A radiopaque marker associated with a stent which is adapted to be implanted into a patient's body lumen to maintain the patency thereof and a convenient and accurate method for affixing the radiopaque marker to the stent. The radiopaque marker defining an acceptable profile and capable of facilitating, under fluoroscopy, the identification of the position, diameter and length of a stent without obscuring the lesion being repaired and without impeding the deformation of an expandable stent.

BACKGROUND OF THE INVENTION 
This invention relates to endoprosthesis devices, generally called stents, 
and, more particularly, radiopaque markers for use with endoprosthesis 
devices. 
Stents are useful in the treatment of atherosclerotic stenoses in blood 
vessels and are generally tubular shaped devices which function to hold 
open a segment of a blood vessel or other anatomical lumen. They are 
particularly suitable for use in supporting and holding back a dissected 
arterial lining which can occlude the fluid passage way therethrough. 
In order to accomplish precise placement of stents, various means are 
employed to identify the position of the stent within a blood vessel. One 
means frequently described for accomplishing precise placement of a stent 
is the attachment of radiopaque markers to the stent so that through the 
use of fluoroscopy, the position of the stent within a blood vessel can be 
identified. Once the stent with its radiopaque markers has been implanted, 
subsequent checkups of the treated segment are easily performed since the 
markers remain visible under fluoroscopy. 
Conventional radiopaque markers, however, have various limitations. Upon 
attachment to a stent, certain conventional radiopaque markers define a 
profile that is readily discernible from that of the stent, thereby 
comprising projections which may undesirably alter the contemplated 
profile of the stent. That is, these conventional radiopaque markers 
protrude from the walls of the stent and depending upon their location 
upon the stent, may either project into the blood flow or into the walls 
of the blood vessel. In addition, these conventional radiopaque markers 
are limited in that their attachment to the stent can be tedious and 
imprecise. 
Other conventional radiopaque markers restrict the expansion capabilities 
of an expandable stent by adding rigidity to the stent in areas designated 
for stent deformation. Still other conventional stents utilize material, 
such as tantalum, that is effective for use in identifying the location of 
a stent within a vessel, but fluoroscopically illuminate so brightly so as 
to obscure proper visibility of the blood vessel lesion, thereby impairing 
the ability to repair the lesion. Finally, conventional radiopaque markers 
do not generally, under fluoroscopy, provide the operator with means to 
accurately assess stent length and diameter. 
To overcome the problems and limitations associated with stents having 
conventional radiopaque markers, it would be desirable to employ 
radiopaque markers that can be consistently and precisely attached to a 
stent, that do not limit the expansion capabilities of an expandable 
stent, that define an acceptable profile, that provide means to assess 
stent length and diameter and that do not obscure the blood vessel lesion 
being repaired. The present invention embodies these characteristics. 
SUMMARY OF THE INVENTION 
The invention provides a radiopaque marker that may be consistently and 
precisely affixed to a stent, that does not limit the expansion 
capabilities of an expandable stent, that has an acceptable profile and 
that may effectively identify the position, diameter and length of a stent 
within a blood vessel without obscuring a lesion being repaired. The 
invention also provides means for affixing to a stent a radiopaque marker 
having the aforementioned characteristics. 
The radiopaque marker of the present invention may be utilized with stents 
having various geometric shapes and materials. In addition, the radiopaque 
markers may be positioned anywhere on a stent and may comprise any 
plateable radiopaque material having various patterns. Further, any 
acceptable means for affixing the radiopaque marker to a stent may be 
employed. It is essential, however, that the means for attaching a 
radiopaque marker, its location upon a stent as well as the material and 
geometric shape of the stent, be selected so that a stent incorporating 
the radiopaque marker of the present invention may benefit from the 
advantages provided thereby. 
