Patent Publication Number: US-8109991-B2

Title: Endoprosthesis having foot extensions

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/228,621, filed Sep. 16, 2005, which is a continuation in part of U.S. patent application Ser. No. 10/992,976 filed Nov. 19, 2004, which is a continuation in part of U.S. patent application Ser. No. 10/430,644 filed May 6, 2003, issued as U.S. Pat. No. 7,128,756 on Oct. 31, 2006, the entireties of which are herein incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an endoprosthesis for delivery and deployment within a body vessel of a human or animal. More particularly, the invention relates to a stent including at least one annular element having one or more foot extensions for improved performance characteristics and at least one connection element having a biodegradable component. 
     BACKGROUND OF THE INVENTION 
     Stents, grafts and a variety of other endoprostheses are well known and used in interventional procedures, such as for treating aneurysms, for lining or repairing vessel walls, for filtering or controlling fluid flow, and for expanding or scaffolding occluded or collapsed vessels. Such endoprostheses can be delivered and used in virtually any accessible body lumen of a human or animal, and can be deployed by any of a variety of recognized means. One recognized indication of endoprostheses, such as stents, is for the treatment of atherosclerotic stenosis in blood vessels. For example, after a patient undergoes a percutaneous transluminal coronary angioplasty or similar interventional procedure, an endoprosthesis, such as a stent, is often deployed at the treatment site to improve the results of the medical procedure and to reduce the likelihood of restenosis. The endoprosthesis is configured to scaffold or support the treated blood vessel; if desired, the endoprosthesis can also be loaded with beneficial agent so as to act as a delivery platform to reduce restenosis or the like. 
     The endoprosthesis is typically delivered by a catheter delivery system to a desired location or deployment site inside a body lumen of a vessel or other tubular organ. To facilitate such delivery, the endoprosthesis must be capable of having a particularly small cross profile to access deployment sites within small diameter vessels. Additionally, the intended deployment site may be difficult to access by a physician and often involves traversing the delivery system through the tortuous pathway of the anatomy. It therefore is desirable to provide the endoprosthesis with a sufficient degree of longitudinal flexibility during delivery to allow advancement through the anatomy to the deployed site. 
     Generally endoprosthesis&#39; are constructed of multiple rings which are connected either through a connection section or a connection element, wherein the flexibility of the endoprosthesis is controlled by the number of connection sections or elements as well as the thickness of the struts which comprise the rings. Although it is not specifically known how much vessel restenosis can be attributed to stent rigidity, it is know that a reasonably stiff stent may injure the vessel during motion (i.e. pulsatile heart movement). Therefore, it is desirable to produce an endoprosthesis which has good stiffness properties for deployment within a vessel and wherein the stiffness properties of the endoprosthesis can be changed after deployment within a vessel. Therefore, there is a need for an endoprosthesis having multiple connections between the rings to aid in deployment of the endoprosthesis within a vessel, though it is also desirable that the connections can be severed or removed after deployment to provide a more flexible endoprosthesis. 
     Once deployed, the endoprosthesis should be capable of satisfying a variety of performance characteristics. The endoprosthesis should have sufficient rigidity or outer bias when deployed to perform its intended function, such as opening a lumen or supporting a vessel wall. Similarly, the endoprosthesis should have suitable flexibility along its length when deployed so as not to kink or straighten when deployed in a curved vessel. It also may be desirable to vary the rigidity or flexibility of the endoprosthesis along its length, depending upon the intended use. Additionally, it may be desirable for the endoprosthesis to provide substantially uniform or otherwise controlled coverage, e.g., as determined by the ratio of the outer surface of the endoprosthesis to the total surface of the vessel wall along a given length. For example, increased coverage may be desired for increased scaffolding, whereas decreased coverage may be desired for side access to branch vessels. Control of the cross profile and length of the endoprosthesis upon deployment also is desirable, at least for certain indications. 
     Numerous designs and constructions of various endoprosthesis embodiments have been developed to address one or more of the performance characteristics summarized above. For example, a variety of stent designs are disclosed in the following patents: U.S. Pat. No. 4,580,568 to Gianturco; U.S. Pat. No. 5,102,417 to Palmaz; U.S. Pat. No. 5,104,404 to Wolff; U.S. Pat. No. 5,133,732 to Wiktor; U.S. Pat. No. 5,292,331 to Boneau; U.S. Pat. No. 5,514,154 to Lau et al.; U.S. Pat. No. 5,569,295 to Lam; U.S. Pat. No. 5,707,386 to Schnepp-Pesch et al.; U.S. Pat. No. 5,733,303 to Israel et al.; U.S. Pat. No. 5,755,771 to Penn et al.; U.S. Pat. No. 5,776,161 to Globerman; U.S. Pat. No. 5,895,406 to Gray et al.; U.S. Pat. No. 6,033,434 to Borghi; U.S. Pat. No. 6,099,561 to Alt; U.S. Pat. No. 6,106,548 to Roubin et al.; U.S. Pat. No. 6,113,627 to Jang; U.S. Pat. No. 6,132,460 to Thompson; and U.S. Pat. No. 6,331,189 to Wolinsky; each of which is incorporated herein by reference. 
     An additional problem with existing endoprosthesis designs is the difficulty in properly placing the endoprosthesis within a vessel prior to deployment of the endoprosthesis. Current endoprosthesis designs have thinner struts which utilize less radiopaque material and therefore do not appear as well under fluoroscopy. An attempt to address the reduced radiopacity is to include at least one marker band disposed on the delivery device, wherein the marker band may be utilized to indicate an end of the endoprosthesis device or any length there along. Other methods of increasing the radiopacity of an endoprosthesis include the addition of radiopaque markers either disposed upon a surface of the endoprosthesis or within a retaining member associated with endoprosthesis. A shortcoming of present designs is that many are very difficult to manufacture and therefore lead to increased costs. Also, due to size limitations of the radiopaque material used, the markers do not provide sufficient visibility for precise placement. 
     Although the various designs for endoprostheses that have been developed to date may address one or more of the desired performance characteristics, there a remains need for a more versatile design for an endoprosthesis that allows improvement of one or more performance characteristics without sacrificing the remaining characteristics. 
     SUMMARY OF THE INVENTION 
     The purpose and advantages of the present invention will be set forth in and are apparent from the description that follows, as well as will be learned by practice of the invention. Additional advantages of the invention will be realized and attained by the methods and devices particularly pointed out in the written description and claims hereof, as well as from the appended drawings. 
     To achieve these and other advantages in accordance with the purpose of the invention, as embodied herein and broadly described, the invention includes an endoprosthesis for delivery and deployment in a body lumen. The endoprosthesis includes at least one annular element defined by a first set of interconnected strut members, wherein each strut member has a first end and a second end. Preferably, the first end of selected circumferentially-adjacent strut members are interconnected to define apices proximate a first longitudinal side of the first annular element and the second end of selected circumferentially-adjacent strut members are interconnected to define apices proximate a second longitudinal side of the first annular element. The annular element further includes a foot extension extending between a pair of circumferentially-adjacent strut members. The foot extension has a first foot portion extending circumferentially from the first end of one of the circumferentially-adjacent strut members of the pair and a second foot portion extending circumferentially from the first end of the other of the circumferentially-adjacent strut members. The first and second foot portions are joined at a toe portion of the foot extension, and generally define an apex between the pair of circumferentially-adjacent strut members. 
     Preferably, the endoprosthesis of the invention further includes a second annular element defined by a second set of interconnected strut members, wherein each strut member of the second annular element also has a first end and a second end. Circumferentially-adjacent strut members are interconnected to define apices on opposite sides of the second annular element. The first annular element and the second annular element are aligned longitudinally adjacent to each other along a longitudinal axis and connected to each other at least one connection location. The second annular element also can include a foot extension. Additional annular elements also can be provided. 
     The annular elements are generally expandable between a delivery configuration and a deployed configuration. Each annular element can be defined as a continuous closed ring, or as a coiled sheet or the like. Preferably, each strut member is a straight member, aligned to be substantially parallel with the longitudinal axis of the endoprosthesis when in the delivery configuration. Selected strut members can have a uniform width or can have varied width, such as a continuous taper or increased midsection width between the opposite ends of the strut member. The apices on either side of each annular element that are not defined by a foot extension can have a V-shape, an arcuate shape, or another shape as desired. 
     The foot extension is contoured to provide at least two areas of flexure, and extends circumferentially at an angle relative to the longitudinal axis of the annular element. The foot extension can include straight portions, curved portions or combinations thereof to define an ankle portion, a toe portion, a base portion and a heel portion. The base portion can be a straight member, or contoured as a V-shape or the like. In a preferred embodiment, the foot extension has an average width greater than that of the remaining strut members of the annular element. With the foot extension located between longitudinally-adjacent annular elements, the base portion of the foot extension generally faces the longitudinally-adjacent annular element. 
     Preferably, the connection location between the longitudinally-adjacent annular elements includes the foot extension. By providing the connection location at the base portion of the foot extension, the apices proximate a side of the first annular element generally can be arranged circumferentially out of alignment, or less than 180 degrees out of phase, with the apices proximate a facing side of the second annular element. The connection location can be defined by an overlapping pattern between the longitudinally-adjacent annular elements, such as the base of a foot extension on one annular element and a corresponding apex on the other annular element. Alternatively, the connection location can include a connector extending between the annular elements. The connector can be a straight member or a shaped member, with opposites ends circumferentially either in or out of alignment, as desired. In a preferred embodiment, the connector has an L-shape, with one leg longer than the other leg. It is further contemplated that the connector may be partially or fully constructed of a bioabsorbable material, wherein after deployment within a vessel, the bioabsorbable component of the connector is absorbed thereby changing the stiffness of the endoprosthesis. In a preferred embodiment, a plurality of connection locations are provided between the adjacent annular elements, with a foot extension provided at some or all of the connection locations. The plurality of foot extensions can all extend in the same circumferential direction, or can be arranged to extend in opposing circumferential directions. 
     A radiopaque material preferably is incorporated in at least a portion of the endoprosthesis. For example, at least one of the annular elements can comprise radiopaque material. Alternatively, radiopaque markers can be attached to at least one of the annular elements, or the annular elements can be formed of radiopaque material. As another example, at least one of the annular elements can be formed with a first layer of base material and a second layer of radiopaque material. 
     In accordance with the present invention there is provided an endoprosthesis for delivery in a body lumen comprising a first set of interconnected strut members defining a first annular element, each strut member of the first annular element including a first end and a second end; a second set of interconnected strut members defining a second annular element, each strut member of the second annular element including a first end and a second end; the first annular element and the second annular element aligned longitudinally adjacent to each other along a longitudinal axis and connected to each other at at least one connection location, the first and second annular elements being expandable between a delivery configuration and a deployed configuration; at least one of the first and second annular elements including a foot extension extending between at least one pair of circumferentially-adjacent strut members, the foot extension including a first foot portion extending circumferentially from the first end of one of the circumferentially-adjacent strut members of the pair and a second foot portion extending circumferentially from the first end of the other of the circumferentially-adjacent strut members, the first and second foot portions joined at a toe portion of the foot extension, the first and second annular elements forming a generally tubular member having open ends; and a marker associated with one of open ends of the generally tubular member. 
     In accordance with the present invention there is provided an endoprosthesis device for delivery in a body lumen, comprising a thin-walled, generally tubular member having open ends with a first diameter and a second diameter; and at least one marker element connected to at least one end of the thin-walled generally tubular member, the at least one marker comprising a marker housing and a rivet, the rivet extending generally beyond an outer surface and an inner surface of the substantially tubular member. 
     In accordance with the present invention there is provided a method of manufacturing an endoprosthesis device, comprising the steps of (a) forming an endoprosthesis for delivery in a body lumen (b) smoothing surfaces of the endoprosthesis by media blasting (c) polishing the surfaces of the endoprosthesis with an electropolishing process (d) disposing a radiopaque marker within an opening formed within a structure of an endoprosthesis device (e) applying a force to said marker, thereby forming two heads on the marker, wherein each of the heads extends beyond and inner and an outer surface of the endoprosthesis device. The method may further include the step of passivation, either prior to placing the marker within the opening or after placement or any combination thereof. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and are intended to provide further explanation of the invention claimed. 
     The accompanying drawings, which are incorporated in and constitute part of this specification, are included to illustrate and provide further understanding of the device of the invention. Together with the description, the drawings serve to explain the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a representative embodiment, in planar format, of an endoprosthesis in accordance with the invention. 
