# Patent

## Title
Dual antenna assembly with user-controlled phase shifting

## Abstract

An electrosurgical ablation system includes an energy source adapted to supply energy to an energy delivery device. The energy delivery device includes a handle assembly configured to couple a pair of antennas extending from a distal end thereof to the energy source for application of energy to tissue. A power splitting device is operatively associated with the handle assembly and has an input adapted to connect to the energy source and a pair of output channels operably coupled to the respective pair of antennas. A phase shifter is operatively associated with the handle assembly and is operably coupled to the pair of output channels. The phase shifter is configured to selectively shift a phase relationship between the pair of output channels.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application is a continuation application of U.S. application Ser. No. 12/837,820, filed on Jul. 16, 2010, the entire contents 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 1⁄4 of the length of a wavelength of the microwave energy, making the aggregate length of the two conductors about 1⁄2 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, an electrosurgical ablation system includes an energy source adapted to supply energy to an energy delivery device. The energy delivery device includes a handle assembly configured to couple a pair of antennas extending from a distal end thereof to the energy source for application of energy to tissue. A power splitting device is operatively associated with the handle assembly and has an input adapted to connect to the energy source and a pair of output channels operably coupled to the respective pair of antennas. A phase shifter is operatively associated with the handle assembly and is operably coupled to the pair of output channels. The phase shifter is configured to selectively shift a phase relationship between the pair of output channels.
According to another embodiment of the present disclosure, a method of providing energy to a target tissue includes the steps of positioning an energy delivery device relative to a target tissue site and equally dividing energy supplied to the energy delivery device from an energy source between a pair of channels in a predetermined phase relationship. The method also includes selectively shifting the phase relationship between the pair of channels and applying the equally divided energy to the target tissue in the selectively adjusted phase relationship.
According to another embodiment of the present disclosure, a method of providing energy to a target tissue includes the steps of positioning a microwave antenna assembly relative to a target tissue site and equally dividing energy supplied to the microwave antenna assembly from an energy source between a pair of channels in a predetermined phase relationship. The method also includes the step of selectively shifting the phase of at least one channel +/−90 degrees to shift the phase relationship between the channels to one of an in-phase configuration and an out-of-phase configuration based on a desired tissue ablation geometry. The method also includes the step of applying the equally divided energy from the pair of channels to a corresponding pair of antennas for application to 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. 2A is a partial schematic diagram of the electrosurgical system of FIG. 1 showing a control circuit in accordance with an embodiment of the present disclosure;
FIG. 2B is a schematic diagram of the control circuit of FIG. 2A;
FIGS. 3A and 3B are schematic diagrams of antennas assemblies illustrating tissue ablation geometries in accordance with various embodiments of the present disclosure; and
FIG. 4 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 an electrosurgical device. An electrosurgical device, such as an ablation antenna, 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.
The present disclosure relates generally to an ablation system that equally splits microwave power between a pair of antennas of an ablation device at a predetermined phase relationship. The phase relationship is user-selected and is based on an ablation procedure being performed and/or on a desired ablation pattern or geometry. As discussed in further detail below, by controlling the phase of ablation antennas with respect to each other, according to embodiments of the present disclosure, a desired effect on tissue between the antennas is produced.
FIG. 1 shows an ablation system 10 that includes an antenna assembly 12 coupled to an output 15 of an electrosurgical generator 14 via a flexible coaxial cable 16. The generator 14 is adapted to provide microwave energy at an operational frequency from about 300 MHz to about 6000 MHz, although other suitable frequencies (e.g., radio frequency) are also contemplated.
In the illustrated embodiment, the antenna assembly 12 includes a pair of antennas 15a and 15b disposed substantially parallel to each other, for example, spaced about 5 millimeters (mm) apart. Antennas 15a, 15b are inserted directly into tissue or placed into the body during surgery by a clinician, or positioned in the body by other suitable methods. Antennas 15a, 15b include radiating portions 18a, 18b, respectively, that are connected by respective feedlines 20a, 20b, to the cable 16. More specifically, the antenna assembly 12 is coupled to the cable 16 through a connection hub or handle 22 that is connected in fluid communication with sheaths 38a, 38b that enclose radiating portions 18a, 18b and feedlines 20a, 20b, respectively. As shown schematically in FIG. 2A and as discussed in further detail below with respect to FIG. 2B, a control circuit 100 disposed within handle 22 is configured to connect to output 15 of generator 14 and equally split energy supplied by generator 14 between a pair of channels 151a and 151b in a predetermined phase relationship to drive antennas 15a and 15b, respectively. Channels 151a, 151b electrically connect to a variable phase shifter 180 disposed within control circuit 100. Phase shifter 180 is operably coupled to a user-accessible switching mechanism 21 disposed on the handle 22 that allows the user to selectively shift the phase of either channel 151a and/or 151b relative to the other channel to achieve a desired phase relationship (e.g., in-phase, out-of-phase) between antennas 15a, 15b, as discussed in detail below.
