Abstract:
An ablation system for directing energy to a target volume of tissue is provided. The ablation system comprises an ablation antenna probe including at least one radiating portion configured to output electromagnetic radiation and at least one electromagnetic shielding reflector configured for removable positioning on the antenna probe. The at least one electromagnetic shielding reflector is configured to block electromagnetic radiation from the at least one radiating portion through the at least one electromagnetic shielding reflector such that a particular directionality of the electromagnetic radiation from the at least one radiation portion to a target volume of tissue is achieved.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to surgical devices for treating tissue. More particularly, the present disclosure relates to ablation antennas including customizable reflectors to facilitate the selective ablation of tissue. 
         [0003]    2. Discussion of Related Art 
         [0004]    Treatment of certain diseases requires the destruction of malignant tissue growths, e.g., tumors. Electromagnetic radiation can be used to heat and destroy tumor cells. Treatment may involve inserting ablation probes into or adjacent tissues where cancerous tumors have been identified. Once the probes are positioned, electromagnetic energy is passed through the probes into surrounding tissue to treat, e.g., heat, ablate and/or coagulate tissue. Microwave energy is sometimes utilized to perform these methods. 
         [0005]    Typically, microwave apparatus for use in ablation procedures include a microwave generator that functions as an energy source, and a microwave surgical instrument (e.g., microwave ablation probe) having an antenna assembly for supplying the energy to the target tissue. There are several types of microwave antenna assemblies, e.g., monopole, dipole and helical, which may be used in tissue ablation applications. In monopole and dipole antenna assemblies, microwave energy generally radiates perpendicularly away from the axis of the conductor. Monopole antenna assemblies typically include a single, elongated conductor. A typical dipole antenna assembly includes two elongated conductors, which are linearly aligned and positioned end-to-end relative to one another with an electrical insulator placed therebetween. Helical antenna assemblies include a helically-shaped conductor connected to a ground plane. Helical antenna assemblies can operate in a number of modes including normal mode (broadside), in which the field radiated by the helix is maximum in a perpendicular plane to the helix axis, and axial mode (end fire), in which maximum radiation is along the helix axis. 
         [0006]    Some ablation targeted lesions are too small or too hard to be punctured by an ablation probe. In these cases, doctors may place the probe as close as possible to the lesion and perform an ablation. With non-directional ablation probes, the ablation may radiate to both sides of the probe, which may damage healthy tissue located on the non-tumor side of the radiating section. During certain procedures, it can be difficult to assess the extent to which the microwave energy will radiate into the surrounding tissue, making it difficult to determine the area or volume of surrounding tissue that will be ablated. Directional ablation probes have been developed that target specific areas of tissue. These devices work simply by orienting the antenna towards the target tissue and away from critical tissue structures that should not be damaged. Typically, directional ablation probes will only emit radiation from specified areas of the antenna, such as windows, slots, or junctions. 
         [0007]    However, directional ablation probes are often more expensive than their non-directional counterparts. Exacerbating the cost, directional ablation probes are used infrequently due to the limited number of procedures that require them. Current directional ablation probes may be designed for a specific procedure, and may have limited versatility. Often, in a surgical procedure requiring tissue ablation, a surgeon may need precision targeting for only part of the procedure. Once the part of the procedure where precision targeting is required is completed, the surgeon must then switch between the directional ablation probe to a non-directional ablation probe when precision targeting is neither required nor sufficient for the remainder of the procedure. The surgeon then is required to retool, or use multiple ablation probes for the same patient, which can be cumbersome, inefficient, and time consuming. There exists a need for achieving cost-effective directional tissue ablation without having to retool or use cumbersome directional ablation probes. 
       SUMMARY 
       [0008]    As can be appreciated, an ablation system for directing energy to a target volume of tissue may prove useful in the surgical arena. 
         [0009]    An aspect of the present disclosure provides an ablation antenna probe including at least one radiating portion configured to output electromagnetic radiation. At least one electromagnetic shielding reflector may be configured for removable positioning on the antenna probe and may be configured to block electromagnetic radiation from the at least one radiating portion through the electromagnetic shielding reflector such that a particular directionality of the electromagnetic radiation from the radiating portion to a target volume of tissue is achieved. 
