US20180296266A1 - System and method for monitoring ablation size - Google Patents

Abstract

A system for monitoring ablation size is provided and includes a power source including a microprocessor for executing at least one control algorithm. A microwave antenna is configured to deliver microwave energy from the power source to tissue to form an ablation zone. An ablation zone control module is in operative communication with memory associated with the power source. The memory includes one or more data look-up tables including one or more electrical parameter associated with the microwave antenna. The one or more electrical parameters corresponding to an ablation zone having a radius. The one or more electrical parameters include a threshold value, wherein when the threshold value is met the power source is adjusted to form an ablation zone of suitable proportion.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• The present application is a continuation application of U.S. patent application Ser. No. 14/532,317 filed Nov. 4, 2014, now U.S. patent Ser. No. 10/004,559, which is a continuation application of U.S. patent application Ser. No. 14/064,846 filed Oct. 28, 2013, now U.S. Pat. No. 8,894,641, which is a divisional application of U.S. patent application Ser. No. 12/606,769 filed on Oct. 27, 2009, now U.S. Pat. No. 8,568,401, the entire contents of each of which are incorporated herein by reference.
BACKGROUNDTechnical Field
• The present disclosure relates to systems and methods that may be used in tissue ablation procedures. More particularly, the present disclosure relates to systems and methods for monitoring ablation size during tissue ablation procedures in real-time.
Background of Related Art
• In the treatment of diseases such as cancer, certain types of cancer cells have been found to denature at elevated temperatures (which are slightly lower than temperatures normally injurious to healthy cells). These types of treatments, known generally as hyperthermia therapy, typically utilize electromagnetic radiation to heat diseased cells to temperatures above 41° C. while maintaining adjacent healthy cells at lower temperatures where irreversible cell destruction will not occur. Procedures utilizing electromagnetic radiation to heat tissue may include ablation of the tissue.
• Microwave ablation procedures, e.g., such as those performed for menorrhagia, are typically done to ablate the targeted tissue to denature or kill the tissue. Many procedures and types of devices utilizing electromagnetic radiation therapy are known in the art. Such microwave therapy is typically used in the treatment of tissue and organs such as the prostate, heart, and liver.
• One non-invasive procedure generally involves the treatment of tissue (e.g., a tumor) underlying the skin via the use of microwave energy. The microwave energy is able to non-invasively penetrate the skin to reach the underlying tissue. However, this non-invasive procedure may result in the unwanted heating of healthy tissue. Thus, the non-invasive use of microwave energy requires a great deal of control.
• Currently, there are several types of systems and methods for monitoring ablation zone size. In certain instances, one or more types of sensors (or other suitable devices) are operably associated with the microwave ablation device. For example, in a microwave ablation device that includes a monopole antenna configuration, an elongated microwave conductor may be in operative communication with a sensor exposed at an end of the microwave conductor. This type of sensor is sometimes surrounded by a dielectric sleeve.
• Typically, the foregoing types of sensor(s) are configured to function (e.g., provide feedback to a controller for controlling the power output of a power source) when the microwave ablation device is inactive, i.e., not radiating. That is, the foregoing sensors do not function in real-time. Typically, the power source is powered off (or pulsed off) when the sensors are providing feedback (e.g., tissue temperature) to the controller and/or other device(s) configured to control the power source.
SUMMARY
• The present disclosure provides a system for monitoring ablation size in real-time. The system includes a power source including a microprocessor for executing at least one control algorithm. The system includes a microwave antenna configured to deliver microwave energy from the power source to tissue forming an ablation zone. An ablation zone control module is in operative communication with a memory associated with the power source. The memory includes one or more data look-up tables including one or more electrical parameters associated with the microwave antenna. The electrical parameter(s) corresponding to a radius of the ablation zone, wherein the ablation zone control module triggers a signal when a predetermined threshold value of the electrical parameter(s) is measured corresponding to the radius of the ablation zone.
