Patent Publication Number: US-11039885-B2

Title: Tissue ablation system with energy distribution

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 15/418,834 filed Jan. 30, 2017, now U.S. Pat. No. 10,016,237, which is a continuation of U.S. patent application Ser. No. 15/005,479 filed Jan. 25, 2016, now U.S. Pat. No. 9,554,855, which is a continuation of U.S. patent application Ser. No. 14/691,710 filed Apr. 21, 2015, now U.S. Pat. No. 9,375,278, which is a continuation of U.S. patent application Ser. No. 12/562,842 filed on Sep. 28, 2009, now U.S. Pat. No. 9,095,359, the entire contents of each of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to apparatus and methods for providing energy to tissue and, more particularly, to devices and electromagnetic radiation delivery procedures utilizing ablation probes and methods of controlling the delivery of electromagnetic radiation to tissue. 
     2. Discussion of Related Art 
     Treatment of certain diseases requires destruction of malignant tumors. Electromagnetic radiation can be used to heat and destroy tumor cells. Treatment may involve inserting ablation probes into tissues where cancerous tumors have been identified. Once the probes are positioned, electromagnetic energy is passed through the probes into surrounding tissue. 
     In the treatment of diseases such as cancer, certain types of cancer cells have been found to denature at elevated temperatures that are slightly lower than temperatures normally injurious to healthy cells. Known treatment methods, such as hyperthermia therapy, use electromagnetic radiation to heat diseased cells to temperatures above 41° C. while maintaining adjacent healthy cells below the temperature at which irreversible cell destruction occurs. These methods involve applying electromagnetic radiation to heat, ablate and/or coagulate tissue. Microwave energy is sometimes utilized to perform these methods. Other procedures utilizing electromagnetic radiation to heat tissue also include coagulation, cutting and/or ablation of tissue. 
     Electrosurgical devices utilizing electromagnetic radiation have been developed for a variety of uses and applications. A number of devices are available that can be used to provide high bursts of energy for short periods of time to achieve cutting and coagulative effects on various tissues. There are a number of different types of apparatus that can be used to perform ablation procedures. Typically, microwave apparatus for use in ablation procedures include a microwave generator, which functions as an energy source, and a microwave surgical instrument having an antenna assembly for directing the energy to the target tissue. The microwave generator and surgical instrument are typically operatively coupled by a cable assembly having a plurality of conductors for transmitting microwave energy from the generator to the instrument, and for communicating control, feedback and identification signals between the instrument and the generator. 
     Microwave energy is typically applied via antenna assemblies that can penetrate tissue. Several types of antenna assemblies are known, such as monopole and dipole antenna assemblies. In monopole and dipole antenna assemblies, microwave energy generally radiates perpendicularly away from the axis of the conductor. A monopole antenna assembly includes a single, elongated conductor that transmits microwave energy. A typical dipole antenna assembly has two elongated conductors, which are linearly aligned and positioned end-to-end relative to one another with an electrical insulator placed therebetween. Each conductor may be about ¼ of the length of a wavelength of the microwave energy, making the aggregate length of the two conductors about ½ of the wavelength of the supplied microwave energy. During certain procedures, it can be difficult to assess the extent to which the microwave energy will radiate into the surrounding tissue, making it difficult to determine the area or volume of surrounding tissue that will be ablated. 
     SUMMARY 
     According to an embodiment of the present disclosure, a microwave ablation system includes an energy source adapted to generate microwave energy and a power splitting device having an input adapted to connect to the energy source and a plurality of outputs. The plurality of outputs are configured to be coupled to a corresponding plurality of energy delivery devices. The power splitting device is configured to selectively divide energy provided from the energy source between the plurality of energy devices. 
     According to another embodiment of the present disclosure, a microwave ablation system includes an energy source adapted to generate microwave energy and a power splitting device having an input adapted to connect to the energy source and a plurality of outputs. The plurality of outputs are configured to be coupled to a corresponding plurality of energy delivery devices via corresponding transmission lines. The power splitting device is configured to selectively divide energy provided from the energy source between the plurality of energy delivery devices either equally or unequally. 
