Patent Publication Number: US-2010129027-A1

Title: Optical Coupler for Rotating Catheter

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 10/615,279, filed on Jul. 8, 2003, which is a continuation-in-part of U.S. patent application Ser. No. 10/309,477, filed on Dec. 4, 2002. The entire contents of each of the foregoing applications are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This invention relates to fiber optic catheters, and more particularly to catheters that accommodate more than one optical fiber. 
     BACKGROUND 
     Vulnerable plaques are lipid filled cavities that form within the wall of a blood vessel. These plaques, when ruptured, can cause massive clotting in the vessel. The resultant clot can interfere with blood flow to the brain, resulting in a stroke, or with blood flow to the coronary vessels, resulting in a heart attack. 
     To locate vulnerable plaques, one inserts a catheter through the lumen of the vessel. The catheter includes a delivery fiber for illuminating a spot on the vessel wall and one or more collection fibers for collecting scattered light from corresponding collection spots on the vessel wall. The delivery fiber, and each of the collection fibers form distinct optical channels within the catheter. The catheter used for locating plaques is thus a multi-channel catheter. 
     In operation, a light source outside the catheter introduces light into the delivery fiber. A detector, also outside the catheter, detects light in the collection fiber and generates an electrical signal representative of that light. This signal is then digitized and provided to a processor for analysis. 
     A vulnerable plaque can be anywhere within the wall of the artery. As a result, it is desirable to circumferentially scan the illuminated spot and the collection spot around the vessel wall. One way to do this is to spin the multi-channel catheter about its axis. However, since neither the light source nor the processor spin with the catheter, it becomes more difficult to couple light into and out of the delivery and collection fibers while the catheter is spinning 
     SUMMARY 
     The described device, method and system are based on the recognition that a lens can be made to focus light onto a fixed point even as the source of that light moves relative to the lens. 
     In one aspect, the invention includes an optical coupler having a housing with a rotatable distal face and a stationary proximal face. The distal face has an eccentric port and a central port. A lens is disposed inside the housing to intercept a rotating collection beam emerging from the eccentric port and to re-direct the collection beam to a focus proximal to the lens as the collection beam rotates. A beam re-director disposed between the lens and the distal face is oriented to direct a delivery beam toward the central port. 
     In some embodiments, the beam re-director is a penta-prism. However, other types of beam re-directors, for example a prism or a mirror, can also be used. 
     Certain embodiments also include a light source disposed to direct a delivery beam radially inward to the beam re-director, and/or a detector disposed at the focus for receiving the rotating collection beam. 
     In some embodiments, the lens is configured to focus the collection beam on an axis of rotation of the distal face. However, in other embodiments, the lens is configured to focus the collection beam off an axis of rotation of the distal face. In yet other embodiments, the lens is an axicon lens. 
     In another aspect, the invention includes a system for identifying vulnerable plaque. The system includes a rotating catheter having a collection fiber and a delivery fiber extending therethrough, and a housing with a rotatable distal face and a stationary proximal face. The distal face has an eccentric port and a central port. A lens is disposed inside the housing to intercept a rotating collection beam emerging from the eccentric port and to re-direct the collection beam to a focus proximal to the lens as the collection beam rotates. A beam re-director disposed between the lens and the distal face is oriented to direct a delivery beam toward the central port. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. 
     Embodiments of the invention may have one or more of the following advantages. By providing a continuous connection to both optical fibers, the rotary coupler permits the entire circumference of an artery to be scanned automatically. 
     A rotary coupler having the features of the invention can also be used to identify other structures outside but near a lumen, or on the surface of the lumen wall. For example cancerous growths within polyps can be identified by a catheter circumferentially scanning the lumen wall of the large intestine, cancerous tissue in the prostate may be identified by a catheter scanning the lumen wall of the urethra in the vicinity of the prostate gland, or Barrett&#39;s cells can be identified on the wall of the esophagus. In addition to its medical applications, the rotary coupler can be used in industrial applications to identify otherwise inaccessible structures outside pipes. 