         FIGS. 2   a  through  2   e  show detail views, in planar format, of various exemplary foot extensions in accordance with the present invention. 
         FIG. 2   f  is an exemplary embodiment of bio-absorbable connectors in accordance with the present invention. 
         FIGS. 3 through 10  show alternative representative embodiments of the present invention in planar format, each of an endoprosthesis having annular elements connected at a plurality of connection locations by connectors. 
         FIGS. 11 through 13  show detail views of various connector alternatives. 
         FIGS. 14   a  through  14   e  show detail views, in planar format, of various alternative connector relationships between adjacent annular elements. 
         FIGS. 15 through 24  show alternative representative embodiments of the present invention in planar format, each of an endoprosthesis having annular elements connected at a plurality of connection locations without connectors. 
         FIGS. 25   a  through  25   f  illustrate alternative embodiments of the present invention, wherein a marker housing and a marker are shown to be associated with the endoprosthesis. 
         FIGS. 26 and 27   a  through  27   d  are detail views, in planar format, showing various embodiments of overlapping patterns of adjacent annular elements defining connection locations. 
         FIG. 28  shows a representative embodiment, in planar format, of an endoprosthesis configured to have varied characteristics along its length. 
         FIGS. 29   a  through  29   f  respectively show a preferred embodiment of a self-expanding stent in accordance with the present invention, (a) in planar format, (b) in a front-half side view as cut and polished from a tube, (c) in a front-half side view of a delivery configuration, (d) in a front-half side view of a deployed configuration, (e) in a perspective view of a deployed configuration, and (f) in a side view as deployed in a curved vessel. 
         FIGS. 30   a  through  30   f  respectively show a preferred embodiment of a balloon expandable stent in accordance with the present invention, (a) in planar format, (b) in a front-half side view as cut and polished from a tube, (c) in a front-half side view of a delivery configuration, (d) in a front-half side view of a deployed configuration, (e) in a perspective view of a deployed configuration, and (f) in a side view as deployed in a curved vessel. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In accordance with the present invention, an endoprosthesis is provided for delivery within a body lumen of a human or animal. The endoprosthesis can include, but is not limited to, stents, grafts, valves, occlusive devices, trocars, aneurysm treatment devices, or the like. The endoprosthesis of the present invention can be configured for a variety of intralumenal applications, including vascular, coronary, biliary, esophageal, urological, gastrointestinal or the like. 
     Generally, the endoprosthesis of the present invention includes a first set of interconnected strut members defining a first annular element, wherein each strut member of the first annular element include a first end and a second end. The endoprosthesis also includes a foot extension extending between a pair of circumferentially-adjacent strut members. As described further below, the foot extension has a first foot portion extending circumferentially from the first end of one of the circumferentially-adjacent strut members and a second foot portion extending circumferentially from the first end of the other of the circumferentially-adjacent strut members. The first and second foot portions are joined at a toe portion of the foot extension. 
     Preferably, and as embodied herein, the endoprosthesis further includes at least a second set of interconnected strut members defining a second annular element. The endoprosthesis can include additional annular elements defined by interconnected strut members as desired or needed. Each annular element generally defines a structure extending circumferentially about a longitudinal axis. The cross profile of each annular element preferably is at least arcuate, and more preferably either circular or spiral, although alternative cross profiles, such as rectilinear or the like, can be used if desired. 
     The first annular element is aligned longitudinally adjacent to the second annular element along the longitudinal axis, and connected to each other at at least one connection location. Preferably, the first and second annular elements generally define a tubular structure. For example, each annular element can define a continuous closed ring such that the longitudinally-aligned annular elements form a closed tubular structure having a central longitudinal axis. Alternatively, each annular element can define an open ring such that a rolled sheet or open tubular type structure is defined by the annular elements. Furthermore, each annular element can define a 360 degree turn of a helical pattern, such that the end of one annular element can be joined with the corresponding end of a longitudinally-adjacent annular element to define a continuous helical pattern along the length of the endoprosthesis. 
     Each strut member of the annular elements includes a first end and a second end. The strut members of each annular element are disposed circumferentially adjacent to each other, and interconnected so as to define an expandable structure. For example, and with reference to the closed tubular structure above, circumferentially-adjacent strut members of each annular element can be interconnected, either directly or indirectly, in an end-to-end format to define a continuous ring having a generally circular cross profile. By altering the angle or distance defined between circumferentially-adjacent strut members, the tubular structure can be radially expanded between a delivery configuration and a deployed configuration. As discussed in detail below, the expandable structure can be expanded by the application of an external force, such as by a balloon, or by a change in delivery conditions, such as an increase in temperature or the removal of a restraint, so as to allow the structure to self expand. 
     With reference to  FIG. 1 , for purpose of illustration and not limitation, a representative embodiment of an endoprosthesis  100  of the present invention in a deployed configuration is depicted in a planar format for clarity. As shown in  FIG. 1 , the endoprosthesis includes a plurality of annular elements  10  aligned longitudinally adjacent to each other along a longitudinal axis  15 . Although only one annular element need be provided in accordance with the invention, it is preferable that the endoprosthesis includes a plurality of annular elements  10 , depicted herein for purpose of illustration by at least a first annular element  10 ′ and a second annular element  10 ″. 
     Each annular element includes a set of interconnected strut members  20 , which are disposed circumferentially about longitudinal axis  15 . Each strut member has a first end  22 ′ and a second end  22 ″, referenced generally as end  22 . The first end  22 ′ of selected circumferentially-adjacent strut members  20  are interconnected to define apices  30  proximate a first longitudinal side  12  of each annular element  10 , and the second end  22 ″ of selected circumferentially-adjacent strut members  20  are interconnected to define apices  30  proximate a second longitudinal side  14  of the annular element. In this manner, each annular element  10  can be expanded to a deployed configuration as shown in  FIG. 1  by altering or “opening” the angle defined between circumferentially-adjacent strut members  20 . It also is recognized in the embodiment of  FIG. 1  that circumferentially-adjacent apices  30  on each side  12 ,  14  of the annular element  10  are spaced apart by a circumferential distance D, such that each annular element is expanded by increasing the distance D between circumferentially-adjacent apices  30 . At any given condition between the delivery configuration and the deployed configuration, the distance D can be balanced or constant from one set of circumferentially-adjacent apices to the next, or can be varied if desired. 
     As shown in  FIG. 1 , certain apices  30  on each side of the annular element  10  can be defined by interconnecting corresponding ends  22  of circumferentially-adjacent strut members directly together to form a zig-zag pattern of alternating V-shapes when deployed. Alternatively, an apex member can be provided between the corresponding ends of adjacent strut members to form a contoured apex, such as by using a straight apex member to form a flat apex as disclosed in U.S. Pat. No. 6,113,627 to Jang, or a curved apex member to form an arcuate apex as disclosed in U.S. Pat. No. 5,514,154 to Lau. 
     In the representative embodiment of  FIG. 1 , the strut members  20  of each annular element  10  are interconnected with adjacent strut members  20  to form a continuous closed ring, such as depicted more clearly in  FIGS. 29   e  and  30   e . As previously noted, however, each annular element can define an open ring to form a rolled sheet or open tubular type structure as described further with regard to  FIG. 3 , or can define adjacent turns of a continuous helical pattern as described with regard to  FIG. 25 , for purpose of illustration. 
       FIG. 1  also depicts each strut member  20  of the annular element  10  as a straight member. Preferably, when in the delivery configuration, the straight strut members  20  are generally aligned parallel with the longitudinal axis  15 , as well as with each other, as shown for example in  FIGS. 29   c  and  30   c . Although not shown, alternative strut member shapes can be used in addition to or in lieu of the straight strut members, such as L or V-shaped strut members or the like as is known in the art. Also, the number of strut members included in each annular element will depend upon the size and desired characteristics of the endoprosthesis. For example, a greater number of strut members and interconnecting apices can be provided for increased coverage of the vessel wall by the endoprosthesis or increased cross profile of the endoprosthesis in the deployed configuration. 
     Similarly, the radial bias or rigidity of each annular element can be controlled or varied by altering the shape or size of the strut members. For example, radial bias or rigidity of an annular element, when deployed, generally can be increased by decreasing the length or by modifying the cross sectional profile of selected strut members of the annular element. It therefore is possible to provide an endoprosthesis in accordance with the present invention having varied radial bias or rigidity along its length by providing one annular element with a radial bias or rigidity that is different from the radial bias or rigidity of another annular element as shown in  FIGS. 12   b  and  28  and described further below. In a similar manner, it is possible to provide an endoprosthesis having a tapered or flare shape formed of adjacent annular elements having different cross profiles when in the deployed configuration but similar or uniform radial bias or rigidity along its length. 
     Further in accordance with the present invention, and as previously noted, at least one annular element includes a foot extension extending between at least one pair of circumferentially-adjacent strut members. The foot extension can thus define an apex between the pair of circumferentially-adjacent strut members of the annular element. The foot extension includes a first foot portion extending circumferentially from an end of one of the adjacent strut members and a second foot portion extending circumferentially from a corresponding end of the other of the circumferentially-adjacent strut members. In combination, the first and second foot portions generally define an ankle portion, a toe portion, a base portion and a heel portion of the foot extension, which in combination define a generally circumferentially-directed apex. 
     With reference to the exemplary embodiment of  FIG. 1 , for illustration and not limitation, foot extension  40  extends between a pair  24  of adjacent strut members  20  of each annular element  10 . As depicted for purpose of illustration, the foot extension  40  includes a first portion  41  extending circumferentially from an end  22  of one of the adjacent strut members  20 , and a second portion  43  extending circumferentially from the corresponding end  22  of the other of the adjacent strut members  20 . The juncture of the first and second foot portions  41 ,  43  defines a circumferentially-extending toe portion  48  of the foot extension  40 . Similarly, and for purpose of discussion and not limitation,  FIG. 1  shows that an ankle portion  44  is defined proximate the juncture of the first foot portion  41  with one of the circumferentially-adjacent strut members  20 , and that a heel portion  42  is defined proximate the juncture of the second foot portion  43  with the other of the circumferentially-adjacent strut members  20 . The toe portion  48  extends in a first circumferential direction a distance greater than the heel portion  42  of the foot extension  40  extends in an opposite circumferential direction. In the embodiment of  FIG. 1 , the entirety of the foot extension  40  extends in the circumferential direction of the toe portion  48 . Furthermore, at least one of the first and second foot portions  41 ,  43  defines a base portion  46  at or proximate to the corresponding side  12  or  14  of the annular element  10 . Defined generally within the boundary of the first and second portions  41 ,  43  is an open foot region  49  (see also,  FIG. 2   a ). 
     A variety of configurations can be used for the foot extension in accordance with the present invention. For purpose of illustration and comparison with the foot extension of  FIG. 1 , exemplary embodiments of various alternative foot extension configurations are depicted in  FIGS. 2   a  through  2   e.    
     For example, the foot extension of the invention generally extends from the pair of circumferentially-adjacent strut members circumferentially at an angle relative to a line parallel to the longitudinal axis of the annular element.  FIG. 1  shows a foot extension generally extending circumferentially at an angle of about 90 degrees relative to the longitudinal axis  15 . However, the foot extension can be configured to extend circumferentially at an angle of less than 90 degrees relative to the longitudinal axis, as shown for example in  FIG. 2   a.    
     Additionally,  FIG. 1  shows a foot extension  40 , wherein the first foot portion  41  and the second foot portion  43  are generally parallel, straight elongate portions joined by curved portions. Particularly, the base portion  46  is defined by a generally straight portion and each of the toe portion  48 , the ankle portion  44  and the heel portion  42  is defined by a curved portion. Each portion of the foot extension  40 , as well as each of the circumferentially-adjacent strut members  20 , has a substantially uniform width W and thickness in the embodiment of  FIG. 1 . In this manner, the circumferentially-adjacent strut members  20  will be substantially parallel to the longitudinal axis  15  and to each other, and region  49  will be substantially closed when in the delivery configuration. As depicted in  FIG. 1 , the foot extension  40  will thus generally define at least two areas of flexure between the pair of circumferentially-adjacent strut members  20 ; that is, one at the heel portion  42  and one at the ankle portion  44 . An additional, or alternative, area of flexure can be defined at the toe portion  48  if desired to facilitate further expansion between the pair of circumferentially-adjacent strut members  20 , such as to define a three point hinge configuration. 