As shown in the illustrated embodiment of FIG. 1, switching mechanism 21 includes a slide button 23 that is disposed about the exterior of the handle 22 and is configured to slide within a groove 25 defined at least partially through the handle 22 to control the phase relationship between channels 151a, 151b in mutual cooperation with variable phase shifter 180. More specifically, variable phase shifter 180 may include an electrical transmission line such as microstrip (not shown) that is suitably positioned within handle 22 relative to groove 25 to be mechanically engaged by slide button 23 for controlling the variable phase shifter 180. For purposes of connecting to and controlling variable phase shifter 180 from the exterior of handle 22, switching mechanism 21 may, in lieu of slide button 23, include any suitable switching mechanism such as, for example without limitation, a toggle switch, a push button, a dial, a potentiometer, an air-gap switch, a paddle actuator, a lever, or the like.
Channels 151a and/or 151b are electrically connected, via corresponding outputs 101a and 101b of variable phase shifter 180, to feedlines 20a and 20b, respectively, to supply electrosurgical energy to radiating portions 18a, 18b for application to tissue. The sheaths 38a, 38b enclose radiating portions 18a, 18b, respectively, and feedlines 20a, 20b to form a chamber (not shown) that allows one or more materials such as, for example, fluid, gas, coolant, chemicals, saline, water, powdered solids, or any combination thereof, to circulate within and/or occupy space within the chamber. In some embodiments, handle 22 may be coupled to a suitable supply pump (not shown) adapted to supply fluid or coolant to the chamber. In some embodiments, antenna assembly 12 may be embodied as, for example without limitation, a radiofrequency monopolar and/or bipolar electrode assembly, an ultrasound transducer, laser fiber, a direct current (DC) heating element, or the like.
Antenna assembly 12 also includes a tip 48a, 48b disposed at a distal end of each radiating portion 18a, 18b, respectively. Each tip 48a, 48b has a respective tapered end 24a, 24b that terminates, in some embodiments, at a respective pointed end 26a, 26b to allow for insertion into tissue with minimal resistance. In those cases where the radiating portions 18a, 18b are inserted into a pre-existing opening, tips 48a, 48b may be rounded or flat. Tips 48a, 48b may be formed from a variety of heat-resistant materials suitable for penetrating tissue, such as metals (e.g., stainless steel) and various thermoplastic materials, such as poletherimide, and polyamide thermoplastic resins.
In embodiments, the antenna assembly 12 is a microwave antenna configured to allow direct insertion or penetration into tissue of a patient. The antenna assembly 12 may be axially rigid to allow for tissue penetration. The antenna assembly 12 is sufficiently small in diameter to be minimally invasive of the body, which may reduce the preparation of the patient as might be required for more invasive penetration of the body. The antenna assembly 12 is inserted directly into tissue, inserted through a lumen (e.g., a vein, a needle, a catheter), placed into the body during surgery by a clinician, or positioned in the body by other suitable methods.
FIG. 2B is a schematic diagram of control circuit 100, according to one embodiment of the present disclosure. Control circuit 100 includes a power splitter 150 that is electrically connected via a transmission line 140 to the output 15 of generator 14. The power splitter 150 may be implemented by any suitable power divider that provides an equal or unequal power split at its output ports while substantially maintaining a predetermined phase relationship. For example, the power splitter 150 may be implemented using a 2-way power divider that provides an equal power split at its output ports while maintaining a phase difference of +/−90 degrees (e.g., via a 90 degree power divider IC).
Power splitter 150 receives, as an input signal, electrosurgical output from the generator 14. The power splitter 150 splits the input signal received from generator 14 equally between a pair of channels 151a and 151b at a phase difference of 90 degrees. Channels 151a and 151b pass through a pair of corresponding directional couplers 160a and 160b that are configured to couple reflected power on channels 151a, 151b to corresponding rectifiers 170a, 170b (e.g., microwave to DC rectifiers) for purposes of reflected power monitoring. Transmission lines 175a and 175b electrically connect rectifiers 170a, 170b, respectively, to generator 14 by way of cable 16 such that rectifiers 170a, 170b may communicate data to generator 14 for processing.
