Abstract:
A catheter enables real-time light measurements, for example, without limitation, diffuse reflectance, fluorescence, etc., from biological materials, such as tissue (including blood), while performing RF ablation. The catheter tip design isolates illumination and collection paths such that light exits the catheter tip and travels through the tissue of interest (e.g., cardiac tissue or blood) before returning to the catheter tip. Such a design advantageously avoids saturation of the optical detector, and ensures diffusion of the illumination light within the medium of interest. The catheter has a catheter body and a tip electrode. The tip electrode has an exterior shell, an inner layer of diffuse material and a hollow cavity, wherein the inner layer is configured to transmit light outside the tip electrode to a tissue via a set of illumination openings in the shell wall and the hollow cavity is configured to receive light from the tissue via a set of collection openings in the shell wall and the inner layer. An inner surface of the inner layer has a reflective coating to isolate light injected into the inner layer from light collected in the hollow cavity. There are a first optical waveguide extending between the catheter body and the tip electrode to inject light into the inner layer and illuminate the tissue, and a second optical waveguide extending between the catheter body and the tip electrode to collect the recaptured light in the hollow cavity.

Description:
FIELD OF INVENTION 
     The present invention relates to ablation catheters, and in particular to ablation catheters with optical monitoring of tissue. 
     BACKGROUND 
     For certain types of minimally invasive medical procedures, real time information regarding the condition of the treatment site within the body is unavailable. This lack of information inhibits the clinician when employing catheter to perform a procedure. An example of such procedures is tumor and disease treatment in the liver and prostate. Yet another example of such a procedure is surgical ablation used to treat atrial fibrillation. This condition in the heart causes abnormal electrical signals, known as cardiac arrhythmias, to be generated in the endocardial tissue resulting in irregular beating of the heart. 
     The most frequent cause of cardiac arrhythmias is an abnormal routing of electricity through the cardiac tissue. In general, most arrhythmias are treated by ablating suspected centers of this electrical misfiring, thereby causing these centers to become inactive. Successful treatment, then, depends on the location of the ablation within the heart as well as the lesion itself. For example, when treating atrial fibrillation, an ablation catheter is maneuvered into the right or left atrium where it is used to create ablation lesions in the heart. These lesions are intended to stop the irregular beating of the heart by creating non-conductive barriers between regions of the atria that halt passage through the heart of the abnormal electrical activity. 
     The lesion should be created such that electrical conductivity is halted in the localized region (transmurality), but care should be taken to prevent ablating adjacent tissues. Furthermore, the ablation process can also cause undesirable charring of the tissue and localized coagulation, and can evaporate water in the blood and tissue leading to steam pops. 
     Currently, lesions are evaluated following the ablation procedure, by positioning a mapping catheter in the heart where it is used to measure the electrical activity within the atria. This permits the physician to evaluate the newly formed lesions and determine whether they will function to halt conductivity. It if is determined that the lesions were not adequately formed, then additional lesions can be created to further form a line of block against passage of abnormal currents. Clearly, post ablation evaluation is undesirable since correction requires additional medical procedures. Thus, it would be more desirable to evaluate the lesion as it is being formed in the tissue. 
     A known method for evaluating lesions as they are formed is to measure electrical impedance. Biochemical differences between ablated and normal tissue can result in changes in electrical impedance between the tissue types. Although impedance is routinely monitored during electrophysiologic therapy, it is not directly related to lesion formation. Measuring impedance merely provides data as to the location of the tissue lesion but does not give qualitative data to evaluate the effectiveness of the lesion. 
     Another approach is to measure the electrical conductance between two points of tissue. This process, known as lesion pacing, can also determine the effectiveness of lesion therapy. This technique, however, measures the success or lack thereof from each lesion, and yields no real-time information about the lesion formation. 
     Thus, there is a need for a catheter capable of measuring characteristics of lesion formation in real-time, and doing so with optical imaging, whether the catheter is parallel, perpendicular or at an angle to the tissue. It would be desirable for the catheter to be adapted for ablation as well. To that end, the catheter tip should be transparent yet also electrically conductive so that optical data can be sensed by the catheter tip during, before or after ablation. 
