System and method for chemically cooling an ablation antenna

Abstract

A method of performing an ablation procedure includes inserting an antenna assembly into tissue and supplying energy thereto for application to tissue. The method also includes causing contact between a first material and at least one other material disposed within the antenna assembly to thermally regulate the antenna assembly. According to another embodiment, an ablation system includes an energy delivery assembly. A first chamber is defined within the energy delivery assembly and is configured to hold a first chemical. Another chamber is defined within the energy delivery assembly and is configured to hold at least one other chemical. The first chamber and the other chamber are configured to selectively and fluidly communicate with each other to cause contact between the first chemical and the at least one other chemical to cause an endothermic reaction and/or an exothermic reaction.

Description

BACKGROUND

1. Technical Field

The present disclosure relates generally to microwave antennas used in tissue ablation procedures. More particularly, the present disclosure is directed to a microwave antenna having a coolant assembly for chemically cooling the microwave antenna.

2. 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° Celsius while maintaining adjacent healthy cells at lower temperatures where irreversible cell destruction will not occur. Other procedures utilizing electromagnetic radiation to heat tissue also include ablation and coagulation of the tissue. Such ablation procedures, e.g., such as those performed for menorrhagia, are typically done to ablate and coagulate 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 therapy is typically used in the treatment of tissue and organs such as the prostate, heart, kidney, lung, brain, and liver.

Presently, there are several types of microwave probes in use, e.g., monopole, dipole, and helical, which may be inserted into a patient for the treatment of tumors by heating the tissue for a period of time sufficient to cause cell death and necrosis in the tissue region of interest. Such microwave probes may be advanced into the patient, e.g., laparoscopically or percutaneously, and into or adjacent to the tumor to be treated. The probe is sometimes surrounded by a dielectric sleeve.

However, in transmitting the microwave energy into the tissue, the outer surface of the microwave antenna typically heats up and may unnecessarily effect healthy tissue immediately adjacent the antenna outer surface. This creates a water or tissue phase transition (steam) that allows the creation of a significant additional heat transfer mechanism as the steam escapes from the local/active heating area and re-condenses further from the antenna. The condensation back to water deposits significant energy further from the antenna/active treatment site. This local tissue desiccation occurs rapidly resulting in an antenna impedance mismatch that both limits power delivery to the antenna and effectively eliminates steam production/phase transition as a heat transfer mechanism for tissue ablation.

To prevent the unintended effects on adjacent tissue, several different cooling methodologies are conventionally employed. For instance, some microwave antennas utilize balloons that are inflatable around selective portions of the antenna to cool the surrounding tissue. Thus, the complications associated with unintended tissue effects by the application of microwave radiation to the region are minimized. Typically, the cooling system and the tissue are maintained in contact to ensure adequate cooling of the tissue.

Other devices attempt to limit the heating of tissue adjacent the antenna by selectively blocking the propagation of the microwave field generated by the antenna. These cooling systems also protect surrounding healthy tissues by selectively absorbing microwave radiation and minimizing thermal damage to the tissue by absorbing heat energy.

SUMMARY

According to an embodiment of the present disclosure, a method of performing an ablation procedure includes the steps of inserting an antenna assembly into tissue and supplying energy to the antenna assembly for application to tissue. The method also includes the step of causing contact between a first material and at least one other material disposed within the antenna assembly to thermally regulate the antenna assembly.

According to another embodiment of the present disclosure, a method of performing an ablation procedure includes the steps of inserting an antenna assembly into tissue and supplying energy to the antenna assembly for application to tissue. The method also includes the steps of causing contact between a first chemical held within a first chamber defined within the antenna assembly and at least one other chemical disposed within at least one other chamber defined within the antenna assembly to cause one of an endothermic reaction and an exothermic reaction to thermally regulate the antenna assembly.

According to another embodiment of the present disclosure, an ablation system includes an energy delivery assembly configured to deliver energy from a power source to tissue. A first chamber is defined within the energy delivery assembly and is configured to hold a first chemical. At least one other chamber is defined within the energy delivery assembly and is configured to hold at least one other chemical. The first chamber and the at least one other chamber are configured to selectively and fluidly communicate with each other to cause contact between the first chemical and the at least one other chemical to cause one of an endothermic reaction and an exothermic reaction to thermally regulate the energy delivery assembly.

