ABSTRACT
Objective To investigate the effects of output power,action time and radiofrequency(RF) needle on the cool-tip radiofrequency ablation(RFA) by experimental tools and to determine the value of ultrasonography in size evaluation of RFA zone.Methods The cool-tip RFA to fresh calf liver were monitored by ultrasound.The experiments by single electrode needle were performed with different combination of output power (80 W,120 W) and time (5 min,8 min,10 min).The cluster needle was used for assessment at 5 min with different output power(80 W,120 W).After the end of trial,the longitudinal specimens were cut open.The view and size of the ablation zone were recorded with naked eyes.The pathological changes displayed by optical microscope were recorded as well.Results The measurement of ablation zone with naked eyes showed with the ablation zone expanded with time in 80 W-power cases,but the pace of expansion slowed down,but in 120 W-power cases,expansion of the ablation zone was not obvious; the ablation zone in 120 W-power was bigger than that in 80 W-power at 5 min,their difference decreased with time,and the ablation zones were similar at 10 min.The cluster needle can produce ablation zone with lesser aspect ratio than that of single electrode needle,consequently similar to circle.Ultrasonic measurement of the ablation zone had real discrepancy.Most of longitudinal diameters were greater than the real ones,while in large ablation lesions,vertical diameters were often less than the real ones.Under optical microscope,no change could be found in shape and structure of the cells in ablation zone.Conclusion The output power and performing time have impact on ablation.The high-power output increased heat production as well as reduction of heat conduction.Compared with single electrode needle,the cluster needle produced ablation zone closer to real hepatic tumor,thus has more reliable effect to small hepatocellular carcinoma with diameter around 2 cm.The ultrasond has a great significance in RFA guidance,but it could not accurately define the border of ablation zone.