Abstract:
Prosthesis delivery devices and methods are provided that enable precise control of prosthesis position during deployment. The prosthesis delivery devices may carry multiple prostheses and include deployment mechanisms for delivery of a selectable number of prostheses. Control mechanisms are provided in the prosthesis delivery devices that control either or both of the axial and rotational positions of the prostheses during deployment. This enables the deployment of multiple prostheses at a target site with precision and predictability, eliminating excessive spacing or overlap between prostheses. In particular embodiments, the prostheses of the invention are deployed in stenotic lesions in coronary or peripheral arteries or in other vascular locations.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     Stents are tubular prostheses designed for implantation in a vessel to maintain patency of the vessel lumen. Stents are used in various vessels throughout the body, including the coronary arteries, femoral arteries, iliac arteries, renal artery, carotid artery, vascular grafts, biliary ducts, trachea, and urethra, to name some examples. Stents are typically implanted by means of long and flexible delivery catheters that carry the stents in a compact, collapsed shape to the treatment site and then deploy the stents into the vessel. In some applications, balloon expandable stents are used. These stents are made of a malleable metal such as stainless steel or cobalt chromium and are expanded by means of a balloon on the tip of the delivery catheter to plastically deform the stent into contact with the vessel wall. In other applications, self-expanding stents are used. These are made of a resilient material that can be collapsed into a compact shape for delivery via catheter and that will self-expand into contact with the vessel when deployed from the catheter. Materials commonly used for self-expanding stents include stainless steel and elastic or superelastic alloys such as nickel titanium (Nitinol™).  
         [0002]     While self-expanding stents have demonstrated promise in various applications, such stents face a number of challenges. One such challenge is that in some cases the disease in a vessel may be so extensive that a stent of very long length, e.g. 30-200 mm, is called for. Currently available stents are typically less than 30 mm in length, and suffer from excessive stiffness if made longer. Such stiffness is particularly problematic in peripheral vessels such as the femoral arteries, where limb movement requires a high degree of flexibility in any stent implanted in such vessels.  
         [0003]     To overcome the stiffness problem, the idea of deploying multiple shorter stents end-to-end has been proposed. However, this approach has suffered from several drawbacks. First, currently available delivery catheters are capable of delivering only a single stent per catheter. In order to place multiple stents, multiple catheters must be inserted, removed and exchanged, heightening risks, lengthening procedure time, raising costs, and causing excessive material waste. In addition, the deployment of multiple stents end-to-end suffers from the inability to accurately control stent placement and the spacing between stents. This results in overlap of adjacent stents and/or excessive space between stents, which is thought to lead to complications such as restenosis, the renarrowing of a vessel following stent placement. With self-expanding stents the problem is particularly acute because as the stent is released from the catheter, its resiliency tends to cause it to eject or “watermelon seed” distally from the catheter tip by an unpredictable distance. During such deployment, the stent may displace not only axially but rotationally relative to the delivery catheter resulting in inaccurate, uncontrollable, and unpredictable stent placement.  
         [0004]     Interleaving stents or stent segments such as those disclosed in co-pending application Ser. No. 10/738,666, filed Dec. 16, 2003, which is incorporated herein by reference, present even greater challenges to conventional delivery systems. Interleaving stents have axially extending elements on each end of the stent that interleave with similar structures on an adjacent stent. Such interleaving minimizes the gap between adjacent stents and increases vessel wall coverage to ensure adequate scaffolding and minimize protrusion of plaque from the vessel wall. However, such interleaving requires that the relative rotational as well as axial positions of the adjacent stents be maintained during deployment to avoid metal overlap and excessive gaps between stents. Conventional delivery systems suffer from the inability to control both the axial and rotational positions of self-expanding stents as they are deployed.  
         [0005]     What are needed, therefore, are stents and stent delivery system that overcome the foregoing problems. In particular, the stents and stent delivery systems should facilitate stenting of long vascular regions of various lengths without requiring the use of multiple catheters. Such stents and delivery systems should also provide sufficient flexibility for use in peripheral vessels and other regions where long and highly flexible stents might be required. In addition, the stents and stent delivery systems should enable the delivery of multiple stents of various lengths to one or more treatment sites using a single catheter without requiring catheter exchanges. Further, the stents and stent delivery systems should facilitate accurate and repeatable control of stent placement and inter-stent spacing to enable deployment of multiple self-expanding stents end-to-end in a vessel at generally constant spacing and without overlap. Moreover, the stents and delivery systems should enable the deployment of interleaving stents or stent segments with precision and control over both the axial spacing and rotational position of each stent or segment.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006]     The present invention provides prostheses, prosthesis delivery systems, and methods of prosthesis deployment that enable the precise and controllable delivery of multiple prostheses using a single delivery catheter. The prostheses, delivery systems, and methods of the invention provide for the precise control of prosthesis placement so that inter-prosthesis spacing is maintained at a constant and optimum distance. In some embodiments, both axial and rotational displacement of the prostheses relative to the delivery catheter is controlled during deployment, enabling the delivery of multiple prostheses that interleave with one another without overlap. The prostheses, prosthesis delivery systems, and methods of the invention further enable the length of prostheses to be customized in situ to match the length of the site to be treated. The invention is particularly useful for delivery of self-expanding prostheses, but balloon expandable prostheses are also contemplated within the scope of the invention. The invention is well-suited to delivery of stents to the coronary arteries and to peripheral vessels such as the popliteal, femoral, tibial, iliac, renal, and carotid arteries. The invention is further useful for delivery of prostheses to other vessels including biliary, neurologic, urinary, reproductive, intestinal, pulmonary, and others, as well as for delivery of other types of prostheses to various anatomical regions, wherever precise control of prosthesis deployment is desirable.  
         [0007]     In a first aspect of the invention, a prosthesis delivery catheter includes an outer shaft having a first lumen; a plurality of self-expanding tubular prostheses carried within the first lumen, the prostheses being adapted to radially expand upon deployment from the first lumen; a deployment mechanism for deploying a selected number of the prostheses from the first lumen; and a control member interactive with the prostheses to control expansion of the prostheses when the prostheses are deployed from the first lumen.  
