Abstract:
The present disclosure relates to devices and methods for the treatment of tissue with microwave energy. The devices and methods disclosed herein incorporate an antenna assembly comprising outer and inner conductors having a dielectric material interposed therebetween, a sealing barrier, and a cooling system to minimize the likelihood that the antenna assembly will overheat.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to U.S. Provisional Application Ser. No. 61/033,196 entitled “INTRACOOLED PERCUTANEOUS MICROWAVE ABLATION PROBE” filed Mar. 3, 2008 by Kenlyn Bonn et al, which is incorporated by reference herein. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates generally to microwave antennas for use in therapeutic or ablative tissue treatment applications. More particularly, the present disclosure relates to devices and methods for regulating, maintaining, and/or controlling the temperature of microwave antennas used in such treatment applications. 
     2. Background of the Related Art 
     Many procedures and devices employing microwave technology are well known for their applicability in the treatment, coagulation, and targeted ablation of tissue. During such procedures, a microwave probe antenna of the monopole, dipole, or helical variety, as is conventional in the art, is typically advanced into the patient, either laparoscopically or percutaneously, to reach target tissue. 
     Following introduction of the microwave probe, microwave energy is transmitted to the target tissue, which may cause the outer surface of the antenna to sometimes reach unnecessarily high temperatures via ohmic heating. Additionally, or alternatively, losses in the feedline, through which energy is communicated to the antenna from a power source, may contribute to heating in the antenna. When exposed to such temperatures, the treatment site, as well as the surrounding tissue, may be undesirably effected. 
     To prevent unnecessarily high temperatures, and the corresponding undesirable effects upon the tissue, several different cooling methodologies are conventionally employed. For example, microwave probes may include external cooling jackets. However, employing these jackets increases the overall size, i.e., the gauge size of the instrument, and consequently, the invasiveness of the procedure. As such, there exists a continuing need in the art for an improved microwave tissue treatment device that includes a cooling system to avoid the realization of unnecessarily high temperatures during treatment, as well as the gauge size of the device, and thereby minimize undesirable effects on the tissue. 
     SUMMARY 
     In one aspect of the present disclosure, a microwave tissue treatment device for the therapeutic treatment or ablation of tissue is disclosed. The microwave tissue treatment device includes an antenna assembly having proximal and distal ends. The antenna assembly includes an elongate member, an outer conductor positioned within the elongate member, a dielectric material disposed within the outer conductor and defining a lumen and one or more longitudinally extending channels, an inner conductor including a distal radiating section and being at least partially disposed within the lumen, a sealing barrier disposed adjacent a distal end of the outer conductor, a radiating portion, and a cooling system. 
     The radiating portion is disposed adjacent the sealing barrier, and includes the radiating section of the inner conductor as well as a sheath with proximal and distal ends that is at least partially disposed about the radiating section to define at least one cavity. The at least one cavity may include two or more regions, e.g., proximal, intermediate, and distal regions. In one embodiment, the regions of the cavity may be at least partially defined by one or more baffle members that are disposed within the cavity. Additionally, the baffle member(s) will also define, at least partially, two or more axial dimensions within the cavity. 
     The cooling system includes inlet and outlet conduits that are configured and dimensioned to circulate a fluid through the antenna assembly. In one embodiment of the present disclosure, the fluid may be a heat dissipative fluid that is selected from the group consisting of water, saline, ammonium chloride, sodium nitrate, and potassium chloride. The inlet and outlet conduits are at least partially disposed within the channel or channels of the dielectric material, and are in communication with the at least one cavity such that at least a portion of the radiating section is in contact with the fluid. 
     It is envisioned that the channel(s) extending through the dielectric material may include at least a first channel and a second channel. In one embodiment, the inlet member(s) may be at least partially disposed in the first channel, and the outlet member(s) may be at least partially disposed in the second channel. 
     It is further envisioned that the microwave tissue treatment device may also include a penetrating member that is disposed at the distal end of the antenna assembly. The antenna assembly may further include a connecting hub that is positioned proximally of the sealing barrier and at least partially about the elongate member. The connecting hub includes at least one conduit that is configured and dimensioned to receive the inlet and outlet member(s) of the cooling system. 
     In one embodiment of the antenna assembly, the outer conductor may include one or more apertures that are configured and dimensioned to receive the inlet and outlet member(s) of the cooling system. Additionally, or alternatively, the microwave tissue treatment may also include at least one temperature sensor that is operatively connected to the radiating section. 
