Abstract:
The present invention relates to a stent delivery system and a process for mounting a stent onto a delivery system. More specifically, the present invention relates to a method of loading a stent onto a balloon and mounting the stent balloon assembly onto a catheter. The premounting of the stent onto the balloon subassembly allows the stent to be crimped in a way that the crimping recoil can be compensated and stent retention is kept at a maximum.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a stent delivery system as well as a process for mounting a stent onto a balloon. More specifically, the present invention relates to a method of increasing stent retention of a balloon expandable stent on a balloon of a balloon catheter by compensating for crimping recoil. 
       BACKGROUND OF THE INVENTION 
       [0002]    A stent is commonly used alone or in conjunction with angioplasty to ensure patency through a patient&#39;s stenosed vessel. Stents overcome the natural tendency of the vessel walls of some patients to restenose after angioplasty. A stent is typically inserted into a vessel, positioned across a lesion, and then expanded to create or maintain a passageway through the vessel, thereby restoring near-normal blood flow through the vessel. 
         [0003]    A variety of stents are known in the art, including self-expandable and expandable stents, as well as wire braid stents. One such stent is described, for example, in U.S. Pat. No. 4,733,665 to Palmaz. Expandable stents are typically delivered to treatment sites on delivery devices, such as balloon catheters or other expandable devices. Balloon catheters may comprise a balloon having a collapsed delivery configuration with wings that are wrapped and folded about the catheter. An expandable stent is then disposed over the balloon and crimped into a collapsed delivery configuration about the balloon by compressing the stent onto the balloon. The stent and balloon assembly may then be delivered, using well-known percutaneous techniques, to a treatment site within the patient&#39;s vasculature, for example, within the patient&#39;s coronary arteries. Once the stent is positioned across a lesion at the treatment site, it is expanded to a deployed configuration by inflating the balloon. The stent contacts the vessel wall and maintains a path for blood flow through the vessel. 
         [0004]    Significant difficulties have been encountered during stent delivery and deployment, including difficulty in maintaining the stent on the balloon and in achieving symmetrical expansion of the stent when deployed. In positioning a balloon expandable stent on the delivery catheter over the fluid expandable balloon, the stent must be smoothly and evenly crimped to closely conform to the overall profile of the catheter and the unexpanded balloon. It has been noted that, due to physical properties of the material used in manufacturing the stent (e.g. stainless steel, tantalum, niobium, platinum, cobalt, chromium or alloys thereof) there is a certain amount of “recoil” of the stent despite the most careful and firm crimping. That is the stent evidences a tendency to slightly open up from the fully crimped position and once the crimping force has been released. For example, in the typical stent delivery and deployment assembly, if the stent has been fully crimped to a first diameter, the stent has been observed to open up or recoil to a second diameter which is approximately 1% to 10% greater than the first diameter. This phenomenon has been characterized as “crimping recoil”. Due to crimping recoil to this slightly enlarged diameter, it can be understood that the stent tends to evidence a certain amount of looseness from its desired close adherence to the overall profile of the underlying catheter and balloon. That is, the stent tends to have a perceptible relatively slack fit in its mounted and crimped position. During delivery, the stent can thus tend to slip and dislocate from its desired position on the catheter or even become separate from the catheter, requiring further intervention by the physician. 
         [0005]    The degree of crimping recoil highly depends on the stent material as well as the stent design itself. Presently there is a desire to manufacture stents not only from stainless steel but also from new materials like e.g. cobalt chromium alloys and niobium tantalum alloys. These new materials show increased strength and radiopacity over prior known stent materials and thus allow reduction of wall thickness of the stent struts while the stent&#39;s radial force and radio-visibility stays the same. Since reduction of strut thickness has clinically shown to reduce in-stent-restenosis there is a great interest in using these novel stent materials in stent manufacturing. The tradeoff of the increased strength of these alloys is that they often show increased recoil behaviour over the prior known stent materials. 
         [0006]    Several techniques have been developed to more securely anchor the stent to the balloon and to ensure more symmetrical expansion. These include plastically deforming the stent so that it is crimped onto the balloon, and sizing the stent such that its internal diameter provides an interference fit with the outside diameter of the balloon catheter. Such techniques have several drawbacks, including less than optimal securement of the stent to the balloon. Consequently, the stent may become prematurely dislodged from the balloon during advancement of the stent delivery system to the treatment site. 
