turning to fig1 , a first embodiment of the present invention is shown , namely a stent catheter 10 and a filter device 30 . the stent catheter 10 typically includes a catheter body 12 , an inflatable balloon 16 , and a stent 20 . the catheter body 12 typically comprises a substantially flexible member having a proximal end ( not shown ) and a distal end 14 . the balloon is mounted on a region at or near the distal end 14 of the catheter body 12 . an inflation lumen 18 extends longitudinally from a region at or near the proximal end of the catheter body 12 to the balloon 16 . the stent 20 is introduced over the balloon 16 , typically by manually compressing it onto the balloon 16 . the stent 20 may comprise a tube , sheet , wire , mesh or spring , although preferably , it is a substantially cylindrical wire mesh sleeve , that is substantially rigid , yet expandable when subjected to radial pressure . many known stent devices are appropriate for use with the present invention , such as those discussed elsewhere in this disclosure . generally the stent is furnished from materials such as stainless steel or nitinol , with stainless steel being most preferred . alternatively , a self - expanding stent ( not shown ) may also be used , such as those disclosed in regan , u . s . pat . no . 4 , 795 , 458 , harada et al ., u . s . pat . no . 5 , 037 , 427 , harada , u . s . pat . no . 5 , 089 , 005 , and mori , u . s . pat . no . 5 , 466 , 242 , the disclosures of which are incorporated herein by reference . such stents are typically provided from nitinol or similar materials which are substantially resilient , yet compressible . when an expandable stent is used , the stent catheter does not generally include an inflatable balloon for the stent . instead , the stent is compressed directly onto the catheter , and a sheath is placed over the stent to prevent it from expanding until deployed . in addition to the catheter 10 , the present invention typically includes a filter device 30 . the filter device 30 generally comprises an introducer sheath 32 , a guidewire 40 , and an expandable filter assembly 50 , although alternatively the guidewire 40 and the filter assembly 50 may be provided directly on the catheter 10 as will be described below ( see fig2 ). the sheath 32 has a proximal end 34 and a distal end 36 , and generally includes a hemostatic seal 38 mounted on its proximal end 34 . the guidewire 40 , typically a flexible , substantially resilient wire , having a distal end 42 and a proximal end 44 , is inserted into the proximal end 34 of the sheath 32 through a lumen 33 . a hub or handle 46 is generally mounted on the proximal end 44 for controlling the guidewire 40 . generally , attached on or near the distal end 42 of the guidewire 40 is an expandable filter assembly 50 which generally comprises an expansion frame 52 and filter mesh 60 . the expansion frame 52 is generally adapted to open from a contracted condition while it is introduced through the lumen 33 of the sheath 32 to an enlarged condition once it is exposed within a blood vessel 70 , as will be discussed more particularly below . the filter mesh 60 is substantially permanently attached to the expansion frame 52 . the construction of the stent catheter 10 should already be familiar to those skilled in the art . the catheter body 12 is typically made from substantially flexible materials such as polyethylene , nylon , pvc , polyurethane , or silicone , although materials such as polyethylene and pvc are preferred . the balloon 16 for delivering the stent 20 is generally manufactured from a substantially flexible and resilient material , such as polyethylene , polyester , latex , silicone , or more preferably polyethylene and polyester . a variety of balloons for angioplasty or stenting procedures are available which have a range of known inflated lengths and diameters , allowing an appropriate balloon to be chosen specifically for the particular blood vessel being treated . the sheath 32 for the filter device 30 generally comprises a conventional flexible sheath or cannula for introducing catheters or guidewires into the blood stream of a patient . exemplary materials include polyethylene , nylon , pvc , or polyurethane with polyethylene and pvc being most preferred . the hemostatic seal 38 generally is an annular seal designed to prevent the escape of blood from the vessel through the sheath 32 , and includes materials such as silicone , latex , or urethane , or more preferably silicone . the hemostatic seal 38 is substantially permanently adhered to the proximal end 34 of the sheath 32 using known surgically safe bonding materials . the guidewire 40 is generally manufactured from conventional resilient wire such as stainless steel or nitinol , although stainless steel is preferred , having a conventional hub or handle 46 formed integral with attached to its proximal end 44 . turning now to fig3 , the filter assembly 50 of the