     In another aspect of the present disclosure, an improved microwave tissue treatment device is disclosed. The improved microwave tissue treatment device includes an outer conductor, an inner conductor with a radiating section, and a radiating portion that includes the radiating section of the inner conductor and a sheath that is at least partially disposed thereabout to define at least one cavity. The device also includes a cooling system with inlet and outlet conduits that are in fluid communication with the radiating section, and a dielectric material that is disposed within the outer conductor. The dielectric material includes a lumen and one or more channels that extend therethrough. The lumen extending through the dielectric material is configured and dimensioned to at least partially receive at least a portion of the inner conductor, and the channel(s) extending through the dielectric material are configured and dimensioned to at least partially receive the inlet and outlet conduits. 
     In one embodiment, the cooling system includes first and second channels that extend longitudinally through the dielectric material. The first and second channels at least partially accommodate the inlet and outlet conduits, respectively. 
     In another embodiment, the at least one cavity defined by the sheath may include at least two regions. In this embodiment, the improved microwave tissue treatment may further including one or more baffle members that are disposed within the at least one cavity to thereby divide the cavity into at least two regions. 
     In yet another aspect of the present disclosure, a method of cooling a microwave antenna including an inner conductor, an outer conductor, and a dielectric material is disclosed. The disclosed method includes the steps of (i) providing a cooling system with one or more inlet and outlet conduits disposed within the dielectric material and in fluid communication with the microwave antenna; and (ii) circulating a cooling fluid through the cooling system such that the cooling fluid is in fluid communication with at least a portion of the inner conductor. 
     In alternative embodiments, the disclosed method may further comprise the step of monitoring the temperature of the inner conductor with at least one temperature sensor operatively connected thereto, and/or regulating the circulation of the cooling fluid with a pump that is in communication with the cooling system. 
     These and other features of the presently disclosed microwave tissue treatment device, and corresponding method of use, will become more readily apparent to those skilled in the art from the following detailed description of various embodiments of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments of the present disclosure are described hereinbelow with references to the drawings, wherein: 
         FIG. 1  is a schematic illustration of a microwave tissue treatment system including a microwave tissue treatment device, in accordance with an embodiment of the present disclosure; 
         FIG. 2A  is a transverse, cross-sectional view of a feedline of the microwave tissue treatment device of  FIG. 1 , as taken through  2 A- 2 A of  FIG. 1 ; 
         FIG. 2B  is a longitudinal, cross-sectional view of a proximal portion of the feedline of the microwave tissue treatment device of  FIG. 1 , as taken through  2 B- 2 B of  FIG. 1 ; 
         FIG. 3  is a schematic, perspective view of a proximal portion of an antenna assembly of the microwave tissue treatment device of  FIG. 1 ; 
         FIG. 4A  is a schematic, perspective view of a connecting hub for use with the antenna assembly of the microwave tissue treatment device of  FIG. 1 ; 
         FIG. 4B  is a longitudinal, cross-sectional view of the connecting hub, as taken through  4 B- 4 B of  FIG. 3 ; 
         FIGS. 5A-5C  are transverse, cross-sectional views of various embodiments of a dielectric for use in the microwave tissue treatment device of  FIG. 1 ; 
         FIG. 6  is a schematic, cross-sectional, perspective view of a sealing barrier for use in the microwave tissue treatment device of  FIG. 1 , as taken through  6 - 6  of  FIG. 1 ; 
         FIGS. 7A-7F  are schematic, cross-sectional, perspective views of various embodiments of a radiating portion of the microwave tissue treatment of  FIG. 1 , as taken through  6 - 6  of  FIG. 1 ; 
         FIG. 8  is a schematic, cross-sectional view of distal and radiating portions of a microwave tissue treatment device, in accordance with an embodiment of the present disclosure; 
         FIG. 9  is a schematic, cross-sectional, perspective view of distal and radiating portions of a microwave tissue treatment device including a cooling system, in accordance with another embodiment of the present disclosure; 
         FIG. 10  is a schematic, cross-sectional, perspective view of an embodiment of distal and radiating portions of the microwave tissue treatment device of  FIG. 9 ; 
         FIG. 11  is a schematic, cross-sectional, perspective view of distal and radiating portions of an antenna assembly of a microwave tissue treatment device in accordance with another embodiment of the present disclosure; 
         FIG. 12  is a schematic, cross-sectional, perspective view of distal and radiating portions of an antenna assembly of a microwave tissue treatment device in accordance with yet another embodiment of the present disclosure; and 
         FIG. 13  is a schematic, cross-sectional, perspective view of distal and radiating portions of an antenna assembly of a microwave tissue treatment device in accordance with still another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Specific embodiments of the presently disclosed microwave tissue treatment device, and corresponding method of use thereof, will now be described in detail with reference to the foregoing figures wherein like reference characters identify similar or identical elements. In the drawings and in the description which follows, the term “proximal” will refer to the end of the microwave tissue treatment device, or component thereof, that is closest to the clinician during proper use, while the term “distal” will refer to the end that is furthest from the clinician, as is conventional in the art. 
