Patent Publication Number: US-2009240249-A1

Title: System and Method for Performing Ablation and Other Medical Procedures Using An Electrode Array with Flexible Circuit

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The application is a continuation-in-part of application Ser. No. 11/268,941, filed Nov. 8, 2005, entitled “System and Method for Performing Ablation and Other Medical Procedures using an Electrode Array with Flex Circuit” which claims priority to U.S. Provisional Application Ser. No. 60/625,859 entitled “System and Method for Performing Ablation and Other Medical Procedures using an Electrode Array with Flex Circuit” and filed Nov. 8, 2004, the contents of both of which are incorporated by reference herein in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to catheters and other medical probes and, more specifically, to using flexible circuits in these devices. 
     BACKGROUND OF THE INVENTION 
     Certain catheters or surgical probe shafts employ a set of braided insulated copper wires that form an intertwined, complicated cross-hatched design running the length of the catheter or probe. This braided shaft then serves as a conduit for radio frequency (RF) current that is delivered to electrodes to ablate tissue, as well as to sense electrophysiological signals that are in turn transmitted along those same lines to a monitoring system. 
     Another pair of copper wires is often soldered to a copper-constantan thermocouple junction located on a gold band proximal to each electrode. This gold band has a high thermal conductivity and the thermocouple junction quickly equilibrates to the sensed environmental temperature at the gold band. The thermocouple junction forms a temperature-to-voltage transducer and the two copper wires transmit information back to the energy source for feedback-control of RF energy delivery. 
     Material and labor costs may increase in the assembly process as the number of electrodes increases with conventional methods of assembly. For example, the number of braided wires for a 24-electrode catheter/probe with 24 thermocouples adds up to 72 wires. The “count and cut” process used during assembly to extricate and expose the correct wire along the shaft to solder onto an electrode or thermocouple has become increasingly time-consuming when performing these labor-intensive production steps. Additionally, when one electrode or one thermocouple connection fails during final electrical testing at the factory, the entire catheter/probe has to be counted as scrap if the fault cannot be reworked. 
     SUMMARY OF THE INVENTION 
     A probe is constructed that uses a flexible circuit that is embedded or otherwise attached to a sheath. Modular construction is used so that parts of the probe can be easily replaced or changed. The use of braided wires is eliminated leading to a simplified assembly process, reduced manufacturing costs, and greater user satisfaction with use of the device. 
     In many of these approaches a probe for use in medical procedures includes a longitudinal member, a flexible sheath, and a flexible circuit. The longitudinal member includes at least one electrode and at least one thermocouple disposed thereon. The flexible sheath is coupled to and at least partially surrounds the longitudinal member. The flexible circuit is coupled to the sheath and is coupled to the electrode and the thermocouple. The flexible circuit is configured to provide power to the electrode and a return path to the thermocouple. The probe may further include connector pins that couple the flexible circuit to the at least one electrode and the at least one thermocouple. 
     Various materials can be used to construct the sheath. In one example, the sheath can be constructed from silicon. Other examples of materials may also be used. The material selected allows for flexibility in movement of the probe but also is of sufficient strength to allow for maneuvering the probe and for protecting the inner components housed in the sheath. 
     In many of these examples, the probe includes a proximal end and a distal end and the flexible circuit includes circuit traces adapted to be attached to a terminal connector. The terminal connector is positioned at the distal end of the probe. In other examples, a plurality of electrodes and thermocouples are used and each of the plurality of electrodes is juxtaposed between a selected two of the plurality of thermocouples. 
     In others of these embodiments, a probe for use in medical procedures includes a longitudinal member, a flexible sheath and a flexible circuit. The longitudinal member has a plurality of coiled electrodes and a plurality of thermocouples disposed longitudinally thereon. Each of the plurality of coiled electrodes are spaced between a selected two of the plurality of thermocouples. The flexible sheath is embedded to and at least partially surrounds the longitudinal member. The flexible circuit is coupled to the sheath and is also coupled to the plurality of electrodes and the plurality of thermocouples. The flexible circuit is configured to provide power to the at least one electrode and a return path to the at least one thermocouple. 