present invention is generally shown extending from the distal end 36 of a sheath or catheter 32 and in an enlarged condition within a blood vessel 70 . the filter assembly 50 includes an expansion frame 52 comprising a plurality of struts , ribs or wires 54 , each strut 54 having a substantially fixed proximal end 56 and a distal end 58 , which may or may not be fixed . the proximal ends 56 are typically connected to the distal end 42 of the guidewire 40 , or alternatively to the outer surface of a distal region ( not shown in fig3 ) of the guidewire 40 , typically using conventional bonding methods , such as welding , soldering , or gluing . the distal ends 58 of the struts 54 are connected to the filter mesh 60 , or alternatively to the distal end of the guidewire ( not shown ). the struts generally comprise substantially resilient materials such as stainless steel or nitinol , with stainless steel being preferred . generally , the filter mesh 60 comprises a fine mesh having an open region 64 substantially engaging the wall 72 of the blood vessel 70 and a closed region 62 , shown here as the apex of a cone . an appropriate mesh is selected , having a pore size that permits blood to flow freely through the mesh , while capturing therein undesired particles of a targeted size . appropriate filter materials are disclosed in co - pending applications barbut et al ., u . s . application ser . no . 08 / 553 , 137 , filed nov . 7 , 1995 , barbut et al ., u . s . application ser . no . 08 / 580 , 223 , filed dec . 28 , 1995 , barbut et al ., u . s . application ser . no . 08 / 584 , 759 , filed jan . 9 , 1996 , barbut et al ., u . s . application ser . no . 08 / 640 , 015 , filed apr . 30 , 1996 , barbut et al ., u . s . application ser . no . 08 / 645 , 762 , filed may 14 , 1996 , and maahs , u . s . application ser . no . 08 / 842 , 727 , filed apr . 16 , 1997 . the disclosure of these references and any others cited herein are expressly incorporated herein by reference . an exemplary embodiment of the mesh has a mesh area of 3 - 8 sq . in ., a mesh thickness of 60 - 200 μm , a thread diameter of 30 - 100 μm , and a pore size of 60 - 100 μm . polyethylene meshes , such as saati tech and tetko , inc . meshes , provide acceptable filter materials , as they are available in sheet form and can be easily cut and formed into a desired shape . the mesh is formed into a desired filter shape and is sonic welded or adhesive bonded to the struts 54 . the present invention is then typically used to introduce a stent into a stenosed or occluded region of a patient , preferably for treating a region within the carotid arteries . referring again to fig1 and 2 , the catheter 10 is first introduced into a blood vessel 70 using known percutaneous procedures , and then is directed through the blood vessel to the stenosed region of the target blood vessel . the catheter 10 is typically introduced in an upstream - to - downstream ( antegrade ) orientation as shown in fig1 and 14 , although the catheter may also be introduced in a downstream - to - upstream ( retrograde ) orientation as will be described below . in a preferred example , the catheter 10 is inserted into a femoral artery and directed using known methods to a carotid artery , as shown in fig1 , or alternatively is introduced through a lower region of a carotid artery and directed downstream to the stenosed location 74 . the sheath 32 is percutaneously introduced into the blood vessel 70 downstream of the stenosed region 74 , and is deployed using conventional methods . the distal end 42 of the guidewire 40 is directed through the lumen 33 of the sheath 32 until the filter assembly 50 is introduced into the blood vessel 70 by pushing distally on the hub 46 on the guidewire 40 . when the distal end 42 of the guidewire 40 enters the blood vessel 70 , the expansion frame 52 is opened to its enlarged condition , extending substantially across the entire cross - section of the vessel 70 . the filter mesh 60 attached to the frame 52 substantially engages the luminal walls 72 of the vessel 70 , thereby capturing any undesirable loose material passing along the blood vessel 70 from the treated region 74 . the catheter 10 is inserted through the stenosed region 74 until the stent 20 is centered across the plaque or embolic material 76 deposited on the walls 72 of the blood vessel 70 . if the region 74 is substantially blocked , it may be necessary to first open the region 74 using a balloon catheter prior to insertion of the stent catheter ( not shown in fig3 ), as will be familiar to those skilled in the art . once the stent 20 is in the desired position , fluid , saline , or radiographic contrast media , but preferably radiographic contrast media , is introduced through the inflation lumen 18 to inflate the balloon 16 . as the balloon 16 expands , the pressure forces the stent 20 radially outwardly to engage the plaque 76 . the plaque 76 is pushed away from