Abstract:
A catheter is adapted to ablate tissue and provide optically-based lesion qualitative and quantitative monitoring, comprising a catheter body and a tip electrode distal the catheter body adapted for ablating tissue, the tip electrode having a shell and an alignment member defining a hollow distal portion therebetween. In accordance with the invention, the catheter further includes a plurality of optical waveguides adapted to transmit optical energy to and from the tip electrode. A distal portion of each waveguide extends through the hollow distal portion and terminates in openings formed in the shell. Advantageously, the alignment member fixedly secures the distal portion of each waveguide against movement relative to the alignment member and the shell.

Description:
FIELD OF INVENTION 
     The present invention relates to ablation catheters, and in particular to ablation catheters with lesion monitoring. 
     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(s) 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 only 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 lesion formation, as well as detecting the formation of charred tissue and coagulated blood around the ablation catheter. Where such measuring and detection use fiber optics, there is a further need for a catheter that provides sufficient room in the tip to accommodate multiple fiber optics for multi-directional emission and collection of light, as well as other components such as a navigational sensors, temperature sensor and/or deflection elements. It is also desirable that such a catheter provide irrigation for cooling the tip electrode and/or creating deeper and larger lesions. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a catheter that is adapted for ablation and provides optically-based lesion qualitative and quantitative information. The catheter comprises a catheter body and a tip electrode distal the catheter body adapted for ablating tissue where the tip electrode has a shell and an alignment member defining a hollow distal portion therebetween. In accordance with the invention, the catheter further includes a plurality of optical waveguides adapted to transmit optical energy to and from the tip electrode. Lesion assessments are accomplished by measuring the light intensity at one or more wavelengths that is recaptured at the catheter tip resulting from the light radiated from the catheter tip onto ablated tissue. A distal portion of each waveguide extends through the hollow distal portion and terminates in openings formed in the shell. Advantageously, the alignment member fixedly secures the distal portion of each waveguide against movement relative to the alignment member and the shell to minimize stress and strain on waveguides that may cause breakage. 
     In a detailed embodiment, the distal portion of each waveguide has a fixed flexure configuration within the hollow distal portion of the tip electrode to provide multi-directional radiation and/or collection of light at the tip electrode. Moreover, the openings in the shell of the tip electrode may include a center opening aligned with a longitudinal axis of the tip electrode and at least one off-center opening. The catheter may also be configured such that the distal portion of each waveguide is directed to transmit or receive light energy in a pattern with a radial component about the longitudinal axis. In a more detailed embodiment, the tip electrode may have three off-center openings configured equally offset from each other at about 120 degrees, to six off-center openings configured equally offset from each other at about 60 degrees. 
     In accordance with the invention, the light energy collected at the tip electrode conveys a tissue parameter of a lesion illuminated by light energy from the tip electrode. The tissue parameter includes at least one of the following: lesion formation, depth of penetration of lesion, cross-sectional area of 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, evaluation of tissue health, status, and disease state, and recognition of steam formation in the tissue for prevention of steam pop. 
     The catheter may also include a temperature sensor, or an electromagnetic location sensor carried at or near the tip electrode for producing electrical signals indicative of a location of the electromagnetic location sensor. The catheter may further include means for deflecting a section of the catheter body, and/or irrigation means to provide fluid to the tip electrode and surrounding surface and tissue. 
     The present catheter is designed to use light. Advantageously, the light used to monitor and assess the lesion 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 fiber optics are disposed in the tip electrode 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 invention. 
         FIG. 2A  is a side cross-sectional view of an embodiment of a catheter body according to the invention, including the junction between the catheter body and intermediate section, taken along a first diameter. 
         FIG. 2B  is a side cross-sectional view of an embodiment of a catheter body according to the invention, including the junction between the catheter body and intermediate section, taken along a second diameter generally perpendicular to the first diameter of  FIG. 2A . 
         FIG. 3  is a is an end view of the distal end of an embodiment of a tip electrode showing a center opening and a plurality of off-center openings. 
         FIG. 3A  is a side cross-sectional view of an embodiment of a tip electrode and a distal portion of an intermediate section, taken along a first diameter. 
         FIG. 3B  is a side cross-sectional view of an embodiment of a tip electrode and a distal portion of an intermediate section, taken along a second diameter generally perpendicular to the first diameter of  FIG. 3A . 
         FIG. 3C  is a longitudinal cross-sectional view of an embodiment of an intermediate section of  FIGS. 3A and 3B , taken along line  3 C- 3 C. 
