Abstract:
An apparatus and method for use in performing ablation or coagulation of organs and other tissue includes a metallized fabric electrode array which is substantially absorbent and/or permeable to moisture and gases such as steam and conformable to the body cavity. Following placement of the ablation device into contact with the tissue to be ablated, an RF generator is used to deliver RF energy to the conductive regions and to thereby induce current flow from the electrodes to tissue to be ablated. As the current heats the tissue, moisture (such as steam or liquid) leaves the tissue causing the tissue to dehydrate. Suction may be applied to facilitate moisture removal. The moisture permeability and/or absorbency of the electrode carrying member allows the moisture to leave the ablation site so as to prevent the moisture from providing a path of conductivity for the current.

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 14/278,741 filed May 15, 2014, now U.S. Pat. No. 8,998,898, which is a continuation of pending U.S. application Ser. No. 13/962,178 filed Aug. 8, 2013, which is a continuation of U.S. application Ser. No. 12/581,506 filed Oct. 19, 2009, now U.S. Pat. No. 8,506,563, which is a continuation of U.S. application Ser. No. 10/959,771 filed Oct. 6, 2004, now U.S. Pat. No. 7,604,633, which is a divisional of U.S. application Ser. No. 09/103,072 filed Jun. 23, 1998, now U.S. Pat. No. 6,813,520, which claims the benefit of U.S. provisional application 60/084,791 filed May 8, 1998. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to the field of apparatuses and methods for ablating or coagulating the interior surfaces of body organs. Specifically, it relates to an apparatus and method for ablating the interior linings of body organs such as the uterus and gallbladder. 
     BACKGROUND OF THE INVENTION 
     Ablation of the interior lining of a body organ is a procedure which involves heating the organ lining to temperatures which destroy the cells of the lining or coagulate tissue proteins for hemostasis. Such a procedure may be performed as a treatment to one of many conditions, such as chronic bleeding of the endometrial layer of the uterus or abnormalities of the mucosal layer of the gallbladder. Existing methods for effecting ablation include circulation of heated fluid inside the organ (either directly or inside a balloon), laser treatment of the organ lining, and resistive heating using application of RF energy to the tissue to be ablated. 
     U.S. Pat. No. 5,084,044 describes an apparatus for endometrial ablation in which a bladder is inserted into the uterus. Heated fluid is then circulated through the balloon to expand the balloon into contact with the endometrium and to ablate the endometrium thermally. U.S. Pat. No. 5,443,470 describes an apparatus for endometrial ablation in which an expandable bladder is provided with electrodes on its outer surface. After the apparatus is positioned inside the uterus, a non-conductive gas or liquid is used to fill the balloon, causing the balloon to push the electrodes into contact with the endometrial surface. RF energy is supplied to the electrodes to ablate the endometrial tissue using resistive heating. 
     These ablation devices are satisfactory for carrying out ablation procedures. However, because no data or feedback is available to guide the physician as to how deep the tissue ablation has progressed, controlling the ablation depth and ablation profile with such devices can only be done by assumption. 
     For example, the heated fluid method is a very passive and ineffective heating process which relies on the heat conductivity of the tissue. This process does not account for variations in factors such as the amount of contact between the balloon and the underlying tissue, or cooling effects such as those of blood circulating through the organ. RF ablation techniques can achieve more effective ablation since it relies on active heating of the tissue using RF energy, but presently the depth of ablation using RF techniques can only be estimated by the physician since no feedback can be provided as to actual ablation depth. 
     Both the heated fluid techniques and the latest RF techniques must be performed using great care to prevent over ablation. Monitoring of tissue surface temperature is normally carried out during these ablation procedures to ensure the temperature does not exceed 100° C. If the temperature exceeds 100° C., the fluid within the tissue begins to boil and to thereby produce steam. Because ablation is carried out within a closed cavity within the body, the steam cannot escape and may instead force itself deeply into the tissue, or it may pass into areas adjacent to the area intended to be ablated, causing embolism or unintended burning. 
     Moreover, in prior art RF devices the water drawn from the tissue creates a path of conductivity through which current traveling through the electrodes will flow. This can prevent the current from traveling into the tissue to be ablated. Moreover, the presence of this current path around the electrodes causes current to be continuously drawn from the electrodes. The current heats the liquid drawn from the tissue and thus turns the ablation process into a passive heating method in which the heated liquid around the electrodes causes thermal ablation to continue well beyond the desired ablation depths. 
     Another problem with prior art ablation devices is that it is difficult for a physician to find out when ablation has been carried out to a desired depth within the tissue. Thus, it is often the case that too much or too little tissue may be ablated during an ablation procedure. 
     It is therefore desirable to provide an ablation device which eliminates the above-described problem of steam and liquid buildup at the ablation site. It is further desirable to provide an ablation method and device which allows the depth of ablation to be controlled and which automatically discontinues ablation once the desired ablation depth has been reached. 
     SUMMARY OF THE INVENTION 
     The present invention is an apparatus and method of ablating and/or coagulating tissue, such as that of the uterus or other organ. An ablation device is provided which has an electrode array carried by an elongate tubular member. The electrode array includes a fluid permeable elastic member preferably formed of a metallized fabric having insulating regions and conductive regions thereon. During use, the electrode array is positioned in contact with tissue to be ablated, ablation energy is delivered through the array to the tissue to cause the tissue to dehydrate, and moisture generated during dehydration is actively or passively drawn into the array and away from the tissue. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front elevation view of a first embodiment of an ablation device according to the present invention, with the handle shown in cross-section and with the RF applicator head in a closed condition. 