the region 74 , opening the vessel 70 . the stent 20 covers the plaque 76 , substantially permanently trapping it between the stent 20 and the wall 72 of the vessel 70 . once the balloon 16 is fully inflated , the stent 20 provides a cross - section similar to the clear region of the vessel 70 . the balloon 16 is then deflated by withdrawing the fluid out of the inflation lumen 18 and the catheter 12 is withdrawn from the region 74 and out of the patient using conventional methods . the stent 20 remains in place , substantially permanently covering the plaque 76 in the treated region 74 and forming part of the lumen of the vessel 70 . as the stenosed region 74 is being opened , or possibly as the catheter 12 is being introduced through the region 74 , plaque may break loose from the wall 72 of the vessel 70 . blood flow will carry the material downstream where it will encounter the filter mesh 60 and be captured therein . once the catheter 12 is removed from the treated region 74 , the expansion frame 52 for the filter mesh 60 is closed to the contracted position , containing any material captured therein . the filter assembly 50 is withdrawn into the lumen 33 of the sheath 32 , and the filter device 30 is removed from the body . in another embodiment , shown in fig2 , the guidewire 40 and the filter assembly 50 are included within the stent catheter 10 , rather than being provided in a separate sheath , thus eliminating the need for a second percutaneous puncture into the patient . as already described , the catheter 12 is provided with an inflatable balloon 16 furnished near its distal end 14 and with a stent 20 compressed over the balloon 16 . in addition to the inflation lumen 18 , a second lumen 19 extends through the catheter 12 from a proximal region ( not shown ) to its distal end 14 . a guidewire 40 , having a filter assembly 50 on its distal end 42 , is introduced through the lumen 19 until its distal end 42 reaches the distal end 14 of the catheter 12 . as before , the filter assembly 50 comprises an expansion frame 52 and filter mesh 60 , which remain within the lumen 19 of the catheter 12 until deployed . as described above , the stent catheter 10 is percutaneously introduced and is directed through the blood vessels until it reaches the stenosed region 74 and the stent 20 is centered across the plaque 76 . the guidewire 40 is pushed distally , introducing the filter assembly 50 into the blood vessel 70 . the expansion frame 52 is opened to the enlarged condition until the filter mesh 60 engages the walls 72 of the blood vessel 70 . the balloon 16 is then inflated , pushing the stent 20 against the plaque 76 , opening the treated region 74 . as before , the stent 20 substantially permanently engages the plaque 76 and becomes part of the lumen 72 of the vessel 70 . after the balloon 16 is deflated , the expansion frame 52 of the filter assembly 50 is closed to the contracted condition , and the filter assembly 50 is withdrawn into the lumen 19 . the stent catheter 10 is then withdrawn from the patient using conventional procedures . alternatively , a self - expanding stent may be substituted for the expandable stent described above . generally , the stent is compressed onto a catheter , and a sheath is introduced over the catheter and stent . the sheath serves to retain the stent in its compressed form until time of deployment . the catheter is percutaneously introduced into a patient and directed to the target location within the vessel . with the stent in position , the catheter is fixed and the sheath is withdrawn proximally . once exposed within the blood vessel , the stent automatically expands radially , until it substantially engages the walls of the blood vessel , thereby trapping the embolic material and dilating the vessel . the catheter and sheath are then removed from the patient . the filter assembly 50 generally described above has a number of possible configurations . hereinafter reference is generally made to the filter device described above having a separate sheath , although the same filter assemblies may be incorporated directly into the stent catheter . turning to fig4 a , 4 b , and 4 c , another embodiment of the filter device 30 is shown , namely a sheath 32 having a guidewire 40 in its lumen 33 and a filter assembly 50 extending from the distal end 36 of sheath 32 . the filter assembly 50 comprises a plurality of struts 54 and filter mesh 60 . the guidewire 40 continues distally through the filter mesh 60 to the closed end region 62 . the proximal ends 56 of the struts 54 are attached to the distal end 36 of the sheath 32 , while the distal ends 58 of the struts 54 are attached to the distal end 42 of the guidewire . in fig4 a , showing the contracted condition , the struts 54 are substantially straight and extend distally . at an intermediate region 57 , the open end 64 of the filter mesh 60 is attached to the struts 54 using the methods previously