Abstract:
The present invention discloses a stent delivery catheter that reduces stent displacement during deployment. In particular, the stent delivery catheter provides expansion of a stent that originates initially from within the stent&#39;s center or medial region, that later proceeds outwardly toward the stent&#39;s ends. Medial expansion of a stent is disclosed using a multi-chambered expandable balloon or a wire member that radially expands when tubular members of the catheter shaft are longitudinally displaced.

Description:
TECHNICAL FIELD 
     The present invention relates generally to the field of intravascular medical devices for stent delivery. More specifically, the present invention relates to an intravascular stent delivery catheter that provides medial balloon inflation for deterring longitudinal displacement of a stent during deployment. 
     BACKGROUND OF THE INVENTION 
     Balloon dilation catheters have been, and continue to be, a popular means of stent delivery. Current balloon catheters, however, are prone to difficulties when attempting to accurately deploy the stent across a stenosed lesion. Accurate deployment of the stent is important to the clinician, as he or she wants to place the stent directly on the diseased tissue of the vessel. Should the stent migrate to either side of the diseased tissue, some of the diseased tissue may be left untreated. In addition, healthy tissue may be adversely affected by the inaccuracy of the stent deployment procedure. 
     Stent misplacements occur because of specific inflation dynamics experienced by the expandable balloon when deploying the stent. Currently existing stent delivery catheters inflate the balloon portion of the catheter preferentially from either the distal or proximal end of the balloon. During inflation, the expanding balloon may form an inflation “wave” that may be said to drive or “plow” the stent so that it opens progressively from one end to the other along the front of the inflation wave. This form of balloon inflation is referred to as “end-to end” preferential inflation. End-to-end balloon inflation causes a deploying stent to displace longitudinally away from its intended delivery site, thereby potentially ineffectively treating the diseased lesion within the patient&#39;s vasculature. 
     In addition to end-to end preferential inflation, preferential balloon inflation may also arise from the initial inflation of the proximal and distal ends of the balloon, wherein the inflation from both ends progresses medially. This form of preferential balloon inflation is referred to as “dog boning.” In some cases, such as with rigid stents, this balloon inflation dynamic may be a preferred means of limiting stent migration. With more flexible stents, however, the dog bone balloon inflation dynamic may cause the ends of the stent to shorten with respect to one another. As the proximal end and the distal end of the stent are expanded, the ends are driven toward one another. In effect, the length of the stent is forced to compress due to this particular balloon inflation dynamic. 
     For many applications, it is desirable to have a stent delivery catheter comprising an inflation balloon that inflates evenly. For other applications, it would additionally be desirable to provide a stent delivery catheter having a balloon that incorporates preferential inflation of a beneficial type, such as initial medial inflation. 
     SUMMARY OF THE INVENTION 
     While inadvertent preferential expansion is to be avoided, some controlled preferential balloon inflations are actually desired. With initial medial inflation, for example, the expandable balloon inflates initially at its center, with inflation then progressing simultaneously towards both ends of the balloon. The center of the balloon is initially maximally inflated, causing the center of the expanding stent to impinge upon the center of the treatable lesion or stenosis. This initial medial impingement greatly reduces longitudinal displacement of the stent during its further expansion. The balloon and stent are then allowed to expand evenly toward their respective ends resulting in securing of the stent over its length in the diseased vessel. 
     Medial balloon inflation is difficult to predict and achieve with currently available expandable balloons. The physics behind fluid dynamics dictates that fluid will always take the path of least resistance when filling open space. Thus, a balloon will inflate where the fluid or inflation media gathers first. From this point, a bolus of fluid will move tangentially across the balloon filling it as it moves. This inflation phenomenon is synonymous with the end-to-end balloon inflation dynamic. Similarly, two boluses of fluid may aggregate at the confining ends of the balloon and fill medially. This inflation phenomenon is synonymous with the dog bone balloon inflation dynamic. 
     The present invention provides a balloon where the inflation dynamics are optimized (preferably from the center outward), thereby providing for the homogeneous expansion of both the expandable balloon and stent. In an alternate embodiment of the present invention, an expandable balloon is provided that incorporates a plurality of inflatable members that may be individually controlled to achieve predictable medial balloon inflation. 
