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 an opaque 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 
       [0001]    The present invention relates to ablation catheters, and in particular to ablation catheters with optical monitoring of tissue. 
       BACKGROUND OF THE INVENTION 
       [0002]    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. 
         [0003]    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. 
         [0004]    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. 
         [0005]    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. 
         [0006]    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. 
         [0007]    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. 
         [0008]    Thus, there is a need for a catheter capable of measuring lesion formation in real-time, if not monitoring tissue in general. Because a catheter may assume various orientation angles at the ablation site, there is a further need for a catheter that is capable of such measuring and detecting whether the catheter is parallel, perpendicular or at an angle to the tissue. Moreover, where such measuring and detecting are accomplished through optical spectroscopy, there is a need for a catheter that can provide separate optical paths for light illuminating the tissue and for light recaptured from the tissue. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention is directed to a catheter that 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 specular reflection and saturation of the optical detector, and ensures diffusion of the illumination light within the medium of interest. 
         [0010]    The light recaptured by the catheter from the tissue conveys tissue parameters that can be evaluated using spectroscopic methods. 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. 
         [0011]    In accordance with the present invention, the catheter has a catheter body and a tip section adapted for ablating tissue, the tip section providing separate optical paths for light illuminating the tissue and light recaptured from the tissue. In one embodiment, a tip electrode has a shell defining a hollow cavity, where the shell has in its wall illumination openings to pass light onto the tissue and collection openings to recapture light from the tissue in the hollow cavity. The optical path for light illuminating the tissue includes passage through an optically diffuse material in the tip section and through the illumination openings. The optical path for light recaptured from the tissue includes passage through the collection openings and collection in the hollow cavity. An opaque coating lining the hollow cavity separates the optically diffuse material and the hollow cavity and therefore the two optical paths from each other. Moreover, the catheter may be adapted with irrigation for flushing the collection openings with fluid, such as saline or other biocompatible fluid. Fiber optic cable(s) extend into the tip section to illuminate the optically diffuse material. Other fiber optic cable(s) extend into the tip section to receive the light recaptured in the hollow cavity. 
         [0012]    In a more detailed embodiment, a catheter adapted to ablate tissue has a catheter body and a tip electrode adapted for ablating tissue. 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 illumination openings in the shell wall, and the hollow cavity is configured to receive light from the tissue via collection openings in the shell wall and the inner layer. An inner surface of the inner layer has an opaque coating to isolate light injected into the inner layer from light collected in the hollow cavity. At least one optical waveguide extends between the catheter body and the tip electrode to inject light into the inner layer to provide the tip electrode with light to illuminate the tissue. To that end, the inner layer of diffuse material may have projections that extend into the illumination openings in the shell wall to facilitate transmission of the light to outside the tip electrode. At least another optical waveguide extends between the catheter body and the tip electrode to collect the light from the tissue recaptured in the hollow cavity. 
         [0013]    As an omnidirectional illuminator and collector, the tip electrode has a distal portion defining a first section that is generally perpendicular to a longitudinal axis of the tip electrode, a second section that is at an angle between about 30 and 60 degrees with the longitudinal axis, and a third section that is generally parallel with the longitudinal axis. The illumination openings are configured in the second section and in the third section but may also be present in the first section. The collection openings are configured in the first and third sections but may also be present in the second section. The catheter may have a deflectable intermediate section between the catheter body and the tip electrode. It may also carry a temperature sensor and a location sensor in the tip section. 
         [0014]    The present invention is also directed to a method of making an ablation tip electrode that also functions as an omnidirectional illuminator and collector. The method includes providing a shell having a wall that defines an open proximal end and a generally dome shape distal end, configuring illumination openings through the shell wall, filling the shell with a moldable or injectable diffuse material, configuring a hollow cavity at the distal end of the shell, and configuring collection openings through the shell wall and the moldable diffuse material and into the hollow cavity. The method includes providing an optical barrier between the moldable plastic material and the hollow cavity, inserting a fiber optic cable into the moldable diffuse material to provide light to the tip electrode, and inserting a fiber optic cable into the hollow cavity to receive recaptured light in the hollow cavity. 
