Abstract:
A tissue ablation device includes an array of elongate electrodes configured to be deployed in tissue, wherein the deployed electrode array defines a tissue ablation region, an inflatable balloon configured to be deployed in tissue, and a coupler securing the balloon relative to the one or more elongate electrodes, wherein the balloon, when inflated, is configured to apply a force to tissue located in the tissue ablation region. An ablation device includes a first array of electrodes, a second array of electrodes, a first inflatable balloon, and a coupler securing the first balloon relative to the first and second electrode arrays. A method of ablating tissue includes positioning an array of elongate electrodes and an inflatable balloon proximate tissue to be ablated, inflating the balloon to compress a tissue region located between the balloon and the electrode array, and energizing the electrode array to ablate the tissue region.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 11/315,426, filed Dec. 21, 2005, now issued as U.S. Pat. No. 7,704,248, the disclosure of which is hereby incorporated by reference. 
    
    
     FIELD 
     The field of the invention relates generally to radio frequency (RF) devices for the treatment of tissue, and more particularly, to electrosurgical devices having multiple tissue-penetrating electrodes that are deployed in an array to treat volumes of tissue. 
     BACKGROUND 
     Tissue may be destroyed, ablated, or otherwise treated using thermal energy during various therapeutic procedures. Many forms of thermal energy may be imparted to tissue, such as radio frequency electrical energy, microwave electromagnetic energy, laser energy, acoustic energy, or thermal conduction. In particular, radio frequency ablation (RFA) may be used to treat patients with tissue anomalies, such as liver anomalies and many primary cancers, such as cancers of the stomach, bowel, pancreas, kidney and lung. RFA treatment involves destroying undesirable cells by generating heat through agitation caused by the application of alternating electrical current (radio frequency energy) through the tissue. 
     Various RF ablation devices have been suggested for this purpose. For example, U.S. Pat. No. 5,855,576 describes an ablation apparatus that includes a plurality of electrode tines deployable from a cannula. Each of the tines includes a proximal end that is coupled to a generator, and a distal end that may project from a distal end of the cannula. The tines are arranged in an array with the distal ends located generally radially and uniformly spaced apart from the distal end of the cannula. The tines may be energized in a bipolar mode (i.e., current flows between closely spaced electrode tines) or a monopolar mode (i.e., current flows between one or more electrode tines and a larger, remotely located common electrode) to heat and necrose tissue within a precisely defined volumetric region of target tissue. To assure that the target tissue is adequately treated and/or to limit damaging adjacent healthy tissues, the array of tines may be arranged uniformly, e.g., substantially evenly and symmetrically spaced-apart so that heat is generated uniformly within the desired target tissue volume. 
     When using heat to kill tissue at a target site, the effective rate of tissue ablation is highly dependent on how much of the target tissue is heated to a therapeutic level. In certain situations, complete ablation of target tissue that is adjacent a vessel may be difficult or impossible to perform, since significant bloodflow may draw the produced heat away from the vessel wall, resulting in incomplete necrosis of the tissue surrounding the vessel. This phenomenon, which causes the tissue with greater blood flow to be heated less, and the tissue with lesser blood flow to be heated more, is known as the “heat sink” effect. It is believed that the heat sink effect is more pronounced for ablation of tissue adjacent large vessels that are more than 3 millimeters (mm) in diameter. Due to the increased vascularity of certain tissue, such as liver tissue and lung tissue, the heat sink effect may cause recurrence of tumors after a radio frequency ablation. 
     SUMMARY 
     In accordance with some embodiments, a tissue ablation device includes an array of elongate electrodes configured to be deployed in tissue, wherein the deployed electrode array defines a tissue ablation region, an inflatable balloon configured to be deployed in tissue, and a coupler securing the balloon relative to the one or more elongate electrodes, wherein the balloon, when inflated, is configured to apply a force to tissue located in the tissue ablation region. 
     In accordance with other embodiments, an ablation device includes a first array of electrodes, a second array of electrodes, a first inflatable balloon, and a coupler securing the first balloon relative to the first and second electrode arrays. 
     In accordance with other embodiments, a method of ablating tissue includes positioning an array of elongate electrodes and an inflatable balloon proximate tissue to be ablated, inflating the balloon to compress a tissue region located between the balloon and the electrode array, and energizing the electrode array to ablate the tissue region. 