When coupling electromagnetic radiation such as microwaves from a source to an applicator, in order to maximize the amount of energy transferred from the source (e.g., generator 14) to the load (e.g., antennas 15a, 15b), the line and load impedances should match. If the line and load impedances do not match (e.g., an impedance mismatch) a reflected wave may be created that can generate a standing wave, which contributes to a power loss associated with the impedance mismatch. In embodiments, the generator 14 is configured to control energy output to the antenna assembly 12 based on an outer feedback loop that monitors a reflectance parameter (e.g., received from rectifier(s) 175a and/or 175b) such as a mismatch detected between the load impedance and the line impedance. Such an impedance mismatch may cause a portion of the power, so called “reflected power,” from the generator 14 to not reach the tissue site and cause the power delivered, the so called “forward power”, to vary in an irregular or inconsistent manner. It is possible to determine ablation completeness based on the impedance mismatch by measuring and analyzing the reflected and forward power. In particular, the generator 14 measures energy delivery properties, namely the reflected power, to determine ablation completeness. When the reflected power detected reaches a particular or predetermined level indicative of ablation completeness or reaches a particular or predetermined rate of change over time indicative of ablation completeness, the generator 14 terminates or adjusts energy output and alerts the user of the ablation completeness via an audible and/or visual indicator (not shown) disposed on the antenna assembly 12 and/or the generator 14.
Channels 151a, 151b pass through variable phase shifter 180 that, as described above, is user-controlled via the switching mechanism 23 disposed on handle 22. At this juncture (e.g., prior to passing through variable phase shifter 180), channels 151a, 151b are 90 degrees out-of-phase, as discussed hereinabove.
Referring for a moment to FIGS. 3A and 3B, by controlling the phase of antennas 15a, 15b with respect to each other, according to embodiments of the present disclosure, a desired effect on tissue between the antennas 15a, 15b is produced. In a resection procedure where a long thin ablation pattern is desired, depicted in phantom and referenced as “A” in FIG. 3A, a 180 degree out-of-phase relationship between antennas 15a, 15b produces a desired effect on tissue. More specifically, the out-of-phase relationship between antennas 15a, 15b generates proximal energy propagation therebetween to produce the elongated ablation pattern “A” suitable for planar tissue coagulation. In an ablation procedure where a generally spherical ablation pattern with a relatively larger radius is desired, depicted in phantom and referenced as “B” in FIG. 3B, an in-phase relationship between antennas 15a, 15b produces a desired effect on tissue. More specifically, the in-phase relationship between antennas 15a, 15b substantially eliminates proximal energy propagation therebetween to produce a generally spherical ablation pattern “B” suitable for focal tissue ablation proximate radiating portions 18a, 18b of antennas 15a, 15b, respectively.
As mentioned above, variable phase shifter 180 is user-controlled via switching mechanism 23 disposed on handle 22 such that channels 151a, 151b may be configured in various phase relationships relative to one another in accordance with a desired tissue ablation pattern or geometry, as described above. For example, phase shifter 180 may include an out-of-phase configuration wherein the phase of one of channels 151a or 151b is shifted 90 degrees such that channels 151a, 151b are changed from being 90 degrees out-of-phase (via the power splitter 150) to being 180 degrees out-of-phase. As described hereinabove, the 180 degree out-of-phase relationship between channels 151a, 151b produces a long thin ablation pattern “A” that is ideal for a tissue resection procedure. In this manner, when channels 151a, 151b are 180 degrees out-of-phase, antenna assembly 12 is said to be operating in a “tissue resection mode”.
Phase shifter 180 may also include, by way of example, an in-phase configuration wherein the phase of one of channels 151a or 151b is shifted 90 degrees such that channels 151a, 151b are changed from being 90 degrees out-of-phase (via the power splitter 150) to being in-phase or having a 0 degree phase difference. As described hereinabove, the in-phase relationship between channels 151a, 151b produces a generally spherical ablation pattern “B” with a relatively larger radius that is ideal for a tissue ablation procedure. In this manner, when channels 151a, 151b are in-phase, antenna assembly 12 is said to be operating in a “tissue ablation mode”.
FIG. 4 is a flowchart illustrating a method for providing energy to a target tissue, according to an embodiment of the present disclosure. Referring initially to step 410, antennas 15a, 15b of antenna assembly 12 are positioned relative to the target tissue. The antenna assembly 12 is inserted directly into tissue, inserted through a lumen (e.g., a vein, needle, or catheter), placed into the body during surgery by a clinician, or positioned in the body by other suitable methods.
In step 420, microwave power is supplied by generator 14 to the antenna assembly 12 and is split equally between a pair of channels 151a, 151b by the power splitter 150 in a predetermined phase relationship (e.g., +/−90 degrees).
In step 430, the phase relationship between channels 151a, 151b is selectively adjusted through use of a user-controlled variable phase shifter 180 in accordance with a desired ablation pattern (e.g., pattern “A” or pattern “B”), a desired phase configuration (e.g., in-phase, out-of-phase), a desired phase relationship (e.g., +/−0 degrees, +/−90 degrees, +/−180 degrees, etc.), and/or a desired mode of operation of antenna assembly 12 (e.g., tissue resection mode, tissue ablation mode).
In step 440, the microwave power is selectively transmitted from channels 151a, 151b to radiating portions 18a, 18b, respectively, via corresponding outputs 101a, 101b of the variable phase shifter 180.
In step 450, microwave energy from radiating portions 18a, 18b is applied to the target tissue to achieve the desired ablation pattern or geometry.
In some embodiments, the method for providing energy to a target tissue includes the step of monitoring reflected power detected on channels 151a, 151b, as described hereinabove in connection with FIG. 2B, and controlling energy supplied to the antenna assembly 12 by generator 14 based on the detected reflected power.
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.