In a preferred embodiment, the radiopaque markers of the present invention 
are affixed to both a distal and a proximal end of a generally cylindrical 
stent. In this embodiment, the radiopaque marker material is gold and is 
affixed to the outside circumference of a generally cylindrical stent by 
means of plating. Although gold is the designated material of this 
embodiment, other biocompatible plateable radiopaque materials, such as 
platinum, are equally desirable. Plating is preferable since it can be 
performed easily and with accuracy and can be utilized to produce an 
acceptable radiopaque marker profile. It is contemplated that the 
thickness of the radiopaque marker material upon a stent be in the range 
of about 0.0003 to 0.003 inches on the exterior surface of the stent, and 
if required for fluoroscopic illumination, the same thickness can be 
plated to the inner stent surface. It is also contemplated that the stent 
may comprise any material, for example any metal or plastic, upon which 
gold may be plated. 
Although radiopaque material may be plated on only a portion of the 
circumference of the stent, in a preferred embodiment it is contemplated 
that the entire circumference of the stent be plated, thereby producing a 
stent with a band of radiopaque material at its distal and proximal ends. 
Moreover, it is significant that only the ends of the stent are plated and 
that gold, or a similarly effective material, may be selected as the 
plating material. Plating provides controlled deposition of the radiopaque 
material on the stent thereby controlling its fluoroscopic illumination. 
By plating only the two ends of the stent, the fluoroscopic illumination 
is thus limited to the ends of the stent. These two features minimize the 
possibility of obscuring the fluoroscopic visualization of the blood 
vessel being treated. 
In addition, by plating with radiopaque material at both ends and upon the 
outside of a generally cylindrical stent, not only can the location of the 
stent be determined under fluoroscopy, but the length and diameter as 
well. This is particularly useful where the subject stent is expandable 
since the degree of expansion can be ascertained by noting the height of 
the radiopaque marker and the relative distances between the radiopaque 
markers. Further, it can be determined under fluoroscopy whether or not 
the stent is twisted or otherwise improperly seated within a blood vessel. 
In order to successfully plate gold, or any acceptable radiopaque marker 
material upon a stent, the stent is placed upon a mandrel, masked and 
plated. In a preferred procedure, the stent is placed upon an elongated 
cylindrical mandrel, masked with shrink tubing, portions of which are 
lased away to expose the areas of the stent desired to be plated and 
thereafter, plated with the desired radiopaque material. It is 
contemplated that the mandrel may comprise annular recesses which function 
to allow portions of an interior circumference of a stent, as well as the 
exterior of the stent, to be plated. 
Subsequent to the completion of the plating procedure, in a preferred 
procedure the shrink tubing is detached from the stent and the stent 
removed from the mandrel. It is contemplated that the shrink tubing may be 
cut from the stent utilizing a laser. Alternatively, the shrink tubing may 
be dissolved with chemicals. It is also contemplated that the shrink 
tubing be pre-fabricated or cut to size (by means of a laser) to precise 
dimensions so that it may properly perform its masking function. 
Since a preferred embodiment contemplates gold plating as the avenue for 
affixing radiopaque markers to a stent and since the gold plating may 
stiffen the stent in the areas of plating, it is contemplated that 
expandable stents may be plated in areas where additional rigidity does 
not affect the expansion capabilities of the stent. Thus, portions of a 
stent that do not deform upon expansion are plated with gold or the 
desired radiopaque material. In this way, the stent can freely and 
uniformly expand and elastically deform without additional restrictions, 
thereby accomplishing its expansion function while still benefitting from 
the advantages of the present invention. 
In another embodiment, the entire exterior surface of a stent is plated 
with radiopaque material. Thereafter, the portions designated to retain 
radiopaque material are masked and the radiopaque material is etched away 
from the remaining portions of the stent. 
In yet another embodiment a generally cylindrical stent is fitted with 
radiopaque markers having some geometrical configuration or placed upon a 
stent in some pattern. For instance, a radiopaque marker may comprise a 
sine wave pattern so that under fluoroscopy, the configuration of the 
stent may be quickly ascertained. That is, it can be readily ascertained 
whether the stent is improperly twisted or contorted and in the case of an 
expandable stent, whether the stent has been properly deformed. 
