Abstract:
Apparatus and methods are provided for measuring axial displacement of an imaging catheter, and for using real-time images acquired by the imaging catheter to measure axial lengths of anatomical sites. The apparatus of the present invention includes a catheter having an imaging element disposed on a distal portion and indicia disposed on a proximal portion. The length of the catheter permits the indicia to be disposed at least partially external to a patient and visible to a medical practitioner when the imaging element is disposed within the blood vessel. Accordingly, the medical practitioner can observe the indicia and associate axial locations of the catheter indicated by the indicia with images obtained by the imaging element.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to apparatus and methods for measuring axial displacement of an imaging catheter, and for using real-time images acquired by the imaging catheter to measure axial lengths of anatomical sites.  
         BACKGROUND OF THE INVENTION  
         [0002]    A large number of medical diagnostic and therapeutic procedures involve the percutaneous introduction of minimally invasive imaging instrumentation into a blood vessel. Exemplary imaging instrumentation includes Intravascular Ultrasound (“IVUS”) catheters, Optical Coherence Tomography (“OCT”) catheters, and Magnetic Resonance Imaging (“MRI”) catheters.  
           [0003]    An often-used technique to determine axial displacement of an imaging catheter within the blood vessel is to couple the imaging catheter to a pullback system. The pullback system has one or more motors that are engaged to and may retract the imaging catheter at a controlled rate. The pullback system also may be electrically coupled to a data acquisition system that records axial displacement of the catheter during pullback. The axial displacement recorded by the data acquisition system may be correlated with displacement observed in imaging data acquired by the imaging catheter.  
           [0004]    Pullback systems add cost to diagnostic or therapeutic procedures, increase the complexity of the procedures, and, because the catheter is mechanically coupled to the pullback system, reduce the clinician&#39;s degree of tactile sensation in maneuvering the catheter.  
           [0005]    In view of these drawbacks, it would be desirable to provide inexpensive apparatus for measuring axial displacement of an imaging catheter within a blood vessel.  
           [0006]    It also would be desirable to provide easy to use apparatus and methods for measuring axial displacement of an imaging catheter within a blood vessel.  
           [0007]    It further would be desirable to provide apparatus and methods for measuring axial lengths of anatomical sites within a blood vessel.  
           [0008]    It still further would be desirable to provide apparatus and methods to determine and retain the axial location of a particular anatomical site within a blood vessel, thereby facilitating relocation of an instrument to that anatomical site.  
         SUMMARY OF THE INVENTION  
         [0009]    In view of the foregoing, it is an object of the present invention to provide inexpensive apparatus for measuring axial displacement of an imaging catheter within a blood vessel.  
           [0010]    It also is an object of the present invention to provide easy to use apparatus and methods for measuring axial displacement of an imaging catheter within a blood vessel.  
           [0011]    It further is an object of the present invention to provide apparatus and methods for measuring axial lengths of anatomical sites within a blood vessel.  
           [0012]    It still further is an object of the present invention to provide apparatus and methods to determine and retain the axial location of a particular anatomical site within a blood vessel, thereby facilitating relocation of an instrument to that anatomical site.  
           [0013]    These and other objects of the present invention are accomplished by providing apparatus and methods for measuring axial displacement of an imaging catheter, and for using real-time images acquired by the imaging catheter to measure axial lengths of anatomical sites. The apparatus of the present invention includes a catheter having an imaging element disposed on a distal portion and indicia disposed on a proximal portion. The length of the catheter permits the indicia to be disposed at least partially external to a patient and visible to a medical practitioner when the imaging element is disposed within the blood vessel. Accordingly, the medical practitioner can observe the indicia and associate axial locations of the catheter indicated by the indicia with images obtained by the imaging element.  
           [0014]    The indicia may embody various styles, including enumerated, width-coded, and color-coded bands.  
           [0015]    The catheter also may include optional radiopaque markers disposed on the distal portion.  
           [0016]    Pursuant to another aspect of the present invention, a clip may be provided to facilitate relocation of the imaging element to a particular axial location within the blood vessel. The clip is configured to releasably engage the catheter on the proximal portion and demarcate an index of the indicia that corresponds to the particular axial location.  