     Other and further aspects and features will be evident from reading the following detailed description of the embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings illustrate the design and utility of embodiments. It should be noted that the figures are not drawn to scale and that elements of similar structures or functions are represented by like reference numerals throughout the figures. In order to better appreciate how the advantages and objects of the embodiments are obtained, a more particular description of the embodiments will be rendered by reference to the accompanying drawings. These drawings depict only typical embodiments and are not therefore to be considered limiting in the scope of the claimed invention. 
         FIG. 1A  is a schematic diagram of a tissue ablation system in accordance with some embodiments, showing the device having electrodes and an inflatable balloon; 
         FIG. 1B  illustrates the system of  FIG. 1A , showing the electrodes being deployed; 
         FIG. 2  illustrates the system of  FIG. 1A , showing the balloon being inflated; 
         FIGS. 3A-3D  are cross-sectional views, showing a method for treating tissue using the system of  FIG. 1A , in accordance with some embodiments; 
         FIG. 4  is a schematic diagram of a tissue ablation system in accordance with other embodiments; 
         FIG. 5A  illustrates a coupler in accordance with some embodiments; 
         FIG. 5B  illustrates a coupler in accordance with other embodiments; 
         FIG. 5C  illustrates a coupler in accordance with other embodiments; 
         FIGS. 6A-6D  are cross-sectional views, showing a method for treating tissue using the system of  FIG. 4 , in accordance with some embodiments; 
         FIG. 7  illustrates a perspective view of a coupler in accordance with other embodiments; 
         FIG. 8  illustrates an ablation system that uses the coupler of  FIG. 7  in accordance with some embodiments; and 
         FIG. 9  illustrates an end view of a tissue being treated by the system of  FIG. 8  in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1A  illustrates a tissue ablation system  2  in accordance with some embodiments. The tissue ablation system  2  includes a probe assembly  4  configured for introduction into the body of a patient for ablative treatment of target tissue, and a radio frequency (RF) generator  6  configured for supplying RF energy to the probe assembly  4  in a controlled manner. 
     The probe assembly  4  also includes an elongate tube  12 , a shaft  20  slidably disposed within the tube  12 , and an array  30  of electrodes  26  carried by the shaft  20 . The tube  12  has a distal end  14 , a proximal end  16 , and a central lumen  18  extending through the tube  12  between the distal end  14  and the proximal end  16 . The tube  12  may be rigid, semi-rigid, or flexible depending upon the designed means for introducing the tube  12  to the target tissue. The tube  12  is composed of a suitable material, such as plastic, metal or the like, and has a suitable length, typically in the range from 5 cm to 30 cm, preferably from 10 cm to 20 cm. The length of the tube  12  can also have other dimensions. If composed of an electrically conductive material, the tube  12  is preferably covered with an insulative material. The tube  12  has an outside cross sectional dimension consistent with its intended use, typically being from 0.5 mm to 5 mm, usually from 1.3 mm to 4 mm. The tube  12  may have an inner cross sectional dimension in the range from 0.3 mm to 4 mm, preferably from 1 mm to 3.5 mm. The tube  12  can also have other outside and inner cross sectional dimensions in other embodiments. 
     It can be appreciated that longitudinal translation of the shaft  20  relative to the tube  12  in a proximal direction  40  retracts the electrodes  26  into the distal end  14  of the tube  12  ( FIG. 1A ), and longitudinal translation of the shaft  20  relative to the tube  12  in a distal direction  42  deploys the electrodes  26  from the distal end  14  of the tube  12  ( FIG. 1B ). The shaft  20  comprises a distal end  22  and a proximal end  24 . Like the tube  12 , the shaft  20  is composed of a suitable material, such as plastic, metal or the like. 
     In the illustrated embodiment, each electrode  26  takes the form of an electrode tine, which resembles the shape of a needle or wire. Each of the electrodes  26  is in the form of a small diameter metal element, which can penetrate into tissue as it is advanced from a target site within the target region. In some embodiments, distal ends  66  of the electrodes  26  may be honed or sharpened to facilitate their ability to penetrate tissue. The distal ends  66  of these electrodes  26  may be hardened using conventional heat treatment or other metallurgical processes. They may be partially covered with insulation, although they will be at least partially free from insulation over their distal portions. 