     Other features and advantages of the invention will be apparent from the following detailed description, and from the claims. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a system for identifying vulnerable plaque in a patient. 
         FIG. 2  is a cross-section of the multi-channel catheter in  FIG. 1 . 
         FIG. 3  is a profile view of the multi-channel coupler of  FIG. 1 . 
         FIG. 4  is an end view of the multi-channel coupler of  FIG. 1 . 
         FIG. 5  is the same profile view of  FIG. 3  with the core rotated 180 degrees. 
         FIG. 6  is a profile view of the multi-channel coupler incorporating additional fibers. 
         FIGS. 7-8  are embodiments that include a delivery beam re-director. 
         FIG. 9  is a penta-prism for use as a beam-redirector in the embodiments of  FIGS. 7-8 . 
         FIG. 10  is a schematic view of a path traced by a collection beam on a lens. 
         FIG. 11  is a schematic view of a catheter core whose axis of rotation is offset from the axis of the lens. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     System Overview 
       FIG. 1  shows a diagnostic system  10  for identifying vulnerable plaque  12  in an arterial wall  14  of a patient. The diagnostic system features a catheter  16  to be inserted into a selected artery, e. g. a coronary artery, of the patient. A delivery fiber  18  and a collection fiber  20  extend between a distal end  21  and a proximal end  23  of the catheter  16 . 
     As shown in  FIG. 2 , the catheter  16  includes a jacket  17  surrounding a rotatable core  19 . The delivery fiber  18  extends along the center of the core  19  and the collection fiber  20  extends parallel to, but radially displaced from, the delivery fiber  18 . The rotatable core  19  spins at rate between approximately 4 revolutions per second and 30 revolutions per second. 
     Referring again to  FIG. 1 , at the distal end  21  of the catheter  16 , a tip assembly  22  directs light traveling axially on the delivery fiber  18  toward an illumination spot  24  on the arterial wall  14 . The tip assembly  22  also collects light from a collection spot  26  on the arterial wall  14  and directs that light into the collection fiber  20 . 
     A multi-channel coupler  28 , which is driven by a motor  30 , engages the proximal end  23  of the catheter  16 . The motor  30  spins the catheter  16 , enabling the diagnostic system  10  to circumferentially scan the arterial wall  14  with the illumination spot  24 . 
     The multi-channel coupler  28  guides a beam from a laser  32  (or other source, such as an LED, a super luminescent LED, or an arc lamp) into the delivery fiber  18  and guides light emerging from the collection fiber  20  into one or more detectors  66 . The multi-channel coupler  28  performs these tasks while the catheter core  19  continuously spins. 
     The detectors provide an electrical signal indicative of light intensity to an amplifier  36  connected to an analog-to-digital (“A/D”) converter  38 . The A/D converter  38  converts this signal into data that can be analyzed by a processor  40  to identify the presence of a vulnerable plaque  12  hidden beneath the arterial wall  14 . 
     Coupler Rotary Junction to Catheter 
     A multi-channel coupler  28  for carrying out the foregoing tasks, as shown in  FIG. 3 , includes a cylindrical housing  42  having a proximal face  44  joined to a distal face  46  by a peripheral wall  48 . The distal face  46  rotates with the catheter core  19 , whereas the proximal face  44  and the remainder of the housing  42  remain stationary. 
     The distal face  46  of the housing  42  has a catheter core port  53  for receiving the catheter core  19 , a central port  52  for receiving the delivery fiber  18 , and an eccentric port  54  for receiving the collection fiber  20 . The central port  52  is located at the intersection of an axis of rotation  50  with the distal face  46 . The eccentric port  54  is radially displaced from the central port  52 . As a result, when the catheter core  19  spins about the axis  50 , the delivery fiber  18  remains stationary and the collection fiber  20  traces out a circular path, as shown in an end view in  FIG. 4 . Bearings  96  at the central port  52 , eccentric port  54 , and catheter core port  53  couple the housing  42  to the catheter core  19 . The bearings  96  also enable the catheter core  19  to spin about the axis of rotation  50  that intersects the proximal and distal faces  44 ,  46  of the housing  42 . 