     Referring now to  FIGS. 1-4B , a microwave tissue treatment system  10  is disclosed. System  10  includes a microwave tissue treatment device  20  having an antenna assembly  100  connected to a power supply  40  through a feedline  60 . Power supply  40  may be any power generating device suitable for the intended purpose of energizing tissue treatment device  20 , e.g., a microwave or RF generator. Microwave tissue treatment device  20  may include one or more pumps  80 , e.g., a peristaltic pump or the like, as a mechanism for circulating a cooling or heat dissipative fluid through antenna assembly  100 , as described below. 
     Feedline  60  may range in length from about 7 feet to about 10 feet, but may be either substantially longer or shorter if required in a particular application. Feedline  60  may be composed of any suitable conductive lead capable of transferring an electrical current to tissue treatment device  20 . In the embodiment seen in  FIG. 2A , feedline  60  includes an elongate member  62  disposed about a coaxial cable having an inner conductor  64 , an outer conductor  66 , and a dielectric  68  interposed therebetween. The dielectric  68  includes respective proximal and distal portions  60   a ,  60   b , and electrically separates and/or isolates the inner conductor  64  from the outer conductor  66 . Elongate member  62  includes respective proximal and distal ends  62   a ,  62   b , and may be any sleeve, tube, jacket, or the like formed of any conductive or non-conductive material. 
     Proximal portion  60   a  of feedline  60  is disposed proximally of antenna assembly  100  and is operatively connected to, or connectable to, power supply  40 . As seen in  FIG. 2B , proximal portion  60   a  includes and defines proximal portions  64   a ,  66   a , and  68   a  of inner conductor  64 , outer conductor  66 , and dielectric  68 , respectively. Distal portion  60   b  ( FIG. 1 ) of feedline  60  forms a component of antenna assembly  100 , and includes and defines respective distal portions  64   b ,  66   b ,  68   b  of inner conductor  64 , outer conductor  66 , and dielectric  68 . Alternatively, however, it is envisioned that the feedline  60  may be separable from, and connectable to, the antenna assembly  100 . Reference may be made to commonly owned U.S. Pat. No. 7,311,703 to Turovskiy, et al., filed Jan. 20, 2005, for further discussion of the structure of feedline  60 . 
     The respective inner and outer conductors  64 ,  66  are each formed, at least in part, of a conductive material or metal, such as stainless steel, copper, or gold. In certain embodiments, the respective inner and outer conductors  64 ,  66  of feedline  60  may include a conductive or non-conductive substrate that is plated or coated with a suitable conductive material. In contrast, dielectric  68  is formed of a material having a dielectric value and tangential loss constant of sufficient value to electrically separate and/or isolate the respective inner and outer conductors  64 ,  66  from one another, including but not being limited to, expanded foam polytetrafluoroethylene (PTFE), polymide, silicon dioxide, or fluorpolymer. However, it is envisioned that dielectric  68  may be formed of any non-conductive material capable of maintaining the desired impedance value and electrical configuration between the respective inner and outer conductors  64 ,  66 . In addition, it is envisioned that dielectric  68  may be formed from a combination of dielectric materials. 
     Antenna assembly  100  ( FIG. 1 ) of microwave tissue treatment device  10  will now be discussed. Antenna assembly  100  includes a proximal portion  110 , a distal or radiating portion  120 , a sealing barrier  140  disposed therebetween, and a cooling system  180 . 
     Proximal portion  110  of antenna assembly  100  includes a connecting hub  160  and distal portion  60   b  of feedline  60 . As seen in  FIGS. 4A-4B , connecting hub  160  defines a first conduit  162  configured and dimensioned to receive distal portion  60   b  ( FIG. 1 ) of feedline  60 , additional conduits  164   a ,  164   b  configured and dimensioned to receive respective inlet and outlet conduits  182 ,  184  of cooling system  180 , which is discussed in detail below, and one or more apertures  166  formed in an internal surface thereof that are configured and dimensioned to receive inlet and outlet conduits  182 ,  184 , respectively. Connecting hub  160  may be formed of any suitable material including, but not limited to, polymeric materials. 
     Distal portion  68   b  of dielectric  68  defines a lumen  70  and a series of channels  72   a - 72   d  disposed thereabout, each extending through dielectric  68 . Lumen  70  is configured and dimensioned to receive distal portion  64   b  of the inner conductor  64 , and channels  72   a - 72   d  are configured and dimensioned to receive the respective inlet and outlet conduits  182 ,  184  of cooling system  180 . Lumen  70  and channels  72   a - 72   d  may be formed in dielectric  68  through any suitable manufacturing method including, but not limited to extrusion, injection molding, or drilling. 
