Patent Publication Number: US-7585317-B2

Title: Stent range transducers

Description:
This application is a Continuation of U.S. patent application Ser. No. 09/669,060, filed Sep. 22, 2000, now U.S. Pat. No. 6,689,156. This application claims priority to U.S. application Ser. No. 09/669,060 to the extent appropriate under the law. U.S. patent application Ser. No. 09/669,060 claims priority to U.S. Provisional Application No. 60/155,611 filed on Sep. 23, 1999, to the extent appropriate under the law. The complete disclosures of U.S. patent application Ser. No. 09/669,060 and U.S. provisional application Ser. No. 09/669,060 are incorporated herein by reference. 

   CROSS-REFERENCES TO RELATED APPLICATIONS 
   This application is related to U.S. patent application Ser. No. 09/668,687, entitled “Differentially Expanding Stent and Methods of Use”; and U.S. patent application Ser. No. 09/668,832, entitled, “Bifurcation Stent Systems and Methods,” the complete disclosures of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   A type of endoprosthesis device, commonly referred to as a stent, may be placed or implanted within a vein, artery or other hollow body organ or lumen for treating occlusions, stenoses, or aneurysms of a vessel by reinforcing the wall of the vessel or by expanding the vessel. Stents have been used to treat dissections in blood vessel walls caused by balloon angioplasty of the coronary arteries as well as peripheral arteries and to improve angioplasty results by preventing elastic recoil and remodeling of the vessel wall. Two randomized multicenter trials have recently shown a lower restenosis rate in stent treated coronary arteries compared with balloon angioplasty alone (Serruys, P W et al.,  New England Journal of Medicine  331: 489-495 (1994) and Fischman, D L et al.  New England Journal of Medicine  331:496-501 (1994)). Stents have been successfully implanted in the urinary tract, the bile duct, the esophagus and the tracheo-bronchial tree to reinforce those body organs, as well as implanted into the neurovascular, peripheral vascular, coronary, cardiac, and renal systems, among others. The term “stent” as used in this Application is a device which is intraluminally implanted within bodily vessels to reinforce collapsing, dissected, partially occluded, weakened, diseased or abnormally dilated or small segments of a vessel wall. 
   One of the drawbacks of conventional stents is that they are difficult to position. In general, positioning a stent involves moving the stent to the desired position and then maintaining the position while the stent is deployed. Accurate positioning is critical to proper operation of the stent. For example, the use of such stents to treat diseased vessels at or near a bifurcation (branch point) of a vessel requires very accurate positioning otherwise, there is a potential for compromising the degree of patency of the main vessel and/or its branches, or the bifurcation point. Compromising the bifurcation point limits the ability to insert a branch stent into the side branch if the result of treatment of the main vessel is suboptimal. Suboptimal results may occur as a result of several mechanisms, such as displacing diseased tissue, plaque shifting, vessel spasm, dissection with or without intimal flaps, thrombosis, and embolism. 
   In light of the foregoing, it would be desirable to provide methods, apparatus and/or systems to increase stent positioning accuracy, particularly when used with bifurcated body lumens. 
   SUMMARY OF THE INVENTION 
   The present invention provides exemplary apparatus, systems and methods for accurately delivering and positioning a stent within a body lumen, particularly within a bifurcated body lumen. In one embodiment, a stent delivery system according to the present invention includes a catheter comprising a catheter body having a distal end, a proximal end, a longitudinal axis and a lumen. An expansion device, which in one embodiment is a balloon, is disposed near the catheter body distal end, and a stent having a side hole is disposed over the expansion device. An ultrasound transducer is disposed near the catheter body distal end and positioned for transmitting and receiving ultrasound signals through the side hole. In this manner, an intravascular ultrasound catheter and system is used to help properly position the stent, and properly align the stent side hole with a branch vessel. 
   The ultrasound transducer is disposed inside the expansion device, or between the expansion device and stent in alternative embodiments. Preferably, the ultrasound transducer is adapted to be axially translated along the longitudinal axis and/or rotated relative to the longitudinal axis. In this manner, the ultrasound transducer may be used to image surrounding fluids and tissue to assure proper stent alignment. 
   In some embodiments, the stent delivery system further includes a transducer housing to which the transducer is coupled. The housing has distal and proximal ends, with a passageway passing therethrough. The passageway has a guidewire partially disposed therein in one embodiment. The housing proximal end is coupled to a drive cable, which in one embodiment is adapted to rotate the housing relative to the catheter distal end. A controller may be included, coupled to the transducer, to facilitate system operation. 
