Microwave Antenna Having a Reactively-Loaded Loop Configuration

[0001] The present disclosure relates to microwave antennas. More particularly, the present disclosure relates to microwave antennas having a reactively-loaded loop configuration defining a portion of a radiating section of the microwave antenna.

[0002] 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.

[0003] 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. Typically, microwave energy is generated by a power source, e.g., microwave generator, and transmitted to tissue via a microwave antenna that is fed with a coaxial cable that operably couples to a radiating section of the microwave antenna.

[0004] For optimal energy delivery efficiency from the microwave generator to the microwave antenna, impedance associated with the coaxial cable, the radiating section and/or tissue need to equal to one another, i.e., an impedance match between the coaxial cable, the radiating section and/or tissue. In certain instances, an impedance mismatch may be present between the coaxial cable, the radiating section and/or tissue, and the energy delivery efficiency from the microwave generator to the microwave antenna is compromised, e.g., decreased, which, in turn, may compromise a desired effect to tissue, e.g., ablation to tissue.

[0005] The present disclosure provides a microwave ablation system. The microwave ablation system includes a power source. A microwave antenna is adapted to connect to the power source via a coaxial cable feed including an inner conductor defining a portion of a radiating section of the microwave antenna, an outer conductor and dielectric shielding. The inner conductor loops back around and toward the outer conductor of the coaxial cable feed such that a distal end of the inner conductor is operably disposed adjacent the dielectric shielding. The inner conductor includes one or more reactive components disposed thereon forming a reactively-loaded loop configuration.

[0006] The present disclosure provides a microwave antenna adapted to connect to a power source for performing a microwave ablation procedure. The microwave antenna includes a coaxial cable feed including an inner conductor defining a portion of a radiating section of the microwave antenna, an outer conductor and dielectric shielding. The inner conductor loops back around and toward the outer conductor of the coaxial cable feed such that a distal end of the inner conductor is operably disposed adjacent the dielectric shielding. The inner conductor includes one or more reactive components disposed thereon forming a reactively-loaded loop configuration.

[0016] Embodiments of the presently disclosed microwave antenna 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.

[0017] Referring now to FIG. 1A, a microwave ablation system 10 adapted for use with a microwave antenna 100 that utilizes a reactively-loaded loop configuration according to an embodiment of the present disclosure is illustrated. The system 10 includes microwave antenna 100 that is adapted to connect to an electrosurgical power source, e.g., an RF and/or microwave (MW) generator 200 that includes or is in operative communication with one or more controllers 300 and, in some instances, a fluid supply pump 40. Briefly, microwave antenna 100 includes an introducer 116 having an elongated shaft 112 and a radiating or conductive tissue piercing tip 114 operably disposed within elongated shaft 112, a cooling assembly 120 having a cooling sheath 121, a handle 118, a cooling fluid supply 122 and a cooling fluid return 124, and an electrosurgical energy connector 126. Connector 126 is configured to connect the microwave antenna 100 to the electrosurgical power source 200, e.g., a generator or source of radio frequency energy and/or microwave energy, and supplies electrosurgical energy to the distal portion of the microwave antenna 100. Conductive tip 114 and elongated shaft 112 are in electrical communication with connector 126 via an internal coaxial cable 126a that extends from the proximal end of the microwave antenna 100 and includes an inner conductor 126b (shown in phantom) operably disposed within the shaft 112 and adjacent a radiating section 138 (shown in phantom) and/or the conductive or radiating tip 114. As is common in the art, the internal coaxial cable 126a includes a dielectric material and an outer conductor surrounding each of the inner conductor 126b and the dielectric material. A connection hub (not explicitly shown) disposed at a proximal end of the microwave antenna 100 operably couples connector 126 to internal coaxial cable 126a, and cooling fluid supply 122 and a cooling fluid return 124 to a cooling assembly 120. Radiating section 138 by way of conductive tip 114 (or in certain instances without conductive tip 114) is configured to deliver radio frequency energy (in either a bipolar or monopolar mode) or microwave energy to a target tissue site. Elongated shaft 112 and conductive tip 114 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 shaft 112 and/or conductive tip 114 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 114 may be deployable from the elongated shaft 112.

