Abstract:
A method, including incorporating a conducting wire into a tubular braid consisting of a multiplicity of supporting wires, and covering the tubular braid with a sheath. The method further includes identifying a location of the conducting wire within the tubular braid and attaching an electrode through the sheath to the conducting wire at the location.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to tubing, and specifically to tubing reinforced by a braid. 
     BACKGROUND OF THE INVENTION 
     A wide range of medical procedures involve placing objects, such as sensors, dispensing devices, and implants, within the body. The objects are typically placed within the body with the help of tubing, which is typically as narrow as possible, while having sufficient rigidity to be manipulated within the body. Typically, the tubing may include a braid for providing the rigidity. 
     U.S. Pat. No. 6,213,995, to Steen, et al., whose disclosure is incorporated herein by reference, describes a flexible tubing which includes a wall provided with a plurality of braided elements forming a braid within the wall of the tube. The braided elements are stated to include one or more signal transmitting elements and one or more metallic or non-metallic structural elements having structural properties different from the signal transmitting elements. 
     U.S. Pat. No. 7,229,437, to Johnson, et al., whose disclosure is incorporated herein by reference, describes a catheter having electrically conductive traces and external electrical contacts. The disclosure states that each trace may be in electrical connection with one or more external electrical contacts. 
     The description above is presented as a general overview of related art in this field and should not be construed as an admission that any of the information it contains constitutes prior art against the present patent application. 
     SUMMARY OF THE INVENTION 
     An embodiment of the present invention provides a method, including: 
     incorporating a conducting wire into a tubular braid having a multiplicity of supporting wires; 
     covering the tubular braid with a sheath; 
     identifying a location of the conducting wire within the tubular braid; and 
     attaching an electrode through the sheath to the conducting wire at the location. 
     Typically, the tubular braid encloses an internal volume, and the sheath is opaque to a human eye when illuminated by radiation external to the sheath, and identifying the location includes: illuminating the tubular braid from the internal volume, so as to render the conducting wire and the supporting wires visible through the sheath; and identifying the location of the conducting wire within the tubular braid while the tubular braid is illuminated from the internal volume. Illuminating the tubular braid may include inserting a fiber optic into the internal volume, and injecting optical illumination into the fiber optic. 
     In a disclosed embodiment the conducting wire consists of a helix having a pitch P, and identifying the location of the conducting wire includes identifying an initial position of the conducting wire within the tubular braid, and determining the location of the conducting wire in response to the pitch P. Typically, identifying the location includes determining an angle for rotation of the tubular braid in response to the pitch and the identified initial position. 
     In another disclosed embodiment attaching the electrode includes drilling a via through the sheath at the location after identifying the location. Typically, attaching the electrode includes inserting conductive cement into the via, and positioning the electrode in contact with the cement and the sheath. 
     In a further disclosed embodiment, the method includes incorporating the tubular braid, the electrode, and the sheath as a medical catheter. 
     In a yet further disclosed embodiment, the method includes configuring the conducting wire to be visually differentiated from the supporting wires. 
     There is further provided, according to an embodiment of the present invention, apparatus, including: 
     a tubular braid having a multiplicity of supporting wires and a conducting wire; 
     a sheath covering the tubular braid; 
     an identified location of the conducting wire within the tubular braid; and 
     an electrode attached through the sheath to the conducting wire at the identified location. 
     The present disclosure will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are respectively schematic cross-sectional and side views of a central section of braided probe tubing, according to an embodiment of the present invention; 
         FIGS. 2A and 2B  show schematic sectional side views of a section of braided tubing that is used for a catheter, in an alignment stage of production of the catheter, according to an embodiment of the present invention; 