     There are available many transparent, electrical conductors but each has its limitations. Carbon nanotube film is one such transparent, electrical conductor. Carbon nanotubes were discovered in or about 1991, but their existence had been suspected earlier based on mathematical calculations. Carbon nanotubes have a large length to diameter ratio and thus can be seen as nearly one-dimensional forms of fullerenes. They possess interesting electrical, mechanical and molecular properties. There are single walled nanotubes (SWNT) where the length to diameter ratio is about 1000. There are multi-walled nanotubes (MWNT) with multiple concentric SWNTs with different diameters. MWNTs have different lengths and diameters from SWNTs and they also have different properties. 
     It is now possible to fabricate ultrathin, transparent, optically homogenous, electrically conducting films of carbon nanotubes and to transfer those films onto various substrates. The challenge had been to deposit nanotubes in a layer thin enough to be optically transparent while maintaining electrical contract through the layer. The films exhibit optical transmittance in the visible spectrum and the infrared. In the near-to-mid infrared, carbon nanotube films have been shown to have good to high transparency for given electrical conductivity of most things currently available. Even in the visible spectrum, the electrical conductivity of nanotube films for given transparency is comparable to commercially available indium tin oxide (ITO) which is another substance that has electrical conductivity and optical transparency. 
     Accordingly, it would therefore be desirable to provide a catheter that is adapted for optical imaging and electrical conductivity such as for ablation, having a tip that is optically omnidirectional and constructed of carbon nanotube film. Such a catheter may also be adapted for ultrasound imaging concurrently with electrical ablation therapy. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a catheter that ablates and enables real-time omnidirectional light measurements, for example, without limitation, diffuse reflectance, fluorescence, etc., from biological materials, such as tissue (including blood). The catheter tip design employs carbon nanotube film which in sufficiently thin form offers electrical conduction and optical transparency. The light recaptured from the tissue through the film-covered electrode tip conveys tissue parameters that can be evaluated using optical spectroscopy. These parameters include, without limitation, lesion formation, depth of penetration of lesion, and cross-sectional area of lesion, formation of char during ablation, recognition of char during ablation, recognition of char from non-charred tissue, formation of coagulum around the ablation site, differentiation of coagulated from non-coagulated blood, differentiation of ablated from healthy tissue, tissue proximity, evaluation of tissue health, status, and disease state, and recognition of steam formation in the tissue for prevention of steam pop. 
     In one embodiment, a catheter has a catheter body and a tip electrode that includes an optically transmissive shell coated with a carbon nanotube film. It is contemplated that the optically transmissive shell is adapted for optical illumination and collection, and the carbon nanotube film is adapted for tissue ablation. Moreover, it is contemplated that the shell is generally shaped as a dome defining a cavity and that the shell is optically transparent. The film is also optically transmissive if not optically transparent. The cavity is illuminated by at least one emitting optical fiber and light entering the cavity from tissue is received by at least one receiving optical fiber which communicates with an optical processing system. 
     In a more detailed embodiment, a catheter has a catheter body and a tip electrode with an optically transparent shell and an electrically conductive and optically transparent film on the shell. The shell defines a cavity to receive light from the tissue and the film is adapted to ablate tissue. A first optical waveguide extends into the cavity to provide light and a second optical waveguide extends into the cavity to collect light. The tip electrode is adapted for RF ablation and the catheter may also include an irrigation tubing to deliver fluid to the cavity and through openings in the shell to reach outside the tip electrode. The catheter may include a deflectable intermediate section between the catheter body and the tip electrode, and a temperature sensor configured to sense temperature in the tip electrode. There may also be an electromagnetic location sensor configured to sense location of the tip electrode. 
     Advantageously, the light used to monitor and assess the tissue (or a lesion formed in the tissue) is generally not affected by the portion of the electromagnetic radiation used for ablation. Moreover, the bandwidth used for monitoring and assessing also transmits through blood with minimal attenuations. The fiber optics are used and disposed in the catheter in a manner that avoids contact with tissue, which can increase the operative lifetime of the catheter and minimize damages caused by abrasion to the fiber optics. Furthermore, the alignment plug in the tip electrode secures the fiber optic cables with minimal bend or strain but increased angular coverage, which can minimize fiber optics breakage during assembly and use, as well as reduce nonlinear optical effects caused by orientation of the fiber optics. In addition, the use of fiber optics to emit and receive light is a generally temperature neutral process that adds little if any measurable heat to surrounding blood or tissue. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features and advantages of the present invention will be better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
         FIG. 1  is a side view of an embodiment of the catheter of the present invention. 
