Abstract:
Apparatus and methods for delivering prosthetic segments to a body lumen include an elongated flexible member having both proximal and distal ends along with a plurality of prosthetic segments releasably arranged axially along the elongated flexible member near the distal end. Additionally, the apparatus has a sheath slidably disposed over at least a portion of the prosthetic segments and an outer shaft slidably disposed over at least a portion of the sheath. A separator is disposed on the outer shaft and is biased into engagement with at least one prosthetic segment so that the outer shaft may be retracted to separate a proximal group of prosthetic segments from a distal group of prosthetic segments which are to be deployed into the body lumen. The sheath is positionable between the separator and the prosthetic segments to selectively disengage the separator from the prosthetic segments.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates generally to medical apparatus and methods, and more specifically to vascular catheters, stents and stent delivery systems for use in the coronary arteries and other vessels. 
         [0003]    Stenting is an important treatment option for patients with vascular occlusive disease. The stenting procedure involves placing a tubular prosthesis at the site of a lesion, typically within a diseased coronary artery. The procedure is performed in order to maintain the patency of the artery and is often performed after a primary treatment such as angioplasty. Early stent results suffered from high rates of restenosis, i.e. the tendency for the stented coronary artery to become re-occluded following implantation of the stent. However, in recent years, restenosis rates have decreased substantially, due in part to drug eluting stents as well as other improvements in stent delivery methods and stent technology. As a result, the number of stent related procedures being performed worldwide continues to dramatically increase. 
         [0004]    Stents are typically either self-expanding or balloon expandable and they are delivered to the coronary arteries using long, flexible vascular catheters typically inserted percutaneously through the patient&#39;s femoral artery. For self-expanding stents, the stent is simply released from the delivery catheter and it resiliently expands into engagement with the vessel wall. For balloon expandable stents, a balloon on the delivery catheter is expanded which expands and deforms the stent to the desired diameter, whereupon the balloon is deflated and removed, leaving the stent in place. 
         [0005]    Current stent delivery technology suffers from a number of drawbacks which can make delivery of stents challenging. In particular, current stent delivery catheters often employ stents having fixed lengths. The proper selection of fixed length stents requires accurate knowledge of the lesion length being treated. While lesion length may be measured prior to stent deployment using angiography and fluoroscopy, these measurements are often inaccurate. Thus, if an improperly sized stent is introduced to a treatment site, the delivery catheter and stent must be removed from the patient and replaced with a different device having the correct size. This prolongs the procedure, increases waste and results in a more costly procedure. 
         [0006]    The use of “custom length” stents as an alternative to fixed length stents has been proposed. One such approach for providing a custom length stent has been to use segmented stents for treatment in which only some of the stents are deployed for treatment. Several exemplary systems are described in several copending, commonly assigned applications which are listed below. In these systems, the stent segments are deployed by selective advancement over the delivery catheter. After delivering an initial group of segments, the catheter may be repositioned to a new treatment site and a further group of segments can then be deployed. These systems can enable treatment of multiple lesions with a single device and may contain up to fifty segments. While this technology represents a significant improvement over earlier stent delivery systems, in the case of smaller, more focal lesions or single lesions, only a small number of stent segments are needed and thus there is considerable waste when a large number of stent segments remain undeployed and end up being discarded at the end of the procedure. 
         [0007]    Another challenge with existing “custom length” stent delivery systems is that to deliver multiple stent segments to multiple lesion sites requires an intricate delivery system that can be somewhat complex to use. Thus, a simpler delivery system that allows length customization with fewer prosthetic segments on the delivery catheter is desirable, especially for use in treating a single lesion. It is also desirable to protect stent segments on the delivery system from being improperly displaced, deformed or damaged during delivery and deployment. 
         [0008]    For the above reasons as well as others, it would be desirable to provide improved prosthetic stents and delivery catheters. It would be particularly desirable to provide catheters which enable stent length to be customized yet have a minimal quantity of stent segments so as to treat common lesion lengths while minimizing stent segment waste. It is also desirable to provide a delivery system that is flexible and can track torturous vessels and that has a simple construction and is less costly and easy to use in deploying a selectable number of stent segments to a single treatment site. 
