Impedance matching in a microwave electrosurgical system

Abstract

A method and apparatus is disclosed for the ablation of biological tissue to produce a therapeutic effect. An adjustment is made to the output frequency of an electrosurgical generator during the ablation cycle to accommodate changes in the electrical properties of the apparatus and the biological tissues that occur as energy is transferred to the tissue. The adjustment is made to better align the source impedance with that of the load.

1 . A method of biological ablation, comprising:
 positioning a microwave antenna within or in proximity to target tissue;   delivering microwave energy, at a predetermined frequency, to the target tissue via the microwave antenna;   sampling a power signal reflected by the target tissue;   measuring a reflected power based on the sampled power signal;   multiplying the measured reflected power by a correction factor to calculate an actual reflected power; and   adjusting a power level of the microwave energy based on the actual reflected power.   
     
     
         2 . The method of  claim 1 , further comprising using a trocar to position the microwave antenna within or in proximity to the target tissue. 
     
     
         3 . The method of  claim 1 , further comprising adjusting a frequency of the microwave energy to adjust a source impedance. 
     
     
         4 . The method of  claim 1 , further comprising adjusting the power level of the microwave energy by adjusting a frequency of the microwave energy. 
     
     
         5 . The method of  claim 1 , further comprising repeatedly comparing the actual reflected power to a predetermined threshold. 
     
     
         6 . The method of  claim 5 , wherein adjusting the power level of the microwave energy includes adjusting a frequency of the microwave energy when the actual reflected power exceeds the predetermined threshold. 
     
     
         7 . A system for tissue ablation, comprising:
 a microwave antenna configured for insertion into a target tissue;   a microwave energy generator coupled to the microwave antenna by a transmission line, the microwave energy generator configured to generate microwave energy;   a coupler coupled between the microwave energy generator and the microwave antenna and configured to sample a power signal reflected from the target tissue;   measurement circuitry configured to receive the sampled power signal from the coupler and measure a reflected power; and   a controller configured to multiply the reflected power by a correction factor to calculate an actual reflected power,   wherein the controller is further configured to control the microwave energy generator to adjust a power level of the microwave energy based on the actual reflected power.   
     
     
         8 . The system of  claim 7 , wherein the coupler is a dual directional coupler. 
     
     
         9 . The system of  claim 7 , further comprising a display configured to display information regarding the actual reflected power on a screen. 
     
     
         10 . (canceled) 
     
     
         11 . (canceled)