Patent Publication Number: US-2018028262-A1

Title: Rf ablation needle

Description:
PRIORITY CLAIM 
     The present disclosure claims priority to U.S. Provisional Patent Application Ser. No. 62/367,468 filed Jul. 27, 2016; the disclosure of which is incorporated herewith by reference. 
    
    
     BACKGROUND 
     The present embodiments relate to systems and methods for ablating tissue in interior regions of the human body and, more particularly, to needle devices permitting tissue ablation and biopsy or target tissue. Radio-frequency (RF) probes have been used to treat tissue. However, these devices have been limited in certain applications by the size of the lesions they are able to create as well as the effects of the delivery of energy to non-targeted tissues. 
     SUMMARY 
     The present disclosure relates to an ablation device which includes a needle extending from a proximal end which, during use, remains outside a body accessible to a user to a tissue penetrating distal tip, the needle defining a lumen extending therethrough to a distal end of the needle; an first ablation electrode mounted on a distal portion of the needle; an inner tube received within the lumen of the needle separating the lumen of the needle into an inner cooling fluid supply lumen and an annular fluid return lumen; and a source of cooling fluid supplying cooling fluid to the cooling fluid supply lumen and withdrawing fluid from the fluid return lumen to remove heat from the first electrode to maintain a temperature of the first electrode below a predetermined threshold temperature. 
     In an embodiment, the needle includes a distal opening and a plug sealing the distal opening to direct fluid from the fluid supply lumen into the fluid return lumen. 
     In an embodiment, the inner tube has a distal end separated proximally from the plug by a distance selected to provide fluid communication between the fluid supply lumen and the fluid return lumen adjacent to the first electrode. 
     In an embodiment, the inner tube is coupled to the plug and wherein the inner tube comprises at least one opening adjacent the first electrode providing fluid communication with the return lumen. 
     In an embodiment, the ablation device further includes an electrically insulative delivery element extending circumferentially around the needle and receiving the needle therein for movement between a retracted position in which the distal tip of the needle is received within the delivery element and an extended position in which the distal tip of the needle is projected distally beyond a distal end of the delivery element. The needle is formed of an electrically conductive material, the needle further comprising an electrically insulative coating extending circumferentially therearound, the coating extending along a portion of a length of the needle and having a distal end separated from the distal tip of the needle by a length selected to permit the portion of the needle extending distally from the coating to function as the first electrode, a proximal end of the coating being positioned so that, when the distal tip is projected distally beyond the distal end of the delivery element by a maximum distance, a part of the coating extends into the delivery element. 
     In an embodiment, the inner tube is slidably received within the needle so that, when the inner tube is withdrawn proximally from the needle, the plug is withdrawn from the distal tip of the needle opening the lumen of the needle to an exterior of the needle so that a tissue sample may be captured therein. 
     In an embodiment, the plug includes a sealing member extending circumferentially therearound to enhance a seal between the plug and the distal tip of the needle. 
     In an embodiment, the ablation device further includes a wall extending across and sealing a proximal part of the lumen of the needle from a distal portion thereof, the wall being spaced from a distal end of the lumen of the needle by a distance selected to form a tissue sample receiving space in the distal tip of the needle. 
     In an embodiment, the wall includes an opening therethrough and wherein the device includes a plunger member on a distal side of the wall and a control member extending from the plunger, through the opening to a proximal end accessible to a user so that, tension applied to the control member draws the plunger into contact with the wall to seal the opening and compression applied to the plunger forces the plunger distally away from the wall to drive tissue out of the tissue sample receiving space. 
     In an embodiment, the ablation device further includes a second electrode formed on a distal portion of the needle and separated longitudinally and electrically isolated from the first electrode, the first and second electrodes being coupled to opposite poles of a power source to function as a bi-polar ablation system. 
     In an embodiment, the needle is formed of an electrically conductive material and includes an electrically insulative coating circumferentially surrounding this electrically insulative coating along at least a portion thereof, and wherein the second electrode is mounted over the electrically insulative coating and the first electrode is mounted on the conductive material of the needle. 
     In an embodiment, a proximal portion of the needle is formed as a first electrically conductive tube and a distal end of the needle is formed as a second electrically conductive tube, the first and second electrically conductive tubes being joined to one another and electrically isolated from one another by an electrically insulative member. 
     In an embodiment, the ablation device further includes an electrically insulative delivery element extending circumferentially around the needle and receiving the needle therein for movement between a retracted position in which the distal tip of the needle is received within the delivery element and an extended position in which the distal tip of the needle is projected distally beyond a distal end of the delivery element; and an electrically insulative coating extending circumferentially around the first electrically conductive tube from a coating proximal end to a coating distal end, the coating proximal end being positioned so that, when the distal tip is projected distally beyond the distal end of the delivery element by a maximum distance, a part of the coating extends into the delivery element, a part of the first tube extending distally beyond a distal end of the coating forming the second electrode and the second tube forming the first electrode. 
     In an embodiment, the device is sufficiently flexible to be passed through a natural body lumen until a distal end of the needle reaches a target site within the body. 
    
    
     
       BRIEF DESCRIPTION 
         FIG. 1  shows a partially cross-sectional view of a monopolar RF ablation device according to an exemplary embodiment of the present disclosure; 
         FIG. 2  shows a partially cross-sectional view of a monopolar RF ablation device according to a second exemplary embodiment of the present disclosure; 
         FIG. 3  shows a partially cross-sectional view of a monopolar RF ablation device according to a third exemplary embodiment of the present disclosure; 
         FIG. 4  shows a partially cross-sectional view of a monopolar RF ablation device according to a fourth exemplary embodiment of the present disclosure; 
         FIG. 5  shows a partially cross-sectional view of a bipolar RF ablation device according to a fifth exemplary embodiment of the present disclosure; 
         FIG. 6  shows a partially cross-sectional view of a bipolar RF ablation device according to a sixth exemplary embodiment of the present disclosure; and 
         FIGS. 7A-7F  show a partially cross-sectional views of a alternate constructions of bipolar RF ablation devices according to further embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure may be further understood with reference to the appended drawings and the following description, wherein like elements are referred to with the same reference numerals. The present disclosure relates to devices and methods for ablating tissue and, more particularly, relates to needle devices for ablating tissue and/or collecting tissue samples. It should be noted that the terms proximal and distal, as used herein, are intended to refer to a direction toward (proximal) and away from (distal) a user of the device (e.g., physician). 
