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PURPOSE: To determine, by means of an ex vivo study, the effect of different NaCl concentrations on the extent of coagulation obtained during radiofrequency (RF) ablation performed using a digitally controlled perfusion device. METHOD: Twenty-eight RF ablations were performed with 40 W for 10 min using continuous NaCl infusion in fresh excised bovine liver. For perfusion, NaCl concentrations ranging from 0 (demineralized water) to 25% were used. Temperature, the amount of energy, and the dimensions of thermal-induced white coagulation were assessed for each ablation. These parameters were compared using the nonparametric Mann-Whitney test. Correlations were calculated according to the Spearman test. RESULTS: RF ablation performed with 0.9% to 25% concentrations of NaCl produced a mean volume of coagulation of 30.7 +/- 3.8 cm(3), with a mean short-axis diameter of 3.6 +/- 0.2 cm. The mean amount of energy was 21,895 +/- 1,674 W and the mean temperature was 85.4 +/- 12.8 degrees C. Volume of coagulation, short-axis diameter, and amount of energy did not differ significantly among NaCl concentrations (p > 0.5). A correlation was found between the NaCl concentration and the short-axis diameter of coagulation (r = 0.64) and between the NaCl concentration and the mean temperature (r = 0.67), but not between the NaCl concentration and volume of coagulation. CONCLUSION: In an ex vivo model, continuous perfusion with high NaCl concentrations does not significantly improve the volume of thermal-induced coagulation. This may be because the use of a low-power generator cannot sufficiently exploit the potential advantage of better tissue conductivity provided by NaCl perfusion.

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PURPOSE: To compare in vivo coagulation necrosis obtained with four radiofrequency (RF) ablation devices, to determine shape and reproducibility of induced coagulation by means of three-dimensional measurements of the ablation zone, and to achieve representations of the coagulated areas in three-dimensional spaces. MATERIALS AND METHODS: Four commercially available RF devices (perfusion, internally cooled cluster, and nine- and 12-tine expandable electrodes) that represent the most widely used systems on the market were tested. Sixteen in vivo ablation procedures were performed in porcine livers (four ablations for each RF system). After macroscopic and histopathologic analyses of 3-mm-thick liver sections, morphometric and volumetric findings in the central zone of white coagulation necrosis were assessed. Coagulation volume, diameter, length, and shape were determined digitally. After analysis of variance, measurements with each system were tested with the Tukey post hoc test. RESULTS: Mean coagulation volumes were 31.5 cm3 +/- 15.8 (SD) for the perfusion electrode, 20.5 cm3 +/- 2.6 for the cluster electrode, 16.2 cm3 +/- 7.3 for the 12-tine electrode, and 9.8 cm3 +/- 3.2 for the nine-tine electrode (P <.05, perfusion vs nine-tine electrode). No significant differences were observed regarding the mean short axis perpendicular to the needle shaft: 2.30 cm +/- 0.94, 3.04 cm +/- 0.26, 3.44 cm +/- 0.21, and 2.70 cm +/- 0.76, respectively. Variation coefficients were 0.50, 0.13, 0.45, and 0.33, respectively. CONCLUSION: Larger coagulation volumes were obtained with the perfusion and internally cooled cluster devices. More spherical volumes of ablation were achieved with the 12-tine and cluster electrodes. The former proved superior with regard to the short axis perpendicular to the needle shaft. The cluster and nine-tine electrode produced better reproducibility, which is suggestive of improved predictability of the extent of coagulation with these systems.

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PURPOSE: To evaluate and compare visibility and artifacts in magnetic resonance (MR) compatible radiofrequency (RF) electrodes for MR-guided RF ablation. MATERIAL AND METHODS: Six different MR compatible electrodes for RF ablation including two internally cooled single needles, one internally cooled cluster needle, two expandable needles and one perfused needle were tested in a phantom study at 0.2 Tesla and at 1.5 Tesla field strength. Fluoroscopic, T1- and T2-weighted fast spin echo (FSE) and gradient echo (GE) sequences, which are usually used for MR-guided interventions, were evaluated. Qualitative and quantitative evaluations were performed. Length, width, noise, tip artifacts, global artifacts and global visualization of the RF electrodes that showed all sequences at different angles. RESULTS: Qualitative analysis showed that electrodes were well visualized at all angles and sequences and on both MR imagers. Quantitative analysis showed that artifact-induced widening of the shaft was increased in all electrodes by: a). use of fluoroscopic sequences, GE sequences, and fat saturation, b). increasing the angle between the needle and main magnetic field, and c). high field strength (1.5 T). Expandable needles produced fewer tip artifacts but broader signal voids along the shaft compared to nonexpandable needles. Cluster electrodes produced less widening than the other electrodes. CONCLUSION: Visibility and artifacts in all six MR compatible RF electrodes are satisfactory and these electrodes could be used for MR-guided radiofrequency ablation procedures.

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RATIONALE AND OBJECTIVES: To evaluate the efficiency of 4 radiofrequency (RF) systems by assessing the amount of delivered energy for each thermal induced lesion after perfusion mediated RF ablation and to compare the influence of perfusion mediation types on the energy efficiency. METHODS: A total of 43 ablations in 16 male landrace pigs with 4 RF devices were performed strictly according to the manufacturers' instructions. Total absorbed energy was computed and then related to 3D volumetry obtained after histopathological evaluation. Sixteen ablations were performed under physiological liver perfusion and 27 ablations with occlusion of portal vein, hepatic artery, or both vessels. Energy efficiency values of the RF systems for different vascular occlusion techniques were compared and analyzed by a nonparametrical rank sum test. RESULTS: Under physiological perfusion, the average energy delivered to produce 1-cm3 lesion size was calculated to 1650 +/- 929, 3097 +/- 389, 8312 +/- 2068, and 5493 +/- 2306 Watt x s/cm3 for the Berchtold, Radionics, Radiotherapeutics, and RITA system, respectively. After perfusion-mediated RF ablation, artery occlusion was not as effective as portal vein occlusion, which reduced the energy to 587 +/- 148, 869 +/- 276, and 903 +/- 394 Watt. s/cm3 for the Berchtold, Radionics, and Radiotherapeutics system, respectively. The occlusion of vessels, portal vein, and artery or portal vein alone increased the energy efficiency compared with physiological liver perfusion or occlusion of the artery (P = 0,003). CONCLUSIONS: Under physiological liver perfusion the open perfused system and the internally cooled system provided the best efficiency values with lowest standard deviations. The energy efficiency was increased markedly for all systems after occlusion of the portal vein either alone or in combination with arterial occlusion. Occlusion of the hepatic artery did not improve the efficiency.

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