Objective To compare the coagulated shape and size using 915MHz and 2450MHz microwave in vitro pig livers at same power output levels.

Methods In vitro study, the microwave antenna was inserted 5-6 cm into pig liver and the thermal needles were placed 5mm,10mm, 15mm and 20mm away from the antenna. The thermal changes in 210 spots/times were recorded during microwave ablation. Ninety coagulated specimens in 50 pig livers were obtained. The specimens were sectioned along the puncture line. The appearance and size of the coagulated area on the cut surface were measured.

Results: Statistical results demonstrated that there were significant differences in maximum coagulated transverse diameter, longitude diameter and coagulated volume at different microwave frequency group (Table 1,2,3) . The coagulated volumes were significantly larger in 915MHz microwave group than that in 2450MHz microwave group.

Conclusions 915MHz microwave has a stronger penetration capability and a lager size of coagulation volume. It may be a powerful microwave source for ablating larger size of tumor clinically.
Table 1 Comparison of Maximum Coagulated Transverse Diameter in Pig Liver in Vitro at Different Microwave Frequency (±SD cm)

Diameter	50W600s	60W600s	70W600s	80W600s
D cm (915MHz)	3.1±0.2	3.6±0.1	3.9±0.2	4.0±0.2
Dcm(2450MHz)	2.7±0.1	2.7±0.1	2.9±0.1	3.1±0.1
P Value	0.003	0.0009	0.0008	0.001

Table 2 Comparison of Maximum Coagulated Longitude Diameter in Pig Liver in Vitro with Different Microwave Frequency (±SD cm)

Diameter	50W600s	60W600s	70W600s	80W600s
D cm (915MHz)	5.7±0.2	6.6±0.2	7.2±0.3	7.7±0.3
D cm(2450MHz)	3.5±0.1	4.1±0.1	4.2±0.1	4.9±0.2
P Value	0.0001	0.0001	0.0001	0.0001

Table 3 Comparison of Maximum Coagulated Volume in Pig Liver
in Vitro with Different Microwave Frequency(±SD cm)

Diameter	50W600s	60W600s	70W600s	80W600s
D cm (915MHz)	34.6±1.2	43.4±1.9	64.7±1.6	88.7±1.9
Dcm(2450MHz)	19.8±1.8	23.9±1.7	28.7±1.3	30.8±1.8
P Value	0.0001	0.0001	0.0001	0.0001