Abstract:
The present disclosure relates to devices and methods for the treatment of tissue with microwave energy. The devices and methods disclosed herein utilize an antenna assembly which includes an elongate member, an outer conductor, an inner conductor, at least a portion of which is deployable, and a cooling system. The cooling system disclosed herein may significantly curtail any theoretical, or potential negative effects upon the target tissue experienced during the transmission of microwave energy to the antenna assembly due to ohmic heating.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of U.S. patent application Ser. No. 12/277,951, filed Nov. 25, 2008, now U.S. Pat. No. 8,292,880, which claims the benefit of, and priority to, U.S. Provisional Patent Application 60/990,350, filed Nov. 27, 2007, the entirety of each of which is hereby incorporated by reference herein for all purposes. 
    
    
     BACKGROUND 
     1. Technical Field 
     The invention relates generally to microwave antennas that may be used in therapeutic or ablative tissue treatment applications. More particularly, the invention relates to devices and methods for regulating, maintaining, and/or controlling a temperature of microwave antennas used in such 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, the antenna of a microwave probe of the monopole, dipole, or helical variety, as is conventional in the art, is typically advanced into the patient either laparoscopically or percutaneously until the target tissue is reached. 
     Following the introduction of the microwave probe, during the transmission of microwave energy to the target tissue, the outer surface of the antenna may sometimes reach unnecessarily high temperatures due to ohmic heating. When exposed to such temperatures, the treatment site, as well as the surrounding tissue, may be unnecessarily and unintentionally effected. The present disclosure contemplates curtailing such tissue effects by providing improved microwave tissue treatment devices, cooling systems, and methods. 
     To prevent such unnecessarily high temperatures, several different cooling methodologies are conventionally employed. 
     SUMMARY 
     A need exists in the art for an improved microwave tissue treatment device incorporating a cooling or temperature control system that minimizes unnecessarily high temperatures during tissue treatment. 
     The present disclosure is directed to a microwave tissue treatment device for the therapeutic treatment or ablation of tissue. In one embodiment, a microwave tissue treatment device is disclosed that includes an antenna assembly having an elongate member with proximal and distal ends that defines a longitudinal axis, outer and inner conductors disposed within the elongate member that extend along the longitudinal axis, a dielectric material interposed between the outer and inner conductors, and a sleeve at least partially disposed about a distal portion of the inner conductor and defining a cavity therearound, the cavity having a proximal end and a distal end. At least a portion of the inner conductor is deployable such that the antenna assembly may transition from a first position to a second position. The device also includes a cooling system associated with the antenna assembly that includes at least one inflow member and at least one outflow member, each of which is configured to circulate at least one fluid within the cavity such that at least a section of the inner conductor is in fluid contact therewith. 
     The cavity defined by the sleeve may include at least two regions, such as, for example, a proximal region, an intermediate region, and a distal region. In one embodiment, the microwave tissue treatment device includes at least one baffle member for defining at least two regions of the cavity. In another embodiment, the at least one baffle member defines at least two axial dimensions within the cavity. 
     In yet another embodiment, the microwave tissue treatment device cooling system includes first, second, and third inflow and outflow members, the first inflow and outflow members, the second inflow and outflow members, and the third inflow and outflow members being in fluid communication with a respective proximal, intermediate, and distal regions of the cavity defined by the sleeve. 
     The microwave tissue treatment device may include at least one temperature sensor operatively connected to the cavity, or a region thereof. 
     In another embodiment, the microwave tissue treatment device includes a first baffle member and a second baffle member disposed within the cavity. The first baffle member and the proximal end of the cavity define a proximal region of the cavity of the sleeve, the first baffle member and the second baffle member define an intermediate region of the cavity, and the second baffle member and the distal end of the cavity define a distal region of the cavity. The first baffle member is configured to substantially prevent the communication of fluid between the proximal and intermediate regions, while the second baffle member is configured to substantially prevent the communication of fluid between the intermediate region and the distal region. The first baffle member and the proximal end of the cavity define a first axial dimension, while the first baffle member and the second baffle member define a second axial dimension, and the second baffle member and the distal end of the cavity define a third axial dimension. In one embodiment, the first axial dimension is greater than the second axial dimension. 