   The present invention further provides methods of positioning a stent having a side opening. In one embodiment, the method includes providing a stent delivery system ostensibly as described herein, positioning the stent delivery system in a body lumen, imaging the body lumen with the transducer to locate an ostium of a branch vessel, and aligning the stent side hole with the ostium. In this manner, the use of ultrasound imaging facilitates proper stent side hole alignment with the branch vessel. 
   In one embodiment, the ultrasound transducer is adapted to rotate relative to the longitudinal axis. The imaging further includes rotating the transducer to image a cross section of the body lumen. Similarly, in one embodiment, aligning the stent side hole includes axially translating the stent along the longitudinal axis and/or rotating the stent about the longitudinal axis. In some embodiments, a body lumen guidewire is introduced, and the catheter is advanced over the guidewire to be near the branch vessel. 
   In one embodiment, the stent delivery system is conveniently part of a kit, which includes instructions for use setting forth a method for positioning the stent in a bifurcated body lumen so that the side hole is substantially aligned with an ostium of a branch vessel. 
   Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description, the appended claims and the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  depicts an overall view of a stent according to the present invention disposed in a body lumen; 
       FIG. 2  depicts an overall view of a stent delivery apparatus according to the present invention; 
       FIGS. 3A ,  3 B and  3 C provide side and front cross-sectional views of embodiments of the apparatus shown in  FIG. 2 ; 
       FIGS. 4A and 4B  depict an overall view and a side cross-sectional view, respectively, of an ultrasound imaging device according to the present invention; 
       FIGS. 5A and 5B  depict simplified views of a stent delivery system according to the present invention disposed in a body lumen; 
       FIGS. 5C and 5D  plot transmitted and received ultrasound energy signals as a function of time for stent delivery systems positioned according to  FIGS. 5A and 5B , respectively; 
       FIGS. 6A and 6B  depict ultrasound images of a stent within a body lumen; 
       FIGS. 7A-7C  depict simplified cross-sectional images of a vessel having a stent delivery system according to the present invention disposed therein; 
       FIGS. 8A-8C  depict simplified views of a stent delivery system disposed in a body lumen in positions which correspond to the images shown in  FIGS. 7A-7C ; 
       FIG. 9  depicts a simplified schematic of a stent delivery system according to the present invention; 
       FIG. 10  depicts a simplified schematic of imaging catheter electronics for use with the present invention; and 
       FIG. 11  depicts a kit including apparatus and instructions for use according to the present invention. 
   

   DESCRIPTION OF THE SPECIFIC EMBODIMENTS 
     FIG. 1  depicts a simplified view showing a stent  10  disposed within a main vessel  14 . Main vessel  14  may comprise an artery, a vein or a wide range of body lumens into which it is desirable to dispose stent  10 . Stent  10  includes a side hole  12 , which is in registry with an ostium of a branch vessel  16 . The stent wall is comprised of struts and connectors forming multiple passageways. In many cases, it is desirable to have side hole  12  aligned with the ostium of branch vessel  16  to, for example, permit the introduction of a branch stent or second stent (not shown) into branch vessel  16 . The alignment of side hole  12  with branch vessel  16  is often crucial to the proper use of stent  10 , and prior art methods for alignment are replete with problems. Apparatus, systems and methods of the present invention are directed, in part, to properly aligning side hole  12  with branch vessel  16  by using an image transducer or catheter with stent  10 . 
   Turning now to  FIGS. 2 ,  3 A,  3 B,  4 A and  4 B, an exemplary stent delivery system  15  according to the present invention will be described. Stent  10  is shown in a non-expanded state, crimped around a balloon  20 . Balloon  20  provides a mechanism for expanding stent  10  when stent  10  is placed at a desired location within a body lumen. It will be appreciated by those skilled in the art that other methods of expanding stent  10  fall within the scope of the present invention. System  15  further includes a transducer  22  to provide an imaging capability to help properly position side hole  12 . Transducer  22  typically comprises piezoelectric materials for the conversion of electrical signals into mechanical energy, more specifically, sound energy. As best shown in  FIG. 3A , transducer  22  is coupled to a housing  24 . In one embodiment, housing  24  is disposed within balloon  20 , as shown in  FIG. 3A . Transducer housing  24  is positioned so that ultrasound signals transmitted from transducer  22  pass through side hole  12  into the surrounding fluid or tissue. In this manner, and as further described below, transducer  22  may be used to indicate when side hole  12  is properly aligned with a branch vessel  16  as opposed to facing a wall of main vessel  14 . In an alternative embodiment (not shown), transducer  22  is mounted on an outer surface of balloon  20  or positioned between balloon  20  and stent  10 . For example, transducer  22  may be mounted on balloon  20  within sidehole  12 . In one embodiment, a guidewire  18  is disposed through balloon  20 , and is used to help guide the stent delivery system to a desired region within a body lumen. 
