Abstract:
The present invention is a catheter or catheter delivery system that incorporates a series of radiopaque markers at discrete, intervals corresponding to units of measurement, such as millimeters, such that structures and blockages within a body lumen can be measured in vitro using the catheter under fluoroscopy. The apparatus and method avoids estimation errors by directly measuring the designated lesion, allowing for improved selection of stents and balloons.

Description:
BACKGROUND 
       [0001]    This invention generally relates to intravascular balloon catheters and systems for performing percutaneous transluminal coronary angioplasty (PTCA) and/or stent delivery, and more particularly to a catheter delivery system that can accurately evaluate and measure objects within a body lumen using incremental radiopaque markers as an illuminated ruler. 
         [0002]    PTCA is a widely used procedure for the treatment of coronary heart disease. In this procedure, a balloon dilatation catheter is advanced into the patient&#39;s coronary artery and the balloon on the catheter is inflated within the stenotic region of the patient&#39;s artery to open up the arterial passageway and thereby increase the blood flow there through. To facilitate the advancement of the dilatation catheter into the patient&#39;s coronary artery, a guiding catheter having a pre-shaped distal tip is first percutaneously introduced into the cardiovascular system of a patient by the Seldinger technique or other method through the brachial or femoral arteries. 
         [0003]    The catheter is advanced until the pre-shaped distal tip of the guiding catheter is disposed within the aorta adjacent the ostium of the desired coronary artery, and the distal tip of the guiding catheter is then maneuvered into the ostium. A balloon dilatation catheter may then be advanced through the guiding catheter into the patient&#39;s coronary artery over a guidewire until the balloon on the catheter is disposed within the stenotic region of the patient&#39;s artery. The balloon is inflated to open up the arterial passageway and increase the blood flow through the artery. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation but not over expand the artery wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter can be removed. 
         [0004]    In a large number of angioplasty procedures, there may be a restenosis, i.e. reformation of the arterial plaque. To reduce the restenosis rate and to strengthen the dilated area, physicians may implant an intravascular prosthesis or “stent” inside the artery at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel. Stents are usually delivered to a desired location within a coronary artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expanded to a larger diameter by expansion of the balloon. The balloon is then deflated to remove the catheter and the stent is left in place within the artery at the site of the dilated lesion. 
         [0005]    To accurately place the balloon at the desired location, visual markers on the catheter are utilized that are read by machines outside the body. For example, in the case where a balloon catheter is used with an fluoroscope, a radiopaque marker may be observed visually on a screen while the procedure is taking place. In many cases, the markers must be precisely located to ensure accurate placement of the balloon in the affected area. 
         [0006]    When performing a procedure such as PTCA, it is crucial that the proper size balloon and stent be utilized. The appropriate sized stent is governed in the radial direction by the diameter of the body lumen at the site of implantation, such that the expanded stent diameter roughly matches the ordinary lumen channel without undue expansion. The proper length of the stent is selected based on the amount and size of the blockage or lesion, which can be a challenge to measure accurately using conventional visual tools. If the stent is too short, it can be ineffective in achieving the desired performance and may require that the patient be subjected to a second procedure to add another stent. If the stent is too long, there is an increased risk of restenosis due to the longer area of injury. Because the accurate determination of the size of the blockage or lesion is critical to the success of the procedure, better methods are needed to determine with high precision the size of the lesion to be addressed by the stent or the balloon. 