         [0010]    The electromagnetic shielding reflector may include an electromagnetic shielding material wherein an adhesive adhered to a bottom surface of the electromagnetic shielding material. The electromagnetic shielding reflector may further include a release liner releasably attached to the adhesive. The adhesive may be pressure sensitive. 
         [0011]    The electromagnetic shielding material may comprise is selected from the group consisting of silver, copper, gold, aluminum, brass, bronze, tin, lead, nickel, stainless steel, electrically conductive polymer, mumetal, and superpermalloy. The electromagnetic shielding material may also be a composite material. The electromagnetic shielding reflector has a configuration selected from the group consisting of a strip of material, a sheet, a foil, a mesh, a tape, and a coating. 
         [0012]    According to another aspect of the present disclosure, the electromagnetic shielding reflector is configured as a tube and configured for fitted placement over at least a portion of the ablation antenna probe. The tube may be a heatshrink tube. Additionally, an adhesive may be disposed on the inner surface of the tube. 
         [0013]    The tube may define at least one window configured to permit passage of electromagnetic radiation therethrough. Further, a removable screen may be configured to cover the at least one window to thereby inhibit electromagnetic radiation therethrough. 
         [0014]    According to another aspect of the present disclosure, the electromagnetic shielding reflector may be a cap configured for positioning about a distal tip of the ablation antenna probe. 
         [0015]    According to yet another aspect of the present disclosure, a kit for use with an ablation device may be provided, comprising a plurality of electromagnetic shielding reflectors. Each electromagnetic shielding reflector may be configured for placement on an ablation antenna probe, wherein each electromagnetic shielding reflector is configured to block electromagnetic radiation from at least one radiating portion of the antenna probe through each electromagnetic shielding reflector such that a particular directionality of the electromagnetic radiation from the at least one radiation portion to a target volume of tissue is achieved. At least two of the plurality of electromagnetic shielding reflectors may define different configurations so as to provide different directionality. 
         [0016]    At least one of the electromagnetic shielding reflectors may include an electromagnetically shielding material, an adhesive adhered to a bottom surface of the electromagnetically shielding material, and a release liner releasably attached to the adhesive. In addition, at least one of the electromagnetic shielding reflectors includes a tube configured for fitted placement over at least a portion of the ablation antenna probe. The kit may further include a cap configured for placement over a distal tip of the ablation antenna probe. 
         [0017]    According to yet another aspect of the present disclosure, a method of directing radiation to a target volume of tissue is provided. The method may comprise providing an ablation antenna probe including a radiating portion configured to output electromagnetic radiation, placing at least one electromagnetic shielding reflector on the ablation antenna probe to achieve a particular directionality of electromagnetic radiation emission, and activating the ablation antenna probe to emit electromagnetic radiation according to the particular directionality of electromagnetic radiation emission defined by the at least one electromagnetic shielding reflector. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    Objects and features of the present disclosure will become apparent to those of ordinary skill in the art when descriptions of various embodiments thereof are read with reference to the accompanying drawings, of which: 
           [0019]      FIG. 1  is a side view of a microwave ablation system provided in accordance with the present disclosure; 
           [0020]      FIG. 2  is a longitudinal, cross-sectional view of a microwave antenna probe of the microwave ablation system of  FIG. 1 ; 
           [0021]      FIG. 3  is an enlarged view of the area of detail indicated as “ 3 ” in  FIG. 2 ; 
           [0022]      FIG. 4  is an enlarged view of the area of detail indicated as “ 4 ” in  FIG. 2 ; 
           [0023]      FIG. 5  is a longitudinal, cross-sectional view of an outer jacket and trocar assembly of the microwave antenna probe of  FIG. 2 ; 
           [0024]      FIG. 6  is a side view of an antenna assembly of the microwave antenna probe of  FIG. 2 ; 
           [0025]      FIG. 7  is an enlarged view of the area of detail indicated as “ 7 ” in  FIG. 6 ; 
           [0026]      FIG. 8  is a perspective view of a portion of a reflector strip for a microwave antenna probe provided in accordance with the present disclosure; 
