Apparatus, System and Method for Monitoring Tissue During an Electrosurgical Procedure

BACKGROUND

p-00021. Technical Field

p-0003The present disclosure relates to an apparatus, system, and method for monitoring tissue modification during an electrosurgical procedure and, more particularly, to an apparatus, system and method that utilize the reflection of electromagnetic waves from a boundary defined by one or more biological materials having different dielectric properties.

p-00042. Description of Related Art

p-0005Electrosurgical generators are employed by surgeons in conjunction with electrosurgical instruments to perform a variety of surgical procedures. An electrosurgical generator generates and modulates electrosurgical energy which, in turn, is applied to the tissue by an electrosurgical instrument. Electrosurgical instruments may be either monopolar or bipolar and may be configured for open or endoscopic procedures.

p-0006Using electrosurgical instruments to ablate, seal, cauterize, coagulate, and/or desiccate tissue may result in some degree of “collateral tissue damage” to adjacent tissue. For example, thermal spread across adjacent tissue structure may result during any of the aforementioned electrosurgical procedures. For the purposes herein the term “thermal spread” refers generally to the heat transfer (heat conduction, heat convection or electrical current dissipation) traveling along the periphery of the electrically conductive surfaces.

p-0007Currently available systems and methods for controlling an electrosurgical generator during electrosurgery may include a clinician monitoring and adjusting, as necessary, the amount of energy delivered to a tissue site through current, voltage, impedance, and/or power measurements such that an appropriate tissue effect can be achieved at the tissue site with minimal collateral damage resulting to adjacent tissue. These systems and/or methods typically require a clinician to translate the desired tissue effect to a power setting on an electrosurgical generator and, if necessary, adjust the power setting to compensate for tissue transformations (e.g., desiccation of tissue) associated with the electrosurgical procedure such that a desired tissue effect may be achieved.

p-0008As can be appreciated, reducing thermal spread or the like during an electrosurgical procedure reduces the likelihood of unintentional or undesirable collateral damage to surrounding tissue structures which are adjacent to an intended treatment site. Controlling and/or monitoring the depth of thermal spread during an electrosurgical procedure may aid a clinician in assessing tissue modification and/or transformation during the electrosurgical procedure.

SUMMARY OF THE DISCLOSURE

p-0009The present disclosure relates to a system for monitoring and/or controlling tissue modification during an electrosurgical procedure. The system includes an electrosurgical apparatus adapted to connect to an electrosurgical generator. The electrosurgical apparatus an electrosurgical apparatus configured to transmit energy to tissue. In an embodiment, the electrosurgical device is bipolar forceps. In an alternate embodiment, the electrosurgical device is a monopolar microwave ablation device. The system includes a control system that includes one or more electromagnetic wave source configured to generate an interrogator wave of one or more frequency adjacent tissue. Located on or in operative communication with one of the pair of jaw members is one or more sensors configured to transmit and sense a reflected portion of the interrogator wave of one or more frequencies. One or more processors are operatively coupled to the control system and to the electrosurgical generator. The processor(s) is configured to control the delivery of electrosurgical energy from the electrosurgical generator to tissue based on information provided by the tissue monitoring system. The control system may be configured to control the electrosurgical generator in real-time during the electrosurgical procedure.

p-0010The control system senses transformation of tissue and is configured to cooperate with the electrosurgical generator via the processor to control the delivery of electrosurgical energy to the tissue. For example, in one embodiment, one or more sensors may be located on one of the pair of jaw members and may include a smart sensor assembly. The one or more sensors may be configured for continuous mode of operation or real-time mode of operation. The sensors may be coupled to or integrally formed with the one or more coaxial cable.

p-0011In one embodiment, one or both jaw members include one or more sensors and include one or more windows operatively coupled to and aligned with the one or more sensor.

p-0012In another embodiment, the information provided by the control system may include propagation velocity calculations and/or phase shift calculations of the reflected portion of the electromagnetic wave of one or more frequency. In yet another embodiment, the electrosurgical apparatus is operatively coupled to a coaxial cable in operative communication with the one or more sensors and configured to transmit a portion of the interrogator wave of one or more frequencies.

p-0013In still another embodiment, the control system includes a transreceiver module configured to transmit a portion of the interrogator wave of one or more frequencies. The transceiver module may use clock signals received from a time source to perform some of the operations associated with the transceiver module. The transceiver module may be configured for amplifying, filtering, and/or digitally sampling the reflected portion of the interrogator wave of one or more frequencies.

p-0014The present disclosure also provides a method for monitoring and/or controlling the delivery of electrosurgical energy to tissue during an electrosurgical procedure. The method includes the initial step of providing an electrosurgical apparatus configured to transmit energy to tissue. The method also includes the steps of: transmitting an interrogator wave of one or more frequencies therethrough from an electromagnetic interrogator wave source; directing electrosurgical energy from an electrosurgical generator through tissue held between jaw members; directing an interrogator wave of one or more frequencies into tissue; analyzing a portion of a reflection of the interrogator wave to determine dielectric boundary data; and controlling the delivery of electrosurgical energy from the electrosurgical generator to tissue based on the dielectric boundary data provided to a processor by the one or more sensors is another step of the method.

p-0015The present disclosure further provides an apparatus for monitoring and/or controlling tissue modification during an electrosurgical procedure. The apparatus includes an electrosurgical apparatus adapted to connect to an electrosurgical generator. The electrosurgical apparatus includes a pair of jaw members configured to grasp tissue therebetween and transmit an interrogator wave of one or more frequencies therethrough. The apparatus includes one or more electromagnetic wave sources configured to generate the interrogator wave of one or more frequencies adjacent tissue and in operative communication with the electrosurgical generator and the electrosurgical apparatus. One or more sensors are configured to transmit and sense a reflected portion of the interrogator wave of one or more frequencies to determine dielectric boundary data. A processor is configured to control the delivery of electrosurgical energy from the electrosurgical generator to tissue based on dielectric boundary data provided by the one or more sensors.