• The present disclosure provides a microwave antenna adapted to connect to a power source configured for performing an ablation procedure. The microwave antenna includes a radiating section configured to deliver microwave energy from a power source to tissue to form an ablation zone. An ablation zone control module is in operative communication with a memory associated with the power source. The memory includes one or more data look-up tables including one or more electrical parameters associated with the microwave antenna. The electrical parameter(s) corresponding to a radius of the ablation zone, wherein the ablation zone control module triggers a signal when a predetermined threshold value of the electrical parameter(s) is measured corresponding to the radius of the ablation zone.
• The present disclosure also provides a method for indirectly monitoring temperature of tissue undergoing ablation by way of probe impedance. The method includes an initial step of transmitting microwave energy from a power source to a microwave antenna to form a tissue ablation zone. A step of the method includes monitoring complex impedance associated with the microwave antenna as the tissue ablation zone forms. A step of the method includes communicating a control signal to the power source when a predetermined complex impedance is reached at the microwave antenna. Adjusting the amount of microwave energy from the power source to the microwave antenna is another step of the method.
BRIEF DESCRIPTION OF THE DRAWINGS
• The above and other aspects, features, and advantages of the present disclosure will become more apparent in light of the following detailed description when taken in conjunction with the accompanying drawings in which:
• FIG. 1 is a perspective view of a system for monitoring ablation size according to an embodiment of the present disclosure;
• FIG. 2 is a functional block diagram of a power source for use with the system depicted inFIG. 1;
• FIG. 3A is a schematic, plan view of the tip of a microwave antenna depicted inFIG. 2A illustrating radial ablation zones having a spherical configuration;
• FIG. 3B is a schematic, plan view of the tip of a microwave antenna depicted inFIG. 1 illustrating radial ablation zones having an ellipsoidal configuration;
• FIG. 4A-1 is a graphical representation of a real impedance (Zr) versus time (t) curve;
• FIG. 4A-2 a graphical representation of a corresponding ablation radii (Ar) versus time (t) curve;
• FIG. 4B-1 is a graphical representation of the imaginary impedance (Zi) versus time (t) curve;
• FIG. 4B-2 is a graphical representation of corresponding ablation radii (Ar) versus time (t) curve; and
• FIG. 5 is a flow chart illustrating a method for monitoring temperature of tissue undergoing ablation in accordance with the present disclosure.
DETAILED DESCRIPTION
• Embodiments of the presently disclosed system and method are described in detail with reference to the drawing figures wherein like reference numerals identify similar or identical elements. As used herein and as is traditional, the term “distal” refers to the portion which is furthest from the user and the term “proximal” refers to the portion that is closest to the user. In addition, terms such as “above”, “below”, “forward”, “rearward”, etc. refer to the orientation of the figures or the direction of components and are simply used for convenience of description.
• Referring now toFIG. 1, a system for monitoring ablation size is designated10. Thesystem10 includes amicrowave antenna100 that is adapted to connect to an electrosurgical power source, e.g., an RF and/or microwave (MW)generator200 that includes or is in operative communication with one ormore controllers300 and, in some instances, afluid supply pump40. Briefly,microwave antenna100 includes anintroducer116 having anelongated shaft112 and a radiating or conductive section ortip114 operably disposed withinelongated shaft112, a coolingassembly120 having a cooling sheath121, ahandle118, a coolingfluid supply122 and a coolingfluid return124, and anelectrosurgical energy connector126.Connector126 is configured to connect themicrowave antenna100 to theelectrosurgical power source200, e.g., a generator or source of radio frequency energy and/or microwave energy, and supplies electrosurgical energy to the distal portion of themicrowave antenna100.Conductive tip114 andelongated shaft112 are in electrical communication withconnector126 via an internalcoaxial cable126athat extends from the proximal end of themicrowave antenna100 and includes an inner conductor tip that is operatively coupled to aradiating section138 operably disposed within theshaft112 and adjacent the conductive or radiating tip114 (seeFIG. 