         FIG. 3A  is a schematic diagram illustrating formation of a via, and  FIG. 3B  is a schematic diagram illustrating connection of an electrode to a conducting wire of tubing using the via, according to embodiments of the present invention; 
         FIG. 4  shows a flow chart of a procedure for attaching an electrode to tubing, according to an embodiment of the present invention; and 
         FIG. 5  shows a flow chart of a procedure for attaching an electrode to tubing, according to an alternative embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Overview 
     An embodiment of the present invention provides a tubular braid, typically for use as part of a medical catheter. The braid comprises a multiplicity of supporting wires, as well as one or more conducting wires, and the braid is covered by a sheath, typically a biocompatible sheath. The supporting wires provide structural rigidity to the braid, and the conducting wires enable signals to be transferred along the braid. 
     A location of the conducting wire, typically near a distal end of the braid, is identified, and an electrode is attached through the sheath to the conducting wire at the identified location. Signals between the electrode and a proximal end of the braid may then be transferred using the conducting wire. 
     The sheath is typically opaque, so that with illumination external to the sheath, the conducting wire (and the supporting wires) is invisible to the human eye. In order to determine the location of the conducting wire, the conducting wire may be configured to be able to be visually differentiated from the supporting wires, for example by having a different diameter. The tubular braid may be illuminated from a volume internal to the braid, causing the conducting wire and the supporting wires to be visible through the sheath to an eye observing from outside the sheath. The visual differences between the conducting and supporting wires enable the position of the conducting wire to be determined along the length of the braid. 
     All the wires of the braid, (the conducting and supporting wires) have substantially the same helical pitch, which is typically determined when the braid is formed. Once a position of the conducting wire has been located, typically near a proximal end of the braid, the value of the pitch may be used to calculate the location of the conducting wire at which the electrode is to be attached, without having to visually track the wire to the distal end location. 
     To attach the electrode to the conducting wire at the identified location, a laser may be used to drill a via in the sheath at the location, and the electrode attached to the wire using conducting cement inserted into the via. 
     System Description 
     Reference is now made to  FIGS. 1A and 1B , which are respectively schematic cross-sectional and side views of a central section  21  of braided probe tubing  20 , according to an embodiment of the present invention. The side view of the section shows tubing  20  in a partially cut-away view. Tubing  20  is formed by forming a tubular braid  22 , on an inner tubular lumen  24 . Lumen  24  encloses an internal generally cylindrical volume  25 . Braid  22  is formed on lumen  24  using a braiding machine, such as is known in the art. 
     Braid  22  is used to strengthen tubing  20 , so that the tubing is relatively inflexible and is torsionally rigid. The braid is partially formed from a multiplicity of strong supporting wires  26 , herein assumed to comprise stainless steel wires. However, wires  26  may be any other material, such as carbon fiber or carbon fiber composite, having physical characteristics similar to those of stainless steel wire. Supporting wires  26  are also herein termed tubing-support wires. 
     In addition to tubing-support wires  26 , tubular braid  22  comprises one or more conducting wires, which are integrated as part of the braid as the braid is being formed on the braiding machine. By way of example, in the following description there are assumed to be three substantially similar conducting wires  28 A,  28 B, and  28 C, also referred to generically herein as conducting wires  28 . Conducting wires  28  comprise conductors  29  covered by insulation  30  surrounding the conductors. In some embodiments conductors  29  are substantially similar in dimensions and composition to tubing-support wires  26 , differing only in being covered by insulation  30 . Thus, if tubing-support wires  26  are of stainless steel, conductors  29  are of the same diameter stainless steel. 
     Alternatively, conductors  29  may differ in dimensions or composition, or in both dimensions and composition, from tubing-support wires  26 . For example, in one embodiment, conductors  29  are formed of copper. 
     Regardless of the dimensions or composition of wires  28 , the conducting wires are configured so that they are able to be visually differentiated from tubing-support wires  26 . In the embodiment described above wherein conductors  29  are copper, the insulated copper wires are configured to have an overall diameter different from tubing-support wires  26 . However, any other visual difference between the two types of wires may be used, such as the color of the insulation. 