     To prevent dog-bone type or end-to-end preferential inflation, and provide instead either no preferential inflation or, in an alternate embodiment, medial inflation, the present invention provides a means for directing and restraining entering inflation fluid within the distensible balloon. In a representative embodiment of the invention, a medially positioned inflation member captures an initial bolus of inflation fluid entering the balloon. This inflation member serves as a dam to gather a bolus of inflation fluid while creating a space for the fluid to fill. In one embodiment, this inflation member is rupturable. Once the member bursts, the unrestrained inflation fluid is released into the remaining portions of the expandable balloon. The expandable balloon is then further inflated to expand the remaining portions of both the balloon and stent. 
     In an alternative embodiment of the present invention, the inflation member does not rupture. The inflation member of this embodiment is comprised of a semi-permeable material. The material forming the inflation member selectively leaks at sufficiently high pressures. Thus, the bolus of fluid restrained within the inflation member slowly leaches from the inflation member, thereby expanding the remaining portions of both the balloon and stent. 
     In another embodiment of the present invention, a wire member is disposed over the distal end of the stent delivery catheter. The wire member expands and contracts with the longitudinal displacement of tubular members within the catheter&#39;s shaft. With the appropriate displacement of the tubular members, the wire member first medially expands, impinging the center of a loaded stent against the diseased lesion. In particular embodiments, an expandable balloon may be disposed over the wire member. The expandable balloon may then be inflated to further expand the remaining portions of both the balloon and stent. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The appended claims particularly point out and distinctly claim the subject matter of this invention. The various objects, advantages and novel features of this invention will be more fully apparent from a reading of the following detailed description in conjunction with the accompanying drawings in which like reference numerals refer to like parts, and in which: 
     FIG. 1 is a partial cross-sectional view of a stent delivery catheter of the present invention having a balloon region where one inflation member, within a deflated second inflation member, is inflated; 
     FIG. 2 is a partial cross-sectional view of the stent delivery catheter of FIG. 1, wherein the first and second inflation members are both inflated; 
     FIG. 3 is a partial plan view of a stent delivery catheter of the present invention, having an expandable wire member region disposed under a stent; and 
     FIG. 4 is a partial plan view of the stent delivery catheter of FIG. 3, wherein the wire member expands causing the radial displacement of the stent. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following detailed description should be read with reference to the drawings, in which like elements in different drawings are numbered identically. The drawings, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention. Examples of construction, materials, dimensions, and manufacturing processes are provided for selected elements. All other elements employ that which is known to those skilled in the field of the invention. Those skilled in the art will recognize that many of the examples provided have suitable alternatives that may be utilized. 
     FIG. 1 shows a partial cross-sectional view of a stent delivery catheter  10  in accordance with the present invention. In particular, FIG. 1 shows a stent delivery catheter  10  that includes a catheter shaft  12  having a proximal end (not shown) and a distal end  14 . A plurality of lumens extend within the catheter shaft  12 . The various lumens connect features of the catheter  10  to a source located at the proximal end of the catheter. Examples of lumens extending within catheter  10  include a guidewire lumen and at least one inflation lumen. In preferred embodiments of the present invention, two or three inflation lumens extend along a portion of the catheter shaft  12 . Connection of a lumen with its corresponding source is generally accomplished using a manifold positioned on the proximal-most end of the catheter  10 . Inflation ports on the manifold fluidly connect and direct ancillary devices to their corresponding lumens. The inflation ports possesses a luer lock fitting on the proximal end of the inflation port that mates with a corresponding connector on the appropriate ancillary device. 
     At the distal-most end of catheter  10  is a distal tip that aids the catheter in navigation through the tortuous vasculature of the patient. Modifications in the shape and size of the distal tip further aid the catheter in crossing stenosed lesions within the vasculature. Proximal the distal-most end of catheter  10  is an expandable dilation balloon  16 . Expandable balloon  16  carries an expandable stent  18  that is loaded over the balloon. Expandable stent  18  of the present invention is shown as a wire-like member comprising a plurality of interconnected strut-like members  20 . Strut-like members  20  are fabricated in defined patterns to provide radial expansion. The wire-like stent  18  expands radially when a pressure is exerted within the inner walls of the stent. Although a wire-like stent is specifically depicted, the use of other expandable stents  18  for intravascular purposes is possible without deviating from the spirit and scope of the present invention. 