         [0015]    The method further includes providing a plug to seal the hollow cavity, and configuring the plug with passages for the fiber optic cables. The portions of the fiber optic cables in the passages may be fixedly secured within the passages by glue, adhesive or the like, to stabilize the fiber optic cables and reduce the risk of breakage or detachment. 
         [0016]    The present catheter and method are designed to use light in conjunction with irrigation and the technology of RF ablation. 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 
         [0017]    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: 
           [0018]      FIG. 1  is a side view of an embodiment of the catheter of the present invention. 
           [0019]      FIG. 2A  is a side cross-sectional view of an embodiment of a catheter according to the invention, including a junction between a catheter body and an intermediate section, taken along a first diameter. 
           [0020]      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 . 
           [0021]      FIG. 3  is a side cross-sectional view of an embodiment of a catheter according to the invention, including a junction between the intermediate section and a tip section, taking along the first diameter. 
           [0022]      FIG. 4A  is a side cross sectional view of an embodiment of a catheter according to the invention, including a junction between a plastic housing and a tip electrode, taken along the first diameter. 
           [0023]      FIG. 4B  is a side cross-sectional view of an embodiment of a catheter according to the invention, including a junction between a plastic housing and a tip electrode, taken along the second diameter generally perpendicular to the first diameter of  FIG. 4A ; 
           [0024]      FIG. 5  is a longitudinal cross-sectional view of an embodiment of an intermediate section of  FIG. 3 , taken along line  5 - 5 . 
           [0025]      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 . 
           [0026]      FIG. 6A  is a detailed cross-sectional view of an embodiment of a lead wire. 
           [0027]      FIG. 6B  is a detailed cross-sectional view of an embodiment of an anchored thermocouple wire pair. 
           [0028]      FIG. 6C  is a detailed cross-sectional view of an embodiment of an anchored distal end of a puller wire. 
           [0029]      FIG. 7  is a perspective view of an embodiment of a shell of the tip electrode. 
           [0030]      FIG. 8  is a side elevational view of an embodiment of an inner layer of the tip electrode. 
           [0031]      FIG. 9  is a front end view of an embodiment of a tip electrode. 
           [0032]      FIG. 10  is an end view of the tip electrode of  FIG. 9 . 
           [0033]      FIG. 11A  is a side view of an embodiment of a tip section whose longitudinal axis is generally perpendicular to tissue surface. 
           [0034]      FIG. 11B  is a side view of an embodiment of a tip section whose longitudinal axis is generally at an angle between zero and 90 to tissue surface. 
           [0035]      FIG. 11C  is a side view of an embodiment of a tip section whose longitudinal axis is generally parallel to tissue surface. 
           [0036]      FIG. 12   a  is an exploded side elevational view of an embodiment of a tip electrode and a plug. 
           [0037]      FIG. 12   b  is a cross sectional view of an embodiment of an assembled tip electrode with a plug and an internal fixture member. 
           [0038]      FIG. 12   c  is a perspective view of an embodiment of an internal fixture member. 
           [0039]      FIG. 13  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 
       [0040]    As shown in  FIGS. 1-11 , 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 . 
         [0041]    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. 
         [0042]    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  52 , fiber optic cables  43 , a first irrigation tube segment  88 , 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. 
         [0043]    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. 
         [0044]    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. 
         [0045]    Referring also to  FIGS. 3 and 5 , 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 polyurethane braded with a 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 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. The tubing also has 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. 
         [0046]    Referring to  FIGS. 2A and 2B , the catheter body  12  may be attached to the intermediate section  14  comprises 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. 
         [0047]    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. 
         [0048]    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. 4A and 4B . 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 comprises an inner circumferential notch  27  ( FIG. 3 ) that receives an outer circumferential notch surface 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  help keep the tip electrode in place. 
         [0049]    The tip electrode  37  has an open proximal end that is in communication with a generally hollow distal portion or cavity  49 , and is of a three-piece construction. The tip electrode comprises an outer shell  38  ( FIG. 7 ) having a wall of generally uniform thickness, an inner layer  39  ( FIG. 8 ) and a press-fit plug or alignment member  44  ( FIG. 6 ) positioned at or near the proximal end of the shell. 
