Abstract:
A bipolar electrosurgical system is provided. The system includes at least one pair of active and return electrodes each including thermally-conductive tubular members with closed distal ends. Each of the tubular members include electrically conductive portions which are adapted to connect to an electrical energy source. The active and return electrodes are further configured to penetrate tissue and create at least one generally elliptical lesion therebetween upon activation of electrical energy. The system also includes a multiplexer disposed between the electrical energy source and each pair of electrically conductive active and return portions. The multiplexer is adapted to selectively switch electrical potentials of each pair of active and return electrically conductive portions to create lesions of varying geometry.

Description:
BACKGROUND  
       [0001]     1. Technical Field  
         [0002]     The present disclosure relates generally to bipolar electrosurgery, and more particularly, to a system and method for creating lesions using bipolar electrodes.  
         [0003]     2. Background of Related Art  
         [0004]     Electrosurgery involves application of high frequency electrical current to a surgical site to cut, ablate, or coagulate tissue. In monopolar electrosurgery, a source or active electrode delivers radio frequency energy from the electrosurgical generator to the tissue and a return electrode carries the current back to the generator. In monopolar electrosurgery, the source electrode is typically part of the surgical instrument held by the surgeon and applied to the tissue to be treated. A patient return electrode is placed remotely from the active electrode to carry the current back to the generator.  
         [0005]     In bipolar electrosurgery, one of the electrodes of the hand-held instrument functions as the active electrode and the other as the return electrode. The return electrode is placed in close proximity to the active (current supplying) electrode such that an electrical circuit is formed between the two electrodes (e.g., electrosurgical forceps). In this manner, the applied electrical current is limited to the body tissue positioned between the electrodes.  
         [0006]     Bipolar electrosurgery has a number of advantages over monopolar electrosurgery. Bipolar electrosurgery generally requires lower power levels which results in less tissue destruction (e.g., tissue charring and scarring due to sparks at the electrodes). Bipolar electrosurgical techniques also reduce the danger of alternate site burns since no return electrodes are used and the only tissue destroyed is that located between the bipolar electrodes.  
         [0007]     Bipolar electrosurgery is conventionally practiced using electrosurgical forceps-type device, where the active and return electrodes are housed within opposing forceps&#39; jaws. Such bipolar electrosurgical devices use RF energy in conjunction with clamping force to coagulate vessels or tissue or seal blood vessels or tissue. Conventional bipolar electrosurgical devices are typically not adapted for creating lesions within organs due to their physical limitations.  
         [0008]     Therefore there is a need for a system and method for creating lesions using bipolar electrosurgical devices.  
       SUMMARY  
       [0009]     The present disclosure provides for a bipolar electrosurgical system. The system includes one ore more elongated active and return electrode(s) configured to penetrate tissue to create one or more lesions having an ellipsoid-shaped cross section therein. The electrodes also include a thermal and electrical conducting rigid tubular member having a proximal and distal end with an insulative layer covering the external surface of the tubular member defining an exposed tip for conducting electrical energy therethrough.  
         [0010]     According to one embodiment of the present disclosure, a bipolar electrosurgical system is disclosed. The system includes at least one pair of active and return electrodes each including thermally-conductive tubular members with closed distal ends. Each of the tubular members include electrically conductive portions which are adapted to connect to an electrical energy source. The active and return electrodes are further configured to penetrate tissue and create at least one generally elliptical lesion therebetween upon activation of electrical energy. The system also includes a multiplexer disposed between the electrical energy source and each pair of electrically conductive active and return portions. The multiplexer is adapted to selectively switch electrical potentials of each pair of active and return electrically conductive portions to create lesions of varying geometry.  
