Abstract:
A system and method that improves and automates the measurement of power generated by an electrosurgical generator. An active load device is coupled to the generator output and is configured to simulate the change in tissue characteristics, such as an impedance change, that occurs when such tissue undergoes electrosurgical treatment. The active load faithfully simulates the change in tissue characteristics caused by a particular mode of electrosurgical energy delivery, such as without limitation, changes caused in response to a cutting mode, a coagulation mode, a blending mode, a sealing mode, and the like. Tests are conducted in accordance with test profiles containing target impedance and power values of the test scenario. A plurality of profiles may be stored for testing under various simulated operating conditions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 13/049,459, now U.S. Pat. No. 9,375,247 filed Mar. 16, 2011, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     Technical Field 
     The present disclosure is directed to electrosurgery and, in particular, to a system and method for electrosurgical generator power measurement. An active load device is employed with an automated control system to accurately measure generator output under simulated tissue impedance conditions. 
     Background of Related Art 
     Electrosurgical generators are employed by surgeons in conjunction with an electrosurgical instrument to cut, coagulate, desiccate and/or seal patient tissue. High frequency electrical energy, e.g., radio frequency (RF) energy, is produced by the electrosurgical generator and applied to the tissue by an electrosurgical tool. Both monopolar and bipolar configurations are commonly used during electrosurgical procedures. 
     Electrosurgical techniques and instruments can be used to coagulate small diameter blood vessels or to seal large diameter vessels or tissue, e.g., veins and/or soft tissue structures, such as lung, and intestine. A surgeon can cauterize, coagulate/desiccate and/or simply reduce or slow bleeding, by controlling the intensity, frequency and duration of the electrosurgical energy applied between the electrodes and through the tissue. For the purposes herein, the term “cauterization” is defined as the use of heat to destroy tissue (also called “diathermy” or “electro-diathermy”). The term “coagulation” is defined as a process of desiccating tissue wherein the tissue cells are ruptured and dried. 
     “Vessel sealing” or “tissue fusion” is defined as the process of liquefying the collagen and elastin in the tissue so that it reforms into a fused mass with significantly-reduced demarcation between the opposing tissue structures (opposing walls of the lumen). Coagulation of small vessels is usually sufficient to permanently close them while larger vessels or tissue need to be sealed to assure permanent closure. It has been known that different waveforms of electrosurgical energy are suited for different surgical affects, e.g., cutting, coagulation, sealing, blend, etc. For example, the “cutting” mode typically entails generating a continuous sinusoidal waveform in the frequency range of 250 kHz to 4 MHz with a crest factor in the range of 1.4 to 2.0. The “blend” mode typically entails generating a periodic burst waveform with a duty cycle in the range of 25% to 75% and a crest factor in the range of 2.0 to 5.0. The “coagulate” mode typically entails generating a periodic burst waveform with a duty cycle of approximately 10% or less and a crest factor in the range of 5.0 to 12.0. In order to effectively and consistently seal vessels or tissue, a pulse-like waveform is desired. 
     In order to optimize sealing or tissue fusion without causing unwanted charring of tissue at the surgical site or possibly causing collateral damage to adjacent tissue, e.g., thermal spread, it is necessary to accurately control the output from the electrosurgical generator, e.g., power, waveform, voltage, current, pulse rate, etc. It follows that accurate measurement of the output power of an electrosurgical generator greatly benefits the design, manufacture, and use thereof. 
     The task of acquiring power data from an electrosurgical generator unit typically involves coupling the RF output of the generator to a dummy load, and manually activating an output power mode and/or level via front panel controls or other actuator. The current value through the load is measured with an RMS voltmeter and recorded manually for each data point along a test sequence. Every data point must then be transferred into a form suitable for design analysis or individual product calibration by a design engineer or line technician. The entire series of measurements may be repeated for different power levels and with different dummy loads. For example, test data may be manually input into a spreadsheet or bench test equipment to calculate load power for each data point. Each power level and mode setting requires at least 20 data points to define a curve with a meaningful level of detail. Typically, at least three power levels are used to define a particular mode. Thus, for each electrosurgical mode, at least 60 data points need to be collected. This means that for an electrosurgical generator that can operate in a cut mode, a blend mode, a coagulation mode, and a sealing mode, 240 data points are required to meet the minimum level of precision required. The result is a time-consuming and labor-intensive product development cycle or manufacturing process which adds considerable cost to the product and negatively impacts time-to-market and margins. 