         FIG. 2  is a front elevation view of the ablation device of  FIG. 1 , with the handle shown in cross-section and with the RF applicator head in an open condition. 
         FIG. 3  is a side elevation view of the ablation device of  FIG. 2 . 
         FIG. 4  is a top plan view of the ablation device of  FIG. 2 . 
         FIG. 5A  is a front elevation view of the applicator head and a portion of the main body of the ablation device of  FIG. 2 , with the main body shown in cross-section. 
         FIG. 5B  is a cross-section view of the main body taken along the plane designated  5 B- 5 B in  FIG. 5A . 
         FIG. 6  is a schematic representation of a uterus showing the ablation device of  FIG. 1  following insertion of the device into the uterus but prior to retraction of the introducer sheath and activation of the spring members. 
         FIG. 7  is a schematic representation of a uterus showing the ablation device of  FIG. 1  following insertion of the device into the uterus and following the retraction of the introducer sheath and the expansion of the RF applicator head. 
         FIG. 8  is a cross-section view of the RF applicator head and the distal portion of the main body of the apparatus of  FIG. 1 , showing the RF applicator head in the closed condition. 
         FIG. 9  is a cross-section view of the RF applicator head and the distal portion of the main body of the apparatus of  FIG. 1 , showing the configuration of RF applicator head after the sheath has been retracted but before the spring members have been released by proximal movement of the shaft. 
         FIG. 10  is a cross-section view of the RF applicator head and the distal portion of the main body of the apparatus of  FIG. 1 , showing the configuration of RF applicator head after the sheath has been retracted and after the spring members have been released into the fully opened condition. 
         FIG. 11  is a cross-section view of a distal portion of an RF ablation device similar to  FIG. 1  which utilizes an alternative spring member configuration for the RF applicator head. 
         FIG. 12  is a side elevation view of the distal end of an alternate embodiment of an RF ablation device similar to that of  FIG. 1 , which utilizes an RF applicator head having a modified shape. 
         FIG. 13  is a top plan view of the ablation device of  FIG. 12 . 
         FIG. 14  is a representation of a bleeding vessel illustrating use of the ablation device of  FIG. 12  for general bleeding control. 
         FIGS. 15 and 16  are representations of a uterus illustrating use of the ablation device of  FIG. 12  for endometrial ablation. 
         FIG. 17  is a representation of a prostate gland illustrating use of the ablation device of  FIG. 12  for prostate ablation. 
         FIG. 18  is a cross-section view of target tissue for ablation, showing ablation electrodes in contact with the tissue surface and illustrating energy fields generated during bi-polar ablation. 
         FIGS. 19A-19C  are cross-section views of target tissue for ablation, showing electrodes in contact with the tissue surface and illustrating how varying active electrode density may be used to vary the ablation depth. 
         FIG. 20  is a side elevation view, similar to the view of  FIG. 2 , showing an ablation device according to the present invention in which the electrode carrying means includes inflatable balloons. For purposes of clarity, the electrodes on the electrode carrying means are not shown. 
         FIG. 21  is a side elevation view of a second exemplary embodiment of an ablation device according to the present invention, showing the array in the retracted state. 
         FIG. 22  is a side elevation view of the ablation device of  FIG. 21 , showing the array in the deployed state. 
         FIG. 23  is a top plan view of the applicator head of the apparatus of  FIG. 21 . 
         FIG. 24  is a cross-sectional top view of the encircled region designated  24  in  FIG. 23 . 
         FIG. 25A  is a perspective view of the electrode array of  FIG. 23 . 
         FIG. 25B  is a distal end view of the applicator head of  FIG. 30A . 
         FIG. 26A  is a plan view of a knit that may be used to form the applicator head. 
         FIG. 26B  is a perspective view of a strand of nylon-wrapped spandex of the type that may be used to form the knit of  FIG. 26A . 
         FIGS. 27A ,  27 B,  27 C are top plan views illustrating triangular, parabolic, and rectangular mesh shapes for use as electrode arrays according to the present invention. 
         FIG. 28  is a perspective view showing the flexures and hypotube of the deflecting mechanism of the applicator head of  FIG. 23 . 
         FIG. 29  is a cross-section view of a flexure taken along the plane designated  29 - 29  in  FIG. 23 . 
         FIG. 30  is a top plan view illustrating the flexure and spring arrangement of an alternative configuration of a deflecting mechanism for an applicator head according to the present invention. 
         FIG. 31  is a cross-sectional side view of the bobbin portion of the apparatus of  FIG. 21 . 
         FIG. 32A  is a side elevation view of the handle of the ablation device of  FIG. 21 . 
         FIG. 32B  is a top plan view of the handle of the ablation device of  FIG. 21 . For clarity, portions of the proximal and distal grips are not shown. 
         FIG. 33  illustrates placement of the applicator head according to the present invention in a uterine cavity. 
         FIG. 34  is a side elevation view of the handle of the ablation apparatus of  FIG. 21 , showing portions of the apparatus in cross-section. 
         FIG. 35  is a front elevation view of the upper portion of the proximal handle grip taken along the plane designated  35 - 35  in  FIG. 32B . 
         FIGS. 36A ,  36 B, and  36 C are a series of side elevation views illustrating the heel member as it becomes engaged with the corresponding spring member. 
         FIGS. 37A and 37B  are cross-sectional top views of the frame member mounted on the proximal grip section, taken along the plane designated  37 - 37  in  FIG. 34  and illustrating one of the load limiting features of the second embodiment.  FIG. 37A  shows the condition of the compression spring before the heel member moves into abutment with frame member, and  FIG. 37B  shows the condition of the spring after the heel member moves into abutment with the frame member. 
     