     According to another embodiment of the present disclosure, a method for providing energy to a target tissue includes the steps of positioning a plurality of energy delivery devices into a portion of the target tissue and selectively dividing energy on a plurality of channels to at least one of the energy delivery devices. The method also includes applying energy from one or more of the energy delivery devices to the target tissue. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an electrosurgical system for treating tissue, according to an embodiment of the present disclosure; 
         FIG. 2  is a schematic diagram of an electrosurgical system for treating tissue, according to one embodiment of the present disclosure; 
         FIG. 3  is a schematic diagram of an electrosurgical system for treating tissue, according to another embodiment of the present disclosure; 
         FIG. 4  is a schematic diagram of an electrosurgical system for treating tissue, according to another embodiment of the present disclosure; and 
         FIG. 5  is a block diagram illustrating a method for treating tissue, according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the presently disclosed tissue ablation systems are described with reference to the accompanying drawings. Like reference numerals may refer to similar or identical elements throughout the description of the figures. As used herein, the term “microwave” generally refers to electromagnetic waves in the frequency range of 300 megahertz (MHz) (3×108 cycles/second) to 300 gigahertz (GHz) (3×1011 cycles/second). As used herein, the phrase “transmission line” generally refers to any transmission medium that can be used for the propagation of signals from one point to another. 
     Various embodiments of the present disclosure provide electrosurgical systems for treating tissue and methods of controlling the delivery of electromagnetic radiation to tissue. Embodiments may be implemented using electromagnetic radiation at microwave frequencies or at other frequencies. Electrosurgical systems for treating tissue, according to various embodiments of the present disclosure, deliver microwave power to a plurality of electrosurgical devices. Electrosurgical devices, such as ablation probes, for implementing embodiments of the present disclosure may be inserted directly into tissue, inserted through a lumen, such as a vein, needle or catheter, placed into the body during surgery by a clinician, or positioned in the body by other suitable methods known in the art. 
       FIG. 1  is a schematic diagram of an electrosurgical system for treating tissue, according to one embodiment of the present disclosure. Referring to  FIG. 1 , the electrosurgical system  100  includes an electrosurgical generator  120  for generating an output signal, a power splitter  150  coupled to the electrosurgical generator  120 , and an electrosurgical instrument or device  130  coupled to the power splitter  150 . The power splitter  150  is coupled to a transmission line  107  that electrically connects the power splitter  150  to an output  124  on the electrosurgical generator  120 . The device  130  includes an antenna assembly  132  for delivery of electromagnetic radiation, coupled to a transmission line  104  that electrically connects the antenna assembly  132  to the power splitter  150 . Although not shown as such in  FIG. 1 , device  130  may include a plurality of antenna assemblies. 
     The electrosurgical generator  120  may include other input or output devices such as knobs, dials, switches, buttons, graphical user interfaces, displays, and the like for control, indication and/or operation. The electrosurgical generator  120  may be capable of generating a plurality of output signals of various frequencies that are input to the power splitter  150 . In one embodiment, the electrosurgical generator  120  generates a plurality of microwave signals at substantially the same frequency. The electrosurgical generator  120  may include a control unit (not shown) that controls operations of the electrosurgical generator  120 , such as time of operation, power output and/or the mode of electrosurgical operation, which may have been selected by the clinician. 
     The electrosurgical system  100  may include a footswitch (not shown) coupled to the electrosurgical generator  120 . When actuated, the footswitch causes the electrosurgical generator  120  to generate microwave energy. The device  130  may include knobs, dials, switches, buttons or the like (not shown) to communicate to the electrosurgical generator  120  to adjust or select from a number of configuration options for delivering energy. Utilizing knobs, dials, switches or buttons on the device  130  and/or a footswitch enables the clinician to activate the electrosurgical generator  120  to energize the device  130  while remaining near the patient P regardless of the location of the electrosurgical generator  102 . 
     Although not shown as such in  FIG. 1 , electrosurgical system  100  may include a plurality of channels defined by a plurality of electrosurgical devices and a plurality of transmission lines that electrically connect the electrosurgical devices to the power splitter  150 . In an embodiment, the power splitter  150  is capable of monitoring the phase of each channel and adjusting the phase of the signal in each channel with respect to the other channel(s) to a predetermined phase relationship. The power splitter  150  provides a plurality of signals to the device  130  in a set of phase relationships between the signals. Although the power splitter  150  is illustrated as a standalone module in  FIG. 1 , it is to be understood that the power splitter  150  may be integrated fully or partially into the electrosurgical generator  120 , the device  130 , and/or other devices. 
     The antenna assembly  132  includes multiple antennas and/or multiple antenna elements, each driven by an output signal of the power splitter  150 . The antenna assembly  132  may also include multiple antenna circuits, each driven by an output signal of the power splitter  150 . 
