Abstract:
A method of performing an ablation procedure includes the steps of inserting an antenna assembly into tissue and supplying energy thereto 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, 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:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation application of U.S. patent application Ser. No. 12/787,639, filed on May 26, 2010, the entire contents of which are incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    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. 
         [0004]    2. Background of Related Art 
         [0005]    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. 
         [0006]    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. 
         [0007]    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. 
         [0008]    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. 
         [0009]    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 
       [0010]    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. 
         [0011]    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. 
         [0012]    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 
         [0013]    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: 
           [0014]      FIG. 1  is a schematic diagram of the microwave ablation system according to an embodiment of the present disclosure; 
           [0015]      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; 
           [0016]      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; 
           [0017]      FIG. 3C  is a perspective view of a component detailing operation of the microwave antenna assembly of either  FIGS. 3A and 3B ; and 
           [0018]      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 
       [0019]    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. 
         [0020]    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. 
         [0021]    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.). 
         [0022]    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. 
         [0023]      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. 
         [0024]    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. 
         [0025]      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  nun 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. 
         [0026]    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. 
         [0027]    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. 
         [0028]      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. 
         [0029]    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 . 
         [0030]    Referring specifically now to  FIG. 3A , one embodiment of the present disclosure is shown and includes separation members  91   a,    91   b  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  89   a  and  89   b.  Sub-chambers  89   a  and  89   b  are configured to retain first and second chemicals “A” and “B”, respectively, therein. Separation members  91   a,    91   b  are configured to hold chemicals “A” and “B” within sub-chambers  89   a  and  89   b,  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. 
         [0031]    In one embodiment, separation members  91   a,    91   b  may be slidable or movable, as discussed in further detail below with reference to  FIG. 3C . In another embodiment, separation members  91   a,    91   b  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  91   a,    91   b  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. 
         [0032]    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 (SOCl 2 ) 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 (CaCl 2 ), alkalis with acids, acids with bases, etc. 
         [0033]    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  189   a  and  189   b.  Separation member  191  is substantially as described above with respect to separation members  91   a,    91   b  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  91   a,    91   b  described above with respect to  FIG. 3A , sub-chambers  189   a  and  189   b  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. 
         [0034]    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  89   a  and  89   b  throughout the following description may be substituted with reference to separation members  91   a,    91   b  and sub-chambers  89   a,    89   b,  respectively. 
         [0035]    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  189   a  and  189   b,  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  95   a  and  95   b  that each include a plurality of apertures  93 . As illustrated by  FIG. 3C , separation member  191  may be actuated such that interfacing surfaces  95   a  and  95   b  move relative to each other or, alternatively, such that one surface (e.g.,  95   a ) moves relative to a stationary surface (e.g.,  95   b ). In either scenario, movement of surface  95   a  and/or surface  95   b  operates to bring apertures  93  of both surfaces  95   a,    95   b  into and out of aligmnent with each other. That is, when apertures  93  of surface  95   a  are brought into substantial alignment with corresponding apertures  93  of surface  95   b,  sub-chambers  189   a  and  189   b  are in communication via apertures  93  such that contact between chemicals “A” and “B” is facilitated, Likewise, when apertures  93  of surface  95   a  are brought out of substantial alignment with apertures  93  of surface  95   b,  communication between sub-chambers  189   a  and  189   b  is prevented. 
         [0036]    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  91   a,    91   b  or separation member  191 . 
         [0037]    Referring to  FIGS. 3A and 3B , the depiction of sub-chambers  89   a,    89   b  and  189   a,    189   b  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 . 
         [0038]    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  295   a  configured to hold chemical “A” and an inner sub-chamber  295   b  configured to hold chemical “B”. Outer sub-chamber  295   a  surrounds inner sub-chamber  295   b  and is separated therefrom at least partially by a breakable membrane  293  (e.g., a shared surface between outer sub-chamber  295   a  and inner sub-chamber  295   b ). Upon insertion of antenna assembly  12  into tissue “T”, as illustrated in  FIG. 4 , outer sub-chamber  295   a  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  295   a  conforms to the surface of tissue “T” (e.g., the patient&#39;s skin, a target organ, etc.). 
         [0039]    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  295   a  and  295   b  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  295   a  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. 
         [0040]    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. 
         [0041]    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.