Study On Thermal Field Of Microwave Ablation Using Internally Cooled Antenna

Objective: To study the thermal field of microwave radiation induced by internally cooled antenna and to assess the accuracy of computer-aided simulation by observing the thermal distribution profile, its corresponding histopathologic change at different power outputs.Materials and Methods: Based on Penne's equation of bioheat transfer, the model of three dimensional thermal distribution of microwave ablation for liver cancer using internally water-cooled system was deduced. Thermal coagulated area and thermal distribution were calculated and predicted by computer simulation with finite element model (FEM) under three power outputs (50W600s, 60W600s, and 70W600s). In liver-equivalent phantom tests, the contour of thermal field was monitored dynamically by thermalcouples pinpointed precisely at designated spots. Egg white coagulation experiments were performed with single, double, and three internally-cooled microwave antennas respectively. For in vitro study, temperatures of 80 spots/times in 26 porcine livers were measured while microwave radiation was induced through signal antenna. For in vivo study, temperatures of 24 spots/times in two swine livers were recorded. Specimen were obtained from above spots through biopsy and examined under light microscopy.Results: (1) In liver-equivalent phantom test, the dT/dt distribution was determined with undetermined-coefficient method. The dT/dt distribution was different at different power outputs. Speed of temperature rise in z > 0 direction was faster than that in z < 0. (2) Temperature rise curve and coagulated area obtained from microwave radiation in the porcine liver induced through the single antenna coincided with value of computer simulation. The maps of the thermal field were mostly consistent with the contours of egg white coagulation zone. With the three energy outputs,...