         FIG. 2A  is a side cross-sectional view of an embodiment of a catheter according to the invention, including the junction between a catheter body and an intermediate section, taken along a first diameter. 
         FIG. 2B  is a side cross-sectional view of an embodiment of a catheter according to the invention, including the junction between the catheter body and the intermediate section, taken along a second diameter generally perpendicular to the first diameter of  FIG. 2A . 
         FIG. 3A  is a side cross-sectional view of an embodiment of a catheter according to the invention, including the junction between the intermediate section and a plastic housing, taken along the first diameter. 
         FIG. 3B  is a side cross-sectional view of an embodiment of a catheter according to the invention, including the junction between the intermediate section and the plastic housing, taken generally along the second diameter. 
         FIG. 4  is a longitudinal cross-sectional view of an embodiment of an intermediate section of  FIGS. 3A and 3B , taken generally along line  4 - 4 . 
         FIG. 5A  is a side cross sectional view of an embodiment of a catheter according to the invention, including a junction between the plastic housing and a tip electrode, taken generally along diameter  5 A- 5 A as shown in  FIG. 6 . 
         FIG. 5B  is a side cross-sectional view of an embodiment of a catheter body according to the invention, including the junction between the plastic housing and the tip electrode, taken generally along diameter  5 B- 5 B as shown in  FIG. 6 . 
         FIG. 6  is a longitudinal cross-sectional view of an embodiment of a plastic housing of  FIGS. 4A and 4B , taken along line  6 - 6 . 
         FIG. 7  is a schematic drawing showing components of an embodiment of an optical processing system for use with the catheter of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in  FIGS. 1-6 , a catheter  10  of the present invention comprises an elongated catheter body  12  having proximal and distal ends, a deflectable (uni- or bi-directionally) intermediate section  14  at the distal end of the catheter body  12 , a tip section  36  at the distal end of the intermediate section, and a control handle  16  at the proximal end of the catheter body  12 . 
     With additional reference to  FIGS. 2A and 2B , the catheter body  12  comprises an elongated tubular construction having a single, axial or central lumen  18 . The catheter body  12  is flexible, i.e., bendable, but substantially non-compressible along its length. The catheter body  12  can be of any suitable construction and made of any suitable material. A construction comprises an outer wall  22  made of an extruded plastic. The outer wall  22  may comprise an imbedded braided mesh of stainless steel or the like to increase torsional stiffness of the catheter body  12  so that, when the control handle  16  is rotated, the catheter body  12 , the intermediate section  14  and the tip section  36  of the catheter  10  will rotate in a corresponding manner. 
     Extending through the single lumen  18  of the catheter body  12  are components, for example, lead wire  40  and thermocouple wires  41 ,  45  protected by a sheath  53 , optical fibers  43 , an irrigation tube  48 , a compression coil  56  through which a puller wire  42  extends, and an electromagnetic sensor cable  74 . A single lumen catheter body can be preferred over a multi-lumen body because it has been found that the single lumen body permits better tip control when rotating the catheter. The single lumen permits the various components such as the lead wire, thermocouple wires, infusion tube, and the puller wire surrounded by the compression coil to float freely within the catheter body. If such wires, tube and cables were restricted within multiple lumens, they tend to build up energy when the handle is rotated, resulting in the catheter body having a tendency to rotate back if, for example, the handle is released, or if bent around a curve, to flip over, either of which are undesirable performance characteristics. 