     In another embodiment, the proximal region of the cavity has a first internal diameter, and the intermediate and distal regions have second and third internal diameters, respectively. In one embodiment, the first internal diameter is greater than the second internal diameter, and the second internal diameter is greater than the third internal diameter. 
     In one embodiment of the present disclosure, at least a portion of the inner conductor has a substantially arcuate profile when deployed, whereas in an alternate embodiment, at least a portion of the inner conductor has a substantially non-arcuate profile when deployed. In another embodiment, at least a portion of the inner conductor has a substantially tapered profile. 
     The fluid may be chosen from the group consisting of water, saline, ammonium chloride, sodium nitrate, and potassium chloride, and the fluid may be circulated with a pump. 
     According to another aspect of the present disclosure, an improved microwave tissue treatment device is disclosed that includes an antenna assembly having an outer conductor and an inner conductor with a dielectric material interposed therebetween, where at least a portion of the inner conductor is deployable. The device also includes a sleeve that is at least partially disposed about a distal portion of the inner conductor, thereby defining at least one cavity, at least one baffle member disposed within the sleeve such that at least two regions of the cavity is defined, and a cooling system. The cooling system includes at least one inflow member and at least one outflow member, each of which is in fluid communication with the cavity defined by the sleeve. 
     According to a further aspect of the present disclosure, a method of cooling a microwave antenna includes providing a cooling system including at least one inflow and outflow member, each being in fluid communication with at least a portion of the microwave antenna, and flowing a cooling fluid through the cooling system such that the cooling fluid is in fluid communication with at least a portion of the microwave antenna. 
     These and other features of the microwave tissue treatment device and method of use disclosed herein 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 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 perspective view of an antenna assembly of a microwave tissue treatment device, in accordance with an embodiment of the present disclosure, shown in a non-deployed condition; 
         FIG. 4  is a perspective view of the antenna assembly of  FIG. 3 , shown in a deployed, linear condition; 
         FIG. 5  is a perspective view of an antenna assembly of a microwave tissue treatment device, in accordance with an embodiment of the present disclosure, shown in a deployed, arcuate condition; 
         FIG. 6  is a perspective view of an antenna assembly of a microwave tissue treatment device, in accordance with another embodiment of the present disclosure, shown in a deployed condition; 
         FIG. 7  is a perspective view of an antenna assembly of a microwave tissue treatment device in accordance with another embodiment of the present disclosure, shown in a deployed condition; 
         FIG. 8  is a perspective view of an antenna assembly of a microwave tissue treatment, including a cooling system, according to one embodiment of the present disclosure; 
         FIG. 8A  is a perspective view of an antenna assembly of a microwave tissue treatment, including a cooling system, according to another embodiment of the present disclosure; 
         FIG. 8B  is a perspective view of an antenna assembly of a microwave tissue treatment device, including a cooling system, according to still another embodiment of the present disclosure; 
         FIG. 8C  is a perspective view of an antenna assembly of a microwave tissue treatment device, including a cooling system, according to yet another embodiment of the present disclosure; 
         FIG. 8D  is a front view of the antenna assembly of  FIG. 8C ; 
         FIG. 9  is a side, plan view of an antenna assembly of a microwave tissue treatment device in accordance with another embodiment of the present disclosure; 
         FIG. 10  is a side, plan view of an antenna assembly of a microwave tissue treatment device in accordance with yet another embodiment of the present disclosure; 
         FIG. 11  is a perspective view of an antenna assembly of a microwave tissue treatment device in accordance with another embodiment of the present disclosure, shown in a deployed condition; and 
         FIG. 12  is a side, plan view of an antenna assembly of a microwave tissue treatment device in accordance with another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     In the drawings and in the description that follows, the term “proximal”, as is traditional, will refer to the end of the apparatus that is closest to the clinician, while the term “distal” will refer to the end that is furthest from the clinician. 