           [0027]      FIG. 9  is a perspective view of a reflector strip adhered to an antenna probe; 
           [0028]      FIG. 10  is a transverse, cross-sectional view taken across section line “ 10 - 10 ” of  FIG. 9 , illustrating a radiation pattern emitted from the antenna probe; 
           [0029]      FIG. 11  is a transverse, cross-sectional view of another reflector strip adhered to the antenna probe of  FIG. 10 , illustrating a radiation pattern emitted therefrom; 
           [0030]      FIG. 12  is a transverse, cross-sectional view of yet another reflector strip adhered to the antenna probe of  FIG. 10 , illustrating a radiation pattern emitted therefrom; 
           [0031]      FIG. 13  is a transverse, cross-sectional view of still another reflector strip adhered to the antenna probe of  FIG. 10 , illustrating a radiation pattern emitted therefrom; 
           [0032]      FIG. 14  is a perspective view of a reflector tube for a microwave antenna probe provided in accordance with the present disclosure; 
           [0033]      FIG. 15  is a perspective view of another reflector tube for a microwave antenna probe provided in accordance with the present disclosure; 
           [0034]      FIG. 16  is a perspective view of a reflector tube adhered to an antenna probe; 
           [0035]      FIG. 17  is a transverse, cross-sectional view taken across section line “ 17 - 17 ” of  FIG. 16 , illustrating a radiation pattern emitted from the antenna probe; and 
           [0036]      FIG. 18  is a perspective view of a reflector cap for a microwave antenna probe provided in accordance with the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0037]    It has been found that non-directional ablation antennas can be made directional by placing metalized reflectors directly onto the radiating section of the antenna, e.g., using adhesives. The metalized reflector acts as an electromagnetic shield and blocks the radiation of energy through the section of the antenna upon which the reflector is disposed. Thus, a desired directionality can be achieved by selectively covering section(s) of the antenna with reflector(s) such that energy will radiate only in the direction(s) of the section(s) of the antenna that are left uncovered. 
         [0038]    Turning now to  FIGS. 1-7 , a microwave ablation system is shown generally identified by reference numeral  10 . It should be appreciated the present disclosure may be used with any suitable microwave ablation system and is not to be limited to the system disclosed herein, which is shown for illustrative purposes. Microwave ablation system  10  includes a microwave antenna probe  12  configured to couple to a microwave generator (not shown) via a flexible coaxial cable  16 . Although the present disclosure is shown and described with reference to microwave antenna probes, the present disclosure is equally applicable for use in any suitable energy-based surgical instrument. 
         [0039]    With continued reference to  FIGS. 1-7 , microwave antenna probe  12  generally includes an antenna assembly  20 , an outer jacket and trocar assembly  70 , and a connection hub  80 . Antenna assembly  20  defines a longitudinal axis “X-X” and includes a radiating section that defines a dipole configuration, e.g., the radiating section includes a feed gap  43  and proximal and distal radiating portions  42 ,  44 . A feedline  30  extends proximally from the radiating section into connection hub  80 , ultimately coupling to cable  16  via transition  60  to connect antenna assembly  20  to the generator (not shown) for supplying energy thereto. Feedline  30  defines a coaxial configuration having an inner conductor  32  surrounded by an insulator  34 . Insulator  34 , in turn, is surrounded by an outer conductor  36 , thus defining the coaxial configuration of feedline  30 . Feedline  30  may be formed from a semi-rigid or flexible coaxial cable, although other configurations are also contemplated. 
         [0040]    As mentioned above, and with reference to  FIGS. 2, 4, and 6-7 , the radiating section of antenna assembly  20  includes feed gap  43 , proximal radiating portion  42 , and distal radiating portion  44 . Feed gap  43  is defined by the portion of inner conductor  32  and insulator  34  of feedline  30  that extends distally from outer conductor  36 , e.g., outer conductor  36  may be stripped from the distal end of coaxial feedline  30  to define feed gap  43 . Proximal radiating portion  42  is defined by the portion of feedline  30  disposed between the proximal end of feed gap  43  and the distal end of the choke  50 . Distal radiating portion  44  is attached to feed gap  43  via any suitable process and extends distally therefrom. For example, as shown in  FIG. 7 , distal radiating portion  44  may be soldered to inner conductor  32  of feed gap  43  to establish electromechanical contact therebetween. 
