Experimental Study On Expanding The Volume And Optimizing The Shape Of Microwave Ablation In Liver

Objective: To study the efficiency of internally cooled microwave electrode and modified interstitial perfusion microwave electrode on expanding the volume and optimizing the shape of microwave ablation in liver; to compare tissue coagulation efficacy of microwave ablation and radiofrequency ablation.Material and methods: The most advanced microwave coagulation electrode (Internally cooled microwave electrode) and most widely used radiofrequency coagulation system (Automated saline-enhanced radiofrequency system) and a modified interstitial perfusion microwave electrode were used in both ex vivo and in vivo pig liver ablation experiments. In ex vivo liver tissue coagulation, for the internally cooled microwave electrode, 12 experimental groups were created base on the coagulation power, duration and total energy; for the radiofrequency system, 60W600s was used because this energy dose is recommended by the manufacture and can create optimal lesion and also this dose is comparable to the internally cooled microwave coagulation; for the modified interstitial perfusion microwave electrode, 6 groups were created base on perfusion mode (pre- or during ablation) and sorts of liquid (distilled water or 4.5% NaCL solution), and the preferable energy dose was used . Six adult pigs were used in in-vivo experiments, for the internally cooled microwave electrode, six groups (50w600s, 50W720s, 60W600s, 60W720s, 70W600s, 80W600s) were tested base on ex vivo coagulation results; For the radiofrequency ablation, 60W600s was selected. Experiments were repeated three times for each group mentioned above. Thermosensors were placed at the surface of the electrodes, 5, 10, 15, and 20mm from the electrodes, and temperatures were recorded using anadvanced temperature monitor system. Ablated lesions were excided along the representable planes. The longitudinal diameter, transverse diameter, and width of the congestive reaction zone were measured. The volume and shape of the coagulation tissue and the volume of the charred zone were determined using a special computer software base on the photos of the gross section. In the in vivo experiments, we noted the vascular influence on coagulation zone.Results: Internally cooled microwave electrode created reproducible ellipsoid coagulation zone in liver tissue, and the maximum transverse diameter was at 15mm backward to the electrode tip. The shaft temperature can be controlled through modulating the water circulation. The coagulation volume enlarged with the increase of power output, but the shape deteriorated with the increase power output especially it exceeded 80W, and 5 0-70W was the preferable power setting for ideal coagulation lesions. An increase in ablation time correlated with an increase in the size of the induced lesions, and during 420s and 720s of the ablation procedure, the coagulation volume grows fast. The optimal volume can be created with power setting of between 50 and 70W and an ablation time between 420s and 720s. The largest and most spherical coagulation with a calculated volume of 41.4 cm~3 and shape value of R=0.98 in ex vivo was created with 60W720s. The ablation volume in vivo was significantly smaller than in ex vivo (P< 0.001), and the lower the power setting the great the differences of lesion' volume between in vivo and ex vivo. For 50W600s, coagulation volume in vivo was only half of that ex vivo. No significant differences were found for the shape of thermal induced lesions between ex vivo and in vivo liver tissue ablation. Reproducible of the thermal induced lesions in vivo was inferior to ex vivo.Microwave created slightly larger volume of coagulation than radio frequency, and radiofirequency produced more spherical lesions than microwave. Coefficient of variation was 0.47 for radiofrequency induced lesion and was 0.21 for microwave. Microwave induced higher temperature in the central part...