       FIG. 2   a  depicts a preferred embodiment of a foot extension similar to that of  FIG. 1 . As previously noted, however, the foot extension  40  of this embodiment extends circumferentially at an angle alpha less than 90 degrees relative to the longitudinal axis  15 . Additionally, the first and second foot portions  41 ,  43  are generally parallel but spaced apart to define a relatively more open region  30  than that of the foot extension of  FIG. 1 . To control expansion of the annular element, the width of the foot extension and circumferentially-adjacent strut members can be varied accordingly. For example, and as previously noted, circumferentially-adjacent apices along each side of the annular element  10  are spaced apart by a circumferential distance D, wherein the distance D generally increases as the annular element is expanded. It is often desirable to balance an annular element so as to expand uniformly, wherein the distance D increases a similar amount and at a similar rate between each pair of circumferentially-adjacent apices. Due to the increased flexure facilitated by the foot extension similar of  FIG. 1 , the distance Df between the circumferentially-adjacent apices located at the end of the pair  24  of circumferentially-adjacent strut members  20  opposite the foot extension  40  can increase to an extent or at a rate greater than the distance Da between other circumferentially-adjacent apices of the annular element. By providing the first and second foot portions  41 ,  43  of the foot extension with an average width greater than the average width of the circumferentially-adjacent strut members  20 , as shown in  FIG. 2   a , the expansion between the circumferentially-adjacent apices  30  can be controlled or even balanced if desired. For example, and as shown in  FIG. 2   a , the first and second foot portions  41 ,  43  can be provided with a substantially constant width. Alternatively the first foot portion  41  can be provided with a width W 1  different than that W 2  of the second foot portion  43 . 
     As previously noted with regard to the exemplary embodiment of  FIG. 1 , the circumferentially-adjacent strut members  20  and the different portions of the foot extension  40  can be provided with a substantially uniform width and thickness throughout. If the foot extension is provided with an increased width, it may be desirable or necessary to distribute stress or eliminate stress concentrations in the pair of circumferentially-adjacent strut members  20 . As embodied in  FIG. 2   a , at least one or both strut member  20  of the pair  24  of circumferentially-adjacent strut members can be provided with a varied width. For example, and as shown in  FIG. 2   a , each strut member of the pair  24  of circumferentially-adjacent strut members can be tapered from a first width W′ substantially similar to or even greater than that of the foot extension at the first end  22 ′ of the strut member to a second width W″ substantially similar to or even greater than that of the adjacent strut member  20  connected at the second end  22 ″. 
     To further control expansion of the annular element, selected apices along the same longitudinal side  12 ,  14  of the annular element  10  as the foot extension also can be modified. For example, an apex  30  can be relaxed by reducing its width to facilitate greater expansion, or stiffened by increasing its width to facilitate less expansion. As shown in  FIG. 2   a , the width of selected apices  30   rw  are reduced to relax the apex  30  and thus control, such as balance, expansion of the annular element as needed or desired. 
     Furthermore, selected apices on the same side of the annular element as the foot extension can be configured to accommodate additional features. For example, and in accordance with another aspect of the present invention, it is desirable to enhance retention of a balloon expandable endoprosthesis on a balloon delivery system. As shown in  FIG. 2   a , the foot extension  40  extends in a first circumferential direction, and a circumferentially-adjacent apex  30   a  is located proximate the foot extension  40  in the first circumferential direction. When in the delivery configuration, this circumferentially-adjacent apex  30   a  is longitudinally aligned with, and preferably can substantially contact, the toe portion  48  of the foot extension so as to define a gap G between the circumferentially-adjacent strut members  20 . Balloon material of the delivery system thus can be captured within this gap G, during crimping or through known heat treatment techniques, to enhance stent retention on a balloon. Additionally, or alternatively, a gap can be defined within an enlarged region  49  of the foot extension  40  for similar stent retention purposes if desired. 
       FIG. 2   b  depicts yet another foot extension configuration in accordance with the invention. The first foot portion  41  of the foot extension  40  is generally angled relative to the second foot portion  43 , rather than aligned in parallel as shown in  FIG. 1 . Additionally, the second foot portion  43  is generally V-shaped to define a base portion  46  extending substantially perpendicular to the longitudinal axis, but with a more angular heel portion  42  than that of  FIG. 1 . In this manner, the first and second foot portions define an enlarged open region  49  relative to that of  FIG. 1 . As with  FIG. 2   a , the embodiment of  FIG. 2   b  includes a foot extension  40  having an increased average width and tapered circumferentially-adjacent strut members, as well as a longitudinally-aligned apex  30   a  circumferentially adjacent to the toe portion  48  of the foot extension  40  for enhanced retention on a balloon delivery system. 
       FIG. 2   c  depicts an alternative preferred embodiment of the foot extension of the present invention. The foot extension  40  of this embodiment is provided with a generally rectilinear configuration, including a first foot portion  41  extending from the ankle portion  44  to the toe portion  48  of the foot extension, and a second foot portion  43  extending from the heel portion  42  to the toe portion  48 . Particularly, the second foot portion defines a contoured base portion  46 , such as a generally V-shape including a first portion  46 ′ and a second portion  46 ″. In this manner, the foot extension can be configured to provide an additional area of flexure for expansion of the annular element if desired, as well as to define a connection location for longitudinally-adjacent annular elements as described further below. 
     As with the embodiments of  FIGS. 2   a  and  2   b , the first and second foot portions  41 ,  43  of  FIG. 2   c  are provided with an increased width to stiffen the apex defined by the foot extension  40 , and thus control, and more preferably, balance expansion of the annular element  10 . For example, in one preferred embodiment, the width W 1  of the first foot portion  41  and the width W 2 ′ of the first portion  46 ′ of the V-shaped base portion are equal to each other, but different than the width W 2 ″ of the second portion  46 ″ of the V-shaped base portion. Unlike the embodiment of  FIGS. 2   a  and  2   b , which are particularly advantageous in combination with a balloon delivery system, the embodiment of  FIG. 2   c  does not include a longitudinally-aligned apex circumferentially adjacent the toe portion of the foot extension. Rather, and as recognized from  FIG. 2   c , at least the apex  30   a  located circumferentially proximate the toe portion  48  of the foot extension  40  is positioned longitudinally so as to mate with the foot extension when in the delivery configuration. For example, and as shown in  FIG. 2   c , this can be accomplished by providing at least one of the strut members  20  of the pair  24  of circumferentially-adjacent strut members with a length greater than the length of the remaining strut members of the annular element. The mating configuration between the foot extension  40  and the circumferentially adjacent apex  30   a  facilitates a reduced cross profile of the annular element  10  when in the delivery configuration. This embodiment is particularly advantageous for an endoprosthesis to be delivered within extremely small vessels, such as certain coronary or neurovascular vessels, or for an endoprosthesis that can be contained within a sheath during delivery, such as a self-expanding stent. 
       FIG. 2   d  is a enlarged detail view of a more rounded version of a foot extension similar to that of  FIG. 2   c , which is depicted with dashed lines for purpose of comparison. Particularly,  FIG. 2   d  demonstrates the used of more rounded contours to shift or eliminate stress concentrations that may occur during expansion. 
       FIG. 2   e  depicts another alternative embodiment of a foot extension the present invention, which incorporates the mating configuration of the foot extension and the circumferentially adjacent apex as described with regard to  FIG. 2   c . Unlike the embodiment of  FIG. 2   c , however, the strut members  20  connected to the circumferentially adjacent apex  30   a  are provided with a length less than that of the remaining strut members so as to accommodate the desired mating relationship between the apex  30   a  and the foot extension  40 . Furthermore,  FIG. 2   e  shows that at least the circumferentially adjacent apex  30   a  is relaxed, such as by providing a reduced width, to open at a greater angle and thus compensate for the decrease of the distance D that would otherwise result during expansion due to the reduced length of the corresponding strut members  20 . As previously described, expansion of the annular element  10  thus can be controlled, and more preferably, balanced. The strut members  20  having a reduced length and the circumferentially-adjacent apex  30   a  also can be provided with a reduced width if desired as shown in  FIG. 2   e.    
     Additional variations of the foot extension are also contemplated. For example, the heel portion of the foot extension can extend in a circumferential direction opposite from the toe, but preferably by a distance less than the distance over which the toe extends in the first direction. 
     Any suitable number of foot extensions can be provided on an annular element in accordance with the present invention. A single foot extension can be provided on an annular element if desired. As shown in the embodiment of  FIG. 1 , however, it is preferable to define a plurality of apices of an annular element with foot extensions  40 , wherein each foot extension extends between a pair  24  of circumferentially-adjacent strut members. The foot extensions can be provided on both longitudinal sides  12 ,  14  of the annular element  10  as shown in  FIG. 1 , or only on a single side of an annular element as shown in  FIG. 8 . Additionally, and as further shown in  FIG. 8 , it is possible to combine an annular element having one or more foot extensions with another annular element having no foot extension if desired. The plurality of foot extensions, if provided, can all extend in the same circumferential direction, or in opposite circumferential directions if desired. For example, and as shown in  FIG. 1 , the foot extensions on one longitudinal side of each annular element can extend in one direction circumferentially  17 , whereas the foot extensions on the other side of the annular element extend in the opposite circumferential direction. In other embodiments, such as  FIG. 6 , all foot extensions  40  can extend in the same circumferential direction, either clockwise or counterclockwise when viewed from one end of the endoprosthesis, regardless of the longitudinal side  12 ,  14  of the annular elements  10  on which the foot extensions  40  are disposed. 
     When a plurality of foot extensions are provided on an annular element, the foot extensions can be evenly spaced along the corresponding side of the annular element as shown in  FIG. 1 , or can be spaced in a staggered fashion as shown in  FIG. 4 . The number of apices that are not defined by a foot extension along the corresponding side of the annular element, and thus disposed between foot extensions, will depend upon the total number of apices desired for the annular element and the total number of such apices to be defined by a foot extension. 
     Further in accordance with the present invention, and as previously noted when a plurality of annular elements is provided, the first annular element and the second annular element are connected to each other at a connection location. A single connection location can be provided between two adjacent annular elements, or a plurality of connection locations can be provided as preferred. Furthermore, and as described below, the connection location can include one or more connectors extending between adjacent annular elements, or the connection location can be defined by an overlapping geometric pattern of two adjacent annular elements. 
     Preferably, the connection location includes a foot extension. As previously noted, each foot extension defines at least two areas of flexure. Such areas of flexure generally are located in the ankle, toe or heel portions of the foot extension. As such, the foot extension can facilitate greater longitudinal flexibility when included at the connection location between two adjacent annular elements. The multiple areas of flexure of the foot extension can also compensate for foreshortening when disposed at the connection location. As the annular element is expanded, the foot extension can be configured to open in a manner to adjust or compensate for some or all of the change that occurs in the longitudinal dimension of the annular element. That is, the foot extension can be configured to have a first longitudinal dimension when in the delivery configuration, and to straighten or retract, as deemed necessary, so as to have a second longitudinal dimension when in the deployed configuration. The difference between the first longitudinal dimension and the second longitudinal dimension of the foot extension preferably is substantially equivalent to the corresponding change in the longitudinal dimension of the annular element. Similarly, the foot extension can be stiffened by increasing the width of one or both of the first and second foot portions, or by otherwise altering the geometry of the foot extension in a suitable manner, to reduce the amount in which the foot extension opens, and thus reduce the extent of related foreshortening that occurs at the connection location. 
     Additionally, when located on a corresponding side between longitudinally-adjacent annular elements, the foot extension of one annular element includes a base portion generally facing the other annular element. The base portion provides an elongated region in which a connection location can be disposed, thus increasing versatility for design alternatives. For example, one alternative for increasing coverage provided by a stent is to configure corresponding zig-zag or sinusoidal patterns of longitudinally-adjacent annular elements less than 180 degrees out of phase with each other. That is, with the first side of a first annular element longitudinally adjacent the second side of a second annular element, it can be desirable for the apices proximate the first side of the first annular element to be circumferentially out of alignment with the apices proximate the second side of the second annular element. The foot extensions of the present invention allow such circumferential offset between longitudinally adjacent apices, even without the use of a connector. The foot extension of the present invention therefore enables greater axial flexibility, foreshortening compensation, radial expansion and coverage of the endoprosthesis. 