         [0008]     The control member may comprise a plurality of axially-extending wires, the prostheses being coupled to the wires and axially slidable thereon, the wires being radially deflectable to allow controlled expansion of the prostheses. The wires may have free distal ends configured to move radially outward as the prostheses expand. The distal ends of the wires may be retractable into the outer shaft following deployment of the selected number of prostheses. The prostheses may have sidewalls with a plurality of openings, the wires being threaded through the openings. The wires may form a loop extending around the outside of the prostheses and through the inside of the prostheses, wherein the wires can be withdrawn from around the prostheses following deployment thereof. In such case, at least one end of each wire is releasable to allow the wire to be withdrawn following prosthesis deployment.  
         [0009]     The delivery catheter may further comprise an inner shaft disposed in the first lumen, the prostheses being slidably disposed around the inner shaft, wherein a distal end of each wire is releasably coupled to the inner shaft. A nosecone may be attached to the inner shaft distally of the prostheses, the distal end of each wire being releasably coupled to the nosecone. The inner shaft may also have an inner lumen and at least one port in communication with the inner lumen, wherein the control wires are slidably disposed through the inner lumen and the port.  
         [0010]     The control member may also comprise a sleeve disposed around the prostheses, the sleeve being expandable to allow controlled expansion of the prostheses. The sleeve may be elastomeric, an expandable mesh or woven material, or other expandable structure. When expanded, the sleeve may form a cone shape that flares in the distal direction. The sleeve may be slidable relative to the outer shaft. The sleeve may have at least one longitudinal slit therein whereby it expands by splitting at the longitudinal slit. The sleeve may have a pair of opposing edges bordering the longitudinal slit, a cone shape being formed by moving the edges at an angle relative to each other. The sleeve may also have a plurality of longitudinal sections or beams separated by longitudinal slits, the longitudinal sections being deflectable outwardly to allow controlled expansion of the prostheses. A retainer may be releasably coupled to the longitudinal sections to selectively prevent radial deflection thereof. The retainer may comprise a capsule coupled to an inner shaft slidably disposed through the first lumen, longitudinal sections being received in the capsule.  
         [0011]     The deployment mechanism of the delivery catheter may comprise a pushing element slidably disposed in the first lumen, the pushing element being in engagement with at least one of the prostheses to advance the prostheses distally relative to the outer shaft. In preferred embodiments, the prostheses are self-expandable, made of resilient or shape memory materials such as stainless steel, Nitinol or suitable polymers. Such self-expanding prostheses are held in an unexpanded state within the outer shaft until deployed therefrom, whereupon they resiliently expand to an expanded shape in contact with the vessel wall or lesion. The delivery systems of the invention will also be useful with balloon expandable prostheses. In either case, expandable balloons, valve members, and other mechanisms may also be included in the delivery catheter to facilitate stent deployment.  
         [0012]     In a further aspect of the invention, the prostheses are releasably interconnected to each other. In this case, the control member may comprise an interconnection structure on the pushing element, the interconnection structure being releasably coupled to at least one of the prostheses to resist distal movement of the prostheses relative to the outer shaft.  
         [0013]     In addition to controlling axial position of the stents relative to the delivery catheter and/or to each other during deployment, the control member of the delivery catheter is preferably configured to maintain rotational position of the prostheses relative to each other. This facilitates the delivery of stents having axially interleaving elements and prevents excessive spacing or overlap between such elements  
         [0014]     In still another aspect of the invention, a prosthesis delivery catheter for delivering prostheses into a vessel lumen comprises an outer shaft having a first lumen; a plurality of self-expanding tubular prostheses carried within the first lumen, the prostheses being adapted to radially expand upon deployment from the first lumen; a deployment mechanism for deploying a selected number of the prostheses from the first lumen; and an anchor member adapted to engage the vessel to limit movement of the outer shaft relative thereto when a prosthesis is being deployed. In one embodiment, the anchor member comprises an expandable member mounted on an inner shaft, the inner shaft being slidably disposed in the first lumen. The expandable member preferably comprises a balloon. The expandable member may be configured to expand within a deployed prosthesis in the vessel lumen. The expandable member is preferably configured to remain expanded within the deployed prosthesis while a second prosthesis is deployed adjacent to the deployed prosthesis. This maintains the relative positions of the deployed prosthesis and the delivery catheter so the second prosthesis is deployed at a predictable distance from the deployed prosthesis.  
         [0015]     In another aspect of the invention, a prosthesis delivery catheter for delivering prostheses into a vessel lumen comprises an outer shaft having a first lumen; a plurality of self-expanding tubular prostheses carried within the first lumen, the prostheses being adapted to radially expand upon deployment from the first lumen, each prosthesis comprising a distal portion and proximal portion, the distal portion being configured to expand into engagement with the vessel while the proximal portion is at least partially disposed in the first lumen; and a deployment mechanism for deploying a selected number of the prostheses from the first lumen. Preferably, the distal portion is configured to engage the vessel prior to deployment of the proximal portion so that the prosthesis remains in a generally constant position relative to the catheter as the proximal portion is deployed.  
         [0016]     In one embodiment, the distal and proximal portions of the prostheses are interconnected by at least one spring member, the spring member having a retracted shape and an elongated shape and being biased into the retracted shape, wherein deployment of the distal portion into the vessel elongates the spring into the elongated shape. In such a case, the deployment of the proximal portion into the vessel allows the spring to return at least partially to the retracted shape to draw the proximal portion toward the distal portion.  
         [0017]     In still another aspect, the invention provides a method of delivering one or more prostheses to a treatment site in a vessel comprising positioning a delivery catheter at the treatment site, the delivery catheter carrying a plurality of self-expanding prostheses; selecting a desired number of the prostheses to deploy; deploying the desired number of prostheses from the delivery catheter into the vessel, each prosthesis expanding into contact with the vessel upon deployment; and controlling the axial displacement of each of the selected number of prostheses relative to the delivery catheter during the deployment thereof.  