         [0050]    With reference to  FIG. 7 , 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  81  is atraumatic, smooth without significant protrusions, and adapted for contact with tissue. The shell wall is configured with a plurality of through-holes or openings of various sizes, including collection openings  87  and illumination openings  89 , at predetermined locations on the shell  38 . The shell is 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-irridium, platinum, gold alloy, or palladium alloy. 
         [0051]    With reference to  FIG. 8 , the inner layer  39  is an injection-moldable optically transmissive plastic material compounded with optical scattering material, for example, Teflon powder or barium sulfate (BaSO 4 ) powder, into which light can be injected for diffusion throughout the inner layer. A material is suitable provided it is biocompatible and optically diffusive. As shown in  FIGS. 9 and 10 , the inner layer  39  is configured (i) to receive light and (ii) to diffuse the light into multiple directions and deliver the light to outside the tip electrode through each illumination opening  89  in the shell wall. In the first instance, a plurality of recesses  94  are provided to receive fiber optic cables that inject light into and illuminate the inner layer  39 . In the second instance, outer surface  86  of the inner layer  39  is configured in general conformity with the inner surface of the shell  38 , and at locations corresponding to the openings  89  in the shell wall projections or extrusions  95  on the outer surface  86  extend into the openings  89  so that light within the inner layer  39  is diffusely transmitted to the openings  89  and to outside the tip electrode. 
         [0052]    The inner layer  39  is also configured to minimize obstruction to the optical collecting function of the tip electrode. To that end, the collection openings  87  of the shell wall extend through the inner layer  39  so there is communication between outside the tip electrode and the hollow cavity  49 . Moreover, the inner surface  91  can provide a rim region  93  that circumscribes a generally conical/parabolic distal portion  92  of the hollow cavity  49  which optimizes diffusion of light injected into the inner layer  39  and optimizes the amount of light received in the hollow cavity  49  from outside the tip electrode  37 . 
         [0053]    The hollow cavity  49  is physically and optically separated from the inner layer  39  by a an opaque barrier. In the disclosed embodiment, the hollow cavity  49  is defined by inner surface  91  of the inner layer  39  which is coated with a layer of opaque material  100 , for example, gold, to keep light in the inner layer  39  from entering the hollow cavity  49  (and vice versa). 
         [0054]    In accordance with the invention, the tip electrode  37  has multiple sections relative to its longitudinal axis  99 , as shown in  FIGS. 4A and 4B , in rendering the tip omnidirectional for optical tissue monitoring. In the illustrated embodiment, there are a distal section  100 , a mid-section  102  and a proximal section  104 . The distal section  100  is generally perpendicular to the axis. The mid-section  102  is generally at an angle ranging between zero and 90 degrees, preferably about 30 to 60 and more preferably about 45 degrees to the axis. The proximal section  104  is generally parallel with the axis. These differently-angled sections enable the tip electrode  37  to operate as an illuminator and a collector for various angles between the tip section  36  and the tissue as shown in  FIGS. 11A-11C . 
         [0055]    Each section can have any number of illumination and/or collection openings as desired or appropriate. In the illustrated embodiment, the distal section  100  has a collection opening  87  at the distal end of the tip electrode along its longitudinal axis  99 . The mid-section  102  has three illumination openings  89  that are equi-angular from each other at about 120 degrees about the axis. The proximal section  104  has six more collection openings  87  that are equi-angular from each other at about 60 degrees about the axis. Three alternating of these six collection openings  87  are generally in radial alignment with the three recesses  94  in the rim section  93  and the other three alternating are generally in radial alignment with the illumination openings  89  in the mid-section  102 . Also in the proximal section  104  proximal the collection openings  87  are another six illumination openings  89  that are equi-angular from each other at about 60 degrees about the axis. These illumination openings  89  are offset from the six collection openings  87  in the proximal section  104 . 
