Tissue impedance measurement using a secondary frequency

A microwave ablation system comprising:

• a generator including a first energy source, a second energy source and a diplexer, said diplexer operable to multiplex a first energy from said first energy source and a second energy from said second energy source, where said second energy source is a radio frequency (RF) generator;
• a cable including a center conductor and an outer sheath, the multiplexed energy being transmitted through said center conductor;
• an antenna operable to receive the multiplexed energy from said center conductor and to deliver the multiplexed energy to a region of tissue;
• a return pad operable to receive said second energy outputted from said antenna, said return pad transmits said second energy to said second energy source;
• and
• a sensor operable to measure at least one parameter of a combined RF energy signal of said second energy generated by said second energy source and the second energy returned from said return pad.

A method of ablating tissue using microwave energy, the method comprising the steps of:

• generating microwave energy;
• generating radio frequency (RF) energy;
• multiplexing said microwave energy and said RF energy and outputting the multiplexed energy to a tissue region;
• receiving said RF energy returned from said tissue region;
• measuring a parameter of the generated RF energy and the RF energy returned from said tissue region;
• and
• controlling a level of microwave energy that is generated based on the measured parameter.