         [0009]    2. Description of the Background Art 
         [0010]    Prior publications describing catheters for delivering multiple segmented stents include: U.S. Publication Nos. 2004/0098081, 2005/0149159, 2004/0093061, 2005/0010276, 2005/0038505, 2004/0186551 and 2003/013266. Prior related unpublished co-pending U.S. patent applications include Ser. No. 11/148,713, filed Jun. 8, 2005 (Attorney Docket No. 14592.4002), entitled “Devices and Methods for Operating and Controlling Interventional Apparatus”; Ser. No. 11/148,545, filed Jun. 8, 2005 (Attorney Docket No. 14592.4005), entitled “Apparatus and Methods for Deployment of Multiple Custom-Length Prosthesis”; Ser. No. 11/344,464, filed Jan. 30, 2006 (Attorney Docket No. 021629-003500US), entitled “Apparatus and Methods for Deployment of Custom-Length Prostheses”; Ser. No. 60/784,309, filed Mar. 20, 2006 (Attorney Docket No. 021629-003600US), entitled “Apparatus and Methods for Deployment of Linked Prosthetic Segments”; Ser. No. ______, filed (Attorney Docket No. 021629-003800US), entitled “Custom Length Stent Apparatus”; and Ser. No. ______, filed (Attorney Docket No. 021629-004000US), entitled “Custom Length Stent Apparatus.” The full disclosures of each of these patents and applications are incorporated herein by reference. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    The invention generally provides for the delivery of prosthetic segments with a flexible delivery catheter capable of navigating torturous vessels such as the coronary arteries. The delivery catheter permits deployment of a selectable number of prosthetic segments at a single treatment site, thus allowing customization of prosthesis length while the delivery catheter is in a body lumen at a treatment site. Customization of prosthesis length in situ permits better matching of the prosthesis length to the lesion length being treated. The delivery catheter has a simplified design including a control mechanism on the catheter handle for selecting prosthetic segments for deployment and a stent valve or separator on the distal end of an outer shaft that facilitates deployment of the selected group of stent segments. A sheath protects the prosthetic segments from damage during delivery and deployment. 
         [0012]    The terms “stent” and “stenting” are defined to include any of the array of expandable prostheses and scaffolds which are introduced into a lumen at a target treatment site and expanded in situ thereby exerting a radially outward force against the lumen wall. The prosthesis of the present invention comprises a closed or an open lattice structure and is typically fabricated from a malleable or elastic material. When a malleable material is used, such as stainless steel, gold, platinum, titanium, cobalt chromium and other alloys, the stent segments are typically expanded by balloon inflation, causing plastic deformation of the lattice so that it remains permanently deformed in the open position after deployment. When formed from an elastic material, including superelastic materials such as nickel-titanium alloys, the lattice structures are commonly constrained radially during delivery and upon deployment the constraining structure is removed, allowing the prosthesis to “self-expand” at the target site. The terms “stent,” “prosthetic segment” and “stent segments” refer broadly to all radially expansible stents, grafts, and other scaffold-like structures which are intended for deployment within a body lumen. 
         [0013]    In a first aspect of the invention, an apparatus for delivering prosthetic segments in a body lumen comprises an elongated flexible member with proximal and distal ends and a plurality of prosthetic segments releasably arranged axially along the elongated flexible member near the distal end. The apparatus also has a sheath that is slidably disposed over at least a portion of the prosthetic segments and an outer shaft that is slidably disposed over at least a portion of the sheath. A separator is disposed on the outer shaft and is biased into engagement with at least one prosthetic segment so that the outer shaft may be retracted to separate a proximal group of prosthetic segments from a distal group of prosthetic segments which are to be deployed in the body lumen. The sheath is also positionable between the separator and the prosthetic segments to selectively disengage the separator from the prosthetic segments. 
         [0014]    In preferred embodiments, the separator is adapted to apply substantially greater axial force against the prosthetic segments when the separator is retracted proximally than when the separator is advanced distally. Often, the sheath is configured to engage the outer shaft such that retraction of the sheath retracts the outer shaft. Both the sheath and outer shaft typically comprise an annular flange that allows the two members to engage one another. The apparatus also usually includes an expandable member near the distal end of the elongate flexible member and typically the expandable member is a balloon. 