         [0018]     In one embodiment, the axial displacement is controlled by an expandable sleeve disposed around the desired number of prostheses. The method may further include retracting the sleeve from around the prostheses after the prostheses have been deployed. The axial displacement may also be controlled by a plurality of wires coupled with the desired number of prostheses. The wires may be threaded through openings in each of the prostheses, and may be retracted from the prostheses after the prostheses have been deployed.  
         [0019]     The method may further include controlling the rotational displacement of the selected number of prostheses relative to the delivery catheter and/or relative to each other during the deployment thereof.  
         [0020]     The axial displacement of the prostheses may be controlled by expanding an expandable member in the vessel during deployment of at least a portion of the desired number of prostheses. Alternatively, the axial displacement may be controlled by first expanding a distal portion of a first of the prostheses into engagement with the vessel while a proximal portion of the first of the prostheses remains in the delivery catheter, then expanding the proximal portion of the first of the prostheses into engagement with the vessel.  
         [0021]     As a further alternative, the prostheses may be releasably interconnected while in the delivery catheter, wherein the axial displacement is controlled by connecting at least one of the prostheses to a restraining member in the delivery catheter. In this case, the selected number of prostheses becomes detached from the prostheses remaining in the delivery catheter upon deployment.  
         [0022]     Further aspects of the nature and advantages of the invention will be apparent from the following detailed description of various embodiments of the invention taken in conjunction with the drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]      FIG. 1  is a side cut-away view of a prosthesis delivery catheter according to the invention.  
         [0024]      FIG. 2A  is a side cross-sectional view of a distal portion of a prosthesis delivery catheter according to the invention in a further embodiment thereof.  
         [0025]      FIG. 2B  is a side cross-sectional view of the prosthesis delivery catheter of  FIG. 2A  showing the deployment of prostheses in a vessel.  
         [0026]      FIGS. 3A-3C  are perspective, side, and end views respectively of a prosthesis coupled to control wires according to further embodiments of the invention.  
         [0027]      FIG. 4A  is a side cross-section of a distal portion of a prosthesis delivery catheter according to the invention in a further embodiment thereof.  
         [0028]      FIG. 4B  is a side cross-section of the prosthesis delivery catheter of  FIG. 4A  showing the deployment of prostheses in a vessel.  
         [0029]      FIG. 5 A  is a side cross-section of a distal portion of a prosthesis delivery catheter according to the invention in a further embodiment thereof.  
         [0030]      FIG. 5B  is an oblique view of a distal portion of a prosthesis delivery catheter according to the invention in yet another embodiment thereof.  
         [0031]      FIGS. 6A-6C  are side cross-sectional views of a distal portion of a prosthesis delivery catheter according to the invention in still another embodiment thereof, showing the outer shaft unretracted, outer shaft retracted with sleeve unexpanded, and sleeve with stents expanded, respectively.  
         [0032]      FIGS. 7A-7B  are side cross-sectional views of a distal portion of a prosthesis delivery catheter according to the invention in another embodiment thereof, showing outer shaft retracted with sleeve unexpanded, and outer shaft retracted with sleeve and stents expanded, respectively.  
         [0033]      FIGS. 8A-8C  are side cross-sectional views of a distal portion of a prosthesis delivery catheter according to the invention in a further embodiment thereof, showing the outer shaft unretracted, outer shaft retracted with sleeve unexpanded, and sleeve with stents expanded, respectively.  
         [0034]      FIGS. 9A-9B  are side cross-sectional views of a distal portion of a prosthesis delivery catheter in a vessel according to the invention in another embodiment thereof, showing outer shaft retracted with prosthesis partially deployed, and prosthesis fully deployed, respectively.  
         [0035]      FIGS. 10A-10B  are side cross-sectional views of a distal portion of a prosthesis delivery catheter in a vessel according to the invention in yet another embodiment thereof, showing outer shaft retracted with prosthesis partially deployed, and prosthesis fully deployed, respectively.  
         [0036]      FIGS. 11A-11C  are side cross-sectional views of a distal portion of a prosthesis delivery catheter in a vessel according to the invention in yet another embodiment thereof, showing a first prosthesis deployed, an expandable member expanded within the first prosthesis, and a second stent deployed with expandable member expanded in the first prosthesis, respectively.  
         [0037]      FIGS. 11D-11F  are side cross-sectional views of a distal portion of a prosthesis delivery catheter according to the invention in another embodiment thereof, showing the delivery catheter prior to stent deployment, the deployment of a first prosthesis in a vessel, and a deployed prosthesis in the vessel, respectively.  
         [0038]      FIG. 12  is a side cross-sectional view of a distal portion of a prosthesis delivery catheter in a vessel according to the invention in still another embodiment thereof, showing a first prosthesis deployed in a lesion. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0039]     Referring to  FIG. 1 , a first embodiment of a prosthesis delivery catheter according to the invention is illustrated. Delivery catheter  20  may have any of various constructions, including that described in co-pending application Ser. No. 10/637,713, filed Aug. 8, 2003 (Attorney Docket No. 21629-000340), which is incorporated herein by reference. Delivery catheter  20  has a handle assembly  21  and an elongated catheter body  22  that includes three concentric tubular shafts all axially slidable relative to one another: an outer shaft  24 , a pusher  26 , and an inner shaft  28 . Pusher  26  has a distal extension  27  to which a pusher ring  29  is fixed. In a distal region of the catheter body  22 , a guidewire tube  30  extends slidably through a port  32  in outer shaft  24  and through pusher ring  29  and has a distal end  34 , to which is mounted a nosecone  36  and a stop member  38 .  
         [0040]     Delivery catheter  20  further includes one or more stent expansion control members, which in the illustrated embodiment comprise a plurality of control wires  40 . Preferably, one or more pairs of control wires  40  are mounted on opposing sides of delivery catheter  20 , e.g. four control wires  40  offset 90° from each other. Control wires  40  are fixed at their proximal ends  42  to inner shaft  28 , and have free distal ends  44 .  