3A, for example). As is common in the art, internalcoaxial cable126aincludes a dielectric material and an outer conductor surrounding each of the inner conductor tip and dielectric material. A connection hub (not shown) disposed at a proximal end of themicrowave antenna100operably couples connector126 to internalcoaxial cable126a, and coolingfluid supply122 and a coolingfluid return124 to acooling assembly120.Radiating section138 by way of conductive tip114 (or in certain instances without conductive tip114) is configured to deliver radio frequency energy (in either a bipolar or monopolar mode) or microwave energy (having a frequency of about 500 MHz to about 10 GHz) to a target tissue site.Elongated shaft112 andconductive tip114 may be formed of suitable conductive material including, but not limited to copper, gold, silver or other conductive metals having similar conductivity values. Alternatively,elongated shaft112 and/orconductive tip114 may be constructed from stainless steel or may be plated with other materials, e.g., other conductive materials, such as gold or silver, to improve certain properties, e.g., to improve conductivity, decrease energy loss, etc. In an embodiment, the conductive tip may be deployable from theelongated shaft112.
• With reference toFIG. 2, a schematic block diagram of thegenerator200 is illustrated. Thegenerator200 includes acontroller300 having one or more modules (e.g., an ablation zone control module332 (AZCM332), apower supply237 and a microwave output stage238). In this instance,generator200 is described with respect to the delivery of microwave energy. Thepower supply237 provides DC power to themicrowave output stage238 which then converts the DC power into microwave energy and delivers the microwave energy to theradiating section138 of themicrowave antenna100. Thecontroller300 may include analog and/or logic circuitry for processing sensed values provided by theAZCM332 and determining the control signals that are sent to thegenerator200 and/orsupply pump40 via amicroprocessor335. The controller300 (or component operably associated therewith) accepts one or more measured signals indicative of calculated complex impedance associated with themicrowave antenna100 and/or tissue adjacent an ablation zone when the microwave antenna is radiating energy.
• One or more modules e.g.,AZCM332, of thecontroller300 analyzes the measured signals and determines if a threshold complex impedance has been met. If the threshold complex impedance has been met, then theAZCM332, amicroprocessor335 and/or the controller instructs thegenerator200 to adjust themicrowave output stage238 and/or thepower supply237 accordingly. Additionally, thecontroller300 may also signal the supply pump to adjust the amount of cooling fluid to themicrowave antenna100 and/or the surrounding tissue. Thecontroller200 includesmicroprocessor335 havingmemory336 which may be volatile type memory (e.g., RAM) and/or non-volatile type memory (e.g., flash media, disk media, etc.). In the illustrated embodiment, themicroprocessor335 is in operative communication with thepower supply237 and/ormicrowave output stage238 allowing themicroprocessor335 to control the output of thegenerator300 according to either open and/or closed control loop schemes. Themicroprocessor335 is capable of executing software instructions for processing data received by theAZCM332, and for outputting control signals to thegenerator300 and/orsupply pump40, accordingly. The software instructions, which are executable by thecontroller300, are stored in thememory336.
• One or more control algorithms for predicting tissue ablation size is implemented by thecontroller300. More particularly, the concept of correlating complex impedance (e.g., real and imaginary portions of the complex impedance) associated with a particular microwave antenna, e.g., themicrowave antenna100, with an ablation zone “A” having a radius “r” may be used to indicate tissue death or necrosis. More particularly, complex impedance associated with themicrowave antenna100 varies over the course of an ablation cycle due to tissue complex permittivity changes caused by temperature increase (seeFIGS. 4A-1 and 4B-1, for example). A relationship of complex impedance as a function of time may be represented by the curves illustrated inFIGS. 