         [0015]    Often, the prosthetic segments are balloon expandable, although they may also be self-expanding. Additionally, the prosthetic segments may carry a therapeutic agent such as an anti-restenosis drug which may be released from the segments. The segments are often in the range of size from about 2 mm to about 10 mm, although they typically have a length about 3 mm to about 6 mm. In some embodiments, the prosthetic segments may have two or more lengths, while in other embodiments, the segments are substantially the same length. Often, the prosthetic segments have interleaved ends in engagement with each other prior to deployment although the segments may also be spaced apart prior to deployment. Spacing the segments apart allows the separator to engage the prosthetic segments at their distal ends. The separator often comprises a plurality of resilient fingers projecting radially inward. At least some of these fingers may be inclined so that the free ends of the fingers point proximally allowing the fingers to pass over the prosthetic segments as the separator is advanced distally but to engage a prosthetic segment when the separator is retracted proximally. In some embodiments, some of the fingers are composed of metal, while they may also be composed of a polymer. Some of the fingers may comprise a radiused end that substantially matches the curvature of the surface of the prosthetic segments thereby providing greater contact surface so as to facilitate engagement between the prosthetic segments and the separator as the separator is retracted proximally while allowing the separator to pass over the prosthetic segments during distal advancement of the separator. 
         [0016]    In other embodiments, the separator further comprises a hinge coupled to the fingers to allow the fingers to deflect radially and this facilitates passage of the separator over the sheath when the separator is advanced distally. Often the separator comprises an annular flange and this flange may be tapered or it can be a tapered conical nose. Other embodiments of the separator comprise a plurality of inclined ramps disposed on an inner surface of the outer shaft and these ramps may be separated by about ninety degrees. In still other embodiments, the separator may comprise a compliant sharp edge. 
         [0017]    In another aspect of the present invention, a method for delivering prosthetic segments to a body lumen comprises introducing a plurality of prosthetic segments that are releasably arranged axially along an elongated flexible member, into a body lumen having a lesion with a lesion length at a first treatment site. An outer shaft having a separator is distally advanced relative to a group of prosthetic segments selected for delivery and the selected group typically has a combined length that matches the lesion length. A sheath, disposed between the separator and the prosthetic segments is then positioned until the separator is allowed to engage the prosthetic segments. The outer shaft is then retracted thereby creating a spacing between prosthetic segments in the selected group and one or more prosthetic segments remaining with the elongated flexible member. The selected group of prosthetic segments is then deployed at the first treatment site. 
         [0018]    In still another aspect of the present invention, a method for selectively delivering prosthetic segments to a lesion in a treatment region in a body lumen comprises advancing a delivery catheter through the body lumen, which may be a blood vessel, to the treatment region. A plurality of prosthetic segments is often disposed axially along the delivery catheter. An outer shaft having a separator is distally advanced. A sheath disposed between the separator and the prosthetic segments is positioned until the separator is allowed to engage the prosthetic segments. The outer shaft can then be retracted proximally so as to create a spacing between prosthetic segments in the selected group and one or more prosthetic segments remaining with the elongate flexible member. Inflating a balloon disposed on the delivery catheter deploys the group of prosthetic segments while any remaining prosthetic segments stay with the delivery catheter. 
         [0019]    Often, the sheath is configured to engage the outer shaft such that retraction of the sheath also retracts the outer shaft. Additionally, the prosthetic segments are typically balloon expandable, but they may also be self-expanding, and they are usually introduced into a blood vessel. Often, deploying the selected group of prosthetic segments comprises plastically deforming the selected group of prosthetic segments, and often this is accomplished with a balloon. Often, the plurality of prosthetic segments carries a therapeutic agent that is adapted to being released from the segments, and typically this agent is an anti-restenosis drug. 
         [0020]    In some embodiments, the prosthetic segments have a length in the range from about 2 mm to about 10 mm, while in others, the segments have a length about 3 mm to about 6 mm. Often prosthetic segments have interleaved ends in engagement with each other prior to deployment, although the segments may also be spaced apart prior to deployment to allow the separator to engage the prosthetic segments at their distal ends. 
         [0021]    Typically, the separator exerts substantially greater axial force against the prosthetic segments when the separator is retracted proximally than when the separator is advanced distally. In some embodiments, the separator comprises a plurality of resilient fingers projecting radially inward. Often, at least some of the fingers are inclined so that free ends of the fingers point proximally allowing the fingers to pass over the prosthetic segments as the separator is advanced distally but to engage a prosthetic segment when the separator is retracted proximally. Some of the fingers may be composed of metal, while in other embodiments, some of the fingers may be composed of a polymer. 