           [0017]    Methods of using the apparatus of the present invention also are provided. 
       
    
    
     BRIEF DESCRIPTIONS OF THE INVENTION  
       [0018]    Further features of the present invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments, in which:  
         [0019]    [0019]FIG. 1 is a schematic perspective view of an imaging catheter of the present invention;  
         [0020]    FIGS.  2 A- 2 C are schematic partial side views of alternative styles of indicia disposed on the imaging catheter of the present invention;  
         [0021]    [0021]FIG. 3 is a schematic perspective view of bands that may be used as the indicia of FIGS. 1 and 2A-C;  
         [0022]    [0022]FIG. 4 is a schematic partial perspective view of a proximal portion of the imaging catheter of the present invention with recesses configured to accept the bands of FIG. 3;  
         [0023]    [0023]FIGS. 5A and 5B are, respectively, a schematic perspective view and an exploded perspective view of a clip for releasably engaging the imaging catheter of the present invention; and  
         [0024]    [0024]FIGS. 6A and 6B are schematic side views describing a method of using the imaging catheter of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]    The following description emphasizes inclusion of indicia on a proximal end of a phased-array intravascular ultrasound (IVUS) catheter. However, it is contemplated that the indicia may be used with catheters of any imaging modality, such as ultrasound, phased-array intravascular ultrasound, linear-array ultrasound, rotational ultrasound, forward-looking ultrasound, radially-looking ultrasound, magnetic resonance imaging, angiography, optical coherence tomography, and combinations thereof.  
         [0026]    Referring to FIG. 1, a preferred embodiment of the present invention is described. Catheter  10  includes catheter body  12  having proximal portion  14 , distal portion  16 , imaging element  18  disposed on distal portion  16 , and indicia  20  disposed on proximal portion  14 . Imaging element  18  illustratively incorporates a phased-array IVUS transducer, which uses an array of discrete ultrasound elements that each provide image data. The image data from each element is combined to form a circumferential image of an interior of a blood vessel into which catheter  10  may be inserted. Phased-array IVUS systems are marketed by JOMED Inc., of Rancho Cordova, Calif., and are described, for example, in U.S. Pat. No. 6,283,920 to Eberle et al., which is incorporated herein by reference.  
         [0027]    Catheter  10  also may include multiplexing circuitry, amplifiers, etc., per se known, which may be disposed on and/or electrically coupled to catheter  10 . Imaging element  18  of catheter  10  is electrically coupled via cable  22  and connector  24  to an imaging system (not shown), per se known, that provides excitation waveforms to the imaging element, and interprets and displays data received therefrom. Catheter  10  optionally may incorporate at least one lumen  25  for irrigation, aspiration, or advancement of additional diagnostic or therapeutic instruments into the patient&#39;s blood vessel.  
         [0028]    In the preferred embodiment of FIG. 1, indicia  20  incorporates enumerated bands  26  that encircle part or all of the circumference of catheter body  12 . The distance between each successive band  26  preferably is on the scale of centimeters, but will depend on the application for which catheter  10  is used.  
         [0029]    It will be apparent to one of ordinary skill in the art that, while enumerated bands  26  are numbered from “1” to “n” in FIG. 1, other ranges may be provided. For example, the number of each enumerated band  26  may correspond to the distance of that band from a reference feature, such as the distal or proximal end of catheter  10  or imaging element  18 .  
         [0030]    Pursuant to another aspect of the present invention, catheter  10  optionally may include radiopaque markers  28  disposed on distal portion  16  of catheter  10 . Preferably, the distance between successive radiopaque markers  28  is equivalent to the distance between successive bands  26  of indicia  20 . Alternatively, catheter  10  may be provided with radiopaque markers  28  in which the distance between adjacent radiopaque markers are larger or smaller than that between adjacent bands  26 . In that case, a scaling factor may be provided or determined prior to insertion of catheter  10  within a patient.  
