fig1 illustrates a stent 15 in accordance with the present disclosure . stent 15 comprises a substantially cylindrical stent segment 12 and a flared stent segment 13 . substantially cylindrical stent segment 12 may be balloon expandable and may comprise stainless steel alloys , cobalt chrome alloys , titanium , tantalum , platinum , gold , or other materials or their alloys as are known in the art . flared stent segment 13 may be self expanding and may be comprise high elastic limit materials such as elgiloy , cobalt chrome alloys , engineering polymers such as polyimide , peek ( polyetheretherketone ), polycarbonate , liquid crystal polymer , polyester , or other materials as are known in the art . the flared stent segment 13 may comprise so - called superelastic or shape - memory metals such as nitinol . shape - memory metal stents can self - expand when thermo mechanically processed to exhibit superelastic material properties . such shape - memory stents can also self - expand through use of a pre - programmed shape memory effect . stents processed to exhibit a shape memory effect experience a phase change at or near the elevated temperature of the human body . the phase change results in expansion of the stent from a collapsed state to an enlarged state . fig1 - 4 show delivery of inventive stent 15 to a treatment site . in use , stent 15 is delivered to the treatment site , typically a renal artery , on catheter 18 with an outer sheath 11 coaxially retractable from inner balloons 10 , 16 , as illustrated in fig1 . outer sheath 11 constrains at least the flared segment 13 of stent 15 . distal balloon 10 is used to expand substantially cylindrical segment 12 of stent 15 . optional proximal balloon 16 may be used to dilate flared segment 13 of stent 15 . at the treatment site , distal balloon 10 is inflated to expand substantially cylindrical segment 12 and dilate artery ra , thereby securing the stent at the treatment site , as illustrated in fig2 . outer sheath 11 is then withdrawn , preferably before deflation of distal balloon 10 , and flared segment 13 is diametrically enlarged to conform to the ( typically ) flared ostial o and / or aortic ao regions near the vessel , as illustrated in fig3 . in some embodiments , flared segment 13 of stent 15 , that is the portion of the stent 15 opposite the ostial o and aortic ao regions , can be further dilated with proximal balloon 16 . inflated distal balloon 10 helps to axially anchor catheter 18 in vessel ra so that proximal balloon 16 can deliver force to flared stent segment 13 and thereby enhance stent segment 13 apposition to ostial and aortic regions of the vessel . balloons 10 and 16 are then deflated . optionally outer sheath 11 is advanced relative to balloons 10 and 16 to cover the balloons in whole or in part , and stent delivery catheter 18 is withdrawn from the treatment site , as illustrated in fig4 . it is not necessary to position substantially cylindrical stent segment 12 in vessel ra with precision because subsequent expansion of the flared stent segment 13 will assure continuous coverage of the vessel wall in regions ra , o , and ao . stenting of the vessel ra , ostium o , and aorta ao is accomplished by delivery of one stent to the region thereby reducing the amount of debris generated during stenting as compared to procedures involving delivery of multiple devices . fig5 a and 5b show alternative embodiments of a delivery system 18 ′ similar in most respects to the delivery system 18 shown in fig1 - 4 . in most respects the delivery system shown in fig5 is used in a manner similar to that described above in conjunction with fig1 - 4 . in these embodiments , balloons 17 , 17 ′ provide the function of both balloons 10 and 16 of delivery system 18 . with sheath 11 covering flared stent segment 13 and balloon portion 17 b , 17 b ′, balloon portion 17 a , 17 a ′ is used to dilate substantially cylindrical stent segment 12 . subsequently , balloon 17 , 17 ′ is deflated to a pressure low enough to allow proximal withdrawal of sheath 11 until it no longer covers flared stent segment 13 and balloon portion 17 b , 17 b ′. next , balloon 17 , 17 ′ is inflated , causing balloon portion 17 a , 17 a ′ to anchor catheter 18 ′ in the vessel and causing balloon portion 17 b , 17 b ′ to further dilate flared stent portion 13 . in this embodiment , balloon 17 , 17 ′ may be constructed from appropriate materials so as to have differing compliance characteristics between sections 17 a , 17 a ′ and 17 b , 17 b ′ at the same inflation pressure , or , balloon 17 , 17 ′ may be formed to assume a profile similar to that illustrated in fig5 a , 5 b , or another profile . fig5 a and 5b illustrate balloons having an enlarged diameter proximal portion 17 b , 17 b ′ as compared to diameter of distal portion 17 a , 17 a ′. in fig5 a an abrupt change in balloon diameter 19 divides proximal portion 17 b from distal portion 17 a . in fig5 b gradual change in balloon diameter divides proximal portion 17 b ′ from distal portion 17 a ′. in other embodiments two or more balloons can be attached to one catheter shaft to provide the above described functions of balloons 17 , 17 ′. fig6 a and 6b illustrate another embodiment of a stent 25 in accordance with the present disclosure . stent 25 comprises a substantially cylindrical stent segment 23 and a flared stent segment 22 . substantially cylindrical stent segment 23 and flared stent segment 22 may be balloon expandable and may comprise stainless steel alloys , cobalt chrome alloys , titanium , tantalum , platinum , gold , engineering polymers such as polyimide , peek ( polyetheretherketone ), polycarbonate , liquid crystal polymer , polyester , or other materials or their alloys as are known in the art . in another embodiment substantially cylindrical stent segment 23 and flared stent segment 22 may be self expanding and may be comprise high elastic limit materials such as elgiloy , cobalt chrome alloys , engineering polymers such as polyimide , peek ( polyetheretherketone ), polycarbonate , liquid crystal polymer , polyester , or other materials as are known in the art . the self expanding stent segments 22 , 23 may comprise so - called superelastic or shape - memory metals such as nitinol . shape - memory metal stents can self - expand when thermo mechanically processed to exhibit superelastic material properties . such shape - memory stents can also self - expand through use of a pre - programmed shape memory effect . stents processed to exhibit a shape memory effect experience a phase change at the elevated temperature of the human body . the phase change results in expansion of the stent from a collapsed state to an enlarged state . self expanding stent segments , in some embodiments , are heat set to a substantially cylindrical expanded shape , and in other embodiments , are shape set into a flared expanded shape . flared segment of stent 25 is shown partially expanded in fig6 a and comprises slits 26 in sidewall of stent . in one embodiment stent 25 has two slits disposed about the perimeter of the tubular body defined by the stent sidewall . in another embodiment , stent 25 has three slits , in another embodiment stent 25 has four slits , in another embodiment stent 25 has 5 or 6 slits , in another embodiment stent 25 has 7 - 10 slits , and in another embodiment stent 25 has more than 10 slits . slits 26 may be equally spaced around perimeter of stent 25 or may be unequally spaced around perimeter of stent 25 . in one embodiment , shown in fig6 b , stent 25 comprises a laser cut tube having struts 21 a , 21 b and radially expandable cells 28 joined at attachment points 27 . a line drawn through attachment points 27 on the surface of the cylindrical stent will traverse a helical path . such an arrangement enables the stent to have good axial and bending properties . slit 26 is represented by dashed lines in fig6 b and forms breaks or discontinuities in the pattern of cells 28 . stent 25 may also comprise one or more radiopaque markers 29 as are known in the art which facilitate fluoroscopic placement of the stent within the body . in one embodiment , the radiopaque markers 29 may be located on the proximal or non - flared end of the stent 25 with the number and position of the radiopaque markers 29 about the perimeter of the stent sidewall having a defined correspondence to the position and number of either the flared segments 22 or slits 26 . for clarity , stent 25 is shown cut along its axial length and laid flat in fig6 b . also , in fig6 b , cylindrical segment 23 is illustrated as shorter than flared segment 22 , however , cylindrical segment 23 may be longer than flared segment 22 or the two segments may have the same length . manufacturing methods other than laser cutting may be used to make stent 25 , including but not limited to chemical etching , grinding , machining , molding , thermoforming , casting , and other methods . in another embodiment , a stent 25 ′ is shown in fig6 c and comprises slits 26 ′ in sidewall of stent . in one embodiment stent 25 ′ has two slits , in another embodiment stent 25 ′ has three slits , in another embodiment stent 25 ′ has four slits , in another embodiment stent 25 ′ has 5 or 6 slits , in another embodiment stent 25 ′ has 7 - 10 slits , and in another embodiment stent 25 ′ has more than 10 slits . slits 26 ′ may be equally spaced around perimeter of stent 25 ′ or may be unequally spaced around perimeter of stent 25 ′. in one embodiment , shown in fig6 c , stent 25 ′ comprises a laser cut tube having struts 21 a ′, 21 b ′ and radially expandable cells 28 ′ joined at attachment points 27 ′. a line drawn through attachment points 27 ′ on the surface of the cylindrical stent will traverse a straight path . such an arrangement enables the stent to have stiff axial and bending properties . slit 26 ′ is represented by dashed lines in fig6 c . stent 25 ′ may also comprise one or more radiopaque markers 29 ′ as are known in the art . for clarity , stent 25 ′ is shown cut along its axial length and laid flat in fig6 c . also , in fig6 c , cylindrical segment 23 ′ and flared segment 22 ′ are illustrated as being similar in length , however , cylindrical segment 23 ′ may be longer or shorter than flared segment 22 . manufacturing methods other than laser cutting may be used to make stent 25 ′, including but not limited to chemical etching , grinding , machining , molding , thermoforming , casting , and other methods . in another embodiment stent 25 , 25 ′ comprise a cylindrical segment 23 , 23 ′ and a flared segment 22 , 22 ′, joined at attachment sites 31 , 31 ′ as illustrated in fig6 d ( partial plan view of unassembled attachment site ) and 6 e ( cross - sectional view of assembled attachment site ). in one embodiment cylindrical segment 23 , 23 ′ is metallic and flared segment 22 , 22 ′ is polymeric , in another embodiment cylindrical segment 23 , 23 ′ is polymeric and flared segment 22 , 22 ′ is metallic . attachment sites 31 , 31 ′ comprise strut 21 a , 21 a ′ having opening 32 , 32 ′ and strut 21 b , 21 b ′ having pin 33 , 33 ′. to attach cylindrical and flared segments , pin 33 , 33 ′ is inserted through opening 32 , 32 ′, respectively . the end of pin 33 , 33 ″ is enlarged to a diameter 34 larger