         FIG. 3D  is a side cross-sectional view of the embodiment of the tip electrode and distal portion of the intermediate section of  FIG. 3B , taken along an axis generally parallel to but laterally offset from the first diameter of  FIG. 3A , the axis intersecting distal ends of a puller wire and a lead wire as anchored in an alignment member of the tip electrode. 
         FIG. 4  is a longitudinal cross-section of an embodiment of a tip electrode of  FIGS. 3A and 3B , taken along line  4 - 4 . 
         FIG. 5  is a side view of an embodiment of a tip electrode whose longitudinal axis is generally perpendicular to tissue surface. 
         FIG. 6  is an end view of the distal end of an alternative embodiment of a tip electrode showing a center opening, a plurality of off-center openings and additional irrigation openings. 
         FIG. 7A  is a side cross-sectional view of another embodiment of a tip electrode and a distal portion of an intermediate section, taken along a first diameter. 
         FIG. 7B  is a side cross-sectional view of another embodiment of a tip electrode and a distal portion of an intermediate section, taken along a second diameter generally perpendicular to the first diameter of  FIG. 7A . 
         FIG. 8  is a side cross sectional view of an alternative embodiment of an intermediate section, including a junction with a housing member. 
         FIG. 9  is a longitudinal cross-sectional view of the intermediate section of  FIG. 8 , taken along line  9 - 9 . 
         FIG. 10  is a longitudinal cross-sectional view of the tip electrode of  FIGS. 7A and 7B , taken along line  10 - 10 . 
         FIG. 11  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 , an embodiment of a catheter  10  in accordance with the present invention comprises an elongated catheter body  12  having proximal and distal ends, a deflectable intermediate section  14  at the distal end of the catheter body  12 , a tip electrode  36  at the distal end of the intermediate section, and a control handle  16  at the proximal end of the catheter body  12 . 
     With reference to  FIGS. 1 ,  2 A and  2 B, 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 electrode  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, a lead wire  40  and thermocouple wires  41  and  45  protected by a sheath  39 , fiber optic cables  43 , a compression coil  44  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 aforementioned components to float freely within the catheter body. If such components 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. 
     Referring also to  FIGS. 3A ,  3 B and  3 C, the intermediate section  14  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 non-braided polyurethane. 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 has a first off-axis lumen  30 , a second off-axis lumen  32 , a third off-axis lumen  34  and a fourth off-axis lumen  35 , that are generally about the same size, each having a diameter of from about 0.032 inch to about 0.038 inch, preferably 0.036 inch. In the illustrated embodiment, the puller wire  42  extends through the first lumen  30  and optical waveguides, e.g., the fiber optic cables  43 , extend through the second lumen  32 . The electrode lead wire  40  extends through the third lumen  34 . The thermocouple wires  41  and  45  can also extend through the third lumen  34 , and an electromagnetic sensor cable  74  can extend through the fourth lumen  35 . 
     As best shown in  FIGS. 2A and 2B , the catheter body  12  in one embodiment is attached to the intermediate section  14  by means of 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 electrode. 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. 
     As illustrated in  FIGS. 3A and 3B , the tip electrode  36  extends from the distal end of the intermediate section  14 . In the illustrated embodiment, the tip electrode has a diameter about the same as the outer diameter of the tubing  19  of the intermediate section  14 . The intermediate section  14  and the tip electrode are attached by glue  27  or the like applied circumferentially around a junction of the tubing  19  and the tip electrode  36 . Moreover, the components extending between the intermediate section  14  and the tip electrode, e.g., the lead wire  40 , the thermocouple wires  41  and  45 , and the puller wire  42 , help keep the tip electrode on the intermediate section. 
     In the illustrated embodiment, the tip electrode  36  has a generally hollow distal portion. The tip electrode comprises a shell  38  of generally uniform thickness and a press-fit alignment member or plug  59  positioned at or near the proximal end of the shell to seal the hollow distal portion. The shell and the plug are formed from any suitable material that is both thermally and electrically conductive which allows for radio frequency ablation using an RF generator. Such suitable materials include, without limitation, platinum, gold alloy, or palladium alloy. A tip electrode and method for manufacturing same are disclosed in application Ser. No. 11/058,434, filed Feb. 14, 2005, the entire disclosure of which is hereby incorporated by reference. 