## Claims

1. An electrosurgical ablation device, comprising:
a handle assembly;
a pair of antennas extending from a distal end of the handle assembly, the pair of antennas configured to be inserted through tissue;
a power splitter disposed within the handle assembly and having an input configured to connect the pair of antennas to an energy source providing an ablative energy and a pair of output channels, each of the pair of output channels operably coupled to a respective one antenna of the pair of antennas; and
a phase shifter operably coupled to the pair of output channels, the phase shifter configured to selectively shift a phase relationship between the pair of output channels.

2. The electrosurgical ablation device according to claim 1, further comprising an energy source configured to supply microwave energy to the pair of antennas.

3. The electrosurgical ablation device according to claim 1, further comprising at least one rectifier configured to monitor reflected power detected on the pair of output channels.

4. The electrosurgical ablation device according to claim 1, further comprising a switch assembly operably coupled to the phase shifter and configured to control the phase shifter.

5. The electrosurgical ablation device according to claim 4, wherein the switch assembly includes a slide switch accessible from an exterior of the handle assembly and configured to slide within a groove defined within the handle assembly to control the phase shifter.

6. The electrosurgical ablation device according to claim 1, wherein the phase shifter is selectively controlled to generate a phase difference of +/−180 degrees between the pair of antennas.

7. The electrosurgical ablation device according to claim 1, wherein the energy delivery device is configured to operate in a tissue resection mode when a phase difference between the pair of antennas is +/−180 degrees.

8. The electrosurgical ablation device according to claim 1, wherein the phase shifter is selectively controllable to generate an in-phase relationship between the pair of antennas.

9. The electrosurgical ablation device according to claim 1, wherein the electrosurgical ablation device is configured to operate in a tissue ablation mode when an in-phase relationship exists between the pair of antennas.

10. The electrosurgical ablation device according to claim 1, wherein the phase shifter is selectively controllable to generate an in-phase relationship between the pair of antennas to produce a generally spherical ablation geometry proximate a radiating portion of each antenna of the pair of antennas.

11. The electrosurgical ablation device according to claim 1, wherein the phase shifter is selectively controllable to generate an out-of-phase relationship between the pair of antennas to produce a generally elongated ablation geometry proximate a radiating portion of each antenna of the pair of antennas.

12. The electrosurgical ablation device according to claim 1, wherein the pair of antennas are parallel to one another.

13. The electrosurgical ablation device according to claim 1, wherein the power splitter is a 90 degree power divider.

14. The electrosurgical ablation device according to claim 1, wherein the power splitter generates a substantially equal power split between the pair of output channels while maintaining a phase difference of +/−90 degrees between the pair of output channels.

15. An electrosurgical ablation device, comprising:
a handle assembly;
a pair of antennas extending from a distal end of the handle assembly;
an input disposed within the handle assembly and configured to couple the pair of antennas to an energy source for application of ablative energy to tissue and a pair of output channels disposed within the handle assembly, each output channel of the pair of output channels configured to operably couple to one antenna of the pair of antennas; and
a phase shifter operably coupled to the pair of output channels and configured to selectively shift a phase relationship between the pair of output channels.