         [0007]    Stent delivery systems utilizing a removable sheath disposed over the exterior surface of the stent, which is removed once the stent is positioned at the treatment site, have also been proposed, for example, in U.S. Pat. No. 5,690,644 to Yurek et al. Such systems may be used with or without retainer rings and are intended to protect the stent during delivery and to provide a smooth surface for easier passage through the patient&#39;s vasculature. However, the exterior sheath increases the crossing profile of the delivery system while decreasing flexibility, thereby decreasing the ability of the device to track through narrowed and tortuous anatomy. 
         [0008]    U.S. Pat. No. 6,106,530 to Harada describes a stent delivery device comprising a balloon catheter having stoppers disposed proximal and distal of a balloon onto which a stent is affixed for delivery. The stoppers are separate from the balloon and maintain the stent&#39;s position in relation to the balloon during delivery. As with the removable sheaths discussed previously, the stoppers are expected to increase delivery profile and decrease flexibility of the stent/balloon system. 
         [0009]    U.S. Pat. No. 6,110,180 to Foreman et al. provides a catheter with a balloon having pre-formed, outwardly-extending protrusions on the exterior of the balloon. A stent may be crimped onto the balloon such that the protrusions extend into the gaps of the stent, thereby securing the stent about the balloon for delivery. A drawback to this device is the added complexity involved in manufacturing a balloon with pre-formed protrusions. Additionally, if the protrusions are not formed integrally with the balloon, there is a risk that one or more of the protrusions may detach during deployment of the stent. The protrusions may also reduce flexibility in the delivery configuration, thereby reducing ability to track through tortuous anatomy. 
         [0010]    U.S. Pat. No. 6,159,227 to Di Caprio et al. provides a catheter with a securement means such as a corrugated tube mounted on the inner shaft underneath the balloon to compensate for crimp recoil and provide increased stent friction. However, similar to what was discussed above with regard to the exterior sheath; the corrugated tube increases the crossing profile of the delivery system while decreasing flexibility, thereby decreasing the ability of the device to track through narrowed and tortuous anatomy. 
         [0011]    In each of the devices and methods described above, the balloon is pre-mounted onto a catheter shaft and the stent is then crimped down onto the balloon and catheter shaft. Typically, catheters shafts are constructed of polymeric materials, and thus compress slightly and also re-coil much like the stent does as described above, thereby contributing to the problem. 
         [0012]    In view of the drawbacks associated with previously known methods and apparatus for loading a stent onto a stent delivery system, it would be desirable to provide methods and apparatus that overcome those drawbacks. 
         [0013]    It would be desirable to provide methods and apparatus for loading a stent onto a stent delivery system that enhance positional stability of the stent during delivery. It would further be desirable to provide methods and apparatus for loading a stent onto a stent delivery system wherein the delivery system comprises a crossing profile and flexibility suitable for use in tortuous and narrowed anatomy. It would still further be desirable to provide methods and apparatus for loading a stent onto a stent delivery system that provide a substantially symmetrical expansion of the stent at deployment. 
       SUMMARY OF THE INVENTION 
       [0014]    In view of the foregoing, it is an object of the present invention to provide a stent delivery system with increase stent retention as well as methods and apparatus for loading a stent onto a delivery system and deployment that overcome drawbacks associated with previously known methods and apparatus. 
         [0015]    In accordance with one embodiment of the present invention there is provided a stent delivery system having a contracted delivery configuration and an expanded deployed configuration, the stent delivery system comprising, a delivery catheter having an inflatable balloon, and a stent being disposed about the balloon, wherein the stent in its contracted delivery configuration exerts a constant elastic force on the balloon. 
         [0016]    In accordance with the present invention there is provided a method of fabricating a stent delivery system comprising the steps of: (1) providing a balloon comprising a cylindrical balloon body having a distal and a proximal balloon cone and a proximal and a distal balloon sleeve, (2) providing a stent which can be transformed between a first configuration to a second collapsed configuration, (3) disposing the stent about at least a portion of the cylindrical balloon body, (4) applying a crimping force to the stent, and (4) mounting the balloon stent assembly onto a catheter. 