         [0011]     According to another embodiment of the present disclosure a method for performing an electrosurgical procedure is disclosed. The method includes the steps of providing at least one pair of active and return electrodes each including thermally-conductive tubular members with closed distal ends. Each of the tubular members includes electrically conductive portions which are adapted to connect to an electrical energy source. The active and return electrodes are configured to penetrate tissue and create at least one generally elliptical lesion therebetween upon activation of electrical energy. The method also includes the step of providing a multiplexer disposed between the electrical energy source and each pair of electrically conductive active and return portions. The multiplexer is adapted to selectively switch electrical potentials of each pair of active and return electrically conductive portions to create lesions of varying geometry.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The above and other aspects, features, and advantages of the present disclosure will become more apparent in view of the following detailed description when taken in conjunction with the accompanying drawings in which:  
         [0013]      FIG. 1  is a schematic diagram of one embodiment of a bipolar electrosurgical system according to the present disclosure;  
         [0014]      FIG. 2  is a diagram of an ablation electrode;  
         [0015]      FIG. 3  is a block and sectional diagram of the ablation electrode of  FIG. 2 ;  
         [0016]      FIG. 4  is a diagram of an ablation site having an active and return electrode;  
         [0017]      FIG. 5  is a schematic block diagram illustrating automatic monitoring circuit according to the present disclosure;  
         [0018]      FIG. 6  is a diagram of a resectioning procedure using the bipolar electrosurgical system of  FIG. 1 ;  
         [0019]      FIG. 7  is a flow chart illustrating a method for performing the resectioning procedure of  FIG. 6 ;  
         [0020]      FIG. 8  is a perspective view of an ablation device having a plurality of bipolar electrodes according to the present disclosure; and  
         [0021]      FIG. 9  is a diagram of an ablation site having the ablation device of  FIG. 8 .  
     
    
     DETAILED DESCRIPTION  
       [0022]     Preferred embodiments of the present disclosure will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail.  
         [0023]     The present disclosure provides for system and method for creating lesions using bipolar electrosurgical techniques and devices. The system includes at least one pair of electrodes, an active electrode and a corresponding return electrode. The electrodes are elongated electrodes configured to penetrate tissue and supply RF energy to the target site therein to create one or more lesions having a particularly-shaped cross section. For example, a plurality of electrode pairs may be utilized to create lesions which overlap to ablate a spherical/circular region of tissue (e.g., tumor) or a plurality of lesions may be created to ablate a strip of tissue to allow for bloodless resectioning of an organ.  
         [0024]      FIG. 1  is a schematic illustration of a electrosurgical system  1  according to the present disclosure. The system  1  includes an active electrode  2  and a return electrode  4  for treating tissue at a surgical site  6  of a patient. Electrosurgical energy is supplied to the active electrode  2  by a generator  10  via a cable  3  allowing the electrodes  2 ,  4  to ablate, cut or coagulate the tissue. The return electrode  4  is placed at the surgical site  14  to return the energy from the patient to the generator  10  via a cable  5 .  
         [0025]     The active and return electrodes  2 ,  4  may be elongated electrodes configured to penetrate tissue and supply RF energy to the target site therein The active and return electrodes  2 ,  4  may also include a temperature control system, e.g., a coolant circulating system. Examples of an elongated electrode having a cooling system are shown and described in commonly-owned U.S. patent Ser. No. 6,506,189 entitled “Cool-tip electrode thermosurgery system” which is hereby incorporated by reference herein in its entirety. However, a brief description of the relevant technology is provided below with reference to  FIGS. 2 and 3 .  
         [0026]     An elongated shaft or cannula body C is used for insertion of the active electrode  2  (or return electrode  4 ) either percutaneously or intraoperatively through an open wound site to the target site. As illustrated the cannula body C is integral with a head or hub element H coupled to remotely support components, collectively designated S.  
         [0027]     As shown in  FIGS. 2 and 3 , the cannula body C incorporates an elongated hollow ablative electrode  11  (e.g., active or return electrode  2 ,  4 ) formed of conductive material, (e.g. metal such as stainless steel, titanium, etc.). At the distal end of the cannula body C, the electrode  11  includes a shaft  15  which defines a tip  12  at a distal end thereof which may be of any shape or form (e.g., rounded or pointed). In one form, the tip  12  may define a trocar point and may be of robust metal construction to facilitate insertion or penetration of tissue. During an ablation procedure, the electrode  11  is inserted into the tissue and the generator  10  provides electrical current which spreads from the conductive portion, e.g. tip  12 , to pass through the surrounding tissue thereby ablating the tissue and creating therapeutic lesions. Hence, when the tip  12  is positioned contiguous to tissue, energy from the generator  10  is dissipated into heat within the tissue.  
         [0028]     As best shown in  FIG. 3 , electrode  11  includes an insulative coating  13  for preventing the flow of electrical current from the shaft  15  of electrode  11  into surrounding tissue. Thus, the insulative coating  13  shields the intervening tissue (i.e., tissue penetrated by the electrode  11  but not targeted for ablation) from RF current, so that such tissue is not substantially heated along the length of the shaft  15  except by the heating effect from the exposed portion or tip  12 . It should be appreciated that the length of the exposed portion or tip  12  is directly related to the size of the lesion created (i.e., the larger the exposed portion of the electrode  11  the larger is the lesion).  