     Thus, the present approaches allow for the replacement of complex braided wire arrangements with a flexible circuit arrangement. The structures described herein are simple to construct and easy to modify when adjustments are needed and/or when failures of components occur after the flexible circuit assembly is placed inside the sheath. 
     In addition, the approaches described herein are useful in a variety of medical therapy applications. For instance, the embodiments described herein can also be employed for the treatment of cardiac arrhythmias such as atrial fibrillation (AF) and ventricular tachycardia (VT). Minimally invasive access or endocardial access methods can be employed with probes/catheters using these approaches. The electrodes described herein can also be used to sense electrical activity from the heart, and the proximal connection of the probe/catheter shaft can be attached to a computerized mapping system. In addition, the present approaches are useful in other tissue desiccation and ablation procedures, for example, in oncology to selectively heat and destroy cancerous tumors. Other uses in different organ systems are possible. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1   a  is perspective view of a flexible circuit assembly for use in an ablation catheter showing a single electrode thermocouple pair according to the present invention; 
         FIG. 1   b  is a front view of a flexible circuit of  FIG. 1  showing twenty four electrode-thermocouple pairings according to the present invention; 
         FIG. 1   c  is a perspective view showing a three-layered flexible circuit assembly according to the present invention; 
         FIG. 2   a  is a perspective view of a flexible circuit assembly with etched electrodes and thermocouples formed into a cylinder according to the present invention; 
         FIG. 2   b  is a perspective view of a flexible circuit assembly with coiled electrodes and thermocouples formed into a cylinder according to the present invention; 
         FIG. 3   a  is a perspective view of a flexible circuit assembly with etched electrodes and thermocouples formed into a cylinder according to the present invention; 
         FIG. 3   b  is a perspective view of a flexible circuit assembly with coiled electrodes and thermocouples formed into a cylinder according to the present invention; 
         FIG. 4  is a perspective view of a flexible circuit assembly fitted into an ablation catheter according to the present invention; and 
         FIG. 5  is a cross-sectional view taken along line  304  of  FIG. 3   a  according to the present invention; 
         FIGS. 6   a - c  are cross-sectional views of a catheter using three flexible circuit layers according to the present invention; 
         FIG. 7  is a perspective view of the catheter using three flexible circuit layers of  FIG. 6  according to the present invention; 
         FIG. 8  is perspective view of a flexible circuit sheet showing the electrodes etched directly onto a conductive sheet according to the present invention; 
         FIG. 9A  is a cutaway side view of a flexible circuit assembly housed in a sheath according to the present invention; 
         FIG. 9B  is a bottom view of the flexible circuit assembly of  FIG. 9A  according to the present invention; 
         FIG. 9C  is a cross-sectional view taken along line “A” of the flexible circuit assembly of  FIG. 9A  with the flexible circuit attached to the sheath according to the present invention; 
         FIG. 9D  is a cross-sectional view taken along line “A” of the flexible circuit assembly of  FIG. 9A  with the flexible circuit embedded into the sheath according to the present invention; 
         FIG. 9E  is a cross-sectional view of another example of a flexible circuit assembly according to various embodiments of the present invention; 
         FIG. 10  is another example of a flexible circuit configuration according to the present invention; 
         FIG. 11  is an example of configuring a flexible circuit so as to provide flexibility for the circuit according to the present invention; 
         FIG. 12  is an example of a connector used in the catheters described herein according to the present invention. 
     
    
    
     Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of the various embodiments of the present invention. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present system and method allows for the replacement of complex braided wire arrangements with a flexible circuit arrangement in catheters and other medical devices. Medical devices constructed according to these approaches are relatively simple to fabricate. Mass production time and costs are also reduced. 
     The approaches described herein can be used in a variety of medical procedures. For example, the approaches described herein can be employed for the treatment of cardiac arrhythmias such as atrial fibrillation (AF) and ventricular tachycardia (VT). Minimally invasive access or endocardial access methods can also be performed with the probes/catheters described in this application. The electrodes utilized in the approaches described herein can also be used to sense electrical activity from the heart, and the proximal connection of the probe/catheter shaft can be attached to a computerized mapping system. In addition, these approaches can be used in tissue desiccation and ablation procedures, for example, in oncology, to selectively destroy cancerous tumors. 
