Abstract:
A wall of a uterus is ablated by expanding a structure in the uterus and applying energy across the wall of the structure into the uterine wall. An exterior surface of the structure conforms to an inner wall of the uterus, and the energy may cause vapor to collect between the wall and the structure. The vapor is released by providing a barrier to release which is inflated at a pressure above which the barrier at least partially collapses to allow the vapor to leave the uterus.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 14/705,224 (Attorney Docket No. 37646-721.301), filed May 6, 2015, which is a continuation of U.S. patent application Ser. No. 13/426,887 (Attorney Docket No. 37646-721.201), which was filed Mar. 22, 2012 and claims the benefit of Provisional Application No. 61/467,906 (Attorney Docket No. 37646-721.101), filed Mar. 25, 2011, the contents of which are incorporated herein by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to electrosurgical methods and devices for global endometrial ablation in a treatment of menorrhagia. More particularly, the present invention relates to applying radiofrequency current to endometrial tissue by means of capacitively coupling the current through an expandable, thin-wall dielectric member enclosing an ionized gas. 
         [0004]    A variety of devices have been d or proposed for endometrial ablation. Of relevance to the present invention, a variety of radiofrequency ablation devices have been proposed including solid electrodes, balloon electrodes, metalized fabric electrodes, and the like. While often effective, many of the prior electrode designs have suffered from one or more deficiencies, such as relatively slow treatment times, incomplete treatments, non-uniform ablation depths, and risk of injury to adjacent organs. 
         [0005]    For these reasons, it would be desirable to provide systems and methods that allow for endometrial ablation using radiofrequency current which is rapid, provides for controlled ablation depth and which reduce the risk of injury to adjacent organs. At least some of these objectives will be met by the invention described herein. 
         [0006]    2. Description of the Background Art 
         [0007]    U.S. Pat. Nos. 5,769,880; 6,296,639; 6,663,626; and 6,813,520 describe intrauterine ablation devices formed from a permeable mesh defining electrodes for the application of radiofrequency energy to ablate uterine tissue. U.S. Pat. No. 4,979,948 describes a balloon filled with an electrolyte solution for applying radiofrequency current to a mucosal layer via capacitive coupling. US 2008/097425, having common inventorship with the present application, describes delivering a pressurized flow of a liquid medium which carries a radiofrequency current to tissue, where the liquid is ignited into a plasma as it passes through flow orifices. U.S. Pat. No. 5,891,134 describes a radiofrequency heater within an enclosed balloon. U.S. Pat. No. 6,041,260 describes radiofrequency electrodes distributed over the exterior surface of a balloon which is inflated in a body cavity to be treated. U.S. Pat. No. 7,371,231 and US 2009/054892 describe a conductive balloon having an exterior surface which acts as an electrode for performing endometrial ablation. U.S. Pat. No. 5,191,883 describes bipolar heating of a medium within a balloon for thermal ablation. U.S. Pat. No. 6,736,811 and U.S. Pat. No. 5,925,038 show an inflatable conductive electrode. 
       SUMMARY OF THE INVENTION 
       [0008]    The following presents a simplified summary of some embodiments of the invention in order to provide a basic understanding of the invention. This summary is not an extensive overview of the invention. It is not intended to identify key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some embodiments of the invention in a simplified form as a prelude to the more detailed description that is presented later. 
         [0009]    The present invention provides methods for ablating a wall of a uterus by expanding a structure in the uterus and applying energy across the wall of the structure into the uterine wall. The exterior surface conforms to an inner wall of the uterus, and the energy may be transferred into the wall in any conventional manner. In the exemplary embodiments described below, the structure which is expanded comprises a dielectric material, and the energy is delivered by generating a plasma in a low pressure gas within the structure and inductively coupling the energy across the dielectric wall. 
         [0010]    Of particular interest to the present invention, a vapor will often be released from the tissue of the uterine cavity and can collect in pockets between an exterior surface of the expanded structure and an inner wall of the uterus. The presence of such collected vapors can reduce the efficiency of energy transfer into the uterine wall and is therefore undesirable. 
         [0011]    The present invention provides methods and systems for releasing vapor from the uterine cavity, particularly vapor which has collected in pockets as described above, whenever the pressure of the vapor exceeds a preselected level. Typically, the vapor will be released whenever the pressure exceeds a pressure in the range from 10 mm Hg to 100 mm Hg, typically being in the range from 25 mm Hg to 75 mm Hg. 
         [0012]    While the vapor release could be effected by a variety of valves and feedback control systems, it will usually be desirable to use a simpler system which releases the pressure based on a balancing of an internal pressure and an external pressure, as will be described in more detail below. For example, releasing can be effected by inflating a barrier in a vapor release path between the uterine cavity and an exterior where the barrier is inflated at the desired release pressure. Thus, whenever the pressure of vapor within the uterine cavity exceeds this preselected release pressure, the barrier will open and the vapor will be bled from the cavity until the pressure falls below the preselected level. In specific examples, the barrier may comprise an inflatable balloon which is disposed in a release path through the cervix and vaginal canal. In other cases, the barrier may comprise a portion of the expandable structure which contains the plasma generating the energy. In still other case, the plasma within the expandable structure will be maintained at the preselected release pressure. 
         [0013]    In many embodiments, the vapor will be released through a path defined by a lumen in a probe which carries the energy delivery structure. The lumen will be open at a distal end to the interior of the uterine cavity in order to receive vapor when the pressure exceeds the preselected level. The balloon or other inflatable barrier will typically be disposed in a distal end of a lumen, where a pressure in excess of the inflation pressure deflects the balloon or other barrier inwardly to allow the vapor to flow through the newly created path into the lumen. 
         [0014]    In other aspects of the present invention, an endometrial ablation device comprises a probe, an expandable energy delivery structure coupled to a distal end of the probe, and an inflatable element disposed on the probe to control flow of vapor from a uterine cavity into a probe lumen. The probe typically is adapted for trans-vaginal introduction into the uterus and includes a proximal end, a distal end, and a vapor release lumen extending from the proximal end to the distal end. The expandable structure is coupled to the distal end of the probe and is typically adapted to receive argon or other low pressure gas suitable for initiating a plasma in order to deliver energy across the wall of the expandable structure by inductive coupling. The structure will be further adapted to conform to an inner wall of the uterus, and so long as the structure is in close contact with the uterine wall, energy delivery can be efficiently achieved. 
         [0015]    The inflatable element is typically disposed in the vapor release lumen, and its distal end and will be inflated to a pressure substantially equal to the desired pressure at which vapor generated within the uterine cavity is to be released. The inflatable element may be a balloon structure which is independently inflatable, i.e. the expandable structure is separately inflatable. Alternatively, the inflatable device may comprise a proximal portion of the expandable structure. When the inflatable device comprises a separate balloon structure, the ablation device typically includes a separate inflation source coupled to deliver an inflation medium to the inflation element, which medium is in addition to the low pressure gas use for generating the plasma. 
         [0016]    Typically, the inflation source and/or plasma source will be adapted to inflate the inflatable element at pressure in the range from 10 mm Hg to 100 mm Hg, usually being in the range for 25 mm Hg to 75 mm Hg. 
         [0017]    In certain embodiment, a distal end of the probe which surrounds the inflatable element maybe slotted or otherwise split in order to facilitate expansion of the probe while still protecting the surrounding issues. 
         [0018]    For a fuller understanding of the nature and advantages of the present invention, reference should be made to the ensuing detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    In order to better understand the invention and to see how it may be carried out in practice, some preferred embodiments are next described, by way of non-limiting examples only, with reference to the accompanying drawings, in which like reference characters denote corresponding features consistently throughout similar embodiments in the attached drawings. 
           [0020]      FIG. 1  is a perspective view of an ablation system corresponding to the invention, including a hand-held electrosurgical device for endometrial ablation, RF power source, gas source and controller. 
           [0021]      FIG. 2  is a view of the hand-held electrosurgical device of  FIG. 1  with a deployed, expanded thin-wall dielectric structure. 
           [0022]      FIG. 3  is a block diagram of components of one electrosurgical system corresponding to the invention. 