         [0022]    In other embodiments, at least some of the fingers comprise a radiused end that substantially matches the curvature of the prosthetic segments thereby providing greater contact surface so as to facilitate engagement between the prosthetic segment and the separator as the separator is retracted proximally while allowing the separator to pass over the prosthetic segments during distal advancement of the separator. Some embodiments may include a separator that comprises a hinge coupled to the fingers. The hinge helps the fingers to deflect radially outward over the sheath when the separator is advanced distally. Often, the separator comprises an annular flange and the flange may be tapered or may have a tapered conical nose. 
         [0023]    In still other embodiments, the separator comprises a plurality of inclined ramps that are disposed on an inner surface of the outer shaft. Often these ramps are separated by about ninety degrees. In yet other embodiments, the separator may comprise a sharp compliant edge. 
         [0024]    These an other embodiments are described in further details in the following description related to the appended drawing figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1  is a perspective view of a stent delivery system in accordance with one embodiment of the present invention. 
           [0026]      FIGS. 2A-2F  show selection and deployment of prosthetic stent segments in accordance with an exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    Referring now to  FIG. 1 , a stent delivery catheter  100  comprises a catheter shaft  120  with an outer shaft  124  slidably disposed over a sheath  144  which is in turn slidably disposed over an inner shaft  216  (seen in  FIG. 2A ). An inflatable balloon  130 , is mounted on the inner shaft  216  and is exposed by retracting outer shaft  124  and sheath  144  relative to the inner shaft  216 . A tapered nosecone  136 , composed of a soft elastomeric material to minimize trauma to the vessel during advancement of the delivery catheter  100 , is attached distally of the inflatable balloon  130 . Prosthesis  126  comprises a plurality of prosthetic segments  128  mounted over the inflatable balloon  130  for expansion. Sheath  144  covers the prosthetic segments  128  and protects them from being damaged during delivery. A guidewire tube  122  is slidably positioned through shaft  124  and sheath  144  proximal to the inflatable balloon  130 . A guidewire  138  is positioned slidably through guidewire tube  122 , inflatable balloon  130  and nosecone  136 , and extends distally thereof.  FIG. 1  illustrates the stent delivery catheter  100  and  FIG. 2A  shows various elements of the delivery catheter  100  in greater detail. 
         [0028]    In  FIG. 2A , a stent delivery catheter  200  is slidably disposed over the guidewire GW into the vessel V so that the nosecone  210  is distal to the lesion L. The delivery catheter  200  has an expandable member  204  disposed over an inner catheter shaft  216  and stent segments  202  having interleaved ends in engagement with each other are disposed over the expandable member  204 , which is a balloon in this embodiment. The stent segments  202  are covered by sheath  208 . The sheath  208  protects stent segments  202  during delivery and also prevents unintended axial displacement of the segments  202 . In this embodiment, six stent segments  202  are disposed on the stent delivery catheter  200 . The prosthetic segments  202  are disposed over a balloon  204  near the distal end of the stent delivery catheter  200 . A stent valve  206  is disposed on the inner surface of outer shaft  211  and is adapted to engage prosthetic segments  202  and facilitates their deployment. Additionally, sheath  208  has an annular flange or tab  212  disposed on its outer surface that is adapted to pass through the stent valve  206  during retraction or advancement and to engage the annular flange or tab  214  disposed on the inner surface of outer shaft  211   
         [0029]    In  FIG. 1 , a handle  106  is attached to a proximal end  112  of the outer shaft  124 . The handle performs several functions, including retracting and advancing the outer shaft  124  and sheath  144  thereby exposing prosthetic segments  128  and allowing the prosthetic segments  128  to be delivered. Additionally, using the handle  106  to displace the sheath  144  permits creation of a spacing between prosthetic segments  128  selected for delivery and the segments  128  that will remain with the delivery catheter  100 . This gap or spacing between segments permits proper balloon inflation and will be described below in further detail along with the handle structure and operation. 