than opening so as to prevent pin from exiting from opening . other attachment methods for stent segments 22 , 22 ′, 23 , 23 ′ will be apparent to those skilled in the art , such as welding , overmolding , thermoforming , bonding , and other methods . in one embodiment , illustrated in fig6 f , a cover 35 is used to join cylindrical segment 23 , 23 ′ to flared segment 22 , 22 ′. in one embodiment , cover 35 is a thin cylinder of expanded polytetrafluoroethylene bonded to stent segments using a thin sheet of polyethylene as an adhesive layer between the stent segments and the cover . other bonding methods will be apparent to those skilled in the art . stents 25 and 25 ′ can be delivered to and deployed in the vicinity of a treatment site using methods similar to those described above for inventive stent 15 with reference to fig1 - 5 . in one embodiment , two inventive stents 25 and 25 ′, each having three slits , are implanted , one coaxial with the other , and rotationally oriented such that the slits of the inner stent align with cells of the outer stent , so as to provide partial or full stent strut coverage of the vessel wall in the ostial and aortic regions , as illustrated conceptually in the end view of fig7 . the process of placement of multiple stents , as described herein , may involve placement of the stent within the body lumen followed by and expansion or flaring of the sidewall segments against the vessel wall so that the flared ends of the stent are disposed within the vessel ostium . the another stent is then positioned coaxially within the previously position to stent and rotationally aligned therewith so that the flared sidewall segments of the second stent at least partially cover any exposed areas of the vessel wall . depending on the number of stents nested in this matter , there may be varying degrees of overlap between the respective flared sidewall segments of the concentrically nested stents . the radiopaque markers described herein facilitate rotational alignment of stents during placement within the body lumen . specifically , if the number and position of radiopaque markers has a defined relationship with each sidewall segment or slit , then a practitioner may position and rotationally align two or more stents by fluoroscopically detecting the pattern of radiopaque markers for each stent and rotationally aligning the same so that the radiopaque markers of different stents are interleaved . such practice provides a fluoroscopically detectable approximation of the position of the slits and wall segments and facilitates overlap positioning of the flared wall segments against the vessel wall in the ostium region in a manner that provides maximum vessel wall coverage , as illustrated in fig7 . in another embodiment , three inventive stents 25 , 25 ′ and 25 ″ each having two or more slits , are implanted , each coaxial with the others , and rotationally oriented such that the slits of the three stents align in such a way as to provide partial or full stent strut coverage of the vessel wall in the ostial and aortic is regions , in a manner similar to that illustrated conceptually in the end view of fig7 . although the embodiment illustrated in fig7 is shown using two stents , each having three slits , other inventive arrangements may be utilized in which two or more stents , each having two or more slits , may be aligned in various arrangements to provide partial or full stent strut coverage of the vessel wall in the ostial and aortic regions . in such inventive arrangements , the struts of different stents may provide overlapping coverage of the vessel wall in the ostial and aortic regions . while this document has described a disclosure mainly in relation to renal artery stenting , it is envisioned that the disclosure can be applied to other conduits in the body as well including arteries , veins , bronchi , ducts , ureters , urethra , and other lumens intended for the passage of air , fluids , or solids . the disclosure can be applied to any site of branching of an artery , vein , bronchus , duct , ureter , urethra , and other lumen including but not limited to the junction of the common , internal , and external carotid arteries , the junction of the main , left anterior descending , and circumflex coronary arteries , the junction of the left main or right coronary artery with the aorta , the junction of the aorta with the subclavian artery , and the junction of the aorta with the carotid artery . while the various embodiments of the present invention have related to stents and stent delivery systems , the scope of the present invention is not so limited . further , while choices for materials and configurations may have been described above with respect to certain embodiments , one of ordinary skill in the art will understand that the materials described and configurations are applicable across the embodiments .
a stent includes a substantially cylindrical segment which is deployed in the renal vessel and a flared segment which is deployed in ostial and aortic regions of the vessel . the substantially cylindrical segment provides superior radial strength for maintaining dilated diameter of the renal vessel . the flared segment , which is formed by plurality of slits extending through the sidewall of the stent , expands to conform to the ostial and aortic regions of the vessel . the flared segment can be balloon dilated to enhance conformance of the flared stented segment to the ostial and aortic regions . a stent delivery system capable of delivering and deploying the substantially cylindrical segment and the flared segment is also disclosed .