Abstract:
The present invention envisions an improved flexible connecting link used in conjunction with in-phase and half-phase circumferential sets of strut members. By increasing the total length and diagonality of the undulating connecting links, the present invention is a stent that provides increased flexibility during delivery and enhanced conformability to the shape of a curved artery when the stent is deployed into a curved vessel such as a tortuous coronary artery.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part of Application Ser. No. ______ entitled Stent with Diagonal Flexible Connecting Links, filed on even date herewith, the disclosure which is incorporated by reference. 
     
    
     
       FIELD OF USE  
         [0002]    This invention is in the field of stents for implantation into a vessel of a human body.  
         BACKGROUND OF THE INVENTION  
         [0003]    Stents are well known medical devices that are used for maintaining the patency of a large variety of lumens of the human body. The most frequent use is for implantation into the coronary vasculature. Stents have been used for this purpose for almost twenty years. Some current stent designs such as the CORDIS BX Velocity™ stent have the required flexibility and radial rigidity to provide excellent clinical results. Yet sometimes such stents are not able to be delivered through extremely torturous or highly calcified vessels.  
           [0004]    Many current tubular stents use a multiplicity of circumferential sets of strut members connected by either straight longitudinal connecting links or undulating longitudinal (flexible) connecting links. The circumferential sets of strut members are typically formed from a series of diagonal sections connected to curved sections forming a closed-ring, generally slotted structure. This structure expands radially outwardly as the balloon on which the stent is mounted is inflated to form the element in the stent that provides structural support for the arterial wall.  
           [0005]    A closed-cell stent is sometimes considered a stent in which (except at the longitudinal ends of the stent) every curved section of each central circumferential set of strut members has a connection to one end of a flexible link leaving no “unconnected” central curved sections. A stent with at least half of its central (non-end) curved sections being “unconnected” can sometimes be considered as an “open-cell” stent. A hybrid design stent is one that has fewer than half of its central curved sections being “unconnected”.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention envisions an improved flexible connecting link used in conjunction with in-phase and half-phase circumferential sets of strut members. The definitions of “in-phase” and “half-phase” which describe the orientation of adjacent circumferential sets of strut members will be given in the detailed description of the invention with the aid of several of the figures. By increasing the total length and diagonalness of the undulating connecting links, the present invention is a stent that provides increased flexibility during delivery and enhanced conformability to the shape of a curved artery when the stent is deployed into a curved vessel such as a tortuous coronary artery. By “increasing diagonalness” is meant that the end points of the flexible connecting links have an increased circumferential displacement each one from the other. That is, more diagonalness means that a line connecting the end points of a flexible links has an increased acute angle relative to a line that lies parallel to the stent&#39;s longitudinal axis.  
           [0007]    The BX Velocity stent uses a balloon in which the folds are straight wrapped, to prevent the stent from twisting in a helical manner during deployment. By “straight wrapped” is meant the fold lines of the balloon lie generally parallel to the stent&#39;s longitudinal axis. Such helical twisting can result in significant foreshortening of the stent. The present invention stent system envisions use of a helically wrapped balloon. By “helically wrapped” is meant that the folds of the balloon lie at an acute angle relative to a line that is parallel to the stent&#39;s longitudinal axis. When properly oriented relative to the stent, a helically wrapped balloon can cause the stent to lengthen when the balloon is inflated as compared to a foreshortening that can occur when the stent is deployed from a straight wrapped balloon.  
           [0008]    Three embodiments of the present invention stent are disclosed herein. Two are closed-cell stent embodiments and one is an open-cell stent embodiment. The first closed-cell stent embodiment uses “N” shaped flexible links to connect the ends of the curved sections of adjacent in-phase circumferential sets of strut members. The second closed-cell stent embodiment includes at least one end-to-end spine wherein the diagonal “N” flexible links connect from the outside of the curved sections of one circumferential set of strut members to the inside of the curved sections of the adjacent circumferential set of strut members. The spine embodiments also utilize “in-phase” circumferential sets of strut members.  
           [0009]    The open-cell stent embodiment of the present invention stent uses diagonal “N” flexible links to connect adjacent circumferential sets of strut members where only half of the curved sections are connected by a flexible link. The unconnected crowns have shorter diagonal segments so as to reduce the potential for fish-scaling (sometimes called dog-bones) during stent delivery around a bend. “Fish-scaling” is defined as the tendency of metal struts of a stent to protrude outwardly from the surface of the balloon (like a fish scale) when the pre-deployed stent is advanced through a curved coronary artery.  