described . the filter mesh 60 may be attached to the struts 54 only at the intermediate region 57 or preferably continuously from the intermediate region 57 to the distal ends 58 . in addition , at the intermediate region 57 , the struts 54 are notched or otherwise designed to buckle or bend outwards when compressed . between the intermediate region 57 of the struts 54 and the distal end 36 of the sheath 32 , the guidewire 40 includes a locking member 80 , preferably an annular - shaped ring made of stainless steel , fixedly attached thereon . inside the lumen 33 near the distal end 36 , the sheath 32 has a recessed area 82 adapted to receive the locking member 80 . the guidewire 40 and filter assembly 50 are included in a sheath 32 as previously described , which is introduced into a blood vessel 70 , as shown in fig4 a , downstream of the stenosed region ( not shown ). with the sheath 32 substantially held in position , the guidewire 40 is pulled proximally . this causes the struts 54 to buckle and fold outward at the intermediate region 57 , opening the open end 64 of the filter mesh 60 as shown in fig4 b . as the guidewire 40 is pulled , the locking member 80 enters the lumen 33 , moving proximally until it engages the recessed area 82 , locking the expansion frame in its enlarged condition , as shown in fig4 c . with the expansion frame 52 in its enlarged condition , the open end 64 of the filter mesh 60 substantially engages the walls 72 of the blood vessel 70 . after the stent is delivered ( not shown ), the expansion frame 52 is closed by pushing the guidewire 40 distally . this pulls the struts 54 back in towards the guidewire 40 , closing the open end 64 of the filter mesh 60 and holding any loose embolic material within the filter assembly 50 . as a further modification of this embodiment , the entire sheath 32 and filter assembly 50 may be provided within an outer sheath or catheter ( not shown ) to protect the filter assembly 50 during introduction into the vessel . once the device is in the desired location , the sheath 32 is held in place and the outer sheath is withdrawn proximally , exposing the filter assembly 50 within the blood vessel 70 . after the filter assembly 50 is used and closed , the sheath 32 is pulled proximally until the filter assembly 50 completely enters the outer sheath , which may then be removed . turning to fig5 a , 5 b and 5 c , another embodiment of the filter assembly 50 is shown . the proximal ends 56 of the plurality of struts 54 are substantially fixed to the distal end 36 of the sheath 32 . the distal ends 58 may terminate at the open end 64 of the filter mesh 60 , although preferably , the struts 54 extend distally through the filter mesh 60 to the closed end region 62 , where they are attached to the distal end 42 of the guidewire 40 . referring to fig5 a , the filter assembly 50 is shown in its contracted condition . the guidewire 40 has been rotated torsionally , causing the struts 54 to helically twist along the longitudinal axis of the guidewire 40 and close the filter mesh 60 . the filter assembly 50 is introduced into a blood vessel 70 as already described , either exposed on the end of the sheath 32 or , preferably , within an outer sheath ( not shown ) as described above . once in position , the sheath 32 is fixed , and the guidewire 40 is rotated torsionally in relation to the sheath 32 . as shown in fig5 b , the struts 54 , which are biased to move radially towards the wall 72 of the vessel 70 , unwind as the guidewire 40 is rotated , opening the open end 64 of the filter mesh 60 . once the struts 54 are untwisted , the expansion frame in its enlarged condition causes the open end 64 of the filter mesh 60 to substantially engage the walls 72 of the vessel 70 , as shown in fig5 c . after the stent is delivered ( not shown ), the guidewire 40 is again rotated , twisting the struts 54 back down until the expansion frame 52 again attains the contracted condition of fig5 a . the sheath 32 and filter assembly 50 are then removed from the blood vessel 70 . another embodiment of the filter assembly 50 is shown in fig6 a and 6b . the struts 54 at their proximal ends 56 are mounted on or in contact with guidewire 40 , and their distal ends 58 are connected to form the expansion frame 52 , and are biased to expand radially at an intermediate region 57 . the proximal ends 56 are attached to the distal end 42 of the guidewire 40 with the distal ends 58 being extended distally from sheath 32 . filter mesh 60 is attached to the struts 54 at the intermediate region 57 . if the filter assembly 50 is introduced in an antegrade orientation as previously described , the filter mesh 60 is typically attached from the intermediate region 57 to the distal ends 58 of the struts 54 , as indicated in fig6 a . alternatively , if introduced in a retrograde orientation , it is preferable to attach the filter mesh 60 between the intermediate region 57 to the