BRIEF DESCRIPTION OF THE DRAWING

p-0016Various embodiments of the present disclosure are described hereinbelow with references to the drawings, wherein:

p-0017<figref idrefs="DRAWINGS">FIG. 1</figref> is a perspective view of an endoscopic bipolar forceps and electrosurgical generator adapted for use with a system for monitoring tissue during an electrosurgical procedure according to an embodiment of the present disclosure;

p-0018<figref idrefs="DRAWINGS">FIG. 2</figref> is a schematic representation of an electrical configuration for connecting the endoscopic bipolar forceps to the electrosurgical generator depicted in <figref idrefs="DRAWINGS">FIG. 1</figref>;

p-0019<figref idrefs="DRAWINGS">FIG. 3A</figref> is an enlarged, side view of the end effector assembly of <figref idrefs="DRAWINGS">FIG. 1</figref>;

p-0020<figref idrefs="DRAWINGS">FIG. 3B</figref> is an enlarged, front perspective view of the end effector assembly of <figref idrefs="DRAWINGS">FIG. 3A</figref> shown in an open configuration;

p-0021<figref idrefs="DRAWINGS">FIG. 4</figref> is a block diagram illustrating components of the system of <figref idrefs="DRAWINGS">FIG. 1</figref> in accordance with an embodiment of the present disclosure;

p-0022<figref idrefs="DRAWINGS">FIG. 5</figref> is a graph showing a Time Domain Reflectometry output as viewed on a spectrum analyzer depicted in <figref idrefs="DRAWINGS">FIG. 4</figref>;

p-0023<figref idrefs="DRAWINGS">FIG. 6</figref> is a graph showing a reflection coefficient as dependent on frequency defined by a dry skin-muscle boundary.

p-0024<figref idrefs="DRAWINGS">FIG. 7</figref> is a graph showing a reflection coefficient as dependent on frequency defined by a muscle-blood boundary;

p-0025<figref idrefs="DRAWINGS">FIG. 8</figref> is a graph showing a reflection coefficient as dependent on frequency defined by liver-blood boundary;

p-0026<figref idrefs="DRAWINGS">FIG. 9</figref> is a graph showing a reflection coefficient as dependent on frequency defined by a muscle-bone boundary;

p-0027<figref idrefs="DRAWINGS">FIG. 10</figref> is a system for monitoring tissue during an electrosurgical procedure according to an embodiment of the present disclosure; and

p-0028<figref idrefs="DRAWINGS">FIG. 11</figref> is a flowchart of a method for monitoring tissue during an electrosurgical procedure according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

p-0029Detailed embodiments of the present disclosure are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the disclosure, which may be embodied in various forms. 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.

p-0030The present disclosure includes an apparatus, system and method that employ principles of time domain reflectometry (TDR) to monitor tissue during various electrosurgical procedures such that a more accurate analysis of tissue reaction during the electrosurgical procedure may be obtained.

p-0031TDR involves transmission of an interrogator wave (e.g., an electromagnetic signal) thru a conductive element (e.g., a transmission line) immersed in (or otherwise in contact with) a substance of interest (e.g., biological material) while simultaneously monitoring the same conductive element for corresponding electromagnetic signals that are reflected along the conductive element. A conductive element can be understood to be any material capable of conveying electromagnetic signals. Electromagnetic signals can be reflected along the same conductive element in response to changes in the conductive element's characteristics (e.g., impedance, water content, etc.) that may be affected by substances that are in contact with the conductive element at particular locations along the conductive element's length.

p-0032As is known in the art, boundaries between biological material (e.g., muscle and membrane) having different dielectric constants can cause reflection of an incident wave as a function of the tissue properties (e.g., permittivity and conductivity). During an electrosurgical procedure the systems and/or methods of the present disclosure use reflected electromagnetic waves caused by a boundary defined by tissue having different dielectric properties to more accurately and effectively measure, amongst other things, the depth of thermal spread properties. More particularly, the present disclosure enables measuring the time period a transmitted electromagnetic wave (e.g., interrogator wave) travels from a launch point, for example, a conductive transmit element, to a boundary between tissue having different dielectric constants, and back to the launch point, the depth of the boundary of a tissue effect (e.g., thermal spread) can be measured. Additionally, the phase shift of the reflected wave may be used to determine the depth of the dielectric boundary, which, in turn, can also provide information about the depth of tissue damage.

p-0033By monitoring change in tissue properties during an electrosurgical procedure, one can better understand which tissue modifications and/or transformations lead to the best tissue effect quality. Further, and if desired, it is possible to incorporate TDR measurements into a feedback loop to facilitate in controlling electrosurgical energy delivery during an electrosurgical procedure, which, in turn, can be used to ensure that tissue modification and/or transformations are optimized.