         [0041]    Antenna assembly  20 , as shown in  FIGS. 2, 4, and 6-7 , further includes a choke or balun  50  disposed about feedline  30 . Choke  50  includes an inner dielectric layer and an outer conductive layer. Choke  50  may be a quarter-wavelength shorted choke that is shorted to outer conductor  36  of feedline  30  at the proximal end of choke  50 , although other configurations are contemplated. The dielectric layer of choke  50  may also be configured to extend distally beyond the conductor layer thereof towards the distal end of antenna assembly  20 . Choke  50  is used to prevent the back travel of radiation through antenna assembly  20 , and confines the radiation to the radiation portions  42 ,  44  of antenna assembly  20 . 
         [0042]    With additional reference to  FIG. 3 , as mentioned above, antenna assembly  20  includes a transition  60  from which feedline  30  extends. Feedline  30  extends into transition  60 , wherein inner conductor  32  is coupled to an inner conductor (not explicitly shown) of coaxial cable  16  and outer conductor  36  is coupled to an outer conductor (not explicitly shown) of coaxial cable  16 , while maintaining the spacing therebetween via an insulator (not explicitly shown). Cable  16  may be secured to feedline  30  within transition  60  via soldering, laser welding, or any other suitable process for establishing electromechanical contact therebetween. Transition  60  is disposed within proximal port  83  of connection hub  80  and is sealingly engaged therein via O-ring  62 . More specifically, during assembly, the radiating section and feedline  30  of antenna assembly  20  are inserted through proximal port  83  and lumen  82  of connection hub  80  such that transition  60  may ultimately be inserted into proximal port  83  of connection hub  80  to sealingly engage transition  60  within proximal port  83  of connection hub  80  via O-ring  62 . Antenna assembly  20  may be engaged within connection hub  80  during manufacturing, or may be assembled by the user. 
         [0043]    Outer jacket and trocar assembly  70 , as best shown in  FIGS. 1-5 , includes an outer jacket  72  configured to surround antenna assembly  20 , e.g., proximal and distal radiating portions  42 ,  44 , feed gap  43 , and feedline  30 , such that a coolant fluid may be circulated thereabout to maintain antenna assembly  20  in a relatively cooled state during use, although in some embodiments, cooling is not provided. A ferrule  74  is molded or otherwise engaged about outer jacket  72  towards the proximal end thereof to facilitate sealing engagement of the proximal end of outer jacket  72  within distal port  85  of connection hub  80  via O-ring  76 . That is, during assembly, ferrule  74  and, thus, the proximal end of outer jacket  72 , are inserted proximally into distal port  85  of connection hub  80  sufficiently such that ferrule  74  is sealingly engaged within connection hub  80  via O-ring  76 . Similarly as above, outer jacket and trocar assembly  70  may be engaged within connection hub  80  during manufacturing, or may be assembled by the user. 
         [0044]    Outer jacket and trocar assembly  70  further includes a trocar  90  defining a tapered distal end that terminates at a pointed distal tip  92  to facilitate insertion of microwave antenna probe  12  into tissue with minimal resistance, although other configurations may also be provided. Trocar  90  may be formed from a variety of heat-resistant materials suitable for penetrating tissue, e.g., metals (stainless steel, for example), various thermoplastic materials (such as polytherimide, polyamide thermoplastic resins, etc.), or any other suitable material. Base  94  of trocar  90  is sealingly engaged within open distal end  78  of outer jacket  72  via any suitable process, e.g., using adhesives or via soldering. As such, trocar  90  sealingly encloses antenna assembly  20  within outer jacket  72  and connection hub  80 . 