[0018] With reference now to FIG. 1B, a microwave antenna 512 that utilizes a reactively-loaded loop configuration according to an embodiment of the present disclosure and adapted for use with the microwave ablation system depicted in FIG, 1A is illustrated. Briefly, microwave antenna 512 operably couples to generator 200 including a controller 300 via a flexible coaxial cable 516. In this instance, generator 200 is configured to provide microwave energy at an operational frequency from about 300 MHz to about 10 GHz. Microwave antenna 512 includes a radiating section or portion 518 that may be connected by a feedline or shaft 520 to coaxial cable 516 that extends from the proximal end of the microwave antenna 512 and includes an inner conductor operably disposed within the shaft 520 and adjacent radiating section 518 and/or a conductive or radiating tissue piercing tip 524. More specifically, the microwave antenna 512 is coupled to the cable 516 through a connection hub 522. The connection hub 522 also includes an outlet fluid port 530 (similar to that of cooling fluid return 124) and an inlet fluid port 532 (similar to that of cooling fluid supply 122) that are connected in fluid communication with a sheath 538. The sheath 538 encloses the radiating portion 518 and the shaft 520 allowing for coolant fluid from the ports 530 and 532 to be supplied to and circulated around the antenna assembly 512 via respective fluid lumens 530a and 532a. The ports 530 and 532 may also couple to supply pump 40. For a more detailed description of the microwave antenna 512 and operative components associated therewith, reference is made to commonly-owned U.S. patent application Ser. No. 12/401,268 filed on Mar. 10, 2009.

[0019] With reference to FIG. 2A, a reactively-loaded loop configuration (“loop 400”) according to an embodiment of the present disclosure is shown and designated 400. As defined herein, “reactively-loaded” is meant to mean including an element or component that opposes alternating current, caused by a build up of electric or magnetic fields in the element or component due to the current. Loop 400 may be operably associated with either of the radiating sections 138 or 518. For illustrative purposes loop 400 is described in terms of the radiating section 518 associated with the microwave antenna 512. Loop 400 is constructed by extending an inner conductor 516a, associated with the coaxial cable 516 distally past a dielectric material 516b and an outer conductor 516c. The inner conductor 516a is looped around and back toward the outer conductor 516c of the coaxial cable 516 such that a radiating section 518 having a generally “loop” like configuration is formed, the significance of which is described in greater detail below. In embodiments, loop 400 includes a diameter that ranges from about 3 mm to about 15 mm. Inner conductor 516a may have any suitable configuration including but not limited to wire, strip, etc. In the illustrated embodiments, inner conductor 516a includes a wire configuration having a diameter that ranges from about 0.0010 inches to about 0.0020 inches. In the instance where the inner conductor 516a includes a strip configuration, the strip may include a width that ranges from about 0.0010 inches to about 0.0020 inches. To optimize electrosurgical energy transfer from the generator 200 to the microwave antenna 512 it is important that an impedance match be present between coaxial cable 516, radiating section 518 and tissue at a target tissue site. In accordance with the present disclosure, a length of the loop 400 is configured for tuning, i.e., impedance matching, an impedance associated with the inner conductor 516a, microwave antenna 512 and tissue at a target tissue site such that optimal transfer of electrosurgical energy is provided from the generator 200 to the radiating section 518 such that a desired tissue effect is achieved at a target tissue site.

[0020] With continued reference to FIG. 2A, one or more reactive elements or components are operably disposed along a length of loop 400 associated with the inner conductor 516a to achieve a desired electrical effect at the radiating section 518. In the embodiment illustrated in FIG. 2A, one or more coiled sections 402 (one coiled section is shown for illustrative purposes) that serves as an inductive component is formed (or in some instances positioned, such as, for example, when an inductive component is utilized) adjacent a proximal end of the inner conductor 516a. The coiled section 402 may include any number of suitable turns such that a desired voltage may be induced therein by an electromagnetic field present in the coiled section 402 when electrosurgical energy is transmitted to the microwave antenna 512 and, more particularly, to the radiating section 518. One or more capacitive components 404 (three capacitive components are shown for illustrative purposes) are operably disposed at distal end of the loop 400 and/or inner conductor 516a. More particularly, capacitive components 404 are positioned adjacent outer conductor 516c and/or dielectric material 516b. The capacitive components 404 are in the form of three capacitor disks 404 that function to provide a capacitive effect at the distal end of the loop 400 when the distal end of the loop 400 is positioned adjacent (or contacts) the outer conductor 516c and/or the dielectric material 516b. The inductive and capacitive components 402 and 404, respectively, may be arranged in any suitable electrical configuration, i.e., series or parallel.