proximal ends 56 of the struts 54 , as shown in fig6 b , thus directing the interior of the filter mesh upstream to capture any embolic material therein . the filter assembly 50 is provided with the struts 54 compressed radially in a contracted condition in the lumen 33 of the sheath 32 ( not shown ). the filter assembly 50 is introduced into the blood vessel 70 by directing the guidewire distally . as the expansion frame 52 enters the blood vessel , the struts 54 automatically expand radially into the enlarged condition shown in fig6 a and 6b , thereby substantially engaging the open end 64 of the filter mesh 60 with the walls 72 of the blood vessel 70 . to withdraw the filter assembly 50 from the vessel 70 , the guidewire 40 is simply pulled proximally . the struts 54 contact the distal end 36 of the sheath 32 as they enter the lumen 33 , compressing the expansion frame 52 back into the contracted condition . fig8 a presents another embodiment of the filter assembly 50 similar to that just described . the expansion frame 52 comprises a plurality of struts 54 having a filter mesh 60 attached thereon . rather than substantially straight struts bent at an intermediate region , however , the struts 54 are shown having a radiused shape biased to expand radially when the filter assembly 50 is first introduced into the blood vessel 70 . the filter mesh 60 has a substantially hemispherical shape , in lieu of the conical shape previously shown . optionally , as shown in fig8 b , the filter mesh 60 may include gripping hairs 90 , preferably made from nylon , polyethylene , or polyester , attached around the outside of the open end 64 to substantially minimize undesired movement of the filter mesh 60 . such gripping hairs 90 may be included in any embodiment presented if additional engagement between the filter mesh 60 and the walls 72 of the vessel 70 is desired . fig7 shows an alternative embodiment of the filter assembly 50 , in which the expansion frame 52 comprises a strut 54 attached to the filter mesh 60 . the open end 64 of the filter mesh 60 is biased to open fully , thereby substantially engaging the walls 72 of the blood vessel 70 . the mesh material itself may provide sufficient bias , or a wire frame ( not shown ) around the open end 64 may be used to provide the bias to open the filter mesh 60 . the filter mesh 60 is compressed prior to introduction into the sheath 32 . to release the filter assembly 50 into the blood vessel 70 , the guidewire 40 is moved distally . as the filter assembly 50 leaves the lumen 33 of the sheath 32 , the filter mesh 60 opens until the open end 64 substantially engages the walls 72 of the blood vessel 70 . the strut 54 attached to the filter mesh 60 retains the filter mesh 60 and eases withdrawal back into the sheath 32 . for removal , the guidewire 40 is directed proximally . the strut 54 is drawn into the lumen 33 , pulling the filter mesh 60 in after it . in a further alternative embodiment , fig9 shows a filter assembly 50 comprising a plurality of substantially cylindrical , expandable sponge - like devices 92 , having peripheral surfaces 94 which substantially engage the walls 72 of the blood vessel 70 . the devices 92 are fixed to the guidewire 40 which extends centrally through them as shown . the sponge - like devices have sufficient porosity to allow blood to pass freely through them and yet to entrap undesirable substantially larger particles , such as loose embolic material . exemplary materials appropriate for this purpose include urethane , silicone , cellulose , or polyethylene , with urethane and polyethylene being preferred . in addition , the devices 92 may have varying porosity , decreasing along the longitudinal axis of the guidewire . the upstream region 96 may allow larger particles , such as embolic material , to enter therein , while the downstream region 98 has sufficient density to capture and contain such material . this substantially decreases the likelihood that material will be caught only on the outer surface of the devices , and possibly come loose when the devices is drawn back into the sheath . the devices 92 are compressed into the lumen 33 of the sheath 32 ( not shown ), defining the contracted condition . they are introduced into the blood vessel 70 by pushing the guidewire 40 distally . the devices 92 enter the vessel 70 and expand substantially into their uncompressed size , engaging the walls 72 of the vessel 70 . after use , the guidewire 40 is pulled proximally , compressing the devices 92 against the distal end 36 of the sheath 32 and directing them back into the lumen 33 . turning to fig1 , another embodiment of the present invention is shown , that is , a stent catheter 10 having a filter assembly 50 provided directly on its outer surface 13 . the stent catheter 10 includes similar elements and materials to those already described , namely a catheter 12 , an inflatable balloon 16 near the distal end 14 of the