     The outer diameter of the catheter body  12  is not critical, but is preferably no more than about 8 french, more preferably 7 french. Likewise the thickness of the outer wall  22  is not critical, but is thin enough so that the central lumen  18  can accommodate the aforementioned components. The inner surface of the outer wall  22  may be lined with a stiffening tube  20 , which can be made of any suitable material, such as polyimide or nylon. The stiffening tube  20 , along with the braided outer wall  22 , provides improved torsional stability while at the same time minimizing the wall thickness of the catheter, thus maximizing the diameter of the central lumen  18 . The outer diameter of the stiffening tube  20  is about the same as or slightly smaller than the inner diameter of the outer wall  22 . Polyimide tubing may be preferred for the stiffening tube  20  because it may be very thin walled while still providing very good stiffness. This maximizes the diameter of the central lumen  18  without sacrificing strength and stiffness. 
     The catheter may have an outer wall  22  with an outer diameter of from about 0.090 inch to about 0.104 inch and an inner diameter of from about 0.061 inch to about 0.075 inch and a polyimide stiffening tube  20  having an outer diameter of from about 0.060 inch to about 0.074 inch and a wall thickness of about 0.001-0.005 inch. 
     Referring also to  FIGS. 3A ,  3 B and  4 , the intermediate section  14  distal of the catheter body  12  comprises a shorter section of tubing  19  having multiple lumens. The tubing  19  is made of a suitable non-toxic material that is preferably more flexible than the catheter body  12 . A suitable material for the tubing  19  is braided polyurethane with low to medium durometer plastic. The outer diameter of the intermediate section  14 , like that of the catheter body  12 , is preferably no greater than about 8 french, more preferably 7 french. The size and number of the lumens is not critical. In an embodiment, the intermediate section  14  has an outer diameter of about 7 french (0.092 inch). The tubing  19  has a first off-axis lumen  30 , a second off-axis lumen  32  and a third off-axis lumen  34  that are generally about the same size, each having a diameter of from about 0.020 inch to about 0.024 inch, preferably 0.022 inch, along with a fourth off-axis lumen  35 , having a larger diameter of from about 0.032 inch to about 0.038 inch, preferably 0.036 inch. 
     Referring back to  FIGS. 2A and 2B , the catheter body  12  may be attached to the intermediate section  14  formed with an outer circumferential notch  24  configured in the proximal end of the tubing  19  that receives the inner surface of the outer wall  22  of the catheter body  12 . The intermediate section  14  and catheter body  12  are attached by glue or the like. Before the intermediate section  14  and catheter body  12  are attached, the stiffening tube  20  is inserted into the catheter body  12 . The distal end of the stiffening tube  20  is fixedly attached near the distal end of the catheter body  12  by forming a glue joint  23  with polyurethane glue or the like. Preferably a small distance, e.g., about 3 mm, is provided between the distal end of the catheter body  12  and the distal end of the stiffening tube  20  to permit room for the catheter body  12  to receive the notch  24  of the intermediate section  14 . If no compression coil is used, a force is applied to the proximal end of the stiffening tube  20 , and, while the stiffening tube  20  is under compression, a first glue joint (not shown) is made between the stiffening tube  20  and the outer wall  22  by a fast drying glue, e.g. cyanoacrylate. Thereafter a second glue joint  26  is formed between the proximal ends of the stiffening tube  20  and outer wall  22  using a slower drying but stronger glue, e.g., polyurethane. 
     If desired, a spacer can be located within the catheter body between the distal end of the stiffening tube and the proximal end of the tip section. The spacer provides a transition in flexibility at the junction of the catheter body and intermediate section, which allows this junction to bend smoothly without folding or kinking. A catheter having such a spacer is described in U.S. patent application Ser. No. 08/924,616, entitled “Steerable Direct Myocardial Revascularization Catheter”, the entire disclosure of which is incorporated herein by reference. 
     Extending from the distal end of the intermediate section  14  is the tip section  36  that includes a tip electrode  37  and a plastic housing  21  as shown in  FIGS. 5A and 5B . The plastic housing  21  connects the tip electrode  37  and the tubing  19  and provides components that extend through its lumen with housing and/or transitional space, as discussed further below. The plastic housing  21  is preferably made of polyetheretherketone (PEEK) and may be about 1 cm long. Its proximal end is received in an outer circumferential notch  27  ( FIGS. 3A and 3B ) formed in the distal end of the tubing  19  of the intermediate section  14 . The intermediate section  14  and the plastic housing  21  are attached by glue or the like. Components such as wires, cables and tube segments that extend between the intermediate section  14  and the tip electrode  38  may help keep the tip electrode in place. 