    
    
     DETAILED DESCRIPTION 
     The invention described in this application is an aspect of a larger set of inventions described in the following co-pending applications which are commonly owned by the assignee of the present invention, and are hereby incorporated by reference: U.S. Provisional Patent Application No. 60/084,724, filed May 8, 1998, entitled “APPARATUS AND METHOD FOR INTRA-ORGAN MEASUREMENT AND ABLATION”; and U.S. Provisional Patent Application No. 60/084,712 filed May 8, 1998, entitled “A RADIO-FREQUENCY GENERATOR FOR POWERING AN ABLATION DEVICE”. 
     The ablation apparatus according to the present invention will be described with respect to two exemplary embodiments. 
     First Exemplary Embodiment—Structure 
     Referring to  FIGS. 1 and 2 , an ablation device according to the present invention is comprised generally of three major components: RF applicator head  2 , main body  4 , and handle  6 . Main body  4  includes a shaft  10 . The RF applicator head  2  includes an electrode carrying means  12  mounted to the distal end of the shaft  10  and an array of electrodes  14  formed on the surface of the electrode carrying means  12 . An RF generator  16  is electrically connected to the electrodes  14  to provide mono-polar or bipolar RF energy to them. 
     Shaft  10  is an elongate member having a hollow interior. Shaft  10  is preferably 12 inches long and has a preferred cross-sectional diameter of approximately 4 mm. A collar  13  is formed on the exterior of the shaft  10  at the proximal end. As best shown in  FIGS. 6 and 7 , passive spring member  15  are attached to the distal end of the shaft  10 . 
     Extending through the shaft  10  is a suction/insufflation tube  17  ( FIGS. 6-9 ) having a plurality of holes  17   a  formed in its distal end. An arched active spring member  19  is connected between the distal ends of the passive spring members  15  and the distal end of the suction/insufflation tube  17 . 
     Referring to  FIG. 2 , electrode leads  18   a  and  18   b  extend through the shaft  10  from distal end  20  to proximal end  22  of the shaft  10 . At the distal end  20  of the shaft  10 , each of the leads  18   a ,  18   b  is coupled to a respective one of the electrodes  14 . At the proximal end  22  of the shaft  10 , the leads  18   a ,  18   b  are electrically connected to RF generator  16  via an electrical connector  21 . During use, the leads  18   a ,  18   b  carry RF energy from the RF generator  16  to the electrodes. Each of the leads  18   a ,  18   b  is insulated and carries energy of an opposite polarity than the other lead. 
     Electrically insulated sensor leads  23   a ,  23   b  ( FIGS. 5A and 5B ) also extend through the shaft  10 . Contact sensors  25   a ,  25   b  are attached to the distal ends of the sensor leads  23   a ,  23   b , respectively and are mounted to the electrode carrying means  12 . During use, the sensor leads  23   a ,  23   b  are coupled by the connector  21  to a monitoring module in the RF generator  16  which measures impedance between the sensors  25   a ,  25   b . Alternatively, a reference pad may be positioned in contact with the patient and the impedance between one of the sensors and the reference pad measured. 
     Referring to  FIG. 5B , electrode leads  18   a ,  18   b  and sensor leads  23   a ,  23   b  extend through the shaft  10  between the external walls of the tube  17  and the interior walls of the shaft  10  and they are coupled to electrical connector  21  which is preferably mounted to the collar  13  on the shaft  10 . Connector  21 , which is connectable to the RF generator  16 , includes at least four electrical contact rings  21   a - 21   d  ( FIGS. 1 and 2 ) which correspond to each of the leads  18   a ,  18   b ,  23   a ,  23   b . Rings  21   a ,  21   b  receive, from the RF generator, RF energy of positive and negative polarity, respectively. Rings  21   c ,  21   d  deliver signals from the right and left sensors, respectively, to a monitoring module within the RF generator  16 . 
     Referring to  FIG. 5A , the electrode carrying means  12  is attached to the distal end  20  of the shaft  10 . A plurality of holes  24  may be formed in the portion of the distal end  20  of the shaft which lies within the electrode carrying means  12 . 
     The electrode carrying means  12  preferably has a shape which approximates the shape of the body organ which is to be ablated. For example, the apparatus shown in  FIGS. 1 through 11  has a bicornual shape which is desirable for intrauterine ablation. The electrode carrying means  12  shown in these figures includes horn regions  26  which during use are positioned within the cornual regions of the uterus and which therefore extend towards the fallopian tubes. 
     Electrode carrying means  12  is preferably a sack formed of a material which is non-conductive, which is permeable to moisture and/or which has a tendency to absorb moisture, and which may be compressed to a smaller volume and subsequently released to its natural size upon elimination of compression. Examples of preferred materials for the electrode carrying means include open cell sponge, foam, cotton, fabric, or cotton-like material, or any other material having the desired characteristics. Alternatively, the electrode carrying means may be formed of a metallized fabric. For convenience, the term “pad” may be used interchangeably with the term electrode carrying means to refer to an electrode carrying means formed of any of the above materials or having the listed properties. 
     Electrodes  14  are preferably attached to the outer surface of the electrode carrying means  12 , such as by deposition or other attachment mechanism. The electrodes are preferably made of lengths of silver, gold, platinum, or any other conductive material. The electrodes may be attached to the electrode carrying means  12  by electron beam deposition, or they may be formed into coiled wires and bonded to the electrode carrying member using a flexible adhesive. Naturally, other means of attaching the electrodes, such as sewing them onto the surface of the carrying member, may alternatively be used. If the electrode carrying means  12  is formed of a metallized fabric, an insulating layer may be etched onto the fabric surface, leaving only the electrode regions exposed. 
     The spacing between the electrodes (i.e. the distance between the centers of adjacent electrodes) and the widths of the electrodes are selected so that ablation will reach predetermined depths within the tissue, particularly when maximum power is delivered through the electrodes (where maximum power is the level at which low impedance, low voltage ablation can be achieved). 
     The depth of ablation is also effected by the electrode density (i.e., the percentage of the target tissue area which is in contact with active electrode surfaces) and may be regulated by pre-selecting the amount of this active electrode coverage. For example, the depth of ablation is much greater when the active electrode surface covers more than 10% of the target tissue than it is when the active electrode surfaces covers 1% of the target tissue. 
     For example, by using 3-6 mm spacing and an electrode width of approximately 0.5-2.5 mm, delivery of approximately 20-40 watts over a 9-16 cm2 target tissue area will cause ablation to a depth of approximately 5-7 millimeters when the active electrode surface covers more than 10% of the target tissue area. After reaching this ablation depth, the impedance of the tissue will become so great that ablation will self-terminate as described with respect to the operation of the invention. 
     By contrast, using the same power, spacing, electrode width, and RF frequency will produce an ablation depth of only 2-3 mm when the active electrode surfaces covers less than 1% of the target tissue area. This can be better understood with reference to  FIG. 19A , in which high surface density electrodes are designated  14   a  and low surface density electrodes are designated  14   b . For purposes of this comparison between low and high surface density electrodes, each bracketed group of low density electrodes is considered to be a single electrode. Thus, the electrode widths W and spacings S extend as shown in  FIG. 19A . 
     As is apparent from  FIG. 19A , the electrodes  14   a , which have more active area in contact with the underlying tissue T, produce a region of ablation A 1  that extends more deeply into the tissue T than the ablation region A 2  produced by the low density electrodes  14   b , even though the electrode spacings and widths are the same for the high and low density electrodes. 
     Some examples of electrode widths, having spacings with more than 10% active electrode surface coverage, and their resultant ablation depth, based on an ablation area of 6 cm2 and a power of 20-40 watts, are given on the following table: 
     
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 ELECTRODE WIDTH 
                   
                 SPACING 
                 APPROX. DEPTH 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 mm 
                 1-2 
                 mm 
                 1-3 
                 mm 
               
               
                 1-2.5 
                 mm 
                 3-6 
                 mm 
                 5-7 
                 mm 
               
               
                 1-4.5 
                 mm 
                 8-10 
                 mm 
                 8-10 
                 mm 
               
               
                   
               
             
          
         
       
     
     Examples of electrode widths, having spacings with less than 1% active electrode surface coverage, and their resultant ablation depth, based on an ablation area of 6 cm2 and a power of 20-40 watts, are given on the following table: 
     
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 ELECTRODE WIDTH 
                   
                 SPACING 
                 APPROX. DEPTH 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 mm 
                 1-2 
                 mm 
                 0.5-1 
                 mm 
               
               
                 1-2.S 
                 mm 
                 3-6 
                 mm 
                 2-3 
                 mm 
               
               
                 1-4.5 
                 mm 
                 8-10 
                 mm 
                 2-3 
                 mm 
               
               
                   
               
             
          
         
       
     