         [0029]     At its proximal end, the electrode  11  is typically integrally associated with an enlarged housing  14  of the hub H which carries electrical and coolant connections as explained in greater detail below. Outside the patient&#39;s body, the housing  14  defines ports for connections to the support components S (e.g., electrical and fluid couplings). As suggested, the housing  14  may be integral with the electrode  11 , formed of metal, or it may constitute a separate subassembly as described below. Alternatively, the housing  14  can be made of plastic, accommodating separate electrical connections. In that regard, a plastic housing  14  is preferred, due to low artifact imaging it exhibits in various imaging techniques (e.g., X-ray, CT, MRI, etc.)  
         [0030]     Referring to  FIG. 2 , the housing  14  mates with a block  18  thereby defining a luer taper lock  19  which seals the block  18  and the housing  14 . In addition, fluid and electrical couplings are provided. Specifically, connection to the generator  10  (e.g., the cables  3 ,  5  of  FIG. 1 ) may be a standard cable connector, a leader wire, a jack-type contact or other connector designs known in the art. The temperature-sensing and radiofrequency electrical connections can be made through the housing  14  and extend to the region of the tip  12 , where an RF line  25  is connected by junction  21  (e.g., a weld, braze, or other secure electrical connection). Sensor line  24  extends to a temperature sensor  23  (a thermistor, a thermocouple, or other type of sensor) which may be fused or in thermal contact with the wall of the tip  12  to sense temperature condition at or proximate of the tip  12 .  
         [0031]     The generator  10  may be connected to reference potential and coupled through the block  18  affixed to the hub H. Specifically, the generator  10  provides RF voltage through the block  18  with an electrical connection to the electrode  11  as indicated by the line  25  (e.g., the cables  3 ,  5 ), to the connection junction  21 . The generator  10  may take the form of an RF generator as exemplified by the RFG-3C RF Lesion Generator System available from Radionics, Inc. of Burlington, Mass.  
         [0032]     The ablation electrode  11  includes a number of systems for regulating the temperature generated at the ablation site. One such system utilizes cooling fluid injected into the ablation electrode  11  based on temperature readings. In that regard, a temperature monitor  20  is electrically connected by lines  22  and  24  to a temperature sensor  23  as in the form of a thermocouple or thermistor typically within or contacting the tip  12 . As illustrated, the temperature sensor  23  is connected to the tip  12 . The sensed temperature is utilized to control either or both of the flow of RF energy or the flow of coolant to attain the desired ablation while maintaining the maximum temperature substantially below 100° C. or another threshold temperature. A plurality of sensors may be utilized including units extending outside the tip  12  to measure temperatures existing at various locations in the proximity of the tip  12 . The temperature monitor  20  may be as exemplified by the TC thermocouple temperature monitoring devices available from Radionics, Inc. of Burlington, Mass.  
         [0033]     Temperatures at, or near the tip  12  may be controlled by controlling the flow of fluid coolant through the ablation electrode  11 . Accordingly, the temperature of the tissue contacting at or near the tip  12  is controlled. In the disclosed embodiment, fluid from a fluid source FS is carried the length of the ablation electrode  11  through a tube  26  extending from the housing H to the distal end of the electrode  11  terminating in an open end  28  at the tip  12 . At the opposite end of the electrode  11 , within the housing H, the tube  26  is connected to receive fluid. As illustrated in the detailed structure of  FIGS. 2 and 3 , the fluid source FS includes a source unit  34  coupled through a control  32  utilizing a hypodermic syringe  30  (or other fluid delivery mechanism) to actuate fluid flow, as represented by an arrow, through a coupling  38 . Thus, fluid flow is regulated in accordance with observed temperature, allowing increased flow of RF energy.  
         [0034]     The fluid coolant may take the form of water or saline solution which is typically used for heat dissipation via convectional removal of heat from the tip  12 . The reservoir or source unit  34  might be a large reservoir of cooled water, saline or other fluid. As a simplistic example, a tank of water with ice cubes can fiction to maintain the coolant at a temperature of approximately 0° C. As another example, the fluid source FS could incorporate a peristaltic pump or other fluid pump, or could merely be a gravity feed for supplying fluid from a flexible bag or rigid tank.  