     The dome tip electrode  37  has an open proximal end that is in communication with a generally hollow distal portion or cavity  49 . The tip electrode includes an optically-transmissive if not optically-transparent shell  38  of generally uniform thickness on which there is deposited electrically conductive carbon nanotube film or coating  39 . The tip electrode also includes a press-fit plug or alignment member  44  is positioned at or near the proximal end of the shell. 
     The shell  38  is configured with a dome or similar shape at its distal end to facilitate omnidirectional illumination and collection of light. Its exterior with the film  39  thereon is configured atraumatically and adapted for contact with tissue. The shell is configured with a plurality of through-holes or openings  87  for irrigation/infusion purposes. The shell is formed from any suitable material that is optically transparent, including glass or plastics. And because the carbon nanotube film  39  is suitably thin for optical transparency, the shell of the tip electrode functions as an omnidirectional illuminator and collector. Accordingly, the dome tip electrode  37  is configured for ablation and illumination and collection of light from tissue for optical spectroscopy. For the latter functions, optical fibers are in communication with the cavity  49 , as explained in detail further below. 
     The plug  44  has a generally elongated cylindrical configuration having a predetermined length and a generally circular cross-section. A distal portion of the plug  44  is press fitted into the open proximal end of the tip electrode  37  to seal the hollow cavity  49 , while a proximal portion of the plug  44  extends proximally from the tip electrode  37  for attachment to the housing  21 . As shown in  FIG. 6 , various blind holes and passages are provided in the plug to allow components to be anchored to the plug or to pass through to the hollow cavity  49 . In the illustrated embodiment, there are blind holes  102 ,  104  and  106  in which distal ends of the lead wire  40 , the thermocouple wires  41  and  45  and the location sensor  72  are anchored, respectively. There are also passages  112   116  through which the optical fibers  43  extend, and a passage  110  through which the irrigation tube segment  48  extends. The portions of the components extending through the passages in the plug are securely fixed in the passages by glue, adhesive or the like. The passages help align, stabilize and secure the various components extending through the plug  44 . 
     In accordance with a feature of the present invention, the catheter  10  is adapted to facilitate optically-based real-time assessment of ablation tissue characteristics, including without limitation, lesion formation, depth of penetration of the lesion, cross-sectional area of the lesion, formation of char during ablation, recognition of char during ablation, differentiation of char from non-charred tissue, formation of coagulum around the ablation site, differentiation of coagulated from non-coagulated blood, differentiation of ablated from healthy tissue, tissue proximity, and recognition of steam formation in the tissue for prevention of steam pop. These assessments are accomplished by measuring the light intensity at one or more wavelengths that is recaptured at the catheter resulting from the light radiated from the catheter tip onto ablated tissue. In that regard, the optical fibers  43 E extend into the tip electrode  37  to transmit light to the tip electrode and the optical fiber  43 R collects light from the tissue for such optically based real-time tissue assessment. 
     The fiber optic cables  43  are protectively housed in the catheter from the control handle  16  to the tip section  36 . As shown in  FIGS. 2B and 4 , they extend through the central lumen  18  of the catheter  12  and the lumens  32 ,  34  and  35  of the intermediate section  14 . They extend through the plastic housing  21  and into the tip electrode  37  via the passages  112  in the plug  44 . The passages help minimize stress on the fibers  43  in their transition between the intermediate section  14  and the tip electrode  37 . 
     In the disclosed embodiment, there are three emitting fibers  43 E and one receiving fiber  43 R. The fibers  43 E function as a light emitters by transmitting light to the tip electrode  37  from a remote light source. The fiber  43 R functions as a light receiver by collecting light from the hollow cavity  49  in the tip electrode  37 . Each of the cables  43 T and  43 R may be a single fiber optic cable or fiber bundles. They may be single mode (also known as mono-mode or uni-mode), multi-mode (with step index or graded index) or plastic optical fiber (POF), depending on a variety of factors, including but not limited to transmission rate, bandwidth of transmission, spectral width of transmission, distance of transmission, diameter of cable, cost, optical signal distortion tolerance and signal attenuation, etc. Moreover, light delivery and collection may be accomplished with other devices, such as air-core fibers, hollow waveguides, liquid waveguides and the like. It is understood by one of ordinary skill in the art that optical waveguides, optical fibers and fiber optic cables in general serve to transmit optical energy from one end to the other, with minimal loss and are therefore used interchangeably herein. These optical devices are not exclusive and other suitable optical devices may be used, as well. 