     Thus it can be seen that the depth of ablation is significantly less when the active electrode surface coverage is decreased. 
     In the preferred embodiment, the preferred electrode spacing is approximately 8-10 mm in the horn regions  26  with the active electrode surfaces covering approximately 1% of the target region. Approximately 1-2 mm electrode spacing (with 10% active electrode coverage) is preferred in the cervical region (designated  28 ) and approximately 3-6 mm (with greater than 10% active electrode surface coverage) is preferred in the main body region. 
     The RF generator  16  may be configured to include a controller which gives the user a choice of which electrodes should be energized during a particular application in order to give the user control of ablation depth. For example, during an application for which deep ablation is desired, the user may elect to have the generator energize every other electrode, to thereby optimize the effective spacing of the electrodes and to decrease the percentage of active electrode surface coverage, as will be described below with respect to  FIG. 18 . 
     Although the electrodes shown in the drawings are arranged in a particular pattern, it should be appreciated that the electrodes may be arranged in any pattern to provide ablation to desired depths. 
     Referring to  FIGS. 6 and 7 , an introducer sheath  32  facilitates insertion of the apparatus into, and removal of the apparatus from, the body organ to be ablated. The sheath  32  is a tubular member which is telescopically slidable over the shaft  10 . The sheath  32  is slidable between a distal condition, shown in  FIG. 6 , in which the electrode carrying means  12  is compressed inside the sheath, and a proximal condition in which the sheath  32  is moved proximally to release the electrode carrying means from inside it ( FIG. 7 ). By compressing the electrode carrying means  12  to a small volume, the electrode carrying means and electrodes can be easily inserted into the body cavity (such as into the uterus via the vaginal opening). 
     A handle  34  attached to the sheath  32  provides finger holds to allow for manipulation of the sheath  32 . Handle  34  is slidably mounted on a handle rail  35  which includes a sleeve  33 , a finger cutout  37 , and a pair of spaced rails  35   a ,  35   b  extending between the sleeve  33  and the finger cutout  37 . The shaft  10  and sheath  32  slidably extend through the sleeve  33  and between the rails  35   a ,  35   b . The tube  17  also extends through the sleeve  33  and between the rails  35   a ,  35   b , and its proximal end is fixed to the handle rail  35  near the finger cutout  37 . 
     A compression spring  39  is disposed around the proximal most portion of the suction/insufflation tube  17  which lies between the rails  35   a ,  35   b . One end of the compression spring  39  rests against the collar  13  on the shaft  10 , while the opposite end of the compression spring rests against the handle rail  35 . During use, the sheath  32  is retracted from the electrode carrying means  12  by squeezing the handle  34  towards the finger cutout  37  to slide the sheath  32  in the distal direction. When the handle  34  advances against the collar  13 , the shaft  10  (which is attached to the collar  13 ) is forced to slide in the proximal direction, causing compression of the spring  39  against the handle rail  35 . The movement of the shaft  10  relative to the suction/insufflation tube  17  causes the shaft  10  to pull proximally on the passive spring member  15 . Proximal movement of the passive spring member  15  in turn pulls against the active spring member  19 , causing it to move to the opened condition shown in  FIG. 7 . Unless the shaft is held in this retracted condition, the compression spring  39  will push the collar and thus the shaft distally, forcing the RF applicator head to close. A locking mechanism (not shown) may be provided to hold the shaft in the fully withdrawn condition to prevent inadvertent closure of the spring members during the ablation procedure. 
     The amount by which the springs  15 ,  19  are spread may be controlled by manipulating the handle  34  to slide the shaft  10  (via collar  13 ), proximally or distally. Such sliding movement of the shaft  10  causes forceps-like movement of the spring members  15 ,  19 . 
     A flow pathway  36  is formed in the handle rail  35  and is fluidly coupled to a suction/insufflation port  38 . The proximal end of the suction/insufflation tube  17  is fluidly coupled to the flow pathway so that gas fluid may be introduced into, or withdrawn from the suction/insufflation tube  17  via the suction/insufflation port  38 . For example, suction may be applied to the fluid port  38  using a suction/insufflation unit  40 . This causes water vapor within the uterine cavity to pass through the permeable electrode carrying means  12 , into the suction/insufflation tube  17  via holes  17   a , through the tube  17 , and through the suction/insufflation unit  40  via the port  38 . If insufflation of the uterine cavity is desired, insufflation gas, such as carbon dioxide, may be introduced into the suction/insufflation tube  17  via the port  38 . The insufflation gas travels through the tube  17 , through the holes  17   a , and into the uterine cavity through the permeable electrode carrying member  12 . 
     If desirable, additional components may be provided for endoscopic visualization purposes. For example, lumen  42 ,  44 , and  46  may be formed in the walls of the introducer sheath  32  as shown in  FIG. 5B . An imaging conduit, such as a fiberoptic cable  48 , extends through lumen  42  and is coupled via a camera cable  43  to a camera  45 . Images taken from the camera may be displayed on a monitor  56 . An illumination fiber  50  extends through lumen  44  and is coupled to an illumination source  54 . The third lumen  46  is an instrument channel through which surgical instruments may be introduced into the uterine cavity, if necessary. 
     Because during use it is most desirable for the electrodes  14  on the surface of the electrode carrying means  12  to be held in contact with the interior surface of the organ to be ablated, the electrode carrying means  12  may be provided to have additional components inside it that add structural integrity to the electrode carrying means when it is deployed within the body. 
     For example, referring to  FIG. 11 , alternative spring members  15   a ,  19   a  may be attached to the shaft  10  and biased such that, when in a resting state, the spring members are positioned in the fully resting condition shown in  FIG. 11 . Such spring members would spring to the resting condition upon withdrawal of the sheath  32  from the RF applicator head  2 . 
     Alternatively, a pair of inflatable balloons  52  may be arranged inside the electrode carrying means  12  as shown in  FIG. 20  and connected to a tube (not shown) extending through the shaft  10  and into the balloons  52 . After insertion of the apparatus into the organ and following retraction of the sheath  32 , the balloons  52  would be inflated by introduction of an inflation medium such as air into the balloons via a port similar to port  38  using an apparatus similar to the suction/insufflation apparatus  40 . 
     Structural integrity may also be added to the electrode carrying means through the application of suction to the proximal end  22   a  of the suction/insufflation tube  17 . Application of suction using the suction/insufflation device  40  would draw the organ tissue towards the electrode carrying means  12  and thus into better contact with the electrodes  14 . 
       FIGS. 12 and 13  show an alternative embodiment of an ablation device according to the present invention. In the alternative embodiment, an electrode carrying means  12   a  is provided which has a shape which is generally tubular and thus is not specific to any particular organ shape. An ablation device having a general shape such as this may be used anywhere within the body where ablation or coagulation is needed. For example, the alternative embodiment is useful for bleeding control during laparoscopic surgery ( FIG. 14 ), tissue ablation in the prostate gland ( FIG. 17 ), and also intrauterine ablation ( FIGS. 15 and 16 ). 
     First Exemplary Embodiment—Operation 
     Operation of the first exemplary embodiment of an ablation device according to the present invention will next be described. 
     Referring to  FIG. 1 , the device is initially configured for use by positioning the introducer sheath  32  distally along the shaft  10 , such that it compresses the electrode carrying means  12  within its walls. 