         [0045]    Referring still to  FIGS. 1-5 , connection hub  80 , as mentioned above, defines a longitudinal lumen  82  that is configured to receive feedline  30  therethrough, while sealingly engaging outer jacket  72  within distal port  85  and transition  60  within proximal port  83 . Connection hub  80  further includes an inlet fluid port  87  and an outlet fluid port  89  that are disposed in fluid communication with lumen  82 . Inlet and outlet ports  87 ,  89  are configured to receive tubes  17 ,  19  (see  FIG. 1 ), respectively, such that coolant fluid from a coolant fluid supply (not shown) may be circulated through connection hub  80  and outer jacket  72 . More specifically, a hub divider  81   a  is sealingly engaged within lumen  82  of connection hub  80  to isolate the inlet and outlet portions of lumen  82  of connection hub  80  from one another. Further, an inflow tube  81   b  is coupled to hub divider  81   a  and extends distally through outer jacket  72 . As such, coolant fluid may flow from the coolant fluid source, through tube  17  and inlet port  87 , into the inlet portion of lumen  82 , and distally through inflow tube  81   b , ultimately returning proximally through outer jacket  72  (exteriorly of inflow tube  81   b ), the outlet portion of lumen  82 , outlet port  89 , tube  19 , and, ultimately, to the coolant fluid source. This configuration allows for the circulation of coolant fluid about antenna assembly  20  to maintain antenna assembly  20  in a relatively cooled state during use. The coolant fluid may be a liquid, gas, other flowable material, or combination thereof. 
         [0046]    In operation, microwave energy having a wavelength, lambda (k), is transmitted through antenna assembly  20 , e.g., along the proximal and distal radiating portions  42 ,  44  and radiated into the surrounding medium, e.g., tissue. Radiation is emitted from antenna assembly  20  in all radial directions. The length of the antenna for efficient radiation may be dependent on the effective wavelength λeff, which is dependent upon the dielectric properties of the medium being radiated. Antenna assembly  20  through which microwave energy is transmitted at wavelength λ may have differing effective wavelengths λeff depending upon the surrounding medium, e.g., liver tissue, as opposed to breast tissue. Frequencies used in microwave ablation systems are in the low-frequency spectrum, such as between 915 MHz and 2.4 GHz, while the frequencies used in RF ablation systems are typically much lower, usually between 450 and 500 kHz. 
         [0047]    As noted above, radiation from antenna assembly  20  is emitted in all radial directions. In order to focus the radiation from antenna assembly  20 , one or more reflector strips is applied to antenna probe  12  to inhibit radiation in certain direction(s). Exemplary reflector strips provided in accordance with the present disclosure are detailed below with respect to  FIGS. 8-14 . 
         [0048]    Referring now to  FIG. 8 , a portion of a reflector strip in accordance with the present disclosure is shown, identified by reference numeral  200 . Reflector strip  200  includes a shield  210  and an adhesive  220  disposed on one of the surfaces of shield  210 . Shield  210  is formed of a metallic reflector configured to inhibit radiation of energy, e.g., microwave radiation, therethrough. Adhesive  220  enables the adherence of reflector strip  200  to another surface, e.g., the outer surface of antenna probe  12  ( FIG. 1 ). In embodiments, reflector strip  200  further includes a release liner  230  disposed over adhesive  220 . Release liner  230  is configured to be removed from reflector strip  200  before use to expose adhesive  220 . Release liner  230  may be used to prevent adhesive  220  from losing its adhesive properties and/or prematurely adhering to a surface during manufacture, packaging, storage, use, etc. Release liner  230  may be composed of, for example, Super Calendared Kraft Paper, Clay Coated Kraft Paper, PET film, or Polyolefins. Release liner  230  may be coated with a release agent  231 , such as silicone, polyvinyl alcohol, or any other release agent with a low surface energy to facilitate removal from adhesive  220 . In embodiments, a common release liner  230  may include a plurality of reflector strips  200  disposed thereon. In such embodiments, when use of one of the reflector strips  200  is desired, the shield  210  together with the adhesive  220  is removed from the release liner  230  to expose the adhesive  220 . 