           [0010]    Although the present invention describes in-phase circumferential sets of strut members where the diagonal flexible links span one-half cycle of circumferential displacement, it is also envisioned that flexible links spanning ⅛ to 1½ cycles are also possible. These configurations of the stents will be described in detail in the detailed description of the invention with the aid of the appropriate drawings.  
           [0011]    It is also envisioned that any of the stent designs as taught herein may be used with plastic coatings such as parylene, antithrombogenic coatings such as heparin or phosphorylcholine or anti-proliferative coatings such as paclitaxel or sirolimus.  
           [0012]    An additional version of the non-spined, closed-cell embodiment includes two additional configurations. The first of these concepts is a specific technique for widening the diagonal sections within a circumferential set of strut members. It is desirable to taper the diagonal sections to be wider at their center, especially for the end circumferential sets of strut members. Such widening of the diagonal sections of each end circumferential set of strut members will increase the visibility of the stent ends under fluoroscopy. If the diagonal section is widened too close to the point where a curved section connects to a diagonal section of a circumferential set of strut members, this configuration will negatively affect the unbending of the curved section as the stent is deployed. This is a result of creating unwanted plastic strain in the metal if the widened region of the diagonal section is too close to the attachment point of that diagonal section to the curved section. The present invention envisions having a strut segment of uniform width for at least approximately 0.001″ between the end point of the curved section and the start of the widened taper in the diagonal section. A distance of approximately 0.002″ to 0.0003″ is more optimium.  
           [0013]    The second of these concepts relates to the longitudinal spacing (i.e., the “gap”) between adjacent circumferential sets of strut members. The end structure of a stent is critical to stent deliverability as the leading edge of the stent must bend first as the stent mounted onto the deployment balloon is advanced through a curved artery. Assuming the flexible links for a stent are optimized to be as long and as thin as possible within the gap allowed between adjacent circumferential sets of strut members, the only way to have increased flexibility of the end flexible links is to increase the longitudinal length of the gap between each end circumferential sets of strut members and its adjacent, central circumferential set of strut members. This increased gap will permit a longer (and more flexible) link to connect each one of the two end circumferential sets of strut members to its adjacent central circumferential set of strut members.  
           [0014]    Thus it is an object of the present invention to have a stent with circumferential sets of strut members connected each to the other by flexible links wherein a line connecting the flexible link end points that attach to each circumferential set of strut members is diagonally oriented relative to the stent&#39;s longitudinal axis.  
           [0015]    Another object of the present invention is to have a closed-cell stent having in-phase circumferential sets of strut members wit h the ends of each diagonal flexible link where they are attached to the circumferential sets of strut members being situated in close proximity to the junction point of a curved section and a diagonal section.  
           [0016]    Still another object of the present invention is to have a stent having in-phase circumferential sets of strut members with diagonal flexible links forming an end-to-end spine to prevent stent foreshortening.  
           [0017]    Still another object of the present invention is to have an open-cell stent having in-phase circumferential sets of strut members with diagonal flexible links wherein the ends of each diagonal flexible link are connected to the circumferential sets of strut members near the junction of a curved section and a diagonal section.  
           [0018]    Still another object of the present invention is to have a closed-cell stent having circumferential sets of strut members with diagonal flexible links wherein the diagonal sections of at least one of the circumferential sets of strut members are tapered to be wider at their center with the taper beginning placed apart from away from the attachment point of the diagonal sections to the curved sections.  
           [0019]    Still another object of the invention to have a closed-cell stent with circumferential sets of strut members connected each to the other by flexible links wherein the end diagonal flexible links are longer than the flexible links elsewhere in the stent.  