     At this time, the electrical connector  21  is connected to the RF generator  16 , and the fiberoptic cable  48  and the illumination cable  50  are connected to the illumination source, monitor, and camera,  54 ,  56 ,  45 . The suction/insufflation unit  40  is attached to suction/insufflation port  38  on the handle rail  35 . The suction/insufflation unit  40  is preferably set to deliver carbon dioxide at an insufflation pressure of 20-200 mmHg. 
     Next, the distal end of the apparatus is inserted through the vaginal opening V and into the uterus U as shown in  FIG. 6 , until the distal end of the introducer sheath  32  contacts the fundus F of the uterus. At this point, carbon dioxide gas is introduced into the tube  17  via the port  38 , and it enters the uterine cavity, thereby expanding the uterine cavity from a flat triangular shape to a 1-2 cm high triangular cavity. The physician may observe (using the camera  45  and monitor  56 ) the internal cavities using images detected by a fiberoptic cable  48  inserted through lumen  42 . If, upon observation, the physician determines that a tissue biopsy or other procedure is needed, the required instruments may be inserted into the uterine cavity via the instrument channel  46 . 
     Following insertion, the handle  34  is withdrawn until it abuts the collar  13 . At this point, the sheath  32  exposes the electrode carrying member  12  but the electrode carrying member  12  is not yet fully expanded (see  FIG. 9 ), because the spring members  15 ,  19  have not yet been moved to their open condition. The handle  34  is withdrawn further, causing the shaft  10  to move proximally relative to the suction/insufflation tube  17 , causing the passive spring members  15  to pull the active spring members  19 , causing them to open into the opened condition shown in  FIG. 10 . 
     The physician may confirm proper positioning of the electrode carrying member  12  using the monitor  56 , which displays images from the fiberoptic cable  48 . 
     Proper positioning of the device and sufficient contact between the electrode carrying member  12  and the endometrium may further be confirmed using the contact sensors  25   a ,  25   b . The monitoring module of the RF generator measures the impedance between these sensors using conventional means. If there is good contact between the sensors and the endometrium, the measured impedance will be approximately 20-180 ohm, depending on the water content of the endometrial lining. 
     The sensors are positioned on the distal portions of the bicornual shaped electrode carrying member  12 , which during use are positioned in the regions within the uterus in which it is most difficult to achieve good contact with the endometrium. Thus, an indication from the sensors  25   a ,  25   b  that there is sound contact between the sensors and the endometrial surface indicates that good electrode contact has been made with the endometrium. 
     Next, insufflation is terminated. Approximately 1-5 cc of saline may be introduced via suction/insufflation tube  17  to initially wet the electrodes and to improve electrode electrical contact with the tissue. After introduction of saline, the suction/insufflation device  40  is switched to a suctioning mode. As described above, the application of suction to the RF applicator head  2  via the suction/insufflation tube  17  collapses the uterine cavity onto the RF applicator head  2  and thus assures better contact between the electrodes and the endometrial tissue. 
     If the generally tubular apparatus of  FIGS. 12 and 13  is used, the device is angled into contact with one side of the uterus during the ablation procedure. Once ablation is completed, the device (or a new device) is repositioned in contact with the opposite side and the procedure is repeated. See.  FIGS. 15 and 16 . 
     Next, RF energy at preferably about 500 kHz and at a constant power of approximately 30 W is applied to the electrodes. As shown in  FIG. 5   a , it is preferable that each electrode be energized at a polarity opposite from that of its neighboring electrodes. By doing so, energy field patterns, designated F 1 , F 2  and F 4  in  FIG. 18 , are generated between the electrode sites and thus help to direct the flow of current through the tissue T to form a region of ablation A. As can be seen in  FIG. 18 , if electrode spacing is increased such by energizing, for example every third or fifth electrode rather than all electrodes, the energy patterns will extend more deeply into the tissue. (See, for example, pattern F 2  which results from energization of electrodes having a non-energized electrode between them, or pattern F 4  which results from energization of electrodes having three non-energized electrodes between them). 
     Moreover, ablation depth may be controlled as described above by providing low surface density electrodes on areas of the electrode carrying member which will contact tissue areas at which a smaller ablation depth is required (see  FIG. 19A ). Referring to  FIG. 19B , if multiple, closely spaced, electrodes  14  are provided on the electrode carrying member, a user may set the RF generator to energize electrodes which will produce a desired electrode spacing and active electrode area. For example, alternate electrodes may be energized as shown in  FIG. 19B , with the first three energized electrodes having positive polarity, the second three having negative polarity, etc. 
     As another example, shown in  FIG. 19C , if greater ablation depth is desired the first five electrodes may be positively energized, and the seventh through eleventh electrodes negatively energized, with the sixth electrode remaining inactivated to provide adequate electrode spacing. 
     As the endometrial tissue heats, moisture begins to be released from the tissue. The moisture permeates the electrode carrying member  12  and is thereby drawn away from the electrodes. The moisture may pass through the holes  17   a  in the suction/insufflation tube  17  and leave the suction/insufflation tube  17  at its proximal end via port  38  as shown in  FIG. 7 . Moisture removal from the ablation site may be further facilitated by the application of suction to the shaft  10  using the suction/insufflation unit  40 . 
     Removal of the moisture from the ablation site prevents formation of a liquid layer around the electrodes. As described above, liquid build-up at the ablation site is detrimental in that provides a conductive layer that carries current from the electrodes even when ablation has reached the desired depth. This continued current flow heats the liquid and surrounding tissue, and thus causes ablation to continue by unpredictable thermal conduction means. 
     Tissue which has been ablated becomes dehydrated and thus decreases in conductivity. By shunting moisture away from the ablation site and thus preventing liquid build-up, there is no liquid conductor at the ablation area during use of the ablation device of the present invention. Thus, when ablation has reached the desired depth, the impedance at the tissue surface becomes sufficiently high to stop or nearly stop the flow of current into the tissue. RF ablation thereby stops and thermal ablation does not occur in significant amounts. If the RF generator is equipped with an impedance monitor, a physician utilizing the ablation device can monitor the impedance at the electrodes and will know that ablation has self-terminated once the impedance rises to a certain level and then remains fairly constant. By contrast, if a prior art bipolar RF ablation device was used together with an impedance monitor, the presence of liquid around the electrodes would cause the impedance monitor to give a low impedance reading regardless of the depth of ablation which had already been carried out, since current would continue to travel through the low-impedance liquid layer. 
     Other means for monitoring and terminating ablation may also be provided. For example, a thermocouple or other temperature sensor may be inserted to a predetermined depth in the tissue to monitor the temperature of the tissue and terminate the delivery of RF energy or otherwise signal the user when the tissue has reached a desired ablation temperature. 