     When deployed from the tube  12 , the array  30  of electrodes  26  has a deployed configuration that defines a volume having a periphery with a radius  84  in the range from 0.5 to 4 cm. However, in other embodiments, the maximum radius can be other values. The electrodes  26  are resilient and pre-shaped to assume a desired configuration when advanced into tissue. In the illustrated embodiments, the electrodes  26  diverge radially outwardly from the tube  12  in a uniform pattern, i.e., with the spacing between adjacent electrodes  26  diverging in a substantially uniform and/or symmetric pattern. 
     In the illustrated embodiments, each electrode  26  has a flared curvilinear profile that resembles a portion of a parabola. Particularly, when the electrodes  26  are deployed, the electrodes  26  each extends proximally, and then everts distally, such that each electrode  26  forms a profile that resembles at least a portion of a parabola. As shown in  FIG. 1B , the deployed electrode  26  is located at the distal end  14  of the cannula, and each deployed electrode  26  has a distal end that points at least partially towards a proximal direction. It should be noted that the electrodes  26  should not be limited to the profiles shown in  FIG. 1B , and that in alternative embodiments, the electrodes  26  can have different deployed profiles. For examples, in other embodiments, each of the electrodes  26  can each have a flared deployed profile, a substantially rectilinear deployed profile, a deployed profile that resembles a 90° bent, or a deployed profile that resembles a portion (e.g., a quarter) of a circle or an ellipse. 
     It should be noted that although a total of two electrodes  26  are illustrated in  FIG. 1B , in other embodiments, the probe assembly  4  can have more or fewer than two electrodes  26 . In exemplary embodiments, pairs of adjacent electrodes  26  can be spaced from each other in similar or identical, repeated patterns and can be symmetrically positioned about an axis of the shaft  20 . It will be appreciated that a wide variety of particular patterns can be provided to uniformly cover the region to be treated. In other embodiments, the electrodes  26  may be spaced from each other in a non-uniform pattern. 
     The electrodes  26  can be made from a variety of electrically conductive elastic materials. Very desirable materials of construction, from a mechanical point of view, are materials which maintain their shape despite being subjected to high stress. Certain “super-elastic alloys” include nickel/titanium alloys, copper/zinc alloys, or nickel/aluminum alloys. Alloys that may be used are also described in U.S. Pat. Nos. 3,174,851, 3,351,463, and 3,753,700, the disclosures of which are hereby expressly incorporated by reference. The electrodes  26  may also be made from any of a wide variety of stainless steels. The electrodes  26  may also include the Platinum Group metals, especially platinum, rhodium, palladium, rhenium, as well as tungsten, gold, silver, tantalum, and alloys of these metals. These metals are largely biologically inert. They also have significant radiopacity to allow the electrodes  26  to be visualized in-situ, and their alloys may be tailored to accomplish an appropriate blend of flexibility and stiffness. They may be coated onto the electrodes  26  or be mixed with another material used for construction of the electrodes  26 . 
     In the illustrated embodiments, RF current is delivered to the electrode array  30  in a monopolar fashion, which means that current will pass from the electrode array  30 , which is configured to concentrate the energy flux in order to have an injurious effect on the surrounding tissue, to a dispersive electrode (not shown), which is located remotely from the electrode array  30  and has a sufficiently large area (typically 130 cm 2  for an adult), so that the current density is low and non-injurious to surrounding tissue. The dispersive electrode may be attached externally to the patient, e.g., using a contact pad placed on the patient&#39;s skin. In other embodiments, RF energy may be delivered in a bipolar fashion in that energy is delivered from one electrode(s)  26  to another electrode(s)  26  on the array  30 . 