           [0023]      FIG. 4  is a block diagram of the gas flow components of the electrosurgical system of  FIG. 1 . 
           [0024]      FIG. 5  is an enlarged perspective view of the expanded thin-wall dielectric structure, showing an expandable-collapsible frame with the thin dielectric wall in phantom view. 
           [0025]      FIG. 6  is a partial sectional view of the expanded thin-wall dielectric structure of  FIG. 5  showing (i) translatable members of the expandable-collapsible frame a that move the structure between collapsed and (ii) gas inflow and outflow lumens. 
           [0026]      FIG. 7  is a sectional view of an introducer sleeve showing various lumens of the introducer sleeve taken along line  7 - 7  of  FIG. 6 . 
           [0027]      FIG. 8A  is an enlarged schematic view of an aspect of a method of the invention illustrating the step introducing an introducer sleeve into a patient&#39;s uterus. 
           [0028]      FIG. 8B  is a schematic view of a subsequent step of retracting the introducer sleeve to expose a collapsed thin-wall dielectric structure and internal frame in the uterine cavity. 
           [0029]      FIG. 8C  is a schematic view of subsequent steps of the method, including, (i) actuating the internal frame to move the a collapsed thin-wall dielectric structure to an expanded configuration, (ii) inflating a cervical-sealing balloon carried on the introducer sleeve, and (iii) actuating gas flows and applying RF energy to contemporaneously ionize the gas in the interior chamber and cause capacitive coupling of current through the thin-wall dielectric structure to cause ohmic heating in the engaged tissue indicated by current flow paths. 
           [0030]      FIG. 8D  is a schematic view of a subsequent steps of the method, including: (i) advancing the introducer sleeve over the thin-wall dielectric structure to collapse it into an interior bore shown in phantom view, and (ii) withdrawing the introducer sleeve and dielectric structure from the uterine cavity. 
           [0031]      FIG. 9  is a cut-away perspective view of an alternative expanded thin-wall dielectric structure similar to that of  FIGS. 5 and 6  show an alternative electrode configuration. 
           [0032]      FIG. 10  is an enlarged cut-away view of a portion of the expanded thin-wall dielectric structure of  FIG. 9  showing the electrode configuration. 
           [0033]      FIG. 11  is a schematic view of a patient uterus depicting a method corresponding to the invention including providing a flow of a fluid media into the uterine cavity and monitoring the flow rate to characterize the patient&#39;s uterine cavity as intact and non-perforated. 
           [0034]      FIG. 12  is a perspective view of the ablation device of  FIGS. 1-2  with a subsystem for checking the integrity of a uterine cavity. 
           [0035]      FIG. 13  represents a block diagram of a subsystem of the invention for providing and monitoring a fluid flow into the patient&#39;s uterine cavity. 
           [0036]      FIG. 14  represents a diagram indicating the steps of an algorithm for providing and monitoring a fluid flow into the patient&#39;s uterine cavity. 
           [0037]      FIG. 15  is a chart illustrating gas flow rates into the uterine cavity over time that will result in three conditions to thereby characterize the uterine cavity as non-perforated or perforated. 
           [0038]      FIG. 16  represents a diagram indicating the steps of an algorithm for providing and monitoring a fluid flow related to the test method of  FIG. 15 . 
           [0039]      FIG. 17  is a schematic view of another system and method for providing and monitoring a fluid flow to characterize the integrity of a uterine cavity. 
           [0040]      FIG. 18  is a schematic view of another system working end of the invention illustrating expansion of the dielectric membrane in a lateral directions with an interior frame. 
           [0041]      FIG. 19A  is a sectional view of the working end of  FIG. 18  taken along line  19 A- 19 A with the dielectric membrane expanded in lateral directions by the interior frame. 
           [0042]      FIG. 19B  is a sectional view of the working end of  FIG. 19A  showing expansion of the dielectric membrane with an inflation medium to expand the membrane in a second direction. 
           [0043]      FIG. 20  is a cut-away view of another working end showing the dielectric membrane and a valve system for releasing pressure from the uterine cavity during an ablation cycle. 
           [0044]      FIG. 21  depicts an alternative working end showing the dielectric membrane that functions as a valve system for releasing pressure during an ablation cycle. 
           [0045]      FIG. 22  is another working end embodiment showing an introducer sleeve with a flexible distal end portion. 
           [0046]      FIG. 23  is another view of the flexible distal end portion of the introducer sleeve of  FIG. 22 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0047]    In the following description, various embodiments of the present invention will be described. For purposes of explanation, specific configurations and details are set forth in order to provide a thorough understanding of the embodiments. However, it will also be apparent to one skilled in the art that the present invention may be practiced without the specific details. Furthermore, well-known features may be omitted or simplified in order not to obscure the embodiment being described. 
         [0048]    In general, an electrosurgical ablation system is described herein that comprises an elongated introducer member for accessing a patient&#39;s uterine cavity with a working end that deploys an expandable thin-wall dielectric structure containing an electrically non-conductive gas as a dielectric. In one embodiment, an interior chamber of the thin-wall dielectric structure contains a circulating neutral gas such as argon. An RF power source provides current that is coupled to the neutral gas flow by a first polarity electrode disposed within the interior chamber and a second polarity electrode at an exterior of the working end. The gas flow, which is converted to a conductive plasma by an electrode arrangement, functions as a switching mechanism that permits current flow to engaged endometrial tissue only when the voltage across the combination of the gas, the thin-wall dielectric structure and the engaged tissue reaches a threshold that causes capacitive coupling across the thin-wall dielectric material. By capacitively coupling current to tissue in this manner, the system provides a substantially uniform tissue effect within all tissue in contact with the expanded dielectric structure. Further, the invention allows the neutral gas to be created contemporaneously with the capacitive coupling of current to tissue. 
         [0049]    In general, this disclosure may use the terms “plasma”, “conductive gas” and “ionized gas” interchangeably. A plasma consists of a state of matter in which electrons in a neutral gas are stripped or “ionized” from their molecules or atoms. Such plasmas can be formed by application of an electric field or by high temperatures. In a neutral gas, electrical conductivity is non-existent or very low. Neutral gases act as a dielectric or insulator until the electric field reaches a breakdown value, freeing the electrons from the atoms in an avalanche process thus forming a plasma. Such a plasma provides mobile electrons and positive ions, and acts as a conductor which supports electric currents and can form spark or arc. Due to their lower mass, the electrons in a plasma accelerate more quickly in response to an electric field than the heavier positive ions, and hence carry the bulk of the current. 
         [0050]      FIG. 1  depicts one embodiment of an electrosurgical ablation system  100  configured for endometrial ablation. The system  100  includes a hand-held apparatus  105  with a proximal handle  106  shaped for grasping with a human hand that is coupled to an elongated introducer sleeve  110  having axis  111  that extends to a distal end  112 . The introducer sleeve  110  can be fabricated of a thin-wall plastic, composite, ceramic or metal in a round or oval cross-section having a diameter or major axis ranging from about 4 mm to 8 mm in at least a distal portion of the sleeve that accesses the uterine cavity. The handle  106  is fabricated of an electrically insulative material such as a molded plastic with a pistol-grip having first and second portions,  114   a  and  114   b , that can be squeezed toward one another to translate an elongated translatable sleeve  115  which is housed in a bore  120  in the elongated introducer sleeve  110 . By actuating the first and second handle portions,  114   a  and  114   b , a working end  122  can be deployed from a first retracted position ( FIG. 1 ) in the distal portion of bore  120  in introducer sleeve  110  to an extended position as shown in  FIG. 2 . In  FIG. 2 , it can be seen that the first and second handle portions,  114   a  and  114   b , are in a second actuated position with the working end  122  deployed from the bore  120  in introducer sleeve  110 . 
         [0051]      FIGS. 2 and 3  shows that ablation system  100  includes an RF energy source  130 A and RF controller  130 B in a control unit  135 . The RF energy source  130 A is connected to the hand-held device  105  by a flexible conduit  136  with a plug-in connector  137  configured with a gas inflow channel, a gas outflow channel, and first and second electrical leads for connecting to receiving connector  138  in the control unit  135 . The control unit  135 , as will be described further below in  FIGS. 3 and 4 , further comprises a neutral gas inflow source  140 A, gas flow controller  140 B and optional vacuum or negative pressure source  145  to provide controlled gas inflows and gas outflows to and from the working end  122 . The control unit  135  further includes a balloon inflation source  148  for inflating an expandable sealing balloon  225  carried on introducer sleeve  110  as described further below. 