     SUMMARY 
     It is an object of the present disclosure to provide a system and method that improves and automates the measurement of power generated by an electrosurgical energy source. It is a further object of the present disclosure to improve surgical tissue effect (e.g., cutting, coagulation, blending, sealing, etc.) by employing an automated method of continuum power measurement. In an embodiment, an active load device is operably coupled to the generator output under test. The active load is configured to simulate the change in tissue characteristics, e.g., an impedance change, that occurs when such tissue undergoes electrosurgical treatment. The active load faithfully simulates the change in tissue characteristics caused by a particular mode of electrosurgical energy delivery, such as without limitation, changes caused in response to a cutting mode, a coagulation mode, a blending mode, a sealing mode, and the like. Real-time measurements of generator voltage, current and computed power are recorded automatically to define and/or determine the accuracy of delivered generator power in view of dynamic changes in tissue characteristics, e.g., tissue impedance. An electrosurgical energy measurement system in accordance with the present disclosure may avoid potential power perturbations caused by discrete load impedances, because discrete load impedances do not provide a continuum energy measurement system. The disclosed measurement system may enable rapid prototyping, shorter manufacturing times, and may ultimately improve the precision and accuracy of electrosurgical generator. 
     According to one aspect of the present disclosure, an active load device that simulates the tissue load impedance change is operably coupled to an output of a generator under test. Real time measurements of generator voltage, current and computed power are recorded automatically to define the delivered generator power accuracy over the dynamic changes in tissue impedance. A controller sweeps the active device load impedance in closed loop control, which is connected to the generator under test to establish a continuum power measurement process. 
     In one embodiment, the disclosed system includes an instrumentation control section, and an active load with monitoring circuitry. A host configuration data file, a look-up table, a control processor, a proportional-integral-derivative (PID) controller (including a Σ error correction network), an input-output processor, and one or more analog to digital (A/D) and digital to analog (D/A) data conversion devices. The active load and monitoring circuitry includes voltage sense and current sense transducers, drive isolators, signal conditioning drivers and an active load element which simulates the dynamic tissue change corresponding to applied RF energy. 
     An electrosurgical generator in accordance with the present disclosure includes a control interface adapted to establish a communication link between the generator and the instrumentation control section to enable the communication of operational commands and status reporting therebetween. The generator may be configured to respond to commands received by the control interface to facilitate automated testing thereof. For example, and without limitation, such commands may cause the generator to activate and deactivate energy generation, select an operating mode (cut, coagulation, blend, seal, etc.), set an output power, set an output frequency, and select a monopolar, bipolar, or polyphase operating mode. 
     An embodiment of an electrosurgical generator measurement system according to the present disclosure includes an active load section and a control section. The active load section includes an input adapted to receive electrosurgical energy from an electrosurgical generator under test. The active load section further includes a voltage sensor in communication with the input and configured to output a voltage sensor signal, and a current sensor in communication with the input and configured to output a current sensor signal. The active load is operably coupled to the input and configured to present a variable load to the electrosurgical generator under test in response to an active load drive signal. 
     The control section includes an input-output processor, a voltage sensor input in communication with the input-output processor and configured to receive a voltage sensor signal, and a current sensor input in communication with the input-output processor and configured to receive a current sensor signal. The control section further includes a PID control module in communication with the input-output processor, and is configured to output an active load drive signal. Also included in the control section is a lookup table in communication with the PID control module that is configured to store a test profile, and a control processor in communication with the input-output processor, the PID control module, and the lookup table, and is configured to output a generator control signal. 
     In embodiments, the control section further includes a data record storage module in communication with the input-output processor. The data record storage module may be utilized to store the results of an electrosurgical generator measurement, which, in turn, may be communicated to an external device through a communication port that is operatively coupled to the input-output processor and/or the data storage module. The control section may include a communication interface operably coupled to the input-output processor that enables the communication of the measurement data to an external device. An analog to digital converter may be interdisposed between the voltage sensor input and the input-output processor and/or the current sensor input and the input-output processor. The active load may be galvanically isolated from the drive signal. 
