METHOD AND APPARATUS FOR ESTIMATING A LOCAL IMPEDANCE FACTOR

1 . A method of treating a treatment zone of a patient with an electromagnetic energy delivery device, the method comprising:

sending a first measurement signal from the electromagnetic energy delivery device at least partially through the treatment zone and back to the electromagnetic energy delivery device;

determining a first measurement value from the first measurement signal;

sending a second measurement signal from the electromagnetic energy delivery device at least partially through the treatment zone and back to the electromagnetic energy delivery device;

determining a second measurement value from the second measurement signal; and

estimating a local impedance factor associated with the treatment zone using the first and second measurement values.

2 . The method of claim 1 wherein determining the first measurement value further comprises:

measuring a current or a voltage associated with the first measurement signal.

3 . The method of claim 1 wherein determining the second measurement value further comprises:

measuring a current or a voltage associated with the second measurement signal.

4 . The method of claim 1 wherein estimating the local impedance factor further comprises:

determining the local impedance factor as a ratio between a patient local impedance associated with the treatment zone and a total system impedance of the device.

5 . The method of claim 1 further comprising:

selecting an energy of a therapeutic signal at least partially based upon the estimated local impedance factor; and

sending the therapeutic signal from the electromagnetic energy delivery device to the treatment zone.

6 . The method of claim 5 further comprising:

repeatedly estimating local impedance factors during the course of the patient treatment.

7 . The method of claim 6 further comprising:

changing the energy of the therapeutic signal sent to the treatment zone as the estimated local impedance factor changes during the course of the patient treatment.

8 . The method of claim 5 wherein the local impedance factor is related to a fraction of the energy of the therapeutic signal absorbed by the patient treatment zone.

9 . The method of claim 5 further comprising:

sending the first measurement signal, the second measurement signal, and the therapeutic signal through different electrodes located adjacent the treatment zone.

10 . The method of claim 9 wherein an area of the electrode used for sending the second measurement signal is equal to the area of the electrode used for sending the therapeutic signal.

11 . The method of claim 9 wherein an area of the electrode used for sending the second measurement signal differs from the area of the electrode used for sending the therapeutic signal.

12 . The method of claim 5 further comprising:

sending the first measurement signal, the second measurement signal, and the therapeutic signal through a plurality of individual electrodes each located adjacent the treatment zone.

13 . The method of claim 5 wherein the device delivers radiofrequency energy, and the return path includes a non-therapeutic electrode of sufficient size such that a non-therapeutic amount of energy is delivered to a patient zone adjacent the non-therapeutic electrode.

14 . The method of claim 1 further comprising:

sending more than two measurement signals through the treatment zone;

determining a corresponding number of measurement values from the more than two measurement signals; and

estimating the local impedance factor from the corresponding number of measurement values.

15 . The method of claim 14 wherein estimating the local impedance factor further comprises:

estimating the local impedance factor by extrapolation.

16 . The method of claim 1 wherein estimating the local impedance factor further comprises:

subtracting the second measurement value from the first measurement value to yield a difference; and

dividing the difference by one minus a ratio of a surface area of a first electrode used to send the first measurement signal to a surface area of a second electrode surface used to send the second measurement signal.

17 . The method of claim 1 wherein estimating the local impedance factor further comprises:

using one or more scaling factors to estimate the local impedance factor.

18 . The method of claim 1 further comprising:

beginning a patient treatment session after the local impedance factor is estimated.

19 . The method of claim 1 further comprising:

repetitively sending respective therapeutic signals through individual treatment zones; and

estimating local impedance factors associated with each of the treatment zones.

20 . The method of claim 19 further comprising:

changing an energy of the therapeutic signal as the estimated local impedance factor changes.

21 . The method of claim 1 wherein one of the first and second measurement values is approximately equal to a total impedance of the electromagnetic energy delivery device.

22 . The method of claim 1 wherein one of the first and second measurement values is approximately equal to a bulk impedance of the electromagnetic energy delivery device.

23 . An apparatus for deliver electromagnetic energy through a skin surface to an underlying treatment zone of a patient, the apparatus comprising:

a generator adapted to generate the electromagnetic energy;

a treatment tip including an electrode operatively coupled with said generator to deliver the electromagnetic energy through the skin surface and into the patient treatment zone; and

a controller electrically coupled with the generator, the controller configured to cause the generator to supply at least first and second measurement signals to the electrode for delivery to the treatment zone, and the controller configured to estimate a local impedance factor of the patient treatment zone from the first and second measurement signals.

24 . The apparatus of claim 23 wherein the generator is adapted to generate radiofrequency energy.

25 . The apparatus of claim 23 wherein the electrode further comprises a first and second electrode segments having different surface areas, and the controller is configured to deliver the first measurement signal through the first electrode and the second measurement signal through the second electrode.

26 . The apparatus of claim 23 wherein the electrode includes a plurality of electrode segments, and and the controller is configured to deliver the first measurement signal through a first group of the electrode segments and the second measurement signal through a second group of the electrode segments, the first and second groups of electrode segments having a different collective surface areas.

27 . The apparatus of claim 23 wherein the controller is configured to cause the generator to supply a therapeutic signal to the electrode based upon the local impedance factor estimated by the controller.