APPARATUS AND METHOD FOR CREATING, MAINTAINING, AND CONTROLLING A VIRTUAL ELECTRODE USED FOR THE ABLATION OF TISSUE

• US 20080015563A1
• Filed: 07/24/2007
• Published: 01/17/2008
• Est. Priority Date: 02/22/1995
• Status: Active Grant

• Current Assignee: Mark Christopherson, Michael Hoey, Steven Goetz
• Original Assignee: Mark Christopherson, Michael Hoey, Steven Goetz
• Inventors: Hoey, Michael, Christopherson, Mark, Goetz, Steven
• Granted Patent: US 9,770,282 B2
• Time in Patent Office: Days
• US Class Current: 606/34
• CPC Class Codes: A61B 18/1206 Generators therefor
• CPC Class Codes: A61B 18/1233 with circuits for assuring patient safety
• CPC Class Codes: A61B 18/14 Probes or electrodes therefor
• CPC Class Codes: A61B 18/1402 Probes for open surgery
• CPC Class Codes: A61B 18/18 by applying electromagnetic radiation, e.g. microwaves radiation therapy A61N5/00
• CPC Class Codes: A61B 18/1815 using microwaves
• CPC Class Codes: A61B 2018/00029 open
• CPC Class Codes: A61B 2018/00196 reciprocating lengthwise
• CPC Class Codes: A61B 2018/00666 using a threshold value
• CPC Class Codes: A61B 2018/00678 upper
• CPC Class Codes: A61B 2018/00702 Power or energy
• CPC Class Codes: A61B 2018/00708 switching the power on or off
• CPC Class Codes: A61B 2018/00779 Power or energy
• CPC Class Codes: A61B 2018/00791 Temperature
• CPC Class Codes: A61B 2018/00797 measured by multiple temperature sensors
• CPC Class Codes: A61B 2018/00821 measured by a thermocouple
• CPC Class Codes: A61B 2018/00875 Resistance or impedance
• CPC Class Codes: A61B 2018/1213 creating an arc
• CPC Class Codes: A61B 2018/1253 monopolar
• CPC Class Codes: A61B 2018/1417 Ball
• CPC Class Codes: A61B 2018/1472 : for use with liquid electrolyte, e.g. virtual electrodes
• CPC Class Codes: A61B 2018/1475 : Electrodes retractable in or deployable from a housing
• CPC Class Codes: A61B 2218/002 : Irrigation
• CPC Class Codes: A61B 2218/007 : Aspiration

Abstract

An apparatus and a method for producing a virtual electrode within or upon a tissue to be treated with radio frequency alternating electric current. An apparatus in accord with the present disclosure includes a supply of a conductive or electrolytic fluid to be provided to the patient, an alternating current generator, and a processor for creating, maintaining, and controlling the ablation process by the interstitial or surficial delivery of the fluid to a tissue and the delivery of electric power to the tissue via the virtual electrode. A method in accord with the present disclosure includes delivering a conductive fluid to a predetermined tissue ablation site for a predetermined time period, applying a predetermined power level of radio frequency current to the tissue, monitoring at least one of several parameters, and adjusting either the applied power and/or the fluid flow in response to the measured parameters.

Claims

1. A system for producing, maintaining, and controlling a virtual electrode for provision of an ablative therapy through the virtual electrode to a target tissue of a body of a patient, the system providing a conductive fluid and an RF power to the target tissue to create the virtual electrode, the system comprising:

a source of conductive fluid selectively providing conductive fluid to the target tissue;

a surgical instrument including an electrode for delivering RF power to distributed conductive fluid to create a virtual electrode;

a primary temperature sensor for sensing a temperature of the body of the patient in an area of the target tissue;

an impedance detector for measuring information indicative of an impedance of the body of the patient in the area of the target tissue to passage of RF current; and

a processor for determining a desired RF power applied by the electrode as Ablation_RF_Power=(max_RF_Power)*(proportional feedback+integral feedback+derivative feedback);

wherein max_RF_Power is a maximum power level determined as a function of the measured impedance, proportional feedback is a function of a proportion of the sensed temperature relative to a threshold temperature, integral feedback is a function of an integral of the sensed temperature relative to the threshold temperature, and derivative feedback is a function of a derivative of the sensed temperature relative to the threshold temperature.

2. The system of claim 1, wherein the processor determines the desired RF power as Ablation_RF_Power=(max_RF_Power)*(Error_Proportion (n)*K_p+Error_Integral/K_i+Error_Derivative*K_d);

wherein Error_Proportion (n) is the difference between the sensed temperature and the threshold temperature, K_p is a proportional gain constant, Error_Integral is a function of a magnitude of the difference between the sensed temperature and the threshold temperature, K_i is an integral gain constant, Error_Derivative is a function of a rate of change of the difference between the sensed temperature and the threshold temperature, and K_d is a derivative gain constant.

3. A method for producing, maintaining, and controlling a virtual electrode for provision of an ablative therapy through the virtual electrode to a target tissue of a body of a patient by applying RF power to a conductive fluid distributed to the target tissue, the method comprising:

a. establishing a total time of RF power application to achieve desired ablation (t_total);

b. distributing conductive fluid to the target tissue;

c. applying RF power to the distributed conductive fluid;

d. pausing application of the RF power; and

e. resuming application of RF power for a time period (t_resume) as a function of a difference between t_total and a time period during which RF power was applied prior to the step of pausing plus a correction factor.

4. The method of claim 3, wherein the correction factor is 15t_pause, wherein t_pause is a time period during which application of RF power was paused.

5. The method of claim 3, wherein the corrective factor is t_reheat, wherein t_reheat is a time period for the target tissue to reach a temperature approximating a temperature of the target tissue prior to the step of pausing application of RF power.