     As discussed in detail further below, the alignment member  59  serves to stabilize, secure and/or support the various components extending into the tip electrode. The alignment member  59  has designated passages for the fiber optic components extending into the tip electrode and is situated at the proximal end of the shell  38  to define a chamber  49  in the distal end of the electrode  36  with a size and dimensions that accommodate the relatively limited flexure of the fiber optics while providing multi-directional radiation and/or collection of light at the tip electrode. The alignment member  59  allows the fiber optic cables  43  to be consistently in an optimal configuration inside the tip electrode to transmit and receive light energy from outside the tip electrode. The tip electrode  36  allows for sufficient space within to provide an optical termination and a stabilizing fixture for the fiber optic cables, and to house and carry components for enabling RF ablation and deflection with any curve shape. This construction design is intended to reduce machining costs and provide a deflection radii that facilitates the use of fiber optic cables in ablation catheters. 
     A tip electrode may have an effective length, i.e., from its distal end to the distal end of the intermediate section  14 , between about 3.5 mm to about 7.5 mm, and an actual length, i.e., from its distal end to its proximal end, between about 4.0 mm to about 8.mm. The wall thickness may be generally equal to or greater than 0.004 inches. 
     The tip electrode  36  is energized for RF ablation by the lead wire  40  that extends through the third lumen  34  of intermediate section  14 , the central lumen  18  of the catheter body  12 , 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 the protective sheath  39 , which can be made of any suitable material, preferably Teflon RTM. The protective sheath  39  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. The lead wire  40  is attached to the tip electrode  36  by any conventional technique. In the illustrated embodiment, connection of the lead wire  40  to the tip electrode  36  is accomplished, for example, by welding the distal end of the lead wire  40  into a first blind hole  31  ( FIG. 3D ) in the alignment member  59  of the tip electrode  36 . 
     A temperature sensing means is provided for the tip electrode  36  in the disclosed embodiment. Any conventional temperature sensing means, e.g., a thermocouple or thermistor, may be used. With reference to  FIGS. 3A and 3B , a suitable temperature sensing means for the tip electrode  36  comprises a thermocouple formed by a wire pair. One wire of the wire pair is the copper wire  41 , e.g., a number 40 copper wire. The other wire of the wire pair is the 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 a second blind hole  33  of the tip electrode  36  ( FIG. 3B ), by epoxy or the like. The wires  41  and  45  extend through the third lumen  34  in the intermediate section  14 . Within the catheter body  12  the wires  41  and  45  extend through the central lumen  18  within the protective sheath  39  along with the lead wire  40 . 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. 2A ,  3 A and  3 D, the puller wire  42  as part of a means for deflecting the catheter extends through the catheter body  12 , is anchored at its proximal end to the control handle  16 , and is anchored at its distal end to the tip electrode  36 . The puller wire is made of any suitable metal, such as stainless steel or Nitinol, and is preferably coated with Teflon.RTM. 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. 
     The compression coil  44  is situated within the catheter body  12  in surrounding relation to the puller wire. The compression coil  44  extends from the proximal end of the catheter body  12  to the proximal end of the intermediate section  14  ( FIG. 2 ). 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.RTM. 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 a protective sheath  39 , 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. 2A , the compression coil  44  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  44  and wicks around the outer circumference to form a glue joint about the entire circumference of the compression coil. 
     With reference to  FIGS. 2A ,  3 A and  3 C, the puller wire  42  extends into the first lumen  30  of the intermediate section  14 . The puller wire  42  is anchored at its distal end to the tip electrode  36  within the third blind hole  73  in the alignment member  59 , as shown in  FIG. 3D . A method for anchoring the puller wire  42  within the tip electrode  36  is by crimping metal tubing  46  to the distal end of the puller wire  42  and soldering the metal tubing  46  inside the blind hole  73 . Anchoring the puller wire  42  within the alignment member  59  provides additional support, reducing the likelihood that the tip electrode  36  will fall off. Alternatively, the puller wire  42  can be attached to the side of the tubing  19  of the intermediate section  14  as understood by one of ordinary skill in the art. Within the first lumen  30  of the intermediate section  14 , the puller wire  42  extends through a plastic, preferably Teflon.RTM., 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 electrode  36 , is accomplished by suitable manipulation of the control handle  16 . A suitable control handle is described in U.S. Pat. No. 6,602,242, the entire disclosure of which is hereby incorporated by reference. 
     In the illustrated embodiment of  FIGS. 3A ,  3 B and  3 D, the tip electrode  36  carries an electromagnetic sensor  72 . The electromagnetic sensor  72  is connected to the electromagnetic sensor cable  74 , which extends through a passage  75  ( FIG. 4 ) in the alignment member  39 , the third lumen  35  of the tip electrode  36 , through the central lumen  18  of the catheter body  12 , and into the control handle  16 . As shown in  FIG. 1 , the electromagnetic sensor cable  74  then extends out the proximal end of the control handle  16  within an umbilical cord  78  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 entire 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. 