4A-1 (real portion of complex impedance) and4B-1 (imaginary portion of complex impedance). When themicrowave antenna100 has heated tissue to a maximum attainable temperature, an ablation zone “A” having a corresponding radius “r” (e.g., rss) is formed (seeFIG. 3A in combination withFIGS. 4A-2 and 4B-2, for example). At this maximum temperature a dielectric constant and conductivity associated with the ablated tissue reach a steady-state condition (this steady-state condition occurs at time tss) that corresponds to a steady-state complex impedance Zss (hereinafter referred to simply as Zss) associated with themicrowave antenna100. That is, because the ablated tissue is in a “near field” of themicrowave antenna100, the ablated tissue essentially becomes part of themicrowave antenna100. Accordingly, when a dielectric constant and conductivity associated with the ablated tissue reaches a steady-state condition, the complex impedance at themicrowave antenna100 also reaches a steady-state condition, e.g., Zss, where Zss includes a real portion Zrss and an imaginary portion Ziss, seeFIGS. 4A-1 and 4B-1, respectively.
• It should be noted, that Zss may vary for a given microwave antenna. Factors that may contribute to a specific Zss for a given microwave antenna include but are not limited to: dimensions associated with the microwave antenna (e.g., length, width, etc.); type of material used to manufacture the microwave antenna (or portion associated therewith, e.g., a radiating section) such as copper, silver, etc; and the configuration of the radiating section (e.g., dipole, monopole, etc.) and/or a conductive tip (e.g., sharp, blunt, curved, etc) associated with the microwave antenna.
• The control algorithm implements one or more model equations and/or curves, e.g., curves depicted inFIGS. 4A-1 and 4B-1, to calculate the Zss associated with themicrowave antenna100 within a specified time range (e.g., t1-tss) not exceeding tss, i.e., time when the ablated tissue is at the steady-state condition (seeFIG. 4A-1 orFIG. 4B-1, for example). More particularly, the real and imaginary portions, Zrss and Ziss, respectively, of the Zss of themicrowave antenna100 may be calculated via monitoring and/or measuring of a signal (or pulse) generated by thegenerator200. More particularly, a phase (for calculating an imaginary impedance Ziss of the complex impedance) and magnitude (for calculating a real impedance Zrss of the complex impedance) associated with a signal (or pulse) generated by thegenerator200 during an ablation procedure may be sampled and monitored. For example, one or more electrical properties (e.g., voltage, current, power, impedance, etc.) associated with a signal (or pulse) generated by thegenerator200 may be sampled and monitored. More particularly, electrical properties associated with a forward and reflected portion of the signal generated by thegenerator200 is sampled and monitored. For example, in one particular embodiment, forward and reflected power, Pfwd and Pref, respectively, of a signal for ablating tissue is measured by theAZCM332,controller300, microprocessor337 or other suitable module associated with thegenerator200 and/orcontroller200. Thereafter, the power standing wave ratio (Pswr) is calculated using the equation:
• $\begin{array}{cc}{P}_{\mathrm{SWR}}=\frac{P_{\mathrm{fwd}}+P_{\mathrm{ref}}}{P_{\mathrm{fwd}}-P_{\mathrm{ref}}}& \left(1\right)\end{array}$
• where Pfwd is the power associated with the generated signal (i.e., forward signal) and Pref is the power associated with the reflected signal. Those skilled in the relative art can appreciate that with the Pswr, Pfwd and Pref calculated the real portion of the complex impedance at the steady-state condition, e.g., Zss, of themicrowave antenna100 may be calculated. More particularly, the phase difference between the forward and reflected power may be used to calculate the imaginary portion Ziss of the complex impedance and the magnitude difference between the forward and reflected power may be used to calculate the real portion Zrss of the complex impedance. With Zrss and Ziss known, Zss may be calculated and, subsequently, communicated and/or relayed to one or more modules associated with thecontroller300, e.g.,AZCM332, to determine if a predetermined threshold value Zss that corresponds to a desired ablation size has been met. For example, in certain instances, known characteristic impedance associated withconnector126 and/orinternal cable126amay be employed to determine Zss. More particularly, measurement of Zss may be determined using the equation:
• $\begin{array}{cc}\frac{Z_{\mathrm{ss}}-Z_o}{Z_{\mathrm{ss}}+Z_o}=\frac{P_{\mathrm{SWR}}-1}{P_{\mathrm{SWR}}+1}& \left(2\right)\end{array}$