catheter 12 , and a stent 20 compressed over the balloon 16 . instead of providing a filter assembly 50 on a guidewire , however , the filter assembly 50 typically comprises an expansion frame 52 and filter mesh 60 attached directly to the outer surface 13 of the catheter 12 . preferably , the expansion frame 52 is attached to the catheter 12 in a location proximal of the stent 20 for use in retrograde orientations , although optionally , the expansion frame 52 may be attached distal of the stent 20 and used for antegrade applications . the filter assembly 50 may take many forms similar to those previously described for attachment to a guidewire . in fig1 , the expansion frame 52 includes a plurality of radially biased struts 54 , having proximal ends 56 and distal ends 58 . the proximal ends 56 of the struts 54 are attached to the outer surface 13 of the catheter 12 proximal of the stent 20 , while the distal ends 58 are loose . filter mesh 60 , similar to that already described , is attached to the struts 54 between the proximal ends 56 and the distal ends 58 , and optionally to the outer surface 13 of the catheter 12 where the proximal ends 56 of the struts 52 are attached . prior to use , a sheath 132 is generally directed over the catheter 12 . when the sheath engages the struts 54 , it compresses them against the outer surface 13 of the catheter 12 . the catheter 12 and the sheath 132 are then introduced into the patient , and directed to the desired location . once the stent 20 is in position , the catheter 12 is fixed and the sheath 132 is drawn proximally . as the struts 58 enter the blood vessel 70 , the distal ends 58 move radially , opening the filter mesh 60 . once the filter assembly 50 is fully exposed within the blood vessel 70 , the distal ends 58 of the struts 54 , and consequently the open end 64 of the filter mesh 60 , substantially engage the walls 72 of the blood vessel 70 . after the stent is deployed , the sheath 132 is pushed distally . as the struts 54 enter the lumen 133 of the sheath 132 , they are compressed back against the outer surface 13 of the catheter 12 , thereby containing any captured material in the filter mesh 60 . the catheter 12 and sheath 132 are then withdrawn from the vessel 70 . turning to fig1 a and 11b , an alternative embodiment of the expansion frame 50 is shown . the proximal ends 56 of the struts 54 are attached or in contact with the outer surface 13 of the catheter 12 . the struts 54 have a contoured radius biased to direct an intermediate region 57 radially . filter mesh 60 is attached between the intermediate region 57 and the proximal ends 56 , or between the intermediate region and the distal end ( not shown ). fig1 a shows the filter assembly 50 in its contracted condition , with a sheath 132 covering it . the sheath 132 compresses the struts 54 against the outer surface 13 of the catheter 12 , allowing the device to be safely introduced into the patient . once in position , the sheath 132 is pulled proximally as shown in fig1 b . as the distal end 136 of the sheath 132 passes proximal of the filter assembly 50 , the struts 54 move radially , causing the intermediate region 57 of the struts 54 and the open end of the filter mesh 60 to substantially engage the walls 72 of the blood vessel 70 . after use , the sheath 132 is directed distally , forcing the struts 54 back against the catheter 12 and containing any material captured within the filter mesh 60 . in another embodiment of the present invention , shown in fig1 a and 12b , a stent catheter 10 , similar to those previously described , is provided with a fluid operated filter assembly 50 attached on or near the distal end 14 of the catheter 12 . the catheter 12 includes a first inflation lumen 18 for the stent balloon 16 , and a second inflation lumen 19 for inflating an expansion frame 52 for the filter assembly 50 . the expansion frame 52 generally comprises an inflatable balloon 102 , preferably having a substantially annular shape . the balloon 102 generally comprises a flexible , substantially resilient material , such as silicone , latex , or urethane , but with urethane being preferred . the second inflation lumen 19 extends to a region at or near to the distal end 14 of the catheter 12 , and then communicates with the outer surface 13 , or extends completely to the distal end 14 . a conduit 104 extends between the balloon 102 and the inflation lumen 19 . the conduit 104 may comprise a substantially flexible tube of material similar to the balloon 102 , or alternatively it may be a substantially rigid tube of materials such as polyethylene . optionally , struts or wires 106 are attached between the balloon 102 and the catheter 12 to retain the balloon 12 in a desired orientation . filter mesh 60 , similar to that previously described , is attached to the balloon 102 . turning more particularly to fig1 a , the filter assembly 50 is shown in its contracted condition . the