     Referring now to  FIG. 1   a , one example of a flexible circuit  100  used in an ablation catheter is described. A flexible circuit pattern is printed on a flat sheet  104  with solder pins  106  at one edge of the sheet  104 . The pins  106  point perpendicular to the surface of the sheet  104 . The pins  106  correspond to connections for electrodes and thermal sensing elements (e.g., thermocouples). The pins are shown in  FIG. 1  as being parallel to the surface of the sheet  104 , but are bent or formed perpendicular to the sheet when the sheet is folded into a cylinder. The following description is made with respect to the thermal sensing elements being thermocouples. However, it will be understood by those skilled in the art that the thermal sensing elements may include not only thermocouples, but thermistors or any other thermal sensing device. 
     A conductive circuit  110  is established on the pattern and is connected to the pins  106 . For example, a metallic conductive circuit  110  is established using techniques that are known in the art. In this case, the conductive circuit  110  includes three lines that conduct electrical energy. 
     In addition, as described with respect to  FIGS. 1   b  and  1   c , repeated similar patterns of the conductive circuits can be printed onto flexible circuit boards. In addition, as described below, this arrangement can be formed into a cylinder and placed into the shaft of a catheter or medical probe. 
     Conducting circuit elements  110  of the sheet  104  are electrically insulated from each other and from the exposed surfaces of the flexible sheet  104 . Preferably, the inter-wire spacings for RF energy and current delivery are predetermined to comply with applicable regulatory, EMC and safety compliance standards. 
     Referring now to  FIG. 1   b , a circuit including 24 electrode and thermocouple pairs is shown. A first electrode thermocouple pair  106  (electrode E 1  and thermocouple TC 1 ) has corresponding conductive paths  110 , which couple the electrode and thermocouples to a connector  150  at the proximal end of the catheter. A second electrode thermocouple pair  120  (electrode E 2  and thermocouple TC 2 ) has corresponding conductive paths  112 , which couple the electrode and thermocouples to the connector  150  at the proximal end of the catheter. A third electrode thermocouple pair  122  (electrode E 3  and thermocouple TC 3 ) has corresponding conductive paths  114 , which couple the electrode and thermocouples to the connector  150  at the proximal end of the catheter. For simplicity, the fourth through twenty-third pairs of electrodes and thermocouples are not shown in  FIG. 1   b . Finally, a twenty-fourth electrode thermocouple pair  124  (electrode E 24  and thermocouple TC 24 ) has corresponding conductive paths  116 , which couple the electrode and thermocouples to the connector  150  at the proximal end of the catheter. 
     It will be understood that the electrode thermocouple pairs and their conductive paths can be split across multiple layers of circuit boards. In other words, the first eight pairs may be placed on a first flexible circuit board, the second eight pairings on a second flexible circuit board, and the third eight pairings placed on a third flexible circuit board. The three boards are stacked onto each other and then formed into a cylinder. Preferably, the three groupings are offset lengthwise from each other when the three layers are rolled into a cylinder for placement in the catheter. 
     Referring now to  FIG. 1   c , a multi-layered flexible circuit assembly is described. A first assembly  180 , second assembly  182 , and third assembly  184  are formed into concentric cylinders with assembly  180  being the outermost protective layer assembly. Assembly  182  is inside assembly  180  and assembly  184  is inside assemblies  180  and  182 . Electrode solder points E 1 , E 2 , and E 3  are formed on the assembly  180 . Other electrode solder points up to and including electrodes En are formed on the other assemblies. The assemblies  180 ,  182 , and  184  are electrically insulated from each other by homogenous polyimide material layers (not shown in  FIG. 1   c ) that are typically used in multi-layer flexible circuit boards. 
     In addition, thermocouple solder points T 1 , T 2  and T 3  are formed on assembly  180 . Other thermocouple solder points up to and including Tn are formed on the assemblies  182  and  184 . Conductive lines  186  are coupled to the respective electrodes and thermocouples. The electrodes and thermocouples are attached to the actual solder points. 
     Referring now to  FIG. 2   a , the flexible sheet  100  is shown folded into a cylinder  206 . For example, the flexible sheet  100  may be folded around a shape-forming mandrel  202 , with the pins  106  at the sheet edge pointing away from the mandrel  202 . In this case, the underside of the edge of the flexible sheet  100  with pins  106  is adhered to the top surface of the other edge of the same sheet  100 , so that the sheet takes on a cylindrical form. The pins  106  are soldered onto etched electrodes  204 . The pins  106  (shown exaggerated in  FIG. 2   a  for clarity) protrude perpendicularly along one longitudinal edge of the cylinder  206 . 