         [0017]    It is an object to provide methods and apparatus for loading a stent onto a stent delivery system that enhance positional stability of the stent during delivery. 
         [0018]    It is an object to provide methods and apparatus for loading a stent onto a stent delivery system wherein the delivery system comprises a crossing profile and flexibility suitable for use in tortuous and narrowed anatomy. 
         [0019]    It is also an object to provide methods and apparatus for loading a stent onto a stent delivery system that provide a substantially symmetrical expansion of the stent at deployment. 
         [0020]    These and other objects of the present invention are achieved by providing methods and apparatus for mounting a stent onto a balloon and mounting the balloon stent assembly onto a catheter. In a preferred embodiment, the stent is a balloon expandable stent and is manufactured in a fully-expanded state or in an intermediate-expanded state (i.e., having a diameter smaller than its fully-expanded, deployed diameter, but larger than its compressed delivery diameter). 
         [0021]    The medical balloon is dimensioned for attachment to a catheter preassembly in order to result in a balloon dilatation catheter as for example described in U.S. Pat. Appl. 2005/0267408, or U.S. Pat. Appl. 2006/0004328 which are herewith incorporated by reference. In a preferred embodiment, the balloon comprises a cylindrical balloon body, a distal and a proximal balloon cone and a proximal and a distal balloon sleeve. The sleeves of the medical balloon are prefixed to a crimping mandrel. The crimping mandrel is configured to allow in/deflation of the balloon once fixated to the mandrel. The stent is then disposed about at least a portion of the cylindrical balloon body. Subsequently the stent is crimped onto the balloon by any suitable crimping technique known in the art. As during crimping the balloon is not mounted on the final catheter assembly but on a crimping mandrel, the diameter to which the stent is crimped down can be easily adjusted by actuation of the crimping tool and/or by adjusting the dimensions of the portion of the crimping mandrel lying underneath the balloon. The crimp diameter is adjusted to be smaller than the final crimped stent diameter is intended to be. Thus, the naturally occurring stent crimping recoil will be compensated by a respective “over crimping” of the stent on the balloon. After the stent is crimped on the balloon, the crimping mandrel is removed and the balloon stent assembly is mounted on a catheter preassembly to result in the final stent delivery device or system. In a preferred embodiment, the distal balloon sleeve of the balloon stent subassembly will be sealingly attached to a distal portion of an guide wire tube of the catheter subassembly, while the proximal balloon sleeve of the balloon stent subassembly will be sealingly attached to the distal portion of the in/deflation tube or outer tube of the catheter subassembly to allow the medical balloon to be inflated for placement of the stent in the target vessel. Preferably, the outer diameter of the guide wire tube is slightly larger than the average inner diameter left open inside the balloon after the stent has been crimped thereon. This can be achieved for example by using a mandrel with an outer diameter underneath the balloon smaller than the outer diameter of the guide wire tube of the catheter subassembly. Once the balloon with the stent crimped thereon, also referred to as balloon stent subassembly, is mounted on the catheter subassembly the stent crimped on the balloon exerts a constant elastic force onto the balloon and the guide wire tube. This constant elastic force leads to a maximum of frictional force between the balloon and the stent. 
         [0022]    In conventional crimping processes the stent is crimped onto the balloon of a balloon dilatation catheter to form the final stent delivery device. In these methods the stent is pressed onto the balloon and the friction forces merely result from the press fit or interference fit between balloon and stent, the stent cannot exert an elastic force onto the guide wire tube. In conventional stent delivery systems stent retention can only be achieved by an unfolding of the balloon to a greater extend than the stent crimping recoil forces the stent to open. 
         [0023]    Apparatus and method of the present invention may be used with a variety of prior art stents, such as balloon expandable stents, and may include tubular slotted stents, connected stents, articulated stents, multiple connected or non-connected stents, and bi-stable stents. In addition to apparatus and methods of production, methods of using the apparatus of the present invention are provided. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    Further features of the invention, its nature and various advantages will be more apparent from the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings, in which like reference numerals refer to like parts throughout, and in which: 
           [0025]      FIG. 1  is a side view of a stent delivery system in accordance with the present invention. 