     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 tip resulting from the light radiated from the catheter tip onto ablated tissue. 
     As shown in  FIGS. 2A ,  3 A and  3 B, optical waveguides, e.g., the fiber optic cables  43  are provided in the catheter to illuminate a lesion for purposes of collecting optical data to conduct the aforementioned assessments. The fiber optic cables  43  transmit light to the tip electrode  36  and collect light at the tip electrode. The fiber optic cables  43  are protectively housed in the catheter along its length. They extend through the lumen  18  of the catheter body  12 , through the second lumen  32  of the intermediate section  14  and into the tip electrode  36 . 
     It is understood by one of ordinary skill in the art that optical waveguides and fiber optic cables in general serve to transmit optical energy from one end to the other, although these are not exclusive. Accordingly, one or more of the cables  43  may function as a light emitting cable by transmitting light energy to the tip electrode  36  from an external and/or internal light source, and one or more of the other cables  43  may function as a light receiving cable in the tip electrode  36  by collecting light energy at the tip electrode and transmitting it to an optical processing system. In either function as a light transmitting or light receiving cable, each of the fiber optic cables  43  passes through a passage  71  configured in the alignment member  59 , as shown in  FIG. 4 , and extends distally toward a respective opening  80  configured in the distal region of the shell  38  of the tip electrode  36 , as shown in  FIGS. 3A and 3B . The distal ends of the fiber optic cables  43  are received and fixedly secured in the openings by glue, adhesive or the like. Accordingly, light can be emitted from and be collected at the tip electrode by the fiber optic cables  43 . 
     In accordance with a feature of the present invention, the shell  38  and the alignment member  59  of the tip electrode  36  are configured to provide the chamber  49  with sufficient length and width to accommodate the flexure of the fiber optic cables as they extend between the alignment member  59  and the openings  80 . To that end, the openings  80  and the passages  71  in the alignment member  29  are positioned relative to each other such that the flexure of the fiber optic cables therebetween does not exceed about 30 degrees within the space constraints of the tip dimensions mentioned above. 
     With reference to  FIG. 3 , the openings  80  are provided in the distal portion of the shell  38 . There is a center opening  80   a  which is located generally at the most distal location on the shell along the longitudinal axis of the electrode  36  for on-axis transmission or collection at the tip electrode. There are also off-center openings  80   b  which are located proximal of the opening  80   a  for off-axis transmission or collection with a greater radial component. It is understood by one of ordinary skill in the art that the number and arrangement of the openings  80   a  and  80   b  may be varied as appropriate or desired. For example, the number of off-center openings  80   b  may range between about 3 to 6, arranged at angles between about 120 to 60 degrees, respectively, about the center opening  80   a . For example, there can be three openings  80   b  equally offset from each other at about 120 degrees, four openings  80   b  equally offset from each other at about 90 degrees, five openings  80   b  equally offset from each other at about 72 degrees, or six openings  80   b  equally offset from each other at about 60 degrees. 
     In the illustrated embodiment of  FIGS. 3 ,  3 A and  3 B, there is one opening  80   a  for a single fiber optic cable  43 E delivering light energy from the opening  80   a  and there are three openings  80   b  for three fiber optic cables  43 R receiving light energy through the openings  80   b . The three openings  80   b  are generally equi-spaced from each other and from the opening  80   a , and equi-angular about the opening  80   a.    
     The shell  38  is configured with a generally spherical, parabolic or at least rounded convex distal portion such that the tip electrode  36  remains of an atraumatic design and provides an on-axis section  100   a  for the center opening  80   a  that opens along the longitudinal axis of the tip electrode, and an off-axis section  100   b  for the off-center openings  80   b  that open in an off-axis direction. 
     With reference to  FIG. 5 , as lesion  92  forms in the tissue  90  from RF ablation carried out by tip electrode  36  (or by another catheter), characteristics of the tissue are altered as understood by one of ordinary skill in the art. As the tip electrode illuminates the lesion with light from the fiber optic cable  43 E through the opening  80   a , the light is scattered and/or reflected back toward the tip electrode  36 . Such light having interacted or otherwise having been affected by the lesion bears qualitative and quantitative information about the lesion  92  as it is collected by the fiber optic cables  43 R through the openings  80   b . It is understood by one of ordinary skill in the art that the number of transmitting and receiving fiber optic cables, the corresponding openings and the pattern of the openings on the shell may be varied as appropriate or desired. It is further understood that the fiber optic cables  43 E and  43 R may be any suitable optical wave guide wherein light introduced at one of the cable is guided to the other end of the cable with minimal loss. Each of the cables  43 E 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. 
