SYSTEMS AND METHODS FOR CALCULATING TISSUE IMPEDANCE IN ELECTROSURGERY

• US 20150282863A1
• Filed: 12/08/2014
• Published: 10/08/2015
• Est. Priority Date: 04/04/2014
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Covidien LP (Medtronic Plc)
• Inventors: Heckel, Donald W., Belous, Andrey
• Granted Patent: US 10,492,850 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: A61B 18/1206 Generators therefor
• CPC Class Codes: A61B 18/1233 with circuits for assuring patient safety
• CPC Class Codes: A61B 18/1445 at the distal end of a shaft, e.g. forceps or scissors at the end of a rigid rod
• CPC Class Codes: A61B 2018/00577 Ablation
• CPC Class Codes: A61B 2018/00589 Coagulation
• CPC Class Codes: A61B 2018/00601 Cutting
• CPC Class Codes: A61B 2018/0063 Sealing
• CPC Class Codes: A61B 2018/00642 with feedback, i.e. closed loop control
• CPC Class Codes: A61B 2018/00648 using more than one sensed parameter
• CPC Class Codes: A61B 2018/00702 Power or energy
• CPC Class Codes: A61B 2018/00755 Resistance or impedance
• CPC Class Codes: A61B 2018/00767 Voltage
• CPC Class Codes: A61B 2018/00779 Power or energy
• CPC Class Codes: A61B 2018/00827 Current
• CPC Class Codes: A61B 2018/00875 Resistance or impedance
• CPC Class Codes: A61B 2018/00892 Voltage
• CPC Class Codes: G05B 15/02 electric
• CPC Class Codes: G06F 17/10 Complex mathematical operations function generation by table look-up G06F1/03; evaluation of elementary functions by calculation G06F7/544

Abstract

An electrosurgical generator and associated methods determine a real part of the impedance of treated tissue. The electrosurgical generator includes an output stage, a plurality of sensors, and a controller that controls the output stage. The controller includes a signal processor that determines an RMS voltage, an RMS current, an average power, and a real part of the impedance of the treated tissue based on measured voltage and current by using a plurality of averaging filters. The controller controls the output stage to generate electrosurgical energy based on at least the determined real part of the impedance.

Claims

1. An electrosurgical generator comprising:

an output stage coupled to an electrical energy source and configured to generate radio frequency (RF) electrosurgical energy;

a plurality of sensors configured to sense a voltage waveform and a current waveform of the electrosurgical energy; and

a controller coupled to the output stage and the plurality of sensors, the controller including;

a signal processor configured to determine a Root Mean Square (RMS) voltage, an RMS current, an average power, and a real part of an impedance based on the sensed voltage waveform and the sensed current waveform using a plurality of averaging filters; and

an output controller configured to generate a control signal to control the output stage based on at least one of the RMS voltage, the RMS current, the average power, and the real part of the impedance.

2. The electrosurgical generator according to claim 1, wherein the signal processor includes:

a plurality of multipliers configured to square the voltage waveform and square the current waveform, and configured to multiply the voltage waveform and the current waveform to obtain a power waveform;

the plurality of averaging filters configured to average the squared voltage waveform and the squared current waveform, and configured to average the power waveform to obtain the average power; and

a calculator configured to calculate the RMS voltage based on the averaged voltage waveform and calculate the RMS current based on the averaged current waveform.

3. The electrosurgical generator according to claim 2, wherein the calculator calculates the real part of impedance based on the average power and the RMS current.

4. The electrosurgical generator according to claim 1, further comprising a plurality of analog-to-digital converters configured to sample the sensed voltage waveform and the sensed current waveform to obtain a predetermined number of samples of each of the sensed voltage waveform and the sensed current waveform.

5. The electrosurgical generator according to claim 4, wherein the predetermined number of samples corresponds to an integer multiple of a RF frequency of the voltage waveform and the current waveform.

6. The electrosurgical generator according to claim 1, wherein the averaging filters are selected from the group consisting of Cascaded Integrator Comb (CIC) filters, boxcar averaging filters, finite impulse response filters, infinite impulse response filters, and any combination of these averaging filters.

7. The electrosurgical generator according to claim 1, wherein the output controller generates the control signal based on a difference between the real part of the impedance and a desired real part of the impedance, the control signal being used to control the output stage.

8. The electrosurgical generator according to claim 2, wherein the plurality of averaging filters are identical to each other.

9. The electrosurgical generator according to claim 2, wherein the plurality of averaging filters are low pass filters.

10. The electrosurgical generator according to claim 4, wherein the plurality of averaging filters operate synchronously over the same predetermined number of samples of each of the voltage waveform and the current waveform.

11. The electrosurgical generator according to claim 6, wherein each of the plurality of averaging filters is a CIC filter having at least one integrator, at least one differentiator, and at least one decimator.

12. The electrosurgical generator according to claim 11, wherein the order of the CIC filter is four, the at least one decimator has a decimation factor of sixteen, and the predetermined number of samples is two.

13. The electrosurgical generator according to claim 1, wherein the output stage generates electrosurgical energy to treat tissue, and wherein the signal processor calculates the real part of the impedance of the tissue by dividing the average power by the RMS current squared.

14. The electrosurgical generator according to claim 2, wherein the calculator further calculates phase information between the voltage waveform and the current waveform by dividing the average power by a produce of the RMS voltage and the RMS current.

15. The electrosurgical generator according to claim 1, wherein the output stage is a RF amplifier.

16. A method for controlling an electrosurgical generator, comprising:

generating electrosurgical energy;

sensing a voltage waveform and a current waveform of the generated electrosurgical energy;

processing the sensed voltage waveform and the sensed current waveform using a plurality of averaging filters to determine a Root Mean Square (RMS) voltage, an RMS current, an average power, and a real part of an impedance; and

controlling the electrosurgical energy based on at least one of the RMS current, the RMS voltage, the average power, and the real part of the impedance.

17. The method according to claim 16, wherein processing the voltage waveform and the current waveform includes:

squaring the sensed voltage waveform;

squaring the sensed current waveform;

multiplying the sensed voltage waveform and the sensed current waveform to obtain a power waveform;

averaging the squared voltage waveform;

averaging the squared current waveform;

averaging the power waveform to obtain the average power;

calculating the RMS voltage based on the average voltage waveform;

calculating the RMS current based on the average current waveform; and

calculating the real part of the impedance based on the average power and the RMS current.

18. The method according to claim 17, wherein controlling the electrosurgical energy includes:

generating a control signal based on a difference between the real part of the impedance and a desired real part of the impedance; and

controlling the generated electrosurgical energy based on the control signal.

19. A processor configured to perform a method for controlling an electrosurgical generator that generates electrosurgical energy, the method comprising:

processing a voltage waveform and a current waveform of the electrosurgical energy using a plurality of averaging filters to determine a Root Mean Square (RMS) voltage, an RMS current, an average power, and a real part of impedance; and

generating a control signal to control the electrosurgical energy based on at least one of the RMS current, the RMS voltage, the average power, and the real part of the impedance.

20. The processor according to claim 19, wherein processing the voltage waveform and the current waveform includes:

squaring the voltage waveform;

squaring the current waveform;

multiplying the voltage waveform and the current waveform to obtain a power waveform;

averaging the squared voltage waveform;

averaging the squared current waveform;

averaging the power waveform to obtain the average power;

calculating the RMS voltage based on the averaged voltage waveform;

calculating the RMS current based on the averaged current waveform; and

calculating the real part of the impedance based on the average power and the RMS current.