         [0056]    Formed of the same or comparable material as the shell  38 , 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 . The distal portion of the plug  44  may also be slip fitted and sealed with solder. 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  101 ,  102 ,  104  and  106  in which distal ends of the puller wire  42 , the lead wire  40 , the pair of thermocouple wires  41  and  45  and the location sensor  72  are anchored, respectively. There are also passages  108 ,  112 ,  114 , and  116  through which the fiber optic cables  43  extend, and a passage  110  through which an irrigation tube segment  48  extends. The blind hole  101  for anchoring the distal end of the puller wire is generally aligned with the lumen  30  of the tubing  19  of the intermediate section  14 . (The distal end of the puller wire can also be anchored in the side wall of tubing  19  at the distal end of the intermediate section  14 .) The passages  108 ,  112  and  114  for three fiber optic cables  43  are generally aligned with the recesses  94  in the rim section  93  of the inner layer  39  of the tip electrode. The portions of the components extending through the passages in the plug are securely fixed in the passages by glue, adhesive or the like. As such, the passages help align, stabilize and secure the various components extending through the plug  44 . 
         [0057]    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 catheter has fiber optic cables  43  extending into the tip electrode  37  to transmit light to the tip electrode and to collect light recaptured from the tissue. 
         [0058]    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 5 , 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  108 ,  112 ,  114  and  116  in the plug  44 . The passages help minimize stress on the cables  43 E and  43 R in their transition between the intermediate section  14  and the tip electrode  37 . In particular, with the portions of the cables extending through the passages being fixedly secured by glue, adhesive or the like to the passages, the distal portions of the cables should also remain fixed relative to the inner layer  39 . 
         [0059]    In the disclosed embodiment, there are three cables  43 E and one cable  43 R. The cables  43 E function as a light emitters by transmitting light to the tip electrode  37  from a remote light source. The cable  43 R functions as a light receiver by collecting light from the hollow cavity  49  in the tip electrode  37 . 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. 
         [0060]    The emitting fiber optic cables  43 E have their distal ends received and fixed in the recesses  94  of the inner layer  39 . As such, light from the cables is injected into the inner layer  39  which diffuses the light throughout the inner layer  39 , including the projections  95  which in turn transmit light out the openings  89  of the tip electrode  37  and onto tissue of interest  111 , as shown in  FIGS. 11A-11C . 
         [0061]    As lesion  113  forms in the tissue  111  from ablation carried out by tip electrode  37  of the catheter  10  (or by another catheter), 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  113  as it is recaptured by the hollow cavity  49  via the collection openings  87  of the tip electrode. 
         [0062]    Within the hollow cavity  49 , the opaque coating  100  lining the inner surface  91  of the inner layer  39  prevents the light from entering the inner layer  39 . With its distal end inserted into the hollow cavity, the receiving fiber optic cable  43 R collects the recaptured light which bears the qualitative and quantitative information and is transmitted to an optical processing system, as described below in further detail. The conical distal portion  92  of the hollow cavity  49  helps direct light entering the hollow cavity from the distal end of the tip electrode and optimizes the collection of light by the fiber optic cable  43 R. 
         [0063]    In accordance with the present invention, the tip electrode  37  provides separate optical paths for the light that illuminates tissue and the light recaptured from the tissue. The optical path from the tip electrode to the tissue begins with light that is injected into the inner layer  39  which is diffusely scattered throughout the layer  39  into multiple angles and directions and into the projections  95  that extend into the illumination openings  89  of the tip electrode  37 . Exiting the tip electrode  37  from the illumination openings  89 , the light is incidental on the tissue of interest, interacts with the tissue and is reflected or scattered back to the tip electrode from the tissue. The separate optical path from the tissue back to the tip electrode begins with entry through the collection openings  87  and then collection in the hollow cavity  49 . The optical barrier in the form of the opaque coating  100  between the inner layer  39  and the hollow cavity  49  helps avoid saturation of the fiber optic cable  43 R, and to ensure diffusion of the illumination light within the tissue. 
         [0064]    As described earlier, the variously-angled sections  100 ,  102  and  104  of the tip electrode  37  enables radiation and collection of lesion optical data at a variety of angles between the tip electrode and the tissue surface. Each emission and collection openings  89  and  87  in the shell  38  defines an optical cone of radiation, the combinations of which envelope the tip electrode. Accordingly, illumination and recapture of light by the fiber optic cables are possible for a most angles between the tissue and the tip electrode. In accordance with a feature of the present invention, the tip section  36  serves as a generally omni-directional optical radiator and collector. The tip electrode may assume a nearly perpendicular angle with the tissue surface ( FIG. 11A ), a nearly parallel angle ( FIG. 11C ) or any angle between about zero and 90 degrees ( FIG. 11B ). It is understood by one of ordinary skill in the art that the plurality and configuration of the sections  100 ,  102  and  104  and of the collection and illumination openings may be varied as appropriate or desired. The size and dimensions of each section may also be varied as appropriate or desired, as well as the shape of the openings, which can be round, ovular, square, polygonal, flat(slit), or any combination of these shapes. 