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 schematic diagram of the microwave ablation system according to an embodiment of the present disclosure;

FIG. 2 is a perspective, internal view of a microwave antenna assembly taken along line X-X according to an embodiment of the present disclosure;

FIGS. 3A and 3B are cross-sectional views taken along line X-X of the microwave antenna assembly of FIG. 1 according to various embodiments of the present disclosure;

FIG. 3C is a perspective view of a component detailing operation of the microwave antenna assembly of either FIGS. 3A and 3B; and

FIG. 4 is a cross-sectional view of a microwave antenna assembly inserted into tissue according to another embodiment of the present disclosure.

DETAILED DESCRIPTION

Embodiments of the presently disclosed apparatus are described in detail below with reference to the drawings wherein like reference numerals identify similar or identical elements in each of the several views. In the discussion that follows, the term “proximal” will refer to the portion of a structure that is closer to a user, while the term “distal” will refer to the portion of the structure that is farther from the user.

Generally, the present disclosure is directed to a microwave antenna assembly having an energy source or generator adapted to deliver energy to tissue via the antenna assembly. The antenna assembly includes one or more chambers configured to receive and accommodate suitable chemicals (e.g., fluid, solid, a fluid and solid combination) therein that, upon mutual contact, mixture, dissolving, or reaction with each other, cause either an endothermic reaction or exothermic reaction depending on the chemicals used. Two or more chemicals are disposed within individual sealed chambers disposed within the antenna assembly. Through use of various methods of the various embodiments of the present disclosure, the chemicals are caused to contact each other at the appropriate time (e.g., during a tissue ablation procedure), thereby causing an endothermic or exothermic reaction, depending on the chemicals used. For example, the individual chambers holding the chemicals may be separated by a breakable membrane. In this scenario, the antenna assembly may be semi-flexible or semi-rigid such that the antenna assembly may be flexed or bent at the appropriate time to cause the membrane to break, thereby allowing the previously separated chemicals to contact each other and cause either an endothermic or exothermic reaction. Additionally or alternatively, the individual sub-chambers holding the chemicals may be separated by a mechanical interface configured to selectively cause communication between the sub-chambers through use of an actuation interface disposed on the antenna assembly.

Embodiments of the present disclosure may also be implemented using a microwave monopolar antenna or other suitable electrosurgical devices such as, for example, radiofrequency monopolar and/or bipolar electrodes, an ultrasound transducer, laser fiber, a direct current (DC) heating element, or the like, and may be implemented in operable cooperation with any suitable energy source (e.g., radiofrequency, direct current, microwave, laser, ultrasound, etc.).

In the scenario wherein an endothermic reaction results from contact between the two or more chemicals, the antenna assembly and/or surrounding tissue is cooled by the endothermic reaction. In use, while the antenna assembly is placed relative to the desired tissue site, the heat generated by the application of microwave energy from the antenna assembly to tissue may be cooled by causing an endothermic reaction within the antenna assembly. In the scenario wherein an exothermic reaction results from contact between the two or more chemicals, the antenna assembly and/or surrounding tissue is heated by the exothermic reaction. In use, while the antenna assembly is placed relative to the desired tissue site, surrounding tissue such as, for example, the insertion tract resulting from the insertion of the antenna assembly or an introducer into the tissue, may be heated or cauterized to stop bleeding or prevent tumor cells from “seeding” the insertion tract.

FIG. 1 shows a microwave ablation system 10 that includes a microwave antenna assembly 12 coupled to a microwave generator 14 via a flexible coaxial cable 16. The generator 14 is configured to provide microwave energy at an operational frequency from about 300 MHz to about 3000 MHz, although other suitable frequencies are also contemplated.

In the illustrated embodiment, the antenna assembly 12 includes a radiating portion 18 connected by feedline 20 (or shaft) 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 a sheath 38. The sheath 38 encloses radiating portion 18 and feedline 20 to form a chamber 89 (FIG. 2) allowing 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 chamber 89. In some embodiments, connection hub 22 may be coupled to a suitable supply pump (not shown) adapted to supply fluid or coolant to chamber 89. 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.