         [0041]     Outer shaft  24  has a distal extremity  46  defining a first lumen  48 . A plurality of stents  50  are disposed in a collapsed configuration within first lumen  48 . Stents  50  are preferably composed of a resilient material such as stainless steel or Nitinol so as to self-expand from the collapsed configuration to a radially expanded configuration when deployed from first lumen  48 . While stents  50  as illustrated have a wave-like or undulating pattern in a plurality of interconnected circumferential members, the pattern illustrated is merely exemplary and the stents of the invention may have any of a variety of strut shapes, patterns, and geometries. From 2 up to 10 or more stents may be carried by outer shaft  24 . Optionally, a valve member  49  is mounted within first lumen  48  to facilitate separating those stents  50  to be deployed from those to remain within outer shaft  24 , as described in co-pending application Ser. No. 10/412,714, filed Apr. 10, 2003, which is incorporated herein by reference.  
         [0042]     Control wires  40  run along the outside of stents  50  or through the interior of stents  50 , are threaded through openings in the walls of stents  50  or are otherwise coupled with stents  50  to control the deployment thereof, as described more fully below. Control wires  40  are composed of a resilient material such as stainless steel, Nitinol, or a suitable polymer, and are preferably generally straight and biased inwardly against guidewire tube  32  or to a position generally parallel to the axial direction. In  FIG. 1 , outer shaft  24  has been retracted to expose a plurality of stents  50  which are partially expanded and remain coupled to or restrained by control wires  40 , as explained in greater detail below.  
         [0043]     Handle assembly  21  has a rotatable retraction knob  52  coupled to a shaft housing  53 , to which outer shaft  24  is fixed. By rotating retraction knob  52 , outer shaft  24  may be retracted proximally relative to pusher  26  and inner shaft  28 . A pull ring  54  is coupled to inner shaft  28 , allowing inner shaft  28 , and hence control wires  40 , to be retracted proximally relative to outer shaft  24 . A switch  56  engages and disengages pusher  26  with outer shaft  28 , so that pusher  26  either moves with outer shaft  24  or remains stationary as outer shaft  24  is retracted. Indicia  58  on shaft housing  53  indicate the extent of retraction of outer shaft  28  by distance, number of stents, or other suitable measure. Other aspects of handle assembly  21  are described in co-pending application Ser. No. 10/746466, filed Dec. 23, 2003 (Attorney Docket No. 21629-002200), which is incorporated herein by reference. Except as stated otherwise, any of the embodiments of the stent delivery catheter described below may incorporate the features and be otherwise constructed as just described.  
         [0044]      FIGS. 2A-2B  illustrate a distal extremity of a stent delivery catheter  60  according to the invention in a further embodiment thereof. In this embodiment, stents  62  have a series of diamond shaped openings  64  in the walls thereof through which a plurality of control wires  66  are threaded. Stents  62  have a plurality of axially-extending V-shaped points  63  on their distal and proximal ends. These points  63  are configured to interleave or nest with the points  63  on the adjacent stent  62 , preferably both in the collapsed and expanded configurations. Various suitable interleaving stent geometries are described in co-pending application Ser. No. 10/736,666, filed Dec. 16, 2003, which is incorporated herein by reference. In order to maintain this interleaving, it is important to maintain the relative rotational and axial positions of the adjacent stents  62  both before and during deployment. By extending through the openings  64  in each stent, control wires  66  keep adjacent stents  62  in rotational alignment as they are advanced forward through the catheter and during deployment. Preferably, each control wire  66  is threaded through at least two openings  64  in each stent  62 , one opening  64   a  near the distal end of each stent  62  and one opening  64   b  near the proximal end of each stent  62 . Alternatively, control wires  66  may be threaded through only a single opening  64  or through three or more openings  64  on each stent  62 . Preferably, however, control wires  66  are threaded so that the distal and proximal ends of stents  64  will expand at a generally uniform rate when released, as described below.  
         [0045]     Control wires  66  are constructed of a resilient and flexible metal or polymer with sufficient stiffness to provide controlled resistance to the expansion of stents  62 . This stiffness may be selected to allow the desired expansion behavior of stents  62  such that “watermelon seeding” is avoided, inter-stent spacing is maintained, and sufficient stent expansion occurs. Control wires  66  may have various cross-sectional geometries, and may be a flat ribbons or blades, round or oval wires, I-beams, or other suitable structures to control stent expansion, maintain spacing and rotational position, and facilitate withdrawal from stents  62  without interference. Control wires  66  may be composed of or coated with a lubricious material such as PTFE to reduce friction during removal from stents  62 . In other embodiments, control wires  66  may have surface features, be wrapped with wire windings, or be coated with “sticky” material to increase friction with stents  62 . Coatings or surface structures such as scales with one-way frictional effects may also be applied to control wires  66 .  
         [0046]     As a further alternative, control wires  66  may comprise flexible hollow tubes which are pneumatically or hydraulically controllable to vary their rigidity or stiffness. For example, control wires  66  may comprise polymeric tubes that radially contract or flatten and are very flexible when evacuated of fluid, but which become more rigid when filled with pressurized fluid, such as saline, air, or other liquid or gas. In such an embodiment, control wires  66  are fluidly connected to a pump, syringe, or other suitable fluid delivery mechanism at the proximal end of the delivery catheter. In this way, control wires  66  may be pressurized to increase stiffness as stents  62  are deployed, then evacuated of fluid to reduce their profile and stiffness during withdrawal from the deployed stents.  
         [0047]     Stents  62  are slidably positioned over an inner shaft  68 , to which is attached a nosecone  70  at the distal end of the device. An outer shaft  72  is slidably disposed over inner shaft  68  and surrounds stents  62 , maintaining them in a collapsed configuration, as shown in  FIG. 2A . A pusher shaft  74  is slidably disposed over inner shaft  68  and is configured to engage the proximal end of the proximal-most stent  62 . Outer shaft  72  is retractable relative to inner shaft  68  in order to expose a desired number of stents  62  as shown in  FIG. 2B . When outer shaft  72  is retracted, the exposed stents  62  self-expand to a larger-diameter expanded shape in engagement with lesion L in vessel V. Preferably, at least the distal end of the distal-most stent  62 , and more preferably a substantial portion of all stents  62  being deployed, is allowed to expand into engagement with lesion L while control wires  66  remain threaded through openings  64 . Control wires  66  are then withdrawn from openings  62 , preferably by holding catheter  60  in position and pulling control wires  66  proximally using a suitable mechanism such as that described above with reference to  FIG. 1 . Alternatively, the entire catheter  60  may be retracted proximally relative to stents  62  to withdraw control wires  66  from openings  62 . Because at least a portion of stents  62  is in engagement with lesion L, stents  62  are held in position in the vessel as control wires  66  are withdrawn.  