         [0035]     Backflow from the tip  12  is through an exit port  40  of the hub H as illustrated by arrows  42 ,  43 . The port  40  may be in the form of simple couplings, rigid units or may comprise flexible tubular couplings to reduce torque transmission to the electrode  11 . Also, the coolant flow members may simply take the form of PVC tubes with plastic luer connectors for ease of use.  
         [0036]     As a result of the coolant flow, the interior of the electrode  11 , more specifically the electrode tip  12 , can be held to a temperature near that of the fluid source FS. The coolant can circulate in a closed system as illustrated in  FIG. 2 . Also, in some situations, it may be desirable to reverse the direction of fluid flow from that depicted in the figures. As treated in detail below, coordinated operation, involving RF heating along with the cooling may be accomplished by a microprocessor  80 , which is coupled to the generator  10 , the temperature monitor  20  and the fluid source FS to receive data on flow rates and temperatures and exercise control. Accordingly, an integrated operation is provided with feedback from the temperature monitor  20  in a controlled format and various functions can be concurrently accomplished. Thus, facilitated by the cooling, the ablation electrode  11  is moderated, changed, controlled or stabilized. Such controlled operation can effectively reduce the temperature of tissue near the tip  12  to accomplish an equilibrium temperature distribution tailored to the desired size of the desired lesion.  
         [0037]     The temperature distribution in the tissue near the tip  12  depends on the RF current from the tip  12  and depends on the temperature of the tissue which is adjacent to the tip  12 . Tip temperature can be controlled by the flow of fluid from the source FS. Thus, a thermal boundary condition is established, holding the temperature of the tissue (near the tip  12 ) to approximately the temperature of the tip itself, e.g. the temperature of the fluid inside the tip  12 . Accordingly, by temperature control, a surgeon may impose a defined temperature at the boundary of the electrode tip  12  which can be somewhat independent of the RF heating process, and in fact, dramatically modify the temperature distribution in the tissue.  
         [0038]     During a bipolar electrosurgical procedure according to the present disclosure, active and return electrodes  2 ,  4  ( FIG. 1 ) are placed at the surgical site  6  in such a way as to create a lesion  50  as shown in  FIG. 4 . The current travels through tissue from the active electrode  2  to the return electrode  4  as represented by the current flow  52 . Due to the current flow  52  forming a generally elliptical pattern, the resulting lesion  50  also has an elliptical shape with a length L (e.g., major axis), a width W (e.g., minor axis), and depth D (not shown). Those skilled in the art will appreciate that the depth D is directly proportional to the length of the exposed conductive tip of the active and return electrodes  2 ,  4  (or electrode  11  of  FIGS. 2 and 3 ).  
         [0039]     It is also envisioned that impedance of the tissue between the active and return electrodes  2 ,  4  is monitored to allow the user to selectively regulate the current applied to the tissue to obtain a desired volumetric measure of the lesion  50 . For example, an impedance reading above a predetermined threshold would signal the generator  10  to shut down, thereby terminating the current flow once the lesion  50  reaches the desired volume. One example of a bipolar system having a generator controlled by an impedance sensor is shown and described in commonly-owned U.S. patent Ser. No. 6,203,541 entitled “Automatic Activation of Electrosurgical Generator Bipolar Output” which is hereby incorporated by reference herein in its entirety. However, a brief description of the relevant technology is provided below with reference to  FIG. 5 .  
         [0040]      FIG. 5  shows a schematic diagram of the bipolar electrosurgical system of the present disclosure. As the impedance of the tissue changes the current changes inversely proportionally if the voltage remains constant. This is defined by Ohm&#39;s law: V=RI, wherein V is the voltage across the electrodes in volts, I is the current through the electrodes (and tissue) in milliamps and R is the resistance or impedance of the tissue measured in Ohms. By this equation it can be readily appreciated that when the tissue impedance increases, the current will decrease and conversely, if the tissue impedance decreases, the current will increase. The electrosurgical system of the present disclosure essentially measures impedance based on the changes in current. Prior to electrosurgical treatment, tissue is more conductive, so when energy is applied, the impedance is relatively low. As the tissue is treated and a lesion is created, the conductivity decreases as the tissue moisture content decreases and consequently tissue impedance increases.  
         [0041]     The active and return electrodes  2 ,  4  are connected to the generator  10 . The electrosurgical generator  10  includes a current sensor  72  electrically connected to the active electrode  2  and a voltage sensor  74  electrically connected between the active and return electrodes  2 ,  4 . The current sensor  72  measures the current and the voltage sensor  74  detects the voltage between the active and return electrodes  2 ,  4  at the target tissue. The current and voltage sensors  72 ,  74  feed analog voltage and current signals to analog to digital converters  76 ,  77  respectively.  
