Determination of the temperature-dependent electric conductivity of liver tissue ex vivo and in vivo: Importance for therapy planning for the radiofrequency ablation of liver tumours

Abstract

Introduction: Knowledge about the changes in the electric conductivity during the coagulation process of radiofrequency ablation of the liver is a prerequisite for the predictability of produceable thermonecrosis in the liver.

Materials and methods: Continuous measurements of the electric conductivity σ in ex vivo porcine liver (n = 25) were done during the coagulation and cooling process at the temperature range of the radiofrequency ablation at a frequency of 470 kHz relevant for the radiofrequency ablation. Measurements of the electric conductivity were performed in both perfused porcine liver (n = 3) and a human surgical specimen from a colorectal liver metastasis.

Results: At a body temperature of 37°C, conductance σ was 0.41 siemens per metre (0.32 S/m; 0.52 S/m). Conductance σ increased continuously and uniformly at a temperature of 77°C. Maximum conductance σ with 0.79 S/m (0.7 S/m; 0.87 S/m) was reached at 80°C. A continuous reduction of conductance was observed during the cooling phase. At 37°C, the specific conductance σ in the healthy perfused porcine liver was 0.52 S/m, 0.55 S/m and 0.57 S/m (mean 0.55 S/m). The electric conductivity of the human colorectal liver metastasis was clearly higher.

Conclusion: Changes in the specific conductivity during the coagulation and the cooling phase play an important role for the produceable size of a coagulation necrosis and necessitates an adaptation of the therapy parameters during radiofrequency ablation.

• impedance
• radio-frequency-induced thermotherapy
• liver metastases