     As shown in  FIG. 1 , a device  100  comprises an electrically insulative delivery element  102  within which an electrically conductive ablation needle  104  is slidably received. The delivery element  102  according to this embodiment may be sized, for example, to pass through the working channel of an endoscope or bronchoscope for delivery to target tissue within a living body. As would be understood by those skilled in the art, the device  100  is preferably sufficiently flexible to pass through a tortuous path through, for example, a natural body lumen without undue trauma to tissue along and adjacent to the lumen or damage to the device  100 . For example, the device  100  may have a flexibility sufficient to permit the device  100  to be slidably inserted through a working channel of a device such as a flexible endoscope or bronchoscope and to pass through any bending radii that these devices may achieve. The delivery element  102  may be formed as a flexible sheath similar to those currently employed for flexible biopsy needles and defines an internal lumen  106  within which the ablation needle  104  is slidably received. In an exemplary embodiment, the delivery element is formed as a sheath of polyether ether ketone (PEEK) having an outer diameter of 0.68″. However, as would be understood by those skilled in the art, other materials and sizes may be used. The ablation needle  104  of this embodiment is formed of a flexible, biocompatible and electrically conductive material such as stainless steel, nitinol, Inconel, platinum and other biocompatible electrically conductive materials. According to the exemplary embodiment, the needle  104  may be formed, for example, as a stainless steel hypotube having an outer diameter of 0.045″ with an inner diameter of 0.037″. Those skilled in the art will understand that these dimensions are exemplary only and other dimensions may be used as desired. 
     The needle  104  of the exemplary embodiment extends between a proximal end which, in use, remains outside the body accessible to a user, and a tissue penetrating distal tip  106 . The needle  104  includes a distal plug  108  that seals the distal end of a lumen  110  of the needle  104 . Those skilled in the art will understand that, in this embodiment, the distal tip  106  of the needle is ground to form a tissue penetrating tip and that the distal end of the ground tube opens the lumen  110  of the needle  104  to the external environment. In this embodiment, this distal opening is sealed by a separate plug element  108  that may be formed of any suitable material such as, for example, metal, rubber or plastic. Alternatively, the end of the needle  104  may be sealed by the same material of which the needle is formed (e.g., stainless steel). An inner tube  112  divides the lumen  110  into a central passage  114  and an outer, annular channel  116 . The inner tube  112  may be formed, for example, as a stainless steel hypotube, a polyimide tube or a nylon tube having, for example, an outer diameter of 0.025″ and an inner diameter of 0.020″. An electrically insulating layer  118  extends circumferentially around a portion of the needle  104 . The layer  118  is separated from the distal tip  106  by a distance selected as a length of a portion of the needle  104  that serves as an ablation electrode  120 . The electrically insulative layer  118  may, for example, be formed as a heat shrunk layer of polyethylene terephthalate (PET) with a thickness of 0.0005″. Those skilled in the art will understand that the materials and dimensions provided are exemplary and other materials and sizes may be used depending on the requirements of specific procedures to be performed. 
     Specifically, the portion  120  of the needle  104  extending distally from the distal end  122  of the electrically insulating layer  118  to the distal tip  206  receives electrical energy supplied to a proximal end of the needle  104  for ablating target tissue adjacent to the portion  120 . The electrically insulative layer  118  preferably has a length selected so that, when the needle  104  is extended distally from the delivery element  102  by a maximum extent, a proximal end  124  of the electrically insulative layer  118  remains within the delivery element  102  to ensure that energy is delivered to tissue only via the portion  120 . Those skilled in the art will understand that any known mechanisms may be employed to advance and retract the needle  104  relative to the delivery element  102  and that any known power source and controller may be used to supply the RF ablation energy to the portion  120 . For example, a Boston Scientific RF3000™ may be used as the power source for any of the embodiments described herein while a Boston Scientific MetriQ™ pump may be used to supply the cooling fluid in any of the disclosed embodiments. 
     During use, cooling fluid (e.g., sterile saline or water) is supplied to the portion  120  of the needle  104  to maintain a temperature of the portion  120  below a desired threshold level. In an exemplary embodiment, this may be the temperature at which tissue charring occurs. For example, a flow rate of, for example, 10-40 ml/minute, either at room temperature or chilled below room temperature, may be maintained to control the temperature as desired to maintain the temperature of the portion  120  below 100 degrees C. to avoid tissue charring. Those skilled in the art would understand that feedback may be obtained from a thermocouple, thermistor or other sensor allowing the system or the user to adjust a flow rate of cooling fluid to maintain a desired temperature of the portion  120 . Those skilled in the art will understand that the temperature of the portion  120  may also be monitored based on a differential between a temperature of fluid supplied to the system and a temperature of the fluid withdrawn from the system after cooling the portion  120 . In one embodiment, the system  100  (e.g., the power supply) controls power supply based on feedback relating to impendance measured between the portion  120  and a grounding patch on the patient (as would be understood by those skilled in the art) which is related to the temperature at the portion  120 . In some cases, preventing the charring of surrounding tissue permits the ablation needle  104  according to this embodiment to ablate larger volumes of tissue as desiccated charred tissue does not efficiently conduct electrical energy. That is, because of the higher electroconductivity of the non-charred tissue, energy can be delivered to larger amounts of tissue by preventing charring. Thus, the needle  104  may create lesions up to 4 cm or larger in diameter which is suitable for the tumor treatment. In use, the tissue penetrating distal tip  106  may be used to penetrate a target portion of tissue (e.g., a tumor). Using any known visualization system, a user may determine when the needle  104  is in a desired position with, for example, the portion  120  centered within a target portion of tissue to be ablated. At this point, power may be supplied to the portion  120  while cooling fluid is supplied to the inner tube  112  as necessary to maintain the desired temperature of the portion  120 . The cooling fluid flows distally out of a distal end  126  of the tube  112  and, as the distal end of the needle  104  is sealed by the distal plug  108 , the fluid enters the annular channel  116  through which it is withdrawn proximally from the portion  120  of the needle  104  carrying away heat. The fluid may be withdrawn from the needle  104  via the annular channel  116  or cooled and recirculated as would be understood by those skilled in the art. In another exemplary embodiment, the direction of flow of the cooling fluid may be reversed. For example, the cooling fluid may be supplied to the annular channel  116  to maintain a desired temperature of the portion  120  and withdrawn proximally through the inner tube  112 . When the target portion of tissue has been ablated as desired, the power supply and flow of cooling fluid are terminated and the needle  104  is withdrawn proximally until the tissue penetrating distal tip  106  is received within the delivery element  102 . The device  100  may then be withdrawn from the body or moved to a new position adjacent to or within a second target portion of tissue to be ablated. The process may then be repeated as desired. 
