In vivo electrical properties of the healthy liver and the hepatic tumor in a mouse model between 1 Hz and 1 MHz during a thermal treatment

Objective: Understansding the changing patterns of in vivo electrical properties for the target tissue is crucial for the accurate temperature monitoring and the treatment efficacy in thermal therapy. Our research aims to investigate the changing patterns and the reversibility of in vivo electrical properties for both healthy livers and liver tumors in a mouse model over a frequency range of 1 Hz to 1 MHz at temperatures between 30 degrees C to 90 degrees C. Methods and materials: The mice were anesthetized and the target organ was exposed. An 808-nm near-infrared laser was employed as the heating source to heat the organ in vivo. The four-needle electrode, connected to an impedance analyzer, was utilized to obtain the impedance at varying temperatures, which were monitored by a thermocouple. Results: The findings indicated a gradual decline in impedance with an increase in temperature. Furthermore, the impedance was normalized to that at 30 degrees C, and the real part of the normalized impedance was defined as the k-values, which range from 0 to 1. The results demonstrated a linear correlation between k-values and temperatures (R-2 > 0.9 for livers and R-2 > 0.8 for tumors). Significant differences were observed between livers and tumors at 1, 10 and 50 kHz (p < 0.05). Additionally, it was demonstrated that the electrical properties could be reversed when the temperature was below or equal to 45 degrees C. Conclusion: We believe that these results will contribute to the advancement of radiofrequency ablation systems and the development of techniques for temperature monitoring during liver thermal treatment.