     With reference again to  FIG. 1 , a plurality of connectors  60  are provided to connect adjacent annular elements  10  at a plurality of connection locations  50 . Each connection location  50  of  FIG. 1  includes a foot extension  40  of one annular element and an apex  30  of another annular element, with a connector  60  having opposite ends  62  connected therebetween. If desired, however, the connection location  50  can extend from a foot extension to a foot extension, or from an apex to an apex, or to a strut member of one or both annular elements if desired. As embodied in  FIG. 1 , each foot extension  40  generally has a circumferentially elongated base portion  46  facing an adjacent annular element  20 . With a connector  60  extending longitudinally from the base portion  46  of a foot extension  40  to an apex  30 , the longitudinally-adjacent apices  30  of adjacent annular elements are circumferentially out of alignment. The foot base portions  46  at the longitudinal ends  102 ,  104  of the endoprosthesis  100  face outward from the remainder of the structure. Preferably, one or more foot extensions at either end  102 ,  104  of the endoprosthesis includes an area that undergoes minimal deformation or strain, such as the base portion  46 , when expanded to the deployed configuration. A wire or strip of radiopaque material can be wrapped around or otherwise secured to this area of minimal strain so as to act as a radiopaque marker  120  for imaging purposes. Alternatively, a marker tab or eyelet can be attached at one or both ends of the endoprosthesis as described in detail with reference to  FIG. 25 , below. 
     For simplicity and clarity, each connector depicted in  FIG. 1  is a straight member. It is recognized, however, that the connector can be contoured or shaped to increase longitudinal flexibility if desired, as shown in  FIGS. 11-13  and described further below. Similarly, the connectors need not extend parallel to the longitudinal axis, but can be aligned diagonally or helically such that the ends of the connector are circumferentially offset as shown for purpose of example in  FIGS. 14   b  and  14   d - 14   e.    
     A variety of design alternatives for different endoprosthesis embodiments can be achieved by selectively combining the various aspects of the present invention. For purpose of illustration and not limitation, a number of exemplary embodiments including the combination of connectors with foot extensions of the present invention are depicted in planar format in  FIGS. 3-10 . As with the embodiment of  FIG. 1 , the connectors are depicted as straight members for clarity and simplicity, but any connector configuration can be used as desired. 
     The connectors  60  may be constructed of the same or similar material of which the annular elements  10  are constructed of, or alternatively, the annular elements  10  may be constructed individually as described herein, wherein the connectors  60  are disposed at connection locations  50  thereby forming an endoprosthesis having more than one annular member. In this alternative embodiment, the connectors  60  may be constructed fully of a bio-absorbable material, partially of a bio-absorbable material or of a different material than that of the annular elements  10 . 
     By forming the connectors  60  of a bio-absorbable material mechanical properties of the endoprosthesis can be tuned or adjusted accordingly. For example, a greater number of connectors  60  may be utilized to connect the annular rings  10  together, thereby providing greater column strength for delivery of the endoprosthesis. Once the endoprosthesis has been placed within a vessel or artery, the connectors  60  would then be absorbed thereby allowing each of the annular rings to move independent of one another. By having each of the annular rings  10  able to move independently of one another the flexibility of the endoprosthesis is greatly improved which may lead to a reduction of restenosis. It is further contemplated that individual connectors  60  may be constructed of different bio-absorbable materials, wherein pairs of connectors  60  or individual connectors  60  may be absorbed at different rates. Additionally, pairs of connectors  60  or single connectors  60  may be constructed of non-absorbable materials, wherein the absorbable connectors provide column strength during delivery of the endoprosthesis and the non-absorbable connectors provide connection points between the individual annular rings  10  thereby preventing the annular rings  10  from moving independently, though still providing increased flexibility of the expanded endoprosthesis from the reduction of connectors  60 . 
     The bio-absorbable material of which the connectors  60  may be constructed of may be an inert material, a beneficial agent, or a combination of the two. An example of a suitable beneficial agent is described in U.S. Pat. No. 6,015,815 and U.S. Pat. No. 6,329,386 entitled “Tetrazole-containing rapamycin analogs with shortened half-lives”, the entireties of which are herein incorporated by reference. It shall be understood that more than one beneficial agent may be combined with one or more inert materials to form the connectors  60 . Examples of suitable bio-absorbable materials include Polygycolic acid (PGA), Polyhydroxybutyric acid, PolyL-Lactic acid (PLLA), Polydilactidel glycolide, Polydilactid acid, PolyDL lactide-co-gycolide. 
     Referring now to  FIG. 2   f  there is shown an alternative embodiment of the connectors  60  in accordance with the present invention. As shown in  FIG. 2   f , the connectors  60  are provided to connect adjacent annular elements  10  at a plurality of connection locations  50 . Each connection location  50  of  FIG. 1  includes a foot extension  40  of one annular element and an apex  30  of another annular element, with a connector  60  having opposite ends  62  connected therebetween. If desired, however, the connection location  50  can extend from a foot extension to a foot extension, or from an apex to an apex, or to a strut member of one or both annular elements if desired. As shown in  FIG. 2   f , the connector  60  is partially constructed having a metallic member  60   a  and a bio-absorbable member  60   b , wherein the bio-absorbable member  60   b  is disposed about the metallic member  60   a . By producing the connector  60  in this manner, the column strength of the endoprosthesis is increased, thereby aiding in tracking and deployment, wherein the bio-absorbable material is then absorbed after deployment and expansion, thereby reducing the column strength of the endoprosthesis. 
     It may be desirable to choose a bio-absorbable material or materials that can be selectively activated to be made absorbable. For example, after expansion of the endoprosthesis within a vessel or artery, an activating agent may be delivered to the site of expansion, whereby the bio-absorbable connectors  60  are activated thereby becoming absorbable. By making the connectors  60  selectively absorbable, the stiffness and column strength of the endoprosthesis can be varied or altered as desired after implantation. For example, if greater flexibility is desired more connectors may be activated to be absorbed. 
     It is further contemplated that the bio-absorbable connectors in accordance with the present invention may be configured to be responsive to radio-frequency (RF) energy or ultrasonic energy, wherein the bio-absorbability of the connectors would be altered in response to applied energy. For example, the absorption rate may be increased or decreased in response to the applied energy; additionally it is contemplated that the connectors may be disconnected from the rings in response to applied energy. Suitable RF devices that may be utilized with the present invention include “The Crosser” from FlowCardia or the “Resolution” from OmniSonics Medical Technologies, Inc. 
     The embodiment of  FIG. 3 , shown in a deployed configuration, is similar to that of  FIG. 1 , but includes a connector extending from each foot extension  40  of one annular element  10  to a longitudinally adjacent apex  30  of another annular element. As previously noted, the endoprosthesis of the invention can be formed as a rolled sheet or similar coiled structure if desired. As depicted in  FIG. 3 , complimentary lateral edges  106 ,  108  can be defined by providing connection locations  50  continuously in longitudinal alignment along the length of the endoprosthesis  100 . Particularly, the connectors  60  and corresponding foot extensions  40  of the connection locations along the lateral edges  106 ,  108  define interlocking projections  109 . The endoprosthesis  100  of this embodiment can be delivered in a contracted, coiled state to a deployment site with the lateral edges  106 ,  108  overlapping each other. Upon deployment, the endoprosthesis  100  will unravel from its coiled state, as well as expand circumferentially from its contracted state due to expansion of the annular elements. Once deployed, the interlocking projections  109  along the lateral edges will engage the “cells”  105  defined in the overlapping layer upon the application of a compressive force to prevent collapse of the endoprosthesis. A “cell”  105  is the opening formed between two circumferentially adjacent connection locations as defined by the closed boundary created by the interconnected struts, and the foot extensions and connectors as provided. Alternative arrangements can be used to define interlocking projections or, if the annular elements are provided with sufficient radial bias or rigidity, no interlocking projections need be provided. 
     The embodiment of  FIG. 4 , shown in a slightly deployed configuration, has free foot extensions  40   a , which are longitudinally free from or unconnected to adjacent annular members, and connected foot extensions  40   b , which are connected to adjacent annular members  10  with connectors  60 . The free foot extensions  40   a  are aligned in the circumferential direction at an angle of about 90 degrees to the longitudinal axis and have substantially slit-shaped foot regions  49   a . The connected foot extensions  40   b  have enlarged foot regions  49   b , for greater radial expansion of the pair  24  of connected strut members, and extend circumferentially at an angle of less than 90 degrees from the longitudinal axis  15 . The connection locations  50  are disposed at selected apices  30  and partway along the foot base portion  46 . The foot base portions  46  of the connected foot extensions  40   b  have two portions  46 ′,  46 ″ oriented at an angle to each other to affect an area of flexure upon expansion. 
     One longitudinal side  12  or  14  of each annular element  10  has pairs of immediately adjacent connection locations  50 . The other longitudinal side of each annular element  10  has connection locations  50  that are spaced from each other by a plurality of apices  30 . Additionally, the foot extensions  40   a ,  40   b  are unevenly spaced along each annular element  10 . Some strut numbers  20  have foot extensions at either end  22  thereof, other strut members  20  include a foot extension  40   a ,  40   b  only at one end, and yet others do not have a foot extension at either end. 
     As with the embodiment of  FIG. 4 , the embodiment of  FIG. 5  has connected foot extensions  40   b  with foot regions  49  that are significantly larger than the foot regions  49  of the free foot extensions  40   a . In this embodiment as shown in a slightly deployed configuration selected apices  30  that are not defined by a foot extension protrude longitudinally more than other such apices for increased coverage. Additionally, the adjacent annular elements are substantially “in phase”, such that longitudinally-adjacent apices of adjacent annular elements are circumferentially offset from each other. The circumferential extent of the connected foot extensions  40   b  allows the annular members to be connected in phase. Thus, the portion  48  of the connected foot members  40   b  preferably extends circumferentially at least or greater than the circumferential station of the connection location of the adjacent annular element  10 . 
     The embodiment of  FIG. 6  includes opposing and connected foot extensions  40  with substantially open foot regions  49 . In the delivery configuration shown in  FIG. 6 , each apex  30   a  that is circumferentially-adjacent a foot extension  40  is positioned to mate with the foot extension in a manner similar to that of  FIG. 2   c . Also, when in the delivery configuration, the strut members  20  are substantially aligned with the longitudinal axis  15  as shown. The embodiment of  FIG. 7  is similar to that of  FIG. 6 , except foot extensions  40  on each annular element  10  circumferentially spaced so as not to include two foot extensions on a single strut member  20 . 
     In the embodiment of  FIG. 8 , which is shown substantially in the delivery configuration, the foot extensions  40  are disposed only on one longitudinal side of each annular element  10 . Preferably, all the foot extensions extend in the same longitudinal and circumferential directions. It is noted that connection locations  50  are evenly spaced circumferentially, with two unconnected apices  30  between circumferentially adjacent connection locations. Each connection location  50  includes a foot extension  40  on one annular element  10  and an apex  30  on the adjacent annular element  10 . Furthermore, the connection locations  50  between adjacent annular elements  10  are circumferentially offset from one set of connected annular elements to the next. 
       FIGS. 9 and 10  depict alternative embodiment in the delivery configuration, wherein connection locations  50  include connectors  60  extending between apices  30  not defined by foot extensions. All of the foot extensions  40  are free or unconnected. In  FIG. 9 , all foot extensions  40  extend in the same circumferential direction; in  FIG. 10 , the foot extensions  40  alternate between clockwise and counterclockwise directions. 
     As previously noted, FIGS.  1  and  3 - 10  depict various endoprosthesis embodiments that include a straight connector between adjacent annular elements for purpose of simplicity and clarity. It is understood, however, that alternative connector shapes can be used within the scope of the invention. For example,  FIG. 11  shows an endoprosthesis in the delivery configuration, which includes a plurality of annular elements connected by substantially sinusoidal connectors  60 . Each annular element  10  includes a plurality of interconnected strut members  20 , wherein every other apex disposed along a longitudinal side  12  and  14  is defined by a foot extension  40 . Each sinusoidal connector  60  extends between a foot extension  40  on one annular element and an apex  30  on an adjacent annular element. The sinusoidal connector includes curved portions  64  between the first and second ends  62 ′,  62 ″ of the connector  60 . In this manner, the longitudinally-adjacent apices of adjacent annular elements can be arranged in circumferential alignment with each other (that is, 180 degrees out of phase) or out of alignment with each other, as preferred.  FIG. 12   a  is directed to an endoprosthesis embodiment similar to that of  FIG. 11 , however, U-shaped connectors, each including a curved portion  64 , are provided in lieu of the sinusoidal connectors. In a further embodiment of the invention, as shown in a slightly deployed configuration in  FIG. 12   b , an endoprosthesis is provided with a connector  60  between foot extensions  40  on longitudinally adjacent apices  30  of adjacent annular elements  10 , in a manner similar to the embodiment of  FIG. 6 . At least one unconnected apex  30  is disposed between circumferentially adjacent foot extensions  40  on each side of the annular element  10 . In this embodiment, however, each connector  60  has a U- or V-shape with at least one curved portion  64 . If desired, the curved portions  64  can all extend in the same circumferential direction, as shown in  FIG. 12   a , or can alternate in circumferential direction from one set of adjacent annular elements to the next as shown in  FIG. 12   b . Furthermore, and as depicted in  FIG. 12   b , the number of connectors, and thus connection locations, between adjacent annular elements can be varied for varied longitudinal flexibility along the length of the endoprosthesis. In another preferred embodiment of the invention an endoprosthesis is provided with the sinusoidal shaped connectors between adjacent annular elements located proximate at least one region of the endoprosthesis as shown in  FIG. 11 , and with the U-shaped connectors between adjacent annular elements located proximate another region of the endoprosthesis, as shown in  FIG. 12   a.    