     The expandable stent  18  is loaded over the balloon  16  in a constricted or compacted state. The manufacturer generally loads stent  18 ; however, a member of the surgical, radiology or cardiology staff may additionally load stent  18  within a clinical environment. When discussing the relative positioning of stent  18 , a “compacted configuration” is when stent  18  is crimped upon the catheter  10  so that the stent&#39;s profile closely mimics the profile of the catheter shaft  12 . An “expanded configuration” is when stent  18  has been radially expanded by inflation of the expandable balloon  16 . It is within the scope of the present invention to have a stent configuration where a portion of the stent is within the compacted configuration, whereas another portion is expanded. 
     Expandable balloon  16  includes two inflatable members, an inner inflation member  22  and an outer inflation member  24 . Both the inner  22  and outer  24  inflation members are attached to the catheter shaft  12 . Laser, adhesive, hot melt and thermal bonding are all acceptable methods for adhering the inflation members  22  and  24  to the catheter shaft  12 . As their names denote, however, the inner inflation member  22  is positioned under the outer inflation member  24 . The inner inflation member  22 , therefore, is adhered to a portion of the shaft  12  within the area defined by the outer inflation member  24 . Only outer tubular member  24  is in physical contact with the expandable stent  18 . The outer wall of the inner inflation member  22  contacts the inner wall of the outer inflation member  24 . 
     Inner inflation member  22  is generally shorter in length and inflated height than the outer inflation member  24 . In alternate embodiments, the inner inflation member  22  has an inflated height equivalent to the inflated height outer inflation member  24 . The length of the inner inflation member  22  is centered, with respect to the length of the outer tubular member  24 , within the outer inflation member  24 . The inner inflation member  22  is preferably stretched longitudinally during its mounting and subsequent adherence to the catheter shaft  12 . Stretching the inner inflation member thins the polymeric material, allowing the inner inflation member  22  to burst under pressure when desired, as discussed in detail below. 
     Material selection for inner inflation member  22  includes those materials having desired expansion and burst pressures. The inner inflation member  22 , therefore, is generally composed of a highly flexible and distensible material. Materials suitable for inner inflation member  22  include highly flexible polymeric materials. In preferred embodiments, the inner inflation member  22  is comprised of latex, a polyolefin such as ethylene vinyl acetate (EVA), as well as other suitable thermoplastic elastomers. 
     In a representative embodiment, the inner inflation member  22  may possess a line of weakness (not shown). A line of weakness includes a perforation or scoring of the material forming the inner inflation member  22 . In preferred embodiments, scoring of the inner inflation member  22  material is made circumferentially about the inflation member. Circumferential scoring allows the inner inflation member  22  to split radially. Under sufficient pressure, a radial split will cause the perforated inner inflation member  22  to “snap back” away from the center of the inflation member. In alternative embodiments, the inner inflation member  22  may be scored longitudinally, or at the inflation member&#39;s ends. The depth of the scoring must provide a balance between sufficient inflation strength and predictable bursting pressures. In one embodiment, an instrument scoring the inner inflation member  22  at a depth that closely approximates one-third of the inflation member&#39;s total wall thickness is proven to provide sufficient inflation and bursting predictability. 
     In an alternative embodiment, the inner inflation member  22  is semi-permeable under certain inflation pressures. The walls of a semi-permeable inner inflation member  22  may be porous. For example, the sizes of the pores found within the walls of the member dilate with the inflation of the inner inflation member  22 . The pores within the walls are too small to permit significant fluid from escaping under little or no inflation pressure. Under sufficiently high inflation pressures, however, inflation fluid may escape through the dilated pores into the surrounding volume (defined under the outer inflation member  24 ). 
     The outer inflation member  24  comprises a less flexible and less distensible material than the inner inflation member  22 . Materials suitable for the outer inflation member  24  include generally noncompliant polymeric materials. In preferred embodiments, the outer inflation member  24  is comprised of polyether block amide (PEBA), polyethylene, polyethylene terephthalate (PET), as well as other suitable thermoplastic polymers. The outer inflation member  24  can also comprise semi-compliant polyamides, polyether block amides or nylons, as well as hinged compliant materials such as polybutylene terephthalate (PBT) and Arnitel. 
     A series of lumen openings  30 , 32 , 34  are depicted along the length of the catheter shaft. The number of lumen openings depicted is for illustrative purposes only. The number of lumen openings may vary depending upon the catheter used and the desired application for the catheter. The lumen openings in FIG. 1 are shown to illustrate possible opening placements and the resulting effects of such placements. 