         [0049]    Once release liner  230  is peeled away or removed, in embodiments where so provided, reflector strip  200  may be placed onto proximal and distal radiating portions  42 ,  44  of antenna probe  12  ( FIG. 1 ) and adhered thereto using adhesive  220 . In embodiments, adhesive  220  is pressure sensitive. Adhesive  220  may be bonded to antenna probe  12  ( FIG. 1 ) by hand through an application of pressure, such as by pushing the top surface of reflector strip  200  downward onto antenna probe  12  ( FIG. 1 ) so that a fluid-tight seal is made between adhesive  220  and antenna probe  12  ( FIG. 1 ). In embodiments, an application tool (not shown) may be used to facilitate application of reflector strip  200  onto antenna probe  12  ( FIG. 1 ) and establishment of a fluid-tight seal therebetween. 
         [0050]    Adhesive  220  may be any suitable adhesive for adhering metallic reflector shield  210  to the outer surface of antenna probe  12  ( FIG. 1 ). For example, adhesive  220  may be formed from acrylic, cyanoacrylate, epoxy, urethane, butyl, foamed cored acrylic mass, rubber, or silicon. In embodiments, adhesive  220  will have a relatively high peel strength and adhesion to the surface of antenna probe  12  ( FIG. 1 ), such that reflector strip  200  remains in place during insertion through tissue, contact with fluids, and during tissue ablation. In embodiments, adhesive  220  may be non-permanent, such that reflector strip  200  may be removed from the surface of antenna probe  12  after tissue ablation is completed, or if directionality is no longer desired or necessary. In embodiments, adhesive  220  is insoluble, resistant to water, chemicals, and radiation. In embodiments, adhesive  220  may be formed of a biocompatible material meeting the ISO 10993 standard. 
         [0051]    In embodiments, adhesive  220  may be thermosetting. For example, adhesive  220  may be activated to bond reflector strip  200  to antenna probe  12  ( FIG. 1 ) when antenna probe  12  ( FIG. 1 ) is powered on and emitting radiation, via the process of cross-linking. In embodiments, an external heat source may be used to set the thermosetting adhesive  220  to bond reflector strip  200  to antenna probe  12 . 
         [0052]    Referring now to  FIGS. 9 and 10 , reflector strip  200  is shown adhered to antenna probe  12 . Reflector strip  200  extends the entire length from proximal radiating portion  42  to distal radiation portion  44  and covers approximately ½ the circumference of antenna probe  12 . As a result of this configuration, as shown in  FIG. 10 , radiation pattern “R 1 ” is emitted when antenna probe  12  is powered on. More specifically, radiation is only emitted from the portions of antenna probe  12  that are not covered by reflector strip  200 . 
         [0053]    It should be appreciated that reflector strip  200  may define any suitable configuration and may be placed at any location, or at any plurality of locations, on proximal and distal radiating portions  42 ,  44  of antenna probe  12 . For example,  FIG. 11  depicts a reflector strip  200  covering ¼ the circumference of the antenna probe  12 , while  FIG. 12  depicts a reflector strip  200  covering ¾ the circumference of antenna probe  12 . Thus, radiation pattern “R 2 ” is larger than radiation pattern “R 1 ,” while radiation pattern “R 3 ” is smaller than that of radiation pattern “R 1 .”  FIG. 13  depicts reflector strips  200  placed at two locations, such that two radiation patterns “R 4 ” and “R 5 ” are emitted from antenna probe  12 . In embodiments, one or more reflector strips  200  may be placed on antenna probe  12  to define a desired radiation pattern having any shape, size, and/or configuration. 
         [0054]    In embodiments, reflector strip  200  may be manufactured in the form of a sheet so that it can be cut into any desired configuration for a specific application. Markings on the sheet may be provided to enable a user to readily identify where to cut to produce a desired reflector strip  200 . For example, markings may be provided to indicate where cuts should be made to produce a reflector strip  200  to cover ¼, ½, or ¾ of the circumference of antenna probe  12 . 
         [0055]    In embodiments, reflector strip  200  may be placed on a roll, similar to those used in label dispensers or label applicators. In embodiments, plural reflector strips  200  on the roll may be pre-cut into different configurations such that a user may remove the appropriate reflector strip  200  corresponding to the radiation pattern desired. 