     A thermocouple band  208  is also constructed. In one example, the thermocouple band  208  may be constructed of a gold band to give the band a high thermal conductivity. These bands can be constructed using techniques known by those skilled in the art. 
     The example described herein with respect to  FIG. 2   a  (and also  FIGS. 3   a  and  5 ) utilizes a single set of electrodes and thermocouple band. However, multiple electrodes and bands can also be used. It will also be understood that multiples of the unit assembly can be organized in a linear pattern to form a linear mapping and ablation electrode array. 
     Preferably, metal etching is used for the production of the electrodes  204  to produce coiled groove, thereby creating a spring-like electrode component. Several techniques may be employed to etch metal sheets into different structural forms. 
     In one example process, a computer-aided design (CAD) drawing of the electrode coil pattern is generated. This drawing serves as the CAD image that is a faithful replica of the electrode. The drawing is printed onto a transparency film. 
     A cylindrical section of metal (e.g. platinum iridium) cut to a specific length is cleaned thoroughly. Then, a photo resist coating is applied to the outer surface so that it is photo-sensitive. 
     The CAD image is then overlaid onto the photo-sensitized metal surface and exposed to a ultra-violet (UV) light source. The metal cylinder is thereafter deposited into a developing solution to create a hardened image of the desired coil pattern on the metal cylinder surface. 
     The metal surface is then treated with an etchant, such as an acid. The etchant eats away the rest of the surface that is devoid of the hardened image, to create a spiral-shaped coil structure that can function as ablation and mapping electrodes  204 . If the desired spiral groove is too fine for acid or other form of chemical etching, then an alternate fabrication technique is to employ three dimensional etching of the spiral pattern via a precision laser cutting process. 
     Yet another alternate process is to etch the electrodes directly onto the flexible circuit board. This approach assumes dissimilar metals are layered onto the board, e.g. platinum for electrodes, copper for conduction lines by an appropriate manufacturing process. 
     Referring now to  FIG. 2   b , another example of a flexible circuit assembly is described. In this case, the assembly is the same as that shown and described with respect to  FIG. 2   a  except that the etched electrodes  204  are replaced with coiled electrodes  204 . 
     In one example, the coiled electrodes  204  may be 0.005″ gauge (0.003″ to 0.006″ range with one preferred type being a 0.005″ gauge) platinum iridium wire that is wound into a spring-like structural unit. These units may be 3 mm to 6 mm long and have outer diameters ranging from approximately 3 Fr to 5 Fr. Other dimensions are also possible. 
     Referring now to  FIG. 3   a , the etched electrodes  204  and thermocouple band  208  are inserted over the cylindrical structure formed by folding the flexible circuit. The electrodes  204  and thermocouple  208  are soldered at the respective protruding pin sites  106  that were spaced out by design to provide the desired inter-electrode and electrode-thermocouple spacing. 
     At one stage of the manufacturing process, the electrodes  204  can be coated with a conductive gel or other ionic material that improves tissue-electrode contact. At the same time, the electrodes  204  may be infused with anti-coagulant chemicals that are time released during the course of an ablation procedure. 
     Multiple layers of such unit assemblies may be utilized to reduce overall catheter or medical probe shaft diameter. These layers can be electrically insulated from each other by a homogenous polyimide material that is typically used in multi-layer flexible circuit boards. 
     An inner hollow shaft  302  of the resulting cylinder from this flexible circuit catheter shaft can serve as a conduit for a guide wire or stylet with deflectable mechanism, permitting the linear assembly of electrodes  204  and thermocouples  208  to be shaped and conformed to a tissue surface to afford excellent electrode-tissue contact that ensures optimal coupling of RF energy with the tissue. The conductive annular gold band for the thermocouple and the etched electrode are then slid along the shaft and soldered over their respective solder points. 
     The flexible circuit assembly is rolled and placed in the shaft of the catheter. The end of the flexible circuit assembly plugs into a connector. The connector is coupled to at least one PC card, which interfaces the arrangement to power and measurement equipment. 