     The active load device may include an N-channel FET and a P-channel FET. In embodiments the drain of the N-channel FET is operably coupled to a positive terminal of the active load, the drain of the P-channel FET is operably coupled to the source of the N-channel FET, and the source of the P-channel FET is operatively coupled to a negative terminal of the active load. 
     Also disclosed is a method for measuring the performance of an electrosurgical generator. In an example embodiment, the disclosed method includes the steps of describing a series of parameters defining a test sequence, the parameters including an impedance and a power level. The outputs of an electrosurgical generator under test are electrically coupled to an active load device having the capability to present a variable impedance to the output of the electrosurgical generator. The electrosurgical generator is activated in accordance with a parameter of the test sequence, and the output of the electrosurgical generator is measured. An impedance value based upon the output of the electrosurgical generator is computed and compared to an impedance parameter of the test sequence to determine a difference, if any, between the computed impedance and the target impedance, and, in turn, generate an active load control signal. The active load device is driven in accordance with the active load control signal, which causes an impedance in accordance with the test sequence to be presented to the output of the electrosurgical generator. 
     In an embodiment, the measured output of the electrosurgical generator is recorded. Additionally or alternatively, the computed impedance may be compared to the impedance parameter of the test sequence to derive an error signal. The error signal and a test parameter may be provided as inputs to a proportional-integral-derivative controller, and an active load control signal is then computed utilizing the proportional-integral-derivative controller. 
     In yet another embodiment, the series of parameters defining a test sequence may be acquired from a host configuration module. The host configuration module includes one or more series of parameters, or “profiles”, that describe an individual test sequence. The desire profile may be selectively loaded into a lookup table from the host configuration file. 
     In still another embodiment, a calibration parameter may be derived in accordance with the error signal, and communicated to the electrosurgical generator wherein the calibration parameter may be stored in the electrosurgical generator for future use. 
     Also disclosed herein is an electrosurgical generator adapted for use with an electrosurgical measurement system. The disclosed electrosurgical generator includes a processor, a controller interface in communication with the processor and adapted to receive a control signal, and an energy source operably coupled to the processor and configured to generate electrosurgical energy. The processor is configured to activate the energy source in accordance with a generator control signal received by the controller interface. The disclosed electrosurgical generator may include a memory operably coupled to the processor, wherein the processor is further configured to store a calibration parameter in the memory in accordance with a generator control signal received by the controller interface. The processor may be further configured to activate the energy source in accordance with a stored calibration parameter. In an embodiment, the electrosurgical measurement system is integral to the electrosurgical generator, which, in turn, enables the electrosurgical generator to perform self-testing and self-calibration. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments of the subject instrument are described herein with reference to the drawings wherein: 
         FIG. 1  is a functional block diagram of an embodiment of an electrosurgical power measurement system in accordance with the present disclosure; 
         FIG. 2  is a schematic diagram of an embodiment of an active load device in accordance with the present disclosure; 
         FIG. 3  is a representation of waveforms associated with an embodiment of an active load device in accordance with the present disclosure; and 
         FIG. 4  is a flow chart of an embodiment of a method for electrosurgical generator measurement in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Particular embodiments of the present disclosure are described hereinbelow with reference to the accompanying drawings; however, it is to be understood that the disclosed embodiments are merely examples of the disclosure, which may be embodied in various forms. The terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. Well-known and/or repetitive functions and constructions are not described in detail to avoid obscuring the present disclosure in unnecessary or redundant detail. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present disclosure in virtually any appropriately detailed structure. It is to be understood that embodiments in accordance with the present disclosure may be practiced in any orientation without limitation. In this description, as well as in the drawings, like-referenced numbers represent elements which may perform the same, similar, or equivalent functions. 