Other features and advantages of the present invention will become apparent 
from the following detailed description, taken in conjunction with the 
accompanying drawings, which illustrate, by way of example, the principles 
of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As is shown in the drawings, which are included for purposes of 
illustration and not by way of limitation, the invention is embodied in a 
radiopaque marker 10 (FIGS. 1A, 1B, 2A, 2B, and 5). Conventional 
radiopaque markers are limited in that they may comprise undesirable 
projections extending from a stent, may be arduous to attach, restrict the 
expansion capabilities of an expandable stent and may be ineffective in 
the identification of the position, orientation and configuration of a 
stent. The radiopaque marker 10 of the present invention defines an 
acceptable, very low profile, may be conveniently affixed to a stent, does 
not impede the expansion capabilities of an expandable stent, and may be 
useful in identifying the position, orientation and configuration of a 
stent within a blood vessel. The radiopaque marker of the present 
invention, therefore, provides superior means of marking a stent. 
The present invention facilitates precise placement of a stent 12 by way of 
its novel configuration, position upon a stent, and material properties. 
The characteristics of a radiopaque marker 10 are selected to assure that 
a stent 12 embodying the radiopaque marker 10 may benefit from the 
advantages which the invention provides. Thus, radiopaque marker 10 may 
have various geometric shapes, comprise various materials and may be 
positioned anywhere on a stent 12, so long as the desired advantages of 
the invention are achieved. 
While stent 12 can include any number of configurations, one preferred 
embodiment includes a plurality of cylindrical elements 13 which are 
interconnected so as to be generally aligned on a common longitudinal 
axis. Stent 12 includes proximal end 14 and distal end 16, and cylindrical 
elements 13 are attached by one or more connecting elements 17. The 
connecting elements 17 interconnect the cylindrical elements so that each 
connecting element 17 connects only cylindrical elements that are adjacent 
to each other. Each cylindrical element is formed from straight segments 
18 connected by curved portions 20 which together form a generally 
serpentine pattern 21. 
In a preferred embodiment, radiopaque marker 10 is plated upon an outer 
circumference of a generally cylindrical stent 12 and upon a proximal end 
14 and a distal end 16 of the stent 12. In another embodiment, it is 
contemplated that an inner circumference underlying the outer 
circumference be plated as well. By utilizing plating as the means for 
affixing radiopaque marker 10 to a stent 12, a minimum profile may be 
achieved. It is contemplated that the thickness of radiopaque marker 10 be 
in the range of about 0.0003 to 0.003 inches. As such, the radiopaque 
marker 10 does not appreciably alter the profile of stent 12 and 
therefore, does not result in stent 12 having substantial projections 
extending into the blood flow or into the walls of the blood vessel being 
repaired. 
In addition, by plating or similarly affixing radiopaque material upon a 
stent, radiopaque markers 10 can be easily and accurately affixed to a 
stent. That is, plating is an improved means of affixing radiopaque 
material to stent 12 over conventional means of affixing radiopaque 
markers, such as sewing or bonding, which can be tedious and imprecise. 
Although it is not necessary for all embodiments, the preferred embodiment 
contemplates that the entire circumference of the stent be plated at both 
its proximal end 14 and distal end 16. It is also contemplated that the 
plating material may be gold or a material, such as platinum, which has 
similar radiopaque characteristics. 
It is significant that gold, or a similar material, is contemplated as the 
preferred radiopaque marker material. Other metals suitable as radiopaque 
markers include, for example, platinum and silver. By selecting such a 
material, the stent may be effectively identified under fluoroscopy. In 
various conventional stents, the radiopaque material employed glows so 
brightly under fluoroscopy so as to obscure the lesion being repaired. In 
contrast, the images of radiopaque markers comprised of gold or platinum 
do not, under fluoroscopy, substantially obscure the lesion being 
repaired. 
It is also significant that the preferred embodiment contemplates affixing 
radiopaque markers 10 to the ends of stents 12 having various geometric 
configurations (see FIGS. 2A and 2B). By doing so, the orientation or 
configuration of the stent 12, irrespective of its geometric 
configuration, can be ascertained, which is particularly important to the 
determination of whether a stent has completely repaired a blood vessel. 
