A microwave ablation system and method include an elongate microwave ablation probe. The probe has a radiating portion for performing microwave ablation. The probe includes a first electrode and a second electrode located along the probe body. A radiofrequency energy source is connected to the first and second electrodes. An impedance of tissue is measured using the first and second electrodes. The impedance is used to detect a change in tissue due to microwave ablation of the tissue. Therapy parameters for the microwave ablation procedure can be adjusted in response to the measured impedance. In some examples, one of the electrodes is proximal and one electrode is distal to the radiating portion.