p-0034With reference to <figref idrefs="DRAWINGS">FIG. 1</figref>, an electrosurgical apparatus <b>10</b> that is adapted for use with a control system <b>400</b> is shown. Electrosurgical apparatus <b>10</b> can be any type of electrosurgical apparatus known in the available art, including but not limited to electrosurgical apparatuses that can grasp and/or perform any of the above mentioned electrosurgical procedures. One type of electrosurgical apparatus <b>10</b> may include bipolar forceps as disclosed in United States Patent Publication No. 2007/0173814 entitled “Vessel Sealer and Divider For Large Tissue Structures”. A brief discussion of bipolar forceps <b>10</b> and components, parts, and members associated therewith is included herein to provide further detail and to aid in the understanding of the present disclosure.

p-0035With continued reference to <figref idrefs="DRAWINGS">FIG. 1</figref>, bipolar forceps <b>10</b> is shown for use with various electrosurgical procedures and generally includes a housing <b>20</b>, a handle assembly <b>30</b>, a rotating assembly <b>80</b>, a trigger assembly <b>70</b>, a shaft <b>12</b>, and an end effector assembly <b>100</b>, which mutually cooperate to grasp, seal and divide large tubular vessels and large vascular tissues. Although the majority of the figure drawings depict a bipolar forceps <b>10</b> for use in connection with endoscopic surgical procedures, the present disclosure may be used for more traditional open surgical procedures.

p-0036Shaft <b>12</b> has a distal end <b>16</b> dimensioned to mechanically engage the end effector assembly <b>100</b> and a proximal end <b>14</b> which mechanically engages the housing <b>20</b>. In the drawings and in the descriptions which follow, the term “proximal,” as is traditional, will refer to the end of the forceps <b>10</b> which is closer to the user, while the term “distal” will refer to the end which is farther from the user.

p-0037With reference to <figref idrefs="DRAWINGS">FIGS. 1 and 2</figref>, forceps <b>10</b> includes an electrosurgical cable <b>310</b> that connects the forceps <b>10</b> to a source of electrosurgical energy, e.g., an electrosurgical generator <b>500</b>, shown schematically in <figref idrefs="DRAWINGS">FIG. 1</figref>. As shown in <figref idrefs="DRAWINGS">FIG. 2</figref>, cable <b>310</b> is internally divided into cable leads <b>310</b>a, <b>310</b>b and <b>325</b>b which are designed to transmit electrical potentials through their respective feed paths through the forceps <b>10</b> to the end effector assembly <b>100</b>.

p-0038With reference again to <figref idrefs="DRAWINGS">FIG. 1</figref>, electrosurgical generator <b>500</b> (generator <b>500</b>) generates electrosurgical energy, which may be RF (radio frequency), microwave, ultrasound, infrared, ultraviolet, laser, thermal energy or other electrosurgical energy. Generator <b>500</b> is operatively and selectively connected to electrosurgical apparatus <b>10</b> for performing an electrosurgical procedure. The electrosurgical procedure can include sealing, cutting, coagulating, desiccating, and fulgurating tissue; all of which may employ RF energy. Additionally, generator <b>500</b> may be configured for monopolar and/or bipolar modes of operation. Generator <b>500</b> includes all necessary components, parts, and/or members needed for system <b>400</b> to function as intended. An electrosurgical module <b>520</b> generates RF energy and includes a power supply <b>550</b> for generating energy and an output stage <b>552</b> which modulates the energy that is provided to the delivery device(s), such as the end effector assembly <b>100</b>, for delivery of the modulated energy to a patient. In one embodiment, the power supply <b>550</b> may be a high voltage DC or AC power supply for producing electrosurgical current, where control signals generated by the system <b>400</b> adjust parameters of the voltage and current output, such as magnitude and frequency. The output stage <b>552</b> modulates the output energy (e.g., via a waveform generator) based on signals generated by the system <b>400</b> to adjust waveform parameters, e.g., waveform shape, pulse width, duty cycle, crest factor, and/or repetition rate. System <b>400</b> is coupled to the generator module <b>520</b> by connections that may include wired and/or wireless connections for providing the control signals to the generator module <b>520</b>.

p-0039With reference to <figref idrefs="DRAWINGS">FIGS. 3A and 3B</figref>, end effector assembly <b>100</b> is attached at the distal end <b>16</b> of shaft <b>12</b> and includes a pair of opposing jaw members <b>110</b> and <b>120</b>. Movable handle <b>40</b> of handle assembly <b>30</b> is operatively coupled to a drive assembly (not explicitly shown) which, together, mechanically cooperate to impart movement of the jaw members <b>110</b> and <b>120</b> from an open position wherein the jaw members <b>110</b> and <b>120</b> are disposed in spaced relation relative to one another, to a clamping or closed position wherein the jaw members <b>110</b> and <b>120</b> cooperate to grasp tissue therebetween.

p-0040Reference is made to United States Patent Publication No. 2007/0173814 for a more detailed explanation of the operation of forceps <b>10</b>. A more detailed description of the functionality of system <b>400</b> now follows.

p-0041As shown, end effector assembly <b>100</b> is provided with one or more conductive transmission elements or sensors <b>416</b> in operative communication with one or more transmitters, receivers, and/or transceivers modules <b>406</b> (<figref idrefs="DRAWINGS">FIG. 4</figref>) by way of optical fiber or a cable <b>410</b>. As shown, each of the jaw members includes sensors <b>416</b>. Sensors <b>416</b> are placed at predetermined locations on, in, or along surfaces of jaw members <b>110</b> and/or <b>120</b>, as best seen in <figref idrefs="DRAWINGS">FIGS. 3A and 3B</figref>. In embodiments, end effector assembly <b>100</b> and/or jaw members <b>110</b> and <b>120</b> may have sensors <b>416</b> placed near a proximal end and/or near a distal end of jaw members <b>110</b> and <b>120</b>, as well as along the length of jaw members <b>110</b> and <b>120</b>. End effector assembly <b>100</b> is also provided with one or more apertures or windows <b>416</b><i>a. </i>Windows <b>416</b><i>a </i>are configured such that sensors <b>416</b> may effectively transmit a signal and detect or sense a reflection of the signal. With this purpose in mind, windows <b>416</b><i>a </i>are substantially aligned with sensors <b>416</b>, as best seen in <figref idrefs="DRAWINGS">FIG. 3B</figref>.