     Although the embodiment of the microwave tissue treatment device  10  discussed with respect to  FIGS. 1-5B  is illustrated as including a distal portion  68   b  of dielectric  68  with a single lumen  70  and four channels, i.e., channels  72   a ,  72   b ,  72   c , and  72   d , that are substantially circular in cross-sectional configuration, it should be appreciated that the number and/or configuration of the lumen  70  and the channels extending through dielectric  68  may be varied depending on the air/polymer/cooling fluid ratio to match the desired impedance, e.g., 50 ohms. For example, lumen  70  and channels  72   a - 72   d  may be present in any number suitable for the intended purpose of accommodating the respective inlet and outlet conduits  182 ,  184  of cooling system  180 , and may exhibit any suitable geometrical configuration, such as that seen in the embodiment illustrated in  FIG. 5C . With reference to  FIGS. 5A and 5B  in particular, it is envisioned that channels  72   a - 72   d  may be oriented such that they are completely or partially defined within the perimeter “P” of distal portion  68   b  of dielectric  68 . 
     Referring now to  FIGS. 1 ,  3 , and  6 , sealing barrier  140  will be discussed. Sealing barrier  140  is disposed between the respective proximal and radiating portions  110 ,  120  ( FIG. 3 ) of antenna assembly  100 . Sealing barrier  140  has proximal and distal ends  142 ,  144  ( FIG. 6 ), respectively, and may be connected to proximal portion  110  of antenna assembly  100  in any suitable manner including, but not limited to, a snap-fit arrangement, adhesives, or a screw-type fit. Sealing barrier  140  defines a lumen  146  and one or more channels  148  that extend axially therethrough. Lumen  146  is adapted to at least partially receive distal portion  64   b  of inner conductor  64 , and channels  148  are adapted to at least partially receive the respective inlet and outlet conduits  182 ,  184  of cooling system  180 . Lumen  146  and channels  148  are respectively aligned with lumen  70  and channels  72   a - 72   d  (only channels  72   a  and  72   c  being shown) formed in distal portion  68   b  of dielectric  68  such that distal portion  64   b  of inner conductor  64  and the respective inlet and outlet conduits  182 ,  184  of cooling system  180  may extend into radiating portion  120  of antenna assembly  100 . 
     Sealing barrier  140  may be formed of any biocompatible material suitable for the intended purpose of preventing the escape of fluids into the proximal portion  110  of antenna assembly  100 , as described below. Sealing barrier  140  may be formed either of a conductive or non-conductive material, and may be either substantially rigid or substantially non-rigid in character. Sealing barrier  140  inhibits fluid from contacting both the inner conductor  64   b  and the outer conductor  66   b , thus substantially reducing the likelihood of an electrical short. Additionally, sealing barrier  140  serves as a dielectric break allowing for the dipole construction of the microwave tissue treatment device  10  ( FIG. 1 ). 
     Referring now to  FIG. 7A , as discussed above, radiating portion  120  of antenna assembly  100  is disposed adjacent distal end  144  of sealing barrier  140 . Radiating portion  120  includes a radiating section  122  of inner conductor  64 , a sheath  124  that is at least partially disposed thereabout, and a penetrating member  126  supported on a distal end  124   b  of sheath  124 . 
     Radiating section  122  of inner conductor  64  serves to transmit the microwave energy supplied by power supply  40  ( FIG. 1 ) to a target area or target tissue (not shown). Radiating section  122  defines an axial dimension “L” and a radial dimension “D”. As would be appreciated by one of ordinary skill in the art, by varying the axial and radial dimensions of the radiating section  122 , the amount of microwave energy that can be transmitted to the target tissue therethrough can be regulated or controlled. 
     In one embodiment, as seen in  FIG. 7A , radiating section  122  of inner conductor  64  may be entirely formed of a conductive material. In an alternative embodiment, as seen in  FIG. 7B , radiating section  122  may only be partially formed of a conductive material. In this embodiment, radiating section  122  includes one or more conductive surfaces  150  disposed on a non-conductive substrate  152 . Conductive surface, or surfaces,  150  may have a particular pattern or distribution for focusing or dispersing the energy transmitted into the radiating section  122 . For example, conductive surfaces  150  may only be present on one side, or in one particular area or region of radiating section  122 . Conductive surfaces  150  may be integrally formed with substrate  152 , or may be fixedly or removably attached thereto. 
