Patent Publication Number: US-2004054403-A1

Title: Angular orientation of a stent

Description:
FIELD OF THE INVENTION  
       [0001] The present invention relates generally to stents, and particularly to determining the angular orientation of a stent, e.g., a bifurcated stent, in a body lumen.  
       BACKGROUND OF THE INVENTION  
       [0002] A stent is a well known device used to support an intraluminal wall, used in procedures, such as but not limited to, percutaneous transluminal coronary angioplasty (PTCA). Various types of stent architectures are known in the art, including braided stents (filaments or wires, wound or braided into a particular configuration), or mesh stents (metal mesh bent or formed into a particular shape), among others.  
       [0003] Typically, a stent may be restrained in a radially compressed configuration by a sheath or catheter, and delivered by a deployment system or “introducer” to the site where it is required. The introducer may enter the body through the patient&#39;s skin, or through a blood vessel exposed by minor surgical means. When the introducer has been threaded into the body lumen to the stent deployment location, the introducer is manipulated to cause the stent to be released. The stent expands to a predetermined diameter at the deployment location, and the introducer is withdrawn. Stent expansion may be effected by spring elasticity, balloon expansion, or by the self-expansion of a thermally or stress-induced return of a shape memory alloy (such as a nickel-titanium alloy, e.g., NITINOL) to a pre-conditioned expanded configuration.  
       [0004] The travel of the stent through the body vessels to the stent deployment location may be imaged by various techniques, such as but not limited to, fluoroscopy. However, imaging equipment can generally map the travel of the stent in only one plane. This provides an inadequate amount of information regarding the spatial location and angular orientation of the stent. For deployment in bifurcated lumen, such as but not limited to, the carotid artery, it is critical to orient the stent properly to match the spatial orientation of the bifurcation. The lack of three-dimensional information makes this orientation difficult and cumbersome guesswork.  
       SUMMARY OF THE INVENTION  
       [0005] The present invention seeks to solve the abovementioned problem of the prior art, and to provide a stent whose angular orientation in three-dimensional space may be easily determined. In an embodiment of the present invention, the stent may be provided with markers discernible by an imaging device. The projections of the markers on an imaging plane uniquely define the angular orientation of the stent with respect to a defined reference. The three-dimensional position and orientation of the stent may thus be determined by the two-dimensional projection of the markers on the imaging plane.  
       [0006] The present invention also provides a novel bifurcated stent construction with a tapered nozzle and branch, which may or may not be off-center with the main body portion of the stent. The bifurcated stent may be constructed from a mesh pattern.  
       [0007] There is thus provided in accordance with an embodiment of the present invention a stent assembly comprising at least two markers located at different angular orientations on the stent assembly, the markers being discernible by an imaging device, wherein a projection of the at least two markers on an imaging plane uniquely defines an angle of rotation of the stent assembly about an axis thereof with respect to a reference. The projection of the at least two markers on an imaging plane may uniquely define an angle of rotation of the stent assembly about a longitudinal axis thereof with respect to the reference.  
       [0008] In accordance with an embodiment of the present invention the at least two markers are orthogonally spaced from one another on the stent assembly.  
       [0009] Further in accordance with an embodiment of the present invention the projection of the at least two markers on an imaging plane uniquely defines at least four mutually orthogonal angles of rotation of the stent assembly about an axis thereof with respect to the reference.  
       [0010] In accordance with an embodiment of the present invention the stent assembly comprises a body portion and a bifurcation extending from the body portion.  
       [0011] Further in accordance with an embodiment of the present invention the stent assembly comprises at least one of a stent, a sheath, a catheter and an introducer, and the markers are formed on a portion of at least one of the stent, the sheath, the catheter, the introducer, the body portion and the bifurcation.  
       [0012] Still further in accordance with an embodiment of the present invention the bifurcation comprises a tapered extension of the body portion and a branch extended at an angle to the tapered extension.  
       [0013] In accordance with an embodiment of the present invention the branch is placed off-center with respect to the body portion. Alternatively, the branch may extend from a centerline of the body portion.  