     Referring now in detail to the figures, in which like references numerals identify similar or identical elements, there is illustrated, in  FIG. 1 , a microwave tissue treatment system  10  in accordance with the present disclosure. System  10  includes a microwave tissue treatment device  1000  having an antenna assembly  100  connected to a power source or supply  20 , e.g. a microwave or RF generator or any suitable power generating device suitable for energizing the tissue treatment device  1000 , through a feedline  30 . Microwave tissue treatment device  1000  may include a pump  40 , e.g. a peristaltic pump or the like, as a mechanism for circulating a cooling or heat dissipative fluid through device  1000 , as described below. Device  1000  may further include a pusher or deployment assembly  50  that includes a deployment knob  52 , where deployment knob  52  is operatively engaged with or coupled to the antenna assembly  100 , as described in further detail below. 
     Referring now to  FIGS. 1-2B , as indicated above, device  1000  is electrically connected to generator or power supply  20  by feedline  30 . Feedline  30  may be any suitable conductive pathway capable of transferring an electrical current to tissue treatment device  1000 . In one embodiment, as seen in  FIGS. 2A-2B , feedline  30  may be a coaxial cable composed of an inner conductor  102 , an outer conductor  104 , and a dielectric  106  interposed between inner and outer conductors  102 ,  104  to electrically separate and/or isolate inner and outer conductors  102 , 104  from one another. Inner and outer conductors  102 ,  104  may each be made of a suitable conductive material that may be semi-rigid or flexible, while dielectric  106  may include any number of suitable non-conductive materials such as ceramic and polytetrafluoroethylene (PTFE). Inner and outer conductors  102 ,  104  of feedline  30  may incorporate any suitable conductive material or metal, including, but not limited to, silver, copper and gold. In certain embodiments, inner and outer conductors  102 ,  104  of feedline  30  may include a conductive or non-conductive substrate plated or coated with a suitable conductive material. 
     Feedline  30  may range in length from about 1 foot (0.3048 m) to about 15 feet (4.572 m), or greater, if required in a particular application. As depicted in  FIG. 1 , feedline  30  has a proximal portion  108  operatively connected to, or connectable to, power supply  20  at proximal end  110 , and a distal portion  112  that forms a part of microwave tissue treatment device  1000 , as disclosed below. 
     Referring now to  FIGS. 1 ,  3  and  4 , microwave tissue treatment device  1000  includes an antenna assembly  100  having an elongate member  114  disposed about a distal portion  112  of feedline  30 , and a sleeve  116  that at least partially surrounds a distal portion  102   a  of the inner conductor, as described in further detail below. 
     Elongate member  114  has proximal and distal ends  118 ,  120  and defines longitudinal axis “A”. Elongate member  114  may be formed of any material suitable for electrically insulating a clinician or operator from the inner and outer conductors  102 ,  104  of feedline  30  disposed therein such that the antenna assembly  100  may be handled during use. 
     Elongate member  114  conceals a distal portion  102   a  ( FIG. 3 ) of the inner conductor  102  when the microwave tissue treatment device  1000  is not in use so as to prevent unintentional damage or injury, as well as the distal portion  112  of feedline  30 , which includes distal portions  102   a ,  104   a , and  106   a  of the inner conductor, the outer conductor, and the dielectric, respectively. Accordingly, the inner conductor, the outer conductor, and the dielectric are not only components of the feedline  30 , but also constitute components of antenna assembly  100 . 
     At least a portion of the inner conductor, i.e. distal portion  102   a , is deployable from distal portion  104   a  of the outer conductor, such that the antenna assembly  100  may transition from a first, non-deployed condition ( FIG. 3 ), to a second, deployed condition during use ( FIG. 4 ), as described in further detail below. In the first condition, the distal portion  102   a  of the inner conductor is at least partially disposed within the distal portion  104   a  of the outer conductor and the elongate member  114 . In the second, deployed condition, the distal portion  102   a  of the inner conductor extends at least partially beyond a distal end  120  of elongate member  114 , such that contact may be made with the target tissue (not shown). 