     Referring to  FIG. 1 , there is shown a block diagram of an embodiment of the presently disclosed electrosurgical power measurement system  10 . The disclosed system includes an active load section  20  operably coupled to an electrosurgical generator  100  and an instrumentation and control section  30 . Electrosurgical generator  100  includes a controller interface  110  configured to facilitate the control of the various functions thereof, e.g., energy activation, energy deactivation, operational mode (cut, coagulate, blend, seal, etc.), output power, operating frequency, waveform, firmware update, calibration, and the like. Generator  100  includes a processor  112  adapted to communicate with controller interface  110  and programmed to manage the operational functions of generator  100  at least in accordance with a generator control signal received by controller interface  110 . Processor  112  is operably coupled to memory  111  that may include operational software instructions executable by processor  112 , calibration data, historical data, and test data. The contents of memory  111  may be modified in accordance with a signal received via controller interface  110 . An energy source  113  having outputs  114   a  and  114   b  is configured to generate electrosurgical energy and is operably coupled to processor  112 . Outputs  114   a  and  114   b  may be configured for monopolar or bipolar operation. Additional outputs may be configured in order to provide polyphase operation. 
     Active load section  20  is configured to receive an electrosurgical signal from electrosurgical generator  100 , to present active load  140  to outputs  114   a  and  114   b  of electrosurgical generator  100 , and to provide measurement signals to and receive drive signals from control section  30 . A pair of inputs  116   a  and  116   b  is provided to receive electrosurgical energy from outputs  114   a  and  114   b  of electrosurgical generator  100  under test. A voltage sensor  115  is electrically disposed in parallel across inputs  116   a  and  116   b . Voltage sensor  115  is configured to provide a voltage measurement signal at voltage measurement signal output  117 . A current sensor  120  is electrically connected in series between input  116   a  and active load device  140  and is configured to provide a current measurement signal at current measurement signal output  118 . In an embodiment, current sensor  120  may additionally or alternatively be connected in series between input  116   b  and active load device  140 . Current and voltage sensing may be achieved using a non-contact method such as a voltage- and/or current-measuring transformer. In an embodiment, the active load device current and/or voltage measuring sensor (e.g., transformer) may provide a sensing output signal representative of, and/or proportional to, the corresponding measured current and/or voltage. 
     Active load section  20  further includes a drive isolator  130  having an input  131  configured to receive an active load drive signal from control section  30 . Drive isolator  130  is further configured to provide galvanic isolation between active load section  20  and control section  30 , and may include a photocoupling arrangement (e.g., an optoisolator), a transformer coupling arrangement, and/or a radio (RF) link arrangement. 
     An output from drive isolator  130  is operably coupled to an input  128  of signal conditioning driver  125 . Signal conditioning driver  125  buffers and/or amplifies the drive signal to provide a pair of control drive signals adapted to drive a balanced active load device  140 . Signal conditioning driver  125  includes a positive control drive output  126  and a negative control drive output  127 . 
     Control section  30  includes a voltage sensor input  151 , a current sensor input  156 , an active load drive signal output  176 , and a control signal output  191 . Control section  30  includes a number of processing and/or storage modules that may be embodied in hardware, software, or a combination thereof. Voltage sensor input  151  is configured to receive a voltage sensor signal from voltage output  117  and couples the voltage sensor signal to an input of analog to digital (A/D) converter  150 . Current sensor input  156  is configured to receive a current sensor signal from current output  118  and couples the current sensor signal to an input of analog to digital (A/D) converter  155 . A/D converters  150 ,  155  are configured to convert the respective input signals thereof into digital form for use by input-output processor  160  as described in detail herein. A/D converters  150 ,  155  may be operated in a continuous sampling mode wherein the respective sensor signal is digitized at a sampling rate, which may range from about 5 MHz (e.g., five million samples per second) to about 40 MHz. A/D converters  150 ,  155  may additionally or alternatively be operated in a supervised mode wherein samples are digitized under control of input-output processor  160  or other control device. In embodiments, A/D converters  150 ,  155  may be operated in a windowed mode wherein a series of samples are collected for a predetermined period of time. A/D converters  150 ,  155  may utilize any suitable encoding scheme for digitally representing the respective analog sensor signals thereof, including without limitation, binary, two&#39;s complement, binary coded decimal (BCD). 