     Referring back to  FIG. 7A , sheath  124  has respective proximal and distal ends  124   a ,  124   b , and is disposed at least partially about radiating section  122  in such a manner so as to define a cavity  128 . At its proximal end  124   a , sheath  124  may be fixedly, releasably, and/or slidably connected to sealing barrier  140 , elongate member  62 , or any other suitable surface of antenna assembly  100  in any appropriate manner including, but not being limited to, the use of welds or adhesives, as would be appreciated by one skilled in the art. In the embodiment seen in  FIG. 7A , distal end  124   b  of sheath  124  is open and configured for coupling to penetrating member  126  such that cavity  128  is defined by the penetrating member  126 , sheath  124 , and sealing barrier  140 . In this embodiment, sheath  124  may be connected to penetrating member  126  in any suitable manner including, but not limited to, a screw-type fit, as seen in  FIG. 7A , via a snap-fit arrangement, or through the use of adhesives. 
     In another embodiment, as seen in  FIG. 7C , distal end  124   b  of sheath  124  is closed or sealed such that cavity  128  is defined by sheath  124  and sealing barrier  140  only. 
     In yet another embodiment, as seen in  FIG. 7D , distal end  124   b  of sheath  124  is closed and formed integrally with penetrating member  126  such that cavity  128  is defined by sheath  124 , sealing barrier  140 , and penetrating member  126 . 
     In still another embodiment, as best seen in  FIG. 7E , a distal-most tip  130  of radiating section  122  of inner conductor  64  extends beyond distal end  124   b  of sheath  124 . In this embodiment, penetrating member  126  may be connected directly to radiating section  122 . 
     As seen in  FIG. 7F , sheath  124  may also be connected directly to radiating section  122  of inner conductor  64  at its distal-most tip  130 . In this embodiment, penetrating member  126  is connected either to sheath  124  or to radiating section  122 . 
     With respect to each of the aforementioned embodiments, sheath  124  may be formed of any biocompatible material suitable for the intended purpose of retaining a fluid therein while allowing for the dispersion of microwave energy. It is contemplated that the sheath  124  may be formed, in whole or in part, of a substantially rigid or a substantially non-rigid material. For example, in those embodiments wherein the inner conductor  64   b  is electrically connected to sheath  124 , sheath  124  can be formed from stainless steel. Additionally, the connection between penetrating member  126  may be either releasably or fixedly coupled with antenna assembly  100  in any suitable manner. 
     Referring now to  FIG. 8 , cavity  128  may include one or more internal baffle members  132 ,  134  that divide radiating portion  120  into respective proximal, intermediate, and distal regions  120   a ,  120   b , and  120   c . Additionally, the baffle members  132 ,  134  act to divide cavity  128  into respective proximal, intermediate, and distal cells  128   a ,  128   b ,  128   c , and radiating section  122  into respective first, second, and third segments  122   a ,  122   b ,  122   c . Although the particular embodiment shown in  FIG. 8  includes two baffle members, any suitable number of baffle members may be employed to divide radiating portion  120 , cavity  128 , and radiating section  122  into any suitable number of regions, cells, and segments, respectively. 
     Proximal cell  128   a  of cavity  128 , and consequently, first segment  122   a  of radiating section  122  of inner conductor  64 , exhibit a first axial dimension L 1 , and are defined by first baffle member  132  and the location where proximal end  124   a  of the sheath  124  meets sealing barrier  140 . Intermediate cell  128   b  of cavity  128 , and consequently, second segment  122   b  of radiating section  122  exhibit a second axial dimension L 2 , and are defined by the location of first baffle member  132  and second baffle member  134 . Distal cell  128   c  of cavity  128  and third segment  122   c  of radiating section  122  exhibit a third axial dimension L 3 , and are defined by the location of second baffle member  134  and distal end  126   c  of sheath  124 . 
     First and second baffle members  132 ,  134 , respectively, serve not only to partially define the metes of the three cells  128   a ,  128   b ,  128   c  of cavity  128  defined by sheath  124 , but also to substantially prevent any co-mingling of fluid or fluids (not shown) that may be circulated throughout each of the respective proximal, intermediate, and distal regions  120   a ,  120   b ,  120   c  of the radiating portion  120 , as discussed in further detail herein below. 
     With continued reference to  FIG. 8 , distal region  120   c  of radiating portion  120  of antenna assembly  100  may comprise the area of active heating during tissue treatment or ablation. It may be desirable, therefore, to prevent the temperature in distal region  120   c  from reaching excessively high temperatures in order to maintain optimal energy delivery and to maintain optimal thermal therapy of the tissue. Intermediate region  120   b  may also become hot due to ohmic and conductive heating from distal region  120   c . Since intermediate region  120   b  may be in contact with the tissue surrounding the target site, it may be desirable to allow intermediate region  120   b  to achieve a particular temperature profile dependent upon the nature of the surgical procedure being performed. 