     As shown in  FIG. 2 , a needle ablation device  200  according to a further embodiment can be used to ablate tissue in a manner similar to that described above in regard to the device  100  and can also be used for aspiration biopsy as will be described below. The device  200  includes an electrically insulative, flexible delivery element  202  which may be substantially the same as the delivery element  102  of the device  100  with an electrically conductive ablation needle  204  slidably received therein. The ablation needle  204  of this embodiment may be formed of the same materials and in the same or different dimensions as described above for the needle  104  as may be dictated by the procedure for which the needle is to be used. 
     The needle  204  of this embodiment extends between a proximal end which, in use, remains outside the body accessible to a user, and a tissue penetrating distal tip  206 . The needle  204  defines a lumen  205  therein and includes a tapered connection  208  between a proximal portion of the needle  204  and the distal tip  206 . A plug  210  is movable between a first position in which it seals a distal opening  212  of the needle  204  and a second position in which the plug  210  is withdrawn from the opening  212  so that tissue samples may be captured within the needle  204  for biopsies as will be described below. The plug  210  in this embodiment includes an optional O-ring  214  to enhance the seal created by the plug  210  when it is in the first position within the opening  212 . 
     An inner tube  216  divides the lumen  205  into a central passage  218  and an outer, annular channel  220 . The inner tube  216  may be formed of the same materials and dimensions described above in regard to the inner tube  112  and extends from a proximal end that, in use remains accessible to a user to a distal end coupled to the plug  210 . The inner tube  216  includes one or more openings  219  adjacent to a distal end thereof to permit cooling fluid supplied to the central passage  218  to pass through the tube  216  into the annular channel  220  to cool the distal portion of the needle  204  as desired. The inner tube  216  is slidably received within the needle  204  so that, during insertion to a target site within the body, the plug  210  seals the opening  212  until a user desires to obtain a tissue sample. At this point (e.g., when the needle  204  is adjacent to a portion of tissue to be sampled), the user can withdraw the inner tube  216  proximally to remove the plug  210  from the opening  212  and expose the lumen  205 . The inner tube  216  and the plug  210  may be withdrawn by any distance desired to permit the capture of a desired tissue sample. As would be understood by those skilled in the art, if desired the inner tube  216  and the plug  210  may be fully withdrawn from the needle  204  permitting tissue captured in the distal portion of the needle  204  to be aspirated out of the proximal end of the needle  204  for study. An electrically insulating layer  222  extends circumferentially around a portion of the needle  204  separated from the distal tip  206  by a distance selected as a length of a portion of the needle  204  that serves as an ablation electrode  224 . The electrically insulative layer  222  may, for example, be similar in material and dimension to the layer  118  described above. Those skilled in the art will understand that the materials and dimensions provided are exemplary and other materials and sizes may be used depending on the requirements of specific procedures to be performed. 
     Specifically, the portion  224  of the needle  204  extending distally from the distal end  226  of the electrically insulating layer  222  to the tapered connection  208  receives electrical energy supplied to a proximal end of the needle  204  for ablating target tissue adjacent to the portion  224 . The electrically insulative layer  222  preferably has a length selected so that, when the needle  204  is extended distally from the delivery element  202  by a maximum extent, a proximal end  228  of the electrically insulative layer  222  remains within the delivery element  202  to ensure that energy is delivered to tissue only via the portion  224 . Those skilled in the art will understand that any known mechanisms may be employed to advance and retract the needle  204  relative to the delivery element  202  and that any known power source and controller may be used to supply the RF ablation energy to the portion  224 . 
     During use, cooling fluid (e.g., sterile saline) is supplied to the portion  220  of the needle  204  to maintain a temperature of the portion  224  below a threshold level. Those skilled in the art will understand that the desired temperature ranges and the desired amounts of power described above in regards to the device  100  will be substantially similar for the device  200 . Thus, the needle  204  may also create lesions up to 4 cm or larger in diameter which is suitable for the tumor treatment. In use, the inner tube  216  is maintained in the distal position with the plug  210  sealing the opening  212  until a desired position has been reached adjacent to or within tissue to be ablated. Specifically, the tissue penetrating distal tip  206  may be used to penetrate a target portion of tissue (e.g., a tumor) while the user (e.g., using a known visualization system) determines when the needle  204  is in a desired position with, for example, the portion  224  centered within a target portion of tissue to be ablated. At this point, power may be supplied to the portion  224  while cooling fluid is supplied to the inner tube  216  as necessary to maintain the desired temperature of the portion  224 . The cooling fluid flows out of the openings  219  into the annular channel  220  and, as the  212  is sealed by the distal plug  210 , the fluid enters the annular channel  220  through which it is withdrawn proximally from the portion  224  of the needle  204  carrying away heat. The fluid may be withdrawn from the needle  204  via the annular channel  220  or cooled and recirculated via the central passage  218  as would be understood by those skilled in the art. When the target portion of tissue has been ablated as desired, the power supply and flow of cooling fluid are terminated and the needle  204  is withdrawn proximally until the tissue penetrating distal tip  206  is received within the delivery element  202 . The device  200  may then be withdrawn from the body or moved to a new position adjacent to or within a second target portion of tissue to be ablated. The process may then be repeated as desired. 