   Turning now to  FIG. 3B , a cross-sectional view taken along line  3 B- 3 B is shown. Stent  10  comprises a plurality of struts  26  configured in a desired relationship. It will be appreciated by those skilled in the art that the precise configuration of stent struts  26  may vary widely within the scope of the present invention. Further, the present invention may use stent configurations disclosed in U.S. application Ser. Nos. 09/668,687 and 09/668,832 the complete disclosures of which have been previously incorporated by reference. Stent  10 , including struts  26 , are crimped around balloon  20 . The imaging catheter, which includes transducer  22 , is disposed within a balloon lumen  30  inside balloon  25 . The imaging apparatus has an outer member  32  and an inner member  34  defining a wire lumen  38  therebetween. A passageway  40  is formed within inner member  34 . Wire lumen  38  is used to maintain transducer wires  36 , which typically connect opposing faces of transducer  22  with a controller (not shown). Passageway  40 , in one embodiment, defines a guidewire lumen  40  through which guidewire  18  extends. In this manner, guidewire  18  extends through housing  24  to facilitate proper alignment between transducer  22  and stent  10 . 
   Transducer housing  24  is adapted to be translated axially along a longitudinal axis  200 . In one embodiment, the axial translation of transducer housing  24  is made relative to stent  10 . Alternatively, balloon  20  and transducer housing  24  are disposed such that they move in parallel, maintaining the proper configuration of transducer  22  with respect to side hole  12 . 
     FIGS. 4A and 4B  depict additional details of transducer  22  and housing  24 . In one embodiment, a drive cable  44  is coupled to a proximal end of housing  24 .  FIG. 4A  further depicts passageway  40 , which extends through housing  24 . In one embodiment, drive cable  44  comprises two counterwound cables made of stainless steel, nitinol or the like. Such a drive cable facilitates its introduction into tortuous vasculatures. Drive cable  44  further permits rotation of housing  24 , and hence the rotation of transducer  22 . Preferably, such rotation is made relative to longitudinal axis  200 . 
     FIG. 4B  is a side cross-sectional view of a portion of the imaging catheter. As shown, an optional sheath  46  may be used to enclose drive cable  44 . Sheath  46  operates to protect balloon  20  during rotation of drive cable  44 . Further, sheath  46  provides a substantially smooth outer surface for embodiments in which the imaging apparatus is translated axially relative to balloon  20  and/or stent  10 . Sheath  46  may comprise polyethylene, as well as a wide range of other materials. In one embodiment, sheath  46 , drive cable  44  and an inner sleeve  48  correspond to outer member  32  depicted in  FIG. 3B . 
   Drive cable  44  defines guidewire lumen  38  into which transducer wires  36  are disposed. Inner member  34  maintains transducer wires  36  within wire lumen  38 . Further, inner member  34  defines passageway  40  through which guidewire  18  may be disposed. In an alternative embodiment, guidewire  18  passes through balloon lumen  30 , adjacent to drive cable  44  or sheath  46 . 
     FIGS. 5A and 5B  depict a simplified view of the imaging of a body lumen with transducer  22 . Similarly,  FIGS. 5C and 5D  depict the intensity of transmitted and reflected signals when transducer  22  is activated at the positions shown in  FIGS. 5A and 5B , respectively. For example, in  FIG. 5A , a voltage is applied across transducer  22  to generate ultrasound signals  42  which are transmitted from transducer  22  to surrounding fluids and tissue. When signals  42  encounter a change in medium, and more specifically a change in the density of the material through which the signals are passing, at least a portion of signals  42  is reflected back toward transducer  22 . Transducer  22  receives the reflected signal and transmits a corresponding voltage through wires  36  to a controller (not shown) for processing. When transducer  22  is positioned as shown in  FIG. 5A , signals  42  travel down a portion of the branch vessels  16  before being reflected by a vessel wall, occlusion, or the like. Hence, as can be seen in  FIG. 5C , the reflected signal is received after some time delay relative to the initial signal pulse. Additionally, the travel time for the reflected signal results in much of the sound energy being lost in blood or other fluid. Hence a comparatively weak signal is returned to transducer  22 . Correspondingly, if transducer  22  is disposed adjacent a wall  80 , such as shown in  FIG. 5B , the reflected signal is received much sooner and occurs at a greater intensity than the alignment shown in  FIG. 5A . The stronger echo or return signal is depicted in  FIG. 5D . In this manner, ultrasound imaging, including the calculated time delay between the original pulse and the reflected signal, can be used to determine whether transducer  22  is in alignment with branch vessel  16 . 