         [0042]     The analog to digital converters  76 ,  77  receive the analog signals and convert it to a digital signal for transmission to the microprocessor  80 , which preferably includes a comparator  84  and a controller  82 . An output port of the microprocessor  80  is electrically connected to a high voltage DC power supply  79 . The microprocessor  80  calculates the impedance according to by Ohm&#39;s law.  
         [0043]     The comparator  84  evaluates the digital impedance signal by comparing it to predetermined impedance values and generates responsive signals for transmission to the controller  82  as described in detail below. In response to the signals received from the comparator  84 , the controller  82  generates and transmits control signals to the power supply  79  which in turn controls the energy output of the RF output stage  78  which delivers current to the active and return electrodes  2 ,  4 .  
         [0044]     The deactivation threshold value is preferably about 2000 Ohms or another threshold (e.g., tissue determined baseline). If the impedance calculation exceeds the deactivation threshold, this indicates that the tissue has been treated since the impedance increases as the tissue is ablates because its conductivity due to moisture loss has decreased. If the deactivation threshold is exceeded, a digital deactivation signal is transmitted from the comparator  84  to the controller  82  ( FIG. 5A ). Thereafter the controller  82  signals the power supply  79  to automatically deactivate the generator so current output from the RF output stage  78  is terminated, thereby preventing overheating and unwanted destruction of tissue. This system provides for automatic deactivation of the generator  10  based on impedance measurements as soon as the lesion is complete.  
         [0045]     Lesions are generally used in electrosurgical procedures where a specific region of the tissue must be destroyed (e.g., a tumor). More specifically, conventional lesions are generally spherical (e.g., circular cross section) since this shape allows for optimum coverage of the target area. Sperical lesions are generally formed using monopolar electrosurgery. During monopolar electrosurgical procedures, current travels outward from an active electrode placed at the center of the tissue throughout the target area resulting in a lesion having a spherical shape.  
         [0046]     Although spherical lesions are useful in ablating regions of tissue due to its optimum area of effect, in certain procedures it is preferred to create lesions of an elongated shape, such as the ellipsoid shape of the lesion  50  ( FIG. 4 ). The elongated ellipsoid shape of the lesion  50  allows for tissue ablation in a narrow area (e.g., a strip) while preserving more of the surrounding tissue. This shape is particularly useful in bloodless resectioning procedures performed on organs containing large amount of blood vessels (e.g., liver) where removal of a section of the organ requires electrosurgically treating of the multitude of blood vessels present therein.  
         [0047]     More particularly and with reference to  FIGS. 6 and 7 , a liver  54  is shown which is to be resectioned, such as that a resectioned portion  55  will be detached from the liver  54  along a resectioning line  56 . In step  80 , a plurality of lesions  50  are created along the resectioning line  56  by inserting the active and return electrodes  2 ,  4  therein separated by a predetermined length L. The lesions  50  are created so that the major axis thereof is along the resectioning line  56  and the lesions  50  are connected end to end (e.g., insertion points of active and return electrodes  2 ,  4 ) with slight overlap of the edges.  
         [0048]     The length L of the lesion  56  is selected by the surgeon depending on the desired shape and size. The size of the length L is inversely proportional to the width W, thus increasing the length L, decreases the width W. However, the separation between the active and return electrodes  2 ,  4  (e.g., length L) also depends on the amount of energy supplied to the active electrode  2 . The lesion  50  having a relatively short length L requires less energy to form, while the lesion  50  with a longer length L requires more power. Therefore, the surgeon has to determine the optimum length L of the lesions  50  based on the desired size, shape, and amount of current prior to creating the lesions  50 . In addition, the depth of the lesion  50  is equivalent to the length of the exposed tip  12 . Thus, by adjusting the insulation (e.g., the insulative coating  13 ) covering the active and return electrodes  2 ,  4  the surgeon controls the depth of the lesion  50 .  