     An input-output processor  160  is in communication with A/D converters  150  and  155 , data record storage unit  165 , summation module  180  and control processor  190 . Input-output processor  160  may include the capability of executing a set of program instructions for executing a method of electrosurgical generator power measurement as described herein. Input-output processor  160  is configured to receive voltage and current measurement data from A/D converters  150  and  155 , respectively. During use, voltage and current measurement data received by input-output processor  160  is stored in data record module  165 . Stored voltage and current measurement data may include set point data (e.g., the desired or intended output voltage and/or current) corresponding thereto, actual (measured) data, and error data (e.g., a difference between measured data and set point). 
     Host configuration module  182  includes a test parameter set, or test “profile”, that describes a series of parameters defining a test sequence, such as without limitation, target load values, impedance values, and power levels, that simulate a tissue response typically seen during an electrosurgical procedure. A test profile may include a series of impedance targets expressed over a predetermined time period. Additionally or alternatively, a profile may include a power level, a voltage level, and/or a current level corresponding to a target impedance value. Host configuration module  182  may include one or more profiles that are selectively loadable into lookup table  184  for use. A profile may include a set of power levels the generator (under test  100 ) is to be operated in association with a set of parameters related to the power levels, including without limitation, target impedance values, target power levels, target voltage levels, target current levels, target reactance levels, and the like. In embodiments, the profile may be stored in a database, an indexed table, or other suitable data structure, and may be encoded using any suitable manner of encoding. 
     Instrumentation and control section  30  includes a control processor  190  that is in operative communication with input-output processor  160 , lookup table  184 , and proportional-integral-derivative (PID) module  170 . Control processor  190  is configured to communicate with a generator  100  under test to, e.g., provide a control signal to generator  100  in accordance with a target value stored in lookup table  184 . In embodiments, control processor  190  includes the capability to download calibration data that may include, without limitation, trim values, bias values, adjustments, offsets, and power parameters, to generator  100 . Generator  100  may include the capability to commit calibration data to a calibration database (not explicitly shown) included within memory  111 . 
     At the start of a measurement cycle, a desired profile that is stored in host configuration module  182  is loaded into lookup table  184  for use. Control processor  190  communicates an energy activation request to generator  100  via control signal output  191  in accordance with the loaded profile in lookup table  184 . A target load value is obtained from lookup table  184  and applied as an initial setpoint value to PID module  170 . Input-output processor  160  computes instantaneously generated power and impedance values from the measured current and voltage. The calculated impedance value is communicated from input-output processor  160  to summation module  180 . Summation module  180  generates an error signal proportionate to an impedance control parameter set point provided by lookup table  184  and the instantaneous impedance calculated by input-output processor  160 . The error signal is communicated to PID module  170 , which, in turn, outputs a drive control signal to digital to analog (D/A) converter  175 . D/A converter  175  includes an analog output  176  that is operably coupled to input  131  of drive isolator  130 , which, in turn, drives active load device  140  via signal conditioning driver  125 . A closed loop control circuit is thereby established wherein the target load setpoint obtained from lookup table  184  is compared to the calculated impedance value to maintain the desired active load presented to generator  100 . 
     Actual measured voltage and current values are stored in data storage module  165  in association with the target setpoint values and/or calculated valued corresponding therewith, e.g., impedance, power, etc. In an embodiment, the values stored in data storage module  165  may be transmitted via a communication port  162  to another device, e.g., a personal computer, for further processing and/or analysis. Communication port  162  may include any suitable communication interface, including without limitation, a network interface (e.g., Ethernet), a wireless interface (e.g., Bluetooth, 802.11 “WiFi”), a legacy interface (e.g, RS-232, EIA-485), a USB interface, and the like. 
     A measurement cycle as described herein is performed iteratively for each control setpoint of the selected profile to establish an impedance sweep profile at one power level (e.g., seal intensity control level) of the generator  100  under test. Once a measured current and or control parameter reaches a steady state value listed in lookup table  184 , or within a tolerance therefrom, control processor  190  communicates with input-output processor  160  to store the instantaneous values of current, voltage, computed power and impedance into data record storage module  165 . This measurement cycle is repeated over the range of impedance values in the impedance sweep profile. The impedance sweep profile may also be represented by a curve fitting function. Over the simulated tissue impedance range, power curve performance parameters can be computed with respect to the power output set point of the generator  100  under test. 