           [0026]      FIG. 2  is a side view of the medical balloon prefixed to a crimping mandrel. 
           [0027]      FIG. 3  depicts a side view of the stent crimped on the medical balloon, the medical balloon prefixed on a crimping mandrel. 
           [0028]      FIG. 4A  is a side view of the crimped stent balloon subassembly. 
           [0029]      FIG. 4B  depicts a side view of the distal portion of a catheter shaft subassembly positioned on a assembly mandrel. 
           [0030]      FIG. 5  is a side view of a stent delivery system according to the present invention in its expanded configuration. 
           [0031]      FIGS. 6A to 6D  are side views, partially in section, of the stent delivery system of  FIG. 1  disposed within a patient&#39;s vasculature, depicting a method of using the apparatus in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    The present invention is directed to a stent delivery system having a contracted delivery configuration and an expanded deployed configuration, the stent delivery system comprising a delivery catheter having an inflatable balloon; and a stent being disposed about the balloon, wherein the stent in its contracted delivery configuration exerts a constant elastic force on the balloon. The present invention further comprises methods and apparatus for mounting a crimped stent and balloon assembly onto a delivery system. More specifically, the present invention provides methods and apparatus for fabricating a stent delivery system comprising a delivery catheter having an inflatable balloon; and a stent being disposed about the balloon, wherein the stent in its contracted delivery configuration exerts a constant elastic force on the balloon. The methods for fabricating a stent delivery system comprise providing a balloon comprising a cylindrical balloon body, a distal and a proximal balloon cone and a proximal and a distal balloon sleeve, providing a stent which can be transformed from a first diameter or collapsed configuration to a second diameter or expanded configuration, disposing a within a lumen of cylindrical balloon body, wherein the mandrel includes a reduced diameter portion, disposing the stent about at least a portion of the cylindrical balloon body, crimping the stent and balloon, and subsequently mounting the balloon stent assembly or also called crimped balloon assembly onto a catheter. 
         [0033]    With reference to  FIG. 1  an apparatus in accordance with the present invention is described. As seen in  FIG. 1 , stent delivery system  10 , illustratively shown in a collapsed delivery configuration, comprises balloon expandable stent  20  loaded on balloon  14  of delivery catheter  12 . Stent  20  comprises an illustrative balloon expandable stent and may be replaced with other stents known in the art. 
         [0034]    Delivery catheter  12  preferably includes markers  17  disposed distal of and proximal to stent  20  that facilitate placement of stent  20  on balloon  14 , and that facilitate positioning of stent delivery system  10  at a treatment site within a patient&#39;s vasculature. Markers  17  are preferably radiopaque and fabricated from a radiopaque material, such as platinum, platinum iridium alloys or gold. Catheter  12  preferably also comprises guide wire lumen  13  and inflation lumen  15 , which is coupled to balloon  14 . It is preferred that the markers  17  are flush with or substantially flush with and outer diameter of the delivery catheter  12 . It is further contemplated that the markers  17  may be constructed of a radiopaque ink or radiopaque polymeric material which may be printed onto or formed within or onto the delivery catheter  12 . 
         [0035]    Balloon  14  is expandable by injection of a suitable medium, such as carbon dioxide, saline, or other biocompatible fluids and gasses via inflation lumen  15 . Balloon  14  preferably expands stent  20  to a deployed configuration under application of pressure in the range of about 3-14 atm. Additionally, balloon  14  preferably has a rated burst pressure above 10 atm, and even more preferably between about 12-14 atm. Balloon  14  may be fabricated from a variety of materials, including polyamides like e.g. Nylon, or modified polyamides, polyethylene terephthalate, polyethylene, and polyether/polyamide block copolymers, such as PEBAX or blends and multilayers thereof. 
         [0036]    Additionally, balloon  14  may be fabricated from an elastomeric polyester block copolymer having an aromatic polyester hard segment and an aliphatic polyester soft segment, such as “Pelprene”, which is marketed by the Toyobo Corporation of Osaka, Japan. Balloon  14  also may be fabricated from a copolymer having a polybutylene terephthalate hard segment and a long chain of polyether glycol soft segment, such as “Hytrel” from the DuPont Corporation of Wilmington, Del. 
