Sonographically guided percutaneous radio-frequency tissue ablation - In vitro examination on bovine liver

Purpose: Sonographically-guided Radio-Frequency Tissue Ablation-applied with a percutaneously placed needle can be used for the palliative treatment of primary or secondary liver tumours. In vitro experiments were carried out to establish the relations of the coagulation zone to histologic findings and sonographic appearence. Method: Fresh bovine livers were obtained and radio-frequency was applied under ultrasound guidance. The coagulation zone was dissected and examined by determining its three-dimensional diameters (macroscopically) and the histologic appearance of the coagulation margin to the surrounding tissue. In our series of 50 experiments the application time ranged from 30 seconds to 10 minutes. Results: The coagulation zone increased with increasing application time in a way that can be described as a negative logarithmic function. The largest volume was 4 x 5 x 5 cm (length, width, depth) approximating 50 ml. It was no problem to judge the coagulation zone sonographically. The macroscopically and sonographically determined width and length correlated with coefficients of 0.90 and 0.96. Microscopically the coagulation necrosis showed sharply outlined margins without any vital cells. Conclusion: Radio-Frequency Tissue Ablation applied under sonographic guidance has certain features which seem to make it a promising method for the palliative treatment of primary and secondary tumours of the liver.