FIG. 2 illustrates a perspective view taken along line X-X of FIG. 1 showing the radiating portion 18 of the antenna assembly 12 according to one embodiment of the present disclosure having a dipole antenna 40. The dipole antenna 40 is coupled to the feedline 20 that electrically connects antenna assembly 12 to the generator 14. The dipole antenna 40 includes a proximal portion 42 and a distal portion 44 interconnected at a feed point 46. The distal portion 44 and the proximal portion 42 may be either balanced (e.g., of equal lengths) or unbalanced (e.g., of unequal lengths). A dipole feed gap “G” is disposed between the proximal and distal portions 42 and 44 at the feed point 46. The gap “G” may be from about 1 mm to about 3 mm. In one embodiment, the gap “G” may thereafter be filled with a dielectric material at the feed point 46. The dielectric material may be polytetrafluoroethylene (PTFE), such as Teflon® sold by DuPont of Willmington, Del. In another embodiment, the gap “G” may be coated with a dielectric seal coating.

With continued reference to FIG. 2, the antenna assembly 12 also includes a choke 60 disposed around the feedline 20. The choke 60 may be a quarter-wavelength shorted choke that is shorted to the feedline 20 at the proximal end (not illustrated) of the choke 60 by soldering or other suitable methods.

Assembly 12 also includes a tip 48 having a tapered end 24 that terminates, in one embodiment, at a pointed end 26 to allow for insertion into tissue with minimal resistance at a distal end of the radiating portion 18. In those cases where the radiating portion 18 is inserted into a pre-existing opening, tip 48 may be rounded or flat. The tip 48 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.

FIGS. 3A and 3B illustrate cross-sectional views of antenna assembly 12 taken along line X-X of FIG. 1 according to various embodiment of the present disclosure. As shown by the illustrated embodiments, at least a portion of the feedline 20 and/or the radiating portion 18 may be formed from a semi-rigid and/or semi-flexible structure (e.g., coaxial cable) and includes an inner conductor 50 (e.g., wire) surrounded by an inner insulator 52 with suitable dielectric properties. The inner insulator 52 is, in turn, surrounded by an outer conductor 56 (e.g., cylindrical conducting sheath). The inner and outer conductors 50 and 56, respectively, may be constructed of copper, gold, stainless steel or other conductive metals with similar conductivity values. The metals may be plated with other materials, e.g., other conductive materials, to improve their properties, e.g., to improve conductivity or decrease energy loss, etc.

Since the radiating portion 18 and the feedline 20 are in direct contact with materials such as fluid and/or solid, these components of the assembly 12 are sealed by a protective sleeve 63 (FIGS. 3A and 3B) to prevent any fluid seeping therein. This may be accomplished by applying any type of melt-processible polymers using conventional injection molding and screw extrusion techniques. In one embodiment, a sleeve of fluorinated ethylene propylene (FEP) shrink wrap may be applied to the entire assembly 12, namely the feedline 20 and the radiating portion 18. The protective sleeve 63 is then heated to seal the feedline 20 and radiating portion 18. The protective sleeve 63 prevents any material from penetrating into the assembly 12.

Referring specifically now to FIG. 3A, one embodiment of the present disclosure is shown and includes separation members 91a, 91b disposed transversely between protective sleeve 63 and an inner surface of sheath 38 along at least a longitudinal portion of chamber 89 to sub-divide chamber 89 into semi-circular sub-chambers 89a and 89b. Sub-chambers 89a and 89b are configured to retain first and second chemicals “A” and “B”, respectively, therein. Separation members 91a, 91b are configured to hold chemicals “A” and “B” within sub-chambers 89a and 89b, respectively, in a seal-tight manner such that chemicals “A” and “B” are selectively prevented from contacting each other until needed to contact each other.