balloon 102 is adapted such that in its deflated condition it substantially engages the outer surface 13 of the catheter 12 . this retains the filter mesh 60 against the catheter 12 , allowing the catheter 12 to be introduced to the desired location within the patient &# 39 ; s blood vessel 70 . the catheter 12 is percutaneously introduced into the patient and the stent 20 is positioned within the occluded region 74 . fluid , such as saline solution , is introduced into the lumen 19 , inflating the balloon 102 . as it inflates , the balloon 102 expands radially and moves away from the outer surface 13 of the catheter 12 . as shown in fig1 b , once the balloon 102 is fully inflated to its enlarged condition , it substantially engages the walls 72 of the blood vessel 70 and opens the filter mesh 60 . once the stent 20 is delivered and the stent balloon 16 is deflated , fluid is drawn back out through the inflation lumen 19 , deflating the balloon 102 . once deflated , the balloon 102 once again engages the outer surface 13 of the catheter 12 , closing the filter mesh 60 and containing any embolic material captured therein . the catheter 12 is then withdrawn from the patient . alternatively , the filter assembly 50 just described may be mounted in a location proximal to the stent 20 as shown in fig1 a and 13b . the open end 64 of the filter mesh 60 is attached to the balloon 102 , while the closed end 62 is attached to the outer surface 13 of the catheter 12 , thereby defining a space for capturing embolic material . in the contracted condition shown in fig1 a , the balloon 102 substantially engages the outer surface 13 of the catheter 12 , thereby allowing the catheter 10 to be introduced or withdrawn from a blood vessel 70 . once the stent 20 is in position across a stenosed region 74 , the balloon 102 is inflated , moving it away from the catheter 12 , until it achieves its enlarged condition , shown in fig1 b , whereupon it substantially engages the walls 72 of the blood vessel 70 . a detailed longitudinal view of a filter guidewire is shown in fig1 . guidewire 40 comprises inner elongate member 207 surrounded by a second elongate member 201 , about which is wrapped wire 211 in a helical arrangement . guidewire 40 includes enlarged segment 202 , 208 which houses a series of radially biased struts 203 . helical wires 211 separate at cross - section 205 to expose the eggbeater filter contained within segment 202 . guidewire 40 includes a floppy atraumatic tip 204 which is designed to navigate through narrow , restricted vessel lesions . the eggbeater filter is deployed by advancing distally elongate member 201 so that wire housing 211 separates at position 205 as depicted in fig1 a . elongate member 207 may be formed from a longitudinally stretchable material which compresses as the struts 203 expand radially . alternatively , elongate member 207 may be slideably received within sheath 201 to allow radial expansion of struts 203 upon deployment . the filter guidewire may optionally include a coil spring 206 disposed helically about elongate member 207 in order to cause radial expansion of struts 203 upon deployment . a typical filter guidewire will be constructed so that the guidewire is about 5f throughout segment 208 , 4f throughout segment 209 , and 3f throughout segment 210 . the typical outer diameter in a proximal region will be 0 . 012 - 0 . 035 inches , more preferably 0 . 016 - 0 . 022 inches , more preferably 0 . 018 inches . in the distal region , a typical outer diameter is 0 . 020 - 0 . 066 inches , more preferably 0 . 028 - 0 . 036 inches , more preferably 0 . 035 inches . guidewire length will typically be 230 - 290 cm , more preferably 260 cm for deployment of a balloon catheter . it should be understood that reducing the dimensions of a percutaneous medical instrument to the dimensions of a guidewire as described above is a significant technical hurdle , especially when the guidewire includes a functioning instrument such as an expansible filter as disclosed herein . it should also be understood that the above parameters are set forth only to illustrate typical device dimensions , and should not be considered limiting on the subject matter disclosed herein . in use , a filter guidewire is positioned in a vessel at a region of interest . the filter is deployed to an expanded state , and a medical instrument such as a catheter is advanced over the guidewire to the region of interest . angioplasty , stent deployment , rotoblader , atherectomy , or imaging by ultrasound or doppler is then performed at the region of interest . the medical / interventional instrument is then removed from the patient . finally , the filter is compressed and the guidewire removed from the vessel . a detailed depiction of an eggbeater filter is shown in fig1 , 16 a , 16 b , and 16 c . with reference to fig1 , the eggbeater filter includes pressure wires 212 , primary wire cage 213 , mesh 52 , and optionally a foam seal 214 which facilitates substantial engagement of the interior lumen of a vessel wall and conforms to topographic irregularities therein . the eggbeater filter is housed within catheter sheath 32 and is deployed when the filter is advanced distally beyond the tip of sheath 32 . this design will accommodate a catheter of size 8f ( 0 . 