     In accordance with a feature of the present invention, the portion of each fiber optic cables  43  within the passages  71  is fixedly secured to the alignment member  59  by glue, adhesive or the like to prevent distal, proximal or rotational movement of the portion of the fiber optic cables in and distal the alignment member  59 . As its name suggests, the alignment member  59  maintains alignment of each fiber optic cable within the tip electrode. In that regard, the passages  71  are generally aligned with the second lumen  32  of the intermediate section  14  to minimize stress and strain that can cause breakage of the fiber optic cables in the transition between the intermediate section  14  and the tip electrode  36 . The portion of the cables  43  proximal the alignment member  59  remains generally parallel with the catheter body  12  and intermediate section  14 , and moves and bends with them. As shown in  FIGS. 2B ,  3 A and  4 A, the cables  43  are protectively housed within the catheter from the tip electrode  36  to the control handle  16 . 
     The openings  80  are sized to receive the distal ends of the cables  43  in a generally snug-fit fashion. However, in an alternative embodiment as illustrated in  FIGS. 7A and 7B , the openings  80  are sized larger than the distal ends of the cables  43  to allow fluid (e.g. saline) to flow through the openings around the cable distal ends to reach outside the tip electrode for cooling the tip electrode and ablation site and/or enabling larger and deeper lesions. Additional openings  80   c , as shown in  FIG. 6 , that are not occupied by a fiber optic cable may be provided allowing further irrigation of the tip electrode. The fluid is fed into the chamber  49  by an irrigation means, as shown in  FIG. 7B , that include a tube segment  48  extending from the distal end of the fourth lumen  35  of the intermediate section  14  and a passage  76  in the plug  59  ( FIG. 10 ). The distal end of the segment  48  is anchored in the passage  76  and the proximal end is anchored in the fourth lumen  35  by polyurethane glue or the like. Accordingly, the passage  76  is generally aligned with the fourth lumen  35  of the intermediate section  14 . The segment  48 , like the puller wires  42 , provides additional support for the tip electrode. The irrigation tube segment  48  is in communication with a proximal infusion tube segment (not shown) that extends through the central lumen  18  of the catheter body  12  and terminates in the proximal end of the fourth lumen  35  of the intermediate section  14 . The proximal end of the first infusion tube segment extends through the control handle  16  and terminates in a luer hub  90  ( FIG. 11 ) 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 segment through the luer hub  90 , through the infusion tube segment  48 , into the chamber  49  in the tip electrode  36 , and out the openings  80 . The infusion tube segments may be made of any suitable material, and is preferably made of polyimide tubing. A suitable infusion tube segment 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. 
     The pump maintains the fluid at a positive pressure differential relative to outside the chamber  49  so as to provide a constant unimpeded flow or seepage of fluid outwardly from the chamber  49  which continuously seeps out from the openings  80 . 
     In the illustrated embodiment of  FIGS. 7A ,  7 B and  8 , a housing  21  extends between the intermediate section  14  and the tip electrode  36  so that the electromagnetic sensor  72  can remain near the tip electrode and remain dry. The housing  21  (e.g., a plastic tube member) is attached to the tubing  19  of the intermediate section by creating a circumferential notch  37  in the distal end of the tubing  19 , placing the proximal end of the housing  21  on the distal end of the tubing  19 , and filling the notch  37  with glue. The distal end of the housing  21  and the tip electrode  36  are attached by glue at a seam  69 . All the components extending into or through the alignment member  59  help keep the tip electrode  36  attached to the housing  21 . 
     It is understood by one of ordinary skill in the art that any desired aspects of the different embodiments described herein may be incorporated within a catheter tip section so as to suit the needs and desires in a particular use and application. For example, the embodiment of  FIGS. 7A ,  7 B and  8  need not include irrigation, but the em sensor  72  can nevertheless be housed outside of the chamber  49 , in tubing  21 , especially if there is insufficient space in the chamber  49  to contain both the em sensor  72  and the fiber optic cables  43 . 
     With reference to  FIG. 11 , an optical processing system  110  for optically evaluating ablation tissue using the catheter  10  is illustrated. A light source  120  supplies a broadband (white; multiple wavelengths) light and/or laser light (single wavelength) radiation to the tip electrode  36  of the catheter  10  via couplings or connections  145  and  143  (couplings and connections used interchangeably herein), and light bearing lesion qualitative and quantitative information from the tip electrode is transmitted to a detection component  130  via connections  143  and  148 . 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  134  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. Nos. 11/281,179 and 11/281,853, the entire disclosures of which are 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.