• where, Zo is the characteristic impedance associated with theconnector126 and/orinternal cable126a. The characteristic impedance Zo is an accurate measure of the impedance of theconnector126 and/orinternal cable126aand takes into account the line losses associated with theconnector126 and/orinternal cable126a. In this instance, after all the necessary calculations have been carried out, the measurement of Zss will be an accurate representation of the steady-state impedance Zss at themicrowave antenna100 adjacent the ablation zone.
• The foregoing algorithms and/or equations are two of many algorithms and/or equations that may be employed to calculate the Zss associated with themicrowave antenna100 such that real-time monitoring of an ablation zone may be achieved. For example, one or more model functions ƒ(t) representative of the model curves illustrated inFIGS. 4A-1 and 4B-1 may be utilized in conjunction with the aforementioned equations (or alone) to obtain additional information relevant to Zss. More particularly, a measurement of a slope of a tangent line at a point along either of the curves (e.g., curve illustrated inFIG. 4A-1) is equal to a derivative (dz/dt) of the curve at that point. The calculation of the derivative at a particular point along the curve(s) may provide additional information, e.g., rate of change of complex impedance with respect to time. This rate of change associated with complex impedance with respect to time may be utilized, for example, to determine the time it takes to go from Z4 to Zss during an ablation procedure.
• Themicrowave antenna100 of the present disclosure may be configured to create an ablation zone “A” having any suitable configuration, such as, for example, spherical (FIG. 3A), hemispherical, ellipsoidal (FIG. 3B where the ablation zone is designated “A-2”), and so forth. In one particular embodiment,microwave antenna100 is configured to create an ablation zone “A” that is spherical (FIG. 3A). As noted above, when themicrowave antenna100 has heated tissue in the “near field” to a maximum temperature, a dielectric constant and conductivity associated with the ablated tissue reaches a steady-state that corresponds to a steady-state complex impedance Zss associated with themicrowave antenna100. Correlating the Zss associated with themicrowave antenna100 with the ablated tissue (i.e., ablated tissue, where the dielectric constant and conductivity are in a steady-state condition), indicates a specific size (e.g., radius rss) and shape (e.g., spherical) of the ablation zone “A.” Thus, a measure of Zss associated with themicrowave antenna100 corresponds to an ablation zone “A” having a radius r, e.g., rss. The control algorithm of the present disclosure uses known or calculated steady state complex impedances associated with specific microwave antennas at specific radii to predict an ablation size. That is, complex impedances, e.g., Zss, associated with a specific microwave antenna, e.g.,microwave antenna100, and corresponding radius, e.g., rss, are compiled into one or more look-up tables “D” and are stored in memory, e.g.,memory336, accessible by themicroprocessor335 and/or theAZCM332. Thus, when the complex impedance for a specific microwave antenna, e.g.,microwave antenna100, reaches Zss one or more modules,e.g. AZCM332, associated with thecontroller300, commands thecontroller200 to adjust the power output to themicrowave antenna100 accordingly. This combination of events will provide an ablation zone “A” with a radius approximately equal to rss.
• In an embodiment, for a given microwave antenna, e.g.,microwave antenna100, impedance measurements may be taken at times prior to tss, e.g., times t1-t4. In this instance, complex impedances, e.g., Z1-Z4 (for illustrative purposes and clarity, Z1-Z4 are defined by both the real and imaginary portions of the complex impedance), associated with themicrowave antenna100 may be correlated with an ablation zone “A” defined by a plurality of concentric ablation zones having radii r1-r4 (collectively referred to as radii “r”) when measured from the center of the ablation zone “A.” More particularly, the complex impedances Z1-Z4 and corresponding radii “r” may be correlated with each other in a manner as described above with respect to Zss and rss (seeFIG. 3A in combination withFIGS. 4A-1 and 4B-1, for example). In this instance, when specific complex impedance, e.g., Z3, is met one or more modules,e.g. AZCM332, associated with thecontroller300, commands thecontroller200 to adjust the power output to themicrowave antenna100 accordingly.