         [0056]    In embodiments, rather than providing reflector strips  200  that are configured to be adhered to antenna probe  12  to achieve a desired radiation pattern, a reflector strip  200  configured to fully cover radiating portions  42 ,  44  of antenna probe  12  may be provided. In such embodiments, reflector strip  200  may have perforations and/or markings to allow a user to remove the portion(s) of reflector strip  200  where radiation emission is desired, similarly as detailed below with respect to reflector tube  300  ( FIG. 14 ). 
         [0057]    In embodiments, various different reflector strips  200  according to some or all of the above-embodiments may be provided as a kit packaged in a disposable sterile surgical pack to enable a user to configure antenna probe  12  to a desired configuration using one or more of the reflector strips  200 . 
         [0058]    Regardless of the particular configuration of reflector strip(s)  200  used, shield  210  of reflector strip  200  provides directionality by providing electromagnetic interference (“EMI”) shielding to the radiating portions of antenna probe  12  it is covering. EMI reduces or eliminates the electromagnetic field in a space by blocking the field with barriers made of conductive materials. In embodiments, shield  210  may be made of any suitable material, such as silver, copper, gold, aluminum, brass, bronze, tin, lead, nickel, stainless steel, electrically conductive polymers, mumetal, superpermalloy, combinations thereof, or the like. Such materials may also aid in radiographic or ultrasound location of the reflector strip  200  during ablation procedures. In embodiments, shield  210  may be a composite material or materials to enhance EMI shielding, such as, for example, having a layer of gold and a separate layer of copper. In yet other embodiments, shield  210  may be a strip of material, foil, thin sheet, tape, mesh, coating, or the like. 
         [0059]    The thickness of shield  210  may be varied depending on the specific surgical application or the level of Shielding Effectiveness (“SE”) required. SE is the ratio of the electromagnetic (or RF) energy before shielding and its intensity after shielding. This value is used for measuring the effectiveness of EMI shielding. SE is expressed in decibels (dB) and represents the sum of all losses in the shielding. The formula used for calculation of SE may be expressed as dB=20 log 10  (F 1 /F 2 ), where F 1  is the field measurement before shielding and F 2  is the field measurement after shielding. The above formula shows dB ranges falling along a logarithmic scale. For example, a rating of 50 dB indicates a shielding strength ten times that of 40 db. 
         [0060]    In general, a SE of 10 to 30 dB provides the lowest effective level of shielding, while anything below that range can be considered little or no shielding. A SE of 40 dB is usually the targeted minimum. SE between 60 and 90 dB is considered a high level of protection, while 90 to 120 dB is exceptional. Generally, for microwave ablation where the operating frequencies are between 915 MHz and 2.4 GHz, a SE of 40 dB to 50 dB will provide at least 99.9% attenuation (protection or blockage) against electromagnetic radiation. 
         [0061]    In embodiments, shield  210  may be coated with Teflon™, or any other suitable non-stick coating to reduce friction during insertion into the body cavity and/or tissue. In embodiments, shield  210  may be preprinted, embossed, or the like, with units of measurement or other locational elements for precision placement onto antenna probe  12  and/or to enable accurate placement of antenna probe  12  within target tissue. In embodiments, the edges of shield  210  may be beveled, rounded, or the like, to prevent reflector strip  200  from catching onto adjacent tissue and other bodily surfaces. 
         [0062]    In accordance with the present disclosure, and with reference to  FIG. 14 , another embodiment of a reflector, in the form of a tube, is shown and generally designated as  300 . Reflector tube  300  may include a metallic reflector shield  310  and one or more windows  320 . Reflector tube  300  is configured such that it is capable of being slipped over and fitted to the radiating portion of antenna probe  12 . Reflector tube  300  may define any suitable size or shape for placement onto any type of antenna. The one or more windows  320  may likewise define any suitable size or shape to achieve a desired radiation pattern when used in conjunction with an antenna. 
         [0063]    Once in place, antenna probe  12  only emits radiation from window  330 , while radiation from any other area covered by reflector tube  300  is blocked (i.e., is shielded). Reflector tube  300  may be manufactured with or without windows  320 . For example, if reflector tube  300  is manufactured without windows, a user may use a skiving tool to form windows  320  at a desired location(s) on reflector tube  300 . Perforations and/or markings on reflector tube  300  may be provided to facilitate formation of windows  320  of a desired configuration. In embodiments, reflector tube  300  may be open at one end, such that it can be slipped over antenna probe  12 , and closed at the other end, such that the tip of the antenna is encased therein. In such embodiments, the closed end of reflector tube  300  may have a geometry sufficient to properly encase the tip of the particular antenna used therewith. Alternatively, both ends of reflector tube  300  may be open, as illustrated in  FIG. 14 . 