       [0014] Further in accordance with an embodiment of the present invention the body portion and the tapered extension are formed from a mesh pattern. The body portion and the tapered extension may be formed with an aperture, and the branch may be secured to the body portion at the aperture.  
       [0015] In accordance with an embodiment of the present invention the mesh pattern comprises a plurality of sub-sections of generally equal length.  
       [0016] Further in accordance with an embodiment of the present invention the mesh pattern comprises a first plurality of sub-sections and a second plurality of sub-sections, wherein the first sub-sections are shorter than the second sub-sections.  
       [0017] Still further in accordance with an embodiment of the present invention the second sub-sections may be arranged in a straight pattern or in a curved pattern.  
       [0018] Additionally in accordance with an embodiment of the present invention the mesh pattern further comprises an additional pattern with an aperture formed therein.  
       [0019] In accordance with an embodiment of the present invention at least one additional set of markers may be provided on the stent assembly angularly spaced from one another. The at least one additional set of markers may be angularly spaced from the at least two markers and/or may be placed on a different portion of the stent assembly than the previously mentioned markers, which may provide better accuracy in determining the angular orientation of the stent assembly or portions thereof or the angular orientation of different portions of the stent assembly with respect to each other.  
       [0020] There is also provided in accordance with an embodiment of the present invention a method for determining an angular orientation of a stent in a body lumen, the method comprising inserting a stent assembly into a body lumen, the stent assembly comprising at least two markers located at different angular orientations on the stent assembly, the markers being discernible by an imaging device, and sensing and processing a projection of the at least two markers on an imaging plane, wherein the projection uniquely defines an angle of rotation of the stent assembly about an axis thereof with respect to a reference. A contrast agent may be passed through the stent assembly. 
     
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
     [0021] The present invention will be further understood and appreciated from the following detailed description taken in conjunction with the drawing in which:  
     [0022]FIGS. 1A and 1B are simplified side-view and end-view illustrations, respectively, of a stent, constructed and operative in accordance with an embodiment of the invention;  
     [0023]FIG. 2 is a simplified illustration of the stent of FIGS. 1A and 1B introduced into a body lumen, and showing a projection of markers on the stent projected on an imaging plane, in accordance with an embodiment of the invention;  
     [0024] FIGS.  3 A- 3 C are simplified pictorial illustrations of one construction of the stent of FIGS. 1A and 1B, in accordance with an embodiment of the invention, comprising a bifurcation with a tapered extension and a branch extending off-center with respect to a body portion of the stent;  
     [0025]FIG. 3D is a simplified pictorial illustration of another construction of the stent of FIGS. 1A and 1B, in accordance with another embodiment of the invention, wherein the branch may extend from a centerline of the body portion; and  
     [0026] FIGS.  4 A- 4 D are simplified illustrations of mesh patterns for forming a stent, wherein FIG. 4A illustrates a pattern which may be used to form a straight stent, FIG. 4B illustrates a pattern which may be used to form a stent with a straight taper, FIG. 4C illustrates a pattern which may be used to form a stent with an offset taper, and FIG. 4D illustrates a pattern which may be used to form a stent with an aperture, in accordance with embodiments of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0027] Reference is now made to FIGS. 1A and 1B, which illustrate a stent assembly  10 , constructed and operative in accordance with an embodiment of the invention.  
     [0028] Stent assembly  10  comprises two or more markers  12  and  14  located at different angular orientations on stent assembly  10 , such as on a stent  11 . Markers  12  and  14  may be discernible by an imaging device, such as but not limited to, a fluoroscope (not shown). In FIGS. 1A and 1B, markers  12  and  14  are spaced axially from one another, although they do not have to be. In one embodiment of the invention, markers  12  and  14  are orthogonally spaced from one another on stent assembly  10 , that is, angularly spaced 90° apart. In another embodiment of the invention, another set of markers  12 ′ and  14 ′ may be provided on stent assembly  10 , as indicated in broken lines in FIG. 1A. The additional set or sets of markers may be orthogonally spaced from one another. Alternatively, markers  12  and  14  and/or the additional set(s) of markers may be angularly spaced from one another at angles other than 90°. Use of multiple sets of markers may increase the accuracy of determining the angular orientation of the stent assembly  10 , and reduce the need for interpolation between markers.  