     Tubing  20  may be used as tubing of a medical catheter, and is assumed to have one or more electrodes attached to a distal end  32  of the tubing. In the present application, by way of example, three substantially similar electrodes  34 A,  34 B,  34 C, (the number of electrodes corresponding to the number of conducting wires  28 ) also referred to generically herein as electrodes  34 , are assumed to be attached to the tubing. (Electrode  34 A is illustrated in  FIG. 3B , which shows distal end  32 .) Those having ordinary skill in the art will be able to adapt the description herein for tubing with other numbers of attached electrodes, and for numbers of electrodes which are not the same as the number of wires  28 . The latter case may occur, for example, if one of wires  28  is to connect to apparatus, such as a coil or a semiconductor device, within tubing  20  at its distal end. Electrodes  34 A,  34 B,  34 C are assumed to be connected to equipment, such as an ablation generator, by respective conducting wires  28 A,  28 B,  28 C. 
     Each wire (wires  26  and  28 ) of braid  22  is in the shape of a helix, the helices being geometrically identical by virtue of being formed on the same lumen  24 . The helices differ by having different translations parallel to an axis  36  of tubing  20 , but have identical spatial periods, i.e., pitches, P. The pitch of each helix is determined at the time the braid is manufactured by the braiding machine, and can be set, within limits, so that the braid formed is “loose,” having a relatively large pitch, or “tight,” having a relatively small pitch. A typical pitch may be in the approximate range of 1.5-8 mm. 
     After formation of braid  22  on lumen  24 , the braid is covered by a sheath  38  which is typically formed from a biocompatible material such as a cross-linked polymer. Sheath  38  is opaque when viewed in illumination external to the sheath, so that under external illumination wires  26  and  28  are invisible to a human eye observing the sheath. 
     Once tubing  20  has been formed as described above, i.e., with lumen  24 , braid  22 , and sheath  38 , the tubing is typically cut into sections of a length suitable for forming a catheter. A typical section length is approximately 1 m. 
       FIGS. 2A and 2B  show schematic sectional side views of a section  50  of braided tubing  20  that is used for a catheter, in an alignment stage of production of the catheter, according to an embodiment of the present invention. Apart from the differences described below, elements indicated by the same reference numerals for section  50  and tubing  20  ( FIGS. 1A, 1B ) are generally similar in construction and in operation. Section  50  has distal end  32 , and a proximal end  52 . By way of example, section  50  is assumed to be mounted in aligning apparatus  54 , which comprises a first rotatable chuck  56  and a second rotatable chuck  58 , the two chucks having a common axis of rotation and being separated by approximately the length of section  50 . Section  50  is assumed to be held by the two chucks so that it is substantially straight. Once mounted, axis  36  of tubing  20  is congruent with the common axis of the chucks. (Chucks  56  and  58  may conveniently be mounted on a lathe bed, although any other arrangement of two chucks having a common axis and separated by approximately the length of section  50  may be used.) 
     Aligning apparatus  54  also comprises a traveling microscope  60 , which is able to travel by measured amounts in a direction parallel to axis  36 . For simplicity, the mounting arrangements for microscope  60  are not shown in  FIGS. 2A and 2B . 
     In the alignment stage referred to above, wires  26  and  28  are separated from each other at proximal end  52 , so that all tubing-support wires  26 , and all conducting wires  28 , are able to be accessed by an operator of apparatus  54 . For clarity, only some of the separated wires are shown in the figures. 
       FIG. 2A  shows the position of the traveling microscope at the beginning of the alignment stage, and  FIG. 2B  shows the travelling microscope at the end of the alignment stage. In the alignment stage, a fiber optic  62  is inserted into volume  25 , typically along substantially the whole length of section of section  50 . Fiber optic  62  is used to illuminate the inside of tubing  20 . In order to accomplish this, fiber optic  62  is configured so that optical illumination injected at the proximal end of the optic exits the optic through the walls of the optic. Such a configuration may be implemented by arranging that fiber optic  62  comprises a single fiber, and that the internal reflection that occurs at the walls of the fiber, rather than being total internal reflection as is usually the case with fiber optics, is partial reflection. Alternatively or additionally, fiber optic  62  comprises a bundle of separate fibers of different lengths, the different lengths being selected so as to at least partially provide the illumination for the inside of tubing  20  through the ends of the separate fibers. The separate fibers may be configured so that either partial or total internal reflection occurs at their walls. 