         [0052]    Referring to  FIG. 2 , the working end  122  includes a flexible, thin-wall member or structure  150  of a dielectric material that when expanded has a triangular shape configured for contacting the patient&#39;s endometrial lining that is targeted for ablation. In one embodiment as shown in  FIGS. 2, 5 and 6 , the dielectric structure  150  comprises a thin-wall material such as silicone with a fluid-tight interior chamber  152 . 
         [0053]    In an embodiment, an expandable-collapsible frame assembly  155  is disposed in the interior chamber. Alternatively, the dielectric structure may be expanded by a neutral gas without a frame, but using a frame offers a number of advantages. First, the uterine cavity is flattened with the opposing walls in contact with one another. Expanding a balloon-type member may cause undesirable pain or spasms. For this reason, a flat structure that is expanded by a frame is better suited for deployment in the uterine cavity. Second, in embodiments herein, the neutral gas is converted to a conductive plasma at a very low pressure controlled by gas inflows and gas outflows—so that any pressurization of a balloon-type member with the neutral gas may exceed a desired pressure range and would require complex controls of gas inflows and gas outflows. Third, as described below, the frame provides an electrode for contact with the neutral gas in the interior chamber  152  of the dielectric structure  150 , and the frame  155  extends into all regions of the interior chamber to insure electrode exposure to all regions of the neutral gas and plasma. The frame  155  can be constructed of any flexible material with at least portions of the frame functioning as spring elements to move the thin-wall structure  150  from a collapsed configuration ( FIG. 1 ) to an expanded, deployed configuration ( FIG. 2 ) in a patient&#39;s uterine cavity. In one embodiment, the frame  155  comprises stainless steel elements  158   a ,  158   b  and  160   a  and  160   b  that function akin to leaf springs. The frame can be a stainless steel such as 316 SS, 17A SS, 420 SS, 440 SS or the frame can be a NiTi material. The frame preferably extends along a single plane, yet remains thin transverse to the plane, so that the frame may expand into the uterine cavity. The frame elements can have a thickness ranging from about 0.005″ to 0.025″. As can be seen in  FIGS. 5 and 6 , the proximal ends  162   a  and  162   b  of spring elements  158   a ,  158   b  are fixed (e.g., by welds  164 ) to the distal end  165  of sleeve member  115 . The proximal ends  166   a  and  166   b  of spring elements  160   a ,  160   b  are welded to distal portion  168  of a secondary translatable sleeve  170  that can be extended from bore  175  in translatable sleeve  115 . The secondary translatable sleeve  170  is dimensioned for a loose fit in bore  175  to allow gas flows within bore  175 .  FIGS. 5 and 6  further illustrate the distal ends  176   a  and  176   b  of spring elements  158   a ,  158   b  are welded to distal ends  178   a  and  178   b  of spring elements  160   a  and  160   b  to thus provide a frame  155  that can be moved from a linear shape (see  FIG. 1 ) to an expanded triangular shape ( FIGS. 5 and 6 ). 
         [0054]    As will be described further below, the bore  175  in sleeve  115  and bore  180  in secondary translatable sleeve  170  function as gas outflow and gas inflow lumens, respectively. It should be appreciated that the gas inflow lumen can comprise any single lumen or plurality of lumens in either sleeve  115  or sleeve  170  or another sleeve, or other parts of the frame  155  or the at least one gas flow lumen can be formed into a wall of dielectric structure  150 . In  FIGS. 5, 6 and 7  it can be seen that gas inflows are provided through bore  180  in sleeve  170 , and gas outflows are provided in bore  175  of sleeve  115 . However, the inflows and outflows can be also be reversed between bores  175  and  180  of the various sleeves.  FIGS. 5 and 6  further show that a rounded bumper element  185  is provided at the distal end of sleeve  170  to insure that no sharp edges of the distal end of sleeve  170  can contact the inside of the thin dielectric wall  150 . In one embodiment, the bumper element  185  is silicone, but it could also comprise a rounded metal element.  FIGS. 5 and 6  also show that a plurality of gas inflow ports  188  can be provided along a length of in sleeve  170  in chamber  152 , as well as a port  190  in the distal end of sleeve  170  and bumper element  185 . The sectional view of  FIG. 7  also shows the gas flow passageways within the interior of introducer sleeve  110 . 
         [0055]    It can be understood from  FIGS. 1, 2, 5 and 6  that actuation of first and second handle portions,  114   a  and  114   b , (i) initially causes movement of the assembly of sleeves  115  and  170  relative to bore  120  of introducer sleeve  110 , and (ii) secondarily causes extension of sleeve  170  from bore  175  in sleeve  115  to expand the frame  155  into the triangular shape of  FIG. 5 . The dimensions of the triangular shape are suited for a patient uterine cavity, and for example can have an axial length A ranging from 4 to 10 cm and a maximum width B at the distal end ranging from about 2 to 5 cm. In one embodiment, the thickness C of the thin-wall structure  150  can be from 1 to 4 mm as determined by the dimensions of spring elements  158   a ,  158   b ,  160   a  and  160   b  of frame assembly  155 . It should be appreciated that the frame assembly  155  can comprise round wire elements, flat spring elements, of any suitable metal or polymer that can provide opening forces to move thin-wall structure  150  from a collapsed configuration to an expanded configuration within the patient uterus. Alternatively, some elements of the frame  155  can be spring elements and some elements can be flexible without inherent spring characteristics. 
         [0056]    As will be described below, the working end embodiment of  FIGS. 2, 5 and 6  has a thin-wall structure  150  that is formed of a dielectric material such as silicone that permits capacitive coupling of current to engaged tissue while the frame assembly  155  provides structural support to position the thin-wall structure  150  against tissue. Further, gas inflows into the interior chamber  152  of the thin-wall structure can assist in supporting the dielectric wall so as to contact endometrial tissue. The dielectric thin-wall structure  150  can be free from fixation to the frame assembly  155 , or can be bonded to an outward-facing portion or portions of frame elements  158   a  and  158   b . The proximal end  182  of thin-wall structure  150  is bonded to the exterior of the distal end of sleeve  115  to thus provide a sealed, fluid-tight interior chamber  152  ( FIG. 5 ). 
         [0057]    In one embodiment, the gas inflow source  140 A comprises one or more compressed gas cartridges that communicate with flexible conduit  136  through plug-in connector  137  and receiving connector  138  in the control unit  135  ( FIGS. 1-2 ). As can be seen in  FIGS. 5-6 , the gas inflows from source  140 A flow through bore  180  in sleeve  170  to open terminations  188  and  190  therein to flow into interior chamber  152 . A vacuum source  145  is connected through conduit  136  and connector  137  to allow circulation of gas flow through the interior chamber  152  of the thin-wall dielectric structure  150 . In  FIGS. 5 and 6 , it can be seen that gas outflows communicate with vacuum source  145  through open end  200  of bore  175  in sleeve  115 . Referring to  FIG. 5 , it can be seen that frame elements  158   a  and  158   b  are configured with a plurality of apertures  202  to allow for gas flows through all interior portions of the frame elements, and thus gas inflows from open terminations  188 ,  190  in bore  180  are free to circulated through interior chamber  152  to return to an outflow path through open end  200  of bore  175  of sleeve  115 . As will be described below (see  FIGS. 3-4 ), the gas inflow source  140 A is connected to a gas flow or circulation controller  140 B which controls a pressure regulator  205  and also controls vacuum source  145  which is adapted for assisting in circulation of the gas. It should be appreciated that the frame elements can be configured with apertures, notched edges or any other configurations that allow for effective circulation of a gas through interior chamber  152  of the thin-wall structure  150  between the inflow and outflow passageways. 