     [0029] Markers  12  and  14  uniquely define an angle of rotation of stent assembly  10  about an axis  16  thereof with respect to a reference  18 . (Axis  16  may be the longitudinal axis of stent assembly  10 .) Referring to FIG. 1B, it is seen that at reference  18  (angular orientation of 0°), marker  12  is pointing to the right and marker  14  is pointing upwards. At the angular orientation of 90°, corresponding to 90° counterclockwise rotation of stent assembly  10  about its longitudinal axis  16  in the sense of FIG. 1B, marker  12  is pointing upwards and marker  14  is pointing to the left. At the angular orientation of 180°, corresponding to 180° rotation of stent assembly  10  about its longitudinal axis  16  in the sense of FIG. 1B, marker  12  is pointing to the left and marker  14  is pointing downwards. At the angular orientation of 270°, corresponding to 270° counterclockwise rotation of stent assembly  10  about its longitudinal axis  16  in the sense of FIG. 1B, marker  12  is pointing downwards and marker  14  is pointing to the right.  
     [0030] Reference is now made to FIG. 2, which illustrates the stent  11  of stent assembly  10  introduced into a body lumen  20 . A projection of the markers  12  and  14  are projected on an imaging plane  22 . It may be appreciated that the projection of markers  12  and  14  in this example is the same for both the upward and downward positions. Nevertheless, the combined projection of markers  12  and  14  on imaging plane  22  uniquely defines the angle of rotation of stent assembly  10  about axis  16  with respect to reference  18 .  
     [0031] The following table summarizes the orthogonal positions of the markers and their projection on imaging plane  22  (the up and down projections are identical and are designated as ‘1’).  
                                       Degrees of Rotation   Marker 12   Marker 14                                            0   Right   ‘1’ (Up)       90   ‘1’ (Up)   Left       180   Left   ‘1’ (Down)       270   ‘1’ (Down)   Right                  
 
     [0032] Accordingly, the projections of markers  12  and  14  on imaging plane  22  uniquely define at least four mutually orthogonal angles of rotation of stent assembly  10  about axis  16  with respect to reference  18 . A processor  23  may process the encoded information as sensed at the imaging plane  22  by appropriate sensors  25  of an imaging system (not shown), in order to determine the angular orientation of stent assembly  10 . For example, the combination of R1 means that stent assembly  10  is at 0°. The combination of 1R means that stent assembly  10  is at 90°, and so forth. Other angular orientations may be determined by interpolation between the four orthogonal angles. The markers may act as encoders from which the angular orientation of stent assembly  10  may be determined. The three-dimensional position and orientation of stent assembly  10  may thus be determined by the two-dimensional projection of the markers  12  and  14  on imaging plane  22 .  
     [0033] As seen in FIG. 2, the stent  11  of stent assembly  10  may be disposed in a sheath or catheter  24  for delivery to a deployment site by an introducer  29 . A bifurcation  32  may extend from body portion  30 . Markers  12  and  14  may be formed on any portion of stent assembly  10 . Accordingly, markers  12  and  14  may be formed, without limitation, on any portion of the stent  11 , sheath or catheter  24 , introducer  29 , body portion  30  or bifurcation  32 . For example, one set of markers may be placed on body portion  30  and another set of markers may be placed on bifurcation  32 . In this manner, the angular orientation of bifurcation  32  with respect to that of body portion  30  may be easily determined by the sets of markers on each corresponding part of the stent assembly  10 .  