     Referring now to  FIG. 3   b , another example of a flexible circuit assembly is described. In this case, the assembly is the same as that shown and described with respect to  FIG. 3   a  except that the etched electrodes  204  are replaced with coiled electrodes  204 . 
     As with the coiled electrodes of  FIG. 2   a , the coiled electrodes  204  of  FIG. 3   b  may be 0.005″ gauge (0.003″ to 0.006″ range with one preferred type being a 0.005″ gauge) platinum iridium wire that is wound into a spring-like structural unit. These units may be 3 mm to 6 mm long and have outer diameters ranging from approximately 3 Fr to 5 Fr. Other dimensions are also possible. 
     Referring now to  FIG. 4 , one example of a catheter system using the flexible circuit and etched electrodes and thermocouples is described. A catheter  400  includes the cylindrical flexible circuit assembly  408  that has been described with respect to  FIGS. 1-3  above. The cylindrical assembly  408  forms the distal end of the catheter  400  and is inserted into the telescopic structure  406  having a handle, which forms the proximal end of the catheter  400 . 
     Etched electrodes  402  are constructed and soldered onto the cylindrical assembly  408  as has been described elsewhere in the application. Alternatively, coiled electrodes may be used. In addition, thermocouples  404  are soldered onto the cylindrical assembly  408  as has also been described elsewhere in the application. The cylindrical assembly  408  may include sub-portions of flexible circuits that are attached together to form the assembly  408 . 
     An inner hollow shaft (not shown in  FIG. 4 ) of the cylinder  408  (i.e., the flexible circuit catheter shaft) may serve as a conduit for a guide wire or stylet with deflectable mechanism (not shown), permitting the linear assembly of electrodes  402  and thermocouples  404  to be shaped and conform to a tissue surface. This gives excellent electrode-tissue contact that ensures optimal coupling of RF energy with tissue  410 . The conductive annular gold band for the thermocouples  404  and the etched electrode  402  may then be slid along the shaft and soldered over their respective solder points. 
     A power and measurement circuit  408  is coupled to the catheter  400  via a personal computer (PC) board  407 . The power and measurement circuit  408  supplies electrical energy to the catheter and its electrodes  402  that can be used, for example, for ablation procedures. The impedance signals received at the electrodes and the information received by the thermocouples reporting tissue temperature can be relayed back to the power and measurement circuit  408  via the cylindrical assembly  408 . The power and measurement circuit  408  can receive information from the thermocouples and display this information to an operator for manual feedback control. In addition, the power and measurement circuit  408  can receive operating instructions from an automated processing unit for feedback and control to adjust various operating parameters pertaining to the RF current being emitted from the catheter  400 , such as the power or current delivered to the tissue  410 . 
     Referring now to  FIG. 5 , a cross-sectional view of the cylindrical assembly  208  taken along line  304  in  FIG. 3   a  is described. A guide wire  502  is in the middle of the hollow shaft  504  of the assembly  408 . The electrodes  204  and thermocouple (not shown in  FIG. 5 ) are soldered at the respective protruding pin sites  106  that were spaced at predetermined distances by design to provide the desired inter-electrode and electrode-thermocouple spacing along the side of the catheter. 
     Referring now to  FIG. 6   a - c  and  FIG. 7 , one example of an assembly using multiple layers of flexible circuits is described.  FIGS. 6   a - c  show cross sectional drawings taken along lines  708 ,  710 , and  712  of  FIG. 7  respectively. A first flexible circuit assembly  602 , second flexible circuit assembly  604 , and third flexible circuit assembly  606  are concentrically located with assembly  602  on the outside, assembly  604  inside of assembly  602  and assembly  606  inside assembly  604 . 
     The assemblies  602 ,  604 , and  606  are electrically insulated from each other by a homogenous polyimide material layers  608  and  610  that is typically used in multi-layer flexible circuit boards. Pin  612  is coupled to the flexible circuit assembly  602 . Pin  614  extends through the assembly  602  and is coupled to the flexible circuit assembly  604 . Pin  616  extends through the assemblies  602  and  604  and is coupled to the flexible circuit assembly  606 . Although only one pin is shown for each assembly (for convenience in viewing), it will be understood that multiple pins for the multiple layers  602 ,  604 , and  606  can be used. In addition, additional pins for thermocouples may also be included. The inner pins  614  and  616  may have holes drilled through the various layers so that the pins  614  and  616  reach above the surface of the cylinder. 