         [0065]    It is 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. Moreover, light delivery and collection may be accomplished with other devices, such as air-core fibers, hollow waveguides, liquid waveguides and the like. 
         [0066]    To keep the collection openings  87  of the tip electrode  37  generally free from obstruction from blood or other bodily fluids and tissue encountered by the tip electrode  37 , the tip electrode is irrigated with fluid, e.g., saline, that is fed into the hollow cavity by an irrigation tube segment  48 , as shown in  FIG. 4A . The tube segment  48  extends through the plastic housing  21  and passage  110  in the plug  44  ( FIG. 6 ). The distal end of the tube segment  48  is anchored in the passage  110  and the proximal end is inserted into and overlaps with a distal end of a proximal infusion tube segment  88  ( FIG. 2A ) that extends through the central lumen  18  of the catheter body  12  and the lumen  35  of the intermediate section  14 . The proximal end of the first infusion tube segment  88  extends through the control handle  16  and 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 segment  88  through the luer hub  90 , and flows through the segment  88 , through the infusion tube segment  48 , into the hollow cavity  49  in the tip electrode  37 , and out the collection openings  87 . 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 0.14 inch to about 0.032 inch. 
         [0067]    In accordance with a feature of the present invention, the pump maintains the fluid at a positive pressure differential relative to outside the hollow cavity  49  so as to provide a constant unimpeded flow or seepage of fluid outwardly from the hollow cavity  49  which continuously flushes the collection openings  87  and minimizes obstruction so light can freely pass through for the aforementioned light collection purposes. In addition to the above, the irrigation adaptation of the catheter  10  may serve other typical functions such as cooling the tip electrode and/or the ablation site and increasing conduction for deeper and larger lesions. 
         [0068]    Included in the present invention is a method for manufacturing the shell  38  and inner layer  39 . The method includes providing a rod of a suitable diameter and length, constructed of a suitable material that is thermally and electrically conductive which allows for radio frequency ablation using an RF generator. Such suitable material may include, without limitation, platinum-irridium, platinum, gold alloy, or palladium alloy. To form the shell  38 , the distal end of the rod is turned (lathed) to form the dome shape and the interior is drilled from the proximal end. The hollow dome shell can also be formed from a flat plate which can provide a more even and smoother reflection surface with less machining and material waste. The openings  89  are drilled in the shell  38 . The openings  87  may also be drilled in the shell  38 . To form the inner layer  39 , a moldable plastic material compounded with optical scattering material is injected or otherwise placed into the shell  38  to fill the interior of the shell and until the moldable plastic material fills and perhaps extrudes from the openings  89  in the shell  38 . After the moldable plastic material sufficiently hardens, it is drilled from the proximal end of the tip electrode to form the hollow cavity  49 . Alternatively, the hollow cavity shape can be incorporated into the mold so no post drilling would be needed. Smaller drill bit(s) may be used to form the distal end  92  of the cavity  49  and/or the recesses  94  in the rim region. From the exterior of the tip electrode, collection openings  87  are drilled and/or extended through the inner layer  39  and into the hollow cavity. The coating  100  made of any suitable biocompatible material is applied to the inner surface  91  of the inner layer  39  after the formation of the hollow cavity  49  with its distal end  92 , but the coating may be applied before or after the formation of the recesses  94  if the recesses are masked off. If appropriate, hardened moldable plastic material extruding from openings  89  in the shell may be milled or sanded down to be flush with the outer surface of the shell  38 . 