         [0049]     Once the lesions  50  have been created, small blood vessels (e.g., capillaries) are treated to reduce/stop blood flow. This allows organs of high vascularity to be resectioned without major blood loss. However, large blood vessels are not sealed during tissue ablation, as performed in step  80 . Therefore, in step  82 , the larger blood vessels are sealed. This may be performed in a plurality of ways. For instance, conventional sealing techniques using mechanical pressure and/or radio frequency energy may be used to create effective seals. One example of treating tissue is by sealing the tissue or vessels to stop bleeding. Sealing is defined as a process which precisely controls closure pressure, distance between the electrodes (i.e., gap distance), energy parameters to fuse opposing tissue structures into a homogenous mass with limited demarcation between tissue structures. Examples of vessel sealing devices are shown in commonly owned U.S. application Ser. No. 10/460,926 entitled “Vessel sealer and divider for use with small trocars and cannulas,” U.S. application Ser. No. 10/953,757 entitled “Vessel sealer and divider having elongated knife stroke and safety for cutting mechanism,” U.S. application Ser. No. 10/873,860 entitled “Open vessel sealing instrument with cutting mechanism and distal lockout,” U.S. application Ser. No. 10/991,157 entitled “Open vessel sealing instrument with cutting mechanism,” and U.S. application Ser. No. 10/962,116 entitled “Open vessel sealing instrument with hourglass cutting mechanism and over-ratchet safety,” the contents of all of which is hereby incorporated by reference herein in its entirety.  
         [0050]     Once the large blood vessels are sealed, in step  82 , the liver  54  is resected along the resectioning line  56  to separate the resectioned portion  55 . A plurality of cutting apparatus may be used, such as conventional scalpels and/or electrosurgical cutting devices.  
         [0051]     Although bipolar systems provide a number of advantages discussed above (e.g., smaller energy requirement, lack of return electrode pads, lack of off-site burns, etc.) the particular lesion  50  created using the bipolar electrosurgical system and method of  FIGS. 4-7  is not well suited for performing other ablation procedures due to the resulting ellipsoid shape. Therefore, it is envisioned that the presently-described bipolar electrosurgical system may also be configured to create spherical lesions as shown in  FIG. 8 .  
         [0052]     For example,  FIG. 8  shows an ablation device  200  having six pairs of bipolar electrodes (e.g., the active and return electrodes  2 ,  4 ) arranged in a generally circular pattern. Those skilled in the art will appreciate that the number of electrodes in the ablation device  200  depends on a number of factors (e.g., size of the lesion, power level, etc.). The electrodes are held by a housing  202  which contains the cables  3 ,  5  providing an electrical connection to the generator  10 . It is envisioned that the housing  202  may have an adjustable circumference thereby allowing the lesion area to be ablated by the electrodes to be regulated according to a specific purpose.  
         [0053]     The ablation device  200  allows for creation of a lesion  64  which more closely approximates a circle by using a series of pairs of bipolar electrodes (e.g., the active and return electrodes  2 ,  4 ) arranged in a circular pattern as shown. As can be appreciated, the lesion  64  is better suited for covering a circular/spherical target area in need ablation (e.g., a tumor  60 ). Lesion  64  is created by multiplexing the RF energy in different directions which involves switching the RF energy through each pair of the active and return electrodes  2 ,  4  as indicated by the arrows representing the current flow. This would be accomplished by passing electrical energy sequentially through the active electrode(s)  2  while including only the corresponding return electrode(s)  4  in the circuit so that the current flows in one particular direction. It is envisioned a multiplexer  260  may be employed to control switching of the active and return electrodes  2 ,  4 . For example, it is envisioned that multiplexer  260  may be configured to regulate the current in any fashion by switching on and off various pairs of active and return electrode pairs to create lesions  50 . Moreover it is also contemplated that multiplexer  260  may be configured to change active and return electrode to reverse polarity and reverse the current therethrough the lesions  50  depending on particular purpose.  
         [0054]     With respect to  FIG. 8  and as a result of multiplexing, each pair of the active and return electrodes  2 ,  4  generates a lesion having an ellipsoid shape. A plurality of the ellipsoid lesions having the same center overlap and form the lesion  64 , which closely approximates a sperical lesion which has been conventionally created using monopolar devices. Those skilled in the art will appreciate that  FIG. 9  shows only a cross section of the lesion  64  and that the lesion  64  has a depth equivalent to the exposed tips of the active and return electrodes  2 ,  4 .  
         [0055]     The described embodiments of the present disclosure are intended to be illustrative rather than restrictive, and are not intended to represent every embodiment of the present disclosure. Various modifications and variations can be made without departing from the spirit or scope of the disclosure as set forth in the following claims both literally and in equivalents recognized in law.