     Referring now to specifically to  FIG. 7 , the assembly of  FIG. 6  shows electrodes and thermocouples  702  coupled to the pins  612 . Electrodes and thermocouples  704  are coupled to the pins  614 . Further, electrodes and thermocouples  706  are coupled to the pins  616 . Since multiple layers are used, the overall catheter or medical probe shaft diameter is reduced. 
     Referring now to  FIG. 8 , one example of a flexible circuit  800  used in an ablation catheter is described where the electrodes are etched directly onto the flexible sheet. A flexible circuit pattern is printed on a flat sheet  804 . Electrodes  806  are constructed on the sheet  804  directly and electrically contact a conductive circuit element  810  on the flexible sheet  804 . Dissimilar metals are layered onto the board, for instance, platinum for electrodes and copper for the conduction circuit element  810 , by an appropriate manufacturing process. 
     Conductive circuit elements  810  of the sheet  804  are electrically insulated from each other and from the exposed surfaces of the flexible sheet  804 . Preferably, the inter-wire spacings for RF energy and current delivery are predetermined to comply with applicable regulatory, EMC and safety compliance standards. 
     Referring now to  FIGS. 9A-D , one example of a flexible circuit arrangement  900  including a sheath  904  is described. As shown, a flexible circuit  902  is embedded in or otherwise attached to the sheath  904 . If the flexible circuit  902  is embedded in the sheath  904  (as shown in  FIG. 9D ), the flexible circuit  902  may be inserted into and surrounded by some portions of the sheath  904  such that the sheath  904  secures the flexible circuit  902  in place. In some of these examples, the flexible circuit  902  may be formed so as to be coextensive with the sheath  904 . 
     If the flexible circuit  902  is attached to the sheath  904  (as shown in  FIG. 9C ), any type of fastening arrangement (e.g., glue, screws, nails, rivets, ultrasonic welding to name a few examples) may be used to secure the two elements together. In the example of  FIG. 9C , the flexible circuit  902  is attached to the sheath  904  by fasteners  927 . In this example, the fasteners  927  are bolts or the like. The flexible circuit  902  includes a sheet  907  and circuit traces  906 . The sheet  907  may be made of a material such as Kapton to give one example. 
     The sheath  904  can be constructed from silicon, silicone rubber, or some other suitable material. The sheath  904  is flexible and as described herein houses the electrically conductive elements of the system. In addition, the sheath  904  is constructed and configured to meet governmental and non-governmental compliance standards concerning, for example, the conduction of RF current and other operating characteristics. 
     In many examples, the sheath  904  is constructed of materials that provide strength for the assembly and allow the assembly to be moved by the user. On the other hand, the materials are not so rigid as to hamper the movement and maneuverability of the assembly  900  when used as intended during a given medical procedure. The sheath  904  also provides protection for the components it houses, for example, from accidental damage caused by misuse of the assembly  900 . 
     In some examples, the sheath  904  is formed over only the distal end of a catheter assembly. In other examples, the sheath  904  may be formed over the entire length of the catheter assembly. It will be appreciated that the dimensions, shape, and extent of the sheath  904  may be varied according to the requirements of the system and the application. 
     The trace elements  906  include a first trace line  906   a  and a second trace line  906   b  and these lines extend to a connector  908 . The connector  908  allows electrical connection to external systems. For simplicity, the example of  FIGS. 9A-D , show two trace lines  906   a  and  906   b  on the sheet  907 . The sheet  907  may be any type of circuit board used to contain electrical trace elements. The first trace line  906   a  is associated with an electrode  910  and the second trace line  906   b  is associated with a thermocouple  912 . It will be appreciated that any number of trace lines can be used that correspond with any number of electrodes and thermocouples. It will also be understood that the sheet  907  can also be configured (e.g., rolled) according to any of the configurations described elsewhere herein. 
