552:Swine; D013696:Temperature; D013997:Time Factors; D014867:Water / Q000008:administration & dosage*
D003287:Contrast Media; D006895:Hydroxyethyl Starch Derivatives; D010952:Plasma Substitutes; D012997:Solvents; D014867:Water; D007483:Iothalamic Acid; D000431:Ethanol; D012965:Sodium Chloride; C002587:ioxitalamic acid; D005947:Glucose; D019786:Gadolinium DTPA