     In embodiments, the antenna assembly  132  is a microwave antenna configured to allow direct insertion or penetration into tissue of the patient P. The antenna assembly  132  may be axially rigid to allow for tissue penetration. The antenna assembly  132  is sufficiently small in diameter to be minimally invasive of the body, which may reduce the preparation of the patient P as might be required for more invasive penetration of the body. The antenna assembly  132  is inserted directly into tissue, inserted through a lumen, such as, for example, a vein, needle or catheter, placed into the body during surgery by a clinician, or positioned in the body by other suitable methods. 
       FIG. 2  is a schematic diagram of an electrosurgical system for treating tissue, according to another embodiment of the present disclosure. Referring to  FIG. 2 , the electrosurgical system  200  includes a microwave signal source  210  providing a microwave frequency output signal to a microwave amplifier unit  220 , a microwave power splitter  230  coupled to the microwave amplifier unit  220 , and a first, a second and a third microwave ablation antenna assembly  270 A,  270 B and  270 C, each coupled to the microwave power splitter  230 . The microwave signal source  210  is capable of generating a plurality of output signals of various frequencies that are input to the microwave amplifier unit  220 . The microwave amplifier unit  220  may have any suitable input power and output power. 
     In the electrosurgical system  200 , a first transmission line  250 A electrically connects the first antenna assembly  270 A to the microwave power splitter  230 , defining a first channel; a second transmission line  250 B electrically connects the second antenna assembly  270 B to the microwave power splitter  230 , defining a second channel; and a third transmission line  250 C electrically connects the third antenna assembly  270 C to the microwave power splitter  230 , defining a third channel. The first, second and third transmission lines  250 A,  250 B and  250 C may each include one or more electrically conductive elements, such as electrically conductive wires. 
     In an embodiment, the first, second, and third transmission lines  250 A,  250 B and  250 C each have substantially the same length, which preserves the phase relationship between the electrical signals in each channel of the electrosurgical system  200 . It is to be understood that “length” may refer to electrical length or physical length. In general, electrical length is an expression of the length of a transmission medium in terms of the wavelength of a signal propagating within the medium. Electrical length is normally expressed in terms of wavelength, radius, or degrees. For example, electrical length may be expressed as a multiple or sub-multiple of the wavelength of an electromagnetic wave or electrical signal propagating within a transmission medium. The wavelength may be expressed in radians or in artificial units of angular measure, such as degrees. The microwave power splitter  230  may be implemented by any suitable power divider that provides equal or unequal power split at the output ports of the microwave power splitter  230  while substantially maintaining phase and amplitude balance. For example, the microwave power splitter  230  may be implemented using a 3-way power divider that provides equal or unequal power split at its output ports while maintaining a phase balance of &lt;+/−45 degrees. 
     Each antenna assembly  270 A,  270 B and  270 C typically includes a plurality of electrodes disposed on a rigid or bendable needle or needle-like structure. The antenna assemblies  270 A,  270 B and  270 C are positioned substantially parallel to each other, for example, spaced about 5 millimeters (mm) apart, and inserted directly into tissue or placed into the body during surgery by a clinician, or positioned in the body by other suitable methods. Although the electrosurgical system  200  illustrated in  FIG. 2  includes three microwave ablation antenna assemblies  270 A,  270 B and  270 C, it is to be understood that any “N” number of antenna assemblies may be utilized and that microwave power splitter  230  may be implemented by any suitable power divider that divides or splits a microwave input signal into “N” number of output signals of equal or unequal power. 
     The electrosurgical system  200  delivers microwave power to one or more antenna assemblies  270 A,  270 B and  270 C of the three-channel system. The electrosurgical system  200  may deliver substantially in-phase microwave power to each antenna assembly  270 A,  270 B and  270 C. By controlling the phase of ablation probes with respect to each other, according to embodiments of the present disclosure, a desired effect on tissue between the probes is produced. In a resection procedure where a long thin ablation line is desired, probes that are 180 degrees out of phase with respect to each other produce a desired effect on tissue. In ablation procedures using in-phase probes, according to various embodiments of the present disclosure, there may be a reduction in energy that might otherwise move between the antenna shafts toward the surface with out-of-phase probes. 
     In an embodiment, the electrosurgical system  200  is implemented with operating frequencies in the range of about 915 MHz to about 5 GHz, which may be useful in performing ablation procedures and/or other procedures. It is to be understood that the electrosurgical system  200  may be implemented with any appropriate range of operating frequencies. 