     In accordance with an additional aspect of the invention, and as shown in  FIG. 13 , an alternative connector  60  is provided having an L-shaped portion  66  between its first and second ends  62 . The L-shaped portion has a first leg  66 ′ and a second leg  66 ″. A bend or circumferential peak  67  is provided between the first and second legs. Preferably, and as shown in  FIG. 13 , the length of the first leg  66 ′ is different than that of the second leg  66 ″. The width of the first leg  66 ′ likewise can be different than that of the second leg  66 ″, as shown if  FIG. 13 . It is preferred that the L-shaped connector be connected between adjacent annular elements  10 , such that the first end  62 ′ of the connector  60  is circumferentially offset from the second end  62 ″ of the connector  60 .  FIG. 13  depicts the L-shaped connectors incorporated in an endoprosthesis embodiment similar to that of  FIGS. 11 and 12 , as shown in the delivery configuration, wherein all of the L-shaped connectors are arranged so as to extend circumferentially in the same direction, as defined by the direction in which the bend  67  of the L-shaped portion  66  extends. 
     The L-shaped connector of this aspect of the invention can be configured to compensate for foreshortening of the endoprosthesis upon deployment, without altering the angle between the first and second legs. That is, the L-shaped connector can be arranged so as to have a first longitudinal dimension when in the delivery configuration, and to rotate relative to the annular elements, as deemed necessary, so as to have a second longitudinal dimension when in the deployed configuration. The difference between the first longitudinal dimension and the second longitudinal dimension of the L-shaped connector preferably is substantially equivalent to the corresponding change in the longitudinal dimension of the annular element to be compensated upon deployment. Rotation of the L-shaped connector can be accomplished or enhanced by weakening the points of connection at either end of the connector with the corresponding annular elements. Furthermore, the degree of compensation, as well as longitudinal flexibility, can be varied by varying the length of the connectors as shown in  FIG. 13 . 
       FIGS. 14   a  through  14   e  show alternative arrangements of the L-shaped connector of the present invention as disclosed in U.S. patent application 60/379,593, which is incorporated in its entirety herein by reference. Particularly, and as shown in  FIGS. 14   a  through  14   e , a plurality of L-shaped connectors can be provided between adjacent annular elements  10  such that selected connectors  60  are arranged to extend circumferentially in opposite directions, as defined by the direction in which the bend  67  of the L-shaped portion is directed. In this manner, the strut members  20  of the annular elements  10  and the connectors form a generally repeating pattern defined by two different, alternating cell shapes. In each embodiment, however, it is recognized that the number of connectors and apices, as well as the dimensions of the components and the angle of alignment between the legs of the L-shaped portion and between the ends of the connector, can be varied to achieve desired characteristics of the stent such as scaffolding, coverage, and flexibility. Although not shown, one or more of the apices of each of these embodiments can be defined by a foot extension in accordance with the invention. 
     For example,  FIG. 14   a  shows circumferentially adjacent L-shaped connectors extending in opposite circumferential directions, wherein each connector  60  is connected between longitudinally adjacent apices  30  of adjacent annular elements  10 .  FIGS. 14   b  and  14   d  show alternative embodiments of an endoprosthesis having L-shaped connectors, wherein the circumferentially-adjacent connectors  60  extend from circumferentially adjacent apices  30  on one annular element  10  to non-adjacent apices  30  on the other annular element  10 . In  FIG. 14   c , the L-shaped connectors extend from respective apices  30  of annular elements  10  to an intermediate location on respective strut members  20  of the annular elements  10 . In  FIG. 14   e , two connectors extend from the same apex  30  of one annular element  10  to different apices  30  on the other annular element  10 . Alternatively, connectors can extend from strut member to strut member without being connected to peaks of the annular members, or two or more connectors can extend from the same apex of both annular elements, respectively Although each of these embodiments depict the selected connectors extending in opposite circumferential directions, it is recognized that the connectors can all be arranged in the same direction as previously shown in  FIG. 13 . 
     Furthermore, the connector peaks  67  can be aligned longitudinally with each other in the circumferential direction, i.e., located on the same transverse plane of the endoprosthesis, but need not be so aligned. In the embodiments having connector peaks that are not aligned, it is contemplated that the endoprosthesis may be more completely or uniformly crimped if the connector peaks  67  extend circumferentially in opposite directions as shown in  FIG. 14   a , because the peaks of adjacent connectors will not interfere with each other. Furthermore, the connection locations  50  and the connectors  60 , if present, on longitudinally-adjacent annular elements  10  are preferably circumferentially displaced with respect to each other to improve flexibility of the stent. However, all of the connection locations can be aligned, if desired. 
     In addition to changing connector shapes, other aspects of the connectors can be altered to facilitate desired performance characteristics for the endoprosthesis. For example, the length and cross-sectional dimensions (e.g., width, thickness) of the connectors can be varied as shown in  FIG. 13 , or the number of connectors between adjacent annular elements can be increased or decreased to alter longitudinal flexibility and coverage accordingly. Hence, longitudinal flexibility can be uniform or varied across the length of the endoprosthesis, as desired. 
     Further in accordance with an additional aspect of the invention, and as previously noted, the connection location between longitudinally-adjacent annular elements need not include a separate connector. Indeed, the connection location can be defined by an overlapping geometric pattern of two adjacent annular elements. As defined herein, “overlapping geometric pattern” and “overlapping pattern” reference the resulting pattern or configuration from two or patterns arranged to share a common surface or area; it does not suggest or require that this overlapping pattern result in an increase in thickness or material of construction. Preferably, the connection location includes a foot extension. 
     For purpose of illustration and not limitation, reference is made to  FIG. 15 , which shows an endoprosthesis substantially similar to that of  FIG. 1 , but without separate connectors.  FIG. 15  shows an endoprosthesis in a deployed configuration including a plurality of annular elements  10 , each having first and second longitudinal sides  14 ,  16  with selected apices defined by foot extensions  40  extending in opposite circumferential directions. Connection locations  50  between the longitudinally-adjacent annular elements  10  are provided by direct connections between opposing foot extensions  40 . As shown in this embodiment, each connection location  50  is generally disposed along the base portion  46  of each foot extension  40  proximate the toe portion  48 , and aligned diagonally or helically along the length of the endoprosthesis. Each foot extension  40  of this embodiment can be construed to define a three point hinge configuration defined generally at the at the toe, heel, and ankle portions  48 ,  42 ,  44 . Furthermore, and as noted with regard to  FIG. 1 , one or more foot extensions at either end  102 ,  104  of the endoprosthesis includes an area that undergoes minimal deformation or strain, such as the base portion  46 , when expanded to the deployed configuration. A wire or strip of radiopaque material can be wrapped around or otherwise secured to this area of minimal strain so as to act as a radiopaque marker  120  for imaging purposes during delivery and deployment. 
     In this embodiment, the strut members  20  that are circumferentially adjacent the foot extensions  40  and within the circumferential extension of the foot extensions  40  when in the delivery configuration are dimensioned so the corresponding apices  30   a  mate with the foot extension  40  as described with regard to the foot extensions of  FIG. 2   c . For example,  FIG. 15  shows two pairs of short strut members  20   a  interconnected sequentially to a medium-length strut member  20   b , a longer strut member  20   c , a medium-length strut member  20   b , two pairs of short strut members  20   a , which connects to the next foot extensions  40 . In the delivery configuration, the medium and longer strut members have apices  30   a  therebetween that are circumferentially displaced from the toe extensions  40 . 
     As with the endoprosthesis embodiments that include a connector for each connection location, a wide variety of alternative endoprosthesis embodiments without connectors at the connection locations are likewise within the scope of the invention. Particularly, and as previously noted, at least one of the first and second foot portions of the foot extension defines a base portion generally facing a longitudinally-adjacent annular element. By defining the connection location as an overlapping pattern of the base portion and a corresponding portion of the longitudinally-adjacent annular element, as shown schematically in  FIG. 26  for clarity, no connector is required. Additionally, and as previously noted, the generally elongate area of the base portion further enables versatility in the circumferential alignment adjacent annular elements, and the multiple areas of flexure of the foot extension enable enhanced longitudinal flexibility between adjacent annular elements without the need for connectors. Furthermore, by eliminating the connectors, an endoprosthesis having more uniform coverage for scaffolding as well as for the delivery of a drug or similar beneficial agent, as described further below, can be provided. 
     A variety of design alternatives for different endoprosthesis embodiments without connectors can be achieved by selectively combining the various aspects of the present invention. For purpose of illustration and not limitation, as well as for comparison with the embodiment of  FIG. 15 , a number of exemplary embodiments including the combination of foot extensions and overlapping patterns at connection locations of the present invention are depicted in planar format in  FIGS. 16-26 . 
     The embodiment of  FIG. 16 , shown substantially in a delivery configuration, includes a plurality of annular elements  10 , wherein each longitudinal side of an annular element has 16 apices. In this embodiment, four apices on a selected side, e.g.  12 , of adjacent annular elements  10  are defined by a foot extension  40 , wherein the foot extensions  40  extend in the same longitudinal direction but in alternate circumferential directions from one annular element  10  to the next. Each foot extension  40  is configured substantially similar to that of  FIG. 2   c , wherein the base portion  46  is contoured to include first and second portions. The contoured pattern of the base portion  46  of each foot extension  40  overlaps with the pattern of an apex  30  of the circumferentially-adjacent annular element. Hence, four connection locations  50  are provided between longitudinally-adjacent annular elements  10 , with three apices  30  disposed between the connection locations  50  along the corresponding longitudinal side  12 ,  14  of each annular element  10 . The annular element  10  at the longitudinal end  102  of the endoprosthesis  100  in which the foot extensions  40  are directed is free of foot extensions  40 .  FIG. 17  shows an alternative embodiment similar to that of  FIG. 16 , wherein the lengths of the strut members  20  disposed circumferentially between the foot extensions  40  are varied to reduce the gap area defined between longitudinally-adjacent annular elements  10 , and thus increase coverage. 
       FIG. 18  shows an alternative embodiment similar to that of  FIG. 16 , wherein the center apex disposed along the longitudinal side  12 , between the foot extensions  40   b  that define connection locations is defined as a foot extension  40   a  In this manner, circumferentially-adjacent foot extensions  40  along a longitudinal side of an annular element  10  are separated by single apex  30 , wherein every other foot extension  40   b  forms a connection location with an apex  30  of a longitudinally-adjacent annular element  10 .  FIG. 19  shows an enlarged detail of an embodiment similar to  FIG. 18 , in the delivery configuration, wherein the base portion  46  of each foot extension  40  has an increased average width as previously discussed with regard to  FIG. 2   c . Particularly, the base portion  46  of each foot extension  40  is contoured with a generally V-shape to include a first portion  46 ′ and second portion  46 ″. The second portion  46 ″ proximate the toe portion has a width greater than the first portion  46 ′ as previously discussed. Furthermore, the foot extensions  40  of  FIG. 19  are all directed in the same circumferential direction. 