     Once the process has self terminated, 1-5 cc of saline can be introduced via suction/insufflation tube  17  and allowed to sit for a short time to aid separation of the electrode from the tissue surface. The suction insufflation device  40  is then switched to provide insufflation of carbon dioxide at a pressure of 20-200 mmHg. The insufflation pressure helps to lift the ablated tissue away from the RF applicator head  2  and to thus ease the closing of the RF applicator head. The RF applicator head  2  is moved to the closed position by sliding the handle  34  in a distal direction to fold the spring members  15 ,  19  along the axis of the device and to cause the introducer sheath  32  to slide over the folded RF applicator head. The physician may visually confirm the sufficiency of the ablation using the monitor  56 . Finally, the apparatus is removed from the uterine cavity. 
     Second Exemplary Embodiment—Structure 
     A second embodiment of an ablation device  100  in accordance with the present invention is shown in  FIGS. 21-37B . The second embodiment differs from the first embodiment primarily in its electrode pattern and in the mechanism used to deploy the electrode applicator head or array. Naturally, aspects of the first and second exemplary embodiments and their methods of operation may be combined without departing from the scope of the present invention. 
     Referring to  FIGS. 21 and 22 , the second embodiment includes an RF applicator head  102 , a sheath  104 , and a handle  106 . As with the first embodiment, the applicator head  102  is slidably disposed within the sheath  104  ( FIG. 21 ) during insertion of the device into the uterine cavity, and the handle  106  is subsequently manipulated to cause the applicator head  102  to extend from the distal end of the sheath  104  ( FIG. 22 ) and to expand into contact with body tissue ( FIG. 33 ). 
     RF Applicator Head 
     Referring to  FIG. 23 , in which the sheath  104  is not shown for clarity, applicator head  102  extends from the distal end of a length of tubing  108  which is slidably disposed within the sheath  104 . Applicator head  102  includes an external electrode array  102   a  and an internal deflecting mechanism  102   b  used to expand and tension the array for positioning into contact with the tissue. 
     Referring to  FIGS. 25A and 25B , the array  102   a  of applicator head  102  is formed of a stretchable metallized fabric mesh which is preferably knitted from a nylon and spandex knit plated with gold or other conductive material. In one array design, the knit (shown in  FIGS. 26A and 26B ) is formed of three monofilaments of nylon  109   a  knitted together with single yarns of spandex  19   b . Each yarn of spandex  109   b  has a double helix  109   c  of five nylon monofilaments coiled around it. 
     This knit of elastic (spandex) and inelastic (nylon) yarns is beneficial for a number of reasons. For example, knitting elastic and relatively inelastic yarns allows the overall deformability of the array to be pre-selected. 
     The mesh is preferably constructed so as to have greater elasticity in the transverse direction (T) than in the longitudinal direction (L). In a preferred mesh design, the transverse elasticity is on the order of approximately 300% whereas the longitudinal elasticity is on the order of approximately 100%. The large transverse elasticity of the array allows it to be used in a wide range of uterine sizes. 
     Another advantage provided by the combination of elastic and relatively inelastic yarns is that the elastic yarns provide the needed elasticity to the array while the relatively inelastic yarns provide relatively non-stretchable members to which the metallization can adhere without cracking during expansion of the array. In the knit configuration described above, the metallization adheres to the nylon coiled around the spandex. During expansion of the array, the spandex elongates and the nylon double helix at least partially elongates from its coiled configuration. 
     One process which may be used to apply the gold to the nylon/spandex knit involves plating the knit with silver using known processes which involve application of other materials as base layers prior to application of the silver to ensure that the silver will adhere. Next, the insulating regions  110  (described below) are etched onto the silver, and afterwards the gold is plated onto the silver. Gold is desirable for the array because of it has a relatively smooth surface, is a very inert material, and has sufficient ductility that it will not crack as the nylon coil elongates during use. 
     The mesh may be configured in a variety of shapes, including but not limited to the triangular shape S 1 , parabolic S 2 , and rectangular S 3  shapes shown in  FIGS. 27A ,  27 B and  27 C, respectively. 
     Turning again to  FIGS. 25A and 25B , when in its expanded state, the array  102   a  includes a pair of broad faces  112  spaced apart from one another. Narrower side faces  114  extend between the broad faces  112  along the sides of the applicator head  102 , and a distal face  116  extends between the broad faces  112  at the distal end of the applicator head  102 . 
     Insulating regions  110  are formed on the applicator head to divide the mesh into electrode regions. The insulated regions  110  are preferably formed using etching techniques to remove the conductive metal from the mesh, although alternate methods may also be used, such as by knitting conductive and non-conductive materials together to form the array. 
     The array may be divided by the insulated regions  110  into a variety of electrode configurations. In a preferred configuration the insulating regions  110  divide the applicator head into four electrodes  118   a - 118   d  by creating two electrodes on each of the broad faces  112 . To create this four-electrode pattern, insulating regions  110  are placed longitudinally along each of the broad faces  112  as well as along the length of each of the faces  114 ,  116 . The electrodes  118   a - 118   d  are used for ablation and, if desired, to measure tissue impedance during use. 
     Deflecting mechanism  102   b  and its deployment structure is enclosed within electrode array  102   a . Referring to  FIG. 23 , external hypotube  120  extends from tubing  108  and an internal hypotube  122  is slidably and co-axially disposed within hypotube  120 . Flexures  124  extend from the tubing  108  on opposite sides of external hypotube  120 . A plurality of longitudinally spaced apertures  126  ( FIG. 28 ) are formed in each flexure  124 . During use, apertures  126  allow moisture to pass through the flexures and to be drawn into exposed distal end of hypotube  120  using a vacuum source fluidly coupled to hypotube  120 . 
     Each flexure  124  preferably includes conductive regions that are electrically coupled to the array  102   a  for delivery of RF energy to the body tissue. Referring to  FIG. 29 , strips  128  of copper tape or other conductive material extend along opposite surfaces of each flexure  124 . Each strip  128  is electrically insulated from the other strip  128  by a non-conductive coating on the flexure. Conductor leads (not shown) are electrically coupled to the strips  128  and extend through tubing  108  ( FIG. 23 ) to an electrical cord  130  ( FIG. 21 ) which is attachable to the RF generator. 
     During use, one strip  128  on each conductor is electrically coupled via the conductor leads to one terminal on the RF generator while the other strip is electrically coupled to the opposite terminal, thus causing the array on the applicator head to have regions of alternating positive and negative polarity. 
     The flexures may alternatively be formed using a conductive material or a conductively coated material having insulating regions formed thereon to divide the flexure surfaces into multiple conductive regions. Moreover, alternative methods such as electrode leads independent of the flexures  124  may instead be used for electrically connecting the electrode array to the source of RF energy. 
     It is important to ensure proper alignment between the conductive regions of the flexures  124  (e.g. copper strips  128 ) and the electrodes  118   a - 118   d  in order to maintain electrical contact between the two. Strands of thread  134  (which may be nylon) ( FIG. 23 ) are preferably sewn through the array  102   a  and around the flexures  124  in order to prevent the conductive regions  128  from slipping out of alignment with the electrodes  118   a - 118   d . Alternate methods for maintaining contact between the array  102   a  and the conductive regions  128  include using tiny bendable barbs extending between the flexures  124  and the array  102   a  to hook the array to the conductive regions  128 , or bonding the array to the flexures using an adhesive applied along the insulating regions of the flexures. 