         [0030]    Handle  106  includes a housing  110  which encloses the internal components of the handle  106 . Handle  106  allows a physician operator to advance or retract outer shaft  124  and sheath  144 , which determines the length of the prosthesis (number of segments) to be deployed. The handle  106  also permits connection of balloon  130  to an inflation source. The inner shaft  216  is preferably fixed to the handle housing  110 , while both outer shaft  124  and sheath  144  are coupled to slide mechanisms  102  and  140 , respectively. Slide mechanisms  102  and  140  allow both the outer shaft  124  and sheath  144  to be independently retracted and advanced relative to handle  106 . An adaptor  108  is attached to handle  106  at its proximal end and is fluidly coupled to the inner shaft  216  in the interior of the housing of handle  106 . The adaptor  108 , preferably a Luer connector, is configured to be fluidly coupled with an inflation device which may be any commercially available balloon inflation device such as those sold under the trade name “Indeflator™,” manufactured by Abbott (formerly Guidant Corporation of Santa Clara, Calif.). The adaptor is in fluid communication with the inflatable balloon  130  via an inflation lumen in the inner shaft  216  to permit inflation of the inflatable balloon  130 . 
         [0031]    Additionally, a control mechanism on the handle  106  includes a slide mechanism  102  that translates along calibrated slot  104 . Slide mechanism  102  is coupled with outer shaft  124  and is adapted to retract or advance the shaft  124  a selected distance. Initially, the distance is selected by advancing slide mechanism  102  distally along slot  104 . This allows the physician operator to select the number of prosthetic segments  128  on the distal end of delivery catheter  100  that will be delivered. The slide mechanism  102  includes visual markers  148  so that an operator can easily determine how many stent segments have been selected. In preferred embodiments, slide mechanism  102  may have detents or a ratchet that provides audible or tactile feedback to the operator to facilitate operation of the stent delivery catheter  100  without requiring direct visualization during operation. 
         [0032]    Handle  106  also comprises a second control mechanism  140  that translates along calibrated slot  142 . Slide mechanism  140  is coupled with the sheath  144  and is adapted to retract or advance the sheath  144  a selected distance. After the number of prosthetic segments  128  has been selected as described above, slide mechanism  140  is retracted so as to cause proximal retraction of sheath  144 . As sheath  144  is retracted, tabs  212  ( FIG. 2A ) engage with tabs  214  ( FIG. 2A ) on outer shaft  124 . Further retraction of sheath  144  also retracts outer shaft  124  and exposes the prosthetic segments  128  selected for delivery and creates a spacing between the segments selected for delivery and the segments remaining with the delivery catheter  100 . Slide mechanism  140  also includes visual markers  150  that help the physician with operation of the control mechanism  140 . Additionally, the slide mechanism  140  may comprise detents or a ratchet that further assists physician operation by providing audible or tactile feedback. This series of steps is illustrated in  FIGS. 2A-2F  and is described in more detail below. 
         [0033]    Additional details on materials and construction of other related handles are described in co-pending U.S. patent application Ser. No. 11/148,713, filed Jun. 8, 2005, (Attorney Docket No. 14592.4002), entitled “Devices and Methods for Operating and Controlling Interventional Apparatus,” and co-pending United States Publication No. 2005/0149159, entitled “Devices and Methods for Controlling and Indicating the Length of an Interventional Element,” and application Ser. No. ______, filed ______, 2006, (Attorney Docket No. 021629-003800US), entitled “Custom Length Stent Apparatus,” the full disclosures of which are incorporated herein by reference. 
         [0034]    Both sheath  144  and outer shaft  124  along with guidewire  138  each extend through a slider assembly  132  slidably disposed on the catheter body  120  at a point between its handle  106  and expandable member  130 . The slider assembly  132  is adapted for insertion into and sealing with a hemostasis valve, such as on an introducer sheath or guiding catheter, while still allowing relative movement of the outer shaft  124  and sheath  144  relative to the slider assembly  132 . The slider assembly  132  includes a slider tube  118 , a slider body  116 , and a slider cap  114 . 