• AZCM332 may be a separate module from themicroprocessor335, orAZCM332 may be included with themicroprocessor335. In an embodiment, theAZCM332 may be operably disposed on themicrowave antenna100. TheAZCM332 may include control circuitry that receives information from one or more control modules and/or one or more impedance sensors (not shown), and provides the information to thecontroller300 and/ormicroprocessor335. In this instance, theAZCM332,microprocessor335 and/orcontroller300 may access look-up table “D” and confirm that a particular complex impedance (e.g., Zss) associated withmicrowave assembly100 that corresponds to a specific ablation zone, e.g., specific ablation zone having a radius rss has been met and, subsequently instruct thegenerator200 to adjust the amount of microwave energy being delivered to the microwave antenna. In one particular embodiment, look-up table “D” may be stored in a memory storage device (not shown) associated with themicrowave antenna100. More particularly, a look-up table “D” may be stored in a memory storage device operatively associated withhandle118 and/orconnector126 of themicrowave antenna100 and may be downloaded, read and stored intomicroprocessor335 and/ormemory336 and, subsequently, accessed and utilized in a manner described above; this would do away with reprogramming thegenerator200 and/orcontroller300 for a specific microwave antenna. The memory storage device may also be configured to include information pertaining to themicrowave antenna100. For example, information such as, the type of microwave antenna, the type of tissue that the microwave antenna is configured to treat, the type of ablation zone desired, etc. may be stored into the storage device associated with the microwave antenna. In this instance, for example,generator200 and/orcontroller300 ofsystem10 may be adapted for use with a microwave antenna configured to create an ablation zone, e.g. ablation zone “A-2,” different from that ofmicrowave antenna100 that is configured to create an ablation zone “A.”
• In the embodiment illustrated inFIG. 1, the generator is shown operably coupled tofluid supply pump40. Thesupply pump40 is, in turn, operably coupled to the supply tank44 (FIG. 2). In embodiments, themicroprocessor335 is in operative communication with thesupply pump40 via one or more suitable types of interfaces, e.g., aport240 operatively disposed on thegenerator200, which allows themicroprocessor335 to control the output of a coolingfluid42 from thesupply pump40 to themicrowave antenna100 according to either open and/or closed control loop schemes. Thecontroller300 may signal thesupply pump40 to control the output of cooling fluid42 from thesupply tank44 to themicrowave antenna100. In this way, coolingfluid42 is automatically circulated to themicrowave antenna100 and back to thesupply pump40. In certain embodiments, a clinician may manually control thesupply pump40 to cause coolingfluid42 to be expelled from themicrowave antenna100 into and/or proximate the surrounding tissue.
• Operation ofsystem10 is now described. In the description that follows, it is assumed that the losses associated with theconnector126 and/or cable162aof themicrowave antenna100 are negligible and thus, are not needed in calculating and/or determining a complex impedance of themicrowave antenna100 adjacent the ablation zone during the ablation procedure. Alternatively, the losses associated with theconnector126 and/or cable162aof themicrowave antenna100 may be calibrated out of measurement (or other suitable methods) and utilized in calculating and/or determining a complex impedance of themicrowave antenna100 adjacent the ablation zone during the ablation procedure. Initially,microwave antenna100 is connected togenerator200. In one particular embodiment, one or more modules, e.g.,AZCM332, associated with thegenerator200 and/orcontroller300 reads and/or downloads data from a storage device associated with theantenna100, e.g., the type of microwave antenna, the type of tissue that is to be treated, etc.Microwave antenna100 may then be positioned adjacent tissue (FIG. 3A). Thereafter,generator200 may be activated supplying microwave energy to radiatingsection138 of themicrowave antenna100 such that the tissue may be ablated. During tissue ablation, when a predetermined complex impedance, e.g., Zss, at themicrowave antenna100 is reached, theAZCM332 instructs thegenerator200 to adjust the microwave energy accordingly. In the foregoing sequence of events theAZCM332 functions in real-time controlling the amount of microwave energy to the ablation zone such that a uniform ablation zone of suitable proportion (e.g., ablation zone “A” having a radius rss) is formed with minimal or no damage to adjacent tissue.