p-0042It is contemplated that one of the jaw members, e.g., jaw member <b>120</b>, may include one or more sensors <b>416</b> configured to transmit an electromagnetic wave (e.g., interrogator wave) and the opposing, e.g., jaw member <b>10</b> may include a receiver configured to sense a reflection of the electromagnetic wave, or portion thereof. The electromagnetic wave may have a frequency occurring on a portion of the electromagnetic spectrum (e.g., radio frequency, microwave, visible light, and so). For illustrative purposes, sensors <b>416</b> transmit an interrogator wave occurring on the RF portion of the electromagnetic spectrum.

p-0043With reference again to <figref idrefs="DRAWINGS">FIG. 4</figref>, the system <b>400</b> for monitoring tissue during an electrosurgical procedure (e.g., RF tissue procedure) is shown. System <b>400</b> is configured to, among other things, determine the dielectric properties of a tissue of interest, such as a dielectric mismatch boundary <b>422</b>. As discussed above, a dielectric mismatch boundary <b>422</b> can refer generally to a surface or region between substances that exhibits different dielectric constants. The dielectric boundary <b>422</b> can be defined by a surface or region between desiccated tissue and hydrated tissue; blood vessel and muscle; neighboring blood vessels; and a return pad and cortical bone.

p-0044System <b>400</b> includes one or more processors <b>402</b> in operative communication with a control module <b>404</b> executable on the processor <b>402</b>. Control module <b>404</b> instructs a transceiver module <b>406</b> to transmit an interrogator wave or signal/pulse <b>408</b>, via cable <b>410</b>, to sensors <b>416</b> that contact (or are adjacent to) one or more tissue of interest “T”. As shown, tissue “T” is defined by tissue segments “T₁” and “T₂”. A reflection signal <b>412</b> that is a reflection of the transmitted interrogator signal <b>408</b> is detected by sensors <b>416</b> in response to the transmitted interrogator signal <b>408</b> encountering dielectric mismatch boundaries, such as the dielectric mismatch boundary <b>422</b>. The reflection signal <b>412</b> is returned along cable <b>410</b> and received by a transreceiver module <b>406</b> and/or sensor module <b>424</b> and subsequently processed by the processor <b>402</b> using a time source <b>428</b> to perform, for example, propagation velocity and/or phase shift analysis between the transmitted interrogator signal <b>408</b> and the reflection signal <b>412</b>.

p-0045The control module <b>404</b> processes information and/or signals (e.g., the dielectric boundary calculations input to the processor <b>402</b>) and generates control signals for modulating the electrosurgical energy in accordance with the input information and/or signals. Information may include pre-surgical data (e.g., parameters of tissue, such as, for example, permittivity and/or conductivity) entered prior to the electrosurgical procedure or information entered and/or obtained during the electrosurgical procedure through sensor module <b>424</b> and/or other suitable device. The information may include requests, instructions, ideal mapping(s) (e.g., look-up-tables, continuous mappings, etc.), sensed information and/or mode selection.

p-0046The control module <b>404</b> regulates the generator <b>500</b>, e.g., the power supply <b>550</b> and/or the output stage <b>552</b>, which adjusts various parameters of the electrosurgical energy delivered to the patient during the electrosurgical procedure. Parameters of the delivered electrosurgical energy that may be regulated include voltage, current, resistance, intensity, power, frequency, amplitude, and/or waveform parameters, e.g., waveform shape, pulse width, duty cycle, crest factor, and/or repetition rate of the output and/or effective energy.

p-0047The control module <b>404</b> includes software instructions executable by the processor <b>402</b> for processing algorithms and/or data received by sensors <b>416</b>, and for outputting control signals to the generator module <b>520</b> and/or other modules. The software instructions may be stored in a storage medium such as a memory internal to the processor <b>402</b> and/or a memory accessible by the processor <b>402</b>, such as an external memory, e.g., an external hard drive, floppy diskette, CD-ROM, etc.

p-0048In embodiments, an audio or visual feedback monitor or indicator (not explicitly shown) may be employed to convey information to the surgeon regarding the status of a component of the electrosurgical system or the electrosurgical procedure. Control signals provided to the generator module <b>520</b> are determined by processing (e.g., performing algorithms), which may include using information and/or signals provided by sensors <b>416</b>.

p-0049The control module <b>404</b> regulates the electrosurgical energy in response to feedback information, e.g., information related to tissue condition at or proximate the surgical site. Processing of the feedback information may include determining: changes in the feedback information; rate of change of the feedback information; and/or relativity of the feedback information to corresponding values sensed prior to starting the procedure (pre-surgical values) in accordance with the mode, control variable(s) and ideal curve(s) selected. The control module <b>404</b> then sends control signals to the generator module <b>520</b> such as for regulating the power supply <b>550</b> and/or the output stage <b>552</b>.