     As shown in  FIG. 1A , the probe assembly  4  also includes an inflatable balloon  100  secured to the tube  12 . The balloon  100  is used to compress tissue between the balloon  100  (when inflated) and the array  30  of electrodes  26  during use. The tube  12  includes a fluid delivery channel  102  within a wall  104  of the tube  12 , and a port  106  in fluid communication with the fluid delivery channel  102 , wherein the fluid delivery channel  102  is used for delivering inflation fluid to the balloon  100 . During use, a fluid supply  110  is coupled to the port  106  (e.g., via a tube), and inflation fluid (gas or liquid) is delivered from the fluid supply  110  to the balloon  100  via the fluid delivery channel  102 , thereby inflating the balloon  100  ( FIG. 2 ). The inflated balloon  100  can have different inflated shapes in different embodiments. For examples, the inflated balloon  100  can have a circular profile, an elliptical profile, a triangular profile, or other customized profiles. In some embodiments, the inflated balloon  100  has a cross sectional dimension  112  which is between 50% of a cross sectional dimension  114  of the deployed array  30  and 150% of the cross sectional dimension  114  of the deployed array  30 . For example, the balloon  100 , when inflated, can have a cross sectional dimension  112  that is larger than the cross sectional dimension  114  of the deployed array  30 . In such cases, the balloon  100  can be located proximal to the tips of the electrodes  26  so that the tips do not puncture the balloon  100  when inflated. In other embodiments, the inflated balloon  100  has a cross sectional dimension  112  that is smaller than an opening  101  defined by the distal ends  66  of the electrodes  26 , thereby allowing the balloon  100  to be positioned at least partially within the opening  101  without being punctured by the electrodes  26 . In other embodiments, the inflated balloon  100  can have other cross sectional dimensions  112  different from those discussed previously. The balloon  100  can be made from a variety of materials, such as a polymer or latex. 
     In some embodiments, at least a portion of the balloon  100  can include electrically conductive material, thereby allowing the balloon  100  to function as an electrode. For example, the balloon  100  can have one or more regions made from a metal, or covered with metal dusts. Electrically conductive balloons have been described in U.S. Pat. Nos. 5,846,239, 6,454,766, and 5,925038, the entire disclosures of which are expressly incorporated by reference herein. One or more electrical wires (e.g., housed within the wall  104  of the tube  12 ) may be used to deliver electrical energy from the RF generator  6  to the balloon  100 . In such cases, the array  30  of electrodes  26  and the balloon  100  are used to deliver RF current in a bipolar fashion, which means that current will pass between the array  30  of electrodes  26  and the balloon  100 . In a bipolar arrangement, the array  30  and the balloon  100  will be insulated from each other in any region(s) where they would or could be in contact with each other during a power delivery phase. If the tube  12  is made from an electrically conductive material, an insulator (not shown) can be provided to electrically insulate the operative balloon  100  from the electrodes  26  in the array  30 . 
     Returning to  FIGS. 1A and 1B , the probe assembly  4  further includes a handle assembly  27 , which includes a handle portion  28  mounted to the proximal end  24  of the shaft  20 , and a handle body  29  mounted to the proximal end  16  of the tube  12 . The handle portion  28  is slidably engaged with the handle body  29  (and the tube  12 ). The handle portion  28  and the handle body  29  can be composed of any suitable rigid material, such as, e.g., metal, plastic, or the like. 
     The handle portion  28  also includes electrical connector(s) (not shown), which allows the electrode array  30  of the probe assembly  4  to be connected directly or indirectly (e.g., via a conductor) to the generator  6  during use. The RF generator  6  is a conventional RF power supply that operates at a frequency in the range from 200 KHz to 1.25 MHz, with a conventional sinusoidal or non-sinusoidal wave form. Such power supplies are available from many commercial suppliers, such as Valleylab, Aspen, and Bovie. More suitable power supplies will be capable of supplying an ablation current at a relatively low voltage, typically below 150V (peak-to-peak), usually being from 50V to 100V. The power will usually be from 20 W to 200 W, usually having a sine wave form, although other wave forms would also be acceptable. Power supplies capable of operating within these ranges are available from commercial vendors, such as Boston Scientific Corporation of San Jose, Calif., which markets these power supplies under the trademarks RF2000 (100 W) and RF3000 (200 W). In other embodiments, generators having other ranges of operating frequency or ranges of voltage can also be used. Other general purpose electrosurgical power supplies can also be used in other embodiments. 
     Referring now to  FIGS. 3A-3D , the operation of the tissue ablation system  2  is described in treating a treatment region within tissue T located beneath the skin S of a patient. The tissue T can be at least a portion of, a lung tissue, a liver tissue, or other tissue within a body. 