     Turning now to  FIGS. 2 and 3 , an active load  140  is illustrated in detail. Active load device  140  includes a series pair of power field effect transistors (FETs) including at least one N-channel FET  145  and one P-channel FET  146 . As shown in the waveform relationship diagram  200  of  FIG. 3 , during a positive half-cycle of an electrosurgical waveform  210  generated by generator  100 , the N-channel FET  145  and the body diode of the P-channel FET  146  are conducting, and the N-channel FET  145  gate-source voltage  220  is biased to a positive bias voltage that is supplied by signal conditioning driver  125 . Conversely, during the negative half-cycle of the generator waveform, the P-channel FET and the body diode of the N-channel are conducting, and the P-channel FET  146  gate-source voltage  230  is biased to a negative bias voltage that is supplied by signal conditioning driver  125 . By this arrangement, the active load device  140  has the capability to present a variable load (e.g., variable impedance) to an alternating-current generator such as, without limitation, those commonly employed in electrosurgery. In this manner, the drive signal presented to gates  143 ,  144  establishes a correct bias within an ohmic region of the FETs  145  and  146 , respectively, which, in turn, establishes the simulated tissue load thereof and hence the desired load value for the respective half-cycle. 
     A method  300  of performing electrosurgical measurement in accordance with the present disclosure is illustrated in  FIG. 4 . The method starts with an entry point  305  wherein various housekeeping and system initializations may be performed. For example, and without limitation, the various modules may perform a self-test, the various interfaces may confirm that proper electrical connections have been established with counterpart modules and/or components, and any hardware or software initializations required to achieve operational readiness are performed. In step  310 , a desired test profile is loaded from a host configuration module to the lookup table for use. In step  315 , an active load device is set to an initial value that presents an initial load to the output of an electrosurgical generator under test, e.g., generator  100 . In step  320 , the generator (under test) is activated in accordance with the first power level of the test profile, thereby delivering electrosurgical energy to the active load device. In step  325 , voltage and current measurements are taken at the active load and, optionally, the measured values are stored in a memory, e.g., data storage module  165 . In step  330 , power and impedance values are computed from the voltage and current measurements taken in step  325 . Optionally, the computed power and impedance values are stored in a memory, e.g., data storage module  165 . 
     In step  335 , the active load control signal is computed by inputting the target (e.g., setpoint) impedance value of the current test profile step and the error (e.g., difference between setpoint impedance value and the computed impedance value) into a proportional-integral-derivative module, which, in turn, outputs an active load control signal. In step  340  the active load control signal is used to drive the active load device towards the desired, e.g., setpoint impedance value. 
     In the step  345  a determination is made whether the present measurement step is sufficiently stabilized to attain a valid reading, e.g., a verification that a power, voltage, current, and/or impedance value(s) (e.g., “P,V,I,Z”) is found to be within a preset tolerance (e.g., +/−5%) for a preset number of consecutive measurement cycles (e.g., until a stable reading is obtained) and/or for a preset period of time (e.g., determined by a stable reading time period). If a determination is made that the reading(s) have not sufficiently stabilized, the present measurement cycle iterates to step  325 , and processing proceeds from step  325  as described hereinabove. Conversely, if it is determined a valid reading has been acquired, the cycle iterates to step  350  wherein a determination is made whether the present test has been completed, e.g., all measurement steps in the present test profile have been performed. If a determination is made that the present test has not completed, the cycle iterates to step  355  wherein the next target a power, voltage, current, and/or impedance setpoint is obtained from the lookup table, and processing proceeds from step  320  as described hereinabove. If, alternatively, in step  350  a determination is made that the present test is completed, the cycle concludes with an exit point at step  360 . 
     The described embodiments of the present disclosure are intended to be illustrative rather than restrictive, and are not intended to represent every embodiment of the present disclosure. The steps of a method disclosed herein may be performed in a different order than that described, and/or the operations performed within an individual step or steps may be desirably be combined into a single step without departing from the scope and spirit of said method. Further variations of the above-disclosed embodiments and other features and functions, or alternatives thereof, may be made or desirably combined into many other different systems or applications without departing from the spirit or scope of the disclosure as set forth in the following claims both literally and in equivalents recognized in law.