     The internal illumination from the fiber optic renders the wires of braid  22  visible, through sheath  38 , to the human eye, typically using microscope  60 .  FIG. 2A  illustrates microscope  60  viewing conducting wire  28 A at the proximal end of tubing  20 , and  FIG. 2B  illustrates the microscope viewing conducting wire  28 A at the distal end of the tubing. 
     The alignment stage illustrated by  FIGS. 2A and 2B , and the identification of conducting wire  28 A using microscope  60 , is described in more detail in the flow chart of  FIG. 4 . 
       FIG. 3A  is a schematic diagram illustrating formation of a via, and  FIG. 3B  is a schematic diagram illustrating connection of an electrode to a conducting wire of tubing  20  using the via, according to embodiments of the present invention. The figures illustrate an electrode attachment stage in production of the catheter referred to above. In the beginning of the electrode attachment stage ( FIG. 3A ) a via  64  is formed in sheath  38  using a laser  66  which drills the via. The via is assumed to penetrate sheath  38  until conducting wire  28 A is exposed, i.e., so that insulation  30  surrounding the wire is removed. 
     Once via  64  has been produced, in the end of the attachment stage ( FIG. 3B ) conducting cement  68  is inserted into the via so as also to cover an outer wall  70  of sheath  38 . Electrode  34 A is positioned over cement  68 , so that when the cement sets the electrode is in contact with the sheath. Electrode  34 A is typically in the form of a flat ring or cylinder having an internal diameter substantially equal to the external diameter of the sheath. In some embodiments electrode  34 A may be in the form of a split flat ring (or cylinder) which is designed to be clamped, so that the ring closes on clamping, and so the ring clamps onto sheath  38 . 
       FIG. 4  shows a flow chart  80 , of a procedure for attaching an electrode to tubing  20 , according to an embodiment of the present invention. The description of the steps of the flow chart refers to elements of the tubing illustrated in  FIGS. 1A-3B . 
     In a tubing formation step  82 , braid  22  is formed so that the braid comprises conducting wires  28  and tubing-support wires  26 . The braid is woven over lumen  24 , and opaque sheath  38  is applied to cover the braid and form tubing  20 . The tubing is then cut to produce section  50 , i.e., a section of tubing suitable for producing the catheter. 
     In an alignment step  84 , section  50  is mounted in alignment apparatus  54  by being clamped into chucks  56  and  58 . Typically, section  50  is arranged so that at proximal end  52  each of the conducting wires  28 , and each of the tubing-support wires  26 , are separated from each other, typically by being spread out. In addition, insulation  30  of conducting wires  28  may be removed so that conductors  29  are available for electrical connection. 
     Once section  50  has been set up in apparatus  54 , fiber optic  62  is inserted into volume  25  up to distal end  32 , and optical illumination is injected into the proximal end of the fiber optic, typically using a high intensity source such as a halogen lamp. As described above, the optical illumination exits from the fiber optic, rendering wires  26  and  28  visible to microscope  60 . 
     The following description assumes that conducting wire  28 A is to be connected to electrode  34 A at a preselected location within distal end  32 . 
     In a conducting wire location step  86 , microscope  60  is traversed at proximal end  52  until an operator controlling the microscope locates conducting wire  28 A. Because conducting wires  28  are configured to be visibly distinct from the tubing-support wires, the operator is able to easily distinguish which are the conducting wires in braid  22 . Since the wires have been separated at the proximal end, and since the microscope is being operated at the proximal end, the operator is able to visually distinguish between conducting wires  28 A,  28 B, and  28 C, and thus ensure that it is conducting wire  28 A that is imaged by the microscope. The position near the proximal end at which conducting wire  28 A is located is herein termed the initial position. 
     In a calculation step  88 , a theoretical position at which to drill via  64  is calculated. The calculation assumes that a distance, X, from the initial position to the theoretical drill position is known, since the latter position corresponds to the required position of the electrode. The calculation also assumes that the pitch P of braid  22  is known. In this case the number N of complete pitches to the theoretical position is given by equation (1): 
     