     [0034] Reference is now additionally made to FIGS.  3 A- 3 C, which illustrate one construction of the stent of stent assembly  10 , in accordance with an embodiment of the invention. Bifurcation  32  may comprise a tapered extension  34  of body portion  30 , and a branch  36  extended at an angle to tapered extension  34 . Branch  36  may be placed off-center with respect to body portion  30 . Alternatively, as shown in FIG. 3D, branch  36  may extend from a centerline  38  of body portion  30 . As seen in FIG. 3A, body portion  30  and tapered extension  34  may be formed with an aperture  40 . Aperture  40  may be formed with mounting structure  42 , such as but not limited to, a rim. As seen in FIG. 3B, branch  36  may be formed with mounting structure  44 , such as but not limited to, a flange. Branch  36  may be secured to body portion  30  at aperture  40 , such as but not limited to, by mating (snapping, clinging, bonding, tight-fitting, or otherwise joining) the mounting structures of branch  36  and aperture  40  together.  
     [0035] For example, body portion  30  may be introduced to the stent deployment site without branch  36 . Afterwards, branch  36  may be introduced and fed through body portion  30 . Branch  36  may then be pushed through aperture  40  and snapped or otherwise fixed in place at aperture  40 , thereby forming bifurcation  32  with tapered extension  34 . During imaging, a contrast agent  46  may be disposed in (e.g., passed through) bifurcation  32  for imaging the projections of markers  12  and  14  on imaging plane  22 , as described hereinabove.  
     [0036] Reference is now made to FIGS.  4 A- 4 D, which illustrate mesh patterns for forming a stent with a branch. Branch  36  may be made with a pattern  50  shown in FIG. 4A, which may be used to form a straight stent. Pattern  50  may be used as a cylindrical pattern with cylindrical coordinates ρθ to form the stent by any suitable method, such as but not limited to, laser etching or cutting. Pattern  50  may also be used as a flat pattern to form the stent by any suitable method, such as but not limited to, laser etching or cutting, followed by bending around a mandrel and welding a seam. Pattern  50  may comprise subsections  51  of generally equal length. A stent formed from pattern  50  may be straight due to the equal lengths of sub-sections  51 .  
     [0037]FIG. 4B illustrates a mesh pattern  52 , which may be used to form a stent with a straight taper. Pattern  52  may comprise a first plurality of sub-sections  53  and a second plurality of sub-sections  54 , wherein first sub-sections  53  are shorter than second sub-sections  54 . The first sub-sections  53  may form a generally straight cylindrical stent portion, whereas the second sub-sections  54 , due to their shorter length, may form a straight taper extending from the straight cylindrical stent portion formed by first sub-sections  53 . Such a stent construction may be used in the embodiment of FIG. 3D wherein branch  36  extends from centerline  38  of body portion  30 .  
     [0038]FIG. 4C illustrates a mesh pattern  56 , which may be used to form a stent with an offset taper. Pattern  56  may comprise a first plurality of sub-sections  57  and a second plurality of sub-sections  58 , wherein first sub-sections  57  are shorter than second sub-sections  58 . The second sub-sections  58  may be arranged in a curved pattern, unlike pattern  52  of FIG. 4B, wherein the second sub-sections  53  may be arranged in a straight pattern. The first sub-sections  57  may form a generally straight cylindrical stent portion, whereas the second sub-sections  58 , due to their shorter length and curved pattern, may form a taper extending in an offset manner from the straight cylindrical stent portion formed by first sub-sections  57 . Such a stent construction may be used in the embodiment of FIG. 3C wherein branch  36  is placed off-center with respect to body portion  30 .  
     [0039]FIG. 4D illustrates a mesh pattern  60 , which may be used to form a stent with an aperture, such as the embodiment of FIG. 3A, which includes body portion  30  and the tapered extension  34  formed with aperture  40 . Pattern  60  may be identical to pattern  56 , with an additional pattern  62  with an aperture formed therein. It is appreciated that the invention is not limited to the patterns shown in FIGS.  4 A- 4 D.  
     [0040] It will be appreciated that the invention is not limited to what has been described hereinabove merely by way of example. Rather, the invention is limited solely by the claims that follow.