     Movement from the first position to the second position may be facilitated through the use of any suitable mechanism, such as, for example, a deployment assembly  50  ( FIG. 1 ). Reference may be made to commonly owned U.S. Patent Publication No. 2004/0267156, filed Apr. 4, 2004, for a detailed discussion regarding the components and functionality of deployment assembly  50 . 
     In one embodiment, as seen in  FIG. 4 , antenna assembly  100  includes a distal portion  102   a  of an inner conductor that exhibits a substantially non-arcuate profile when deployed. In an alternate embodiment, as seen in  FIG. 5 , antenna assembly  200  includes an inner conductor with a distal portion  202   a  that exhibits a substantially arcuate profile when deployed. Reference may be made to commonly owned U.S. Pat. No. 7,197,363 for a detailed discussion of the structure of arcuate microwave antenna configurations. 
     In another embodiment, as seen in  FIG. 6 , antenna assembly  300  includes a distal portion  302   a  of an inner conductor that is not entirely formed of a conductive material. In this embodiment, distal portion  302   a  of the inner conductor includes a radiating member  324  with one or more conductive surfaces  326 . Conductive surface or surfaces  326  may have a particular pattern or distribution for focusing or dispersing the energy transmitted into distal portion  302   a  of the inner conductor. For example, radiating member  324  may have a conductive surface  326  on only one side or in one particular area or region thereof. 
     Referring back to  FIGS. 3 and 4 , sleeve  116  is disposed about distal portion  102   a  of the inner conductor in such a manner so as to define a cavity  128 . Sleeve  116  may be fixedly, releasably, or slidably connected to distal portion  102   a  in any suitable manner including, but not being limited to, welding or adhering, as would be appreciated by one skilled in the art. Sleeve  116  has proximal and distal ends  130 ,  132  defined by the points at which sleeve  116  is connected to distal portion  102   a . In one embodiment, as best seen in  FIG. 4 , the distal-most tip  134  of distal portion  102   a  extends beyond the distal end  132  of sleeve  116 . In another embodiment, however, as best seen in  FIG. 7 , antenna assembly  400  may include a sleeve  416  connected to a distal portion  402   a  of an inner conductor at the distal-most tip  434  thereof, or at a point therebeyond (not shown). 
     Referring again to  FIGS. 3 and 4 , proximal end  130  of sleeve  116  may be located at any suitable location along the length of distal portion  102   a  of the inner conductor, dependent upon the desired volume of cavity  128 . Although depicted as substantially incisive, the present disclosure contemplates that distal-most tip  134  may be substantially arcuate, duckbilled, or any other such configuration suitable for facilitating the entry of the microwave tissue treatment device into the tissue of a patient. 
     Sleeve  116  may be formed of any suitable biocompatible, impermeable material capable of retaining fluid therein, including and not limited to PTFE and tetrafluorethylene-perfluorpropylene (FEP). The present disclosure contemplates that sleeve  116  may be either substantially rigid, or substantially non-rigid in character. 
     In one embodiment, as seen in  FIG. 8 , antenna assembly  500  includes a sleeve  516  defining a cavity  528  around a distal portion  502   a  of an inner conductor, and one or more baffle member(s)  542 ,  544  disposed within sleeve  516  that function to divide or compartmentalize cavity  528  into individual regions  536 ,  538 ,  540 . Each region  536 ,  538 ,  540  defines a respective section  546 ,  548 ,  550  of the distal portion  502   a  of the inner conductor. In an alternate embodiment, as seen in  FIG. 8A , the individual regions  536 ,  538 ,  540  are not defined by physical baffle members  542 ,  544  ( FIG. 8 ), but are rather defined constructively as virtual baffle members  542   A ,  544   A  by the interaction of a corresponding number of fluids, e.g. one fluid within each of individual regions  536 ,  583 ,  540 , which may be immiscible. The incorporation of one or more fluids into antenna assembly  500  will be discussed in further detail below. 