         [0058]    Now turning to the electrosurgical aspects of the invention,  FIGS. 5 and 6  illustrate opposing polarity electrodes of the system  100  that are configured to convert a flow of neutral gas in chamber  152  into a plasma  208  ( FIG. 6 ) and to allow capacitive coupling of current through a wall  210  of the thin-wall dielectric structure  150  to endometrial tissue in contact with the wall  210 . The electrosurgical methods of capacitively coupling RF current across a plasma  208  and dielectric wall  210  are described in U.S. patent application Ser. No. 12/541,043; filed Aug. 13, 2009 (Atty. Docket No. 027980-000110US) and U.S. application Ser. No. 12/541,050 (Atty. Docket No. 027980-000120US), referenced above. In  FIGS. 5 and 6 , the first polarity electrode  215  is within interior chamber  152  to contact the neutral gas flow and comprises the frame assembly  155  that is fabricated of an electrically conductive stainless steel. In another embodiment, the first polarity electrode can be any element disposed within the interior chamber  152 , or extendable into interior chamber  152 . The first polarity electrode  215  is electrically coupled to sleeves  115  and  170  which extends through the introducer sleeve  110  to handle  106  and conduit  136  and is connected to a first pole of the RF source energy source  130 A and controller  130 B. A second polarity electrode  220  is external of the internal chamber  152  and in one embodiment the electrode is spaced apart from wall  210  of the thin-wall dielectric structure  150 . In one embodiment as depicted in  FIGS. 5 and 6 , the second polarity electrode  220  comprises a surface element of an expandable balloon member  225  carried by introducer sleeve  110 . The second polarity electrode  220  is coupled by a lead (not shown) that extends through the introducer sleeve  110  and conduit  136  to a second pole of the RF source  130 A. It should be appreciated that second polarity electrode  220  can be positioned on sleeve  110  or can be attached to surface portions of the expandable thin-wall dielectric structure  150 , as will be described below, to provide suitable contact with body tissue to allow the electrosurgical ablation of the method of the invention. The second polarity electrode  220  can comprise a thin conductive metallic film, thin metal wires, a conductive flexible polymer or a polymeric positive temperature coefficient material. In one embodiment depicted in  FIGS. 5 and 6 , the expandable member  225  comprises a thin-wall compliant balloon having a length of about 1 cm to 6 cm that can be expanded to seal the cervical canal. The balloon  225  can be inflated with a gas or liquid by any inflation source  148 , and can comprise a syringe mechanism controlled manually or by control unit  135 . The balloon inflation source  148  is in fluid communication with an inflation lumen  228  in introducer sleeve  110  that extends to an inflation chamber of balloon  225  (see  FIG. 7 ). 
         [0059]    Referring back to  FIG. 1 , the control unit  135  can include a display  230  and touch screen or other controls  232  for setting and controlling operational parameters such as treatment time intervals, treatment algorithms, gas flows, power levels and the like. Suitable gases for use in the system include argon, other noble gases and mixtures thereof. In one embodiment, a footswitch  235  is coupled to the control unit  135  for actuating the system. 
         [0060]    The box diagrams of  FIGS. 3 and 4  schematically depict the system  100 , subsystems and components that are configured for an endometrial ablation system. In the box diagram of  FIG. 3 , it can be seen that RF energy source  130 A and circuitry is controlled by a controller  130 B. The system can include feedback control systems that include signals relating to operating parameters of the plasma in interior chamber  152  of the dielectric structure  150 . For example, feedback signals can be provided from at least one temperature sensor  240  in the interior chamber  152  of the dielectric structure  150 , from a pressure sensor within, or in communication, with interior chamber  152 , and/or from a gas flow rate sensor in an inflow or outflow channel of the system.  FIG. 4  is a schematic block diagram of the flow control components relating to the flow of gas media through the system  100  and hand-held device  105 . It can be seen that a pressurized gas source  140 A is linked to a downstream pressure regulator  205 , an inflow proportional valve  246 , flow meter  248  and normally closed solenoid valve  250 . The valve  250  is actuated by the system operator which then allows a flow of a neutral gas from gas source  140 A to circulate through flexible conduit  136  and the device  105 . The gas outflow side of the system includes a normally open solenoid valve  260 , outflow proportional valve  262  and flow meter  264  that communicate with vacuum pump or source  145 . The gas can be exhausted into the environment or into a containment system. A temperature sensor  270  (e.g., thermocouple) is shown in  FIG. 4  that is configured for monitoring the temperature of outflow gases.  FIG. 4  further depicts an optional subsystem  275  which comprises a vacuum source  280  and solenoid valve  285  coupled to the controller  140 B for suctioning steam from a uterine cavity  302  at an exterior of the dielectric structure  150  during a treatment interval. As can be understood from  FIG. 4 , the flow passageway from the uterine cavity  302  can be through bore  120  in sleeve  110  (see  FIGS. 2, 6 and 7 ) or another lumen in a wall of sleeve  110  can be provided. 
         [0061]      FIGS. 8A-8D  schematically illustrate a method of the invention wherein (i) the thin-wall dielectric structure  150  is deployed within a patient uterus and (ii) RF current is applied to a contained neutral gas volume in the interior chamber  152  to contemporaneously create a plasma  208  in the chamber and capacitively couple current through the thin dielectric wall  210  to apply ablative energy to the endometrial lining to accomplish global endometrial ablation. 
         [0062]    More in particular,  FIG. 8A  illustrates a patient uterus  300  with uterine cavity  302  surrounded by endometrium  306  and myometrium  310 . The external cervical os  312  is the opening of the cervix  314  into the vagina  316 . The internal os or opening  320  is a region of the cervical canal that opens to the uterine cavity  302 .  FIG. 8A  depicts a first step of a method of the invention wherein the physician has introduced a distal portion of sleeve  110  into the uterine cavity  302 . The physician gently can advance the sleeve  110  until its distal tip contacts the fundus  324  of the uterus. Prior to insertion of the device, the physician can optionally introduce a sounding instrument into the uterine cavity to determine uterine dimensions, for example from the internal os  320  to fundus  324 . 
         [0063]      FIG. 8B  illustrates a subsequent step of a method of the invention wherein the physician begins to actuate the first and second handle portions,  114   a  and  114   b , and the introducer sleeve  110  retracts in the proximal direction to expose the collapsed frame  155  and thin-wall structure  150  within the uterine cavity  302 . The sleeve  110  can be retracted to expose a selected axial length of thin-wall dielectric structure  150 , which can be determined by markings  330  on sleeve  115  (see  FIG. 1 ) which indicate the axial travel of sleeve  115  relative to sleeve  170  and thus directly related to the length of deployed thin-wall structure  150 .  FIG. 2  depicts the handle portions  114   a  and  114   b  fully approximated thus deploying the thin-wall structure to its maximum length. 
         [0064]      FIG. 8C  illustrates several subsequent steps of a method of the invention.  FIG. 8C  first depicts the physician continuing to actuate the first and second handle portions,  114   a  and  114   b , which further actuates the frame  155  (see  FIGS. 5-6 ) to expand the frame  155  and thin-wall structure  150  to a deployed triangular shape to contact the patient&#39;s endometrial lining  306 . The physician can slightly rotate and move the expanding dielectric structure  150  back and forth as the structure is opened to insure it is opened to the desired extent. In performing this step, the physician can actuate handle portions,  114   a  and  114   b , a selected degree which causes a select length of travel of sleeve  170  relative to sleeve  115  which in turn opens the frame  155  to a selected degree. The selected actuation of sleeve  170  relative to sleeve  115  also controls the length of dielectric structure deployed from sleeve  110  into the uterine cavity. Thus, the thin-wall structure  150  can be deployed in the uterine cavity with a selected length, and the spring force of the elements of frame  155  will open the structure  150  to a selected triangular shape to contact or engage the endometrium  306 . In one embodiment, the expandable thin-wall structure  150  is urged toward and maintained in an open position by the spring force of elements of the frame  155 . In the embodiment depicted in  FIGS. 1 and 2 , the handle  106  includes a locking mechanism with finger-actuated sliders  332  on either side of the handle that engage a grip-lock element against a notch in housing  333  coupled to introducer sleeve  110  ( FIG. 2 ) to lock sleeves  115  and  170  relative to introducer sleeve  110  to maintain the thin-wall dielectric structure  150  in the selected open position. 