       
         
           
             
               
                 
                   N 
                   = 
                   
                     ⌊ 
                     
                       X 
                       P 
                     
                     ⌋ 
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     The theoretical position is typically not a whole number of pitches, in which case there is a fraction F, 0&lt;F&lt;1, of a pitch between the position of the last whole pitch and the theoretical position. Equation (2) gives F: 
     
       
         
           
             
               
                 
                   F 
                   = 
                   
                     
                       X 
                       P 
                     
                     - 
                     
                       ⌊ 
                       
                         X 
                         P 
                       
                       ⌋ 
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     To find the correct theoretical position at which to drill, an angle A by which section  50  needs to be rotated is given by:
 
 A= 360 ·F   (3)
 
     In a setup step  90 , while the interior illumination of tubing  20  is maintained, the travelling microscope is moved by distance X, and chucks  56  and  58  are rotated by angle A. While microscope motion and the chuck rotations are theoretically the correct values for aligning conducting wire  28 A with the microscope, in practice the rotations need to be checked, since tubing  20  may undergo some, possibly small, twisting, stretching, and/or sagging (from the horizontal). Thus the microscope motion by distance X, and the chuck rotations A, may be considered coarse alignments. 
     After the coarse alignments have been implemented, the apparatus operator may perform a fine alignment, observing through microscope  60  to ensure that conducting wire  28 A aligns with the microscope. The fine alignment typically comprises rotating the chucks from the theoretical rotation angle A until alignment is achieved. The fine alignment may also include small movements of the microscope. The fine alignment ensures that the microscope is aligned with the location in sheath  38  where via  64  is to be drilled. 
     In a drill step  92 , laser  66  is aligned to drill at the via location, and the laser is activated to drill via  64 . 
     In an electrode assembly step  94 , once via  64  has been formed, it is filled with conducting cement  68 , which is typically biocompatible. Electrode  34 A is then positioned over sheath  38  in contact with the cement, and the cement is allowed to set. The setting cement provides a galvanic contact between the electrode and wire  28 A, as well as maintaining the electrode in good mechanical contact with the sheath. 
     The above procedure may be repeated for each different electrode, e.g., electrodes  34 B,  34 C, that is to be attached to section  50  of the catheter tubing. 
     The procedure described by flow chart  80  assumes that a particular conducting wire is connected to a particular electrode. An alternative procedure, where an electrode is connected to any conducting wire, is described below, with reference to  FIG. 5 . 
       FIG. 5  shows a flow chart  100 , of a procedure for attaching an electrode to tubing  20 , according to an alternative embodiment of the present invention. The procedure described by flow chart  100  assumes that positions for electrodes at the distal end of section  50  are known, and that each electrode may be connected to any conducting wire  28 . 
     Steps  102  and  104  are respectively substantially the same as steps  82  and  84 , described above. 
     In a set up step  106 , microscope  60  is moved to one of the known distal end positions, where an electrode is to be attached. In this position, section  50  is rotated, using chucks  56  and  58 , until one of the conducting wires  28  is imaged by and is aligned with the microscope. 
     Steps  108  and  110  are respectively substantially the same as steps  92  and  94  described above. 
     In a measurement step  112 , the operator of apparatus determines, by measuring resistances between the positioned electrode and the exposed conductors  29  at the proximal end, which of the conducting wires is connected to the electrode. 
     The procedure described above may be repeated for all subsequent electrodes that are to be positioned at the distal end, except for the following difference: 
     In step  106 , in aligning subsequent conductors, the operator of the microscope should ensure that a conductor that has already been connected to an electrode is not the one aligned with the microscope. Typically, the operator may ensure this by visual inspection of the conducting wires. The visual inspection ensures that a conductor, once connected to one electrode, is not connected to a second electrode. 
     It will be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.