     Referring again to  FIG. 23 , internal flexures  136  extend laterally and longitudinally from the exterior surface of hypotube  122 . Each internal flexure  136  is connected at its distal end to one of the flexures  124  and a transverse ribbon  138  extends between the distal portions of the internal flexures  136 . Transverse ribbon  138  is preferably pre-shaped such that when in the relaxed condition the ribbon assumes the corrugated configuration shown in  FIG. 23  and such that when in a compressed condition it is folded along the plurality of creases  140  that extend along its length. Flexures  124 ,  136  and ribbon  138  are preferably an insulated spring material such as heat treated 17-7 PH stainless steel. 
     The deflecting mechanism is preferably configured such that the distal tips of the flexures  124  are sufficiently flexible to prevent tissue puncture during deployment and/or use. Such an atraumatic tip design may be carried out in a number of ways, such as by manufacturing the distal sections  124   a  ( FIG. 28 ) of the flexures from a material that is more flexible than the proximal sections  124   b . For example, flexures  124  may be provided to have proximal sections formed of a material having a modulus of approximately 28×106 psi and distal sections having a durometer of approximately 72 D. 
     Alternatively, referring to  FIG. 30 , the flexures  124  may be joined to the internal flexures  136  at a location more proximal than the distal tips of the flexures  124 , allowing them to move more freely and to adapt to the contour of the surface against which they are positioned (see dashed lines in  FIG. 30 ). Given that uterine sizes and shapes vary widely between women, the atraumatic tip design is further beneficial in that it allows the device to more accurately conform to the shape of the uterus in which it is deployed while minimizing the chance of injury. 
     The deflecting mechanism formed by the flexures  124 ,  136 , and ribbon  138  forms the array into the substantially triangular shape shown in  FIG. 23 , which is particularly adaptable to most uterine shapes. As set forth in detail below, during use distal and proximal grips  142 ,  144  forming handle  106  are squeezed towards one another to withdraw the sheath and deploy the applicator head. This action results in relative rearward motion of the hypotube  120  and relative forward motion of the hypotube  122 . The relative motion between the hypotubes causes deflection in flexures  124 ,  136  which deploys and tensions the electrode array  102   a.    
     Measurement Device 
     The ablation device according to the second embodiment includes a measurement device for easily measuring the uterine width and for displaying the measured width on a gauge  146  ( FIG. 21 ). The measurement device utilizes non-conductive (e.g. nylon) suturing threads  148  that extend from the hypotube  122  and that have distal ends attached to the distal portion of the deflecting mechanism ( FIG. 23 ). As shown in  FIG. 24 , threads  148  are preferably formed of a single strand  150  threaded through a wire loop  152  and folded over on itself. Wire loop  152  forms the distal end of an elongate wire  154  which may be formed of stainless steel or other wire. 
     Referring to  FIG. 31 , wire  154  extends through the hypotube  122  and is secured to a rotatable bobbin  156 . The rotatable bobbin  156  includes a dial face  158  preferably covered in a clear plastic. As can be seen in  FIG. 32   b , dial face  158  includes calibration markings corresponding to an appropriate range of uterine widths. The bobbin is disposed within a gauge housing  160  and a corresponding marker line  162  is printed on the gauge housing. A torsion spring  164  provides rotational resistance to the bobbin  156 . 
     Expansion of the applicator head  102  during use pulls threads  148  ( FIG. 23 ) and thus wire  154  ( FIG. 24 ) in a distal direction. Wire  154  pulls against the bobbin  156  ( FIG. 31 ), causing it to rotate. Rotation of the bobbin positions one of the calibration markings on dial face  158  into alignment with the marker line  162  ( FIG. 32B ) to indicate the distance between the distal tips of flexures  124  and thus the uterine width. 
     The uterine width and length (as determined using a conventional sound or other means) are preferably input into an RF generator system and used by the system to calculate an appropriate ablation power as will be described below. Alternately, the width as measured by the apparatus of the invention and length as measured by other means may be used by the user to calculate the power to be supplied to the array to achieve the desired ablation depth. 
     The uterine width may alternatively be measured using other means, including by using a strain gauge in combination with an A/D converter to transduce the separation distance of the flexures  124  and to electronically transmit the uterine width to the RF generator. 
     Control of Ablation Depth 
     The most optimal electrocoagulation occurs when relatively deep ablation is carried out in the regions of the uterus at which the endometrium is thickest, and when relatively shallower ablation is carried out in areas in which the endometrium is shallower. A desirable range of ablation depths includes approximately 2-3 mm for the cervical os and the cornual regions, and approximately 7-8 mm in the main body of the uterus where the endometrium is substantially thicker. 
     As discussed with respect to the first embodiment, a number of factors influence the ablation depth that can be achieved using a given power applied to a bipolar electrode array. These include the power supplied by the RF generator, the distance between the centers of adjacent electrodes (“center-to-center distance”), the electrode density (i.e., the porosity of the array fabric or the percent of the array surface that is metallic), the edge gap (i.e. the distance between the edges of adjacent electrode poles), and the electrode surface area. Other factors include blood flow (which in slower-ablating systems can dissipate the RF) and the impedance limit. 
     Certain of these factors may be utilized in the present invention to control ablation depth and to provide deeper ablation at areas requiring deeper ablation and to provide shallower regions in areas where deep ablation is not needed. For example, as center-to-center distance increases, the depth of ablation increases until a point where the center to center distance is so great that the strength of the RF field is too diffuse to excite the tissue. It can been seen with reference to  FIG. 33  that the center to center distance d 1  between the electrodes  118   a ,  118   b  is larger within the region of the array that lies in the main body of the uterus and thus contributes to deeper ablation. The center to center distance d 2  between electrodes  118   a ,  118   b  is smaller towards the cervical canal where it contributes to shallower ablation. At the distal end of the device, the shorter center to center distances d 3  extend between top and bottom electrodes  118   b ,  118   c  and  118   a ,  118   d  and again contribute to shallower ablation. 
     Naturally, because the array  102   a  expands to accommodate the size of the uterus in which it is deployed, the dimensions of the array  102   a  vary. One embodiment of the array  102   a  includes a range of widths of at least approximately 2.5-4.5 cm, a range of lengths of at least approximately 4-6 cm, and a density of approximately 35%-45%. 
     The power supplied to the array by the RF generator is calculated by the RF generator system to accommodate the electrode area required for a particular patient. As discussed above, the uterine width is measured by the applicator head  102  and displayed on gauge  146 . The uterine length is measured using a sound, which is an instrument conventionally used for that purpose. It should be noted that calibration markings of the type used on a conventional sound device, or other structure for length measurement, may be included on the present invention to allow it to be used for length measurement as well. 
     The user enters the measured dimensions into the RF generator system using an input device, and the RF generator system calculates or obtains the appropriate set power from a stored look-up table using the uterine width and length as entered by the user. An EPROM within the RF generator system converts the length and width to a set power level according to the following relationship:
 