         [0048]     Optionally, inner shaft  68  may have a balloon  76  mounted thereto near its distal end to enable pre- or post-dilatation of lesion L. In this embodiment, inner shaft  68  has an inflation lumen through which inflation fluid may be delivered to balloon  76 . Balloon  76  is preferably as long as the longest lesion that might be treated using catheter  60 . To dilate lesion L prior to stent deployment, or to further expand stents  62  after deployment, outer shaft  72  and those of stents  62  remaining therein are retracted relative to inner shaft  68  to expose a desired length of balloon  76 . The exposed portion of balloon  76  may then be inflated within the lesion L and/or the deployed stents  62 .  
         [0049]     Following deployment and any post-dilatation, inner shaft  68  is retracted into outer shaft  72  while maintaining pressure against pusher shaft  74 . This slides stents  62  distally along control wires  66  and repositions stents  62  to the distal end of inner shaft  68  so as to be ready for deployment. Catheter  60  may then be repositioned to another vascular location for deployment of additional stents  62 .  
         [0050]     Control wires  66  may be coupled to stents  62  in various ways, some of which depend upon the configuration of stents  62 . For example, as shown in FIGS.  3 A-B, the points  63  at the ends of each stent  62  may be bent inwardly such that a portion of the openings  64 ′ are oriented axially. Control wires  66  may then be threaded through these axially-oriented openings  64 ′. Preferably, upon deployment, points  63  are adapted to deform with stent expansion so as to be more parallel to the axial direction, thereby providing a smooth and open flow path through the stent.  
         [0051]     In another embodiment, shown in  FIG. 3C , stents  80  have axially-aligned eyelets  82  through which control wires  84  are threaded. These eyelets  82  may be in the interior of stents  82  as shown in  FIG. 3C , or such eyelets may be on the exterior surface of stents  82 , or could be drilled through one or more of the struts of stents  82 . Various other structures may also be used for coupling the stents of the invention to control wires, including hooks, channels, holes, sleeves, and others, disposed on the interior, exterior or end surfaces of the stent, or through the struts themselves. Such structures may by integral with stent struts and of the same material, may be attached to the stent struts and be of same or different material, or may be a biodegradable material that erodes and eventually is absorbed into the body following deployment.  
         [0052]     Referring now to  FIGS. 4A-4B , in a further embodiment, a stent delivery catheter  90  has an outer shaft  92  slidably disposed over an inner shaft  94 , and at least one stent  96  (shown schematically in  FIG. 4A ) in a collapsed shape within outer shaft  92 . A plurality of control wires  97  have an outer extremity  98  outside of inner shaft  94  and an inner extremity  100  extending through one or more lumens  102  and distal ports  103  in inner shaft  94 . Both outer portion  98  and inner portion  100  extend proximally to the proximal end of delivery catheter  90 . Outer extremities  98  are threaded through openings in the wall of stent  96  or are otherwise coupled thereto as described above so as to resist expansion of stent  96  upon deployment. Control wires  97  thus form a continuous loop from the proximal end of stent delivery catheter  90 , through stent  96  and back to the proximal end of the catheter.  
         [0053]      FIG. 4B  illustrates this embodiment of delivery catheter  90  positioned in a vessel V and carrying plurality of stents  96 ′. Stents  96 ′ have axial projections  104  at their distal and proximal ends configured to interleave when stents  96 ′ are collapsed within outer shaft  92  and when deployed in vessel V. When outer shaft  92  is retracted to expose one or more stents  96 ′, the expansion of stents  96 ′ can be resisted and controlled by maintaining tension on control wires  97 . Tension may be controllably relaxed to allow stents  96 ′ to expand into contact with lesion L, as shown in  FIG. 4B . By controlling the expansion in this way, the axial spacing and rotational positions of adjacent stents  96 ′ may be maintained so that gaps and overlaps are minimized and the interleaving of axial projections  104  is maintained. When stents  96 ′ are fully expanded, one end of each control wire  97  may be released at the proximal end of delivery catheter  90  while the other end is pulled to retract the control wires from stents  96 ′.  
         [0054]     In a further embodiment, illustrated schematically in FIGS.  5 A-B, delivery catheter  108  is constructed as described above except that control wires  110  are releasably coupled to the distal end of an inner shaft  112  or to nose cone  114 . In an exemplary embodiment, control wires  110  have balls  116  at their distal ends configured to be received within slots  118  on the outer surface of nosecone  114  ( FIG. 5A ) or on the proximal face of nosecone  114  ( FIG. 5B ; outer shaft not shown for clarity). Slots  118  have an enlarged portion  120  of sufficient size to receive ball  116  and a narrow portion  122  through which balls  116  may not pass. Inner shaft  112  is axially rotatable relative to control wires  110 . As in the embodiment of FIGS.  4 A-B, with balls  116  held within slots  118 , tension may be maintained on control wires  110  to resist expansion of stent  124 . Stent  124  may be allowed to expand by gradually relaxing tension on control wires  110 . Once stent  124  is fully expanded tension on control wires  110  may be fully relaxed and nosecone  114  then rotated by rotating inner shaft  112 , thereby allowing balls  116  to pass through enlarged portions  120 . Control wires  110  may then be withdrawn from the deployed stent  124 . Nosecone  114  is then retracted or control wires  110  advanced so as to reinsert balls  116  into slots  118 . Nosecone  114  is then rotated to align balls  116  with narrow portions  122 , again securing the control wires to nosecone  114 . Delivery catheter  108  may then be repositioned to deploy additional stents.  