• With reference toFIG. 5 amethod400 for monitoring temperature of tissue undergoing ablation is illustrated. Atstep402, microwave energy fromgenerator200 is transmitted to amicrowave antenna100 adjacent a tissue ablation site. At step,404, complex impedance associated with the microwave antenna is monitored. Atstep406, a detection signal is communicated to thegenerator200 when a predetermined complex impedance Zss is reached at themicrowave antenna100. Atstep408, the amount of microwave energy from thegenerator200 to themicrowave antenna100 may be adjusted.
• From 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, one or more directional couplers (not shown) may be operatively associated with thegenerator200,controller300 and/orAZCM332, and configured to sample the forward, reflected, and/or load power portions of an output signal (or pulse) and direct the sampled signal to theAZCM332. More particularly, the directional coupler provides samples of the forward and reflected signal (or pulse) generated by thegenerator200. The power, magnitude and phase of the generated output signal may be obtained or calculated from the measured forward and reflected signals by conventional algorithms that may employ one or both of the aforementioned equations (1) (2), or other suitable equation.
• It should be noted that energy values or parameters (e.g., power, voltage, current, impedance, magnitude and phase) of an output pulse are valid at the output ofgenerator200. That is, theconnector126 and/orinternal cable126amay include transmission line losses. In order to get a more accurate reading and/or measurement of the energy values or parameters that are delivered to themicrowave antenna100 and/or reflected back to thegenerator200, one would have to know the actual transmission line losses associated withconnector126 and/orinternal cable126a. Accordingly, in some instances, AZCM332 (or other suitable module or component associated with the controller300) may be configured to adjust and/or calibrate Zss to compensate for losses associated withconnector126 and/orinternal cable126a. For example, line loss information associated with theconnector126 and/orinternal cable126amay be determined and stored intomemory336 and accessed during an ablation procedure by theAZCM332 and, subsequently, used in determining if a predetermined threshold value of Zss has been met. Thus, in an embodiment, loss information forconnector126 and/orinternal cable126amay be determined and, subsequently, stored inmemory336 and accessed by one or more modules, such as, for example, acalibration module600 or other suitable module (e.g., AZCM332) for later use. The loss information forconnector126 and/orinternal cable126amay be determined by any suitable device and/or method. For example, the loss information forconnector126 and/orinternal cable126amay be determined vianetwork analyzer602. In one particular embodiment, thenetwork analyzer602 may be an integral part of generator200 (e.g., part of calibration module600) or alternatively, thenetwork analyzer602 may be a separate handheld device that is in operative communication withgenerator200. Thenetwork analyzer602 may be used to perform a diagnostic test ofconnector126 and/orinternal cable126a. Thenetwork analyzer602 may function in a fashion similar to most conventional network analyzers that are known in the available art. That is, thenetwork analyzer602 may determine the properties that are associated withconnector126 and/orinternal cable126a, and more particularly, those properties that are associated withconnector126 and/orinternal cable126athat affect the reflection and/or transmission of an output signal, such as, for example, the characteristic impedance Zo ofconnector126 and/orinternal cable126a. In embodiments, thenetwork analyzer602 may be narrow band or single frequency, e.g., microwave frequency utilized bysystem10, which, in turn, may reduce the complexity of thesystem10.
• As noted above, the control algorithm of the present disclosure implements one or more model equations and/or curves to calculate Zss within the time range t1-tss. In certain instances, however, for a particular probe,system10 and operative components associated therewith, e.g.,AZCM332, may be configured to monitor ablation zone size after time tss. More particularly,system10 may be configured to deliver “x” amount of electrosurgical energy tomicrowave antenna100 for “n” more seconds such that an ablation zone “A” having a radius “y” is achieved.
• While several embodiments of the disclosure have been shown in the drawings and/or discussed herein, 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.