     The distal face  46  of the housing  42  is rotatably coupled to the catheter  16 . Two optical fibers extend through the catheter  16 : a delivery fiber  18  for illuminating the arterial wall  14  and a collection fiber  20  that collects light scattered from the arterial wall  14 . The catheter core  19  spins about the axis  50  while the housing  42  remains stationary. 
     A laser  32  directed towards the distal face  46  produces a delivery beam  58  centered on the axis  50  as shown in  FIG. 3 . A first collimating lens  62  collimates the delivery beam  58  and directs it through the housing  42  and through an aperture  94  of a rotation-to-stationary (R-S) lens  92 . The R-S lens aperture  94  is a circular opening that is centered on the axis  50  and has a diameter slightly larger than the delivery beam  58 . A first optical relay  64  within the housing  42  then receives the collimated delivery beam  58  and directs it distally across the housing  42  toward the central port  52 , where it enters the delivery fiber  18 . As used herein, an optical relay refers to a set of optical elements, such as lenses, prisms, and mirrors, arranged to direct light from a source to a destination. 
     In  FIG. 3 , this first optical relay  64  includes a converging lens focused at the central port  52 . However, the first optical relay  64  can include components other than, or in addition to that shown in  FIG. 3 . Between the proximal face  44  and the central port  52 , the delivery beam  58  is not constrained to travel along the axis  50  as shown in  FIG. 3 . The delivery beam  58  may travel on any path that leads to the delivery fiber  18 . One design option, shown in  FIG. 7 , includes locating the laser  32  or directing the delivery beam  58  to start between the R-S lens  92  and the distal face  46 . This would eliminate the need for the R-S lens aperture  94 . 
     In the embodiment of  FIG. 7 , the light source  32  directs the delivery beam  58  radially toward a centrally mounted beam re-director  51 . The beam re-director  51 , which can be a prism, (including a penta-prism), or a mirror, re-directs the delivery beam  58  along the axis  50 , toward the distal face  46 . A first optical relay  64 , disposed to intercept the delivery beam  58  on its way to the distal face  46 , directs the delivery beam  58  into the delivery fiber  18 . 
     A second optical relay  70  receives a collection beam  68  from the eccentric port  54  and directs it along a circular path that traverses a peripheral portion of the lens  92 . The lens  92  brings the collection beam  68  to a focus at a detector  66 , which generates an electrical signal in response thereto. This electrical signal is provided to the amplifier  36 . 
     In  FIG. 7 , the detector  66  is disposed at a point offset from the axis  50 . However, the lens  62  and the path traced by the collection beam  68  can be configured to direct the collection beam  68  toward the axis  50 , as shown in  FIG. 8 . When this is the case, the detector  66  is placed on the axis  50 , as shown in  FIG. 8 . A beam re-director  51  in the form of a penta-prism  98 , shown in  FIG. 9 , is particularly useful because an input beam  100  incident on a penta-prism  98  always emerges as an output beam  102  orthogonal to the input beam  100 . This property of a penta-prism  98  reduces the need for precision alignment. 
     The collection beam  67  is divided into a proximal side extending from the detector  66  to the R-S lens  92  and a distal side  67  extending from the R-S lens  92  to the eccentric port  54 . A second optical relay  70  receives the collection beam  68  from the eccentric port  54  and directs it to the R-S lens  92 . The R-S lens  92  directs the collection beam  68  to the detector  66  located towards the proximal face  44 . The second optical relay  70  and the distal side of the collection beam  67  rotate circularly about the axis  50  and trace a circular path on the R-S lens  92 . Without itself moving, the R-S lens  92  continuously redirects the collection beam  68  onto the stationary detector  66 . 