     The tube  12  is first introduced within a treatment region, so that the distal end  14  of the tube  12  is located at a target site, as shown in  FIG. 3A . This can be accomplished using any one of a variety of techniques. In some cases, the tube  12  and shaft  20  may be introduced to the target site TS percutaneously directly through the patient&#39;s skin or through an open surgical incision. In this case, the tube  12  (or the electrode  26 ) may have a sharpened tip, e.g., in the form of a needle, to facilitate introduction to the target site. In such cases, it is desirable that the tube  12  be sufficiently rigid, i.e., have a sufficient column strength, so that it can be accurately advanced through tissue T. In other cases, the tube  12  may be introduced using an internal stylet that is subsequently exchanged for the shaft  20  and electrode array  30 . In this latter case, the tube  12  can be relatively flexible, since the initial column strength will be provided by the stylet. More alternatively, a component or element may be provided for introducing the tube  12  to the target site. For example, a conventional sheath and sharpened obturator (stylet) assembly can be used to initially access the tissue T. The assembly can be positioned under ultrasonic or other conventional imaging, with the obturator/stylet then removed to leave an access lumen through the sheath. The tube  12  and shaft  20  can then be introduced through the sheath lumen, so that the distal end  14  of the tube  12  advances from the sheath to the target site. 
     After the tube  12  is properly placed, the electrode array  30  is deployed out of the lumen  18  of the tube  12 , as shown in  FIG. 3B . 
     Next, inflation fluid is delivered from the fluid source  110  to inflate the balloon  100 , thereby compressing the tissue region TR that is between the balloon  100  and the electrodes  26  ( FIG. 3C ). In some embodiments, the size of the balloon  100  can be adjusted (e.g., by varying the amount of inflation fluid that is delivered into the balloon  100 ) to thereby change a degree of compression of the tissue region TR. For example, an increase in the amount of inflation fluid delivered to the balloon  100  will cause the balloon  100  to increase in size, thereby increasing the amount of compression created on the tissue region TR, and vice versa. In other embodiments, the amount of compression on the tissue region TR can be adjusted by positioning the balloon  100  relative to the deployed electrodes  26 . For example, the tube  12  can be positioned relative to the shaft  20  to vary a distance between the balloon  100  and the electrodes  26 , thereby changing an amount of compression on the tissue region TR. 
     Next, with the RF generator  6  connected to the probe assembly  4 , the RF generator  6  is operated to deliver ablation energy to the electrodes  26  either in a monopolar mode or a bipolar mode. While ablation energy is being delivered, compression of the tissue region TR between the balloon  100  and the electrodes  26  is maintained. The compression on the tissue region TR reduces blood flow to the tissue region TR, thereby preventing or reducing heat from being carried away by blood flow, which in turn, improves a tissue ablation rate. After a desired amount of ablation energy has been delivered, the treatment region TR is necrosed, thereby creating a lesion on the treatment region TR ( FIG. 3D ). 
     In many cases, a single ablation may be sufficient to create a desired lesion. However, if it is desired to perform further ablation to increase the lesion size or to create lesions at different site(s), the electrodes  26  may be introduced and deployed at different target site(s), and the same steps discussed previously may be repeated. When desired lesions have been created, the electrodes  26  are retracted into the lumen  18  of the tube  12 , and the probe assembly  4  is removed from the patient. 
     In other embodiments, instead of placing the balloon  100  within tissue T, the balloon  100  can be placed next to a periphery of the tissue, such as, at a surface of the tissue. In such cases, after deploying the electrodes  26  within the tissue T, the tube  12  can be retracted proximally until the balloon  100  is outside the tissue T. The balloon  100  is then inflated to press against a surface of the tissue T, thereby compressing tissue region that is within tissue T. 
     In the above embodiments, the relative position between the balloon  100  and the array  30  of electrodes  26  is established using the tube  12  and the shaft  20 . In other embodiments, the relative position between the balloon  100  and electrode(s)  26  may be established using other structures. Also, in further embodiments, the balloon  100  needs not be located on the tube  12  that carries the electrodes  26 . Instead, the balloon  100  can be carried by a separate structure. 
       FIG. 4  illustrates an ablation system  200  in accordance with other embodiments. The ablation system  200  includes an ablation device  202  having one or more electrodes  206  and a structure  204  for carrying the electrode(s)  206 , a balloon  210 , a shaft  208  for carrying the balloon  210 , and a coupler  212  for establishing a relative position between the balloon  210  and the electrode(s)  206 . The electrode(s)  206  each has a rectilinear profile, but can have other shapes in other embodiments. In some embodiments, the ablation device  202  includes one electrode  206 . In other embodiments, the ablation device  202  includes a plurality of electrodes  206 . For examples, the electrodes  206  can be arranged in a row, multiple rows, or in other customized patterns. The ablation system  200  also includes a RF generator  220  for providing RF energy to the electrode(s)  206  (e.g., in a monopolar or bipolar fashion), and a fluid source  222  for delivering inflation fluid (gas or liquid) to inflate the balloon  210 . The shaft  208  includes a fluid delivery channel  209  for delivering fluid from the fluid source  222  to the balloon  210 . In some embodiments, the balloon  210  can include one or more conductive regions, thereby allowing the balloon  210  to function as an electrode. In such cases, the balloon  210  is electrically connected to the generator  220  during use. 