     As an illustrative example, where coagulation of the insertion tract may be desirable, the clinician may want to allow intermediate region  120   b  of radiating portion  120  to attain a particular predetermined temperature capable of creating a coagulation effect in the insertion tract. In other applications, it may also be desirable, to prevent the temperature in intermediate region  120   b  from rising beyond a particular threshold level to protect surrounding sensitive tissue structures from undesired effects. 
     During use, proximal region  120   a  of radiating portion  120  may also come into contact with the skin or tissue of a patient. As proximal region  120   a  may also be subject to ohmic and/or conductive heating, it may be desirable to maintain the temperature of proximal region  120   a  below a specific temperature, particularly in percutaneous or laparoscopic procedures, to mitigate or substantially prevent any undesired effects upon the patient&#39;s tissue. In other procedures, such as in applications where lesions are located deep within the tissue, it may be desirable to allow the proximal region  120   a  to become heated to allow for the coagulation of the insertion tract. 
     Referring now to  FIG. 1  as well, the specific components and features of the presently disclosed cooling system  180  reduce the radial or transverse dimensions of antenna assembly  100 , thereby potentially improving the performance of the antenna assembly  100 . However, reducing the dimensions of antenna assembly  100  may necessitate an increase in the amount of energy flowing through antenna assembly  100  to achieve the same therapeutic effect that could otherwise be achieved by using a larger, more conventional antenna assembly and lower energy levels. The presently disclosed cooling system  180  reduces the likelihood that the increased amount of energy flowing through antenna assembly  100  will have negative results, e.g., losses, overheating, and potential failure of microwave tissue treatment device  20 , and counteracts the impact of any such results should they occur. 
     Referring now to  FIGS. 1 and 9 , cooling system  180  will be discussed. Cooling system  180  is adapted to circulate a fluid “F”, either constantly or intermittently, throughout radiating portion  120  ( FIG. 1 ) of antenna assembly  100 . Fluid “F” may be a liquid, e.g., water, saline, liquid chlorodifluoromethane, perfluorocarbon, such as Fluorinert®, distributed commercially by Minnesota Mining and Manufacturing Company (3M), St. Paul, Minn., USA, or any combination thereof. In various embodiments, gases, such as air, nitrous oxide, nitrogen, carbon dioxide, etc., may be utilized as an alternative to, or in conjunction with, any of the aforementioned liquids. The composition of fluid “F” may be varied depending upon the desired cooling rate and the desired impedance of the feedline  60 . 
     Cooling system  180  includes an inlet conduit  182  having a proximal end  182   a  ( FIG. 1 ) and a distal end  182   b  ( FIG. 9 ), and an outlet conduit  184  having a proximal end  184   a  ( FIG. 1 ) and a distal end  184   b  ( FIG. 9 ). Proximal ends  182   a ,  184   a  of inlet and outlet conduits  182 ,  184 , respectively, are connected to, and are in fluid communication with, pump  80  ( FIG. 1 ), and distal ends  182   b ,  184   b  of inlet and outlet conduits  182 ,  184 , respectively, are in fluid communication with cavity  128  ( FIG. 9 ) defined by sheath  124 . Inlet and outlet conduits  182 ,  184 , respectively, act in concert with pump  80  to circulate fluid “F” through cavity  128 , thereby cooling radiating section  122  of inner conductor  64  (see, e.g.,  FIG. 2A ). Cooling system  180  may include any number of inlet and outlet conduits  182 ,  184  suitable for the intended purpose of circulating dissipative fluid “F” throughout cavity  128 . 
     With additional reference to FIGS.  3  and  4 A- 4 B, the respective inlet and outlet conduits  182 ,  184  extend from pump  80  and enter conduits  164   a ,  164   b  of connecting hub  160 . The respective inlet and outlet conduits  182 ,  184  pass through elongate member  62  and enter channels  72   a - 72   d  formed in distal portion  68   b  of dielectric  68  through apertures  166  formed in connecting hub  160 . The respective inlet and outlet conduits  182 ,  184  extend distally through channels  148  ( FIG. 9 ) formed in sealing barrier  140  and into radiating portion  120  ( FIG. 1 ) of antenna assembly  100 , thereby facilitating the circulation of fluid “F” within the radiating portion  120   
     Including a cooling system  180 , e.g., the respective inlet and outlet conduits  182 ,  184 , that extends through the dielectric  68 , as opposed a cooling system that includes an external cooling chamber that is positioned about the antenna assembly  100 , creates a size reduction benefit. That is, by eliminating the need for an external cooling chamber, the transverse outer dimension of the outer conductor  66   b  will constitute the transverse outer dimension of the antenna assembly  100 . This allows for the employment of larger inner and outer conductors  64   b ,  66   b , respectively, which reduces loss effects, without increasing the overall transverse dimension of the antenna assembly  100 . 