     In another embodiment, the electrosurgical system  200  delivers microwave power to particular channels individually or any combination of one or more channels equally or unequally. The microwave signal source  210  and/or antenna assembly  270 A,  270 B and  270 C may include input or output devices such as knobs, dials, switches, buttons, graphical user interfaces, displays, and the like to facilitate selective activation of energy delivery to particular channels or combination of channels. For example, a user may select channels to which energy is delivered. In this scenario, if the second and third channels are selected, energy delivery may be divided equally (e.g., P/2) between the second and third channels and, thus, unequally between the first channel and the second and third channels since no energy is delivered to the first channel in this scenario. Further, in this scenario, energy may be delivered to individual channels according to selected time intervals by dynamically changing the channels to which energy is delivered. For example, energy may be delivered to the first channel at a time interval t 1 . At a subsequent time interval t 2 , energy is delivered to the first channel and the third channel. At a subsequent time interval t 3 , energy delivery to the first channel is stopped and energy delivery to the third channel continues. At a subsequent time interval t 4 , energy delivery to all channels is stopped. 
     In another embodiment, the microwave power splitter  230  divides energy between the antenna assemblies  270 A,  270 B and  270 C to tailor the size and shape of ablation lesions. With this purpose in mind, electrosurgical system  200  may include a suitable storage device (not shown) integrated within the microwave signal source  210 , the microwave power splitter  230 , or be a stand-alone device, that is configured to store settings or data corresponding to particular ablation geometries (e.g., ablation images, antenna tip geometries, power division settings, power amplitude settings, etc.). Based on the stored settings or data, the microwave signal source  210  modifies delivery of microwave power to the microwave power splitter  230  and/or the microwave power splitter  230  modifies the division of microwave power between the channels to achieve the desired ablation geometry. 
       FIG. 3  is a schematic diagram of an electrosurgical system for treating tissue, according to an embodiment of the present disclosure. Referring to  FIG. 3 , the electrosurgical system  300  includes a microwave signal source  310  providing a microwave frequency output signal to a microwave power splitter  330 , and a first, a second, a third, and a fourth microwave ablation antenna assembly  370 A,  370 B,  370 C, and  370 C, each coupled to the microwave power splitter  330 . The microwave signal source  310  is capable of generating a plurality of output signals of various frequencies that are input to the microwave power splitter  330 . 
     The microwave power splitter  330  includes a first quarter wavelength transmission line  350 A that electrically connects the first antenna assembly  370 A to the microwave signal source  310 , defining a first channel; a second quarter wavelength transmission line  350 B that electrically connects the second antenna assembly  370 B to the microwave signal source  310 , defining a second channel; a third quarter wavelength transmission line  350 C that electrically connects the third antenna assembly  370 C to the microwave signal source  310 , defining a third channel; and a fourth transmission line  350 D that electrically connects the fourth antenna assembly  370 D to the microwave signal source  310 , defining a fourth channel. Transmission lines  350 A,  350 B,  350 C, and  350 D each include one or more electrically conductive elements, such as electrically conductive wires. In an embodiment, transmission lines  350 A,  350 B,  350 C, and  350 D each have substantially the same length, which preserves the phase relationship between electrical signals in each channel of the electrosurgical system  300 . 
     As is known in the art, for maximum power transfer between a power source (e.g., microwave signal source  310 ) and a load (e.g., antenna assemblies  370 A,  370 B,  370 C,  370 D), the load impedance must be equal to the source impedance. For the case wherein the transmission line between the power source and the load is quarter wavelength, as described with reference to the embodiment of  FIG. 3 , an impedance of the microwave signal source  310  is calculated using the following equation (1):
 
 Z   in   =Z   o   2   /Z   L   (1)
 
     In equation (1), Z in  is the input impedance to the quarter wavelength transmission lines  350 A,  350 B,  350 C, and  350 D (e.g., the impedance at the microwave signal generator  310 ), Z o  is the characteristic impedance of the quarter wavelength transmission lines  350 A,  350 B,  350 C, and  350 D (e.g., the impedance at the microwave power splitter  330 ), and Z L  is the impedance of the antenna assemblies  370 A,  370 B,  370 C,  370 D. Applying equation (1) to the illustrated embodiment of  FIG. 3 , yields the following equation (2) to account for the four inputs to the quarter wavelength transmission lines  350 A,  350 B,  350 C, and  350 D:
 
4* Z   in   =Z   o   2   /Z   L   (2)
 
     Since Z L  must equal Z in  to achieve maximum power transfer, as discussed hereinabove, solving for the characteristic impedance Z o  of the quarter wavelength transmission line yields the following equation (3):
 
 Z   o =2* Z   in   (3)
 
     By way of example, given that Z L =Z in =50 ohms, the characteristic impedance Z o  of the transmission lines  350 A,  350 B,  350 C, and  350 D is equal to 100 ohms, and the electrical length of the transmission lines  350 A,  350 B,  350 C, and  350 D is set to a quarter wavelength, the load impedance Z L  of the antenna assemblies  370 A,  370 B,  370 C,  370 D at the input of the power splitter  330  is transformed from 50 ohms, which corresponds to a full wavelength, to 200 ohms, which corresponds to a quarter wavelength (i.e., 50 ohms 0.25=200 ohms). Since the four antenna assemblies  370 A,  370 B,  370 C,  370 D are in parallel with microwave signal generator  310 , the equivalent resistance Z L  of the antenna assemblies  370 A,  370 B,  370 C,  370 D is equal to 200 ohms divided by four antenna assemblies or 50 ohms. Since Z IN =50 ohms=Z L , maximum power transfer will occur between microwave signal generator  310  and each of antenna assemblies  370 A,  370 B,  370 C,  370 D. 