Claims (21)

1-20. (canceled)

21. A method for monitoring tissue ablation, the method comprising:

delivering electrosurgical energy to tissue;

measuring power of the electrosurgical energy;

determining a complex impedance resulting from the delivery of electrosurgical energy to tissue based on the measured power;

comparing the determined complex impedance with a threshold complex impedance; and

controlling the delivery of electrosurgical energy to tissue based on the comparison.

22. The method according toclaim 21, wherein measuring power of the electrosurgical energy includes measuring at least one of a forward power of the electrosurgical energy or a reflected power of the electrosurgical energy.

23. The method according toclaim 21, wherein determining a complex impedance includes measuring a phase difference between a first portion of the measured power and a second portion of the measured power.

24. The method according toclaim 21, wherein determining a complex impedance includes measuring a magnitude difference between a first portion of the measured power and a second portion of the measured power.

25. The method according toclaim 21, wherein the threshold complex impedance is based on a steady-state impedance resulting from the delivery of electrosurgical energy to tissue.

26. The method according toclaim 21, further comprising determining a size of a tissue ablation zone resulting from the delivery of electrosurgical energy to tissue based on the comparison between the determined complex impedance and the threshold complex impedance.

27. The method according toclaim 21, further comprising determining a shape of a tissue ablation zone resulting from the delivery of electrosurgical energy to tissue based on the comparison between the determined complex impedance and the threshold complex impedance.

28. The method according toclaim 21, further comprising determining a radius of a tissue ablation zone resulting from the delivery of electrosurgical energy to tissue based on the comparison between the determined complex impedance and the threshold complex impedance.

29. The method according toclaim 21, wherein controlling the delivery of electrosurgical energy includes adjusting at least one electrical property of the electrosurgical energy selected from the group consisting of voltage, current, and power.

30. A method for monitoring tissue ablation, the method comprising:

delivering electrosurgical energy to tissue;

measuring power of the electrosurgical energy;

determining a complex impedance resulting from the delivery of electrosurgical energy to tissue based on a difference between a first portion of the measured power and a second portion of the measured power;

comparing the determined complex impedance with a threshold complex impedance; and

controlling the delivery of electrosurgical energy to tissue based on the comparison between the determined complex impedance and the threshold complex impedance.

31. The method according toclaim 30, wherein determining a complex impedance includes measuring a phase difference between the first portion of the measured power and the second portion of the measured power.

32. The method according toclaim 30, wherein determining a complex impedance includes measuring a magnitude difference between the first portion of the measured power and the second portion of the measured power.

33. The method according toclaim 30, wherein the threshold complex impedance is based on a steady-state impedance resulting from the delivery of electrosurgical energy to tissue.

34. The method according toclaim 30, further comprising determining a size of a tissue ablation zone resulting from the delivery of electrosurgical energy to tissue based on the comparison between the determined complex impedance and the threshold complex impedance.

35. The method according toclaim 30, further comprising determining a shape of a tissue ablation zone resulting from the delivery of electrosurgical energy to tissue based on the comparison between the determined complex impedance and the threshold complex impedance.

36. The method according toclaim 30, further comprising determining a radius of a tissue ablation zone resulting from the delivery of electrosurgical energy to tissue based on the comparison between the determined complex impedance and the threshold complex impedance.

37. The method according toclaim 30, wherein controlling the delivery of electrosurgical energy includes adjusting at least one electrical property of the electrosurgical energy selected from the group consisting of voltage, current, and power.

38. A method for monitoring tissue ablation, the method comprising:

delivering electrosurgical energy to tissue;

measuring a complex impedance resulting from the delivery of electrosurgical energy to tissue;

comparing the measured complex impedance with a threshold complex impedance; and

adjusting a property of the electrosurgical energy selected from the group consisting of voltage, current, and power based on the comparison.

39. The method according toclaim 38, wherein measuring a complex impedance includes measuring power of the electrosurgical energy.

40. The method according toclaim 38, wherein measuring a complex impedance includes measuring at least one of a forward power of the electrosurgical energy or a reflected power of the electrosurgical energy.

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