     When a user wishes to use the device  200  to obtain a tissue sample, the user moves the device  200  to a location adjacent to the tissue to be sampled (e.g., with the inner tube  216  and the plug  210  in the distal position sealing the opening  212 . The user then withdraws the inner tube  216  and the plug  210  proximally through the lumen  205  until the plug  210  has been withdrawn a desired distance into the lumen  205  or removed entirely therefrom as desired. The user then advances the distal tip  206  into the target tissue to capture a tissue sample therein as would be understood by those skilled in the art. This tissue sample may then be aspirated from the needle  204  by providing suction to the lumen  205 . After the sample has been aspirated from the lumen  205 , additional samples may be captured in the same manner. As would be understood by those skilled in the art, the inner tube  216  may then be reinserted as desired to perform additional ablations or to reposition the needle  204  for sampling of tissue at a different location. 
     As seen in  FIG. 3 , a device  300  is substantially similar to the device  200  described above except as described below. The device  300  includes an electrically insulative, flexible delivery element  302  which may be substantially the same as the delivery elements  102  and  202  with an electrically conductive ablation needle  304  slidably received therein. The ablation needle  304  of this embodiment may be formed of the same materials and in the same or different dimensions as described above for the needles  104 ,  204  as may be dictated by the procedure for which the needle is to be used. 
     The needle  304  of this embodiment extends between a proximal end which, in use, remains outside the body accessible to a user, and a tissue penetrating distal tip  306 . The needle  304  defines a lumen  305  therein and extends to a distal tip  306 . A wall  310  is mounted in the lumen  305  at a position proximal of the distal tip  306  by a distance selected to create a tissue receiving space  308  in a portion of the lumen  305  between a distal opening  312  of the needle  304  and distal of the of the wall  310 . Thus, the portion of the lumen  305  proximal to the wall  310  is sealed with respect to the space  308  and the environment external to the needle  304 . In this embodiment, the needle  304  further includes a vent hole  307  located just distally of the wall  310  and open to the receiving space  308  to allow fluid to flow out of the receiving space  308  when target tissue is pierced. 
     An inner tube  316  divides the lumen  305  into a central passage  318  and an outer, annular channel  320 . The inner tube  316  may be formed of the same materials and dimensions described above in regards to the inner tubes  112 ,  216  and extends from a proximal end that, in use remains accessible to a user to a distal end  322  separated from a proximal side of the wall  310  by a space open to the annular channel  320 . The inner tube  316  may be permanently mounted within the needle  304  to maintain the space between the distal end  322  and the wall  310 . A first electrically insulating layer  324  extends circumferentially around a portion of the needle  304  with a portion of the needle  304  extending distally therefrom to serve as an ablation electrode  326 . Specifically, in this embodiment, the electrode  326  extends from a distal end  328  of the first layer  324  to a proximal end  330  of a second electrically insulative layer  332 . In this embodiment, the second layer  332  covers a portion of the needle  304  extending distally of the wall  310  so that substantially an entire length of the electrode  326  can be cooled by the cooling fluid circulating in the lumen  305 . However, those skilled in the art will understand that the second layer  332  may be extended proximally or distally or eliminated entirely as necessary to achieve the desired temperature range of the electrode  326  which will be substantially similar to that described in regard to the device  100 . The electrically insulative layers  324 ,  332  may, for example, be similar in material and dimension to the layers  118 ,  222  described above. Those skilled in the art will understand that the materials and dimensions provided are exemplary and other materials and sizes may be used depending on the requirements of specific procedures to be performed. 
     Specifically, the electrode  326  receives electrical energy supplied to a proximal end of the needle  304  for ablating target tissue adjacent to the electrode  326 . The first electrically insulative layer  324  preferably has a length selected so that, when the needle  304  is extended distally from the delivery element  302  by a maximum extent, a proximal end  334  of the first electrically insulative layer  324  remains within the delivery element  302  to ensure that energy is delivered to tissue only via the electrode  326 . That is, similar to the devices  100  and  200 , electrically conductive portions of the needle  304  extending proximally from the proximal end  334  of the first electrically insulative layer  324  remain within the delivery element  302  to prevent current from being delivered from this proximal portion of the needle  302  to non-targeted tissue. Those skilled in the art will understand that any known mechanisms may be employed to advance and retract the needle  304  relative to the delivery element  302  and that any known power source and controller may be used to supply the RF ablation energy to the portion  326 . 