     As lesion forms in the tissue from ablation carried out by tip electrode  37  of the catheter  10 , its characteristics are altered as understood by one of ordinary skill in the art. In particular, as the lesion is radiated by light, the light is scattered and/or reflected back toward the tip electrode  37 , where such light having interacted or otherwise having been affected by the lesion bears qualitative and quantitative information about the lesion as it reenters the hollow cavity  49 . 
     With its distal end inserted into the hollow cavity, the receiving optical fiber  43 R collects recaptured light which bears the qualitative and quantitative information and is transmitted to an optical processing system, as described below in further detail. In accordance with a feature of the present invention, the tip section  36  serves as a generally omni-directional optical radiator and collector, as well as an ablation tip. 
     The present catheter may also be adapted for irrigation or infusion at the tip electrode, such as for cooling the tissue site and to improve electrical conduction for deeper and larger lesions. Fluid, e.g., saline, is fed into the hollow cavity by an irrigation tube segment  48 , as shown in  FIG. 5B . The distal end of the tube segment  48  is anchored in the passage  110  ( FIG. 6 ) and extends proximally through the plastic housing  21 , the fourth lumen  35  of the intermediate section  14  ( FIG. 2A ), the central lumen  18  of the catheter body  12 , and through the control handle  16  where it terminates in a luer hub  90  ( FIG. 1 ) or the like at a location proximal to the control handle. In practice, fluid may be injected by a pump (not shown) into the infusion tube  48  through the luer hub  90 , and flows into the hollow cavity  49  in the tip electrode  37 , and out the openings  87 . The infusion tube  48  may be made of any suitable material, and is preferably made of polyimide tubing. A suitable infusion tube has an outer diameter of from about 0.32 inch to about 0.036 inch and an inner diameter of from about 0.28 inch to about 0.032 inch. 
     To energize the tip electrode  37 , in particular the carbon nanotube film  39  for RF ablation, a lead wire  40  is provided. The lead wire  40  extends through the third lumen  34  of intermediate section  14  ( FIG. 4 ), the central lumen  18  of the catheter body  12  ( FIGS. 2A and 2B ), and the control handle  16 , and terminates at its proximal end in an input jack (not shown) that may be plugged into an appropriate monitor (not shown). The portion of the lead wire  40  extending through the central lumen  18  of the catheter body  12 , control handle  16  and distal end of the intermediate section  14  is enclosed within a protective sheath  52 , which can be made of any suitable material, preferably Teflon®. The protective sheath  52  is anchored at its distal end to the distal end of the intermediate section  14  by gluing it in the lumen  34  with polyurethane glue or the like. 
     In the disclosed embodiment, the carbon nanotube film  39  is energized by the lead wire  40  via a ring electrode  55  that is mounted to overlap a junction between the plastic housing  21  and the carbon nanotube film  39  on the shell  38  of the dome tip electrode  37 , as shown in  FIGS. 5A and 5B . The ring electrode can be made of any suitable solid conductive material, such as platinum or gold, preferably a combination of platinum and iridium, and mounted with glue or the like. Alternatively, the ring electrode can be formed by coating the junction with an electrically conducting material, like platinum, gold and/or iridium. The coating can be applied using sputtering, ion beam deposition or an equivalent technique. In another alternative embodiment, the ring electrode can be formed by repeatedly wrapping an end of the electrode lead wire around the junction and stripping off the coating of the lead wire to expose a conductive surface. Other methods for forming ring electrode can also be used in accordance with the invention. In the disclosed embodiment, the ring electrode is mounted by first forming a hole in the wall of the plastic housing  21 . The electrode lead wire  40  is fed through the hole, and the ring electrode is welded in place over the lead wire and the carbon nanotube film  37 . 
