Rationale and Objectives
To explore the morphological characteristics of ablated lesions and find which combination of duration, temperature, and power was preferable to create largest lesion size with monopolar perfusion electrodes.
Materials and Methods
Using monopolar perfusion electrodes to create 72 lesions in 30 excised porcine livers with radiofrequency radiation at different durations (5, 10, 15, and 20 minutes), temperatures (83°C, 93°C, 103°C, and 113°C), and powers (20, 30, and 40 W). Lesion volumes were calculated from longitudinal diameters and transverse diameters. Morphological characteristics were assessed microscopically from slides stained with hematoxylin and eosin.
Results
Positive correlations were found between duration and longitudinal diameter ( r = 0.66; P < .001), transverse diameter ( r = 0.66; P < .001), distance of ablation beyond the electrode tip ( r = 0.56; P < .001), and volume of lesions ( r = 0.66; P < .001). Temperature was also positively correlated with longitudinal diameter ( r = 0.70; P < .001), transverse diameter ( r = 0.72; P < .001), distance of ablation beyond the electrode tip ( r = 0.61; P < .001), and lesion volume ( r = 0.711; P < .001). Lesion size did not increase when duration was longer than 15 minutes and temperature was higher than 103°C. Power was not correlated with lesion size. Lesion size did not increase with increasing power. Macroscopically, all lesions were elliptical in cross section and appeared three zones: a central zone (I), a coagulated necrotic zone (II), and a hemorrhagic and edematous zone (III) from inside to outside. Microscopically, cells morphology and the nucleus were irregular or even disappeared in zone I. In zone II and III, cells did not appear deformation.
Conclusion
Duration and temperature, not power, affected lesion size. The largest lesion size was about 3.5 cm × 2.5 cm × 2.5 cm as temperature and duration was 15 minutes/103°C.
In the last two decades, percutaneous radiofrequency ablation (RFA) has been designed to destroy tumors by means of heat and has become increasingly popular as an alternative form of minimally invasive therapy for controlling primary and secondary hepatic malignancies because it is safe, effective, simple, and has fewer postoperative complications and higher survival rates than other ablative techniques when surgery is not indicated . However, a major limitation of RFA is its inability to create an large enough lesion size of coagulation necrosis produced by a monopolar radiofrequency electrode, which does not encompass the entire tumors and the required safety margin of 0.5–1.0 cm . Initially, radiofrequency electrodes available produced small volumes of necrosis with destruction of liver limited to less than 1.6 cm in diameter after a single insertion because of carbonization, desiccation, and tissue boiling, which increase impedance around electrodes . Proposed approaches to solve this lesion size limitation have been studied. Irrigating the electrode with cooling liquid (cool-tip electrode) maintains the electrode low temperature and prevents the impedance rise . Another approach is to infuse saline through the holes at the end of perfusion electrode tip to improve the ablated tissues conductivity and enhance radiofrequency energy distribution outward .
We produced ablation lesions in excised porcine livers with RITA UniBlate, a type of monopolar perfusion electrode. The purpose of this study was to evaluate the morphological characteristics of these lesions. We varied the duration, temperature, and power to find which combination is preferable to create the largest lesion size.
Materials and methods
RFA System
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Experimental Design
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Table 1
Characteristics of Lesions Created by Radiofrequency Ablation in Excised Porcine livers
Group Subgroup Combination ∗ (minutes/°C/W) Longitudinal Diameter (cm) Transverse Diameters (cm) Distance of Ablation Beyond the Electrode Tip (cm) Volume (cm 3 ) A 1 5/103/30 2.58 ± 0.05 1.57 ± 0.09 0.07 ± 0.04 3.34 ± 0.42 2 10/103/30 3.01 ± 0.07 1.97 ± 0.03 0.44 ± 0.04 6.13 ± 0.30 3 15/103/30 3.50 ± 0.09 2.46 ± 0.13 0.75 ± 0.12 11.12 ± 1.15 4 20/103/30 3.48 ± 0.13 2.47 ± 0.04 0.64 ± 0.24 11.13 ± 0.72 B 5 15/83/30 2.53 ± 0.03 1.51 ± 0.06 0.01 ± 0.01 3.02 ± 0.23 6 15/93/30 3.05 ± 0.09 1.95 ± 0.05 0.49 ± 0.03 6.08 ± 0.42 3 15/103/30 3.50 ± 0.09 2.46 ± 0.13 0.75 ± 0.12 11.12 ± 1.15 7 15/113/30 3.56 ± 0.05 2.50 ± 0.14 0.71 ± 0.17 11.67 ± 1.32 C 8 15/103/20 3.49 ± 0.06 2.44 ± 0.04 0.78 ± 0.13 10.84 ± 0.50 3 15/103/30 3.50 ± 0.09 2.46 ± 0.13 0.75 ± 0.12 11.12 ± 1.15 9 15/103/40 3.50 ± 0.14 2.46 ± 0.04 0.85 ± 0.12 11.04 ± 0.68
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Measurements and Calculations
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Statistical Methods
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Results
Diameters and Volumes of Ablated Lesions
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Morphologic and Pathologic Features of Ablated Lesions
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Discussion
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Conclusion
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