       FIG. 5A  illustrates a top view of the coupler  212  of  FIG. 4  in accordance with some embodiments. The coupler  212  includes a first opening  214  sized to mate with the structure  204  of the ablation device  202 , and a second opening  216  sized to mate with the shaft  208 . In the illustrated embodiments, the coupler  212  is detachably coupled to the structure  204  and the shaft  208 . In other embodiments, the coupler  212  is permanently secured (e.g., via a glue or a suitable adhesive) to the structure  204 , the shaft  208 , or both. 
       FIG. 5B  illustrates a top view of the coupler  212  of  FIG. 4  in accordance with other embodiments. The coupler  212  includes a plurality of second openings  216   a - 216   c , each of which is sized to mate with the shaft  208 . Such configuration allows a distance between the balloon  210  and the electrode(s)  206  be adjusted by selectively mating the shaft  208  to a desired one of the openings  216   a - 216   c . In other embodiments, instead of, or in addition to, the plurality of second openings  216   a - 216   c , the coupler  212  can include a plurality of first openings  214 , thereby allowing the structure  204  to be secured to different portion of the coupler  212 . 
       FIG. 5C  illustrates a top view of the coupler  212  of  FIG. 4  in accordance with other embodiments. The coupler  212  includes a first portion  230  and a second portion  232  that is moveable relative to the first portion  230 . The first portion  230  includes a first opening  234  sized to mate with the structure  204  of the ablation device  202 , and the second portion  232  includes a second opening  236  sized to mate with the shaft  208 . In the illustrated embodiments, the coupler  212  is detachably coupled to the structure  204  and the shaft  208 . In other embodiments, the coupler  212  is permanently secured (e.g., via a glue or a suitable adhesive) to the structure  204 , the shaft  208 , or both. During use, the second portion  232  can be translated relative to the first portion  230 , thereby allowing a distance between the openings  234 ,  236  be adjusted. This, in turn, allows adjustment of a spacing between the balloon  210  and the electrode(s)  206 . A securing device, such as a screw  238 , can be provided to secure the second portion  232  relative to the first portion  230  after a desired spacing between the openings  234 ,  236  is obtained. 
     In the above embodiments, the opening  214  is sized such that it provides a frictional contact against a surface of the structure  204  when the structure  204  is inserted within the opening  214 , thereby allowing the coupler  212  to be secured to the structure  204  via friction. Similarly, the opening  216  is sized such that it provides a frictional contact against a surface of the shaft  208  when the shaft  208  is inserted within the opening  216 , thereby allowing the coupler  212  to be secured to the shaft  208 . In other embodiments, the coupler  212  can be detachably secured to the structure  204  and/or the shaft  208  by other techniques. For example, the coupler  212  can include one or more screws, one or more snap-fit connections, or one or more pins for detachably securing itself to the structure  204  and/or the shaft  208 . Also, in other embodiments, instead of the shafts  208 , the opening  216  can be sized to mate with another structure that is used to carry (or is coupled to) the balloon  210 . In addition, in other embodiments, the coupler  212  can have other shapes and configurations as long as the coupler  212  is capable of establishing a relative position between the electrode(s)  206  and the balloon  210 . 
     Referring now to  FIGS. 6A-6D , the operation of the tissue ablation system  200  is described in treating a treatment region TR within tissue T located beneath the skin S of a patient. First, an incision is made at the patient&#39;s skin S to thereby create an opening, and the electrodes  206  carried by the structure  204  are inserted through the opening ( FIG. 6A ). The electrodes  206  are advanced to penetrate the tissue T beneath the skin S, and are positioned until they are placed at a desired location. The tissue T can be at least a portion of, a lung tissue, a liver tissue, or other tissue within a body. 