           [0020]    These and other objects and advantages of this invention will become apparent to a person of ordinary skill in this art upon reading of the detailed description of this invention including the associated drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    [0021]FIG. 1 is a flat layout view of a prior art stent having out-of-phase circumferential sets of strut members connected by “N” shaped flexible links;  
         [0022]    [0022]FIG. 2A is a flat layout view of a closed-cell embodiment of the present invention having diagonal flexible links that are connected to in-phase circumferential sets of strut members;  
         [0023]    [0023]FIG. 2B are flat layout views of portions of three embodiments of the present invention showing different circumferential offsets between adjacent circumferential sets of strut members;  
         [0024]    [0024]FIG. 2C are flat layout views illustrating three different types of diagonal flexible links;  
         [0025]    [0025]FIG. 3 is a flat layout view of an embodiment of the present invention having diagonal flexible links, in-phase circumferential sets of strut members and also having two end-to-end spines to reduce stent foreshortening;  
         [0026]    [0026]FIG. 4 is a flat layout view of an open-cell embodiment of the present invention having diagonal flexible links with in-phase circumferential sets of strut members;  
         [0027]    [0027]FIG. 5 is a flat layout view of an alternative closed-cell embodiment of the present invention having circumferential sets of strut members with a ¼ cycle (half-phase) circumferential offset;  
         [0028]    [0028]FIG. 6 is an enlargement of the area  70  of the stent of FIG. 5, and  
         [0029]    [0029]FIGS. 7 a, b, c , and  d  are schematics describing the interaction between a stent as in the present invention and the balloon onto which the stent is emplaced. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0030]    [0030]FIG. 1 shows a flat layout view of an embodiment of a prior art closed-cell, cylindrical stent such as that described by Fischell et al in U.S. Pat. No. 6,190,403, incorporated herein by reference. The stent  10  of FIG. 1 is shown in its crimped, pre-deployed state as it would appear if it were cut longitudinally and then laid out into a flat, two-dimensional configuration. FIG. 1 is the 2-dimensional layout view that the stent  10  would have when it is crimped onto a balloon prior to the balloon being inflated to expand the stent  10  radially outward against the wall of an artery. The stent  10  has two end sets of strut members  4  and three central sets of strut members  1  that are each connected by sets of longitudinally extending, undulating “N”-shaped flexible links  8 . The end sets of strut members  4  consist of alternating curved sections  6  that are attached to diagonal sections  5 . The central sets of strut members  1  located longitudinally between the end sets of strut members  4  consist of alternating curved sections  3  attached to diagonal sections  2 . In the prior art stent  10 , the diagonal sections  5  of the end sets of strut members  4  are shorter in length than the diagonal sections  2  of the central sets of strut members  1 . The shorter diagonal sections  5  will reduce the stiff longitudinal length of metal at the ends of the stent  10  to improve stent deliverability by reducing “fish-scaling”. The shorter longitudinal length of the end diagonals  5  will also increase the post-expansion strength of each end set of strut members  4  as compared with the strength of each central set of strut members  6 . In this prior art stent, the width of the curved sections  3  and  6  and the diagonal sections  2  and  5  are all the same. There is no variation in width within any set of strut members or between the end sets of strut members  4  and the central sets of strut members  1 .  
         [0031]    From FIG. 1 it should be noted that the flexible links  8  are designed to accommodate one another as the stent is crimped down to allow the smallest possible outside diameter of the stent  10  as it is crimped onto a delivery balloon. The flexibility of the stent  10  is dependent on the ability of the flexible links  8  to lengthen or shorten as the stent is bent through a curved artery. Analysis of flexible link flexibility has shown that increasing the circumferential extent of the “N” flexible links  8  increases the stent&#39;s flexibility. In FIG. 1, each circumferential set of strut members is circumferentially displaced each from the other by 180 degrees. This arrangement is defined as being “out-of-phase.” For an out-of-phase design, the adjacent curved sections of each circumferential set of strut members is straight across from the adjacent curved section. If instead of connecting from curved sections that are straight across from each other as shown in FIG. 1, the flexible links could be connected in a more diagonal fashion, the circumferential extent of the flexible links would be longer and the stent would be more flexible.  
         [0032]    [0032]FIG. 2A is a flat layout view of a closed-cell stent  20  which has diagonally connected flexible links with in-phase circumferential sets of strut members. The stent  20  is shown as cut from a metal tube before crimping the stent onto a balloon of a stent delivery system. The fact that the stent  20  that has circumferential sets of strut members that are “in-phase” is best illustrated by the orientation of a line connecting the points  29 . The dotted line joining the center points  29  of the curved sections  23  or  26  that are curved in the same direction would lie essentially parallel to the longitudinal axis L of the stent  20 . It can also be said that each center point  29  is not circumferentially displaced from the center point  29  of the curved section  23  or  26  of the adjacent circumferential set of strut members. It is certainly envisioned that the flexible links  8  (of FIG. 1) or  28  could be attached diagonally to opposing curved sections that are in-phase, out-of-phase, or anywhere in between these two states. It is also envisioned that the flexible links can be even more diagonally attached as illustrated by the 1¼ cycles connection as shown in FIG. 2C.  