         [0007]    One of the challenges that is faced when trying to accurately measure a lesion or other arterial blockage is that the standard methods for observing the lesion uses two dimensional technology to measure three dimensional structures. At two dimensional picture cannot show the true length where the vessel is oblique or offset from the normal view of the viewing instrument. Two dimensional imaging lacks the capability to show tortuosity, overlap, suboptimal projections, and individual anatomic variation, leading to poor measurements. In a study by scientists at the University of Colorado Health Sciences Center in Denver, Colo., it was determined that vessel foreshortening in angiographic images using two dimensional technology resulted in an error of up to fifty percent (50%). See  Angiographic Views Used For Percutaneous Coronary Interventions , C ATHETERIZATION AND  C ARDIOVASCULAR INTERVENTIONS  64:451-459 (2005). 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention is a catheter or catheter delivery system that incorporates a series of radiopaque markers at discrete, intervals corresponding to units of measurement, such as millimeters, such that structures and blockages within a body lumen can be measured in vitro using the catheter under fluoroscopy. The apparatus and method avoids estimation errors by directly measuring the designated lesion, allowing for improved selection of stents and balloons. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is an elevated, perspective view of a catheter delivery system of the present invention; 
           [0010]      FIG. 2  is an enlarged view of the balloon catheter in a collapsed condition within a body lumen; 
           [0011]      FIG. 3  is an enlarged view of a second embodiment of the balloon catheter; 
           [0012]      FIG. 4  is an enlarged view of the balloon catheter of  FIG. 3  in an expanded condition; 
           [0013]      FIG. 5  is an enlarged view of the inner member with a spiral wound radiopaque ribbon wrapped around the inner member having a pitch with a predetermined value; and 
           [0014]      FIG. 6  is an enlarged, cross-sectional view of the inner member with a plurality of raised beads spaced along the inner member. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0015]      FIG. 1  shows a balloon catheter that can be used to illustrate the features of the invention. The catheter  10  of the invention generally comprises an elongated catheter shaft  11  having a proximal section  12 , a distal section  13 , an inflatable balloon  14  on the distal section  13  of the catheter shaft  11 , and an adapter  17  mounted on the proximal section  12  of shaft  11 . In  FIG. 1 , the catheter  10  is illustrated within a greatly enlarged view of a patient&#39;s body lumen  18 , prior to expansion of the balloon  14 , adjacent the tissue to be acted upon by the balloon. 
         [0016]    In the embodiment illustrated in  FIG. 1 , the catheter shaft  11  has an outer tubular member  19  and an inner tubular member  20  disposed within the outer tubular member and defining, with the outer tubular member, inflation lumen  21 . Inflation lumen  21  is in fluid communication with the interior chamber  15  of the inflatable balloon  14 . The inner tubular member  20  has an inner lumen  22  extending therein which is configured to slidably receive a guidewire  23  suitable for advancement through a patient&#39;s coronary arteries. The distal extremity of the inflatable balloon  14  is sealingly secured to the distal extremity of the inner tubular member  20  and the proximal extremity of the balloon is sealingly secured to the distal extremity of the outer tubular member  19 . 
         [0017]    The balloon  14  can be inflated by a fluid such as air, saline, or other fluid that is introduced at the port in the side arm  25  into inflation lumen  21  contained in the catheter shaft  11 , or by other means, such as from a passageway formed between the outside of the catheter shaft  11  and the member forming the balloon  14 , depending on the particular design of the catheter. The details and mechanics of the mode of inflating the balloon vary according to the specific design of the catheter, and are omitted from the present discussion. 
         [0018]    In a typical procedure to open the body lumen  18 , the guide wire  23  is advanced through the patient&#39;s vascular system by well known methods so that the distal end of the guide wire is advanced past the location for the placement of the balloon or stent in the body lumen  18 . The cardiologist may then perform an angioplasty procedure or other procedure (i.e., atherectomy) in order to open the vessel and remodel the diseased area. This involves inflating the balloon  14  so that the walls of the body lumen  18  are expanded, and any plaque or obstruction is cleared from the center of the artery. In some cases, this procedure is followed by the implantation of a vascular stent. A stent delivery catheter assembly similar to  10  is advanced over the guide wire  23  so that the stent is positioned in the target area. The balloon  14  is inflated so that it expands radially outwardly and in turn expands the stent radially outwardly until the stent bears against the vessel wall of the body lumen  18 . The balloon  14  is then deflated and the catheter withdrawn from the patient&#39;s vascular system, leaving the stent in place to dilate the body lumen. The guide wire  23  typically is left in the lumen for post-dilatation procedures, if any, and subsequently is withdrawn from the patient&#39;s vascular system. As depicted in  FIG. 2 , the balloon  14  is in its delivery configuration positioned adjacent a portion of the body lumen  18  to be treated, and in  FIG. 4 , the balloon is fully inflated to widen the diameter of the body lumen and press against the walls of the artery. When the balloon  14  is then deflated and removed, the walls of the artery will remain open. 