p-0050Regulation of certain parameters of the electrosurgical energy may be based on a tissue response such as recognition of when a proper seal is achieved, when a predetermined depth of thermal spread is reached, and/or when a user is approaching a substantial or large blood vessel. Recognition of the event may automatically switch the generator <b>500</b> to a different mode of operation (e.g., coagulation mode or higher mode of operation) and subsequently switch the generator <b>500</b> back to an original mode after the event has occurred. In embodiments, recognition of the event may automatically switch the generator <b>500</b> to a different mode of operation (e.g., coagulation mode or higher mode of operation) and subsequently shutoff the generator <b>500</b>.

p-0051Transceiver module <b>406</b> may be digital and/or analog circuitry that can receive instructions from and provide status to a processor <b>402</b> (via, for example, a digital-to-analog or analog-to-digital converter). Transceiver module <b>406</b> is also coupled to control module <b>404</b> to receive one or more interrogator waves <b>408</b> at a frequency and amplitude specified by the processor <b>402</b>, and/or transmit the interrogator waves <b>408</b> along cable <b>410</b> to sensors <b>416</b>. In one illustrative embodiment, the transceiver module <b>406</b> uses clock signals received from a pulse rate frequency clock in the time source <b>428</b> to perform at least some of its operations. Transceiver module <b>406</b> can also amplify, filter, and digitally sample the return signal <b>412</b> received by sensor <b>416</b> and transmitted along cable <b>410</b>.

p-0052Time source <b>428</b> may be digital circuitry that can, for example, provide a pulse rate, variable-delayed frequency clock that operates on an equivalent time sampling detector that may be contained within a transceiver <b>404</b> and which can detect and/or be used to construct a representation of the received signal <b>424</b>. In one illustrative embodiment, the time source <b>428</b> may include a delay controller, such as a voltage integrator op-amp ramp circuit with capacitor discharge reset to produce a precise linear time ramp for the delay circuit.

p-0053The sensor module <b>424</b> senses electromagnetic, electrical, and/or physical parameters or properties at the operating site and communicates with the control module <b>404</b> and/or transceiver module <b>406</b> to regulate the output electrosurgical energy. The sensor module <b>424</b> may be configured to measure, i.e., “sense”, various electromagnetic, electrical, physical, and/or electromechanical conditions, such as at or proximate the operating site, including: thermal spread, tissue impedance, tissue temperature, and so on. For example, sensors of the sensor module <b>424</b> may include sensors <b>416</b> and/or other suitable sensors, such as, for example, optical sensor(s), proximity sensor(s), pressure sensor(s), tissue moisture sensor(s), temperature sensor(s), and/or real-time and RMS current and voltage sensing systems. The sensor module <b>424</b> measures one or more of these conditions continuously or in real-time such that the control module <b>404</b> can continually modulate the electrosurgical output in real-time.

p-0054Sensors <b>416</b> are illustrated in <figref idrefs="DRAWINGS">FIG. 4</figref> as exhibiting substantially the same characteristics (e.g., length), but those skilled in the art will recognize that their width, length, orientation, or other characteristics can vary. In one embodiment, the characteristics of each of the sensor <b>416</b> can be varied, while their transmission line impedance remains substantially constant. In another embodiment, their characteristics can be varied according to a predetermined arrangement for impedance matching and/or to obtain a desirable signal response (e.g., a coupled return at a predetermined point on the sensor that can serve as a point of reference). Sensors <b>416</b> may be separate structure coupled to a distal end of cable <b>410</b>, or sensors <b>416</b> may be integrally formed at a distal end of cable <b>410</b> and configured for transmitting and sensing a reflection <b>412</b> of the transmitted signal <b>408</b>.

p-0055In embodiments, sensor <b>416</b> includes a smart sensor assembly <b>416</b><i>a </i>(e.g., a smart sensor, smart circuit, computer, and/or feedback loop, etc.). For example, the smart sensor assembly <b>416</b><i>a </i>may include a feedback loop which indicates when a tissue seal is complete based upon one or more of the following parameters: depth of thermal spread, tissue temperature, tissue impedance at the seal, change in impedance of the tissue over time and/or changes in the power or current applied to the tissue over time. An audible or visual feedback monitor <b>440</b> may be employed to convey information to the surgeon regarding the overall seal quality or the completion of an effective tissue seal.

p-0056Cable <b>410</b> and/or sensors <b>416</b> may be any suitable structure suitable for carrying an electromagnetic signal, including but not limited to coaxial-arranged conductors, one or more twisted wires, fiber optics, dielectric rods, microstrip lines, coplanar striplines, coplanar waveguides, and so forth. Cable <b>410</b> operatively connects sensor <b>416</b> to one or modules of system <b>400</b>. Cable <b>410</b> may follow substantially the same path as cable feed <b>310</b> and may extend within jaw members <b>110</b> and/or <b>120</b>.

p-0057With continued reference to <figref idrefs="DRAWINGS">FIG. 4</figref>, system <b>400</b> is configured to analyze one or more properties associated with the reflection and transmission of an interrogator wave, for example, “time of flight” or propagation velocity measurements and/or phase shift measurements. System <b>400</b> includes any suitable analysis device for analyzing the reflected signal <b>412</b> and/or transmitted interrogator wave <b>408</b>. For example, system <b>400</b> may include optical spectrum analyzers (e.g., analog and digital spectrum analyzers), network analyzers <b>420</b>, Fabry-Perot interferometers, dispersive spectrometers, or any combination of analysis devices thereof.