By noting the distance between the radiopaque bands, the length of the 
stent 12 can be ascertained and compared to an expected stent length. By 
observing the height or width of the radiopaque markers 10, the extent of 
expansion of an expandable stent 12 can be ascertained and compared with 
expected values. Similarly, by examining the radiopaque markers of the 
present invention under fluoroscopy, it can be determined whether the 
stent 12 is twisted or otherwise improperly seated within a vessel. 
The plating of radiopaque markers upon a stent may add some rigidity to a 
stent in the areas of plating. Since this is the case, the preferred 
embodiment contemplates affixing radiopaque markers 10 to only those 
portions of an expandable stent 12 that do not deform upon expansion. As 
shown in FIGS. 1A and 1B for example, radiopaque markers 10 may be affixed 
to straight segments 18 of the proximal end 14 and distal end 16 of a 
stent. Upon expansion, the curved portions 20 of the stent 12 may deform 
so as to allow the stent 12 to expand, while the straight portions 18 may 
remain undeformed. By affixing radiopaque markers 10 to the straight 
portions 18 of stent 12 as shown in FIGS. 1A and 1B, the additional 
rigidity added to the stent 12 by the radiopaque markers 10 does not 
impede expansion. Therefore, an expandable stent having radiopaque markers 
10 of the present invention can uniformly and predictably expand. 
In order to plate a radiopaque marker 10 upon a stent 12, a mandrel 30 may 
be employed (see FIG. 3A). The mandrel 30 may comprise any suitable 
material formed into an elongate cylindrical shape having a main portion 
21 with a cross-sectional diameter sized for receiving stent 12. The 
mandrel may further embody a collar 22 formed or attached to one end of 
the mandrel 30 that has a cross-sectional diameter larger than that of 
stent 12 and two annular recesses 23 formed in the main portion 21 which 
have cross-sectional diameters less than that of the main portion 21. The 
collar 22 functions as a stop and may aid in registering stent 12 upon the 
mandrel 30. Annular recesses 23 function to allow interior surfaces of 
stent 12 to be plated. In another embodiment of mandrel 30 (FIG. 3B), 
recesses 23 may be sufficiently shallow or be missing entirely from 
mandrel 30 so that, where desirable, interior surfaces of stent 12 are not 
plated with radiopaque material. 
In a preferred method, stent 12 is placed upon mandrel 30 and heat shrink 
tubing 32 (see FIGS. 4A and 4B) is slipped over stent 12. The heat shrink 
tubing 32 is then exposed to heat to shrink the tubing on the stent 12. It 
is contemplated that the heat be concentrated at a midpoint of the heat 
shrink tubing 32 and then gradually apply heat towards each end so as to 
prevent distortion of the stent. The shrink tubing 32 may be any polyester 
having heat shrink properties and the ability to mask the stent during the 
electroplating process. 
Once the heat shrink tubing 32 is snug upon stent 12, the stent may be 
precisely positioned on the mandrel 30 and then temporarily secured in 
place using a high temperature wax. Where it is desired to plate an 
interior as well as an exterior surface of stent 12, the annular recesses 
23 may be aligned with the interior portions of the stent 12 desired to be 
plated (see FIG. 4A). Where it is deemed undesirable to plate the interior 
surface, no such further alignment is necessary (see FIG. 4B). Next, the 
curved portions 20 (FIG. 1B) of stent 12 as well as the ends of the 
mandrel 30 can be dipped in high temperature wax to prevent them from 
being plated. 
In order to plate the desired portions of stent 12, the heat shrink tubing 
32 surrounding portions of the stent 12 to be plated may be cut away using 
a standard CO.sub.2 laser or its equivalent. The laser output is to be 
limited so that stent 12 and mandrel 30 are not affected. By utilizing a 
mandrel 30 without annular recesses (see FIGS. 3B and 4B), portions of the 
heat shrink tubing 32 may be lased away so that only the outer 
circumferences of stent 12 may be plated. By employing the mandrel 30 
illustrated in FIGS. 3A and 4A, portions of the heat shrink tubing 32 
overlaying annular recesses 23 may be lased away, thereby resulting in a 
stent 12 having desired portions of its interior as well as its exterior 
12 plated with radiopaque material (see FIG. 2B). 