     The embodiment of  FIG. 20 , which is shown substantially in a delivery configuration, includes 18 apices on each longitudinal side  12 ,  14  of each annular element  10 . On each longitudinal side of an annular element  10  that faces an adjacent annular element, three pair of apices are defined by a pair of foot extensions  40  with each pair of foot extensions  40  having an apex  30   a  disposed therebetween. Furthermore, each pair of foot extensions  40  includes one foot extension  40   b  at a connection location  50  with a foot extension  40   b  on a corresponding side of a longitudinally-adjacent annular element  10 . Hence, three connection locations  50  are provided between adjacent annular elements  10 . Each foot extension  40  has a generally enlarged foot region  49 . Particularly, each foot extension  40  at a connection location  50  has a contoured base portion  46  similar to that of  FIG. 16 , although more elongate in the longitudinal direction. The connection location  50  is thus defined by the base portions of the corresponding foot extensions  40   b . It is noted that the foot extensions  40   a  that share a common strut member  20  in this embodiment are not at connection locations  50 . The three pairs of foot extensions on each side  12 ,  14  are separated from each other in this embodiment by three apices  30 . 
       FIG. 21  shows an embodiment, substantially in a delivery configuration, including 18 apices on each side of each annular element  10 , wherein every other apex on a side facing an adjacent annular element  10  is defined by a foot extension  40 . Three pairs of circumferentially adjacent foot extensions  40   b  are connected to three corresponding pairs of foot extensions  40   b  on a longitudinally-adjacent annular element, so as to define six connection locations  50  as shown. Hence, three remaining foot extensions  40   a  on each side of the annular element  10  are interspersed between the three pair of foot extensions  40   b  of the connection locations  50 . The foot extensions  40  on each side of the annular elements  10  extend in the same circumferential direction, but in a direction opposite the foot extensions  40  disposed on the opposite longitudinal side of the annular element  10 . 
       FIG. 22  shows an embodiment similar to that of  FIG. 16 , however, each annular element includes additional strut members and apices. Particularly, the embodiment of  FIG. 22  includes 20 apices, rather than 16 apices, on each side of each annular element  10 , with every other apex defined by a foot extension  40 . Hence, five connection locations  50  are defined between adjacent annular elements  10 . The embodiments of  FIGS. 23 and 24  are similar to the embodiment of  FIG. 22 ; however, selected apices  30   s  of one annular element are longitudinally aligned to be disposed between circumferentially adjacent foot extensions  40  of an adjacent annular element. As previously noted, and in accordance with the invention, the apices on longitudinally adjacent sides of adjacent annular elements  10  can be disposed so as to be circumferentially out of alignment with each other. Hence, the strut members  20   s  that are interconnected at the apices  30   s  disposed between adjacent foot extensions  40  of an adjacent annular element, are provided with a greater length than the remaining strut members so as to dispose the apex  30   s  generally between the foot extensions  40 . In this manner, resulting coverage and scaffolding can be increased. Each of  FIGS. 22-24  is shown substantially in a delivery configuration. 
       FIG. 25   a  discloses an embodiment in a slightly deployed configuration having eight apices per side of each annular element  10 . Each annular element  10  is arranged in a diagonal format to define a 360-degree turn of a helical pattern. In this manner, the circumferential end  18  of one annular element can be joined with the corresponding circumferential end  16  of a longitudinally-adjacent element to form a continuous helical pattern along the length of the endoprosthesis  100 . Two apices on one side of each annular element are defined by foot extensions  40  similar to that of  FIG. 2   b . Each foot extension  40  forms an overlapping pattern with the apex  30  on a circumferentially adjacent side of an adjacent annular element. Hence, two connection locations  50  are defined between adjacent annular elements  10 . As previously noted with regard to  FIG. 2   b , the apex  30   a  circumferentially adjacent to the foot extension  40  is longitudinally positioned to substantially contact the toe portion  48  when in the delivery configuration to increase coverage, as well as to capture balloon material if desired. The embodiment of  FIG. 25   a  also includes an eyelet or tab to incorporate a radiopaque marker  120  at one or both ends  102 ,  104  of the endoprosthesis if desired. Alternative techniques for incorporating radiopaque material are described below. 
       FIG. 25   b  discloses an alternative embodiment of the endoprosthesis according to the present invention, wherein the endoprosthesis includes at least one marker housing adjacent to one end of the endoprosthesis wherein a marker may be disposed therein. As shown in  FIG. 25   b , the endoprosthesis includes a plurality of strut members having first and second ends, wherein at least one pair of adjacent strut members further include a foot extension as previously described. The foot extension further includes a marker housing  121 , wherein the marker housing is configured to retain a marker  120 . As shown in  FIG. 25   b , the marker housing is attached to an apex  30  on one end  104  of the endoprosthesis and extends from a foot extension  40  on the opposite end  102 . The marker housing(s) as shown in  FIG. 25   b  are shown extending along an axis of either the apex or foot extension, though it is contemplated that the marker housings may extend from the apex and foot extension at and angle relative to an axis of the apex or foot extension. Marker housing  121  is designed such that the mechanical properties of the foot extension and/or the endoprosthesis are not affected. Alternatively, it is contemplated that the marker housing  121  may be design such that the marker housing  121  functions as a structural member of the endoprosthesis. As shown, the marker housing  121  includes an aperture formed therein, whereby the aperture is formed having a generally circular shape. Although, the aperture formed in the marker housing is described as being generally circular in shape, it is contemplated that the aperture may be formed having other shapes, such as rectangular, square, oval, octagonal, and the like. As shown in  FIG. 25   b , at least one marker housing may be additionally formed on the opposite side of the endoprosthesis device  100 , wherein the second marker housing  121  is configured to be in association with one of the apices formed by the plurality of strut members as described previously. 
     As described above, a marker  120  may be disposed within the aperture of the marker housing. The marker may be composed of any material having greater radiopacity than the material from which the endoprosthesis device  100  is constructed. Examples of suitable material include, stainless steel, gold, silver, cobalt, platinum, iridium, tantalum, and alloys thereof or similar biocompatible or bioabsorbable materials. In a preferred embodiment, the marker comprises tantalum. The marker may be embodied in the form of a rivet, wherein the rivet includes first and second ends and is formed as a generally cylindrical member. It is contemplated that the marker may be manufactured as a composite, wherein one material may be radiopaque and the other material may be a beneficial agent. Wherein the beneficial agent may be configured to elute from the marker after implantation of the endoprosthesis. The marker  120  is preferably formed of a biocompatible material such as those described above. 
     Referring now to  FIG. 25   c  there is shown an exemplary embodiment of a rivet in accordance with the present invention. As shown in  FIG. 25   c , the rivet  120  includes a first end  120   a  and a second end  120   b , wherein an enlarged diameter portion  122  is disposed adjacent to the first end  120   a  The enlarged diameter portion  122  being configured to retain the rivet within the aperture of the marker housing  121  prior to deformation of the rivet. As shown in  FIG. 25   d , there is shown a marker housing wherein a rivet has been disposed within the aperture of the housing, wherein the enlarged diameter portion  122  of the rivet extends beyond the outer surface of the endoprosthesis device  100  and the second end  120   b  of the rivet has been deformed to form a second enlarged diameter portion as shown. By forming the second enlarged diameter portion adjacent the second end  120   b  of the rivet, the rivet  120  is retained within the marker housing with a frictional fit and/or a mechanical interference of the enlarged diameter portions and the inner and outer walls of the endoprosthesis device. It is further contemplated that the rivet as shown in  FIG. 25   c  may be constructed of multiple pieces which may then be assembled to form a single member when disposed within a marker housing in accordance with the present invention. For example, the rivet may comprise upper, middle, and lower pieces, wherein the middle piece includes means to affix the upper and lower pieces thereto, such as a protrusion extending from each end of the middle piece, wherein the upper and lower pieces include an aperture or recessed area configured to receive the protrusion. Alternatively, a fourth piece may be utilized to affix the upper, middle and lower pieces together to form a marker in accordance with the present invention. 
     The rivet may be manufactured from a sheet of material, wherein the rivets are produced by stamping and a second process is performed to form the enlarged diameter section. Alternatively, the rivets may be manufactured by cutting the rivets from round stock, wherein the cut portions may then be tumbled to radius the edges then machined to produce the increased radius portion. Further still, the rivets may be manufactured utilizing other known techniques such as injection molding, casting, machining, hydroforming and the like. 
     It is further contemplated that the marker  120  may be formed with alternative methods, for example, the marker may be integrally formed with the endoprosthesis device during the initial manufacturing step. Such a process would involve manipulating a tubular member or a sheet of material from which the endoprosthesis device is constructed from prior to the formation of the endoprosthesis device. For example, if the endoprosthesis were to be formed from a thin-walled tubular member, a groove or other feature may be formed in one of the walls of the tube, wherein a radiopaque material may then be disposed within the groove or feature. Alternatively, the locations of the marker housing may be preformed on the device wherein markers may pre-disposed within the marker housings prior to the manufacture of the endoprosthesis device, which may then be formed according to known methods and those described herein. 
     Although the marker housings are shown and described as being disposed on either end of the endoprosthesis device of the present invention, it is further contemplated that marker housings may be formed anywhere along the length and/or radius of the endoprosthesis device in accordance with the present invention. Markers disposed anywhere along the length of the endoprosthesis may be utilized to denote the location where the physical properties of the endoprosthesis changes, or where a diameter change occurs, or the location of a side opening formed in the wall of the tubular member. 
       FIG. 25   e  illustrates yet another alternative embodiment of the endoprosthesis in accordance with the present invention, wherein the endoprosthesis includes a plurality of markers disposed along at least one of the strut members. The markers may be comprised of rivets disposed within openings formed in the strut members as described above or alternatively, the markers may be integrally formed upon the strut member during fabrication of the endoprosthesis. For example, as described herein, the endoprosthesis may be formed from a tubular member, wherein the struts and foot extensions are formed in the tubular member utilizing laser cutting or similar processes, the markers  120   e  formed on the strut members  20 , may be formed by cutting away, machining away, chemical milling, or electropolishing material away from the strut member to form the markers  120   e . The markers  120   e  may be formed having any shape or profile. 
       FIG. 25   f  illustrates an alternative radiopaque marker in accordance with the endoprosthesis of the present invention. As shown in  FIG. 25   f , the marker  120   f  comprises a clip or a band that may be attached to one of or a plurality of strut members along the length of the endoprosthesis device  100 . The marker  120   f  may be constructed of a material such as tantalum, gold, gold plating, silver, silver plating, alloyed metals, polymers, plastics, or similar biocompatible or bioabsorbable materials, wherein the marker would be configured to be retained on the endoprosthesis by deforming the marker such that the marker would be frictionally retained on the endoprosthesis. It is further contemplated that the marker may be affixed to the endoprosthesis utilizing other methods such as welding, gluing, swaging, or similar methods. 
     In addition to the embodiments shown above in  FIGS. 25   a  through  25   f , it is contemplated that the marker housings may be formed within an apex of one or more strut members or within a portion of the foot extension of the embodiments shown and described herein. Additionally, it is contemplated that a marker housing may be formed anywhere along the length of the endoprosthesis in accordance with the present invention. For example, it may be desirable to have markers disposed anywhere along the length of the endoprosthesis between each end of the endoprosthesis. Therefore, in accordance with the present invention, it is contemplated that marker housings may be formed for example in the middle of the endoprosthesis to indicate a specific area or property of the endoprosthesis. As such, markers may be disposed in marker housings formed within the struts, apices, or foot members of the endoprosthesis, or marker housings such as those shown in  FIGS. 25   a  and  25   b  maybe integrated in the endoprosthesis anywhere along the length of the endoprosthesis. Further still, a variety of the marker embodiments described and shown herein may be utilized in any combination along the length of an endoprosthesis according to the present invention, wherein different marker embodiments may be utilized to mark locations of interest. 
       FIG. 26  is an enlarged view of a connection location similar to that of  FIG. 25   a , wherein the overlapping geometric pattern of a connection location is schematically depicted for purpose of illustration. Particularly,  FIG. 26  shows an annular element having a foot extension similar to that of  FIG. 2   a . The pattern of the foot extension  40   b  along the base portion  46  is aligned longitudinally to overlap with a portion of the pattern of a circumferentially adjacent annular element  10 . The resulting configuration of the overlapping pattern defines the connection location  50  between the two annular elements  10 . The amount or extent of overlap between the two patterns can be varied as desired. For example, the patterns can be substantially in tangential contact, or can be fully overlapping. Additionally, fillets or a similar transition can be included to smooth or eliminate any sharp or abrupt edges. It is noted that the thickness at the juncture defined by the overlapping patterns need not be, and preferably is not, increased. Rather, the overlapping pattern refers to the resulting configuration when two separate patterns share a common surface or area. 