     In  FIG. 5 , the second optical relay  70  and the distal side of the collection beam  67  have rotated 180 degrees from the position depicted in  FIG. 3 . The R-S lens  92  directs the distal side of the collection beam  67 , now located 180 degrees from its position in  FIG. 3 , back to the stationary detector  66  regardless of where the proximal side of the collection beam  67  intersects the R-S lens  92 . The R-S lens  92  continuously directs the collection beam  68  onto the stationary detector  66  as the rotation of the core causes the optical relay and the distal side of the collection beam  67  to traverse a circular path on the R-S lens  92 . 
     In one embodiment, the geometry or grading index of the R-S lens  92  is not symmetric about the axis  50 . Instead, the geometry or grading index of the R-S lens  92  varies as a function of angle. For example, the portion of the lens through which the collection beam  68  passes in  FIG. 3  refracts the collection beam  68  less than the portion of the lens through which the collection beam  68  passes in  FIG. 5 . As a result, the R-S lens  92  redirects the distal side of the collection beam  67  to the stationary detector  66  even as the proximal side of the collection beam  67  traces a circular path on R-S lens  92 . The R-S lens  92  can include a variety of optical elements, such as lenses, prisms, and mirrors, arranged to direct light from a rotating source to a fixed destination. A central portion of the lens can be removed or made transparent to allow the delivery beam  58  to pass unaltered. A peripheral portion of the R-S lens  92  can be reduced to only the portion of the lens through which the collection beam  68  passes, thereby forming a donut shaped lens. This donut shaped lens would reduce the material needed to produce the R-S lens  92 . 
     In another embodiment, the R-S lens  92  is symmetric about the axis  50 , however the center of a circular path  104  traced out by the collection beam  68  is offset from the axis  50 , as shown in  FIG. 10 . This can be achieved, for example, by offsetting the lens  92  relative to the catheter core  19  as shown in  FIG. 11 . Note that in this embodiment, as well as in the embodiment of  FIG. 3 , the collection beam  68  traverses a path through portions of a  92  lens having different optical characteristics, the difference being that in  FIG. 3 , the lens  92  is radially asymmetric and the axis of rotation  50  is coincident with the center of the lens  92 , whereas in  FIG. 7 , the lens  92  is radially symmetric, but the axis of rotation  50  is offset from the center of the lens. 
     In another embodiment, the R-S lens  92  is an axicon lens, also known as a conical lens, or a rotationally symmetric prism. Such lenses cause the collection beam  68  to pass through the same location regardless of the angle of the collection fiber  20  and to do so without focusing the collection beam  68 . 
     OTHER EMBODIMENTS 
     The optical couplers shown in  FIGS. 1-5  are two-channel couplers. Each has a delivery channel that carries the delivery beam  58  and a collection channel for carrying a collection beam  68 . However, additional collection or delivery channels can be added by providing additional collection ports or delivery ports, each of which is in communication with an additional collection fiber or delivery fiber. 
     In the embodiment of  FIG. 6 , an additional eccentric port  55  and optical relay  71  are provided in the distal face  46 . The collection beams  68  and  72  emerging from the apertures and relays form concentric nested traces on the R-S lens  92 . The R-S lens  92  then directs these traces to their perspective stationary detectors  66  and  69 . Analogous to the depiction and discussion of  FIGS. 3 and 5 , the R-S lens continuously directs the collection beams  68  and  72  onto the stationary detectors  66  and  69  as the optical relays  70  and  71  and the distal side of the collection beams rotate from 0 to 360 degrees in a circular path. This embodiment is not limited to a single additional collection beam. The embodiment would include the capacity to handle a plurality of additional collection fibers. In addition, the embodiment is not limited to only additional collection fibers. Additional delivery fibers could also be present. 
     All lenses and optical relays referred to herein are shown as having a single optical element. However, each of these structures can include two or more optical elements in optical communication with each other. 
     It is to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.