   Turning now to  FIGS. 6A and 6B , cross-sectional ultrasound images of a stent disposed in a body lumen are shown.  FIG. 6A  depicts a two-dimensional image showing stent struts  26  disposed about a center catheter or transducer  22 . The imaging performed by transducer  22  reveals blood speckles  68 , guidewire  18  and a guidewire shadow  64 , as well as a plaque  66  or other vessel wall imperfections.  FIG. 6A  depicts a generally uniform strut  26  structure and may exemplify the cross-sectional view of a stent that does not have a side hole, or the cross-sectional view of stent  10  when transducer  22  is not aligned with side hole  12 . For example, transducer  22  may be located proximal or distal to side hole  12 .  FIG. 6B  depicts a similar view as shown in  6 A, except the imaging transducer  22  is aligned with side hole  12 . As a result, a gap  62  is seen in the strut  26  pattern. It is the imaging of gap  62  which helps align side hole  12  with branch vessel  16  according to one embodiment of the present invention. 
   Images depicted in  FIGS. 6A and 6B  may be created in several ways according to the present invention. In one embodiment as previously described, transducer  22  is rotated about the longitudinal axis  200  by drive cable  44 . In this manner, a single transducer  22  can produce a two dimensional, 360 degree image plane as shown in  FIGS. 6A and 6B . In an alternative embodiment, a ring of transducer elements (not shown) are disposed in the catheter distal end to produce a two dimensional, 360 degree image plane without the need to rotate the ring of elements, although the elements may be rotated in another embodiment. The fixed ring of transducer elements may be disposed on an outer surface of balloon  25 , between balloon  25  and stent  10 . Preferably, such an embodiment has at least some of the transducer elements disposed on balloon  25  where sidehole  12  overlies. In this manner, some of the transducer elements will produce gap  62  as shown in  FIG. 6B . In an alternative embodiment, the ring of transducer elements are disposed on the outer surface of a sheath, similar to outer member  32  shown in  FIG. 3B . In this embodiment, the ring of transducer elements are disposed inside balloon lumen  30 . In still another embodiment, the ring of transducer elements are not used to produce an image as in  FIGS. 6A and 6B , but instead are used to indicate side hole to branch vessel alignment in accordance with the discussion accompanying  FIG. 10 . 
     FIG. 7 , in conjunction with  FIG. 8 , are helpful in explaining methods of the present invention.  FIGS. 7A-7C  depict simplified ultrasound cross-sectional images of a stent delivery apparatus disposed within a body lumen, such as main vessel  14 . The images shown in  FIGS. 7A-7C  correspond to the stent and ultrasound transducer  22  positions shown in  FIGS. 8A-8C . For example,  FIGS. 7A and 8A  depict stent  10  disposed within main vessel  14  where stent  10  is not adjacent to or aligned with branch vessel  16 . Hence, the image of  FIG. 7A  shows a generally uniform main vessel wall  80  not adjacent to the bifurcation. As a result, gap  62  corresponding to side hole  12  is not aligned with branch vessel  16 . In such a configuration, it is desirable to axially translate transducer  22  and stent  10  to continue to search for the desired branch vessel  16 . 
     FIGS. 7B and 8B  depict stent  10  in axial or longitudinal alignment with branch vessel  16 , however, side hole  12  is facing away from the ostium of branch vessel  16 . The image shown in  FIG. 7B  has an extended region  70  corresponding to the delayed signal return associated with the signals traveling at least partially down branch vessel  16 . In other words, the branch vessel  16  opening is now in view of transducer  22 . However, as shown in  FIG. 7B , gap  62  is still depicted facing main vessel wall  80 . In such a configuration, it is then desirable to rotate stent  10  to properly align side hole  12  with the ostium of branch vessel  16 . The desired configuration showing the alignment of side hole  12  with the ostium of branch vessel  16  is shown in  FIGS. 7C and 8C .  FIG. 7C  now depicts gap  62  in registry with extended region  70 . Such an image corresponds with the alignment of side hole  12  with the ostium of branch vessel  16 , as shown in  FIG. 8C . In this manner, the use of ultrasound imaging helps facilitate the alignment of side hole  12  with branch vessel  16 . Preferably, ultrasound transducer  22  is aligned with side hole  12  at all times, so ultrasound signals are transmitted to and from transducer  22  through side hole  12 . In this manner, gap  62  will be seen on the ultrasound images. Alternatively, transducer  22  may move freely relative to stent  10 . In such an embodiment, it may be desirable to first image with transducer  22  to locate side hole  12 , with reference to the images of  FIGS. 6A and 6B  as guidance. 