         [0065]      FIG. 8C  further illustrates the physician expanding the expandable balloon structure  225  from inflation source  148  to thus provide an elongated sealing member to seal the cervix  314  outward from the internal os  320 . Following deployment of the thin-wall structure  150  and balloon  225  in the cervix  314 , the system  100  is ready for the application of RF energy to ablate endometrial tissue  306 .  FIG. 8C  next depicts the actuation of the system  100 , for example, by actuating footswitch  235 , which commences a flow of neutral gas from source  140 A into the interior chamber  152  of the thin-wall dielectric structure  150 . Contemporaneous with, or after a selected delay, the system&#39;s actuation delivers RF energy to the electrode arrangement which includes first polarity electrode  215  (+) of frame  155  and the second polarity electrode  220  (−) which is carried on the surface of expandable balloon member  225 . The delivery of RF energy delivery will instantly convert the neutral gas in interior chamber  152  into conductive plasma  208  which in turn results in capacitive coupling of current through the dielectric wall  210  of the thin-wall structure  150  resulting in ohmic heating of the engaged tissue.  FIG. 8C  schematically illustrates the multiplicity of RF current paths  350  between the plasma  208  and the second polarity electrode  220  through the dielectric wall  210 . By this method, it has been found that ablation depths of three mm to six mm or more can be accomplished very rapidly, for example in 60 seconds to 120 seconds dependent upon the selected voltage and other operating parameters. In operation, the voltage at which the neutral gas inflow, such as argon, becomes conductive (i.e., converted in part into a plasma) is dependent upon a number of factors controlled by the controllers  130 B and  140 B, including the pressure of the neutral gas, the volume of interior chamber  152 , the flow rate of the gas through the chamber  152 , the distance between electrode  210  and interior surfaces of the dielectric wall  210 , the dielectric constant of the dielectric wall  210  and the selected voltage applied by the RF source  130 , all of which can be optimized by experimentation. In one embodiment, the gas flow rate can be in the range of 5 ml/sec to 50 ml/sec. The dielectric wall  210  can comprise a silicone material having a thickness ranging from a 0.005″ to 0.015 and having a relative permittivity in the range of 3 to 4. The gas can be argon supplied in a pressurized cartridge which is commercially available. Pressure in the interior chamber  152  of dielectric structure  150  can be maintained between 14 psia and 15 psia with zero or negative differential pressure between gas inflow source  140 A and negative pressure or vacuum source  145 . The controller is configured to maintain the pressure in interior chamber in a range that varies by less than 10% or less than 5% from a target pressure. The RF power source  130 A can have a frequency of 450 to 550 KHz, and electrical power can be provided within the range of 600 Vrms to about 1200 Vrms and about 0.2 Amps to 0.4 Amps and an effective power of 40 W to 100 W. In one method, the control unit  135  can be programmed to delivery RF energy for a preselected time interval, for example, between 60 seconds and 120 seconds. One aspect of a treatment method corresponding to the invention consists of ablating endometrial tissue with RF energy to elevate endometrial tissue to a temperature greater than 45 degrees Celsius for a time interval sufficient to ablate tissue to a depth of at least 1 mm. Another aspect of the method of endometrial ablation of consists of applying radiofrequency energy to elevate endometrial tissue to a temperature greater than 45 degrees Celsius without damaging the myometrium. 
         [0066]      FIG. 8D  illustrates a final step of the method wherein the physician deflates the expandable balloon member  225  and then extends sleeve  110  distally by actuating the handles  114   a  and  114   b  to collapse frame  155  and then retracting the assembly from the uterine cavity  302 . Alternatively, the deployed working end  122  as shown in  FIG. 8C  can be withdrawn in the proximal direction from the uterine cavity wherein the frame  155  and thin-wall structure  150  will collapse as it is pulled through the cervix.  FIG. 8D  shows the completed ablation with the ablated endometrial tissue indicated at  360 . 
         [0067]    In another embodiment, the system can include an electrode arrangement in the handle  106  or within the gas inflow channel to pre-ionize the neutral gas flow before it reaches the interior chamber  152 . For example, the gas inflow channel can be configured with axially or radially spaced apart opposing polarity electrodes configured to ionize the gas inflow. Such electrodes would be connected in separate circuitry to an RF source. The first and second electrodes  215  (+) and  220  (−) described above would operate as described above to provide the current that is capacitively coupled to tissue through the walls of the dielectric structure  150 . In all other respects, the system and method would function as described above. 
         [0068]    Now turning to  FIGS. 9 and 10 , an alternate working end  122  with thin-wall dielectric structure  150  is shown. In this embodiment, the thin-wall dielectric structure  150  is similar to that of  FIGS. 5 and 6  except that the second polarity electrode  220 ′ that is exterior of the internal chamber  152  is disposed on a surface portion  370  of the thin-wall dielectric structure  150 . In this embodiment, the second polarity electrode  220 ′ comprises a thin-film conductive material, such as gold, that is bonded to the exterior of thin-wall material  210  along two lateral sides  354  of dielectric structure  150 . It should be appreciated that the second polarity electrode can comprise one or more conductive elements disposed on the exterior of wall material  210 , and can extend axially, or transversely to axis  111  and can be singular or multiple elements. In one embodiment shown in more detail in  FIG. 10 , the second polarity electrode  220 ′ can be fixed on another lubricious layer  360 , such as a polyimide film, for example KAPTON®. The polyimide tape extends about the lateral sides  354  of the dielectric structure  150  and provides protection to the wall  210  when it is advanced from or withdrawn into bore  120  in sleeve  110 . In operation, the RF delivery method using the embodiment of  FIGS. 9 and 10  is the same as described above, with RF current being capacitively coupled from the plasma  208  through the wall  210  and endometrial tissue to the second polarity electrode  220 ′ to cause the ablation. 
         [0069]      FIG. 9  further shows an optional temperature sensor  390 , such as a thermocouple, carried at an exterior of the dielectric structure  150 . In one method of use, the control unit  135  can acquire temperature feedback signals from at least one temperature sensor  390  to modulate or terminate RF energy delivery, or to modulate gas flows within the system. In a related method of the invention, the control unit  135  can acquire temperature feedback signals from temperature sensor  240  in interior chamber  152  ( FIG. 6  to modulate or terminate RF energy delivery or to modulate gas flows within the system. 
         [0070]    In another embodiment of the invention,  FIGS. 11-14  depict systems and methods for evaluating the integrity of the uterine cavity which may be perforated or otherwise damaged by the transcervical introduction of probes and instruments into a uterine cavity. If the uterine wall is perforated, it would be preferable to defer any ablation treatment until the uterine wall is healed. A method of the invention comprises introducing transcervically a probe into a patient&#39;s uterine cavity, providing a flow of a fluid (e.g., CO 2 ) through the probe into the uterine cavity and monitoring the rate of the flow to characterize the uterine cavity as perforated or non-perforated based on a change in the flow rate. If the flow rate drops to zero or close to zero, this indicates that the uterine cavity is intact and not perforated. If the flow rate does not drop to zero or close to zero, this indicates that a fluid flow is leaking through a perforation in the uterine cavity  302  into the uterine cavity or escaping around an occlusion balloon that occludes the cervical canal. 
         [0071]    In  FIG. 11 , it can be seen how a pressurized fluid source  405  and controller  410  for controlling and monitoring flows is in fluid communication with lumen  120  of introducer sleeve  110  (see  FIG. 7 ). In one embodiment, the fluid source can be a pressurized cartridge containing CO 2  or another biocompatible gas. In  FIG. 12 , it can be seen that fluid source  405  communicates with a flexible conduit  412  that is connected to a “pig-tail” tubing connector  414  extending outward from handle  106  of the hand-held probe. A tubing in the interior of handle component  114   a  provides a flow passageway  415  to the lumen  120  in the introducer sleeve. In another embodiment, the fluid source  405  and flexible conduit  408  can be integrated into conduit  136  of  FIG. 1 . 