     A temperature sensing means is provided for the tip electrode  37  in the disclosed embodiment. Any conventional temperature sensing means, e.g., a thermocouple or thermistor, may be used. With reference to  FIGS. 5B and 6 , a suitable temperature sensing means for the tip electrode  37  comprises a thermocouple formed by a wire pair. One wire of the wire pair is a copper wire  41 , e.g., a number  40  copper wire. The other wire of the wire pair is a constantan wire  45 , which gives support and strength to the wire pair. The wires  41  and  45  of the wire pair are electrically isolated from each other except at their distal ends where they contact and are twisted together, covered with a short piece of plastic tubing  63 , e.g., polyimide, and covered with epoxy. The plastic tubing  63  is then attached in the hole  104  of the plug  44 , by epoxy or the like. As shown in  FIGS. 2A and 5 , the wires  41  and  45  extend through the second lumen  32  in the intermediate section  14 . The wires  41  and  45  extend through the central lumen  18  of the catheter body  12  and the lumen  32  of the intermediate section  14  within the protective sheath  53 . The wires  41  and  45  then extend out through the control handle  16  and to a connector (not shown) connectable to a temperature monitor (not shown). Alternatively, the temperature sensing means may be a thermistor. A suitable thermistor for use in the present invention is Model No. AB6N2-GC14KA143T/37C sold by Thermometrics (New Jersey). 
     Referring to  FIGS. 2B and 3B , the puller wire  42  extends through the catheter body  12  and is anchored at its proximal end to the control handle  16 . The puller wire is made of any suitable metal, such as stainless steel or Nitinol, and is preferably coated with Teflon® or the like. The coating imparts lubricity to the puller wire. The puller wire preferably has a diameter ranging from about 0.006 to about 0.010 inches. A compression coil  56  is situated within the catheter body  12  in surrounding relation to the puller wire. The compression coil  56  extends from the proximal end of the catheter body  12  to the proximal end of the intermediate section  14 . The compression coil is made of any suitable metal, preferably stainless steel, and is tightly wound on itself to provide flexibility, i.e., bending, but to resist compression. The inner diameter of the compression coil is preferably slightly larger than the diameter of the puller wire  42 . The Teflon® coating on the puller wire allows it to slide freely within the compression coil. If desired, particularly if the lead wire  40  is not enclosed by the protective sheath  52 , the outer surface of the compression coils can be covered by a flexible, non-conductive sheath, e.g., made of polyimide tubing, to prevent contact between the compression coils and any other wires within the catheter body  12 . 
     As shown in  FIG. 2B , the compression coil  56  is anchored at its proximal end to the proximal end of the stiffening tube  20  in the catheter body  12  by glue joint  50  and at its distal end to the intermediate section  14  by glue joint  51 . Both glue joints  50  and  51  preferably comprise polyurethane glue or the like. The glue may be applied by means of a syringe or the like through a hole made between the outer surface of the catheter body  12  and the central lumen  18 . Such a hole may be formed, for example, by a needle or the like that punctures the outer wall  22  of the catheter body  12  and the stiffening tube  20  which is heated sufficiently to form a permanent hole. The glue is then introduced through the hole to the outer surface of the compression coil  56  and wicks around the outer circumference to form a glue joint about the entire circumference of the compression coil. 
     With reference to  FIGS. 3B and 4 , the puller wire  42  extends into the first lumen  30  of the intermediate section  14 . In the disclosed embodiment, the puller wire  42  is anchored at its distal end to a side wall of the plastic tubing  21 . The distal end of the puller wire  42  comprises a T-bar anchor  61  and is anchored by glue in notch  63  in the side wall of the plastic housing  21  as shown in  FIG. 3B . Such anchoring is described in U.S. Pat. No. 6,064,908, the entire disclosure of which is incorporated herein by reference. Within the first lumen  30  of the intermediate section  14 , the puller wire  42  extends through a plastic, preferably Teflon®, sheath  81 , which prevents the puller wire  42  from cutting into the wall of the intermediate section  14  when the intermediate section is deflected. Longitudinal movement of the puller wire  42  relative to the catheter body  12 , which results in deflection of the tip section  36 , is accomplished by suitable manipulation of the control handle  16 . Suitable control handles are described in U.S. Pat. No. 6,602,242, the entire disclosure of which is hereby incorporated by reference. 