     As seen in  FIG. 10 , in one embodiment, the number of respective inlet and outlet conduits  182 ,  184  corresponds to the number of regions, segments, and cells of the radiating portion  120  of antenna assembly  100 , radiating section  122  of inner conductor  64 , and cavity  128 , respectively. In particular, inlet and outlet conduits  182 ′,  184 ′ circulate fluid “F” throughout proximal cell  128   a  of cavity  128  such that fluid “F” may contact proximal segment  122   a  of radiating section  122 , and thereby cool proximal region  120   a  of radiating portion  120  of assembly  100 . In likewise fashion, respective inlet and outlet conduits  182 ″,  184 ″ circulate fluid “F” throughout intermediate cell  128   b  of cavity  128  such that fluid “F” may contact intermediate segment  122   b  of radiating section  122 , and thereby cool intermediate region  120   b  of radiating portion  120  of antenna assembly  100 , and respective inlet and outlet conduits  182 ′″,  184 ′″ circulate fluid “F” throughout distal cell  128   c  of cavity  128  such that fluid “F” may contact distal segment  122   c  of radiating section  122 , and thereby cool distal region  120   c  of radiating portion  120  of antenna assembly  100 . While  FIG. 10  depicts each cell  128   a - 128   c  in contact with fluid “F,” the present disclosure also envisions, the alternative, that fluid “F” may not be circulated through one or more of cells  128   a - 128   c.    
     Referring still to  FIG. 10 , upon entering proximal cell  128   a  through inlet conduit  182 ′, i.e., in the direction of arrows “A”, fluid “F” comes into direct contact with proximal segment  122   a  of radiating section  122  of inner conductor  64 , allowing for the direct convective cooling thereof. As the fluid “F” cools proximal segment  122   a , pump  80  ( FIG. 1 ) removes fluid “F” from proximal cell  128   a , in the direction of arrows “B”, through outlet conduit  184 ′. In so doing, the heat generated by proximal segment  122   a  during the operation of antenna assembly  100  may be regulated and/or dissipated. Accordingly, the temperature of proximal region  120   a  of radiating portion  120  may be controlled. 
     As with proximal cell  128   a , fluid “F” may be circulated into and out of intermediate cell  128   b  by pump  80  ( FIG. 1 ) through inlet and outlet conduits  182 ″,  184 ″, respectively, thereby dissipating the heat generated by the intermediate segment  122   b  during the operation of antenna assembly  100  through fluid “F”. 
     Similarly, fluid “F” may be circulated into and out of the distal cell  128   c  by pump  80  ( FIG. 1 ) through inlet and outlet conduits  182 ′″,  184 ′″, respectively, thereby dissipating the heat generated by the distal segment  122   c  during the operation of antenna assembly  100  through fluid “F”. 
     To circulate fluid “F” through proximal cell  128   a  of cavity  128 , inlet and outlet conduits  182 ′,  184 ′ pass through corresponding channels  148  ( FIGS. 6 ,  9 ) in sealing barrier  140 . To circulate fluid “F” through intermediate cell  128   b , inlet and outlet conduits  182 ″,  184 ″ pass through channels  148 , as well as through apertures  136  in first baffle member  132 . To circulate fluid “F” through distal cell  128   c , inlet and outlet conduits  182 ′″,  184 ′″ pass through channels  148 , through apertures  136  in first baffle member  132 , through intermediate cell  128   b , and finally through apertures  136  in second baffle member  134 . 
     Sealing barrier  140 , first baffle member  132 , and second baffle member  134  may each include seal members (not shown) respectively associated with channels  148  and apertures  136  to substantially prevent fluid “F” from commingling between cells  128   a - 128   c  of cavity  128 , and the seal members may be any member suitable for this intended purpose including but not being limited to seals, gaskets, or the like. The seal members may be formed of any suitable material, including but not being limited to, a polymeric material. 
     Referring still to  FIG. 10 , given the desirability of controlling heating and temperature regulation within the individual segments  122   a - 122   c  of radiating section  122  ( FIG. 9 ) of inner conductor  64  (see, e.g.,  FIG. 2A ), and the corresponding regions  120   a - 120   c  of radiating portion  120  of antenna assembly  100 , the axial locations of baffle members  132 ,  134  within cavity  128  may be varied as desired or necessary such that the respective axial dimensions L 1 , L 2 , and L 3  of the proximal, intermediate, and distal cells  128   a - 128   c  of cavity  128  may also be varied. In varying the axial length of a particular cell of cavity  128 , the overall volume of that cell may be varied, and consequently, so too may the volume of fluid “F” circulated therein. As would be appreciated by one of ordinary skill in the art, an inverse relationship exists between the volume of fluid “F” within a particular cell of cavity  128  and the temperature of the corresponding region of radiating portion  120 , in that as the volume of fluid “F” is increased, the temperature of the region will decrease. 