     A first lumen opening  30  is positioned under inner inflation member  22  only. Two additional lumen openings,  32  and  34 , are positioned only under the outer inflation member  24 . Lumen openings along catheter shaft  12  may share a common inflation lumen, or the openings may correspond to individual inflation lumens extending within the catheter shaft  12 . Multiple inflation lumens permit an operator to vary fluid pressures experienced at different regions within the expandable balloon  16 . For example, assuming the two lumen openings  32  and  34  under the outer inflation member  24  are connected, while separate from the lumen opening  30 , an operator may increase the fluid pressure within inner inflation member  22  while at the same time reducing the fluid pressure within outer inflation member  24 . This regulation is all done by controlling the inflation fluid flow rates entering and exiting the corresponding lumen openings. 
     Stent movement during deployment is reduced when the stent  18  is first expanded medially. Medial balloon inflation causes the center of stent  18  to expand first. This initial expansion impinges the center of stent  18  against the surrounding vessel wall and reduces longitudinal displacement during further expansion of the balloon  16  and stent  18 . Additionally, homogeneous expansion of the stent  18  also reduces longitudinal displacement. The expandable balloon  16  of the present invention provides for either medial or homogeneous expansion of the expandable stent  18  by selectively controlling the inflation fluid pressure and rate of inflation within the various portions of the balloon. 
     Medial expansion of stent  18  occurs through initial inflation within the center of the expandable balloon  16 . In preferred embodiments, the inner inflation member  22  has at least one dedicated inflation lumen feeding the member. An operator of the stent of the present invention, therefore, may inflate only the center of the expandable balloon  16  when desired. The operator feeds inflation fluid through the appropriate inflation lumen into the inner inflation member  22 . The inner inflation member  22  then expands, having the uninflated outer inflation member  24  draped over the inner inflation member&#39;s profile. The center of the stent  18  additionally expands roughly following the profile of the inner inflation member  22 , as seen in FIG.  1 . The inner inflation member  22  is generally expanded until stent  18  engages the surrounding vessel wall. Impinging stent  18  against the vessel wall greatly reduces the possibility of stent displacement along the vessel&#39;s longitudinal axis. 
     In certain embodiments, sufficient inflation pressures within the inner inflation member  22  may cause the inner inflation member to burst. Bursting pressures generally occur after the inner inflation member  22  can no longer radially inflate (e.g., after the inner inflation member  22  has set stent  18  against the surrounding vessel wall). Confining the expansion of balloon  16  increases internal balloon pressure. The highly flexible and distensible material of the inner inflation member  22  is finally stressed to a bursting point where the member ruptures. 
     Rupturing of the inner inflation member  22  allows inflation fluid from within the inner inflation member  22  to disperse into the outer inflation member  24 . Additional inflation fluid is then supplied to the outer inflation member  24  to further expand the unexpanded portions of stent  18 . The additional inflation fluid may continue to be supplied through lumen opening  30 , dedicated to the inner inflation lumen, or additional inflation lumens may be used that have lumen openings  32  and  34  dedicated only within the outer inflation member  24 . The outer inflation lumen  24  is then radially expanded to impinge the remaining portions of stent  18  against the vessel wall. 
     An inner inflation member  22  capable of bursting under controlled circumstances is also useful in drug delivery applications. Therapeutic drugs that treat stenotic lesions often require mixing at the point of delivery. Few methods exist for mixing solutions deep within the vasculature of a patient. The combination of a rupturable inner inflation member  22  with a porous outer inflation member  24  creates an effective device for therapeutic drug treatment. 
     In operation, one therapeutic drug may be used to inflate the inner inflation member  22  while a second therapeutic drug is used to partially inflate the outer tubular member  24 . When the highly flexible and distensible material of the inner inflation member  22  ruptures, the bolus of drugs held in the inner inflation member  22  disperses into the outer inflation member  24 . The rupturing of the inner inflation member  22  causes the two therapeutic drugs to thoroughly mix. Increasing the inflation pressure within the outer inflation member  24  allows the mixed therapeutic drugs to disperse out of the outer inflation member  24 , and onto the lesion. 