       FIGS. 27   a  through  27   d  show alternative connection locations  50  defined by different degrees of geometrical overlap between adjacent annular elements  10 . The connected foot extension  40   b  and apex  30  of  FIG. 27   a  have a slight geometrical overlap, such as a tangential surface contact.  FIG. 27   b  shows an overlapping pattern, wherein the connected apex  30  and foot extension  40   b  fully overlap to substantially share a common member. As depicted, the apex  30  at the connection location  50  extends longitudinally further than the unconnected apices  30 . In  FIG. 27   c , the apex  30  at the connection location  50  protrudes into the foot region of the corresponding foot extension  40   b . In this embodiment, the foot extension  40   b  is generally enlarged and rounded at the base portion  46  compared to free foot extensions  40   a  to stiffen and reinforce the connection location  50 . Additional areas of flexure can be defined by the contour of this configuration, as compared to that of the other foot extensions. By contrast, connected foot extension  40   b  of  FIG. 27   d  includes a flattened base portion  46  substantially perpendicular to the longitudinal axis to define a more relaxed configuration. As with  FIG. 27   c , the connected apex  30  of this embodiment overlaps with the foot extension  40   b  and protrudes into the foot region  49 . 
     As noted above, the various aspects of the present invention allow for a variety of different endoprosthesis embodiments, based upon selective combinations of the features previously described and shown. Similarly, the endoprosthesis of the present invention can be made using any of a number of known manufacturing techniques and materials. 
     The material of construction is preferably selected according to the performance and biological characteristics desired. For example, the endoprosthesis of the invention can be made to be expanded by the change of a delivery condition, such as by the removal of a restraint or exposure to the environment within the body lumen, so as to be self expanding, or by the application of an external force or energy, such as by a balloon or by a radio frequency. For purpose of illustration and not limitation, reference is made generally to “self-expanding” embodiments and “balloon expandable” embodiments of the endoprosthesis of the present invention. 
     Self-expanding embodiments can be made from any of a variety of known suitable materials including super elastic or shape memory materials, such as nickel-titanium (NiTi) alloys, Elgiloy, and suitable polymers, such as suitable shape memory polyurethane copolymers, or any equivalents thereof. An endoprosthesis made of a suitable super elastic material can be compressed or restrained in its delivery configuration on a delivery device using a sheath or similar restraint, and then deployed to its deployed configuration at a desired location by removal of the restraint as is known in the art. An endoprosthesis made of shape memory material generally can be delivered in a like manner, and if thermally sensitive, can be deployed by exposure of the endoprosthesis to a sufficient temperature to facilitate expansion as is known in the art. It also is possible to make the self-expanding embodiment of a biocompatible material capable of expansion upon exposure to the environment within the body lumen, such as a suitable hydrogel or hydrophilic polymer, including biodegradable or bioabsorbable polymers, such as polycaprolactone (PCL), poly-D,L-lactic acid, Poly-L-lactic acid, poly (lactide-co-glycolide), poly(hydroxybutyrate), polyanhydrides, poly(glycolic acid). For example, if made of an expandable hydrophilic material, the endoprosthesis can be delivered to the desired location in an isolated state, and then exposed to the aqueous environment of the body lumen to facilitate expansion. Alternative known delivery devices and techniques for a self-expanding endoprosthesis likewise can be used. Prior to crimping of the self-expanding endoprosthesis for loading into a delivery system, the endoprosthesis may be coated with a lubricant such as silicone oil to reduce force between the endoprosthesis and the crimping device and additionally to reduce forces of disposing the endoprosthesis in a delivery device. Additionally, the lubricant may reduce deployment force thereby increasing accuracy of endoprosthesis placement within a patient. The lubricant may be introduced prior to, during, or after the crimping or loading process. 
     It is further contemplated that the markers in accordance with the present invention may improve the deliverability of a self-expanding endoprosthesis when used with a movable sheath delivery system. The markers projecting above the outer surface of the tubular body of the endoprosthesis contact the sheath of the delivery system and hold the sheath above the surface of the endoprosthesis, thereby reducing friction between the sheath and the endoprosthesis. Additionally, by having point contact between the sheath and the endoprosthesis it is possible the system may be more flexible and thus have better delivery characteristics compared to a similar system where the sheath is in continuous contact with the endoprosthesis. In addition to providing improved deliverability, it is contemplated that by having the markers protrude about the surface of the endoprosthesis this may provide less trauma to the tissue surrounding the endoprosthesis after delivery of the endoprosthesis by holding the surface of the endoprosthesis off the tissue and providing only points of contact. 
     Balloon expandable embodiments or the like can be made of any of a variety of known suitable deformable materials, including stainless steel, silver, platinum, cobalt chromium alloys such as L605, MP35N or MP20N or any equivalents thereof. “L605” is understood to be a trade name for an alloy available from UTI Corporation of Collegeville, Pa., including about 53% cobalt, 20% chromium and 10% nickel. “MP35N” and “MP20N” are understood to be trade names for alloys of cobalt, nickel, chromium and molybdenum available from Standard Press Steel Co., Jenkintown, Pa. MP35N generally includes about 35% cobalt, 35% nickel, 20% chromium, and 10% molybdenum. MP20N generally includes about 50% cobalt, 20% nickel, 20% chromium and 10% molybdenum. For delivery, the endoprosthesis of a suitable material is mounted in the delivery configuration on a balloon or similar expandable member of a delivery device. Once properly positioned within the body lumen at a desired location, the expandable member is expanded to expand the endoprosthesis to its deployed configuration as is known in the art. Additionally, or alternatively, balloon expandable embodiments can be made of suitable biocompatible polymers, including biodegradable or bioabsorbable materials, which are either plastically deformable or capable of being set in the deployed configuration. If plastically deformable, the material is selected to allow the endoprosthesis to be expanded in a similar manner using an expandable member so as to have sufficient radial strength and scaffolding and also to minimize recoil once expanded. If the polymer must be set in the deployed configuration, the expandable member can be provided with a heat source or infusion ports to provide the required catalyst to set or cure the polymer. Alternative known delivery devices and techniques for a self-expanding endoprosthesis likewise can be used. 
     Additional materials or compounds also can be incorporated into or on the endoprosthesis if desired. For example, the endoprosthesis can be provided with one or more coatings of biocompatible material to enhance the biocompatibility of the device. Such coatings can include hydrogels, hydrophilic and/or hydrophobic compounds, and polypeptides, proteins or amino acids or the like, including poly vinyl pyrrolidone (PVP), poly vinyl alcohol (PVA), parylene, and heparin. A preferred coating material includes phosphorylcholine, as disclosed in U.S. Pat. Nos. 5,705,583 and 6,090,901 to Bowers et al. and U.S. Pat. No. 6,083,257 to Taylor et al., each of which is incorporated by reference herein. Such coatings can also be provided on the endoprosthesis to facilitate the loading or delivery of beneficial agents or drugs, such as therapeutic agents, pharmaceuticals and radiation therapies. Alternatively, the surface of the endoprosthesis can be porous or include one or more reservoirs or cavities formed therein to retain beneficial agent or drug therein as is known in the art. For purposes of illustration and not limitation, the drug or beneficial agent can include antithrombotics, anticoagulants, antiplatelet agents, thrombolytics, antiproliferatives, anti-inflammatories, agents that inhibit hyperplasia, inhibitors of smooth muscle proliferation, antibiotics, growth factor inhibitors, or cell adhesion inhibitors, as well as antineoplastics, antimitotics, antifibrins, antioxidants, agents that promote endothelial cell recovery, antiallergic substances, radiopaque agents, viral vectors, antisense compounds, oligionucleotides, cell permeation enhancers, and combinations thereof. 
     The endoprosthesis can also be provided with coverings, such as PTFE, ePTFE, Dacron, woven materials, cut filaments, porous membranes, harvested vessels and/or arteries, or others such materials to form a stent graft prosthesis. Similarly, a medical device, such as a valve, a flow regulator or monitor device, can be attached to the endoprosthesis, such that the endoprosthesis functions as an anchor for the medical device within the body lumen. 
     Additionally, an imaging compound or radiopaque material can be incorporated with the endoprosthesis. For example, one or more of the annular elements of the endoprosthesis can be made of a suitable radiopaque material, such as gold, tantalum or a similar material. Alternatively, the radiopaque material can be applied on selected surfaces of one or more of the annular elements using any of a variety of known techniques, including cladding, bonding, adhesion, fusion, deposition or the like. In a preferred embodiment, the material used for fabrication of the endoprosthesis includes a composite structure having multilayers of different materials or compositions. Generally, at least one layer is a base material such as stainless steel, nickel-titanium alloy or cobalt chromium alloy to impart the intended structural characteristic of the endoprosthesis, and at least another layer is a radiopaque material such as gold or tantalum for imaging purposes. For example, a tri-layer structure of 316L-Ta-316L is preferred for a balloon expandable stent and a tri-layer structure of NiTi—Ta—NiTi is preferred for a self-expanding stent. Suitable multi-layered composite structures are available in sheet or tube form from UTI Corporation of Collegeville, Pa., and are disclosed in U.S. Pat. No. 5,858,556, which is incorporated herein by reference. In yet another embodiment, one or more marker elements of radiopaque material can be attached to the endoprosthesis. For example, and as previously shown in  FIG. 25 , eyelets or tabs can be provided on one or more annular elements, preferably at at least a distal or proximal longitudinal end of the endoprosthesis. A rivet or bead of radiopaque material can then be attached to the eyelet or tab in a manner as known in the art. Alternatively, the separate marker can be attached directly to annular element. For example, and in accordance with a preferred embodiment of the invention as shown in  FIGS. 1 and 15 , a wire or strip of radiopaque material can be wrapped around and secured to a base portion of one or more foot extensions at one or both longitudinal ends of the endoprosthesis; preferably by providing the foot extension with a geometry to enable limited strain in the base portion of the foot extension upon deployment. 
     A variety of manufacturing techniques are well known and may be used for fabrication of the endoprosthesis of the present invention. For example, and in a preferred embodiment, the endoprosthesis can be formed from a hollow tube of suitable material using a known technique, such as by laser cutting, milling or chemical etching. The structure is mechanically blasted with a media and then electropolished or otherwise finished to remove burrs and eliminate sharp edges and contaminates. An additional de-scaling process may be performed after electropolishing, wherein the de-scaling process involves the use of an acid bath. Alternatively, the endoprosthesis can be fabricated from a sheet of suitable material using a similar cutting, milling or etching technique, and then rolled or bent about a longitudinal axis into the desired shape. If desired, the lateral edges of the structure can be joined together, such as by welding or bonding, to form a closed tubular structure, or the lateral edges can remain unattached to form an coiled, rolled sheet or open tubular structure. Conversely, a suitable material of construction can be applied selectively to a substrate to define the desired pattern of the endoprosthesis structure, and then the substrate can be removed. Other methods of manufacture also can be used for the endoprosthesis of the present invention, such as by bending toroidal rings or elongate lengths of wire into appropriately shaped members, such as that corresponding to each annular element, and then joining the appropriately shaped members together at connection locations by a welding or bonding technique or the like. If a shape memory material is used, such as a nickel titanium alloy, the fabricated structure can be heat treated on a mandrel or the like using known techniques to establish the desired endoprosthesis shape and dimensions at a predetermined temperature, e.g. when above austenitic transition temperature. 
     An additional step of passivation may be performed during the manufacturing stage of the endoprosthesis in order to form a homogeneous oxide layer for corrosion resistance. The passivation process may be performed prior to installation of the markers in accordance with the present invention or it may be performed after installation of the markers. Alternatively, multiple passivation processes may be performed, once prior to insertion of the markers and again after insertion of the markers. 
     As originally cut or fabricated, the endoprosthesis can correspond to its delivery configuration or to a deployed configuration or a configuration therebetween. Preferably, however, the endoprosthesis is fabricated with a configuration at least slightly larger than the delivery configuration as shown in the planar formats of  FIGS. 6-10  and  16 - 24 , for example. In this manner, the endoprosthesis can be crimped or otherwise compressed into its delivery configuration on a corresponding delivery device. In another preferred embodiment, the endoprosthesis is originally fabricated from a tube having a diameter corresponding to the deployed configuration. In this manner, the longitudinally-free portions of the annular elements (e.g., apices not at a connection location) and circumferentially-free portions (e.g., the toe portion of the foot extensions) can be maintained within the general cylindrical shape (e.g., diameter) of the endoprosthesis when deployed, so as to avoid such portions from extending radially inwardly when in the deployed configuration. The endoprosthesis is therefore designed to match the target vessel in which the endoprosthesis is to be deployed. For example a stent will typically be provided with an outer diameter in the deployed configuration ranging from about 1 mm for neurological vessels to about 25 mm for the aorta. Similarly, a stent will typically be provided with a length ranging from 5 mm to 200 mm. Variations of these dimensions will be understood in the art based upon the intended application or indication for the endoprosthesis. 