     Baffle members  132 ,  134  may be located at any suitable or desired point within the cavity  128 . In one embodiment, baffle members  132 ,  134  may be positioned such that the respective first, second and third axial dimensions, L 1 , L 2 , and L 3  of proximal, intermediate, and distal cells  128   a - 128   c  are substantially equivalent. In another embodiment, baffle members  132 ,  134  are positioned such that the first axial dimension L 1  of proximal cell  128   a  is greater than the respective second and third axial dimensions L 2  and L 3  of intermediate and distal cells  128   b ,  128   c . In yet another embodiment, baffle members  132 ,  134  may be positioned such that the third axial dimension L 3  of distal cell  128   c  is greater than the respective first and second axial dimensions L 1  and L 2  of proximal and intermediate cells  128   a ,  128   b . In alternative embodiments, baffle members  132 ,  134  may be located such that the overall volume of the cavity  128  may be distributed amongst any individual cells thereof in any suitable manner. 
     With reference now to  FIG. 11 , in another embodiment, proximal, intermediate, and distal cells  128   a ,  128   b ,  128   c  of cavity  128  define respective first, second, and third radial dimensions D 1 , D 2 , and D 3 . As shown, radial dimension D 1  is greater than radial dimension D 2 , which is in turn greater than radial dimension D 3 . However, the respective first, second, and third radial dimensions D 1 , D 2 , and D 3  may also be substantially equivalent. 
     The respective radial dimensions D 1 , D 2 , and D 3  of proximal, intermediate, and distal cells  128   a ,  128   b ,  128   c  may be varied in any suitable manner so as to regulate the volume thereof, and consequently, the volume of fluid “F” that may be circulated therethrough. By varying the volume of fluid “F” circulated through each cell  128   a - 128   c  of cavity  128 , the temperature of each corresponding region  120   a - 120   c  of radiating portion  120  of antenna assembly  100  may be substantially regulated, as discussed above. 
     As seen in  FIG. 12 , in another embodiment, cavity  128  defines a radial dimension D that is varied in a continuously decreasing manner over the axial length thereof such that a generally tapered profile is exhibited. The tapered profile exhibited in this embodiment may also be applied to any of the embodiments disclosed herein above. 
       FIG. 13  illustrates yet another embodiment in which antenna assembly  100  includes one or more temperature sensors  190  adapted, coupled, or operatively connected to segments  122   a - 122   c  of radiating section  122  of inner conductor  64 . Temperature sensors  190  may be used to monitor any fluctuation in temperature in regions  120   a - 120   c  of radiating portion  120 . It may be desirable to monitor the temperature of the radiating portion  120 , and/or the tissue that may come into contact therewith, in an effort to guard against over heating and/or any unintended therapeutic effects on the tissue. This may be particularly useful in applications where microwave energy is used for treating or ablating tissue around the radiating portion. In alternative embodiments, temperature sensors  190  may be adapted, coupled, operatively connected, or incorporated into antenna assembly  100  at any suitable location, including, but not being limited to on sheath  124 . Temperature sensors  190  may be located on or within the sheath  124  using any conventional means, e.g., adhesives. Temperature sensors  190  may also be located on one or more baffle members, e.g., baffle member  132 ,  134 , if any. Temperature sensors  190  may be configured and adapted for electrical connection to a power supply  40  ( FIG. 1 ). 
     Temperature sensors  190  may be a semiconductor-based sensor, a thermistor, a thermal couple or other temperature sensor that would be considered as suitable by one skilled in the art. An independent temperature monitor (not shown) may be connected to the temperature sensor, or alternatively, power supply  40  ( FIG. 1 ) may include an integrated temperature monitoring circuit (not shown), such as one described in U.S. Pat. No. 5,954,719, to modulate the microwave power output supplied to antenna assembly  100 . Other physiological signals, e.g. EKG, may also be monitored by additional medical instrumentation well known to one skilled in the art and such data applied to control the microwave energy delivered to the antenna assembly  100 . 
     A closed loop control mechanism, such as a feedback controller with a microprocessor, may be implemented for controlling the delivery of energy, e.g., microwave energy, to the target tissue based on temperature measured by temperature sensors  190 . 
     The above description, disclosure, and figures should not be construed as limiting, but merely as exemplary of particular embodiments. It is to be understood, therefore, that the disclosure is not limited to the precise embodiments described, and that various other changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the disclosure. Additionally, persons skilled in the art will appreciate that the features illustrated or described in connection with one embodiment may be combined with those of another, and that such modifications and variations are also intended to be included within the scope of the present disclosure.