 P=L×W× 5.5
 
     Where P is the power level in watts, L is the length in centimeters, W is the width in centimeters, and 5.5 is a constant having units of watts per square centimeter. 
     Alternatively, the user may manually calculate the power setting from the length and width, or s/he may be provided with a table of suggested power settings for various electrode areas (as determined by the measured length and width) and will manually set the power on the RF generator accordingly. 
     Handle 
     Referring again to  FIGS. 21 and 22 , the handle  106  of the RF ablation device according to the second embodiment includes a distal grip section  142  and a proximal grip section  144  that are pivotally attached to one another at pivot pin  166 . 
     The proximal grip section  144  is coupled to the hypotube  122  ( FIG. 23 ) via yoke  168 , overload spring  170  and spring stop  172 , each of which is shown in the section view of  FIG. 34 . The distal grip section  142  is coupled to the external hypotube  120  via male and female couplers  174 ,  176  (see  FIGS. 32A and 32B ). Squeezing the grip sections  142 ,  144  towards one another thus causes relative movement between the external hypotube  120  and the internal hypotube  122 . This relative sliding movement results in deployment of the deflecting mechanism  102   b  from the distal end of the sheath and expansion of the array  102   a  to its expanded state. 
     Referring to  FIGS. 32A  and B, rack  180  is formed on male coupler  174  and calibration markings  182  are printed adjacent the rack  180 . The calibration markings  182  correspond to a variety of uterine lengths and may include lengths ranging from, for example, 4.0 to 6.0 cm in 0.5 cm increments. 
     A sliding collar  184  is slidably disposed on the tubing  108  and is slidable over male coupler  174 . Sliding collar  184  includes a rotating collar  186  and a female coupler  176  that includes a wedge-shaped heel  188 . A locking spring member  190  ( FIGS. 32B and 35 ) extends across an aperture  192  formed in the proximal grip  144  in alignment with the heel  188 . When the distal and proximal handle sections are squeezed together to deploy the array, the heel  188  passes into the aperture  192 . Its inclined lower surface gradually depresses the spring member  190  as the heel moves further into the aperture  192 . See  FIGS. 36A and 36B . After passing completely over the spring member, the heel moves out of contact with the spring member. The spring member snaps upwardly thereby engaging the heel in the locked position. See  FIG. 36C . 
     A release lever  194  ( FIG. 35 ) is attached to the free end of the spring member  190 . To disengage the spring lock, release lever  194  is depressed to lower spring member  190  so that the inclined heel can pass over the spring member and thus out of the aperture  192 . 
     Referring again to  FIGS. 32A and 32B , sliding collar  184  is configured to allow the user to limit longitudinal extension of the array  102   a  to a distance commensurate with a patient&#39;s predetermined uterine length. It does so by allowing the user to adjust the relative longitudinal position of male coupler  174  relative to the female coupler  176  using the rotating collar  186  to lock and unlock the female coupler from the rack  180  and the male coupler  174 . Locking the female coupler to the rack  180  and male coupler  174  will limit extension of the array to approximately the predetermined uterine length, as shown on the calibration markings  182 . 
     Once the uterine length has been measured using a conventional sound, the user positions sliding collar  184  adjacent to calibration marks  182  corresponding to the measured uterine length (e.g. 4.5 cm). Afterwards, the user rotates the collar section  186  to engage its internally positioned teeth with the rack  180 . This locks the longitudinal position of the heel  188  such that it will engage with the spring member  190  on the proximal grip when the array has been exposed to the length set by the sliding collar. 
     The handle  106  includes a pair of spring assemblies which facilitate controlled deployment and stowage of the array  102   a . One of the spring assemblies controls movement of the grips  142 ,  144  to automatically stow the array  102   a  into the sheath  104  when the user stops squeezing the grips  142 ,  144  towards one another. The other of the spring assemblies controls the transverse movement of the spring flexures  124  to the expanded condition by limiting the maximum load that can be applied to the deployment mechanism  102   b.    
       FIG. 34  shows the distal and proximal grips  142  and  144  in partial cross-section. The first spring assembly for controlled stowage includes a handle return mandrel  196  that is slidably disposed within the proximal grip  144 . A compression spring  198  surrounds a portion of the return mandrel  196 , and a retaining ring  200  is attached to the mandrel  196  above the spring  198 . A spring stop  202  is disposed between the spring  198  and the retaining ring. 
     The lowermost end of the return mandrel  196  is pivotally engaged by a coupling member  204  on distal grip  142 . Relative movement of the grips  142 ,  144  towards one another causes the coupling member  204  to pull the return member downwardly with the proximal grip  144  as indicated by arrows. Downward movement of the mandrel  196  causes its retaining ring  200  and spring stop  202  to bear downwardly against the compression spring  198 , thereby providing a movement which acts to rotate the grips  142 ,  144  away from one another. When tension against the grips  142 ,  144  is released (assuming that heel  188  is not locked into engagement with spring member  190 ) the grips rotate apart into the opened position as the compression spring  198  returns to the initial state, stowing the applicator head inside the sheath. 
     The second spring assembly for controlling array deployment is designed to control separation of the flexures. It includes a frame member  178  disposed over yoke  168 , which is pivotally attached to proximal grip  144 . Tubing  108  extends from the array  102   a  (see  FIG. 23 ), through the sheath  104  and is fixed at its proximal end to the frame member  178 . Hypotube  122  does not terminate at this point but instead extends beyond the proximal end of tubing  108  and through a window  206  in the frame member. Its proximal end  208  is slidably located within frame member  178  proximally of the window  206  and is fluidly coupled to a vacuum port  210  by fluid channel  212 . Hypotube  120  terminates within the frame. Its proximal end is fixed within the distal end of the frame. 
     A spring stop  172  is fixed to a section of the hypotube within the window  206 , and a compression spring  170  is disposed around the hypotube between the spring stop  172  and yoke  168 . See  FIGS. 32B and 34 . 
     When the distal and proximal grips are moved towards one another, the relative rearward motion of the distal grip causes the distal grip to withdraw the sheath  104  from the array  102   a . Referring to  FIGS. 37A and 37B , this motion continues until female coupler  176  contacts and bears against frame member  178 . Continued motion between the grips causes a relative rearward motion in the frame which causes the same rearward relative motion in external hypotube  120 . An opposing force is developed in yoke  168 , which causes a relative forward motion in hypotube  122 . The relative motion between the hypotubes causes deflection in flexures  124 ,  136  which deflect in a manner that deploys and tensions the electrode array. Compression spring  170  acts to limit the force developed by the operator against hypotubes  120 ,  122 , thus limiting the force of flexures  124 ,  136  acting on the array and the target tissue surrounding the array. 
     Referring to  FIG. 21 , collar  214  is slidably mounted on sheath  104 . Before the device is inserted into the uterus, collar  214  can be positioned along sheath  104  to the position measured by the uterine sound. Once in position, the collar provides visual and tactile feedback to the user to assure the device has been inserted the proper distance. In addition, after the applicator head  102  has been deployed, if the patient&#39;s cervical canal diameter is larger than the sheath dimensions, the collar  214  can be moved distally towards the cervix, making contact with it and creating a pneumatic seal between the sheath and cervix. 
     Second Exemplary Embodiment—Operation 
     In preparation for ablating the uterus utilizing the second exemplary embodiment, the user measures the uterine length using a uterine sound device. The user next positions sliding collar  184  ( FIG. 32B ) adjacent to calibration marks  182  corresponding to the measured uterine length (e.g. 4.5 cm) and rotates the collar section  186  to engage its internally positioned teeth with the rack  180 . This locks the longitudinal position of the heel  188  ( FIG. 32A ) such that it will engage with the spring member  190  when the array has been exposed to the length set by the sliding collar. 
     Next, with the grips  142 ,  144  in their resting positions to keep the applicator head  102  covered by sheath  104 , the distal end of the device  100  is inserted into the uterus. Once the distal end of the sheath  104  is within the uterus, grips  142 ,  144  are squeezed together to deploy the applicator head  102  from sheath  104 . Grips  142 ,  144  are squeezed until heel  188  engages with locking spring member  190  as described with respect to FIGS.  3 BA through  36 C. 
     At this point, deflecting mechanism  102   b  has deployed the array  102   a  into contact with the uterine walls. The user reads the uterine width, which as described above is transduced from the separation of the spring flexures, from gauge  146 . The measured length and width are entered into the RF generator system  250  ( FIG. 21 ) and used to calculate the ablation power. 
     Vacuum source  252  ( FIG. 21 ) is activated, causing application of suction to hypotube  122  via suction port  210 . Suction helps to draw uterine tissue into contact with the array  102 . 
     Ablation power is supplied to the electrode array  102   a  by the RF generator system  250 . The tissue is heated as the RF energy passes from electrodes  118   a - d  to the tissue, causing moisture to be released from the tissue. The vacuum source  252  helps to draw moisture from the uterine cavity into the hypotube  122 . Moisture withdrawal is facilitated by the apertures  126  formed in flexures  124  by preventing moisture from being trapped between the flexures  124  and the lateral walls of the uterus. 
     If the RF generator  250  includes an impedance monitoring module, impedance may be monitored at the electrodes  118   a - d  and the generator may be programmed to terminate RF delivery automatically once the impedance rises to a certain level. The generator system may also or alternatively display the measured impedance and allow the user to terminate RF delivery when desired. 
     When RF delivery is terminated, the user depresses release lever  194  to disengage heel  188  from locking spring member  190  and to thereby allow grips  142 ,  144  to move to their expanded (resting) condition. Release of grips  142 ,  144  causes applicator head  102  to retract to its unexpanded condition and further causes applicator head  102  to be withdrawn into the sheath  104 . Finally, the distal end of the device  100  is withdrawn from the uterus. 
     Two embodiments of ablation devices in accordance with the present invention have been described herein. These embodiments have been shown for illustrative purposes only. It should be understood, however, that the invention is not intended to be limited to the specifics of the illustrated embodiments but is defined only in terms of the following claims.