         [0033]    The stent  20  has end sets of strut members  24  located at each end of the stent  20  and eight central sets of strut members  21  connected each to the other by sets of longitudinally extending undulating diagonal flexible links  28 . The end sets of strut members  24  consist of alternating curved sections  26  and diagonal sections  25 . The central sets of strut members  21  located longitudinally between the end sets of strut members  24  consist of alternating curved sections  23  and diagonal sections  22 . In the stent  20 , the diagonal sections  25  of the end sets of strut members  24  are shorter and wider than the diagonal sections  22  of the central sets of strut members  21 . The shorter diagonal sections  25  will reduce the stiff longitudinal length of metal at the ends of the stent  20  to improve deliverability by reducing “fish-scaling”. The shorter diagonal sections  25  will also increase the post-expansion strength of the end sets of strut members  21 .  
         [0034]    The wider diagonal sections  25  of the end circumferential sets of strut members  24  enhance the radiopacity of the ends of the stent  20 . This is particularly important because the interventional cardiologist who implants the stent can place the stent more accurately at an arterial stenosis when there is clear visualization of the ends of the stent. In the stent  20 , the width of the curved sections  23  and  26  can be tapered to improve the ratio of strength to maximum plastic strain, as described in U.S. patent application Ser. No. 09/797,641 incorporated herein by reference. The curved sections  26  or  23  that connect to the ends of the diagonal flexible links  28  are, in this embodiment, displaced circumferentially by a one-half cycle.  
         [0035]    This relationship essentially defines the relative circumferential positions of the circumferential sets of strut members for an in-phase stent configuration. That is, FIG. 2A and the left portion of FIG. 2B show that each of the circumferential sets of strut members are “in-phase” with each other. This is contrasted with the stent  10  of FIG. 1, wherein despite the diagonal (spiral) nature of the connections of the flexible links  8 , the flexible links  8  connect to opposing curved sections  3  or  6  that have a zero cycle circumferential displacement. In other words, the present invention stents are different than the prior art stent  10  of FIG. 1 where out-of-phase adjacent circumferential sets of strut members  1  and  4  are mirror images of each other. The in-phase design of the stent  20  of FIG. 2A permits more circumferential displacement of the end point connections of the flexible links  28  to the curved sections  23  or  26  as compared with the connections for the flexible links  8  of FIG. 1. This increased circumferential displacement of the connection points for the diagonal flexible links  28  makes them longer, and thus more easily stretched or compressed as the stent  20  is bent. Therefore, the stent  20  of FIG. 2A is envisioned to be more flexible than the stent  10  of FIG. 1.  
         [0036]    The stent  20  shown in FIG. 2A has five connecting diagonal flexible links  28  between each adjacent set of circumferential sets of strut members  21  or  24 . It is also envisioned that three, four, six or more than six such connecting links could also be used. The stent  20  having five flexible links is a design that is ideally suited for placement into arteries having a diameter between 2.5 and 3.5 mm. Fewer connecting links (e.g., three) with fewer cells around are typically applicable to smaller diameter vessels. Stents with more connecting links and therefore having more cells around the stent&#39;s circumference are better suited for larger vessels. This is because good scaffolding of the vessel wall is maintained when the area of each cell of the stent remains fairly constant irrespective of the stent&#39;s final diameter when expanded against the arterial wall. Thus larger diameter stents require more cells around the stent&#39;s circumference as compared to smaller diameter stents that have fewer cells around.  