     During use, cooling fluid (e.g., sterile saline) is supplied to the electrode  326  to maintain a temperature of the electrode  326  below a threshold level. Those skilled in the art will understand that the desired temperature ranges and the desired amounts of power described above in regards to the device  100 ,  200  will be substantially similar for the device  300 . Thus, the needle  304  may also create lesions up to 4 cm or larger in diameter which is suitable for the tumor treatment. In use, the needle  304  is withdrawn proximally into the delivery element  302  and the device is advanced (e.g., through an endoscope or bronchoscope) to a position in the body adjacent to tissue to be ablated. The needle  304  is then advanced distally from the distal end of the delivery element  302  to expose the distal tip  306 . The tissue penetrating distal tip  306  may then be inserted into a target portion of tissue (e.g., a tumor) to capture a tissue sample and/or to position the electrode  326  as desired within a mass of tissue to be ablated. When the tissue penetrating distal tip  306  is inserted into the target portion of tissue, any fluid retained within the tissue receiving space  308  may be forced out of the receiving space  308  through vent hole  307  by the target tissue. This flow of the fluid out of the distal end of the needle  304  prevents the tissue receiving space  308  from hydrolocking and allows tissue to be received within the tissue receiving space  308 . When the user has determined that the electrode  326  is at a desired position within or adjacent to tissue to be ablated (e.g., using a known visualization system), power may be supplied to the electrode  326  while cooling fluid is supplied to the inner tube  316  as necessary to maintain the desired temperature of the electrode  326 . The cooling fluid flows out of the distal end of the central passage  318  and into the annular channel  320  through which it is withdrawn proximally from the electrode  326  carrying away heat to maintain the temperature of the electrode  326  in a desired range. The fluid may be withdrawn from the needle  304  via the annular channel  320  or cooled and recirculated via the central passage  318  as would be understood by those skilled in the art. When the target portion of tissue has been ablated as desired, the power supply and flow of cooling fluid are terminated and the needle  304  is withdrawn proximally until the tissue penetrating distal tip  306  is received within the delivery element  302 . The device  300  may then be withdrawn from the body or moved to a new position adjacent to or within a second target portion of tissue to be ablated. The process may then be repeated as desired. Any tissue sample collected in the tissue receiving space  308  may be retrieved when the device  300  is withdrawn from the body. 
     As seen in  FIG. 4 , a device  400  is substantially similar to the device  300  described above except for the inclusion of a plunger as described below. The device  400  includes an electrically insulative, flexible delivery element  402  which may be substantially the same as the delivery elements  102 ,  202 ,  302  with an electrically conductive ablation needle  404  slidably received therein. The ablation needle  404  of this embodiment may be formed of the same materials and in the same or different dimensions as described above for the needles  104 ,  204 ,  304  as may be dictated by the procedure for which the needle is to be used. 
     The needle  404  of this embodiment extends between a proximal end which, in use, remains outside the body accessible to a user, and a tissue penetrating distal tip  406 . The needle  404  defines a lumen  405  therein and extends to a distal tip  406 . A wall  410  is mounted in the lumen  405  at a position proximal of the distal tip  406  by a distance selected to create a tissue receiving space  408  in a portion of the lumen  405  between a distal opening  412  of the needle  404  and distal of the of the wall  410 . Thus, the portion of the lumen  405  proximal to the wall  410  is sealed with respect to the space  408  and the environment external to the needle  404 . In this embodiment, the needle  404  further includes a vent hole  407  located just distally of the wall  410  and open to the receiving space  408  to allow fluid to flow out of the receiving space  408  when target tissue is pierced. 
     An inner tube  416  divides the lumen  405  into a central passage  418  and an outer, annular channel  420 . The inner tube  416  may be formed of the same materials and dimensions described above in regards to the inner tubes  112 ,  216 ,  316  and extends from a proximal end that, in use remains outside the body accessible to a user to a distal end  422  separated from a proximal side of the wall  410  by a space open to the annular channel  420 . The inner tube  416  may be permanently mounted within the needle  404  to maintain the space between the distal end  422  and the wall  410 . A first electrically insulating layer  424  extends circumferentially around a portion of the needle  404  with a portion of the needle  404  extending distally therefrom to serve as an ablation electrode  426 . Specifically, in this embodiment, the electrode  426  extends from a distal end  428  of the first layer  424  to a proximal end  430  of a second electrically insulative layer  432 . In this embodiment, the second layer  432  covers a portion of the needle  404  extending distally of the wall  410  so that substantially an entire length of the electrode  426  can be cooled by the cooling fluid circulating in the lumen  405 . However, those skilled in the art will understand that the second layer  432  may be extended proximally or distally or eliminated entirely as necessary to achieve the desired temperature range of the electrode  426  which will be substantially similar to that described in regard to the devices  100 ,  200  and  300 . The electrically insulative layers  424 ,  432  may, for example, be similar in material and dimension to the layers  118 ,  222 ,  324  described above. Those skilled in the art will understand that the materials and dimensions provided are exemplary and other materials and sizes may be used depending on the requirements of specific procedures to be performed. 
     Specifically, the electrode  426  receives electrical energy supplied to a proximal end of the needle  404  for ablating target tissue adjacent to the electrode  426 . The first electrically insulative layer  424  preferably has a length selected so that, when the needle  404  is extended distally from the delivery element  402  by a maximum extent, a proximal end  434  of the first electrically insulative layer  424  remains within the delivery element  402  to ensure that energy is delivered to tissue only via the electrode  426 . That is, similar to the devices  100 ,  200  and  300 , electrically conductive portions of the needle  404  extending proximally from the proximal end  434  of the first electrically insulative layer  424  remain within the delivery element  402  to prevent current from being delivered from this proximal portion of the needle  402  to non-targeted tissue. Those skilled in the art will understand that any known mechanisms may be employed to advance and retract the needle  404  relative to the delivery element  402  and that any known power source and controller may be used to supply the RF ablation energy to the portion  426 . 
     In contrast to the device  300 , the wall  410  of the device  400  includes an opening  411  extending therethrough. A control member  413  extends within the lumen  405  from a proximal end that remains accessible to a user (e.g., via an actuator coupled to a device handle (Not shown)) and passes through the opening  411 . A distal end of the control member  413  is coupled to a plunger  415 . The plunger  415  can be operated by a user to seal the opening  411  to facilitate the flow of cooling fluid from the central passage  418  to the annular channel  420  by applying tension to the control member  413 . In addition, the user can operate the plunger  415  to force a captured tissue sample out of the space  408  by advancing the control member  413  distally into the lumen  405  to push the plunger  415  distally into the space  408  thereby forcing tissue stored in the space  408  out of the distal opening  412  for retrieval and analysis. 