         [0055]     Optionally, delivery catheter  108  may include a middle shaft or balloon  126  over which stents  124  are positioned, as shown in  FIG. 5A . In this case, inner shaft  112  is slidably and rotatably disposed in an inner lumen though middle shaft or balloon  126 . If a balloon is included, it may be used for pre-dilatation of lesions prior to stent deployment, or for further expansion of stent  124  following deployment.  
         [0056]     In the foregoing embodiment, control wires  110  will be constructed to have sufficient stiffness to resist rotation, twisting or bending as nosecone  114  is rotated to release control wires  110 . Maintaining some tension on control wires  110  as nosecone  114  is rotated may facilitate the release process. In addition, control wires  110  will have sufficient column strength to facilitate reinsertion into slots  118  following deployment of stents  124 . Thus the size, material and geometry of control wires  110  will be selected to enable these actions while providing the desired level of control of stent expansion.  
         [0057]     In a further embodiment of a stent delivery catheter according to the invention, an expandable sleeve  130  is slidably positioned within outer shaft  132  and carries stents  134  as shown in FIGS.  6 A-C. A pusher shaft  136  is slidable within sleeve  130  and engages the proximal-most stent  134 . An inner shaft  138  extends through pusher shaft  136  and has a nosecone  140  fixed to its distal end. Sleeve  130 , or at least a distal extremity thereof, may be a tube constructed of a resilient deformable material such as urethane or other medical grade elastomer, or may be a tubular mesh, cage, grating, or other suitable structure of flexible and resilient polymer or metal such as stainless steel or Nitinol. The elasticity and stiffness of sleeve  130  are selected to allow stents  134  to expand at the desired rate when deployed from outer shaft  132  without excessive axial or rotational displacement relative to each other or to outer shaft  132 . Sleeve  130  is resiliently biased toward an unexpanded shape so that following stent deployment, sleeve  130  returns to a generally tubular shape. Outer shaft  132  is constructed of a material with sufficient radial strength and stiffness to resist expansion of stents  134  and sleeve  130 , and may include a metallic or polymeric braid, ribs, rings or other structural reinforcement near its distal end for such purpose.  
         [0058]     The interior surface of sleeve  130  optionally may have surface features such as bumps, scales, bristles, ribs, or roughness to enhance friction with stents  134 . These features may be configured to have a grain such that they provide more friction against movement in the distal direction than in the proximal direction, or vice versa. Further, such features may be adapted to provide more friction when sleeve  130  is in an unexpanded shape than when it is expanded by stents  134 . For example, bristles may be provided that point more in the proximal direction when sleeve  130  is in its unexpanded cylindrical shape, but which point more distally or radially (perpendicular to the surface of sleeve  130 ) when sleeve  130  is expanded. This allows sleeve  130  to be more easily withdrawn from stents  134  when stents  134  are deployed.  
         [0059]     In order to deploy stents  134 , delivery catheter  129  is positioned across a vascular lesion so that nosecone  140  is disposed just distally of the distal end of the lesion. Outer shaft  132  is then retracted to expose the desired number of stents  134  (and the associated length of sleeve  130 ) which will cover the length of the lesion, as shown in  FIG. 6B . As outer shaft  132  is retracted, stents  134  are allowed to expand into contact with the lesion as shown in  FIG. 6C . Sleeve  130  controls the rate of expansion and maintains the positions of stents  134  so they are deployed precisely at the intended location. Once stents  134  are fully expanded, sleeve  130  may be retracted from between the stents and the lesion until sleeve  130  is again disposed in outer shaft  132 . Pressure is maintained on pusher shaft  136  during this process so that the stents  134  remaining in delivery catheter  129  are advanced to the distal end of sleeve  130  and outer shaft  132 . Delivery catheter  129  may then be repositioned for deployment of additional stents at other locations.  
         [0060]     Referring now to FIGS.  7 A-B, in a further embodiment, a delivery catheter  142  may be constructed largely as described in connection with FIGS.  6 A-C, including an outer shaft  144 , an expandable sleeve  146  slidably disposed therein, a pusher shaft  148 , and inner shaft  150 . A plurality of stents  152  are carried in expandable sleeve  146  (shown in  FIG. 7B ). In order to facilitate expansion, expandable sleeve  146  includes a longitudinal slit  154  in at least a distal extremity thereof. When outer shaft  144  is retracted relative to sleeve  146 , sleeve  146  may be controllably expanded by axially twisting sleeve  146  such that the opposing edges  156  along longitudinal slit  154  pivot away from one another, forming a cone shape ( FIG. 7B ). In this way, the expansion of stents  152  is further controllable after retraction of outer shaft  144  by controlling the rate of twisting of sleeve  146 . An actuator may be provided at the proximal end of delivery catheter  142  to control such twisting. Optionally, sleeve  146  may have a helical thread on its outer surface that mates with a complementary thread on the interior of outer shaft  144  such that sleeve  146  is automatically twisted as outer shaft  144  is retracted. As in the embodiment of FIGS.  6 A-C, following stent deployment, sleeve  146  is retracted from the space between the deployed stents and the vessel wall and returned within outer shaft  144 . Sleeve  146  may be resiliently biased to return to its unexpanded configuration, or may be manually twisted back to an unexpanded shape by the operator.  
         [0061]     In another embodiment, shown in FIGS.  8 A-C, delivery catheter  160  is again constructed much like delivery catheter  129  of FIGS.  6 A-C, including an outer shaft  162 , a slidable expandable sleeve  164  carrying stents  166 , a pusher shaft  168 , and an inner shaft  170 . A nosecone  172  is attached to the distal end of inner shaft  170  and has a concavity  174  at its proximal end configured to receive the distal end of sleeve  164 . A distal extremity of sleeve  164  includes a plurality of axial slits  176  defining separate deflectable longitudinal beams  178 . Sleeve  164  includes at least two, preferably four, and as many as six, eight, or more slits  176  to provide a corresponding number of longitudinal beams  178 . Longitudinal beams  178  are resiliently biased into an axial orientation wherein sleeve  164  is generally cylindrical. Longitudinal beams  178  have sufficient stiffness against lateral deflection to resist and control the expansion of stents  166 .  