         [0037]    Although the in-phase circumferential sets of strut members  21  and  24  of the stent  20  create a one-half cycle additional circumferential displacement of the diagonal flexible links  28  as compared with the flexible links  8  of FIG. 1, it is envisioned that circumferential displacements of one-eighth cycle or more can achieve improvement in stent flexibility through an increase in the circumferential extent of the diagonal flexible links  28 . FIG. 2B illustrates ¼, ½ and 0 cycle circumferential displacements of the adjacent circumferential sets of strut members. It should be understood that any circumferential displacement of the circumferential sets of strut members that lies between in-phase and out-of-phase is envisioned. Even circumferential displacements greater than ½ cycle (e.g., ¾ cycle) are also envisioned. A probable maximum circumferential displacement for the flexible link connection points is 1¼ cycles as shown to the left in FIG. 2C.  
         [0038]    [0038]FIG. 2B shows alternate embodiments of the stent  20  of FIG. 2A. The stent portion on the left that is labeled C=½ CYCLE shows the ½ cycle circumferential offset of the curved sections  23  at each end of a diagonal flexible link  28 . This is identical to the stent design shown in FIG. 2A. The stent portion at the center of FIG. 2B labeled C′=¼ CYCLE shows the ¼ cycle circumferential offset of the curved sections  23 ′ that are joined by the diagonal flexible links  28 ′. The stent portion on the right that is labeled C″=0 CYCLE is identical to the prior art stent shown as stent  10  of FIG. 1. This 0 CYCLE is an out-of-phase design stent having curved sections  23 ″ attached to flexible links  28 ″.  
         [0039]    [0039]FIG. 2C illustrates other variations for flexible links connected to adjacent circumferential sets of strut members. Specifically, the left part of FIG. 2C shows a C′″=1¼ CYCLES with a very large circumferential displacement for the end points of the flexible links  28 ′″. The center portion of FIG. 2C shows a “J” type flexible link  28 J which also can be used for connecting adjacent circumferential sets of strut members. The right portion of FIG. 2C shows a very undulating form of flexible connector  28 JW which would impart a high degree of flexibility to the stent. Any of these flexible links could be designed to impart more or less flexibility to various portions of a stent.  
         [0040]    [0040]FIG. 3 shows a stent  30  that is another embodiment of the present invention using diagonally connected “N” flexible links. The stent  30  has two end-to-end spines  48  that will reduce foreshortening when such a stent is expanded against a vessel wall. The stent  30  is, in most other ways, similar to the stent  20  of FIG. 2 in that the central and end circumferential sets of strut members  31 ,  34 P and  34 D of the stent  30  are “in-phase.” The stent  30  of FIG. 3 is shown in its pre-deployed state before crimping onto a balloon.  
         [0041]    [0041]FIG. 3 shows the stent  30  as it would appear if it were cut longitudinally and then laid out into a flat, 2-dimensional configuration. The stent  30  has end sets of strut members  34 P and  34 D located respectively at the proximal and distal ends of the stent  30  and seven central sets of strut members  31  connected each to the other by sets of longitudinally extending, undulating, diagonally connected flexible links  38 A and  38 B.  
         [0042]    The end sets of strut members  34 P and  34 D consist of alternating curved sections  36  attached to widened diagonal sections  35 . The central sets of strut members  31  located longitudinally between the end sets of strut members  34 P and  34 D consist of curved sections  33  and  44  and diagonal sections  32  and  42 . In the stent  30 , the diagonal sections  35  of the end sets of strut members  34 P and  34 D are wider than the diagonal sections  32  and  42  of the central sets of strut members  21 . The wider diagonal sections  35  of the end circumferential sets of strut members  34 P and  34 D enhance the radiopacity of the ends of the stent  30 . In the stent  30 , the width of the curved sections  33  and  36  may be tapered to improve the ratio of radial strength to maximum plastic strain when the stent is expanded.  
         [0043]    The flexible links  38 A connect between the outside of curved sections  36  or  33  of adjacent circumferential sets of strut members  34 P,  34 D or  31  while the flexible links  38 B connect between the outside of one curved section  36  or  33  and the inside of a curved section  33  or  36  of the adjacent circumferential set of strut members. The flexible links  38 B form most of the spines  48  that run the length of the stent  30 . One key feature of the stent  30  is that the outside of every distally extending curved section  36  or  33  is attached to a flexible link. This will reduce the extent of fish-scaling of the stent  30  as the stent is advanced in a forward (i.e., distal) direction. As seen in FIG. 3, the diagonal sections  42  that attach to the unconnected curved sections  44  are shorter that the diagonal sections  32  that connect to connected curved sections  33  of the central circumferential sets of strut members  31 . Because these diagonals  42  that attach to the unconnected curved sections  44  are shorter, the potential for fish-scaling when the stent is pulled back in the proximal direction is reduced.  