[0021] In the embodiment illustrated in FIG. 2A, the inductive and capacitive components 402 and 404, respectively, are arranged in series with respect to each other. In an alternate embodiment, the respective inductive and capacitive components 402 and 404 may be arranged in a parallel configuration with respect to each other. That is, inner conductor 516a may be split into two branches forming a parallel configuration, wherein each branch includes a respective reactive component. More particularly, one branch may include one or more inductive components 402 and one branch may include one or more capacitive component 404. To achieve desired capacitive or inductive effects at the loop 400 formed by the inner conductor 516a, a thickness of the inner conductor 516a may varied (i.e., increased or decreased) as needed. Loading the loop 400 with one or more reactive components described herein enables the radiating section 518 to be shortened or lengthened during the manufacturing process such that a desired electrical effect (e.g., impedance) or output may be achieved at the radiating section 518 and/or conductive tip 524. Additionally, reactive loading of the loop 400 allows for miniaturization of the radiating section 518, which, in turn, provides for a more practical invasive microwave antenna 512 and/or radiating section 518.

[0022] In an alternate embodiment, see FIG. 3, the loop 400 may include a spiral loop configuration. In this instance, the loop 400 includes one or more spiral sections 406 that provide one or more reactive effects, e.g., an inductive effect described above. Not unlike the loop 400 illustrated in FIG. 2A, a distal end of the spiral section 406 of loop 400 and/or the inner conductor 516a is positioned adjacent (or contacts) the outer conductor 516c and/or the dielectric material 516b. While not explicitly shown, it is within the purview of the present disclosure that one or more of the reactive components described above, e.g., an inductive component 402 and/or a capacitive component 404, may be operably disposed within the electrical path of the spiral section 406 of the loop 400. That is, the an inductive component 402 and/or a capacitive component 404 may be arranged in series or parallel configurations with respect to each other and/or the spiral section 406 of loop 400.

[0023] In one particular embodiment, one or more structure(s) or device(s) may be employed to concentrate the electrosurgical energy radiating from the radiating section 518 and/or conductive tip 524 to tissue at a target tissue site. More particularly, and with reference to FIG. 4, a reflector or shield 408 may be operably positioned adjacent and partially wrapped (or in some instances substantially wrapped) around the loop 400, e.g., configuration of loop 400 illustrated in FIG. 2A (or other suitable configuration of loop 400). More particularly, the shield 408 is operably secured to and disposed at a distal end of the coaxial cable 516 adjacent the loop 400. Shield 408 may be secured to coaxial cable 516 by any suitable securement methods including but not limited to soldering, brazing, welding, adhesives, etc. In the illustrated embodiments, shield 408 is secured to coaxial cable 516 by way of brazing. In certain embodiments, shield 408 may be monolithically formed with the radiating section 518. In another embodiment, shield 408 may be grounded or secured to an internal portion of the shaft 520 of the microwave antenna 512. Shield 408 may be made from any suitable material including but not limited to materials that are conductive, non-conductive or partially conductive. More particularly, shield 408 may be made from metal, metal alloys, plastic, ceramic, etc. In one particular embodiment, shield 408 is made from metal, such as, for example, a metal selected from the group consisting of copper, silver, gold, platinum, stainless steel and titanium.