         [0037]    Illustrative stent  20  may be fabricated from a variety of materials, including polymers and metals or a combination thereof (for example and not limitation stainless steel, tantalum, niobium, platinum, cobalt, chromium or alloys thereof), and may comprise any of a variety of prior art stents, such as balloon expandable stents, including tubular slotted stents, connected stents, articulated stents, multiple connected or non-connected stents, and bi-stable stents. Stent  20  also may include external coating C configured to retard restenosis or thrombus formation in the vessel region surrounding the stent. Alternatively, coating C may deliver therapeutic agents into the patient&#39;s blood stream or vessel wall. 
         [0038]    The delivery catheter according to the present invention is preferably a catheter that is guided over a guide wire to a target site in a patient&#39;s vessel. The catheter may be an over-the-wire type catheter or a rapid-exchange catheter. Further, the configuration of the guide wire tube and the inflation lumen tube may be a coaxial constriction, a side-by-side construction, a smiley lumen or any variation or combination thereof. 
         [0039]    Referring now to  FIGS. 2-5  there is shown a method of producing the stent delivery system  10  in accordance with the present invention. As shown in  FIG. 2 , a balloon  14  is provided, the balloon comprises a cylindrical balloon body  2  having a distal balloon cone  5  and a proximal balloon cone  3  and a proximal balloon sleeve  4  and a distal balloon sleeve  6 . The balloon may be constructed of any of the materials described above. As shown in  FIG. 2 , a crimping mandrel  7  is disposed through a lumen of the balloon. 
         [0040]    The crimping mandrel  7  is formed from at least two parts, a proximal crimping mandrel portion  9  and a distal crimping mandrel portion  10  that are detachably connected at a joint  11 . The outer diameter of the mandrel&#39;s middle portion that is located underneath the balloon  14  is less than the outer diameter underneath the balloon-sleeves  4 ,  6  and less than the outer diameter of the inner body/guide wire lumen that is desired to be mounted underneath the balloon. The outer diameter of the mandrel  7  underneath the proximal balloon sleeve  4  corresponds to the inner diameter of the proximal balloon sleeve  4  whereas the outer diameter of the mandrel  7  underneath the distal balloon sleeve  6  corresponds to the inner diameter of the distal balloon sleeve  6 . The joint  11  of the two crimping mandrel portions  9  and  10  is located at a position underneath the balloon where its outer diameter is minimal. One part of this mandrel  7 , preferably the proximal part  9  comprises an inner lumen that can be used to in-/deflate the balloon for folding and embedding. The crimping mandrel  7  is used for folding the balloon and crimping/embedding the stent into the balloon as will be described in detail below. 
         [0041]    The balloon  14  is sealingly attached to the crimping mandrel  7  in a liquid tight manner at both balloon-sleeves  4 ,  6  by either welding, adhesive bonding, by wrapping an elastic band or ring about the sleeve or simply by shaping of the mandrel such that interference between the mandrel and the balloon sleeve  4 ,  6  forms a fluid tight seal. Once the balloon  14  is fixed and sealed on the crimping mandrel  7 , the balloon  14  can be inflated and deflated over the inflation lumen  8  of the crimping mandrel  7  to ensure that a fluid tight seal is formed between the balloon sleeves and the mandrel. In a preferred embodiment the balloon  14  gets folded or pleated around the crimping mandrel  7  in order to obtain a small cross sectional profile of the balloon. 
         [0042]    Generally, the crimping mandrel  7  should not have any sharp edges so that it cannot scratch the balloon  14 . It may entirely consist of polymer (e.g. Polyimide, PEEK or PTFE) or of a metallic core that is polished or entirely or partly coated e.g. with Parylene, Polyimide, Teflon, or PTFE. 
