Rationale and Objectives
An in vitro perfused bovine liver model was used to evaluate the relationship between the sizes of radiofrequency ablation lesions and variation in portal venous blood flow.
Materials and Methods
Fourteen bovine livers were perfused with autologous heparinized blood at 37°C and 40% to 50% oxygenation via the portal vein. Flow rates were adjusted from 10 to 50 mL/min/100 g tissue. A 480-kHz generator and a 3.0-cm monopolar internally cooled electrode were used to create 57 ablations. The long-axis diameter, short-axis diameter (SAD), and volume of each ablation zone were measured and calculated from the dissected livers. Correlations between SAD, long-axis diameter, and volume versus blood flow were assessed using linear regression analysis.
Results
SAD and lesion volume demonstrated inverse linear correlations with blood flow (for SAD, y = −0.044 x + 3.925, r = 0.836, P < .001; for volume, y = −0.556 x + 31.574, r = 0.842, P < .001). A 10 mL/min/100 g change in flow rate produced an average 4.4 ± 0.4 mm change in SAD and an average 5.6 ± 0.5 cm 3 change in volume. Long-axis diameter was not correlated with blood flow ( y = −0.7694 x + 4.1899, r = 0.2173, P = .111).
Conclusions
The SAD and volume of radiofrequency ablation lesions have statistically significant inverse linear correlations with portal venous blood flow, with an average 4.4-mm change in SAD and an average 5.6-cm 3 change in volume for each 10 mL/min/100 g change in flow rate.
Percutaneous radiofrequency (RF) ablation is an accepted minimally invasive technique for the treatment of primary and secondary malignant hepatic tumors ; however, there is substantial variation in the reported success rate of local tumor eradication . Although multiple factors affect the success rate, unpredictable, marked variability in the size of the ablation zone produced by the same and different RF ablation devices is a major factor associated with local treatment failure . Not knowing the size of the coagulation necrosis that will be created by an RF ablation device prevents accurate treatment planning and increases the chance of an inadequate treatment.
It has been shown that variation in hepatic blood flow is the primary variable controlling the size of coagulation necrosis produced by RF ablation in the liver . Although multiple studies have shown that a reduction in hepatic blood flow is associated with an increase in the size of RF ablation zones, the experimental designs of previous studies did not allow analysis of direct incremental changes in hepatic blood flow on the size of RF ablation zones . A precise delineation of this relationship would add additional knowledge to the field, which could be useful for predicting the performance of RF ablation devices and enhancing RF ablation treatment planning.
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Materials and methods
Liver Procurement and Perfusion
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RF Ablation Equipment
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Ablation Location and Technique
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Examination of the Ablation Specimens
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Statistical Analysis
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Results
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Table 1
Sizes of Radiofrequency Ablation Lesions in Different Lobes of Bovine Liver
Location Number of Ablations LAD (cm) SAD (cm) Volume (cm 3 ) RLA 25 4.0 ± 0.5 (3.0–46) 2.6 ± 0.5 (1.6–3.5) 15.0 ± 6.8 (4.8–28.8) LL 21 3.9 ± 0.3 (3.5–4.5) 2.8 ± 0.5 (1.7–3.6) 17.2 ± 6.5 (5.3–28.5) RLP 11 4.0 ± 0.3 (3.8–5.5) 2.8 ± 0.5 (1.7–3.5) 17.4 ± 7.2 (6.1–26.9)
LAD, long-axis diameter; LL, left lobe; RLA, right liver anterior; RLP, right liver posterior; SAD, short-axis diameter.
Data are expressed as mean ± standard deviation.
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Discussion
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Conclusions
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