p-0058System <b>400</b> is in operative communication with one or more network analyzers <b>420</b>. Network analyzer <b>420</b> may be a Scalar Network Analyzer (SNA), which measures amplitude properties, or a Vector Network Analyzer (VNA), which measures both amplitude and phase properties. Network analyzer <b>420</b> may be configured to determine the dielectric properties of tissue.

p-0059As noted above, biological materials with different dielectric constants cause reflection of interrogator waves incident thereto as a function of the material properties. As further noted above, control module <b>404</b> processes information and/or signals (e.g., the dielectric boundary calculations input to the processor <b>402</b>) and generates control signals for modulating the electrosurgical energy in accordance with the input information and/or signals. One or more control algorithms use the below formulas to calculate the reflection coefficient. The calculated reflection coefficient is processed by the control module <b>404</b> and is executable by the processor <b>402</b> for subsequent use at a latter time. For perpendicular incidence the magnitude of the reflection coefficient Γ is given by the equation:

p-0060<maths id="MATH-US-00001" num="00001"><math overflow="scroll"><mtable><mtr><mtd><mrow><mi>Γ</mi><mo>=</mo><mfrac><mrow><msub><mi>η</mi><mn>2</mn></msub><mo>-</mo><msub><mi>η</mi><mn>1</mn></msub></mrow><mrow><msub><mi>η</mi><mn>2</mn></msub><mo>-</mo><msub><mi>η</mi><mn>1</mn></msub></mrow></mfrac></mrow></mtd><mtd><mrow><mo>(</mo><mn>1</mn><mo>)</mo></mrow></mtd></mtr></mtable></math></maths>

p-0061where η is the wave impedance which is given by the equation:

p-0062<maths id="MATH-US-00002" num="00002"><math overflow="scroll"><mtable><mtr><mtd><mrow><mi>η</mi><mo>=</mo><msqrt><mfrac><mi>jωμ</mi><mrow><mi>σ</mi><mo>+</mo><mi>jωɛ</mi></mrow></mfrac></msqrt></mrow></mtd><mtd><mrow><mo>(</mo><mn>2</mn><mo>)</mo></mrow></mtd></mtr></mtable></math></maths>

p-0063where ω is the angular velocity, μ is the magnetic permeability, σ is the electrical conductivity, and ε is the permittivity. For biological materials, the permittivity and conductivity are both functions of frequency.

p-0064As indicated in <figref idrefs="DRAWINGS">FIG. 5</figref>, the magnitude of the reflections of interrogator waves is shown as peaks in the signal at specific frequencies. With knowledge of the permittivity ε, the permeability μand the conductivity σ for selected tissue types, system <b>400</b> determines the distance from sensor <b>416</b> to the dielectric boundary <b>422</b> that causes the reflection signal <b>412</b> of the transmitted interrogator wave <b>408</b> such that tissue modifications during electrosurgical procedures may be controlled and/or monitored.

p-0065Control module <b>404</b> determines the specific frequency that maximizes the reflection coefficient Γ for selected tissue types. Here, one or more algorithms under the control of processor <b>402</b> use the following equation to predict dielectric behavior over a wide frequency range:

p-0066<maths id="MATH-US-00003" num="00003"><math overflow="scroll"><mtable><mtr><mtd><mrow><mrow><mover><mi>ɛ</mi><mo>^</mo></mover><mo></mo><mrow><mo>(</mo><mi>ω</mi><mo>)</mo></mrow></mrow><mo>=</mo><mrow><msub><mi>ɛ</mi><mi>ω</mi></msub><mo>+</mo><mrow><munder><mo>∑</mo><mi>n</mi></munder><mo></mo><mfrac><mrow><mi>Δ</mi><mo></mo><mstyle><mspace width="0.3em" height="0.3ex" /></mstyle><mo></mo><msub><mi>ɛ</mi><mi>n</mi></msub></mrow><mrow><mn>1</mn><mo>+</mo><msup><mrow><mo>(</mo><msub><mi>jωτ</mi><mi>n</mi></msub><mo>)</mo></mrow><mrow><mo>(</mo><mrow><mn>1</mn><mo>-</mo><msub><mi>α</mi><mi>n</mi></msub></mrow><mo>)</mo></mrow></msup></mrow></mfrac></mrow><mo>+</mo><mfrac><msub><mi>σ</mi><mn>1</mn></msub><msub><mi>jωɛ</mi><mn>0</mn></msub></mfrac></mrow></mrow></mtd><mtd><mrow><mo>(</mo><mn>3</mn><mo>)</mo></mrow></mtd></mtr></mtable></math></maths>

p-0067where ε_∞ is permittivity at frequencies where ωτ>>1 and Δε is the difference between ε_∞ and ε_s(the permittivity at •τ<<1). The values for τ are time constants and α is a distribution constant. Experimental data from selected tissue types provides values for the above parameters. Using the continuous data supplied by equation (3) and experimental data preloaded into one or more memory of the control module <b>404</b> and executable by the processor <b>402</b>, the frequency corresponding to the highest or maximum reflection coefficient Γ is determined.

p-0068In a first application, the maximum reflection coefficient Γ for a boundary defined by desiccated tissue on a background of hydrated tissue is determined. In this application, dry tissue, which has low moisture content, is used as an analog for the desiccated tissue. In the following example, water content drives the dielectric behavior of tissue.

p-0069With reference to <figref idrefs="DRAWINGS">FIG. 6</figref>, a graph of the reflection coefficient Γ vs. frequency for a boundary defined by dry skin and hydrated tissue (e.g., muscle) is shown. As evidenced by the graph, the only non-negative values for the reflection coefficient Γ are between 2.0×10⁶and 1.4×10⁸Hz. Thus, the maximum value for Γ is 0.1856 at a frequency of 9.6×10⁶Hz.