         [0031]    As shown in FIG. 1, radiopaque markers  29  having a width greater than that of markers  28  may be provided immediately proximal and/or distal to imaging element  18  to respectively demarcate the proximal and/or distal extremities thereof.  
         [0032]    Alternative styles of indicia  20  are schematically illustrated in FIGS.  2 A-C. In FIG. 2A, indicia  20  includes width-coded bands  30 , disposed on proximal portion  14  of catheter body  12  in a configuration analogous to Roman numerals. More specifically, each thin band  32  corresponds to, e.g., one unit length and each thick band  34  corresponds to, e.g., five unit lengths. Accordingly, to indicate, e.g., seven unit lengths, a combination of one thick band  34  and two thin bands  32  are provided.  
         [0033]    In FIG. 2B, indicia  20  includes color-coded bands  36 . Each successive band  36  may comprise a different color representing a different numerical value, or colors may be replicated for every, e.g., five bands in succession. In the latter embodiment, the distance between succeeding bands of the same color would correspond to, e.g., five unit lengths.  
         [0034]    In FIG. 2C, indicia  20  also incorporates bands  38  of varying widths. Like width-coded bands  30  of FIG. 2A, bands  38  also include thin bands  40  and thick bands  42 . The difference between the two embodiments lies in the configuration of the thick and thin bands along proximal portion  14 . Specifically, in FIG. 2C, bands  38  are serially arranged so that thick bands  42  are interposed between a predetermined number of thin bands  40 . Thus, each band  38  represents, e.g., one unit length from adjacent bands  38 .  
         [0035]    of course, it will be evident to one of ordinary skill in the art that catheter  10  may be provided with a combination of the styles of indicia  20  described hereinabove or with alternative styles. Furthermore, it will be evident that the distance between successive bands depends on the application for which catheter  10  is used. For example, for catheters to be used in treatment of abdominal aortic aneurysm, the distance between adjacent bands is preferably approximately 0.5-1.0 cm. For the treatment of vascular stenosis, the distance between adjacent bands may be on the order of millimeters. As will be apparent, a ruler-type scale, per se known, may be provided having indicia and sub-indicia (not shown).  
         [0036]    During manufacture, indicia  20  may be printed or laser etched onto catheter  10 . Alternatively, indicia  20  may comprise independently manufactured bands  40 , as shown in FIG. 3, having numerals thereon, different widths, and/or a variety of colors. These bands may be embedded into catheter body  12  during manufacture of catheter body  12 .  
         [0037]    Alternatively, the bands may be made of a thermally responsive polymer that, upon exposure to heat, contracts bands  40  in diameter. Accordingly, during manufacture, bands  40  may be threaded onto proximal portion  14  of catheter body  12  and placed at predetermined locations along the axial length thereof. To ensure that bands  40  do not increase the outer diametrical profile of catheter  10  and to facilitate proper location of bands  40  on catheter body  12 , catheter body  12  optionally may have recesses  42  (see FIG. 4) of widths approximately equal to those of corresponding bands  40  and depths approximately equal to the thickness of bands  40 . Upon exposure to heat, bands  40  shrink in diameter to fixedly engage catheter body  12  and recesses  42 , if present. It will be apparent to one of ordinary skill in the art that the widths and depths of recesses  42  should account for the slight change in the widths and thickness of bands  40  after bands  40  are exposed to heat.  
         [0038]    Referring now to FIGS. 5A and 5B, imaging catheter  10  of the present invention further includes clip  44  that may be removably engaged to proximal portion  14  to demarcate a particular index of indicia  20 . Clip  44  has first piece  46 , which includes first jaw  48 , first actuator lever  50 , and first mounts  52  fixedly disposed on first actuator lever  50 . Clip  44  also has second piece  54 , which includes second jaw  56 , second actuator lever  58 , and second mounts  60  fixedly disposed on second actuator lever  58 . First and second pieces  46  and  54  are rotatably coupled via shaft  59  that is disposed through first and second mounts  52  and  60 . First and second jaws  48  and  56  comprise inner surfaces  61  that are contoured to engage proximal portion  14 . Clip  44  optionally may incorporate lining  63  that is disposed on inner surfaces  61 , and that is made of a material, e.g., rubber, that would resist longitudinal displacement of jaws  48  and  56  along proximal portion  14  of catheter  10 , thus decreasing the likelihood that clip  44 , and thus a particular index of indicia  20  demarcated by clip  44 , will be inadvertently dislodged.  