         [0072]    In  FIG. 11 , it can be seen that the flow of fluid is introduced into the uterine cavity  302  after the balloon  225  in the cervical canal has been inflated and after the working end and dielectric structure  150  has been expanded into its triangular shape to occupy the uterine cavity. Thus, the CO 2  gas flows around the exterior surfaces of expanded dielectric structure  150  to fill the uterine cavity. Alternatively, the flow of CO 2  can be provided after the balloon  225  in the cervical canal is inflated but before the dielectric structure  150  is expanded. 
         [0073]      FIG. 13  is a block diagram that schematically depicts the components of subsystem  420  that provides the flow of CO 2  to and through the hand-held probe  105 . It can be seen that pressurized fluid source  405  communicates with a downstream pressure regulator  422 , a proportional valve  424 , flow meter  440 , normally closed solenoid valve  450  and one-way valve  452 . The valve  450  upon actuation by the system operator allows a flow of CO 2  gas from source  405  at a predetermined flow rate and pressure through the subsystem and into the uterine cavity  302 . 
         [0074]    In one embodiment of the method of operation, the physician actuates the system and electronically opens valve  450  which can provide a CO 2  flow through the system. The controller  410  monitors the flow meter or sensor  440  over an interval that can range from 1 second to 60 seconds, or 5 second to 30 seconds to determine the change in the rate of flow and/or a change in the rate of flow. In an embodiment, the flow sensor comprises a Honeywell AWM5000 Series Mass Airflow Sensor, for example Model AWM5101, that measure flows in units of mass flow. In one embodiment, the initial flow rate is between 0.05 slpm (standard liters per minute) and 2.0 slpm, or between 0.1 slpm and 0.2 slpm. The controller  410  includes a microprocessor or programmable logic device that provides a feedback signal from the flow sensors indicating either (i) that the flow rate has dropped to zero or close to zero to thus characterize the uterine cavity as non-perforated, or (ii) that the flow rate has not dropped to a predetermined threshold level within a predetermined time interval to thus characterize the uterine cavity as perforated or that there is a failure in occlusion balloon  225  or its deployment so that the cervical canal is not occluded. In one embodiment, the threshold level is 0.05 slpm for characterizing the uterine cavity as non-perforated. In this embodiment, the controller provides a signal indicating a non-perforated uterine cavity if the flow drops below 0.05 slpm between the fifth second of the flow and the flow time-out, which can be, for example, 30 seconds. 
         [0075]      FIG. 14  depicts aspects of an algorithm used by controller  410  to accomplish a uterine cavity integrity check, with the first step comprising actuating a footswitch or hand switch. Upon actuation, a timer is initialized for 1 to 5 seconds to determine that a fluid source  405  is capable of providing a fluid flow, which can be checked by a pressure sensor between the source  405  and pressure regulator  422 . If no flow is detected, an error signal is provided, such as a visual display signal on the control unit  135  ( FIG. 1 ). 
         [0076]    As can be understood from  FIG. 14 , after the fluid source  405  is checked, the controller opens the supply solenoid valve  450  and a timer is initialized for a 1 to 5 second test interval to insure fluid flows through the subsystem  420  of  FIG. 13 , with either or both a flow meter  440  or a pressure sensor. At the same time as valve  450  is opened, a timer is initialized for cavity integrity test interval of 30 seconds. The controller  410  monitors the flow meter  440  and provides a signal characterizing the uterine cavity as non-perforated if, at any time after the initial 5 second check interval and before the end of the timed-out period (e.g., the 30 second time-out), the flow rate drops below a threshold minimum rate, in one embodiment, to below 0.05 slpm. If the interval times out after 30 seconds and the flow rate does not drop below this threshold, then a signal is generated that characterizes that the uterine cavity is perforated. This signal also can indicate a failure of the occlusion balloon  225 . 
         [0077]    Referring to  FIG. 14 , in one embodiment, in response or otherwise as a result of the signal that the uterine cavity is not perforated, the controller  410  can automatically enable and activate the RF ablation system described above to perform an ablation procedure. The controller  410  can provide a time interval from 1 to 15 seconds to allow CO 2  gas to vent from the uterine cavity  302  before activating RF energy delivery. In another embodiment, the endometrial ablation system may include the optional subsystem  275  for exhausting fluids or gas from the uterine cavity during an ablation treatment (see  FIG. 4  and accompanying text). This subsystem  275  can be actuated to exhaust CO 2  from the uterine cavity  302  which include opening solenoid valve  285  shown in  FIG. 4 . 
         [0078]    The system can further include an override to repeat the cavity integrity check, for example, after evaluation and re-deployment of the occlusion balloon  225 . 
         [0079]      FIGS. 15 and 16  represent another system and method for characterizing the uterine cavity as being non-perforated so as to safely permit an ablation procedure. This system and method utilizes variations in the algorithms that introduce a gas media fluid into the uterine cavity and thereafter measure the changes in flow rates in the gas media. The system again is configured to introduce a gas into the uterine cavity after deployment and expansion of an ablation device in the cavity. If the flow rate of the gas drops to approximately zero, this indicates that the uterine cavity is intact and not perforated. In the event the flow rate of the gas does not drop, there is likely a gas escaping from the uterine cavity  302  through a perforation in the uterine wall. Thus, the gas flow failing to drop may be an indication of a perforation. 
         [0080]      FIG. 15  schematically illustrates three different conditions that may occur when operating the system, which indicate whether the system is functioning properly, and whether the uterine wall is non-perforated or perforated. In  FIG. 15 , the vertical axis indicates a gas flow rate measure in slpm (standard liters per minute), and the horizontal axis represents time in seconds. In one system variation, a gas source  405  such as a pressurized cartridge containing CO 2  is controlled by a controller  410 , and the gas is introduced into the uterine cavity through a passageway in the device introducer sleeve  110  as described above ( FIGS. 11-13 ). The controller  410  and flowmeter monitor flows from the device into the uterine cavity ( FIG. 13 ). The initial flow rate can be in the range of 0.010 splm to 0.20 splm. In one aspect of the invention, a minimum flow rate has been found to be important as a system diagnostic check to insure gas flow is reaching the uterine cavity. Thus,  FIG. 15  illustrates gas flow rate curve in a “condition 1” that may occur when the system fails in delivering gas through the passageways of the system. In one variation, the “condition 1” will be represented by a flow rate over time wherein the flow rate does not achieve a minimum threshold flow rate, which can be from 0.010 splm to 0.050 splm over a predetermined time interval. In one variation, the minimum flow rate is 0.035 splm. The time interval can be from 1 second to 15 seconds. This “condition 1” as in  FIG. 15  could occur, for example, if the gas supply tubing within the device were kinked or pinched which would then prevent gas flow through the system and into the uterine cavity. In a related variation that indicates system failure, a controller algorithm can calculate the volume of gas delivered, and if the volume is less than a threshold volume, then a system failure or fault can be determined. The gas volume V 1  is represented by the “area under the curve” in  FIG. 15 , which is a function of flow rate and time. 
         [0081]      FIG. 15  further illustrates a flow rate curve in a “condition 2” which corresponds to an intact, non-perforated uterine cavity. As can be understood from a practical perspective, a gas flow into an intact uterine cavity at a set pressure from a low pressure source, for example within a range of 0.025 psi to 1.0 psi, would provide an increasing flow rate into the cavity until the cavity was filled with gas, and thereafter the flow rate would diminish to a very low or zero flow rate. Such a “condition 2” flow rate curve as in  FIG. 15  further assumes that there is an adequate sealing mechanism in the cervical canal. Thus, if controller obtains flow rate data from the flowmeter indicating “condition 2”, then the patient&#39;s uterus is non-perforated and is suitable for an ablation. In operation, the controller can look at various specific aspects and parameters of the flow rate curve of “condition 2” in  FIG. 15  to determine that the uterine cavity integrity test has passed, wherein such parameters can comprise any single parameter or a combination of the following parameters: (i) the flow rate falling below a threshold rate, for example between 0.010-0.10 splm; (ii) a change in rate of flow; (iii) a peak flow rate; (iii) the total gas volume V 2  delivered; (iv) an actual flow rate at a point in time compared to a peak flow rate; (v) a derivative of flow rate at a point in time, and (vi) any of the preceding parameters combined with a predetermined time interval. In one embodiment, a constant pressure (0.85 psi) gas is introduced and a minimum threshold flow is set at 0.035 splm. A peak flow is calculated after a time interval of 2 to 15 seconds, and thereafter it is determined if the flow rate diminished by at least 10%, 20%, 30%, 40% or 50% over a time interval of less than 30 seconds. 