     During use, cooling fluid (e.g., sterile saline) is supplied to the electrode  426  to maintain a temperature of the electrode  426  below a threshold level. Those skilled in the art will understand that the desired temperature ranges and the desired amounts of power described above in regards to the device  100 ,  200 ,  300  will be substantially similar for the device  400 . Thus, the needle  404  may also create lesions up to 4 cm or larger in diameter which is suitable for the tumor treatment. In use, the needle  404  is withdrawn proximally into the delivery element  402  and the device is advanced (e.g., through an endoscope or bronchoscope) to a position in the body adjacent to tissue to be ablated. The needle  404  is then advanced distally from the distal end of the delivery element  302  to expose the distal tip  406 . The tissue penetrating distal tip  406  may then be inserted into a target portion of tissue (e.g., a tumor) to capture a tissue sample and/or to position the electrode  426  as desired within a mass of tissue to be ablated. When the distal tip  406  is inserted into the target portion of tissue, any fluid retained within the tissue receiving space  408  may be forced out of the receiving space  408  through vent hole  407  by the target tissue. This flow of the fluid out of the distal end of the needle  404  prevents the tissue receiving space  408  from hydrolocking and allows tissue to be received within the tissue receiving space  408 . When the user has determined that the electrode  426  is at a desired position within or adjacent to tissue to be ablated (e.g., using a known visualization system), the control member  413  may be drawn proximally to seal the opening  411  and power may be supplied to the electrode  426  while cooling fluid is supplied to the inner tube  416  as necessary to maintain the desired temperature of the electrode  426 . The cooling fluid flows out of the distal end of the central passage  418  and into the annular channel  420  through which it is withdrawn proximally from the electrode  426  carrying away heat to maintain the temperature of the electrode  426  in a desired range. The fluid may be withdrawn from the needle  404  via the annular channel  420  or cooled and recirculated via the central passage  418  as would be understood by those skilled in the art. When the target portion of tissue has been ablated as desired, the power supply and flow of cooling fluid are terminated and the needle  404  is withdrawn proximally until the tissue penetrating distal tip  406  is received within the delivery element  402 . The device  400  may then be withdrawn from the body or moved to a new position adjacent to or within a second target portion of tissue to be ablated. The process may then be repeated as desired. Any tissue sample collected in the tissue receiving space  408  may be retrieved when the device  400  is withdrawn from the body by advancing the control member  413  distally to force the plunger  415  distally through the space  408 , thereby ejecting the tissue collected therein. 
     As seen in  FIG. 5 , a device  500  is substantially similar to the device  100  and comprises an electrically insulative, flexible delivery element  502  within which an electrically conductive ablation needle  504  is slidably received. The delivery element  502  according to this embodiment may be sized, for example, to pass through the working channel of an endoscope or bronchoscope for delivery to target tissue within a living body. As would be understood by those skilled in the art, the device  500  is preferably sufficiently flexible to pass through a tortuous path through, for example, a natural body lumen without undue trauma to tissue along and adjacent to the lumen or damage to the device  500 . For example, the device  500  may have a flexibility sufficient to permit the device  500  to be slidably inserted through a working channel of a device such as a flexible endoscope or bronchoscope and to pass through any bending radii that these devices may achieve. The delivery element  502  may be formed as a flexible sheath similar to those currently employed for flexible biopsy needles and defines an internal lumen  506  for slidably receiving ablation needle  504 . In an exemplary embodiment, the delivery element  502  is formed as a sheath of polyether ether ketone (PEEK) having an outer diameter of 0.68″. However, as would be understood by those skilled in the art, other materials and sizes may be used. The ablation needle  504  of this embodiment is formed of a flexible, biocompatible and electrically conductive material such as stainless steel, nitinol, Inconel, platinum and other biocompatible electrically conductive materials. According to the exemplary embodiment, the needle  504  may be formed, for example, as a stainless steel hypotube having an outer diameter of 0.045″ with an inner diameter of 0.037″. 
     The needle  504  of the exemplary embodiment extends between a proximal end which, in use, remains outside the body accessible to a user, and a tissue penetrating distal tip  506 . The needle  504  includes a distal plug  508  that seals the distal end of a lumen  510  of the needle  504 . Those skilled in the art will understand that, in this embodiment, the distal tip  506  of the needle is ground to form a tissue penetrating tip and that the distal end of the ground tube opens the lumen  510  of the needle  504  to the external environment. In this embodiment, this distal opening is sealed by a separate plug element  508  that may be formed of any suitable material such as, for example, metal, rubber or plastic. Alternatively, the end of the needle  504  may be sealed by the same material of which the needle  504  is formed (e.g., stainless steel). An inner tube  512  divides the lumen  510  into a central passage  514  and an outer, annular channel  516 . The inner tube  512  may be formed, for example, as a stainless steel hypotube, a polyimide tube or a nylon tube having, for example, an outer diameter of 0.025″ and an inner diameter of 0.020″. An electrically insulating layer  518  extends distally around a portion of the needle  504  extending from a proximal end on a portion of the needle  504  that always remains within the delivery element  502  even when the needle  504  is extended distally therefrom by a maximum amount. Thus, the layer  518  prevents the delivery of electric energy to non-targeted portions of tissue that may come into contact with the needle  504 . The layer  518  wraps circumferentially around the needle  504  and extends distally to a proximal end  520  of a first electrode  522 . The first electrode  522  that extends circumferentially around a distal portion of the needle  504  adjacent to the distal tip  506 . The first electrode is in contact with the electrically conductive material of the needle  504  to receive electrical energy directly therefrom. A second electrode  524  extends circumferentially around a portion of the needle  504  proximal of the first electrode  522 . A distal end  526  of the second electrode  524  is separated from the proximal end  520  of the first electrode  522  by a distance selected to electrically isolate the first electrode  522  from the second electrode  524 . The first and second electrodes  522 ,  524 , respectively, are separately coupled to a source of electrical potential of opposite polarity to form a bipolar ablation device as would be understood by those skilled in the art. The second electrode  524  is coupled to an electrode  525  which runs inside or outside the needle  504  and is electrically isolated therefrom. The electrode  525  extends from a proximal end (not shown) coupled to a power source and passes through the needle  504  to couple to the second electrode  524 . Those skilled in the art will understand that the electrode  525  may, alternatively, extend to the second electrode  524  outside the needle  504  within the delivery element  502 . 