     It will further be appreciated that the electrodes and thermocouples associated with the flex circuit  902  are often used in pairs. However, it will also be understood that in some situations only a single element (e.g., a single electrode) may be used. In other examples, single electrodes may be matched with multiple thermocouples and in still other examples, single thermocouples may be matched with multiple electrodes. 
     The connector  908  may be coupled to an external power generating and monitoring system such as the INTELLITEMP® system manufactured by Cardima, Inc. In one example, the connector  908  is a plug-in type connector that plugs into an external power generating and monitoring system. Other types of connectors may also be used. The trace line  906   a  is connected to the electrode  910  via a first pin  911  at a first soldering point  930  and the trace line  906   b  is attached to the thermocouple  912  via a second pin  913  at a second soldering point  932 . 
     The trace elements  906  may be printed on the flat sheet of material  907  with the pins  911  and  913  being soldered at one edge of the sheet. The pins  911  and  913  themselves may extend perpendicular to the surface of the sheet  907 . However, in other examples, the pins  911  and  913  are bent when the sheet  907  is folded into a cylinder. 
     The pins  911  and  913  mate with/are attached to proximal exit points of the conducting trace elements  906  and these pins are any type of suitable medical grade terminal connectors. One pin  911  is soldered to solder points  930  of the electrode  910  and the other pin  913  is soldered to solder point  932  of the thermocouple  912  to form connections between the electrode  910  and the trace line  906   a , and the thermocouple  912  and the trace line  906   b  respectively. 
     The trace elements  906  form a conductive circuit that transmits electrical energy that is established on the sheet  907  and is connected to the pins  913  and  915 . For example, the trace elements  906  are established on the sheet  907  using techniques (e.g., circuit printing) that are known in the art. 
     The trace elements  906  are electrically insulated from each other on the sheet  907  and are electrically insulated from the exposed surfaces of the sheet  907 . The inter-wire spacing of trace line  906   a  and trace line  906   b  for RF energy and current delivery are selected to comply with applicable regulatory, EMC and safety compliance standards. 
     The electrode  910  and the thermocouple  912  are assembled along a longitudinal member  917  (e.g., a hollow polymer tube having a suitable diameter). The longitudinal assembly  917  is constructed from flexible and/or pliable materials and is securely fastened (e.g., by glue) or otherwise fastened by any type of fastening arrangement (e.g., screws, rivets, ultrasonic welding to name a few examples) to the interior of the sheath  904 . 
     It will be understood that the electrode and thermocouple pairs and their conductive paths can be split across multiple sheets or circuit boards. In other words and as describe elsewhere herein, first grouping of electrode/thermocouple pairs may be placed on a first flexible circuit board, a second grouping of the pairs on a second flexible circuit board, and a third grouping of the pairs placed on a third flexible circuit board. The three boards are stacked onto each other and then formed into a cylinder. Preferably, the three groupings are offset lengthwise from each other when the three layers are rolled into a cylinder for placement in the catheter. 
     The thermocouple  912  (e.g., a thermocouple band) may be constructed of various materials. In one example, the thermocouple band  912  may be constructed of gold give the band a high thermal conductivity. These bands can be constructed using techniques known by those skilled in the art. The thermocouple  912  provides temperature information that is returned to an external device (e.g., the INTELLITEMP® system manufactured by Cardima, Inc.) via the trace elements of flexible circuit  902 , which act as a return path. 
     Various techniques can be used to construct the electrode  910 . In one example and as described elsewhere herein, metal etching is used for the production of the electrode  910  to produce a coiled groove, thereby creating a spring-like electrode component. The etching process allows precisely-dimensioned parts to be constructed with precise tolerances. Various techniques may be employed to etch metal sheets into different structural forms. Alternatively, a coiled electrode that is not produced using an etching process may also be used. 
     In one example of constructing the assembly  900 , the sheath  904  is initially and separately formed and then the flexible circuit  902  is embedded or otherwise attached to the sheath  904 . In another example, the sheath  904  is formed together with the flexible circuit  902 . Various manufacturing techniques and tools may be used to form these elements that are well known to those skilled in the art. The connector pins  913  and  915  may be formed with the flexible circuit  902  or formed separately and then attached to the flexible circuit  902 . 