         [0082]      FIG. 15  next illustrates a flow rate curve in “condition 3” which represents a gas flow when there is a perforated wall in a uterine cavity, which would allow the gas to escape into the abdominal cavity. In  FIG. 15 , a gas flow at a constant pressure is shown ramping up in flow rate until it levels off and may decline but not the rate of decline to may not go below a threshold value or may not decline a significant amount relative to a peak flow rate. Such a flow rate curve over time would indicate that the gas is leaking from the uterine cavity. 
         [0083]    Now turning to  FIG. 16 , an algorithm diagram is shown that describe one variation in a method of operating a uterine cavity integrity test based on measuring gas flow rates over a selected time interval. At the top of the diagram, the physician actuates the system in which a valve  450  is opened to provide a CO 2  flow through the system ( FIG. 14 ). The controller  410  provides a flow at a pressure, for example 0.85 psi. The actuation of the system also starts a timer wherein a first interval is 30 seconds or less. Over this 30-second interval, the controller records the peak flow rate which typically can occur within 2 to 10 seconds, then monitors the flow rate over the remainder of the 30 second interval and determined whether the flow rate drops 20% or more from the peak flow rate. Then, the controller additionally monitors whether the flow rate falls below a threshold value, for example 0.035 splm. If these two conditions are met, the test indicates that there is no leakage of gas media from the uterine cavity. If the flow rates does not drop 20% from its peak with 30 seconds together with flow being below threshold value, then the test fails indicating a leak of gas from the uterine cavity. Thereafter, the diagram in  FIG. 16 , indicates one additional test which consists of calculating the volume of gas delivered and comparing the volume to the maximum volume within a kinked gas delivery line. If the delivered gas volume is less than the capacity of the gas delivery line, then the test fails and the signal on the controller can indicate this type of test failure. If the delivered gas volume is greater than the capacity of a gas delivery line, then the test passes. In one variation of the controller algorithm can then automatically actuate the delivery of RF energy in an ablation cycle. Alternatively, the controller can provide a signal that the test has passed, and the physician can manually actuate the RF ablation system. 
         [0084]      FIG. 17  schematically illustrates another system and method for characterizing integrity of the walls of a uterine cavity. As can be seen in  FIG. 17 . an introducer sleeve  510  carrying an expandable working end  520  is deployed in the uterine cavity  302 . The working end includes a balloon-like member  522  with a fluid-tight interior chamber  524 . In one embodiment, the working end  510  is expanded laterally by frame elements  526   a  and  526   b , which is similar to previously described embodiments. In addition, a pressurized gas source  540  is actuated to provide an inflation gas through interior sleeve  542  and ports  544  therein that further expands and opens the working end  520  transverse to opening forces applied by frame elements  526   a  and  526   b . The inflation gas can comprise an argon gas that later is converted to a plasma as described previously. The inflation gas can pressurize the working end to a selected pressure ranging from 0.10 psi to 10 psi. In one variation, the pressure can be 0.50 psi. 
         [0085]    As can be seen in  FIG. 17 , an expandable member  548  or balloon is expanded to prevent any gas flow outwardly through the bore  550  in introducer sleeve  510 . Thereafter, a gas inflow system  410  similar to that of  FIG. 13  is utilized to flow a gas source, such as CO 2  into the uterine cavity  302  ( FIG. 17 ). In  FIG. 17 , the gas inflow is indicated by arrows  555  which can comprise an inflow at a predetermined pressure through passageway  558  as described above, and in one variation can be 0.85 psi. The test for uterine cavity integrity then can monitor one or more gas leakage parameters relating to the inflation gas in the interior chamber  524  of the working end  520 . For example, the flow into the uterine cavity  302  will cause an outflow of gas from the interior chamber  524  through passageway  558  which can be measure by a flow meter, or the volume of gas outflow can be measured or the change in gas pressure can be measured. If there is no leak in the uterine cavity, the parameter of the inflation can in the interior chamber  524  will reach an equilibrium in relation to the CO 2  inflow into the cavity. If the inflation gas parameter does not reach an equilibrium, then the change in parameter (flow, volume or pressure) will indicate a leakage of gas from the uterine cavity through a perforation. In general, a method of characterizing the integrity of a patient&#39;s uterus comprises positioning a probe working end is a patient&#39;s uterine cavity, the working end comprising an inflated resilient structure, introducing a flow of a gas through the probe into a uterine cavity exterior about the exterior of the working end, and measuring a gas flow, gas volume or gas pressure parameter of the inflation media in the inflated resilient structure in response to the gas flow into the uterine cavity. 
         [0086]      FIGS. 18 and 19A-19B  schematically illustrates another embodiment of working end  600  and a method of use.  FIG. 18  is a plan view of an expandable dielectric member or membrane  605  carried at distal end of introducer  610  that extend along longitudinal axis  615 . The working end  600  is similar to previously described embodiments, which includes an expandable-collapsible frame of a spring material within a fluid-tight interior chamber  616  of an elastic dielectric member  605 . In one embodiment the frame comprises flexible outward frame elements  618   a  and  618   b  that can bowed outwardly from shape have width W to a shape with width W′ to fully expanded width W″ as shown in  FIG. 18 . The outward frame elements  618   a  and  618   b  are flexed by distal movement of inner frame elements  620   a  and  620   b  that are coupled at proximal ends  622   a  and  622   b  to slidable inner sleeve  624 . It can be understood from  FIG. 18  that the distal tips of inner frame elements  620   a  and  602   b  are welded to distal tips of outward frame elements  618   a  and  618   b , respectively as indicated by welds  628   a  and  628   b . The frame elements are thus configured to provide lateral expansion forces to expand the dielectric member  605  and its ablation surface  630  ( FIG. 19A ) laterally relative to axis  615 . 
         [0087]      FIGS. 19A-19B  illustrates another aspect of the invention wherein the working end  600  and more particularly the dielectric member  605  can be expanded in a second direction relative to axis  615  that is transverse to the plane P of the frame expansion.  FIG. 19A  shows the dielectric membrane  605  stretched and expanded laterally by the frame elements as in  FIG. 18 .  FIG. 19B  shows the dielectric membrane  605  further expanded by inflation of the interior chamber  616  by means of a pressurized inflow of gas from a gas inflow source  635  that is in communication with the interior chamber. In one embodiment, the gas flow into the dielectric member  605  comprises the Argon gas inflow that is ionized as described previously to enable the electrosurgical energy delivery aspects of the invention. 
         [0088]    Referring to  FIG. 19B , it has been found that positive pressure in the interior chamber  616  during operation is useful in ablating tissue since the positive pressure can help in maintaining the ablation surface  630  in contact with tissue, which in turn permits more effective capacitive coupling through the dielectric membrane  605  and passive heating from the membrane when heated by ion bombardment. In one embodiment, the pressure in the balloon is at least 20 mm Hg, at least 30 mm Hg, at least 40 mm Hg or at least 50 mm Hg. Since the Argon gas is circulating as described above, the gas inflow rate and gas outflow rate can be modulated with valve assemblies to provide a net positive pressure in the interior chamber. It also has been found that positive pressure in the interior chamber  616  can be useful in causing plasma filaments to be more uniform and more widely dispersed since the dielectric membrane is spaces away from the frame elements  620   a  and  620   b  in the central region of the interior chamber. 
         [0089]    In another aspect of the invention, the gas pressure in the interior chamber  616  of the dielectric membrane  605  can be modulated during the initiation and duration of a treatment cycle. In one variation, the pressure in the interior chamber prior to actuating RF delivery can be lowered to less than ambient pressure. At the time of RF actuation, the lower Argon pressure will permit more instantaneous ignition of the plasma due to such lowered pressure. Since the Argon gas is circulating, the gas inflow and outflow rates can be modulated with the valve subsystems to provide a negative pressure in interior chamber  616 . The pressure can be at least 5% below ambient pressure, at least 10% below ambient pressure, at least 15% below ambient pressure, or at least 20% below ambient pressure. After ignition of plasma in the interior chamber  616 , the pressure can be regulated to a higher pressure as described above to expand the dielectric membrane away from the frame elements  620   a  and  620   b.    