         [0043]    It is obvious to the person skilled in the art that the crimping mandrel  7  can be of various shapes and constructions. For example the mandrel can be of dog bone shape with a first distal outer diameter which is equal to the inner diameter of the distal balloon sleeve  6 , a second outer diameter which is smaller that the first outer diameter and smaller than the outer diameter of the inner body of the catheter device and a third outer diameter which is equal to the inner diameter of the proximal balloon sleeve  4 . Instead of a joint in the region of the smallest outer diameter, the mandrel may comprise a predetermined breaking point. In another preferred embodiment the mandrel  7  has a first distal outer diameter which is equal to the inner diameter of the distal balloon sleeve  6  and second outer diameter which is smaller than the first outer diameter. In the region underneath the proximal balloon sleeve, an additional removable ring or short tube with an outer diameter corresponding to the inner diameter of the proximal balloon sleeve  4  and an inner diameter configured to pressfit to the second diameter of the mandrel is provided to allow liquid tight sealing of the proximal and distal balloon sleeve  4 ,  6  to the crimping mandrel  7 . Alternatively, the mandrel&#39;s outer diameter underneath the distal balloon sleeve  6  can be adapted to the inner diameter of the distal balloon sleeve  6  by an additional removable ring or short tube while the proximal diameter of the crimping mandrel  7  is fixed. Further, the mandrel  7  may have one constant outer diameter corresponding to the smallest diameter required underneath the cylindrical balloon body and removable adaptor rings or short tubes corresponding to the dimensions of distal and proximal balloon sleeves, respectively, will be employed to sealingly attach the balloon  14  to the crimping mandrel  7 . 
         [0044]    In another embodiment the mandrel may be configured as a two part mandrel wherein the two parts of the mandrel are not affixed to each other. In this embodiment the outer diameter of the first part of the mandrel corresponds to the inner diameter of the distal balloon sleeve and the outer diameter of the second part of the mandrel corresponds to the inner diameter of the proximal balloon sleeve in order to allow to sealingly attach the balloon  14  to the two parts of the mandrel. No part of the mandrel is located underneath the cylindrical balloon body  2 , thus allowing a minimal crimping diameter. 
         [0045]    Referring now to  FIG. 3 , there is shown the next step in forming a stent delivery catheter in accordance with the present invention. As shown in  FIG. 3 , a stent  20  is radially disposed about the balloon and mandrel assembly, wherein the stent  20 , balloon  14  and the mandrel  7  is placed into a crimping device. The stent  20  can be transformed to a collapsed configuration from an expanded configuration. As shown, the stent is disposed over at least a portion of the cylindrical balloon body  2  of the optionally folded balloon  14  and the stent is crimped onto the balloon  14  /crimping mandrel  7  assembly. 
         [0046]    Crimping of the stent on the medical balloon is performed by standard crimping techniques as for example described in U.S. Pat. No. 5,836,965 to Jendersee et al; U.S. Pat. Appl. No. 2005/0143752 to Schwager et al; or U.S. Pat. No. 5,976,181 to Whelan et al, which are herewith incorporated by reference. 
         [0047]    Once the stent  20  is crimped on the balloon  14  and preferably also embedded into the balloon  14  the crimping mandrel  7  can be split into its two parts  9 ,  10  and both crimping mandrel portions  9 ,  10  can be retrieved in proximal and distal direction, respectively. This results in a stent balloon preassembly  24  as shown in  FIG. 4A  wherein the stent is crimped down to the cylindrical balloon portion  2  to an inner stent diameter preferably smaller than the inner diameter of the proximal and/or distal balloon sleeve  4 ,  6 . 
         [0048]    The smaller diameter of the crimping mandrel  7  in its middle portion is adjusted to compensate for the crimp-recoil of the stent  20 . With the crimping tongs of a commonly known crimping tool fully closed, the stent  20  and balloon material  14  will create a tight fit on the crimping mandrel  7 . As soon as the crimping tongs get released the recoil of the stent material will cause the stent to open up again slightly and loosen the grip of the stent  20  and balloon-material  14  to the mandrel  7 . Ideally the crimping mandrel&#39;s smaller diameter is dimensioned in a way that the stent  20  just opens up that much that its inner diameter in combination with the balloon material is slightly less than the outer diameter of the inner body  23  that is intended to be mounted inside the balloon  14 . In any case crimping mandrel&#39;s smaller outer diameter in its middle portion is smaller than the outer diameter of the inner body  23  of the catheter device  12 . 