         [0062]     Advantageously, by containing the distal ends of longitudinal beams  178  in concavity  174 , outer shaft  162  may be retracted to expose the desired number of stents to cover a target lesion without immediate expansion of stents  166 , as shown in  FIG. 8B . When the desired number of stents  166  is exposed, inner shaft  170  may be advanced distally relative to sleeve  164 , releasing longitudinal beams  178  from concavity  174 . This permits longitudinal beams  178  to laterally deflect, allowing stents  166  to expand, as shown in  FIG. 8C . When full expansion is achieved, longitudinal beams  178  may be retracted from between stents  166  and the vessel wall. Longitudinal beams  178  then return to their undeflected axial orientation, allowing inner shaft  170  to be retracted so as to return the distal ends of longitudinal beams  178  into concavity  174 . Inner shaft  170  and sleeve  164  may then be retracted into outer shaft  162  while maintaining pressure on pusher shaft  168 , thereby advancing additional stents  166  toward the distal end of sleeve  164  for additional deployments.  
         [0063]     In some embodiments of the stent delivery catheter of the invention, the stents themselves are configured to provide greater control and precision in stent deployment. For example,  FIGS. 9A-9B  illustrates a delivery catheter  180  having a plurality of stents  182  disposed in an outer shaft  184 . An inner shaft  186  with optional balloon  188  and nosecone  190  extends through outer shaft  184  and stents  182  and is axially movable relative thereto. A pusher shaft (not shown) is slidably disposed over inner shaft  186  and engages stents  182  for purposes of deploying stents  182  from outer shaft  186  and repositioning the remaining stents  182  within outer shaft  186 , as in earlier embodiments. In this embodiment, stents  182  comprise a plurality of struts  191  forming a series of rings  192  interconnected at joints  193 . Each ring  192  has a series of closed cells  194  interconnected circumferentially and having an “I” shape in the unexpanded configuration.  
         [0064]     As outer shaft  184  is retracted to deploy one or more stents  182 , at least a distal ring  192 ′ is configured to expand into engagement with the vessel wall before the entire length of the stent  182  is deployed from outer shaft  184  ( FIG. 9A ). Once in engagement with the lesion L in vessel V, distal ring  192 ′ anchors stent  182  in position as the remainder of the stent is deployed ( FIG. 9B ), preventing “watermelon seeding” of the stent from the catheter. The axial length of stent  182 , the length of each ring  192 , the number of rings, the stiffness of struts  191 , and the flexibility of joints  193  are all selected to optimize this deployment behavior. Each stent  182  has at least two, and preferably four or more rings  192 , each ring being about 2-5 mm in length, giving stent  182  an overall length of at least about 8-20 mm. Of course, stents of shorter or longer length are also contemplated within the scope of the invention. Lesions longer than each stent  182  may be treated by deploying multiple stents  182  end-to-end. Advantageously, each stent  182  can be deployed precisely at a desired spacing from a previously-deployed stent  182  because the distal ring  192 ′ of each stent  182  can be first allowed to expand into engagement with the vessel at the target location, anchoring the stent in position as the remainder is deployed.  
         [0065]     Rings  192  are preferably formed from a common piece of material and are integrally interconnected at joints  193 , making joints  193  relatively rigid. In this embodiment, the majority of flexibility between rings  192  is provided by struts  191  rather than by joints  193 . Alternatively, joints  193  may comprise welded connections between rings  192  which are also fairly rigid. As a further alternative, joints  193  may comprise hinge or spring structures to allow greater deflection between adjacent rings  192 , as exemplified in  FIGS. 10A-10B , described below.  
         [0066]     In the embodiment of  FIG. 10A-10B , stents  200  are constructed similarly to stents  182  of  FIGS. 9A-9B , including a plurality of interconnected rings  202  having I-shaped cells  204 . However, in this embodiment, some of rings  202  are interconnected by spring members  206  that may be elongated to increase the distance between rings  202  and that are resiliently biased into a shortened configuration to draw rings  202  toward each other. In one embodiment, spring members  206  have a wave-like shape and extend from the tip of an axial projection  208  on one ring  202  to a concave portion  210  between axial projections  208  on the adjacent ring  202 . Of course a variety of spring configurations and connection locations are possible, including zig-zags, coils, spirals, accordian or telescoping structures, and the like. Further, resilient elongatable elastomeric elements may link the adjacent rings  202 . In the illustrated embodiment, stent  200  comprises two pairs of rings  202 , with the rings of each pair interconnected by integral joints  212  as in FIGS.  9 A-B and the pairs of rings  202  being connected to each other by spring members  206 . Stents  200  may alternatively include two, three, five, six or more rings  202 , and spring members  206  may interconnect all or only a portion of rings  202 .  
         [0067]     Spring members  206  may be formed of the same or different material as that of rings  202 , depending upon the desired performance characteristics. In addition, spring members  206  may be biodegradable so as to erode and eventually disappear, leaving the adjacent pairs of rings  202  unconnected.  
         [0068]     During deployment, as outer shaft  184  is retracted to expose a stent  200 , the distal pair of rings  202 ′ first expands into engagement with lesion L in vessel V ( FIG. 10A ). Spring members  206  elongate to allow rings  202 ′ to fully expand without pulling the second pair of rings  202 ″ from outer shaft  184 . As retraction of outer shaft  184  continues, the second pair of rings  202 ″ expands and simultaneously is drawn toward distal ring pair  182 ′ by contraction of spring members  206  ( FIG. 10B ). This results in a predictable and constant axial spacing between the adjacent pairs of rings  202 . In addition, spring members  206  maintain rotational alignment of rings  202  to maintain the interleaving of axial projections  208  without overlap. As in previous embodiments, multiple stents  200  may be deployed sequentially from delivery catheter  180  to cover longer lesions. The ability to precisely deploy each stent permits the relative axial spacing and rotational position of such stents to be controlled to avoid excessive space or overlap.  