     As previously noted, the geometry of each component of the endoprosthesis, such as the width, thickness, length and shape of the strut members and foot portions, as well as of the connectors if provided, is preferably selected to obtain predetermined expansion, flexibility, foreshortening, coverage scaffolding, and cross profile characteristics. For example, longer strut members can promote greater radial expansion or scaffolding coverage. The phase difference or circumferential alignment between adjacent annular elements likewise can be altered to control coverage and flexibility as well as facilitate more uniform drug delivery. Similarly, the number and placement of connection locations and, if present, the connectors, between longitudinally-adjacent annular elements are preferably selected to obtained the desired flexibility of the endoprosthesis. The number of apices and foot extensions between connection locations also can be varied to achieve desired performance characteristics.  FIG. 28  depicts a representative embodiment depicting such variations within an endoprosthesis of strut lengths and strut widths for varied rigidity, and of connector locations for varied flexibility. 
     As recognized from the detailed description above, the foot extensions particularly enhance and provide versatility in the design of the endoprosthesis of the present invention. The foot extension can be configured and dimensioned relative to the strut members and the remainder of the endoprosthesis to compensate for longitudinal foreshortening upon stent expansion. For example, the areas of flexure of the foot extensions can be adjusted by contouring the foot geometry and dimensions, as well as by altering the lengths of selected strut members. Alternatively, the geometry of the foot extension can be configured to provide a desired amount of lengthening or shortening of the endoprosthesis upon expansion. The foot extensions can be configured to balance or assist in evenly distributing strain or expansion of the endoprosthesis. The foot extensions also can improve and control the flexibility of the endoprosthesis, preferably without substantially impacting the desired coverage or scaffolding of the endoprosthesis. The circumferentially elongated base portion of each foot extension provides a wide range of connection locations, and allows adjacent annular elements to be attached over a range of phase differences or circumferential alignment. The foot extensions can be configured to produce a torque on longitudinally free portions, such as unconnected apices, to maintain these longitudinally free portions within the general cross profile of the endoprosthesis when flexed along its longitudinal axis or expanded to its deployed configuration. This feature can be adjusted if it is desired to embed portions of the endoprosthesis into the vessel wall or other tissue. 
     Reference is now made to two exemplary preferred embodiments of a stent of the present invention; a self-expanding stent as shown in  FIGS. 29   a  through  29   f , and a balloon expandable stent as shown in  FIGS. 30   a  through  30   f.    
       FIG. 29   a  shows the planar format of a preferred embodiment of a self-expanding stent as cut and polished in a slightly deployed configuration. As depicted herein, the self-expanding stent comprises ten annular elements  10  with five connection locations  50  between longitudinally-adjacent annular elements  10  for an approximate stent length of about 21 mm. Annular elements can be added to increase the stent length, or omitted to decrease the stent length, as desired. Each annular element  10  includes fifteen apices per longitudinal side. On one longitudinal side  12  of each annular element  10 , five apices are defined by foot extensions  40 . Two circumferentially-adjacent apices  30  are located between adjacent foot extensions. On the other longitudinal side  14  of each annular element  10 , no foot extensions are provided. Each foot extension  40  has a shape similar to that of  FIG. 2   c , as previously described in detail. Each of the five connection locations  50  between adjacent annular elements  10  is defined by a slightly overlapping pattern of the base portion  46  of each foot extension  40  with a corresponding apex  30  of a longitudinally-adjacent annular element in a manner similar to that of  FIG. 27   a  In this manner, longitudinally-adjacent apices of adjacent annular elements are out of circumferential alignment with each other so as to be less than 180 degrees out of phase. Furthermore, connection locations  50  are circumferentially displaced or offset from one set of annular elements to the next. 
     The self-expanding stent of this preferred embodiment is made from a suitable tube stock of nickel-titanium alloy, such as SE508 or SM508, ASTM Standard F2063-00, comprising about 54.5 to about 57% wt. nickel and about 45.5 to about 42.7% wt. titanium, which is commercially available from Minitubes, Inc. of Grenoble, France. It is recognized, however, that alternative alloy compositions can be used if desired. For fabrication of a self-expanding stent having a deployed configuration diameter of about 7 mm to about 8 mm, the tube stock has an outer diameter of about 0.091 inch and a uniform wall thickness of about 0.010 inch. The tube stock is laser cut with the configuration shown in  FIG. 29   b  as a continuous pattern around the circumference of the tube; wherein only the front half of the structure is shown for clarity. The cut tube is then mechanical blast and sequentially heat treated on a series of cylindrical mandrels of increasing diameter using known techniques to set the desired deployed configuration of the stent when in an austenitic state as shown in  FIG. 29   d . The heat set stent is then electropolished using known techniques. The relevant dimensions of the strut members for this preferred embodiment, after electropolishing, include a nominal strut length of about 0.055 inch, a nominal strut width of about 0.004 inches and a generally uniform thickness of about 0.008 inches. Regarding each foot extension, after electropolishing, the first portion of the foot extension has a width of about 0.005 inch and a length of about 0.013, as measured along its outer edge, and the base portion of the foot extension includes total length of about 0.033, as measured along its outer edge, with a first portion proximate the heel portion having a width of about 0.005 inch and a second portion proximate the toe portion having a width of about 0.007 inch. The strut member extending from the ankle portion of the foot extension tapers from a width of about 0.005 inch at the end proximate the foot extension to about 0.004 inch at the opposite end, with a length of about 0.059 inch. The strut member extending from the heel portion of the foot extension tapers from a width of about 0.005 inch at the end proximate the foot extension to about 0.004 inch at the opposite end, with a length of about 0.068 inch. After polishing, additional cleaning or preparation may be required. 
     Once prepared, the self-expanding stent of this embodiment is compressed to a delivery configuration as shown in the front-half view of  FIG. 29   c , preferably with the strut members generally parallel to the longitudinal axis of the stent and each other. The stent can then be delivered using a conventional retractable sheath delivery catheter, as is known in the art.  FIGS. 29   d  and  29   e  show the self-expanding stent of this embodiment in a deployed configuration. For purpose of clarity, only the front half of the stent is shown in  FIG. 29   d . As depicted, the stent of this embodiment has been balanced for generally uniform expansion.  FIG. 29   f  shows a self-expanding stent of greater length of this embodiment deployed in a curved vessel, wherein the apices proximate the inner radius of the curve generally open less than the apices proximate the outer radius of the curve. 
       FIG. 30   a  shows the planar format of a preferred embodiment of a balloon expandable stent as cut and polished in a slightly deployed configuration. As depicted herein, the balloon expandable stent comprises fifteen annular elements  10  with two connection locations  50  between longitudinally-adjacent annular elements for an approximate stent length of about 18 mm. Annular elements can be added to increase the stent length, or omitted to decrease the stent length, as desired. Each annular element includes ten apices per longitudinal side. On one longitudinal side  12  of each annular element  10 , two apices are defined by foot extensions  40 . Four circumferentially-adjacent apices  30  are located between adjacent foot extensions. On the other longitudinal side  14  of each annular element  10 , no foot extensions are provided. Each foot extension  40  has a shape similar to that of  FIG. 2   a , as previously described in detail. Each of the two connection locations  50  between adjacent annular elements  10  is defined by an overlapping pattern of the base portion  46  of each foot extension  40   b  with a corresponding apex  30  of a longitudinally-adjacent annular element in a manner similar to that of  FIG. 26 . In this manner, longitudinally-adjacent apices of adjacent annular elements are out of circumferential alignment with each other so as to be less than 180 degrees out of phase. Furthermore, connection locations  50  are circumferentially displaced or offset from one set of annular elements to the next. 
     The balloon expandable stent of this preferred embodiment is made from a suitable tube stock of composite material including an inner layer of 316L stainless steel, a middle layer of tantalum, and an outer layer of 316L stainless steel, which is available from UTI Corporation of Collegeville, Pa. It is recognized, however, that alternative material compositions can be used if desired. For fabrication of a balloon expandable stent having a deployed configuration diameter of about 2.75 mm to about 3.0 mm, the tube stock has an outer diameter of about 0.062 inch and a generally uniform wall thickness of about 0.004 inch, with the tantalum layer constituting between about 3% to about 50% of the wall thickness, and more preferably between about 10% to about 25% of the wall thickness depending upon the intended indication. For example, a coronary stent of this dimension preferably would have a tantalum layer of between about 15% to about 17% of the tube stock thickness. The tube stock is laser cut with the configuration shown in  FIG. 30   b  as a continuous pattern around the circumference of the tube; only seven annular elements are depicted for purpose of clarity. The cut tube is then mechanically blasted and electropolished using known techniques. The relevant dimensions of the strut members for this preferred embodiment, after electropolishing, include a nominal strut length of about 0.036 inches, a nominal strut width of about 0.003 inches and a generally uniform thickness of about 0.003 inches. Regarding each foot extension, after electropolishing, the first portion of the foot extension has a width of about 0.005 inch and a length of about 0.008 inch, as measured along the outer edge, and the base portion of the foot extension has a width of about 0.005 inch and a length of about 0.021 inch as measure along the outer edge. The strut member extending from the ankle portion of the foot extension tapers from a width of about 0.004 inch at the end proximate the foot extension to about 0.003 inch at the opposite end, with a length of about 0.034 inch. The strut member extending from the heel portion of the foot extension tapers from a width of about 0.005 inch at the end proximate the foot extension to about 0.003 inch at the opposite end, with a length of about 0.042 inch. After electro polishing, additional cleaning or preparation may be required. 
     Once prepared, the balloon expandable stent of this embodiment is compressed to a delivery configuration as shown in  FIG. 30   c , with only seven annular elements depicted for purpose of clarity. Preferably, the strut members are generally parallel to the longitudinal axis of the stent and each other when in the delivery configuration. The stent can then be delivered using a conventional balloon delivery device, as is known in the art. Preferably, a portion of balloon material of the delivery device is captured in the gap defined by the foot extension and the circumferentially-adjacent strut member.  FIGS. 30   d  and  30   e  show the balloon expandable stent of this embodiment in a deployed configuration; only seven annular elements are depicted for purpose of clarity. For purpose of clarity, only the front half of the stent is shown in  FIG. 30   d . As depicted, the stent of this embodiment has been balanced for generally uniform expansion.  FIG. 30   f  shows the balloon expandable stent of this embodiment deployed in a curved vessel, wherein the apices proximate the inner radius of the curve generally open less than the apices proximate the outer radius of the curve. It is further contemplated that the endoprosthesis may include eyelets or tabs such as those shown in  FIG. 25   a , wherein the eyelets or tabs may be utilized to retain the endoprosthesis onto a balloon delivery device, wherein the balloon material may be received within the eyelet or tab during the crimping and/or heat setting process. Further still, a biocompatible adhesive may be disposed within the eyelet or tab after the endoprosthesis has been crimped onto the balloon delivery device such that the adhesive would releasably affix the endoprosthesis to the surface of the balloon of the balloon delivery device. 
       FIG. 31  is an exemplary cross-sectional view of an endoprosthesis device in accordance with the present invention. As shown in  FIG. 31 , the endoprosthesis device is manufactured having a cross-sectional profile which may be shaped to improve blood flow by decreasing the likelihood of turbulent currents and eddies formed near the struts of the endoprosthesis. An exemplary cross-sectional profile may be hemispherical in nature, wherein the rounded portion would be disposed on the inner radius of the endoprosthesis device, thereby placing the radiused portion within the blood flow. It shall be understood that he profiled illustrated in  FIG. 31  should be considered exemplary, in that the inventors of the present invention contemplate that alternative cross-sectional profiles may be utilized to reduce the formation of thrombosis and/or turbulence of blood flow through the endoprosthesis device where the device is disposed in an expanded condition within a body lumen. 
     While illustrative embodiments of the invention have been disclosed herein, numerous modifications and other embodiments may be devised by those skilled in the art in accordance with the invention. For example, the various features depicted and described in the embodiments herein can be altered or combined to obtain desired endoprosthesis characteristics in accordance with the invention. Therefore, it will be understood that the appended claims are intended to cover all such modifications and embodiments, which are within the spirit and scope of the present invention.