         [0035]    Outer shaft  124  and sheath  144  may be composed of any of a variety of biocompatible materials, such as but not limited to a polymer like PTFE, FEP, polyimide, Nylon or Pebax, and may be reinforced with a metallic or polymeric braid to resist radial expansion of inflatable balloon  130 , and/or the like. Inflatable balloon  130  may be formed of a semi-compliant polymer such as Pebax, Nylon, polyurethane, polypropylene, PTFE or other suitable polymers. Additional aspects of the luminal prosthesis delivery system are described in U.S. patent application Ser. No. 10/306,813, filed Nov. 27, 2002 (Attorney Docket No. 021629-000320US); U.S. patent application Ser. No. 10/637,713, filed Aug. 8, 2003 (Attorney Docket No. 021629-000340US); U.S. patent application Ser. No. 10/738,666, filed Dec. 16, 2003 (Attorney Docket No. 021629-000510US); U.S. patent application Ser. No. 11/104,305, filed Apr. 11, 2005 (Attorney Docket No. 021629-003300US); and U.S. application Ser. No. 11/148,585, filed Jun. 8, 2005, the full disclosures of which are hereby incorporated by reference. 
         [0036]    Delivery catheter  100  also includes a separator or “stent valve” disposed near the distal end of outer shaft  211  and an exemplary embodiment of this is seen in  FIG. 2A . In  FIG. 2A , outer shaft  211  is retracted so that its distal tip is proximal to the proximal-most end of the prosthetic stent segments  202 . At the same time, sheath  208  is advanced fully distally, covering the plurality of prosthetic segments  202  which are disposed over expandable member  204 . Expandable member  204  acts as a carrier which supports the prosthetic segments  202 . 
         [0037]    Separator  206  contacts and engages prosthetic segments  202 . As shown in  FIG. 2A , separator  206  includes proximally inclined resilient fingers configured to frictionally engage stent segments  202  when sheath  208  has been retracted and prosthetic segments  202  are exposed. Thus, when outer shaft  211  is retracted proximally, the separator  206  engages the prosthetic segments  202 , while the separator  206  slides over the prosthetic segments  202  when the segments  202  are covered by sheath  208 . The separator  206  may be a polymeric or metallic material integrally formed with outer shaft  211 , or it may be bonded or otherwise mounted to the interior of the outer shaft  211 . The geometry of separator  206  can also be toroidal with a circular or ovoid cross-section (like an O-ring) or the separator  206  may have another cross-sectional shape such as triangular, trapezoidal, pyramidal, or other shapes as described in embodiments discussed more fully herein below. The separator  206  can be a polymer such as silicone or urethane, sufficiently soft, compliant and resilient to provide frictional engagement with stent segments  202 , in some embodiments without damaging any coating deposited thereon, including therapeutic drug coatings. The separator  206  extends radially inwardly a sufficient distance to engage the exterior of stent segments  202  with sufficient force to allow the stent segments not selected for delivery to be retracted proximally with outer shaft  211  so as to create a spacing relative to those stent segments selected for delivery. Other exemplary embodiments of separators along with additional aspects of separator  206  are described in U.S. patent application Ser. No. 10/412,714, filed Apr. 10, 2003 (Attorney Docket No. 021629-000330US); U.S. patent application Ser. No. 11/344,464, filed Jan. 30, 2006 (Attorney Docket No. 021629-003500US); and U.S. patent application Ser. No. ______, filed ______ (Attorney Docket No. 021629-004000US), the entire contents of which are incorporated herein by reference. 
         [0038]    Prosthesis  126  is composed of one or more prosthetic segments  128 . Prosthetic stent segments  128  are disposed over an inflation balloon  130 . Each stent segment is about 2-20 mm in length, more typically about 2-10 mm in length and preferably being about 2-8 mm in length. Usually 2-20, more typically 2-10 and preferably 2-6 stent segments  128  may be positioned axially over the inflation balloon  130  and the inflation balloon  130  has a length suitable to accommodate the number of stent segments. Stent segments  128  may be positioned in direct contact with an adjacent stent segment so that segment ends are interleaved or there may be a spacing between segment ends. When the segments are spaced apart from one another, the spacing is typically between 0.5 mm and 1 mm. Furthermore, the stent segments  128  may be deployed individually or in groups of two or more at a single treatment site within the vessel lumen. 
         [0039]    Prosthetic stent segments  128  are preferably composed of a malleable metal so they may be plastically deformed by inflation balloon  130  as they are radially expanded to a desired diameter in the vessel at the target treatment site. The stent segments  128  may also be composed of an elastic or superelastic shape memory alloy such as Nitinol so that the stent segments  128  self-expand upon release into a vessel by retraction of the sheath  124 . In this case, an inflation balloon  130  is not required but may still be used for predilation of a lesion or augmenting expansion of the self-expanding stent segments (e.g. postdilation or tacking). Other materials such as biocompatible polymers may be used to fabricate prosthetic stent segments and these materials may further include bioabsorbable or bioerodable properties. 