In one embodiment, separation members 91a, 91b may be slidable or movable, as discussed in further detail below with reference to FIG. 3C. In another embodiment, separation members 91a, 91b are formed of a breakable material, such as a breakable membrane, the structural integrity of which is compromised upon the application of a sufficient force mechanically, electrically, or electro-mechanically thereto (e.g., bending of semi-rigid feedline 20). In this scenario, once the separation members 91a, 91b are broken or ruptured, contact between chemicals “A” and “B” is facilitated and, depending on the identity of chemicals “A” and/or “B”, an endothermic or exothermic reaction ensues to cool or heat the antenna assembly 12, respectively.

Chemical pairs used to generate an endothermic reaction through contact, reaction, dissolving, or mixture may include, without limitation, barium hydroxide octahydrate crystals with dry ammonium chloride, ammonium chloride with water, thionyl chloride (SOCl₂) with cobalt(II) sulfate heptahydrate, water with ammonium nitrate, water with potassium chloride, and ethanoic acid with sodium carbonate. Chemical pairs used to generate an exothermic reaction may include, without limitation, concentrated acid with water, water with anhydrous copper(II) sulfate, water with calcium chloride (CaCl₂), alkalis with acids, acids with bases, etc.

Referring specifically now to FIG. 3B, another embodiment of the present disclosure includes a concentric separation member 191 disposed longitudinally through at least a portion of a cross-section of chamber 89 to subdivide chamber 89 into longitudinal sub-chambers 189a and 189b. Separation member 191 is substantially as described above with respect to separation members 91a, 91b of FIG. 3A and will only be described to the extent necessary to describe the differences between the embodiments of FIGS. 3A and 3B. Similar to separation members 91a, 91b described above with respect to FIG. 3A, sub-chambers 189a and 189b are configured to hold chemicals “A” and “B” therein. Separation member 191 may be slidable or movable, as discussed in further detail below with reference to FIG. 3C. In another embodiment, separation member 191 is formed of a breakable material, such as a breakable membrane, the structural integrity of which is compromised upon the application of a sufficient force mechanically, electrically, or electro-mechanically thereto (e.g., bending of semi-rigid feedline 20). In this scenario, once separation member 191 is broken, contact between chemicals “A” and “B” is facilitated and, depending on the identity of chemicals “A” and/or “B”, an endothermic or exothermic reaction ensues to cool or heat the antenna assembly 12, respectively.

For purposes of simplifying the description of FIG. 3C to follow, FIG. 3C will be described below with respect to the embodiment of FIG. 3B. However, the following description may also apply to the operation of the embodiment of FIG. 3A and, as such, any reference to separation member 191 or sub-chambers 189a and 189b throughout the following description may be substituted with reference to separation members 91a, 91b and sub-chambers 89a, 89b, respectively.

Separation member 191 may, in certain embodiments, be configured to be moved, actuated, slid, or the like, to permit or prevent communication between sub-chambers 189a and 189b, respectively, such that contact between chemicals “A” and “B” is selectively facilitated or prevented. More specifically, separation member 191 includes a pair of interfacing surfaces 95a and 95b that each include a plurality of apertures 93. As illustrated by FIG. 3C, separation member 191 may be actuated such that interfacing surfaces 95a and 95b move relative to each other or, alternatively, such that one surface (e.g., 95a) moves relative to a stationary surface (e.g., 95b). In either scenario, movement of surface 95a and/or surface 95b operates to bring apertures 93 of both surfaces 95a, 95b into and out of alignment with each other. That is, when apertures 93 of surface 95a are brought into substantial alignment with corresponding apertures 93 of surface 95b, sub-chambers 189a and 189b are in communication via apertures 93 such that contact between chemicals “A” and “B” is facilitated. Likewise, when apertures 93 of surface 95a are brought out of substantial alignment with apertures 93 of surface 95b, communication between sub-chambers 189a and 189b is prevented.

Actuation of separation member 191 may be facilitated by an actuation member (not shown) disposed on the exterior of the antenna assembly 12 at a location suitable for operation by a user during an ablation procedure (e.g., the connection hub 22). The actuation member, in this scenario, is operably coupled to separation member 191 by any suitable number of configurations, components, mechanical connections, and/or components (e.g., gears, links, springs, rods, etc.), and/or electro-mechanical connections, configurations, and/or components such that separation member 191 may operate as intended. The actuation member may be embodied as, for example without limitation, a button, slide button, knob, lever, or the like. For example, in the scenario wherein the actuation member is a slide button, the slide button may be configured to slide longitudinally along the exterior of the antenna assembly 12 (e.g., along the connection hub 22) to actuate separation members 91a, 91b or separation member 191.