p-0070In a second application, the maximum reflection coefficient Γ for a boundary defined by muscle to blood (e.g., approaching a blood vessel) is determined.

p-0071With reference to <figref idrefs="DRAWINGS">FIG. 7</figref>, a graph of the reflection coefficient Γ vs. frequency for a boundary defined by muscle and blood is shown. As evidenced by the graph, the only non-negative values for the reflection coefficient Γ are at frequencies below 3.8×10⁵Hz with maximum values of Γ of 0.9721 at 1 Hz; however, because electrical stimulation of tissue may cause neuromuscular stimulation at low frequencies (e.g., frequencies below 1.0×10⁴Hz), a lower limit for selecting an integration frequency will be set at 1.0×10⁴Hz. Thus, at 1.0×10⁴Hz the reflection coefficient Γ is 0.3792.

p-0072In a third application, the maximum reflection coefficient Γ for a boundary defined by liver and blood is determined. Using the same justification as for the muscle to blood interrogation frequency selection, an integration frequency has a lower limit of 1.0×10⁴Hz.

p-0073With reference to <figref idrefs="DRAWINGS">FIG. 8</figref>, a graph of the reflection coefficient Γ vs. frequency for a boundary defined by liver and blood is shown. As shown by the graph, the only non-negative values for the reflection coefficient Γ are at frequencies lower than 2.2×10⁵Hz. At an interrogation frequency of 1.0×10⁴the reflection coefficient is 0.4026.

p-0074In a fourth application, the maximum reflection coefficient Γ for a boundary defined by muscle tissue to cortical bone is determined. Using the same justification as for the muscle to blood, and liver and blood interrogation frequency selections, an integration frequency having a lower limit of 1.0×10⁴Hz is set.

p-0075With reference to <figref idrefs="DRAWINGS">FIG. 9</figref>, a graph of the reflection coefficient Γ vs. frequency for a boundary defined by muscle and bone is shown. As shown by the graph, the reflection coefficient Γ at an interrogation frequency of 1.0×10⁴is 0.7515.

p-0076Electromagnetic waves propagate through homogenous medium at a speed defined by the following equation:

p-0077<maths id="MATH-US-00004" num="00004"><math overflow="scroll"><mtable><mtr><mtd><mrow><mi>v</mi><mo>=</mo><mfrac><mi>c</mi><mi>n</mi></mfrac></mrow></mtd><mtd><mrow><mo>(</mo><mn>4</mn><mo>)</mo></mrow></mtd></mtr></mtable></math></maths>

p-0078where c is the speed of light and n is the index of refraction defined by the equation:

p-0079<maths id="MATH-US-00005" num="00005"><math overflow="scroll"><mtable><mtr><mtd><mrow><mi>n</mi><mo>=</mo><msqrt><mfrac><mi>ɛμ</mi><mrow><msub><mi>ɛ</mi><mn>0</mn></msub><mo></mo><msub><mi>μ</mi><mn>0</mn></msub></mrow></mfrac></msqrt></mrow></mtd><mtd><mrow><mo>(</mo><mn>5</mn><mo>)</mo></mrow></mtd></mtr></mtable></math></maths>

p-0080where all variables use previously described definitions. Because biological material has a magnetic permittivity of free space, equation (5) may be replaced by the approximation defined by equation:

p-0081<br />n≅√{square root over (ε_r)}  (6)

p-0082where ε_ris the relative permittivity.

p-0083Using equations (4) and (6) along with the continuous data provided by equation (3), control module <b>404</b> determines the propagation velocity of the reflection signal <b>412</b> for a given dielectric boundary as a function of frequency.

p-0084Data calculated from any of the aforementioned equations is stored into a memory and accessible by one or more of the previously described modules and/or processors such that real-time or continuous data calculations may be performed.

p-0085Thus, for a given dielectric boundary where the maximum reflection coefficient Γ at a specific frequency is known, time measurements taken of a reflection signal <b>412</b> for a given transmitted interrogator wave <b>408</b> allow any of the aforementioned modules and/or processors to manipulate one or more control algorithms to calculate the distance from one or more sensors <b>416</b> to the dielectric boundary <b>422</b> such that tissue transformation during an electrosurgical procedure can be controlled and/or monitored.

p-0086Operation of system <b>400</b> is now described in terms of use with bipolar forceps <b>10</b>. In the following example, thermal spread of tissue during a sealing process is monitored such that the depth of the desiccation of tissue during the electrosurgery can be determined.

p-0087In an illustrative operation and with reference again to <figref idrefs="DRAWINGS">FIG. 4</figref>, a processor <b>402</b> can instruct a transceiver module <b>406</b> to generate an interrogator wave of interest <b>408</b>. In response to the processor instructions, the transceiver module <b>406</b> can access a pulse rate frequency clock associated with time source <b>428</b> to form an interrogator wave <b>408</b> exhibiting the attributes (e.g., amplitude and frequency) specified by the processor <b>402</b> and can transmit such wave <b>408</b> on one or more cables <b>410</b> to sensor <b>416</b>. In another embodiment, the processor does not specify attributes of the interrogator wave <b>408</b>, but rather instructs/triggers other circuitry to form the electromagnetic signal <b>408</b> and/or performs timing measurements on signals conditioned and/or filtered by other circuitry.