     First or proximal region  536  and first section  546  of distal portion  502   a  have a first axial dimension L 1 , and are defined by the location of the proximal end (not shown) of the sleeve  516  and the location of first baffle member  542 . Second or intermediate region  538  and second section  548  of distal portion  502   a  have a second axial dimension L 2 , and are defined by the location of first baffle member  542  and the location of second baffle member  544 . And third or distal region  540  and third section  550  of distal portion  502   a  have a corresponding third axial dimension L 3 , and are defined by the location of second baffle member  544  and the location of distal end  532  of sleeve  516 . 
     In this embodiment, first and second baffle members  542 ,  544 , respectively, serve not only to define the metes of the three regions  536 ,  538 ,  540  of cavity  528  of sleeve  516 , in conjunction with the proximal end  528  (not shown) and the distal end  530  thereof, but also serve to substantially prevent any co-mingling of cooling fluid or fluids that may be circulated throughout each of the proximal, intermediate, and distal regions  536 ,  538 ,  540 , as described below. The present disclosure contemplates that cavity  528  of sleeve  516  may be divided into any suitable number of regions dependent upon the requirements of the procedure and the application in which the microwave tissue treatment device may be employed. 
     With continued reference to  FIG. 8 , third or distal section  550  of the distal portion  502   a  of the inner conductor may comprise the area of active heating during tissue treatment or ablation. It may be desirable, therefore, to prevent the temperature in distal section  550  from reaching excessively high temperatures in order to maintain optimal energy delivery and to maintain optimal thermal therapy of the tissue. Second or intermediate section  548  of distal portion  502   a  may also become hot due to ohmic and conductive heating from distal section  550 . Since intermediate section  548  may be in contact with the tissue surrounding the target site, it may be desirable to allow intermediate section  548  to achieve a particular temperature profile dependent upon the procedure in which the antenna assembly  500  is employed. 
     As an illustrative example, where coagulation of the insertion tract may be desirable, the clinician may want to allow intermediate section  548  of distal portion  502   a  of the inner conductor to attain a particular predetermined temperature capable of creating a coagulating effect in the insertion tract. In other applications, it may also be desirable, however, to prevent the temperature in intermediate section  548  from rising beyond a particular threshold to protect surrounding sensitive tissue structures from undesired effects. During use, first or proximal section  546  of distal portion  502   a  may also come into contact with the skin of a patient. Accordingly, since proximal section  546  of distal portion  502   a  may also be subject to ohmic and/or conductive heating, it may therefore be desirable to maintain the temperature of this section below a specific temperature, particularly in percutaneous or laparoscopic procedures, to prevent undesired effects upon the skin surface of the patient. In other procedures, such as in applications where lesions are located deep within the tissue, it may be desirable to allow the proximal section  546  to become heated to allow for the coagulation of the insertion tract. 
     With continued reference to  FIG. 8 , antenna assembly  500  further includes a cooling system  552  for regulating the temperature of distal portion  502   a  of the inner conductor. The cooling system  552  operates in conjunction with, and is fluidly connected to, cavity  528  of sleeve  516  such that one or more cooling or heat dissipative fluids “F” may be circulated therethrough. Fluid “F” serves to dissipate some of the heat generated by the antenna assembly  500  during use and may also act as a medium that modifies the dielectric constant of the distal portion of the antenna assembly. Potential dissipative fluids include, but are not limited to, water, saline, liquid chlorodifluoromethane, or any suitable perfluorocarbon fluid, such as Fluorinert®, distributed commercially by Minnesota Mining and Manufacturing Company (3M™), St. Paul, Minn., USA. The fluid circulated through cooling system  552  may vary depending upon the desired cooling rate and the desired tissue impedance matching properties. In various embodiments, gases, such as air, nitrous oxide, nitrogen, carbon dioxide, etc., may also be utilized as the dissipative fluid. In yet another variation, a combination of liquids and/or gases may be utilized. 