     Although the electrosurgical system  300  illustrated in  FIG. 3  includes four microwave ablation antenna assemblies  370 A,  370 B,  370 C, and  370 D and four quarter wavelength transmission lines  350 A,  350 B,  350 C, and  350 D, it is to be understood that any N number of antenna assemblies and any N number of quarter wavelength transmission lines may be utilized. 
       FIG. 4  is a schematic diagram of an electrosurgical system  400  for treating tissue, according to another embodiment of the present disclosure. Referring to  FIG. 4 , the electrosurgical system  400  illustrated is a three-channel system that includes a microwave signal source  410 , a microwave amplifier  420 , a first, a second, and a third microwave ablation antenna assembly  470 A,  470 B, and  470 C, and a controller  430  that includes one input  432  and a first, a second, and a third output  434 A,  434 B, and  448 C. 
     The electrosurgical system  400  includes a first transmission line  475 A that electrically connects the first antenna assembly  470 A to the first output  434 A, defining a first channel; a second transmission line  475 B that electrically connects the second antenna assembly  470 A to the second output  434 B, defining a second channel; and a third transmission line  475 C that electrically connects the third antenna assembly  470 C to the third output  434 C, defining a third channel. The first, second, and third transmission lines  475 A,  475 B, and  475 C each include one or more electrically conductive elements, such as electrically conductive wires. In an embodiment, the first, second, and third transmission lines  475 A,  475 B, and  475 C each have substantially the same length, which preserves the phase relationship between electrical signals in each channel of the electrosurgical system  400 . 
     The microwave signal source  410  provides a microwave frequency output signal to the amplifier  420 . The microwave amplifier  420  provides an output signal through an output terminal that is electrically coupled to the input  432  of the controller  430 . Although the amplifier  420  is illustrated as a standalone module in  FIG. 4 , it is to be understood that the amplifier  420  may be integrated fully or partially into the controller  430 . Controller  430  includes a first output-side directional coupler  465 A, a second output-side directional coupler  465 B, and a third output-side directional coupler  465 C. Output-side directional couplers  465 A,  465 B,  465 C are configured to measure power at each output  434 A,  434 B,  434 C, respectively, and to transmit a microwave signal, received as input, to antenna assemblies  470 A,  470 B, and  470 C. 
     The controller  430  includes a first isolator  422  electrically coupled between the input  432  and an input-side directional coupler  424 . The first isolator  422  operates to appear as a fixed matching load to the microwave signal source  410  to prevent detuning thereof due to variations in load impedance caused by, for example, antenna assemblies  470 A,  470 B, and  470 C and/or transmission lines  475 A,  475 B, and  475 C. The first isolator  422  transmits the microwave signal from the amplifier  420  to the input-side directional coupler  424 . The input-side directional coupler  424  measures the microwave signal received from the amplifier  420  as input and transmits the microwave signal to a first switching device  440  electrically coupled thereto. The first switching device  440  transmits the microwave signal to any one or more of a 1:2 power divider  450 , a 1:3 power divider  452 , and/or a second switching device  442 , individually or in any combination thereof. 