         [0040]    Stent segments  128  may have any of a variety of common constructions, such as but not limited to those described in U.S. patent application Ser. No. 10/738,666 filed Dec. 16, 2003 (Attorney Docket No. 02169-000510US), which was previously incorporated by reference. Constructions may include for example, closed cell constructions including expansible ovals, ellipses, box structures, expandable diamond structures, etc. In addition, the closed cells may have complex slotted geometries such as H-shaped slots, I-shaped slots, J-shaped slots, etc. Suitable open cell structures include zigzag structures, serpentine structures, and the like. Such conventional stent structures are well described in the patent and medical literature. Specific examples of suitable stent structures are described in the following U.S. patents, the full disclosures of which are incorporated herein by reference: U.S. Pat. Nos. 6,315,794; 5,980,552; 5,836,964; 5,527,354; 5,421,955; 4,886,062; and 4,776,337. 
         [0041]    In preferred embodiments, prosthetic stent segments  128  may be coated, impregnated, infused or otherwise coupled with one or more drugs that inhibit restenosis, such as Rapamycin, Everolimus, Paclitaxel, analogs, prodrugs, or derivatives of the aforementioned, or other suitable agents, preferably carried in a durable or bioerodable polymeric carrier. Alternatively, stent segments  128  may be coated with other types of drugs or therapeutic materials such as antibiotics, thrombolytics, anti-thrombotics, anti-inflammatories, cytotoxic agents, anti-proliferative agents, vasodilators, gene therapy agents, radioactive agents, immunosuppressants, chemotherapeutics and/or stem cells. Such materials may be coated over all or a portion of the surface of stent segments  128 , or stent segments  128  may have a porous structure or include apertures, holes, channels, or other features in which such materials may be deposited. 
         [0042]    Referring now to  FIGS. 2A-2F , the deployment of selected prosthetic segments to treat a stenotic lesion is shown in accordance with an exemplary embodiment. While the embodiment will be described in the context of a coronary artery stent procedure, it should be understood that the invention may be employed in any variety of blood vessels and other body lumens in which stents or tubular prostheses are deployed, including the carotid, femoral, iliac and other arteries and vein, as well as non-vascular body lumens, such as the ureter, urethra, fallopian tubes, the hepatic duct and the like. A guide catheter (not illustrated) is first inserted into a peripheral artery such as the femoral artery, typically using a percutaneous procedure such as the Seldinger technique or by surgical cutdown, and then advanced to the ostium of the right or left coronary artery. Guidewire GW is then inserted through the guiding catheter and advanced to the target vessel V, where the lesion L to be treated is located. The proximal end of guidewire GW is then inserted through nose cone  210 , through the catheter shaft  216  and exits guidewire tube  122  (seen in  FIG. 1 ) which is outside the patient&#39;s body. 
         [0043]      FIG. 2A  shows stent delivery catheter  200  slidably advanced over the guidewire GW into the vessel V so that the nosecone  210  is distal to the lesion L. The delivery catheter  200  has an expandable member  204  disposed over a catheter shaft  216  and stent segments  202  having interleaved ends in engagement with each other are disposed over the expandable member  204 , which is a balloon in this embodiment. The stent segments  202  are covered by sheath  208 . The sheath  208  protects stent segments  202  during delivery and also prevents unintended axial displacement of the segments  202 . In this embodiment, six stent segments  202  are disposed on the stent delivery catheter  200 , each having a length approximately 6 mm long. Thus, in this embodiment, the delivery catheter  200  is adapted to deliver a prosthesis having a length ranging from 6 mm long, up to 36 mm long in 6 mm increments. Other lengths and quantities of stent segments may be employed and this exemplary embodiment is not meant to limit the scope of the present invention. A separator or stent valve  206  is disposed on the inner surface of outer shaft  211  and is adapted to engage prosthetic segments  202  and facilitates their deployment. Additionally, sheath  208  has an annular flange or tab  212  disposed on its outer surface that is adapted to pass through the stent valve  206  during retraction or advancement and to engage the annular flange or tab  214  disposed on the inner surface of outer shaft  211 . 
