balloon expandable stent structures are well known in the art . in this invention , as schematically depicted in fig1 a balloon - expandable stent structure 1 deliverable by catheter 21 has an opening 2 at each end of the stent end or edge . in one aspect of the invention , stent structure 1 includes a plurality of radially expandable members that include a first radially expandable member 22 and a second radially expandable member 23 , where the first and second radially expandable members 22 , 23 are curved into peaks 24 and valleys 25 . in one example , the first radially expandable member 22 includes an integral portion that forms a perimeter of the opening 2 . fig1 depicts the first radially expandable member 22 forming a first end 34 of the stent 1 . in addition , the peaks and valleys of the first radially expandable member 22 are arranged with the peaks and valleys of the second radially expandable member 23 such that the first and second radially expandable members have peaks and valleys that are paired with each other in an in - phase relationship . interconnecting links 27 , each having a curved conformation , extend between first and second radially expandable members 22 , 23 such that , for each opening 2 , as least one interconnecting link 27 is connected to first radially expandable member 22 at a point on the circumference 28 ( perimeter ) of the opening 2 . in addition , interconnecting links 27 , having the curved conformation , are connected by a connection at a first end 36 to a point 38 intermediate a peak and a valley on the first radially expandable member 22 and at a second end 40 to a point 42 intermediate a peak and a valley on the radially second expandable member 23 . the interconnecting links 27 illustrated in fig1 have at least one bend 44 adjacent to the connecting point 38 on the first radially expandable member 22 and at least one bend 46 adjacent the connecting point 38 on the second radially expandable member 23 and at least one straight section 48 there between . in a first embodiment of the invention , the opening 2 are round . fig2 shows a cross - section of the stent 1 and shows opening 2 passing radially from the external stent surface into the internal stent surface . according to the invention a marker having radiopaque qualities is inserted through the opening at each end or edge of the stent to mark the ends of the stent so that the position of the stent can be determined by the location of its ends when the markers are seen under x - ray . because the markers are placed securely into and through holes or openings , they are referred to as “ rivets ”. fig3 illustrates the placement of a rivet 3 into a stent opening 2 . rivet 3 comprises a short rod made from a radiopaque material , which is compressed into the opening 2 in the axial direction 4 , thereby compressing the radiopaque material and causing a circumferential force 5 that enables rivet 3 to be held within opening 2 of stent 6 . because retention of the marker rivet requires an opening whose aperture size does not vary while the rivet is inserted therein , the preferred location of the marker rivet is a region of the stent that is not deformed during expansion of the stent . in particular , for a balloon - expandable stent , this will usually be at an edge of the stent , at the end of the stent &# 39 ; s lattice - like structure . as shown in fig4 an alternative manner of assuring that the rivet remains in the stent opening 2 is to form the rivet edges 7 with a cone - like , outwardly radiating shape , i . e ., with beveled edges . then , after the radiopaque rivet 8 is compressed into opening 2 , the rivet 3 cannot leave the stent due to the friction between the edges 7 of the rivet and the outer edges of the inner walls of opening 2 . another means of securing the rivet within the lumen is shown in fig5 in which the marker rivet 9 is made with chamfered edges 10 . after rivet 9 is inserted into the opening 2 , the stent 1 is pressed at points 11 so the marker rivet 9 cannot displace from the stent . in a further embodiment of the invention illustrated in fig6 an enlarged head portion 13 of rivet 12 protrudes from opening 2 on one side of the stent in a diameter larger than that of the rivet portion situated within opening 2 . thus , when the stent is viewed through x - ray , a larger height and greater diameter of the rivets and , therefore , a better visualization of the markers of the ends of the stent , is achieved . fig7 illustrates a variation of this embodiment of the rivet in which the enlarged head portion 13 protrudes from both sides of the stent , achieving even larger height and greater diameter of the rivet and still better visualization of the rivet , and thus the stent ends , under x - ray . fig8 illustrates a second embodiment of the invention . fig8 includes a first radially expandable member 50 with an integral portion that forms a perimeter 54 of opening 14 . the opening 14 of the stent 17 is non - round , such as oval . the non - round opening 14 allows a non - round rivet to be inserted therein . this serves to enlarge the rivet surface without interfering with the fluid flow within the stent . fig8 further includes a second radially expandable member 56 at a second end 58 of the stent 17 . the second radially expandable member 56 can include an integral portion that forms a perimeter of at least one opening . a third radially expandable member can be included intermediate the first and second radially expandable members , where the stent can further include an integral portion of the radially expandable member that forms a perimeter of at least one opening . in one embodiment , the openings formed in the first and second radially expandable members are aligned with at least one opening formed in the third radially expandable member . the openings can also be located in a region of the stent that is not deformed during radial expansion of the stent . in the embodiment of this invention illustrated in fig1 through fig8 marker rivets are completely surrounded by the stent material ( e . g ., perimeter ) so that they either are contained within the stent material or project only from the external and internal surfaces of the stent . another embodiment of the invention and an additional type of marker rivet is shown in fig9 in which the integral portion of the stent 18 where the marker is placed is not a loop or an opening passing radially through the stent material 18 but is rather a circumferential space defined by a perimeter 60 that includes two circumferential detent projections 16 . the corresponding marker 15 is pressed circumferentially into the space defined by the perimeter 60 and is held there by specially designed projections 16 into adequate shape in the marker . this method enables an insertion of a marker with larger visible surface area by allowing the larger surface area to fit along and be co - extensive with the stent circumference as opposed to projecting radially into and out of the stent shape . the above - described markers are designed for both stent extremities in order to define the ends of the stent during fluoroscopy . nonetheless these markers can be combined onto the entire stent length and also on several places located along the stent circumference , so that the stent diameter can be detected during fluoroscopy , as well . it is within the scope of the invention that a stent could have , for example , from 2 to 20 marker rivets , located from about 0 . 5 to 5 cm apart longitudinally and / or from 1 to 4 rivets spaced radially , preferably equidistantly , or a combination thereof . as described above , the rivets are preferably compressed into the stent material . optionally , in addition to or in place of compression , the surface between the rivets and the stent can be heated to weld or fuse the rivets into position . preferably such heating would be focused heating , for example , with a laser , where only the rivet and stent material would be present . this invention is intended primarily for use with balloon - expandable stents , although it is envisioned that the technology disclosed herein is applicable to other medical devices , including , but not limited to , self - expanding stents . an important factor is that the material of the rivet be more radiopaque than the primary material used in the device . for example , if a balloon - expandable stent is comprised of stainless steel or nitinol , then rivets comprised of gold , platinum , or titanium would be useful . the invention herein is not limited to a particular lattice - work for a balloon - expandable stent . however , the invention is especially useful with the balloon - expandable stents described in co - pending u . s . patent application ser . no . 08 / 543 , 337 , filed oct . 16 , 1995 , now u . s . pat . no . 5 , 776 , 161 incorporated herein by reference . it will be further apparent to one skilled in this art that the improvements provided for in the present invention , while described with relation to certain specific physical embodiments also lend themselves to being applied in other physical arrangements not specifically provided for herein , which are nonetheless within the spirit and scope of the invention taught here .
stents which are inserted into a body lumen preferably are made of materials which are not radiopaque enough , such as s . s . 316l . x - ray visualization of a stent enables an accurate positioning of the stent and also a follow - up of its functioning within the patient &# 39 ; s body . the radiopaque markers described here are rivets made of a material which is more radiopaque than the stent substance so the location of the stent can be identified .