         [0090]      FIG. 20  illustrates another embodiment of an endometrial ablation system  800  with an elongated sleeve  810  having axis  812  and carrying expandable dielectric structure  815  that is expanded by a frame  818  in an interior chamber  820  of the dielectric. The system operates to apply ablative energy to endometrial tissue as described previously with a first polarity electrode  825  in the interior chamber  820  of the dielectric and second polarity electrodes  828   a ,  828   b  on the exterior of the dielectric  815 . Plasma is formed in the interior chamber  820  which allows capacitive coupling of RF current across dielectric wall  832  which thus causes tissue heating as described previously. The embodiment of working end depicted in  FIG. 20  is configured to allow steam and/or fluid media to escape from the uterine cavity  830  during a treatment cycle if pressure exceeds a predetermined level. It has been found that the surface of silicone wall  832  can intermittently generate steam within the cavity  830  which will locally push the uterine wall out of contact with the dielectric structure  815 .  FIG. 20  depicts the dielectric structure  815  expanded in the uterine cavity during an ablation cycle wherein pockets or regions  836  are created by steam expansion around the cavity (see arrows in regions  836 ). In  FIG. 20 , an inflatable balloon  840  is disposed in the distal end of sleeve  810  to function as a relief valve. The balloon  840  has an annular configuration and surrounds the axial-extending member  842  that carries the frame  818  and the dielectric structure  815 . The balloon  840  can have any suitable axial length ranging from about 5 mm to 5 cm. The inflatable valve balloon  840  is in communication with an inflation source  845  and controller  848  for expanding the balloon in lumen  846  of sleeve  810 . The balloon  840  is controlled at a pressure ranging from 10 mmHg to 100 mmHg in the interior chamber of the valve balloon  840 . In one variation, the balloon  840  is inflated to a pressure of between 25 to 50 mmHg, and during a treatment cycle, transient steam pockets  836  may form and the increase in uterine cavity pressure compresses the balloon  840  and permits fluid media to escape around the balloon into lumen  846  as indicated by arrows  850  ( FIG. 20 ). The lumen  846  in sleeve  810  is configured to direct any escaped fluid media in the proximal direction to vent or collect such fluid. The fluid pathway can further include an aspiration or negative pressure source coupled to lumen  846  ( FIG. 20 ). In this embodiment, the valve balloon  840  is independent of the fluid-tight dielectric structure  815  which also can be characterized as a balloon. The surface of balloon  840  and the surface of lumen  846  can be designed to cooperate in sealing the lumen  846  at low pressure and then functioning at a relief valve at a predetermined higher pressure. For example, the interior surface of the lumen  846  can be configured with annular or axial ridges that cooperate with the modulus and wall thickness of the valve balloon  840 . Also, the sleeve lumen  846  can have a hydrophilic or hydrophobic surface to provide a releasable sealing effect against the balloon  840 . Likewise, the surface of balloon  840  can be configured with annular or axial ridges that cooperate a smooth lumen wall or a grooved lumen wall. Also, the balloon can have a hydrophilic or hydrophobic surface to provide the desired releasable sealing effect. As can be seen in  FIG. 20 , the system provides positive and negative pressure sources,  855  and  860 , to circulate a neutral gas such as Argon through the interior chamber  820  of the dielectric  815  as described previously. The RF source  870  and controller  848  also operate as described previously to generate plasma within the dielectric  815  and to apply energy to tissue through the dielectric. 
         [0091]      FIG. 21  illustrates another system embodiment  800 ′ for endometrial ablation in which elongated sleeve  810  carries an expandable dielectric structure  815 ′ that again is expanded laterally by frame  818  in interior chamber  820  of the dielectric. The system utilizes an RF electrode  825  in interior chamber  820  and opposing polarity electrodes  828   a ,  828   b  on the exterior of the dielectric  815  as described previously to allow capacitive coupling of RF current across dielectric wall  832 . The embodiment of  FIG. 21  uses positive and negative pressure sources  855  and  860  to circulate a neutral gas through interior chamber  820  and control pressure in the fluid-tight interior chamber  820  of the dielectric  815 ′ during a treatment cycle. As can be seen in  FIG. 21 , the proximal portion  872  of the inflatable dielectric  815 ′ extends into lumen  875  of sleeve  810 . Thus, the proximal portion  872  of dielectric  815 ′ can function as a balloon valve as described in the embodiment of  FIG. 20  to allow steam and/or fluid media to escape from the uterine cavity  830  during a treatment cycle if pressure exceeds a predetermined level. In the embodiment of  FIG. 21 , the system parameters for plasma generation are adapted to provide a pre-determined pressure (e.g., 50 mmHg) for releasing pressure from the uterine cavity.  FIG. 21  depicts vapor/fluid escape from the uterine cavity along arrows  850  from transient vapor pockets  836 . In all other respects, the embodiment of  FIG. 21  functions as the embodiment of  FIG. 20 . The advantage of the system embodiment  800 ′ of  FIG. 21  is that a single expandable member  815 ′ functions the ablation structure and the balloon valve. This aspect of the invention reduces complexity and eliminates the need for independent inflation source  845  for inflating an independent balloon valve. 
         [0092]      FIGS. 22 and 23  illustrates another system embodiment  800 ″ for endometrial ablation. In this embodiment, the distal end portion  880  of sleeve  810  includes a plurality of slots  882  which allow the end portion  880  to flex outward to provide a larger cross section when the expandable dielectric structure  815 ″ is expanded. The slots  882  can extend axially and have a length of from about 5 mm to 25 mm. The flexibility of the distal end portion  880  reduces the risk of the distal edge  884  cutting the elastomeric wall  832  of the dielectric structure after its expansion. The slots  882  can range in number from one to 10 or more and can be symmetric or asymmetric around the sleeve.  FIG. 23  shows one variation in which the slots  882  are asymmetric and are configured to cooperate with the height dimension H of the laterally-expandable frame  818 . It can be seen that radial angle R 1  is less than radial angle R 2  and in use the lateral elements  886   a  and  886   b  would flex outward upon expansion of the frame  818  and dielectric structure  815 ″. In one embodiment, the height H of the frame is about 2.5 to 3.0 mm and the diameter of the sleeve  810  is from 6 mm to 8 mm. The distal end portion  880  of the sleeve  810  also can be covered with a thin wall elastomer to cover the slots  882  (not shown) which permits outward flexing under expansion of the dielectric to provide further protection of the dielectric structure. Referring to  FIG. 22 , the dielectric structure  815 ″ can extend proximally a distance of 5 to 20 mm proximal from the slots  882  to permit the dielectric to function as a valve as in the embodiment of  FIG. 21 . In  FIG. 22 , vapor or fluid media is indicated at  850  escaping around the inflated dielectric  815 ″. 
         [0093]    Although particular embodiments of the present invention have been described above in detail, it will be understood that this description is merely for purposes of illustration and the above description of the invention is not exhaustive. Specific features of the invention are shown in some drawings and not in others, and this is for convenience only and any feature may be combined with another in accordance with the invention. A number of variations and alternatives will be apparent to one having ordinary skills in the art. Such alternatives and variations are intended to be included within the scope of the claims. Particular features that are presented in dependent claims can be combined and fall within the scope of the invention. The invention also encompasses embodiments as if dependent claims were alternatively written in a multiple dependent claim format with reference to other independent claims. 
         [0094]    Other variations are within the spirit of the present invention. Thus, while the invention is susceptible to various modifications and alternative constructions, certain illustrated embodiments thereof are shown in the drawings and have been described above in detail. It should be understood, however, that there is no intention to limit the invention to the specific form or forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention, as defined in the appended claims. 
         [0095]    The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. The term “connected” is to be construed as partly or wholly contained within, attached to, or joined together, even if there is something intervening. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate embodiments of the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
         [0096]    Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context. 
         [0097]    All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.