         [0049]    As shown in  FIGS. 4A and 4B , the next step in accordance with the present invention is to secure the crimped balloon/stent assembly about a catheter shaft  12 . Referring now to  FIG. 4B  there is shown a distal end portion of a catheter subassembly  12  in accordance with the present invention as described above. A mandrel is inserted into the guidewire lumen of the catheter subassembly  12 , a distal end  18  of the mandrel is formed having a conical shape. The distal end of the catheter subassembly, including the mandrel  22 , is disposed through the lumen of the crimped balloon/stent assembly as indicated by the arrow. Due to the elastic behaviour of the stent  20  and its crimped inner diameter of slightly less than the outer diameter of the inner tube  23 , the stent  20  exerts a constant elastic force on the balloon  14  and the inner catheter body  23 . Thereby a maximum of frictional force between the stent  20  and the balloon  14  is achieved resulting in a maximum of stent retention. 
         [0050]    Finally, the distal balloon sleeve  6  is attached to the inner body  23  and the proximal balloon sleeve  4  is attached to the outer body  19  of the catheter preassembly  12 . For better illustration  FIG. 5  shows a side view of a distal part of one embodiment of the stent delivery system according to the present invention in its expanded configuration. In this embodiment an over-the-wire or rapid-exchange catheter with a coaxial shaft configuration is illustrated, however any other catheter construction like side-by-side or smiley lumen may be employed. The distal balloon sleeve  6  of the balloon  14  carrying the stent  20  is sealingly attached to a distal portion of the inner tube or guide wire tube  23  of the catheter subassembly  12 , whereas the proximal balloon sleeve  4  of the balloon is sealingly attached to the distal end of the outer tube  19  of the catheter subassembly  12 . The attachment of the balloon to the catheter subassembly can be done for example and not for limitation by light welding, laser welding, hot jaw welding, hot air welding or by applying an adhesive. 
         [0051]    In an alternative method of production of the stent delivery catheter according to the present invention, the outer body and proximal balloon sleeve may be attached to each other before the stent is disposed and crimped onto the balloon. 
         [0052]    In a preferred embodiment the stent delivery catheter according to the present invention further comprises radiopaque markers  17  on the inner tube  23  underneath the stent  20  or adjacent to the stent ends. In a more preferred embodiment these radiopaque markers  17  do preferably consist of a polymeric material (e.g. barium sulphate dotted polymers) avoiding sharp edges as on commonly used metallic markers. Alternatively the metallic markers can be swaged with rounded edges and/or covered by a thin polymeric film. In an even more preferred embodiment the metallic or polymeric markers may be incorporated into the tube to result in a flush outer surface of the markers and the inner lumen tube. The markers can be very accurately positioned/adjusted to the position of the stent. 
         [0053]    Referring now to  FIGS. 6 , a method of using stent delivery system  10  of the present invention is described. Stent delivery system  10  is disposed in a contracted delivery configuration with stent  20  disposed over balloon  14  of delivery catheter  12 . The stent exerts a constant elastic force on the balloon  14 . As seen in  FIG. 6A , the distal end of catheter  12  is delivered to a target site T within a patient&#39;s vessel V using, for example, well-known percutaneous techniques. Target site T may, for example, comprise a stenosed region of vessel V. The radiopacity of markers  17  may facilitate positioning of system  10  at the target site. Alternatively, stent  20  or other portions of catheter  12  may be radiopaque to facilitate positioning. 
         [0054]    In  FIG. 6B , balloon  14  is inflated, for example, via an inflation medium delivered through inflation lumen  15  of catheter  12 . Stent  20  expands to the deployed configuration in which it contacts the wall of vessel V at target site T. Balloon  14  is then deflated, as seen in  FIG. 6C , and delivery catheter  12  is removed from vessel V, as seen in  FIG. 6D . 
         [0055]    Stent  20  remains in place within vessel V in the deployed configuration in order to reduce restenosis and recoil of the vessel. Stent  20  also may comprise external coating C configured to retard restenosis or thrombus formation around the stent. Alternatively, coating C may deliver therapeutic agents into the patient&#39;s blood stream or a portion of the vessel wall adjacent to the stent. 
         [0056]    Although preferred illustrative embodiments of the present invention are described hereinabove, it will be evident to those skilled in the art that various changes and modifications may be made therein without departing from the invention. 
         [0057]    It is intended in the appended claims to cover all such changes and modifications that fall within the true spirit and scope of the invention.