     Upon receiving the microwave signal from switching device  440 , power divider  450  divides the microwave signal as output between the second switching device  442  and a third switching device  444 . Upon receiving the microwave signal from switching device  440 , power divider  452  divides the microwave signal as output between the second switching device  442 , the third switching device  444 , and the third output-side directional coupler  465 C. The third output-side directional coupler  465 C powers antenna assembly  470 C by transmitting the microwave signal received from power divider  452  to the third output  434 C. 
     Upon receiving the microwave signal from any combination of the first switching device  440 , power divider  450 , and/or power divider  452 , the second switching device  442  transmits the microwave signal to the first output-side directional coupler  465 A. The first output-side directional coupler  465 A powers antenna assembly  470 A by transmitting the microwave signal received from the second switching device  442  to the first output  434 A. 
     Upon receiving the microwave signal from any combination of power divider  450  and/or  452 , the third switching device  444  transmits the microwave signal to the second output-side directional coupler  465 B. The second output-side directional coupler  465 B powers antenna assembly  470 B by transmitting the microwave signal received from the third switching device  444  to the second output  434 B. 
     In operation of electrosurgical system  400 , depending on the configuration of switching devices  440 ,  442 , and  444 , the output power values corresponding to the three outputs  434 A,  434 B, and  434 C for a given power P will be either P, 0, and 0; P/2, P/2, and 0; or P/3, P/3, and P/3. 
     Controller  430  further includes a first isolator  460 A electrically coupled between the second switching device  442  and the first output-side directional coupler  465 A; a second isolator  460 B electrically coupled between the third switching device  444  and the second output-side directional coupler  465 B; and a third isolator  460 C electrically coupled between power divider  452  and the third output-side directional coupler  465 C. First, second, and third isolators  460 A,  460 B, and  460 C are configured to appear as a fixed matching load to the microwave signal generator  410  to prevent detuning thereof due to variations in load impedance caused by, for example, antenna assemblies  470 A,  470 B, and  470 C and/or transmission lines  475 A,  475 B, and  475 C. 
     Switching devices  440 ,  442 ,  444  may be any suitable switching device configured to output power to a load connected thereto based on more than one inputs such as, for example, a single pole double throw switch (SPDT), a single pole triple throw switch (SP3T), etc. 
     In embodiments, any one or more of isolator  422  and isolators  460 A,  460 B,  460 C may be a three-port circulator, as is known in the art, having one of its three ports terminated in a fixed matching load to the microwave signal source  410  to effectively operate substantially as described above with reference to isolator  422  and/or isolators  460 A,  460 B,  460 C. 
     The controller  430  may include one or more phase detectors (not shown) to compare the respective phases of electrical signals inputted through the input  432 . By comparing a reference signal, such as a clock signal, to a feedback signal using a phase detector, phase adjustments may be made based on the comparison of the electrical signals inputted, to set the phase relationship between electrical signals in each channel of the electrosurgical system  400 . 
     In an embodiment, the controller  440  delivers phase-controlled microwave power through the outputs  434 A,  434 B and  434 C to the antenna assemblies  470 A,  470 B and  470 C, respectively, irrespective of the phase of the electrical signal inputted through the input  432 . 
       FIG. 5  is a flowchart illustrating a method for providing energy to a target tissue, according to an embodiment of the present disclosure. Referring to  FIG. 5 , in step  510 , a plurality of energy delivery devices are positioned into a portion of the target tissue. The energy delivery devices may be implemented using any suitable electrosurgical instruments or devices, such as, for example, the device  130 , according to embodiments of the present disclosure described in connection with  FIG. 1 . 
     The energy delivery devices are positioned into a portion of a target site on the tissue or adjacent to a portion of a target site on the tissue. The energy delivery devices are inserted directly into tissue, inserted through a lumen, such as a vein, needle or catheter, placed into the body during surgery by a clinician or positioned in the body by other suitable methods. The energy delivery devices include any suitable antenna assemblies for the delivery of electromagnetic radiation, such as, for example, the antenna assemblies  270 A,  270 B and  270 C, according to embodiments of the present disclosure described in connection with  FIG. 2 . 
     In step  520 , microwave power is selectively transmitted on a plurality of channels to any one or more of the energy delivery devices. The microwave power may be transmitted to the energy delivery devices from the microwave power splitter  230 , according to embodiments of the present disclosure described in connection with  FIG. 2 , the microwave power splitter  330 , according to embodiments of the present disclosure described in connection with  FIG. 3 , or the controller  440 , according to embodiments of the present disclosure described in connection with  FIG. 4 . 
     In step  530 , microwave energy from any one or more energy delivery devices is applied to the target tissue. 
     While 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.