     The electrode  910  and thermocouple  912  are attached to the longitudinal member  917  by gluing, soldering, or some other fastening approach. Then, the connector pins  913  and  915  (on the flexible circuit  902 ) are aligned to the electrode soldering point  930  (on the electrode  910 ) and the thermocouple soldering point  932  (on the thermocouple  912 ). The electrode  910  and the thermocouple  912  are soldered to the pins  913  and  915  and the assembly is complete. 
     Referring now to  FIG. 9E , another example of a catheter structure is described. In this example, the trace elements  906 A are embedded in the sheath  904 . Consequently, the flexible circuit  902  is not used in this example. In other examples, some of the trace elements are embedded in the sheath while others are present on a flexible circuit board. 
     Consequently, the need to use and construct a braided wire assembly as used in previous approaches is eliminated. More specifically, there is no need to “count and cut” the braided wires and thread the wires through the assembled as required in previous approaches. In other words, the prefabricated silicon sheath with embedded flexible circuit takes on the functions of the braided wires and the associated problems with maneuvering these wires are eliminated. Consequently, manufacturing and assembly costs are reduced due to the ease and speed by which the assembly  900  can be constructed. 
     As can also be appreciated, the assembly  900  is modular in structure. Various parts of the assembly  900  can be replaced without disassembling the entire structure. For example, the pins, electrodes, and thermocouples can be removed easily and quickly in contrast to previous systems where the entire assembly needed to be disassembled to replace a malfunctioning part. Further, the flexible circuit boards themselves can also be easily removed and replaced in the present approaches thereby obviating the need for removing braided wires and avoiding the problems associated with rewiring the system. Potentially, during the assembly process, a technician can easily replace damaged parts of the circuit with new flexible circuit components as required using all the present approaches. 
     Referring now to  FIG. 10 , another example of a flexible circuit configuration is described. In this example, the thermocouples have a constantan lead and a copper lead. However, it will be appreciated that other configurations or materials may be used. 
     As shown, the circuit includes 24 electrode and thermocouple pairs. A first electrode thermocouple pair  1006  (electrode E 1  and thermocouple TC 1 ) has corresponding conductive path  1010  for the electrode, and a conductive path  1011  coupled to the constantan lead of TC 1 . The copper lead of the thermocouple TC 1  is coupled to a common path  1050  (e.g., common copper path). The conductive paths  1010 ,  1011 , and  1050  couple the electrode and thermocouples to a connector  1051  at the proximal end of the catheter. 
     A second electrode thermocouple pair  1020  (electrode E 2  and thermocouple TC 2 ) has a corresponding conductive path  1012  to couple the electrode E 2  to the proximal end of the catheter. A conductive path  1013  couples the constantan lead of TC 2  to the connector  1051 . The copper lead of the thermocouple TC 2  is coupled to the connector  1051  via the common copper conductor  1050 . Similarly, a third electrode thermocouple pair  1022  (electrode E 3  and thermocouple TC 3 ) up through a twenty-fourth electrode thermocouple pair  1024  (electrode E 24  and thermocouple TC 24 ) are connected to the connector  1051  in a similar manner. It will be appreciated that the use of a common conductor  1050  eliminates the need for 23 trace lines thereby reducing the size of the catheter assembly. 
     In another example, mechanical flexibility can be provided to the flexible circuit structure by adding cuts in this structure. As shown in  FIG. 11 , cuts  1102  are added to the flexible circuit  1104  in a longitudinal direction of the circuit  1104  as it is positioned in the catheter (e.g., in the sheath). This allows flexibility by allowing the structure to bend and/or move back and forth. The dimensions and frequency of the cuts along the circuit  1104  may be varied according to the requirements of the system. 
     In other examples and now referring to  FIG. 12 , a connector pin  1202  connects a flexible circuit  1204  and an electrode  1206 . The pin  1202  is configured in an “S”-like shape and is constructed from a material that provides at least some bounce (between the flexible circuit and electrode or other components) and helps absorb shocks that the catheter may experience during use. It will be appreciated that the exact dimensions and shape of the pin  1202  may vary depending upon the requirements of the system. 
     While there has been illustrated and described particular embodiments of the present invention, it will be appreciated that numerous changes and modifications will occur to those skilled in the art, and it is intended in the appended claims to cover all those changes and modifications which fall within the true scope of the present invention.