     During circulation, the heat dissipative fluid is in contact with those sections  546 ,  548 ,  550  of distal portion  502   a  of the inner conductor within respective regions  536 ,  538 ,  540  of cavity  528  defined by sleeve  516  such that the heat generated therein may be dissipated through the fluid “F”. The cooling system  552  includes one or more inflow tubes  554 ,  556 ,  558 , and one or more respective outflow tubes  560 ,  562 ,  564  to circulate the dissipative fluid “F”. Cooling system  552  may also include at least one pump  40  ( FIG. 1 ) in fluid communication with each inflow tube  554 ,  556 ,  558  and each outflow tube  560 ,  562 ,  564  for facilitating the circulation of the dissipative fluid “F”. 
     Cooling system  552  may include any number of inflow and outflow tubes suitable for circulating a dissipative fluid throughout the cavity  528  defined by sleeve  516 , anti/or any individual regions thereof. Cooling system  552  may also employ any number of inflow and outflow members in fluid communication with each section  546 ,  548 ,  550  of distal portion  502   a  of the inner conductor. In some embodiments, one or more regions of cavity  528  may not be in fluid communication with cooling system  552 . 
     As seen in  FIG. 8 , each of the proximal, intermediate, and distal regions  536 ,  538 ,  540 , respectively, has a corresponding inflow tube  554 ,  556 , and  558  in fluid communication therewith, and a corresponding outflow tube  560 ,  562 , and  564  in fluid communication therewith. In particular, a proximal end (not shown) of first inflow tube  554  may be connected to pump  40  ( FIG. 1 ), while a distal end  566  of first inflow tube  554  is in fluid communication with proximal region  536 , thereby allowing dissipative fluid to flow, either constantly or intermittently, into the proximal region  536  of cavity  528  defined by sleeve  516 . Upon entering proximal region  536 , the dissipative fluid “F” comes into direct contact with the proximal section  546  of distal portion  502   a  of the inner conductor, allowing for the direct convective cooling of proximal section  546 . In conjunction with first inflow tube  554 , a proximal end (not shown) of first outflow tube  560  may be connected to pump  40  ( FIG. 1 ), while a distal end  572  of first outflow tube is in fluid communication with proximal region  536 , thereby allowing the dissipative fluid “F” to flow, either constantly or intermittently, out of the proximal region  536 , and return to the pump  40  ( FIG. 1 ). In so doing, during operation, heat generated by proximal section  546  of distal portion  502   a  of the inner conductor, disposed within the proximal region  536  of the cavity  528  defined by sleeve  516 , may be regulated and/or dissipated. 
     As with the proximal region  536 , a dissipative fluid may be pumped into and out of intermediate region  538  through respective distal ends  568 ,  574  of the second inflow and outflow tubes  556 ,  562  thereby dissipating the heat generated by the intermediate section  548  of distal portion  502   a  of the inner conductor through the fluid circulated therein. 
     Likewise, a dissipative fluid may also be circulated into and out of the distal region  540  through respective distal ends  570 ,  576  of the third inflow and outflow tubes  558 ,  564  thereby dissipating the heat generated by the distal section  550  of distal portion  502   a  of the inner conductor through the fluid circulated therein. In some embodiments, the fluid may act as a medium that modifies the dielectric constant of the antenna. 
     With continuing reference to  FIG. 8 , inflow tubes  554 ,  556 ,  558  may enter cavity  528  through apertures (not shown) at the proximal end of sleeve  516  (not shown). First inflow tube  554  and first outflow tube  560  are configured such that their respective distal ends  568 ,  580  are in fluid communication with proximal region  536 . Second and third inflow tubes  556 ,  558  and second and third outflow tubes  562 ,  564  may continue through proximal region  536 , through apertures  590  in first baffle member  542 , and into intermediate region  538 . Second inflow tube  556  and second outflow tube  562  are configured such that their respective distal ends  572 ,  584  are in fluid communication with intermediate region  538 . Third inflow and outflow tubes  558 ,  564  continue through intermediate region  538 , through apertures  590  in second baffle member  544 , and into distal region  540 . Third inflow and outflow tubes  558 ,  564  are configured such that their respective distal ends  576 ,  588  are in fluid communication with distal region  540 . 