     FIG. 9  depicts an exemplary stent delivery system  100  according to the present invention. Delivery system  100  includes a console  110  having a controller  120  and a display  130 . Controller  120  is coupled to a drive motor  140 , which in one embodiment is used to rotate an ultrasound transducer  180 . Transducer  180  is similar to transducer  22  described in conjunction with earlier Figures. Further, transducer  180  may be an array of transducers as previously described. As shown in  FIG. 9 , a catheter  150  is provided having a proximal end  152  and a distal end  154  to which transducer  180  is coupled. Catheters for delivering stents according to the present invention are described in further detail in U.S. application Ser. No. 09/663,111, entitled “Catheter with Side Sheath And Methods”, and U.S. application Ser. No. 09/600,348 entitled “Extendible Stent Apparatus,” the complete disclosures of which are incorporated herein by reference. 
   As shown, system  100  includes a guidewire  190  over which a balloon  170  and a stent  160  are disposed. A control circuitry, as shown in  FIG. 10 , is used to transmit an electrical signal from a voltage source to transducer  180  to generate imaging ultrasound signals as is well known in the art. Transducer  180  is then used to position stent  160  such that a side hole (not shown) of stent  160  is properly aligned with an ostium of a branch vessel. 
     FIG. 10  depicts a simplified schematic of one embodiment of control circuitry  300  for use with the present invention. A high voltage source  310  is coupled to an RF pulse generator  320  which generates an electrical pulse for transmission to transducer  330  by way of a transmit/receive switch  340 . Transducer  330  receives the electrical signal as voltage applied across opposing surfaces of transducer  330 . The transducer material, preferably piezoelectric material, generates a soundwave, which propagates from the surface of transducer  330 . As previously noted, the soundwaves reflect off changes in medium density, such as the wall of a vascular vessel, and a portion of the signal returns to transducer  330 . Transducer  330  then transmits the received signal to transmit/receive switch  340  and a receiver filter  350 . Timing control and logic circuitry  360  coordinates RF pulse generator  320 , transmit/receive switch  340  and receiver filter  350  operation. 
   As previously described, the time delay of signals received from echoes off the branch vessel are greater than the time delay from signals received off of the main vessel walls. In one embodiment, receiver filter  350  may be used to indicate to a user of system  100  that side hole  12  is aligned, or not aligned, with branch vessel  16 . For example, one or more indicator lights  380  may be used to indicate side hole alignment (green) or non-alignment (red). In some embodiments, circuitry  300  does not produce a visual image of the body lumen. Instead, the signals received from transducer  330  are used to indicate sidehole to branch vessel alignment. A power supply  370  facilitates operation of the individual electrical components. 
   As shown in  FIG. 11 , stent, catheter and/or system  410  may be conveniently included as part of a kit  400 . Kit  400  includes instructions for use  420  which set forth various procedures for deploying stent  10  and imaging using transducer  22  using any of the techniques previously described. Instructions for use  420  may be in written or in machine readable form. Further, it will be appreciated that kit  400  may alternatively include any of the other elements described herein, such as imaging catheter  15 , balloon  20 , and the like. Further, instructions  420  may describe use of any of the other elements. 
   The invention has now been described in detail for purposes of clarity of understanding. However, it will be appreciated that certain changes and modifications may be practiced within the scope of the appended claims. For example, while transducer  22  is generally described as coupled to a drive cable  44  facilitating transducer rotation, transducer  22  also may be fixed relative to stent  10 . In such an embodiment, transducer  22  would comprise a side-looking transducer facing side hole  12 . In this manner, transducer  22  would be aligned with side hole  12  to facilitate side hole  12  alignment with branch vessel  16 . Such a configuration would produce images similar to that shown in  FIG. 6B , but comprising a pie-shaped portion of the image. Rotation of transducer  22  could then occur by rotating stent  10 , with transducer  22  maintaining a vigilant eye towards side hole  12 .