         [0064]    Referring also to  FIG. 15 , reflector tube  300  may have one or more window screens  340  covering one or more of the windows  320  thereof, and a pull tab  330  associated with each window screen  340 . A user may thus pull on pull tab  330  to facilitate remove of the associated window screen  340  to reveal the corresponding window  320 . In embodiments, the window screens  340  may be repositioned within the corresponding window  320  when exposure of that particular window  320  is no longer wanted. The above-detailed configuration of screens  340  and windows  320  may be advantageous, for example, if a user desires to have a plurality of windows  320  emitting radiation therefrom. For example, a surgeon may ablate a cancerous tumor in a patient, which requires only a single window  320 . The same patient may have additional tumors, such as, for example, two adjacent tumors opposing each other, which require opposing radiation fields. The surgeon may then simply remove a second window screen  340  from reflector tube  300  to reveal a second window  320  and ablate both tumors at once, all in a single procedure without the need for retooling.  FIGS. 16 and 17  depict a reflector tube  300  adhered to the surface of an antenna probe  12  with two windows  320  such that two opposing radiation fields “R 6 ” and “R 7 ” are emitted from antenna probe  12  during use. 
         [0065]    In embodiments, the surgeon may use reflector tube  300  for only part of a surgical procedure where precision tissue targeting is required. The reflector tube  300  may then be removed and antenna probe  12  used there without for the remainder of the procedure (or until reflector tube  300  or another reflector tube is once again required) to target other areas of tissue, where such precision is not necessary. Reflector tube  300  may be rolled, peeled, tore, or cut off antenna probe  12  after use. In embodiments, reflector tube  300  may have for example, perforations, or the like, along its surface to aid in its removal from antenna probe  12 . 
         [0066]    In embodiments, reflector tube  300  may be a shrinkable tube, such as, for example, a heat shrink. After slipping reflector tube  300  over antenna probe  12 , reflector tube  300  may be heat-shrunk onto antenna probe  12  by powering on microwave ablation system  10 , which provides sufficient heat to shrink reflector tube  300  and provide a tight seal over antenna probe  12 . An external heat source may also be used to fit reflector tube  300  to antenna probe  12  via heatshrinking. Additionally or alternatively, a thermoplastic adhesive on the inner surface of reflector tube  300  may be used to establish a fluid-tight seal between reflector tube  300  and antenna probe  12 . In embodiments, reflector tube  300  may alternatively be vacuum sealed onto antenna probe  12 . 
         [0067]    Referring now to  FIG. 18  in conjunction with  FIG. 4 , a cap is shown and generally designated as  400 . Cap  400  is placed over trocar  90  and distal tip  92  of antenna probe  12 . Cap  400  may be used alone or in combination with reflector strip  200  and/or reflector tube  300  to prevent unwanted emission of radiation from the distal tip  92  of antenna probe  12 . In embodiments, cap  400  may be formed of any material and having the same or similar properties described in the embodiments of the reflectors  200  or  300  above. Usually, the distal tips of antennas have a triangular, cone-shaped, or semi-circular geometry, such that a strip of material may be difficult to adhere without folds or kinks or may otherwise be unable to provide sufficient coverage. Accordingly, cap  400  is configured to fit over the tip geometry of an antenna and provide sufficient shielding. In embodiments, cap  400  may also have windows or slots  410 , pre-formed or formed via user-removal of material, such that directionality can be achieved in the tip of the antenna itself, thus achieving further directional precision for tissue ablation. In embodiments, cap  400  may be placed in a surgical kit with reflector strip  200  and/or reflector tube  300 . 
         [0068]    It will be understood that various modifications may be made to the embodiments disclosed herein. Therefore, the above description should not be construed as limiting, but merely as exemplifications of preferred embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended thereto.