         [0044]    [0044]FIG. 4 shows an open-cell alternative embodiment of the present invention that also has diagonal flexible links. The stent  40  of FIG. 4 is shown in its layout state as it would appear if it were cut longitudinally and then laid out into a flat, 2-dimensional configuration. As with the stents of FIGS. 2 and 3, FIG. 4 illustrates a 2-dimensional view of how the cylindrical stent  40  would look after it is cut out of thin-walled metal tube before it is crimped onto a balloon of a stent delivery system. The stent  40  comprises end sets of strut members  54  located at each end of the stent  40  and eight central sets of strut members  51  connected each to the other by sets of longitudinally extending, undulating, diagonal flexible links  58 . The end sets of strut members  54  consist of alternating curved sections  56 E,  56 U and  56 C with diagonal sections  55 S and  55 L. The curved sections  56 E are located on the actual ends of the stent  40 . The curved sections  56 U and  56 C are so designated because the curved sections  56 C are connected to diagonal flexible links  58  while the curved sections  56 U are unconnected. The unconnected curved sections  56 U attach to shorter end diagonal sections  55 S than the connected curved sections  56 C that connect to the longer end diagonal sections  55 L. The central sets of strut members  51  located longitudinally between the end sets of strut members  54  consist of alternating curved sections  53 C and  53 U with diagonal sections  52 S,  52 M and  52 L. The curved sections  53 U and  53 C are so designated because the curved sections  53 C are connected to diagonal flexible links  58  while the curved sections  53 U are unconnected. The unconnected curved sections  53 U attach to the shortest central diagonal section  52 S while the connected curved sections  53 C connect to the longer central diagonal sections  52 M and  52 L. The advantage of having the unconnected curved sections  56 U and  53 U attach to shortest diagonal sections  55 S and  52 S is that, as the stent  40  is delivered mounted onto a delivery balloon into a curved vessel, any unconnected portion of the stent  40  can protrude outward from the balloon on which it is mounted. Thus unconnected curved sections, such as curved sections  56 U and  53 U could be caught on tight vessel blockages or on the arterial wall as the stent is advanced through curved arteries. Because the diagonal sections  55 S and  52 S are short, the extent of this phenomena called “fish scaling” is minimized.  
         [0045]    In the stent  40 , the diagonal sections  55 S and  55 L of the end sets of strut members  54  are wider than the diagonal sections  52 S,  52 M and  52 L of the central sets of strut members  51 . The wider diagonal sections  55 S and  55 L of the end circumferential sets of strut members  54  enhance the radiopacity of the ends of the stent  40  where it is most important. In the stent  40 , the width of the curved sections  53 C,  53 U,  56 E,  56 C and  56 U may be tapered to improve the ratio of strength to maximum plastic strain. The central and end circumferential sets of strut members  51  and  54  of the stent  20  are “in-phase.” The in-phase design of the stent  40  of FIG. 4 permits more circumferential displacement for the attachment points for the flexible links  58  as compared to the stent  10  shown in FIG. 1. The increased circumferential displacement of the diagonal flexible links  58  makes them longer and thus more easily stretched or compressed as the stent  40  is advanced through highly curved arteries. This enhances the flexibility and hence the deliverability of the stent  40 .  
         [0046]    The open-cell stent  40  shown in FIG. 4 has four connecting diagonal flexible links  58  between each adjacent circumferential set of strut members. It is also envisioned that three, five, six or more such connecting links could also be used. Typically, the greater the diameter of the deployed stent, the greater would be the number of flexible links between each adjacent circumferential set of strut members.  
         [0047]    The stent  60  of FIG. 5 is shown in its pre-crimped state as it would appear if it were cut longitudinally and then laid out into a flat, 2-dimensional configuration. The stent  60  has end sets of strut members  64  located at each end of the stent  60  and five central sets of strut members  61  connected each to the other by sets of flexible links  68  and  69 ; each set comprising 5 individual flexible links  78  or  79 . The end flexible links  79  that connect adjacent circumferential sets of strut members at the ends of the stent  60  are longer than the central flexible links  78  connecting all other adjacent circumferential sets of strut members. This increased length is possible because of the increased longitudinal gap G e  between the adjacent circumferential sets of strut members at the end of the stent as compared with the gap G c  between all central circumferential sets of strut members  61 . The increased length of the end flexible links  79  increases the flexibility at the ends of the stent during deployment in curved vessels. The shorter gap G c  will place the central circumferential sets of strut members  61  closer together thereby increasing the stent&#39;s radial strength where there is the highest plaque burden in a dilated arterial stenosis.  