         [0069]    To form the plug, a rod of the aforementioned suitable material with a suitable diameter and length is provided. The passages  108 ,  110 ,  112 ,  114  and  116  for the fiber optic cables are drilled. The plug is press-fitted or soldered around the periphery into the proximal opening of the tip electrode, but preferably after the fiber optic cables are inserted into the passages and received in the recesses  94  in the inner layer  39  of the tip electrode. The plug is in electrical contact with the shell  38 . Glue, adhesive or the like is injected into the passages to fix the portions of the fiber optic cables extending through the passages. These fixed portions are intended to hold distal portions of the fiber optic cables stationary within the tip electrode as a measure against breakage in or detachment from the tip electrode. 
         [0070]    A shell  38  of the tip electrode may have an actual length, i.e., from its distal end to its proximal end, between about 2.5 mm to about 8 mm. A plug  44  of the tip electrode may have an actual length, i.e., from its distal end to its proximal end, between about 1.5 mm to about 4.0 mm. The tip electrode as a combination of the shell and the plug may have an actual length, i.e., from its distal end to its proximal end, between about 3.5 mm to about 11.0 mm. Preferably the tip electrode  37  has a diameter about the same as the outer diameter of the tubing  19  of the intermediate section  14 . As shown in  FIGS. 4A and 4B , the tip electrode  37  and the plastic housing  21  are each attached to the plug  44  by, respectively, press-fitting or soldering, and by glue, adhesive at their interfacing surfaces. 
         [0071]    To energize the tip electrode  37  for RF ablation, a lead wire  40  is anchored in the plug  44 . With reference to  FIG. 1 ,  2 A and  5 , the lead wire  40  extends through the lumen  32  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) or connector  77  that may be plugged to an generator or the like (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, which can be made of any suitable material, preferably Teflon®. The protective sheath is anchored at its distal end to the distal end of the intermediate section  14  by gluing it in the lumen  32  with polyurethane glue or the like. The lead wire  40  is attached to the tip electrode  37  by any conventional technique. In the illustrated embodiment, connection of the lead wire  40  to the tip electrode  37  is accomplished, for example, by welding the distal end of the lead wire  40  into the blind hole  102  ( FIGS. 6 and 6A ) in the plug  44  of the tip electrode  37 . 
         [0072]    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. 6 and 6B , 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 40 gauge or similar size 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 3 , the wires  41  and  45  extend through the 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  52 . The wires  41  and  45  then extend out through the control handle  16  and to the connector  77 . 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). 
         [0073]    Referring to  FIGS. 2B and 5 , 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, or fiber such as Spectra or Vectran, 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 0.012 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 . 
         [0074]    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. 
         [0075]    With reference to  FIGS. 2B and 5 , 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  37  within the blind hole  101  in the plug  44  ( FIGS. 6 and 6C ). A method for anchoring the puller wire  42  within the tip electrode  37  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  101 . Anchoring the puller wire  42  within the tip electrode  37  provides additional support, reducing the likelihood that the tip electrode  37  will fall off. Alternatively, the puller wires  42  can be attached to the side of the tubing  19  at the distal end of the intermediate section  14 . 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 wires  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. 
         [0076]    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. 4A ,  4 B and  6 . The electromagnetic sensor  72  is connected to an electromagnetic sensor cable  74 . As shown in  FIGS. 2A and 5 , the sensor cable  74  extends through the 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. 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. 
         [0077]    As illustrated in  FIGS. 12   a - 12   c,  an internal fixture member  200  can be positioned in the hollow cavity  49  to stabilize, secure and or protect the various fibers  43  relative to the tip electrode and shell. In the illustrated embodiment of  FIG. 12   b,  the member  200  has a trapezoidal cross section. In the illustrated embodiment of  FIG. 12   c,  the member  200  has an “x” cross section and a thickness t. In both embodiments, there are internal passages  202  connecting openings  204  on a surface of the member are provided through which the fibers extend from the plug  44  and toward the shell  38 . The fibers can be affixed in the internal passages  202  and/or the openings  204  with glue, adhesives and the like, and/or the member  200  can be affixed by glue, adhesives and the like within the hollow cavity  49 . The member can be used for electrical wires, optical fibers or any fragile tensile members  210  that are positioned in the tip electrode and can be configured with any number or patterns of passages and openings as appropriate or needed. 
         [0078]    With reference to  FIG. 13 , 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 . 
         [0079]    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. 
         [0080]    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. 
         [0081]    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.