     As would be understood by those skilled in the art, a size of the first and second electrodes  522 ,  524 , respectively, will be selected based on the application parameters such as the size of the lesion that is desired, an amount of power that can safely be delivered and constraints of the anatomy. In this embodiment, the first and second electrodes  522 ,  524 , respectively, are each 1 cm in length and are separated from one another by a gap of 1 cm. Each of the first and second electrodes  522 ,  524 , respectively, extends around the circumference of the needle  504  which, in this embodiment, has an outer diameter of approximately 0.045″. In addition, the layer  518  in this embodiment is formed as a 0.005″ thick heat shrunk layer of PET although other suitable materials may be employed. Those skilled in the art will understand that the materials and dimensions provided are exemplary and other materials and sizes may be used depending on the requirements of specific procedures to be performed. In addition, those skilled in the art will understand that any known mechanisms may be employed to advance and retract the needle  504  relative to the delivery element  502  and that any known power source and controller may be used to supply the RF ablation energy to the portion  520 . As the second electrode  524  rests on the electrically insulative layer  518 , the second electrode  524  may be made longer to allow power dispersal from the second electrode  524  to equal that from the first electrode  522 . As would be understood by those skilled in the art, the addition of the layer  518  between a longer second electrode  524  and the needle  504  results in a lower current density with compensated for by an increased surface area. 
     During use, cooling fluid (e.g., sterile saline) is supplied to the distal portion of the needle  504  (i.e., the areas adjacent to both the first and second electrodes  522 ,  524 ) to maintain a temperature of this portion of the needle  504  below a desired threshold level. In an exemplary embodiment, this may be the temperature at which tissue charring occurs. As described above, by preventing the charring of surrounding tissue, the ablation needle  504  according to this embodiment can ablate larger volumes of tissue as desiccated charred tissue does not efficiently conduct electrical energy. Thus, the needle  104  may create lesions up to 4 cm or larger in diameter which is suitable for the tumor treatment. In use, the tissue penetrating distal tip  506  may be used to penetrate a target portion of tissue (e.g., a tumor). Using any known visualization system, a user may determine when the needle  504  is in a desired position with, for example, the first and second electrodes  522 ,  524  centered within a target portion of tissue to be ablated. At this point, power may be supplied to the first and second electrodes  522 ,  524  while cooling fluid is supplied to the inner tube  512  as necessary to maintain the desired temperature of the distal portion of the needle  504 . The cooling fluid flows distally out of a distal end  526  of the tube  512  and, as the distal end of the needle  504  is sealed by the distal plug  508 , the fluid enters the annular channel  516  through which it is withdrawn proximally from the portion  520  of the needle  504  carrying away heat. The fluid may be withdrawn from the needle  504  via the annular channel  516  or cooled and recirculated as would be understood by those skilled in the art. When the target portion of tissue has been ablated as desired, the power supply and flow of cooling fluid are terminated and the needle  504  is withdrawn proximally until the tissue penetrating distal tip  506  is received within the delivery element  502 . The device  500  may then be withdrawn from the body or moved to a new position adjacent to or within a second target portion of tissue to be ablated. The process may then be repeated as desired. 
     As shown in  FIG. 6 , a bipolar ablation device  600  according to a further embodiment is substantially similar to the device  500  except as described below. The device  600  is substantially similar to the device  500  and comprises an electrically insulative, flexible delivery element  602  within which an electrically conductive ablation needle  604  is slidably received. The delivery element  602  according to this embodiment may be sized, for example, to pass through the working channel of an endoscope or bronchoscope for delivery to target tissue within a living body. Furthermore, those skilled in the art will understand that a non-conductive cooling fluid such as, for example, distilled water may be desirable in this embodiment. 
     The needle  604  of the exemplary embodiment extends between a proximal end which, in use, remains outside the body accessible to a user, and a tissue penetrating distal tip  606 . The needle  604  includes a distal plug  608  that seals the distal end of a lumen  610  of the needle  604 . Those skilled in the art will understand that, in this embodiment, the distal tip  606  of the needle  604  is ground to form a tissue penetrating tip and that the distal end of the ground tube opens the lumen  610  of the needle  604  to the external environment. In this embodiment, this distal opening is sealed by a separate plug element  608 . An inner tube  612  divides the lumen  610  into a central passage  614  and an outer, annular channel  616 . A first electrically insulating layer  618  extends wraps circumferentially around and extends distally along a portion of the needle  604  extending from a proximal end  619  on a portion of the needle  604  that always remains within the delivery element  602  even when the needle  604  is extended distally therefrom by a maximum amount. The layer  618  extends to a distal end  620 . Distally of the distal end  620  of the first layer  618  the electrically conductive material of the needle  604  is exposed to form a first electrode  622 . The electrically conductive portion  623  of the needle  604  ends distally just beyond the first electrode  622 . At this point, there is a gap  625  between the electrically conductive proximal portion  623  of the needle  604  and a distal conductive portion  626  that extends to the distal tip  606 . The proximal portion  623  is joined to the distal portion  626  via a ring of electrically insulative material  628  to electrically isolate the proximal portion  623  from the distal portion  626 . The inner tube  612  in this embodiment is formed of an electrically conductive material and is connected to the power source at a proximal end with the distal end of the inner tube  612  being electrically coupled to a conductive member  627  which electrically couples the distal portion  626  to the tube  612 . A part of the distal portion  626  extending distally beyond the ring  628  forms a second electrode  630  of polarity opposite that of the first electrode  622 . 
     The structure and operation of the device  600  is identical to that of the device  500  except that the inner tube  612  extends distally to the plug  608 . Thus, to provide fluid communication between the central passage  614  and the annular channel  616  is facilitated via openings  634  formed in a distal end of the inner tube  612 . 