         [0048]    The end sets of strut members  64  consist of alternating curved sections  66  and diagonal sections  65 . The central sets of strut members  61  located longitudinally between the end sets of strut members  64  consist of alternating curved sections  63  and diagonal sections  62 . In the stent  60 , the diagonal sections  65  of the end sets of strut members  64  are shorter and tapered to be wider than the diagonal sections  62  of the central sets of strut members  61 . The shorter diagonal sections  65  will reduce the stiff longitudinal length of metal at the ends of the stent  60  to improve deliverability. The wider diagonal sections  65  of the end circumferential sets of strut members  64  enhance the radiopacity of the ends of the stent  60  where it is most important for accurate placement of the stent relative to a stenosis that is being dilated by the stent. In the stent  60 , the width of the curved sections  63  and  66  may be tapered to improve the ratio of strength to maximum allowed plastic strain. The curved sections  66  or  63  that connect to the ends of the diagonal flexible links  79  and  78  are, in this embodiment, displaced circumferentially by a one-quarter cycle. This is the same as the central portion of FIG. 2B and is defined as a “half-phase” orientation of the circumferential sets of strut members. “Half-phase” is appropriate nomenclature because one-quarter cycle is half way between an in-phase configuration and an out-of-phase configuration.  
         [0049]    The end circumferential sets of strut members  64  have tapered diagonal sections  65 . The tapered diagonal sections  65  and  62  are wider at their center. FIG. 6 is an enlargement of the area  70  of the stent  60  of FIG. 5. As seen more clearly in FIG. 6, the tapered diagonal section  65  has end straight sections  65   e  and central tapered sections  65   c . The tapered section  65   c  begins a distance S from the attachment point  67  of the diagonal section  65  to the curved section  66 . The regions  65   e  have a uniform strut width as opposed to a changing strut width of the diagonal section  65   c  and the curved section  66 . The length “S” of uniform strut width should be approximately between 0.0001″ and 0.0003″.  
         [0050]    It is seen that a stent  100  as in FIG. 7 a  has a large degree of stent flexibility by increasing the circumference offset of the flexible links. That is, the start point and end point of the flexible connectors as seen in FIG. 7 a  are transverse to the longitudinal direction. A result of this stent configuration is that the larger the circumferential offset, the larger the rotation of the stent along a rotation axis R as seen in FIG. 7 a . The larger the rotation of the stent, the greater the amount of foreshortening of the stent in the longitudinal direction.  
         [0051]    Any attributes of stent foreshortening can be overcome by providing for a novel type of balloon to be used in conjunction with the stent of the present invention. As seen in FIGS. 7 b, c  and  d , the stent  100  is placed on a balloon which has a twist directly counter that of the unfurling direction of the stent as seen in FIG. 7 a . That is, the stent is helically placed with its pleats along the longitudinal axis so that when the balloon  200  unfurls, it unfurls in the opposite direction of the stent preferential rotation direction. The interaction therefore of the stent and the balloon causes the stent to foreshorten much less than had the stent been placed on a typically pleated balloon. Such a typically pleated balloon is seen in FIG. 7 c.    
         [0052]    A modified type of balloon  300  is also seen in FIG. 7 d . Therein, we see a combination type balloon  300  which has a typical pleat  305  at the center  310  of the balloon but a twisted pleat  320  at the ends  330 ,  340  of the balloon (as compared to the balloon  200  in FIG. 7 b ). This may be preferred in that this type of pleat will only unfurl in the opposite direction at the ends, which is typically where more foreshortening takes place. On the other hand, more uniform unfurling of the balloon will take place at the center of the stent so that any potential “skewing” will not occur at the center of the stent. Various other modifications, adaptations, and alternative designs are of course possible in light of the above teachings. Therefore, it should be understood at this time that within the scope of the appended claims the invention may be practiced otherwise than as specifically described herein.