p-0088The transmitted interrogator <b>408</b> (e.g., one or more electromagnetic signal/pulses) travels along cable <b>410</b> to sensor(s) <b>416</b> that is/are in contact with, and/or otherwise adjacent to tissue. The transmitted interrogator wave <b>408</b>, or portion thereof, is reflected from the tissue “T” as a result of the dielectric mismatch boundaries <b>422</b>, that is, the boundary between dry desiccated tissue and hydrated tissue. The reflected signal <b>412</b>, or portion thereof, is detected by sensors <b>416</b> and, under the control of the processor <b>402</b> the reflected signal <b>412</b> can be sampled by the transceiver module <b>406</b> and/or sensor module <b>424</b> using a controlled time delay of the pulse rate frequency clock of the time source <b>428</b> to form a representation of the reflected signal <b>412</b>. The reflected signal and/or the representation of the reflected signal can also be amplified to increase the amplitude of the signal and/or filtered to remove harmonics and other interfering signals, such as signals from parasitic coupling between the transceiver-side circuitry located on a common printed circuit board, signals coupled from reflections on the sensors <b>416</b>, and so forth.

p-0089The amplified and filtered reflection signal <b>412</b> can be processed by the processor <b>402</b> and/or transceiver module <b>404</b> relative to the transmitted signal <b>406</b> to determine attributes (e.g., propagation velocity measurements and/or phase shift) that can be used to derive characteristics (e.g., level and/or volume of thermal spread) associated with the tissue “T” that formed the dielectric mismatch boundary <b>422</b>. The processor <b>402</b> can subsequently transmit and/or otherwise communicate the attributes of the return signal and/or the characteristics of the tissue “T” to control module <b>404</b> such that output power from generator <b>500</b> may be adjusted accordingly. The processor <b>402</b> can also subsequently transmit and/or otherwise communicate the attributes of the return signal and/or the characteristics of the tissue “T” to a local digital data processing device, a remote digital data processing device, an LED display, a computer program, and/or to any other type of entity (none of which being explicitly shown) capable of receiving the attribute and/or characteristic information.

p-0090From the foregoing and with reference to the various figure drawings, those skilled in the art will appreciate that certain modifications can also be made to the present disclosure without departing from the scope of the same. For example, it may be preferable to have sensors <b>416</b> and/or any optical fiber or cable <b>410</b> associated therewith, proximally located, and operatively and selectively connected to an electrosurgical apparatus <b>600</b>; this, of course, will depend on the contemplated needs of a user. Having the sensor <b>416</b> configured in such a manner may prove useful during microwave ablation procedures.

p-0091<figref idrefs="DRAWINGS">FIG. 10</figref> illustrates system <b>400</b> configured for use with an alternative electrosurgical apparatus <b>602</b> (e.g., monopolar apparatus configured for use with a microwave ablation procedure). Here, sensor(s) <b>416</b> are in operative communication with a microwave generator <b>700</b> and/or microwave ablation device <b>602</b>. Microwave ablation device <b>602</b> includes an active electrode <b>604</b> configured to transmit energy to tissue and in operative communication with a return pad (not explicitly shown). Sensor(s) <b>416</b> may be configured to attach adjacent to an area of tissue that is to be treated. In this instance, barring structural attributes, sensor(s) <b>416</b> is configured to function as described above.

p-0092It is further contemplated that system <b>400</b> and any members, components, and/or parts associated therewith can be activated, deactivated, and/or controlled via forceps <b>10</b>, and/or electrosurgical generator <b>500</b> via any handles, switches and/or buttons associated therewith.

p-0093It is envisioned that system <b>400</b> may employ phase shift measurements instead of, or in combination with time measurements such that the depth of dielectric boundary may be determined.

p-0094Those skilled in the art will recognize that it may be difficult to characterize adjacent substances that exhibit similar dielectric constants, where such conditions could result in, for example, a relatively low amplitude in the reflected signal <b>412</b>, and/or where the transmit-to-receive time between the transmitted interrogator wave <b>408</b> and reflected signal <b>412</b> is comparatively small (which may, for example, experience interference from parasitic coupling). Accordingly and optionally, the disclosed technology can include a coupler composed at least in part of a material exhibiting a comparatively high dielectric constant (e.g., ceramics, plastics, etc.), conductive properties (e.g., metals, metalized materials, ferrites, etc.), and/or other properties that can be positioned at or near the dielectric mismatch boundary and that can create a coupled return signal of substantially consistent attributes (e.g., amplitude), which is independent of the dielectric properties of the substances forming the dielectric mismatch boundary.

p-0095<figref idrefs="DRAWINGS">FIG. 11</figref> shows a method <b>800</b> for monitoring and/or controlling the delivery of electrosurgical energy to tissue during an electrosurgical procedure. At step <b>802</b>, an electrosurgical apparatus including a pair of jaw members configured to grasp tissue therebetween and is provided. At step <b>804</b> an interrogator wave of at least one frequency from an electromagnetic interrogator wave source is transmitted through tissue. At step <b>806</b>, electrosurgical energy from an electrosurgical generator is directed through tissue held between the jaw members. At step <b>808</b>, the interrogator wave of one or more frequencies is directed into tissue. At step <b>810</b>, at least a portion of a reflection of the electromagnetic wave is analyzed to determine dielectric boundary data. And, at step <b>812</b>, the delivery of electrosurgical energy from the electrosurgical generator to tissue is controlled based on the dielectric boundary data provided to a processor.

p-0096While several embodiments of the disclosure have been shown in the drawings, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. Therefore, the above description should not be construed as limiting, but merely as exemplifications of particular embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.