Referring to FIGS. 3A and 3B, the depiction of sub-chambers 89a, 89b and 189a, 189b is illustrative only in that antenna assembly 12 may include a plurality of sub-chambers, each of which is configured to hold a chemical therein. In this scenario, an endothermic or exothermic reaction may be caused by the contact, mixture, dissolving, or reaction between three or more chemicals to thermally regulate the antenna assembly 12.

Referring now to FIG. 4, another embodiment of antenna assembly 12 is shown and includes a flexible sheath 291 disposed on at least a portion of the sheath 38 enclosing radiating portion 18 and feedline 20. Flexible sheath 291 includes an outer sub-chamber 295a configured to hold chemical “A” and an inner sub-chamber 295b configured to hold chemical “B”. Outer sub-chamber 295a surrounds inner sub-chamber 295b and is separated therefrom at least partially by a breakable membrane 293 (e.g., a shared surface between outer sub-chamber 295a and inner sub-chamber 295b). Upon insertion of antenna assembly 12 into tissue “T”, as illustrated in FIG. 4, outer sub-chamber 295a is configured to conform to the surface of antenna assembly 12 along a portion thereof inserted through tissue “T” and disposed within the insertion tract. Along the portion of antenna assembly 12 exterior to the tissue “T” or outside the insertion tract, outer sub-chamber 295a conforms to the surface of tissue “T” (e.g., the patient's skin, a target organ, etc.).

In use, once antenna assembly 12 is inserted into tissue “T”, the structural integrity of membrane 293 may be compromised to cause communication between outer and inner sub-chambers 295a and 295b and facilitate contact between chemicals “A” and “B”. As discussed hereinabove, contact between materials “A” and “B” causes an endothermic or exothermic reaction depending on the identity of materials “A” and/or “B”. In the scenario wherein an exothermic reaction results, for example, the antenna assembly 12 may be heated sufficient to thermally modify tissue in the insertion tract to stop bleeding upon removal of antenna assembly 12 from tissue “T”. An exothermic reaction may also be used to simply heat the antenna assembly 12 if the antenna assembly 12 becomes too cold. In the scenario wherein an endothermic reaction results, for example, the antenna assembly 12 may be cooled sufficient to cool the insertion tract and stop bleeding upon removal of antenna assembly 12 from tissue “T”. An endothermic reaction may also be used to cool the surface of the tissue “T” facilitated by the conforming of outer sub-chamber 295a to the surface of the tissue “T” as described hereinabove. An endothermic reaction may also be used to simply cool the antenna assembly 12 if the antenna assembly 12 becomes too hot.

The above-discussed system provides for the generation of endothermic and exothermic reactions within antenna assembly 12. The endothermic reaction removes the heat generated by the antenna assembly 12. By keeping the antenna assembly 12 and/or the ablation zone cooled, there is significantly less sticking of tissue to the antenna assembly 12. In addition, the endothermic reaction acts as a buffer for the assembly 12 and prevents near field dielectric properties of the assembly 12 from changing due to varying tissue dielectric properties. For example, as microwave energy is applied during ablation, desiccation of the tissue around the radiating portion 18 results in a drop in tissue complex permittivity by a considerable factor (e.g., about 10 times). The dielectric constant (er′) drop increases the wavelength of microwave energy in the tissue, which affects the impedance of un-buffered microwave antenna assemblies, thereby mismatching the antenna assemblies from the system impedance (e.g., impedance of the cable 16 and the generator 14). The increase in wavelength also results in a power dissipation zone which is much longer in length along the assembly 12 than in cross sectional diameter. The decrease in tissue conductivity (er″) also affects the real part of the impedance of the assembly 12. The fluid dielectric buffering according to the present disclosure also moderates the increase in wavelength of the delivered energy and drop in conductivity of the near field, thereby reducing the change in impedance of the assembly 12, allowing for a more consistent antenna-to-system impedance match and spherical power dissipation zone despite tissue behavior.