     In this embodiment, each of the proximal end of the cavity  528 , the first baffle member  542 , and the second baffle member  544  include seal members  592  associated with apertures  590 . Seal members  592  may be any member suitable to substantially prevent the escape of any fluid contained within respective regions of cavity  528 , through the apertures  590 , including, and not limited to a seal, gasket, or the like. Seal members  592  may be formed of any suitable material, including and not limited to, a polymeric material. Seal members  592  may also substantially prevent the intermingling of the cooling fluids circulated through each of the proximal, intermediate, and distal regions  536 ,  538 ,  540  of cavity  528 . 
     Referring momentarily to  FIG. 8B , antenna assembly  600  includes a cooling system  652  having inflow tubes  654 ,  656 ,  658  and outflow tubes  660 ,  662 ,  664 . In this embodiment, inflow tubes  654 ,  656 ,  658  and outflow tubes  660 ,  662 ,  664  enter cavity  628  defined by sleeve  616  through apertures  690  formed therein. In this embodiment, inflow tubes  654 ,  656 ,  658  may traverse elongate member  614  along its outer surface, connecting to either a common pump  40  ( FIG. 1 ), or to individual pumps, as described above. Correspondingly, outflow tubes  660 ,  662 ,  664  may also traverse the outer surface of elongate member  116 , connecting to either the common pump  40  ( FIG. 1 ) or to the individual pumps. In this embodiment, sleeve  616  is adapted with sealing member or members  692  at apertures  690  to substantially prevent the escape of any fluid contained in cavity  628  defined by sleeve  616  through apertures  690 . 
     In another embodiment, as seen in  FIGS. 8C-8D , antenna assembly  600  may include one or more channels  694  formed in the elongate member  614  that are configured to respectively receive at least a portion of inflow tubes  654 ,  656 ,  658  and outflow tubes  660 ,  662 ,  664 . Alternatively, channels  694  may be formed in outer conductor  604 , dielectric material  606 , or in any other suitable location. 
     Referring again to  FIG. 8 , given the desirability of controlled heating and temperature regulation within the individual sections  546 ,  548 , and  550  of distal portion  502   a  of the inner conductor and the corresponding regions  536 ,  538 , and  540  of the cavity  528 , the axial locations of first and second baffle members  542 ,  544  within cavity  528  may be varied as desired or necessary. By varying the location of baffle members  542  and  544  in different embodiments, the axial length of the proximal, intermediate and distal regions  536 ,  538 , and  540  may be varied. In varying the axial length of a region, the overall volume of that region may be varied, and accordingly, the volume of dissipative fluid circulated within that region may also be varied. As would be appreciated by one of ordinary skill in the art, an inverse relationship exists between the volume of dissipative fluid within a particular region of the cavity  528  and the temperature of that region, in that as the volume of fluid is increased, the temperature of the region will decrease. As an additional means of regulating temperature, the flow rate of fluid “F” into each regions  536 ,  538 , and  540  of the cavity  528  may be controlled or varied, e.g. through the use of multiple pumps (not shown). 
     The baffle members  542 ,  544  may be located at any suitable or desired point within the cavity  528  defined by the sleeve  516 . In one embodiment, baffle members  542 ,  544  are positioned such that the first, second and third axial dimensions, L 1 , L 2 , and L 3 , respectively, of proximal, intermediate, and distal regions  536 ,  538 ,  540  are substantially equivalent. In another embodiment, baffle members  542 ,  544  are positioned such that the first axial dimension L 1 , of proximal region  536 , is greater than the second and third axial dimensions L 2  and L 3 , respectively, of intermediate and distal regions  538 ,  540 . In yet another embodiment, baffle members  542 ,  544  are positioned such that the third axial dimension L 3 , of distal region  540 , is greater than the first and second axial dimensions L 1  and L 2 , respectively, of proximal and intermediate regions  536 ,  538 . In alternate embodiments, the present disclosure contemplates locating the baffle members  542 ,  544  such that the overall volume of the cavity  528  may be distributed amongst any individual regions thereof in any suitable manner. 