     As described above, the bursting pressure and/or direction of rupturing experienced by the inner inflation member  22  may be controlled through preferential scoring or perforation of the member wall. Circumferential scoring of the vessel wall is particularly useful when the lumen opening  30  is centrally positioned under the inner inflation member  22 . The combination of proper lumen opening placement and circumferential scoring helps ensure that lumen opening  30  remains patent after rupturing. Because the circumferential scoring forces a radial split of the inflation member  22 , the resulting “snap back” of the remaining member material away from the center of the inflation member reduces the chance that the balloon will cover the centrally located lumen opening  30 . Maintaining patency of lumen opening  30  is particularly important for deflation purposes. Catheter  10  must be withdrawn from the patient&#39;s vasculature after treatment. In order to withdraw catheter  10 , balloon  16  must first be deflated. The combination of central lumen opening placement and circumferential scoring is believed to enhance the deflation procedure. 
     In alternative embodiments having multiple inflation ports and/or lumens, another lumen opening may be used to deflate the expanded balloon. Specifically to FIGS. 1 and 2, lumen openings  32  and  34 , positioned only under outer inflation member  24 , can be used to deflate the outer inflation member  24  following completion of the medical procedure. 
     Operating multiple inflation lumens that terminate distally within an expandable balloon  16  requires a certain degree of skill. Lumens that are not active in the process of pressurization or deflation of the expandable balloon  16  need to be sealed off. Failure to seal dormant inflation lumens may prevent the expandable balloon  16  from reaching operational inflation pressures. While one inflation lumen is inflating the balloon, another unsealed inflation lumen may be deflating the balloon. The use of additional apparatus to plug dormant inflation lumens during critical inflation and deflation procedures may ensure proper pressurization of expandable balloon  16 . 
     In a preferred embodiment, a solid rod plug is inserted within a portion of a dormant inflation lumen. The solid rod plug comprises a flexible shaft having a proximal end, a distal end and a length that closely approximates the length of the inflation lumen. Shorter length plugs may also be used. The outer diameter of the plug&#39;s flexible shaft sealably slides within the inner diameter of the dormant inflation lumen. The proximal end of the plug generally possesses a luer lock fitting. This luer lock fitting mates and seals with a corresponding luer connector on the inflation port of the catheter manifold. In operation, the distal end of the plug is advanced through the dormant inflation lumen until the proximal end of the plug connects with the inflation port connector. The plug is then sealably connected to the manifold, thereby preventing inflation fluid from escaping through the dormant lumen. When the dormant inflation lumen is to be utilized, the plug may be withdrawn from the lumen, thereby allowing the lumen to be operational for inflation or deflation of expandable balloon  16 . 
     In an alternative embodiment, a hollow rod may be inserted within the dormant inflation lumen. The hollow rod has a proximal end, a distal end and a flexible lumen shaft extending the length therethrough. The outer diameter of the flexible hollow rod sealably slides within the inner diameter of the dormant inflation lumen. The flexible hollow rod generally extends the length of the inflation lumen. At the proximal end of the hollow rod are matching openings that correspond with the inflation lumen openings, for example  30 ,  32  and  34 , which fluidly connect expandable balloon  16  with the inflation lumen. In a first position, the openings within the hollow rod synchronize with the inflation lumen openings. This position allows the hollow rod to be in fluid communication with the expandable balloon  16 . When the shaft of the hollow rod is rotated, however, the openings no longer match. The lumen wall of the hollow rod sealably obstructs the inflation lumen openings. The expandable balloon  16  lacks fluid communication with either the hollow rod or the inflation lumen when the hollow rod is rotated into this configuration. Therefore, the openings of the hollow rod must align properly with the inflation lumen openings in order to utilize an inflation lumen having the hollow rod inserted therein. 
     Medial expansion of a stent  18  may be provided using additional embodiments. In one such embodiment, the inner inflation member  22  comprises a semi-permeable, porous wall material, as described above. As with previous embodiments, an inflation fluid is supplied only to the inner inflation member  22 . Inner inflation member  22  inflates radially, resulting in the medial impingement of stent  18  against the treated vascular wall. The inner inflation member  22  continues to expand until the internal pressure within the member causes inflation fluid to escape through the member&#39;s wall. A constant stream of inflation fluid, directed only within inner inflation member  22 , eventually inflates the outer inflation member  24 . To expedite the process, additional inflation fluid may be supplied through lumen openings  32  and  34 , dedicated to the inflation of outer inflation member  24 . FIG. 2 shows inflation fluid filling both the inner  22  and outer  24  inflation members concurrently. With or without the additional inflation fluid, the outer inflation member  24  eventually expands to impinge the remaining portions of stent  18  against the treated vascular wall. 