         [0039]    To maintain clip  44  in engagement with proximal portion  14 , spring  62  preferably is provided to apply a spring force to actuator levers  50  and  58  that clamps jaws  48  and  56  together. The spring force can be overcome by squeezing actuator levers  50  and  58  together. Clip  44  is preferably made of sterilizable materials.  
         [0040]    Referring now to FIGS. 6A and 6B, a method of using catheter  10  is provided. As shown in FIG. 6A, catheter  10  of the present invention is disposed through guide catheter  64 . Guide catheter  64  includes body  66  having proximal Y-adaptor  68  and lumen  72 . Y-adaptor  68  includes port  76  that accepts imaging catheter  10  of the present invention, and port  78  that may be used for irrigation, aspiration, and/or advancement of additional diagnostic or therapeutic instruments.  
         [0041]    Upon insertion and placement of guide catheter  64  in a desired position within blood vessel V, imaging catheter  10  is advanced past port  76 , through lumen  72 , and out of guide catheter  64  to a target region within blood vessel V. As imaging element  18  is advanced past an area of interest, such as stenosis S, images acquired by the imaging element are displayed on a graphical user interface (not shown). Once imaging element  18  is advanced distal to stenosis S, as confirmed by observation of the images displayed on the graphical user interface, clip  44  may be engaged to proximal portion  14  of catheter  10  to demarcate the appropriate index of indicia  20  that corresponds to the distal position of stenosis S. Specifically, clip  44  is engaged to proximal portion  14  immediately proximal to port  76  of guide catheter  64 , as shown in FIG. 6A.  
         [0042]    Imaging catheter  10  then is proximally retracted across stenosis S. Once images displayed on the graphical user interface indicate that the proximal end of stenosis S has been reached, a clinician can note the appropriate index of indicia  20  that corresponds to the proximal end of stenosis S (i.e., the index of indicia  20  immediately proximal to port  76  of guide catheter  64 ). Subtraction of that index from the index demarcated by the distal edge of clip  44  affixed to proximal portion  14  equals the axial length of stenosis S. It will be evident to one of ordinary skill that the axial length of the target region, e.g. stenosis S, alternatively may be determined by counting the number of indices between the index demarcated by clip  44  and the index corresponding to the proximal end of the target region, for example, when catheter  10  is provided with indicia of the style described in FIGS.  2 B-C. In this manner, a measurement of the axial length of an anatomical site within a patient&#39;s blood vessel may be obtained based on observation of images acquired by imaging element  18 .  
         [0043]    A further advantage of the present invention is that, after clip  44  is affixed to proximal portion  14  to demarcate a particular anatomical site of interest, such as the distal extremity of stenosis S, that site of interest can be immediately relocated if imaging element  18  is inadvertently or deliberately displaced therefrom. For example, if the medical practitioner displaces imaging element  18  during advancement of additional diagnostic or therapeutic instruments through lumen  25  of catheter  10  (see FIG. 1) or through port  78  of guide catheter  64 , stenosis S can be easily and quickly relocated by distally advancing imaging catheter  10  until clip  44  contacts port  76 , as in FIG. 6A. This disposes imaging element  18  just distal to stenosis S.  
         [0044]    It will be apparent to one of ordinary skill that clip  44  may be used to demarcate and facilitate relocation of any anatomical sites of interest within blood vessel V. The above description emphasizes relocation of a stenosis only as an exemplary illustration of the use and advantages of the present invention.  
         [0045]    While preferred illustrative embodiments of the present invention are described above, it will be apparent to one skilled in the art that various changes and modifications may be made therein without departing from the invention. The appended claims are intended to cover all such changes and modifications that fall within the true spirit and scope of the invention.