         [0019]      FIG. 2  illustrates an enlarged view, partially cut away, of the balloon  14  showing a series of markers  26  arranged circumferentially around the inner tubular member  20  at axially spaced intervals. The markers  26  can be formed from painted lines using a radiopaque paint that can be viewed under fluoroscopy. If the markers  26  can be placed at equal intervals, and even more precisely, at intervals corresponding to units of measure such as, for example, millimeters, then the physician can use the balloon once placed adjacent the lesion or blockage to accurately “measure” the obstruction  30  with the balloon  14  as if the physician had a ruler in the body lumen. This measurement can be used to determine what size balloon or stent is appropriate should such a device be needed, as well as provide information on the relative position of the lesion with respect to other body physiology. That is, measurements can be made with respect to arterial branches, lumen openings, spacings of perceived weaknesses, etc. that can be used to determine the appropriate selection of stent, procedure, and the like. 
         [0020]    The shape or length of the markers  26  can vary, as long as they can serve as a measure device for evaluating objects adjacent the balloon  14  under fluoroscopy or other visual means. The markers  26 , if they are spaced apart by a known and recognized measurement such as a millimeter, eighth inch, etc., can be observed under the fluoroscope or other means and can be used to precisely locate the catheter, the balloon  14 , and the stent if present and measure the length of any obstructions  30 , lesions, tears or damage, and the like. This information can be critical to a physician in selecting the appropriate balloon, stent, or other equipment. 
         [0021]    The radiopaque material that may be used to create the divisional markers can be selected from platinum-iridium alloys, barium sulfate, or other known materials used in the art to establish indicators that can be seen under fluoroscopy. The platinum-iridium material can be formed into bands that are implanted into or crimped onto the tubular member, or painted directly on to its outer surface. In yet an alternative embodiment, the markers are incorporated into the guidewire  23  of the catheter. 
         [0022]    Another embodiment of the invention is depicted in  FIGS. 3 and 4 , where the markers  28  are placed directly on the outer surface of the balloon  14 . If the markers  28  are established to be, for example, one millimeter apart, the balloon  14  can be advanced into the body lumen  18  adjacent the obstruction  30 . A priori, the physician may not have a good understanding of the length of the obstruction and what size stent may be required to completely address the obstruction  30 . The balloon  14  is maneuvered into place adjacent the obstruction  30 , such that the markers  28  (or markers  26  for the embodiment of  FIGS. 1 and 2 ) are aligned with the obstruction. The physician notes that the markers  28  are one millimeter apart, and that the lesion spans twenty-one markers, or twenty millimeters in length. Thus, if a stent is to be implanted to completely address the obstruction  30 , it must be at least 20 millimeters. This type of accuracy is pivotal in such procedures and was heretofore unavailable without the present invention. The balloon  14  can be withdrawn after inflation and deflation and a stent can be implanted at the site with the dimensions obtained from the measurement with the markers  26 , ensuring that the full length of the obstruction is adequately accounted for. 
         [0023]    The benefit of using the tubular member  20  (or the guidewire  23 ) rather than the balloon  14  to locate the markers is that there is no distortion of the tubular member  19  when the balloon is inflated, whereas the balloon can undergo some elongation as it inflates, or distortion as it is crimped, which would disturb the actual distances used to measure the lesions. Thus, in the case of markers  28  directly on the balloon surface, the measurement must either be made prior to inflation of the balloon, or the balloon must be made of a low compliant material that inflates without axial elongation to preserve the proportion of the markers and maintain an accurate “ruler.” 
         [0024]      FIGS. 5 and 6  illustrate another embodiment of the present invention, where a radiopaque ribbon or thread is wrapped around the inner member so as to provide a predetermined spacing between each successive winding. That is, the pitch of the spiral wound radiopaque ribbon is constant and selected so as to provide a continuous ruler three hundred and sixty degrees around the inner member. This allows the physician to view the spacings from any angle and provides a more effective means of evaluating a lesion&#39;s length. 
         [0025]    Similarly, markings can comprise raised radiopaque beads that could provide greater contrast due to the three dimensional nature of the beads. This can be helpful is evaluating certain structures outside the catheter body where it is a challenge to obtain a normal view. The beads can be seen from a wider set of angles, making them preferable in some circumstances. The beads, like the ribbon of  FIG. 5 , can be located anywhere on the catheter body including the balloon itself. Having the measurement markings on the balloon has the benefit of proximity to the lesion itself, thereby reducing the error due to parallax, but care is needed to ensure that there is no distortion to the markings as the balloon is inflated if measurements are to be taken post-inflation. 
         [0026]    While particular forms of the invention have been illustrated and described, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited except by the appended claims.