         [0069]     In a further embodiment, shown schematically in  FIGS. 11A-11C , a delivery catheter  216  has an outer shaft  218  carrying a plurality of stents  220 . An inner shaft  222  extends through outer shaft  218  to a nosecone  224 , and a pusher shaft  226  is slidably disposed over inner shaft  222 . An anchoring balloon  228  is mounted to inner shaft  222  proximal to nosecone  224 . Anchoring balloon  228  has an axial length sufficient to frictionally engage the wall of vessel V and remain stable so as to anchor delivery catheter  216  in place as further described below. Preferably, anchoring balloon  228  has a length about equal to the length of one of stents  220 .  
         [0070]     In use, outer shaft  218  is retracted so that a first stent  220 ′ is released therefrom and expands into engagement with lesion L ( FIG. 11A ). Anchoring balloon  228  is then inflated until it engages the interior of stent  220 ′ ( FIG. 11B ). This not only stabilizes delivery catheter  216 , but may be used to further expand stent  220 ′ and/or dilate lesion L to firmly implant stent  220 ′. While keeping anchoring balloon inflated within stent  220 ′, outer shaft  218  is further retracted to release a second stent  220 ″, which expands into engagement with lesion L ( FIG. 11C ). Advantageously, anchoring balloon  228  stabilizes delivery catheter  216  and anchors it in position relative to first stent  220 ′ as second stent  220 ″ is deployed. Second stent  220 ″ is thus deployable precisely at the intended spacing and rotational position relative to first stent  220 ′. Anchoring balloon  228  may then be deflated and retracted into outer shaft  218 , with pressure maintained upon pusher shaft  226  to reposition remaining stents  220  at the distal end of inner shaft  222 .  
         [0071]      FIGS. 11D-11F  illustrate another embodiment of a delivery catheter  219  in which a plurality of self-expanding stents  221  are slidably disposed over an elongated balloon  223 . Balloon  223  preferably has a length as long as the longest lesion that is to be treated with the device, e.g. 50-200 mm. A pusher  225  is slidable relative to balloon  223  and has a tubular distal portion  227  disposed over balloon  223  which engages the proximal-most stent  221 P. A sheath  229  is slidably disposed over pusher  225 , stents  221  and balloon  223  and maintains stents  221  in a radially contracted configuration. In this embodiment, moderate pressure is maintained within balloon  223  during deployment of stents  221  so that the balloon expands simultaneously with each stent. As shown in  FIG. 11B , as sheath  229  is retracted, a first stent  221 A and a distal portion of balloon  223  are exposed. By maintaining moderate inflation pressure in balloon  223  as sheath  220  is retracted the exposed portion of balloon  223  expands with the first stent  221 A, inhibiting distal migration of the stent from delivery catheter  219 . One or more additional stents  221  may be deployed by further retraction of sheath  229 , during which balloon  223  remains expanded within first stent  221  anchoring the delivery catheter  219  in position (not shown). As each additional stent is exposed from sheath  229 , the pressure in balloon  223  causes it to expand with the stent so as to control its rotational and axial position. Of course, stents  221  may have any of a variety of different configurations, including having open or closed cells, zig-zag or wave-shaped struts, and/or axially interleaving elements as described above.  
         [0072]     Optionally, balloon  223  may have surface features or coatings on its periphery that enhance retention of stents  221  thereon. Such features may include structures such as scales or protuberances that are activated by pressurization of the balloon so that retention is lessened when the balloon is deflated, but heightened when the balloon is pressurized. Following stent deployment, pressure can optionally be increased in balloon  223  for post-dilation of stents  221  and the target lesion L. Balloon  223  is then deflated and retracted within sheath  229  as distal pressure is maintained against pusher  225 , repositioning stents  221  near the distal end of balloon  223  within sheath  229  for deployment at another location, as shown in  FIG. 11C .  
         [0073]     In a further embodiment, the stents in the delivery catheter of the invention may releasably interconnect with one another and/or with the pusher shaft to enable greater control and precision during deployment. As illustrated in  FIG. 12 , delivery catheter  230  carries a plurality of stents  232  having a structure much like that described above in connection with  FIGS. 9A-9B . However, in this embodiment, the axial projections  234  extending distally and proximally from stents  232  are configured to interconnect with concavities  236  on adjacent stents  232  until expanded. In one embodiment, axial projections  234  have enlarged heads  246  and concavities  236  have necks  248  that retain heads  246  within concavities  236  in the unexpanded configuration. Pusher shaft  250  has a distal end  252  having projections  254  and concavities  256  like those of stents  232 , thus being able to interconnect with the proximal-most stent  232 ′. When a stent  232 ″ expands, the interconnecting structures thereon are configured to separate from the adjacent stent or pusher shaft, thus releasing the deployed stent  232 ″ from delivery catheter  230 . In the example shown, as stent  232 ″ expands, heads  246 ″ contract in size while necks  248 ″ enlarge, thereby allowing heads  246 ″ on the expanded stent to be released from concavities  236  in the adjacent unexpanded stent, and vice versa. By exerting traction on pusher shaft  250  during the deployment process, the line of stents  232  is kept from moving distally relative to outer shaft  231 , thus preventing the deployed stent  232 ″ from “watermelon seeding” as it expands.  
         [0074]     Various types of interconnecting structures between adjacent stents and between the stents and the pusher shaft are possible within the scope of the invention, including those described in co-pending application Ser. No. 10/738,666, filed Dec. 16, 2003, which is incorporated herein by reference. Such interconnecting structures may also be breakable or frangible to facilitate separation as the stent expands. In addition, a mechanism such as an expandable balloon or cutting device may be disposed at the distal end of delivery catheter  230  to assist in separating stents  232  upon deployment. Further, the interconnections between stents may be different than the interconnection between the proximal-most stent and the pusher shaft. For example, the pusher shaft may have hooks, magnets, or other mechanisms suitable for releasably holding and maintaining traction on the proximal end of a stent until it is deployed.  
         [0075]     While the above is a complete description of the preferred embodiments of the invention, various alternatives, modifications, improvements and additions are possible without departing from the scope thereof, which is defined by the claims.