     Next, the balloon  210  is inserted through the skin S, and the coupler  212  is detachably secured to the structure  204  and the shaft  208  that carries the balloon  210 , thereby establishing a relative position between the balloon  210  and the electrodes  206  ( FIG. 6B ). Alternatively, if the coupler  212  is permanently secured to the structure  204 , then the coupler  212  is detachably secured to the shaft  208  and not to the structure  204 . In other embodiments, if the coupler  212  is permanently secured to the shaft  208 , then the coupler  212  is detachably secured to the structure  204  and not to the shaft  208 . As shown in the figure, the balloon  210 , in its non-inflated state, is positioned next to a tissue surface TS. 
     Next, inflation fluid is delivered from the fluid source  222  to inflate the balloon  210 , thereby compressing the tissue region TR that is between the balloon  210  and the electrodes  206  ( FIG. 6C ). In some embodiments, the size of the balloon  210  can be adjusted (e.g., by varying the amount of inflation fluid that is delivered into the balloon  210 ) to thereby change a degree of compression of the tissue region. For example, an increase in the amount of inflation fluid delivered to the balloon  210  will cause the balloon  210  to increase in size, thereby increasing the amount of compression created on the tissue region TR, and vice versa. 
     When the tissue region TR is desirably compressed, the RF generator  220  is operated to deliver ablation energy to the electrodes  206  either in a monopolar mode or a bipolar mode. The compression on the tissue reduces blood flow to the tissue, thereby preventing or reducing heat from being carried away by blood flow, which in turn, improves a tissue ablation rate. After a desired amount of ablation energy has been delivered, the tissue region TR is necrosed, thereby creating a lesion at the tissue region TR ( FIG. 6D ). In some embodiments, while ablation energy is being delivered, the degree of compression at the tissue region can be varied (e.g., by delivering additional inflation fluid to, or by removing delivered inflation fluid from, the balloon  210 ). 
     In many cases, a single ablation may be sufficient to create a desired lesion. However, if it is desired to perform further ablation to increase the lesion size or to create lesions at different site(s) within the same tissue T or elsewhere, the electrodes  206  may be introduced and deployed at different target site(s), and the same steps discussed previously may be repeated. When all desired lesions have been created, the electrodes  206  and the balloon  210  are removed from the patient. 
     In the above embodiments, the coupler  212  is configured to secure a relative position between the balloon  210  and the electrode(s)  206 . In other embodiments, the coupler  212  can be configured to secure relative positions among two or more balloons and the electrode(s)  206 , or among the balloon  210  with two or more sets of electrode(s)  206 .  FIG. 7  illustrates a coupler  300  in accordance with other embodiments. The coupler  300  includes a first opening  302  sized to mate with a first structure  310  that carries a first set of electrodes  322 , a second opening  304  sized to mate with a second structure  312  that carries a second set of electrodes  324 , a third opening  306  sized to mate with a first shaft  314  that carries a first balloon  318 , and a fourth opening  308  sized to mate with a second shaft  316  that carries a second balloon  320  ( FIG. 8 ). During use, the coupler  300  establishes relative positions among the balloons  318 ,  320 , the first set of electrodes  322 , and the second set of electrodes  324 . Inflation of the balloons  318 ,  320  compresses tissue region TR surrounded by the balloons  318 ,  320  and electrodes  322 ,  324  ( FIG. 9 ). 
     In other embodiments, instead of having a plurality of electrodes, each of the structures  310 ,  312  can carry a single electrode. Also, in other embodiments, instead of the rectilinear profile shown, each of the electrodes  322 ,  324  can have other shapes. In further embodiments, instead of the shafts  314 ,  316 , the openings  306 ,  308  can be sized to mate with other structures that are used to carry (or are coupled to) the respective balloons  318 ,  320 . Also, in other embodiments, the coupler  300  can have other shapes and configurations as long as the coupler  300  is capable of establishing a relative position between sets of the electrode(s) and balloon(s). For example, in other embodiments, instead of a unitary structure shown, the coupler  300  can include two or more components that may or may not be moveable relative to each other. 
     Although particular embodiments have been shown and described, it should be understood that the above discussion is not intended to limit the claimed invention. It will be obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the present invention. For example, the array  30  of electrodes  26  can be manufactured as a single component. As such, the “array of electrodes” should not be limited to a plurality of separate electrodes, and includes a single structure (e.g., an electrode) having different conductive portions. Also, in any of the embodiments described herein, instead of delivering RF energy, the electrode(s) can be configured to deliver microwave energy, or other forms of energy. Thus, the present invention is intended to cover alternatives, modifications, and equivalents that may fall within the spirit and scope of the present invention as defined by the claims.