     In yet another embodiment, additionally depicted by FIG. 2, inflation fluid is supplied to both the inner inflation member  22  and the outer inflation member  24  concurrently. Different from prior embodiments, however, all regions of the expandable balloon  16  are inflated concurrently, resulting in the homogenous radial expansion of stent  18 . Incorporating a dedicated inflation lumen and inflation member within the center of expandable balloon  16  ensures proper medial inflation. Providing dedicated inflation lumen openings  32  and  34  within the remaining sections of balloon  16  similarly controls inflation within those regions. More specifically to FIG. 2, lumen openings  32  and  34  at the ends of expandable balloon  16  either can share or be individually connected to inflation lumens in order to ensure proper fluid distribution within the balloon. 
     Homogeneous radial expansion of stent  18  occurs when an operator inflates the outer inflation member  24  concurrently with the inner inflation member  22 . Controlling the inflation rates within the expandable balloon  16  causes stent  18  to expand radially in a homogeneous fashion. The stent  18 , therefore, uniformly impinges upon the treated vessel. Uniform impingement greatly reduces the possibility of stent  18  displacing along the vessel&#39;s longitudinal axis during deployment. 
     FIG. 3 shows a stent delivery catheter  10  having an expandable wire member  40 . In particular, FIG. 3 shows a stent delivery catheter  10  that includes a catheter shaft  12  having a proximal end (not shown) and a distal end  14 . Catheter shaft  12  in FIG. 3 includes at least two tubular members, an outer tubular member  42  and an inner tubular member  44 . The inner tubular member  42  extends from the proximal-most end of catheter  10  to the distal-most end of catheter  10 . The outer tubular member  44  is circumferentially disposed over a portion of the inner tubular member  42 . More specifically, the outer tubular member  44  extends from the proximal-most end of catheter  10  to a point proximal the distal-most end of catheter  10 . The inner tubular member  42  and the outer tubular member  44  may be relatively displaced with respect to one another. In particular, inner tubular member  42  may be longitudinally displaced within the outer tubular member  44 . 
     An expandable wire member  40  spans distally from the distal-most end of outer tubular member  44  to a distal portion of inner tubular member  42 . The expandable wire member  40  includes a plurality of wire elements  50  that are woven in patterns to provide radial expansion. Materials suitable for the wire elements  50  include nitinol, stainless steel, and semi-rigid polymeric materials. One end of a wire element  50  is anchored to the outer tubular member  44 , while the other end is anchored to the inner tubular member  42 . In a preferred embodiment, a balloon material (not shown) is disposed over the expandable wire member  40 , as with the outer inflation member of previous embodiments. 
     Similar to previous embodiments, an expandable stent  18  is loaded upon the expandable wire member  40 . The expandable stent  18  expands radially when a pressure is exerted from within its inner walls. Although a wire stent is specifically depicted, the use of other stents for intravascular purposes is possible without deviating from the spirit and scope of the present invention. 
     Longitudinal displacement between the inner  42  and outer  44  tubular members forces wire member  40  to radially expand, as shown in FIG.  4 . In preferred embodiments, wire member  40  expands first medially, and then from the center outward. Medial expansion of wire member  40  impinges the center of stent  18  into the patient&#39;s vascular wall. As with medial inflation, medial expansion of wire member  40  greatly reduces the possibility of stent displacement along the vessel&#39;s longitudinal axis. Further longitudinal displacement of the inner  42  and outer  44  tubular members of the catheter shaft permits the wire member  40  to fully expand, thereby impinging the remaining portions of stent  18  against the surrounding vessel wall. 
     As described above, an expandable balloon (not shown) may overlay the wire member  40  of the present invention. With certain procedures, the expandable balloon complements the expansive properties of wire member  40 . More specifically, inflation of the expandable balloon, following medial expansion with wire member  40 , may further set and impinge stent  18  against the surrounding vascular wall. Balloon inflation generally provides greater uniform pressure on the inner walls of a stent. This increased surface contact aids in stent deployment when particularly difficult stenosed lesions are involved. 
     Numerous characteristics and advantages of the invention covered by this document have been set forth in the foregoing description. It will be understood, however, that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size and ordering of steps without exceeding the scope of the invention. The invention&#39;s scope is of course defined in the language in which the appended claims are expressed.