As with any electroplating process, an electrical current is used in the 
process of putting a metallic coating on a metal or other conducting 
surface. In the preferred embodiment, a gold solution exists in the form 
of positively charged ions that have lost one or more electrons. The stent 
is connected to the cathode or negative terminal and the anode, or 
positive electric terminal, is connected to the stainless steel mandrel 30 
which is dipped into the gold solution. The ions are attracted to the 
cathode and the coating is deposited on the stent metal surface. As is 
known in the art, the thickness of the layer deposited depends on the 
amperage of the electric current, the concentration of the metallic ions 
and the length of time that the stent is plated. The plating process 
should be at a low enough amperage to prevent mapping, nodules, and a 
matte surface. 
After plating the gold on the stent, the wax is removed from stent 12 and 
mandrel 30 by inserting them in acetone or an equivalent solution. 
As can be appreciated from the drawings (FIGS. 2A and 2B), the end portions 
36,38 of a stent 12 which are not masked, are plated with radiopaque 
material and the portions of the stent 12 which are masked, are not 
plated. 
Once the stent 12 is plated with a radiopaque marker 10, it is removed from 
the mandrel 30 and the heat shrink tubing 24 is stripped away. The heat 
shrink tubing 24 may be removed, for example, by cutting it with a laser 
or in the alternative, dissolved with chemicals. Finally, the mandrel is 
withdrawn from the plated stent 12 and the stent 12 may be cleaned with an 
Alcomox or equivalent solution. 
In another embodiment, the entire exterior surface of a stent may be plated 
with radiopaque material. Subsequent to plating, the stent 12 is masked 
and subjected to etching. In this embodiment, the areas designated to 
retain radiopaque material are masked and the radiopaque material is 
etched away from the remaining portions of the stent. 
In yet another embodiment, radiopaque markers having some pattern are 
affixed to a generally cylindrical stent so as to facilitate the 
identification, position and configuration of a stent 12 within a blood 
vessel. For example, the pattern of a radiopaque marker 10 may be in the 
form of a sine wave. As the sine wave expands along with the stent during 
deployment, it is visible under fluoroscopy and it can be determined 
whether the stent 12 is properly seated within a blood vessel by viewing 
the amplitude and shape of the sine wave radiopaque marker. As another 
example, as depicted in FIG. 5, the pattern of a radiopaque marker 10 may 
be a continuous or dashed line extending from the proximal end 14 to the 
distal end 16 of stent 12. A longitudinal marker of the type described 
will allow the doctor to determine if the stent has twisted upon 
deployment or if it expanded unevenly. 
In an alternative embodiment, a radiopaque plastic may be coated or affixed 
to all or a portion of a stent. In this embodiment, a radiopaque plastic 
is formed by loading a plastic material with a radiopaque material such as 
barium sulfate or bismute trioxide. The resultant mixture is then coated 
or affixed to the stent. Several methods of affixing the radiopaque 
material to the stent are contemplated and include: (1) melting the 
radiopaque material and then dipping the stent into the melt; (2) solvent 
casting; and (3) vacuum deposition. These methods are generally known and 
various process steps are apparent to those skilled in the art. As with 
the plating process steps described above, the stent can be masked and 
mounted on a mandrel and then coated by dipping, solvent casting, or 
vacuum deposition. 
From the foregoing it will be appreciated that the radiopaque marker of the 
invention effectively identifies the location and configuration of a stent 
within a patient's body lumen and provides a method and apparatus for 
constructing the same. 
While several particular forms of the invention have been illustrated and 
described, it will also be apparent that various modifications can be made 
without departing from the spirit and scope of the invention. Thus, it 
should be understood that various changes in form, and detail, and 
application of the present invention may be made without departing from 
the spirit and scope of this invention.