       FIGS. 7A-7F  show various alternate configurations of needles for bi-polar ablation devices similar to devices  500  and  600 . These devices differ only in the construction of the needles but are otherwise internally and operationally similar. The needle  700  of  FIG. 7A  includes a proximal portion  702  formed as an electrically conductive tube (e.g., a stainless steel hypotube) with a first reduced diameter conductive tube  704 . An electrically insulative sleeve  706  in turn receives a second reduced diameter conductive tube  708  around a distal end of the tube  704 . A distal end of the second reduced diameter tube  708  is received within a distal conductive tube  710 . Thus, this needle  700  includes electrically separated electrodes at the tube  710  and a distal portion of the proximal portion  702  with an electrically insulative layer (not shown) defining a proximal end of the electrode formed by the proximal portion  702 . A tissue piercing distal tip  712  is formed at a distal end of the distal tube  710 . 
     The needle  720  of  FIG. 7B  includes a proximal, conductive tube  722  including a reduced diameter distal end  724  (e.g., a swaged hypotube) connected to a distal conductive tube  726  that includes a reduced diameter proximal end  728  (e.g., a swaged hypotube) by an electrically insulative sleeve  730 . The tube  726  includes a tissue piercing tip  732  at its distal end and the tubes  722 ,  726  form the two poles of a bi-polar ablation needle. 
     As shown in  FIG. 7C , the needle  740  includes a proximal electrically insulative tube  742  that receives a first electrode  744  therein. The first electrode  744  includes reduced diameter extensions  746  with a proximal one of the extensions  746  received in the distal end of the tube  742  and a distal extension  746  received within an electrically insulative connector  748 . The connector  748  receives a reduced diameter extension  754  of a second electrode  750  therein with the second electrode  750  extending to a tissue piercing tip  752 . The first and second electrodes  744 ,  750 , respectively, are connected to opposite poles of a power source to serve as electrodes of a bi-polar ablation device as would be understood by those skilled in the art. The extensions  746  of the first electrode  744  are machined to have a reduced outer diameter compared to a central portion of the first electrode  744 . Similarly, the extension  754  of the second electrode  750  is machined to a reduced outer diameter permitting it to be inserted into the distal opening of the connector  748 . This permits the needle to have a substantially continuous outer profile while separating the first and second electrodes  744 ,  750  from one another electrically as desired. 
     As shown in  FIG. 7D , the needle  760  includes a proximal electrically insulative tube  762  that receives a first electrode  764  therein. The first electrode  764  includes reduced diameter extensions  766  with a proximal one of the extensions  766  received in the distal end of the tube  762  and a distal extension  766  received within an electrically insulative connector  768 . The connector  768  receives a reduced diameter extension  774  of a second electrode  770  therein with the second electrode  770  extending to a tissue piercing tip  772 . The first and second electrodes  764 ,  770 , respectively, are connected to opposite poles of a power source to serve as electrodes of a bi-polar ablation device as would be understood by those skilled in the art. The extensions  766  of the first electrode  764  are swaged to have a reduced outer diameter compared to a central portion of the first electrode  764 . Similarly, the extension  774  of the second electrode  770  is swaged to a reduced outer diameter permitting it to be inserted into the distal opening of the connector  768 . This permits the needle to have a substantially continuous outer profile while separating the first and second electrodes  764 ,  770  from one another electrically as desired. 
     As shown in  FIG. 7E , a needle  780  is formed as an electrically insulated member  782  extending from a proximal end (not shown) to a tissue penetrating distal tip  784 . Those skilled in the art will understand that this electrically insulated member may be formed of or coated in an electrically insulative material such as the materials described above. The needle  780  includes two conductive sleeves  786  that serve as electrodes for a bi-polar ablation device. Those skilled in the art will understand that the electrodes may be coupled to separate poles of a power source using any known conductors including the inner material of the needle  780  itself when that needle is formed of a conductive material. 
     As shown in  FIG. 7F , a needle  790  is formed as a tube  792  of electrically insulative material with a proximal conductor  794  formed within a first part of the tube  792  and a distal conductor  796  formed in a part of the tube  792  separated circumferentially from the proximal conductor  794 . The proximal conductor is electrically coupled to each of a plurality of ring electrodes  798  grouped in a first part of the needle  792  and separated along a length of the needle  792  from a group of distal conductors  800  by a distance selected to isolate the distal conductors electrically from the proximal conductors  798 . Each of the distal conductors is electrically connected to the distal conductor  796  which passes by the proximal conductors  798  while electrically insulated therefrom. Those skilled in the art will understand that the proximal electrodes  798  may be coupled to a first pole of a power source while the distal conductors  800  are connected to an opposite pole to operate as electrodes of a bi-polar ablation system. 
     Variations may be made in the structure and methodology of the present disclosure, without departing from the spirit and the scope of the disclosure. For example, those skilled in the art will understand that any combination of chambers, seals and plungers as described in regard to the devices  100 ,  200 ,  300  and  400  may be applied in any of the bi-polar devices described to achieve the same results for tissue collection in a bi-polar device as described in regard to these mono-polar devices and that any of the cooling fluid handling internal structures of any of the devices  100 ,  200 ,  300 ,  400 ,  500  and  600  may be applied within any of the devices of  FIGS. 7A-7F . In another example, any of the devices  100 ,  200 ,  300 ,  400 ,  500 ,  600  and  700  may be formed as rigid percutaneous probes as well as the flexible sheathed devices for passage through scopes. In further example, any of the devices of the devices  100 ,  300 ,  400 ,  500 ,  600  and  700  may also use gas as a cooling option rather than liquid cooling. In another example, the devices  500 ,  600  may have the option of including the mono-polar biopsy capabilities of the devices  200 ,  300  and  400 . Thus, it is intended that the present disclosure cover the modifications and variations of this disclosure that may be contemplated by a person of skill in the art. For example, any or all of the devices herein may be adapted for percutaneous applications by stiffening the delivery element or through any other modifications as would be apparent to those skilled in the art.