[0024] Shield 408 is configured to provide enhanced directionality of the radiating pattern of the electrosurgical energy transmitted to the radiating section 518 and/or conductive tip 524. In one particular embodiment, the shield 408 may include a generally hemispherical or clamshell configuration (FIG. 5). In another embodiment, the shield 408 may be elongated having a generally triangular cross-section configuration (FIG. 6). In either instance, the shield 408 concentrates and/or directs the electrosurgical energy transmitted to the radiating section 518 and/or conductive tip 524 to the target tissue site. Examples of other suitable types of reflectors or shields (and operative components associated therewith) are described in commonly-owned U.S. patent application Ser. Nos. 12/542,348 and 12/568,524 filed on Aug. 17, 2009 and Sep. 28, 2009, respectively.

[0025] In the embodiment illustrated in FIG. 1A, the generator is shown operably coupled to fluid supply pump 40. The supply pump 40 is, in turn, operably coupled to a supply tank 44. In embodiments, the supply pump 40 is operatively disposed on the generator 200, which allows the generator to control the output of a cooling fluid 42 from the supply pump 40 to the microwave antenna 512 according to either open and/or closed control loop schemes. As can be appreciated providing the cooling fluid 42 (see FIGS. 2A and 3) to the radiating section 518 and/or the loop 400 increases the power handling capability of the microwave antenna.

[0026] As noted above, in some instances it may prove useful to utilize a microwave antenna (e.g., microwave antenna 100) that includes a deployable tip 114. In this instance, the deployable conductive tip 114 includes a configuration of loop 400 proportioned small enough in diameter to facilitate deployment of the conductive tip 114. During a surgical procedure, e.g., ablation procedure, a portion of the loop 400 may be positioned around a tumor or soft tissue.

[0027] In certain embodiments, a portion of the microwave antenna may be coated with a non-stick material 140 (see FIG. 1A, for example), such as, for example, polytetrafluoroethylene, commonly referred to and sold under the trademark TEFLON® owned by DuPont™.

[0028] In certain embodiments, a dielectric material 517 (see FIG. 2A, for example) may surround the radiating section 518 and/or the loop 400 and reactive components associated therewith to achieve an impedance match between the microwave antenna 100 and tissue to emit a radiating pattern from the radiating section 518 of the microwave antenna 512.

[0029] Operation of system 10 is now described with respect to FIGS. 1B and 2. A portion of the microwave antenna, e.g., a radiating section 518 and/or conductive tip 524, is positioned adjacent tissue at a target tissue site (or in some instances, a portion of the microwave antenna 512, e.g., a portion of loop 400, may be wrapped around tissue, e.g., a tumor). In certain instances, a fluid 42 may be circulated through the fluid lumens 530a and 532a and around the radiating section 518, see FIG. 2A, for example. Thereafter, electrosurgical energy is transmitted from the generator 200 to the radiating section 518 and/or conductive tip 524 of the microwave antenna 512 such that a desired tissue effect may be achieved at the target tissue site. In accordance with the present disclosure, the loop 400 improves electrosurgical energy transfer from the generator 200 to the microwave antenna 512 and/or the target tissue site and allows the microwave antenna 512 or portion associated therewith, e.g., radiating section 518 and/or conductive portion 524, to be utilized with more invasive ablation procedures.

[0030] 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 modules associated with the generator 200 and/or controller 300 may be configured to monitor the reactive elements or components, e.g., inductive element 402, associated with the loop 400 such that a specific electromagnetic field is generated by the reactive elements or components during the transmission of electrosurgical energy from the generator 200 to the microwave antenna 512. More particularly, one or more sensors (e.g., one or more voltage and current sensors) may be operably positioned at a predetermined location and adjacent the radiating section 518 and/or loop 400. More particularly, the sensor(s) may be operably disposed along a length of the loop 400 and in operative communication with the module(s) associated with the generator 200 and/or controller 300. The sensor(s) may react to voltage and/or current fluctuations associated with the loop 400 and caused by electromagnetic fields fluctuations generated by one or more of the reactive components, e.g., inductive element 402, associated with the loop 400. In this instance, the sensor(s) may be configured to trigger a control signal to the module(s) when an electromagnetic field of predetermined strength is generated. When the module(s) detects a control signal, the module may send a command signal to the generator 200 and/or controller 300 such that the electrosurgical power output to the microwave antenna 512 may be adjusted accordingly.

[0031] 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.