         [0044]    The length of the lesion to be treated is typically visualized by introducing contrast media into the target vessel V and observing the resulting image under a fluoroscope. Radiopaque markers  226 ,  228 , one at the distal end of the balloon  204  and one at the distal end of the outer shaft  211  may be used to visualize the length of stent segments  202  exposed for deployment relative to the target lesion. This is accomplished by advancing the delivery catheter  200  so that radiopaque marker  226  is at the distal edge of the lesion and then outer shaft  211  is advanced until radiopaque marker  228  is at the proximal edge of the lesion. Retraction of sheath  208  engages outer shaft  211  and then both sheath  208  and outer shaft  211  are retracted distally, resulting in a number of stent segments  218  being selected to match the length of lesion L, as shown in  FIG. 2B . In  FIG. 2B , outer shaft  211  is advanced distally so as to select two prosthetic segments  218  having a combined length of approximately 12 mm. Additional prosthetic segments  202  may be selected if necessary, although here, four prosthetic segments  202  will remain with the delivery catheter  200 . As outer shaft  211  is advanced, stent valve  206  is angled inwardly and adapted so that it will slide over sheath  208  without hindering distal motion of outer shaft  211 . Advancement of outer shaft  211  may be controlled by the control mechanism  106  illustrated in  FIG. 1 , although other actuators may be employed. After an appropriate number of prosthetic segments have been selected for deployment, the selected segments  218  are exposed in preparation for delivery. In  FIG. 2C , sheath  208  is retracted proximally and thus the selected prosthetic segments  218  are no longer constrained from expansion. As sheath  208  is retracted, its annular flange  212  slides past the stent valve  206 . Retraction of sheath  208  continues until the sheath annular flange  212  engages the outer shaft annular flange  214 . The two flanges  212 ,  214  are designed to provide a positive stop to one another. Thus, continued retraction of sheath  208  results in simultaneous retraction of outer shaft  211 , as shown in  FIG. 2D . Retraction of sheath  208  can be accomplished using the control mechanism  140  depicted in  FIG. 1 . 
         [0045]    Additionally, once annular flange  212  on the sheath  208  has passed through stent valve  206 , stent valve  206  is no longer disposed over sheath  208 . The stent valve  206  now engages the distal-most prosthetic segment  202  in the group of prosthetic segments remaining with the delivery catheter  200 , and this is shown in  FIG. 2D . Stent valve  206  is inclined such that further retraction of sheath  208  not only retracts outer shaft  211 , but stent valve  206  also retracts the group of prosthetic segments  202  that remain with the delivery catheter  200 , thereby creating a spacing between prosthetic segments  202  remaining with the delivery catheter  200  and the prosthetic segments  218  to be delivered. This spacing is typically between 0.5 mm and 5 mm and is required in order to allow a balloon taper to form during balloon inflation. In addition to the inclined stent valve  206  shown in this embodiment, other stent valves are contemplated, including those disclosed in co-pending application Ser. No. ______, filed ______ (Attorney Docket No. 021629-004000US), entitled “Custom Length Stent Apparatus,” the contents of which have previously been incorporated herein by reference. 
         [0046]    Referring now to  FIG. 2E , the selected prosthetic segments  218  are deployed. Expandable member  204 , here, a balloon, is inflated with a fluid such as contrast media and/or saline to achieve an expanded diameter  222 . Radial expansion of the balloon  204  to an enlarged diameter  222  correspondingly expands stent segments  218  to an expanded diameter  220  outward against the vessel wall across lesion L. The proximal portion of expandable member  204  is constrained by sheath  208  and radiopaque marker  228 , preventing its expansion and deployment of the remaining prosthetic segments  202 . After stent segments  220  are deployed, expanded balloon  222  is deflated and removed from the deployed stent segments  220 , leaving them in a plastically deformed, expanded configuration in the vessel V, at the site of the lesion, L. This is shown in  FIG. 2F . Stent segments  202  remain with the delivery catheter  200  which is then removed and retracted from the vessel V. 
         [0047]    While the exemplary embodiments have been described in some detail for clarity of understanding and by way of example, a variety of additional modifications, adaptations and changes may be clear to those of skill in the art. Hence, the scope of the present invention is limited solely by the appended claims.