The described embodiments of the present disclosure are intended to be illustrative rather than restrictive, and are not intended to represent every embodiment of the present disclosure. Embodiments of the present disclosure may also be implemented in a microwave monopolar antenna or other suitable electrosurgical devices (monopolar or bipolar) and may be applied with any suitable energy source (e.g., radiofrequency, direct current, microwave, laser, ultrasound, etc.) where, for example, reduction of heat and/or an increase in localized heating is desired. Various modifications and variations can be made without departing from the spirit or scope of the disclosure as set forth in the following claims both literally and in equivalents recognized in law.

Claims

1. An energy-delivery assembly configured to deliver energy to tissue, the energy-delivery assembly comprising: a radiating portion;a first sheath disposed about the radiating portion and defining a longitudinally-extending chamber configured to receive a fluid therein;a second sheath disposed over at least a portion of the first sheath and defining: an outer chamber; andan inner chamber disposed within the outer chamber, wherein the outer chamber and the inner chamber are disposed around the first sheath;a first composition disposed within the outer chamber; anda second composition disposed within the inner chamber, wherein the outer chamber and the inner chamber are configured to selectively and fluidly communicate with each other to cause contact between the first composition and the second composition to cause one of an endothermic reaction or an exothermic reaction.

2. The energy-delivery assembly according to claim 1, wherein the second sheath is flexible.

3. The energy-delivery assembly according to claim 1, wherein the second sheath has a proximal end portion connected to the first sheath, and a distal end portion connected to the first sheath.

4. The energy-delivery assembly according to claim 1, wherein each of the inner chamber and the outer chamber has a distal end portion, the distal end portion of the outer chamber extending distally beyond the distal end portion of the inner chamber.

5. The energy-delivery assembly according to claim 1, wherein the outer chamber is separated from the inner chamber by a membrane.

6. The energy-delivery assembly according to claim 5, wherein the membrane is selectively rupturable such that the membrane is configured to break down upon an application thereto of at least one of a mechanical force, an electro-mechanical force, or an electrical force.

7. The energy-delivery assembly according to claim 5, wherein the membrane has a proximal end portion connected to the first sheath, and a distal end portion connected to the first sheath.

8. The energy-delivery assembly according to claim 1, further comprising a third composition disposed in the longitudinally-extending chamber of the first sheath.

9. The energy-delivery assembly according to claim 8, wherein the third composition is at least one of a coolant, saline, or water.

10. The energy-delivery assembly according to claim 1, wherein the first composition is selected from the group consisting of barium hydroxide octahydrate, ammonium chloride, thionyl chloride, water, and ethanoic acid.

11. The energy-delivery assembly according to claim 1, wherein the second composition is selected from the group consisting of ammonium chloride, water, cobalt sulfate heptahydrate, ammonium nitrate, potassium chloride, sodium carbonate, anhydrous copper sulfate, and calcium chloride.

12. The energy-delivery assembly according to claim 1, further comprising a feedline electrically coupled to the radiating portion.

13. A method of treating tissue, comprising: inserting a radiating portion of an energy-delivery assembly into tissue;circulating a fluid through a longitudinally-extending chamber defined within a first sheath that is disposed about the radiating portion; andcontacting a first composition, disposed within an outer chamber defined by a second sheath that is disposed over at least a portion of the first sheath, with a second composition, disposed within an inner chamber disposed within the outer chamber, to thermally regulate the radiating portion.

14. The method of treating tissue according to claim 13, further comprising forming a pathway through a membrane that defines the inner chamber, at least one of the first composition or the second composition passing through the pathway to contact one another.

15. The method of treating tissue according to claim 14, wherein forming the pathway through the membrane includes rupturing the membrane using at least one of a mechanical force, an electro-mechanical force, or an electrical force.

16. The method of treating tissue according to claim 13, wherein each of the inner chamber and the outer chamber has a distal end portion, the distal end portion of the outer chamber extending distally beyond the distal end portion of the inner chamber.

17. The method of treating tissue according to claim 13, wherein circulating the fluid through the longitudinally-extending chamber of the first sheath reduces a temperature of the radiating portion.