     Referring now to  FIGS. 9 and 12 , in other embodiments, antenna assembly  700  includes a sleeve  716  that defines a cavity  728  having proximal, intermediate, and distal regions  736 ,  738 , and  740  defined by first and second baffle members  742 ,  744 . In this embodiment, proximal, intermediate, and distal regions  736 ,  738 , and  740  have a first, a second, and a third radial dimension or diameter D 1 , D 2 , and D 3 , respectively. In accordance with the present disclosure, radial dimensions D 1 , D 2 , and D 3  of the proximal, intermediate, and distal regions  736 ,  738 , and  740  may be varied so as to control the volume of each region, and accordingly, the volume of dissipative fluid circulated therethrough. By varying the volume of dissipative fluid circulated through each individual region  736 ,  738 , and  740  of the cavity  728 , the temperature of each region may be substantially regulated, as discussed above. 
     In one embodiment, the first, second and third radial dimensions, D 1 , D 2 , and D 3 , respectively, are substantially equivalent. In another embodiment, as illustrated in  FIG. 9 , the first radial dimension D 1 , of proximal region  736 , is greater than the radial dimensions D 2  and D 3 , respectively, of intermediate and distal regions  738  and  740 . In yet another embodiment, as illustrated in  FIG. 12 , the third radial dimension D 3 , of distal region  740 , is greater than the radial dimensions D 1  and D 2 , respectively, of proximal and intermediate regions  736  and  738 . In alternate embodiments, the present disclosure contemplates that the radial dimensions D 1 , D 2 , and D 3 , respectively, of each region  736 ,  738 , and  740  of the cavity  728  defined by the sleeve  716 , may be varied in any suitable manner. 
     Referring now to  FIG. 10 , in one embodiment, the present disclosure contemplates an antenna assembly  800  that includes a sleeve  816  defining a cavity  828  with a radial dimension D. In this embodiment, radial dimension D of cavity  828  is varied in a continuously decreasing manner over the axial length thereof, such that a generally tapered profile is exhibited. While the antenna assembly  800  includes a sleeve  816  defining a cavity  828  that is not compartmentalized into any regions, the tapered profile may be applicable to any of the embodiments disclosed herein above. 
     In another embodiment, seen in  FIG. 11 , an antenna assembly  900  is disclosed that includes one or more temperature sensors  994  coupled to a distal portion  902   a  of an inner conductor for monitoring a temperature fluctuation at or about the distal portion  902   a . It may be desirable to monitor the temperature of the distal portion  902   a , and/or the tissue that may come into contact therewith, or with sleeve  916 , in an effort to guard against overheating and/or the 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 alternate embodiments, temperature sensors  994  may be coupled or otherwise incorporated into antenna assembly  900  at any suitable location, including, but not being limited to sleeve  916 , such that the temperature of the distal portion  902   a  of the inner conductor and/or the cavity  928  may be monitored. In various embodiments, temperature sensor or sensors  994  may be located on the sleeve  916 , e.g., on an external surface thereof, or within the sleeve  916 , e.g., within the cavity  928  which the sleeve  916  defines, using any suitable means, e.g. adhesives. The temperature sensor or sensors  994  may be located on a baffle member or members  942 ,  944 , if any. Temperature sensors  994  may be configured for electrical connection to power source  20  ( FIG. 1 ). 
     The temperature sensor or sensors  994  may be a semiconductor-based sensor, a thermister, a thermocouple or other temperature sensor that would be considered as suitable by one skilled in the art. An independent temperature monitor (not shown) may be coupled to the temperature sensor. Alternatively, a power supply with an integrated temperature monitoring circuit (not shown), such as one described in U.S. Pat. No. 5,954,719, may be used to modulate microwave power output supplied to the antenna assembly. Other physiological signals, e.g. EKG, may also be monitored by other medical instrumentation well known to one skilled in the art and such data applied to control the microwave energy delivered to the antenna assembly. 
     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 the temperature sensor or sensors  994 . 
     Although the illustrative embodiments of the present disclosure have been described herein with reference to the accompanying drawings, the above description, disclosure, and figures should not be construed as limiting, but merely as exemplifications of particular embodiments. It is to be understood, therefore, that the disclosure is not limited to those precise embodiments, 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.