     In the illustrated embodiment, the tip section  36  carries an electromagnetic sensor  72 , and as mentioned, the electromagnetic sensor may be carried in the plastic housing  21 , with its distal end anchored in the blind hole  106  in the plug  44  as shown in  FIGS. 5A ,  5 B and  6 . The electromagnetic sensor  72  is connected to an electromagnetic sensor cable  74 . As shown in  FIGS. 2A and 4 , the sensor cable  74  extends through the fourth lumen  35  of the tip section  36 , through the central lumen  18  of the catheter body  12 , and into the control handle  16 . The electromagnetic sensor cable  74  then extends out the proximal end of the control handle  16  within an umbilical cord  78  ( FIG. 1 ) to a sensor control module  75  that houses a circuit board (not shown). Alternatively, the circuit board can be housed within the control handle  16 , for example, as described in U.S. patent application Ser. No. 08/924,616, entitled “Steerable Direct Myocardial Revascularization Catheter”, the disclosure of which is incorporated herein by reference. The electromagnetic sensor cable  74  comprises multiple wires encased within a plastic covered sheath. In the sensor control module  75 , the wires of the electromagnetic sensor cable  74  are connected to the circuit board. The circuit board amplifies the signal received from the electromagnetic sensor  72  and transmits it to a computer in a form understandable by the computer by means of the sensor connector  77  at the proximal end of the sensor control module  75 , as shown in  FIG. 1 . Because the catheter can be designed for single use only, the circuit board may contain an EPROM chip which shuts down the circuit board approximately 24 hours after the catheter has been used. This prevents the catheter, or at least the electromagnetic sensor, from being used twice. Suitable electromagnetic sensors for use with the present invention are described, for example, in U.S. Pat. Nos. 5,558,091, 5,443,489, 5,480,422, 5,546,951, 5,568,809, and 5,391,199 and International Publication No. WO 95/02995, the disclosures of which are incorporated herein by reference. An electromagnetic mapping sensor  72  may have a length of from about 6 mm to about 7 mm and a diameter of about 1.3 mm. 
     With reference to  FIG. 7 , an optical processing system  126  for optically evaluating ablation tissue using the catheter  10  is illustrated. A light source  128  supplies a broadband (white; multiple wavelengths) light and/or laser light (single wavelength) radiation to the tip section  36  of the catheter  10  via cable  127  which is split by a beamsplitter  131  outputting to the emitting cables  43 E. The light bearing lesion qualitative information from the tip section is transmitted by the receiving cable  43 R to a detection component  130 . The detection component may comprise, for example, a wavelength selective element  131  that disperses the collected light into constituent wavelengths, and a quantification apparatus  140 . The at least one wavelength selective element  131  includes optics  132 , as are known in the art, for example, a system of lenses, mirrors and/or prisms, for receiving incident light  34  and splitting it into desired components  136  that are transmitted into the quantification apparatus  140 . 
     The quantification apparatus  140  translates measured light intensities into an electrical signal that can be processed with a computer  142  and displayed graphically to an operator of the catheter  10 . The quantification apparatus  140  may comprise a charged coupled device (CCD) for simultaneous detection and quantification of these light intensities. Alternatively, a number of different light sensors, including photodiodes, photomultipliers or complementary metal oxide semiconductor (CMOS) detectors may be used in place of the CCD converter. Information is transmitted from the quantification device  140  to the computer  142  where a graphical display or other information is generated regarding parameters of the lesion. A suitable system for use with the catheter  10  is described in U.S. application Ser. No. 11/281,179, the entire disclosure of which is hereby incorporated by reference. 
     The preceding description has been presented with reference to presently preferred embodiments of the invention. Workers skilled in the art and technology to which this invention pertains will appreciate that alterations and changes in the described structure may be practiced without meaningfully departing from the principal, spirit and scope of this invention. 
     Accordingly, the foregoing description should not be read as pertaining only to the precise structures described and illustrated in the accompanying drawings, but rather should be read consistent with and as support to the following claims which are to have their fullest and fair scope.