062 inches , 2 . 7 mm ), and for such design , the primary wire cage 213 would be 0 . 010 inches and pressure wires 212 would be 0 . 008 inches . these parameters can be varied as known in the art , and therefore should not be viewed as limiting . fig1 a and 16b depict the initial closing sequence at a cross - section through foam seal 214 . fig1 c depicts the final closing sequence . fig1 and 17a depict an alternative filter guidewire which makes use of a filter scroll 215 disposed at the distal end of guidewire 40 . guidewire 40 is torsionally operated as depicted at 216 in order to close the filter , while reverse operation ( 217 ) opens the filter . the filter scroll may be biased to automatically spring open through action of a helical or other spring , or heat setting . alternatively , manual , torsional operation opens the filter scroll . in this design , guidewire 40 acts as a mandrel to operate the scroll 215 . an alternative embodiment of a stent deployment blood filtration device is depicted in fig1 , 18 a , and 18 b . with reference to fig1 , catheter 225 includes housing 220 at its proximal end 221 , and at its distal end catheter 225 carries stent 223 and expandable filter 224 . in one embodiment , expandable filter 224 is a self - expanding filter device optionally disposed about an expansion frame . in another embodiment , filter 224 is manually operable by controls at proximal region 221 for deployment . similarly , stent 223 can be either a self - expanding stent as discussed above , or a stent which is deployed using a balloon or other radially expanding member . restraining sheath 222 encloses one or both of filter 224 and stent 223 . in use , distal region 226 of catheter 225 is disposed within a region of interest , and sheath 222 is drawn proximally to first exposed filter 224 and then exposed stent 223 . as such , filter 224 deploys before stent 223 is radially expanded , and therefore filter 224 is operably in place to capture any debris dislodged during stent deployment as depicted in fig1 a . fig1 b shows an alternative embodiment which employs eggbeater filter 224 in the distal region . an alternative design for the construction of an eggbeater filter is shown in fig1 . this device includes inner sheath 231 , outer sheath 230 , and a plurality of struts 232 which are connected to outer sheath 230 at a proximal end of each strut , and to inner sheath 231 at a distal end of each strut . filter expansion is accomplished by moving inner sheath 231 proximal relative to outer sheath 230 , which action causes each strut to buckle outwardly . it will be understood that the struts in an eggbeater filter may be packed densely to accomplish blood filtration without a mesh , or may include a mesh draped over a proximal portion 233 or a distal portion 234 , or both . in another embodiment , a filter guidewire is equipped with a distal imaging device as shown in fig2 . guidewire 40 includes eggbeater filter 224 and restraining sheath 222 for deployment of filter 224 . the distal end of guidewire 40 is equipped with imaging device 235 which can be any of an ultrasound transducer or a doppler flow velocity meter , both capable of measuring blood velocity at or near the end of the guidewire . such a device provides valuable information for assessment of relative blood flow before and after stent deployment . thus , this device will permit the physician to determine whether the stent has accomplished its purpose or been adequately expanded by measuring and comparing blood flow before and after stent deployment . in use , the distal end of the guidewire is introduced into the patient &# 39 ; s vessel with the sheath covering the expandable filter . the distal end of the guidewire is positioned so that the filter is downstream of a region of interest and the sheath and guidewire cross the region of interest . the sheath is slid toward the proximal end of the guidewire and removed from the vessel . the expandable filter is uncovered and deployed within the vessel downstream of the region of interest . a percutaneous medical instrument is advanced over the guidewire to the region of interest and a procedure is performed on a lesion in the region of interest . the percutaneous medical instrument can be any surgical tool such as devices for stent delivery , balloon angioplasty catheters , atherectomy catheters , a rotoblader , an ultrasound imaging catheter , a rapid exchange catheter , an over - the - wire catheter , a laser ablation catheter , an ultrasound ablation catheter , and the like . embolic material generated during use of any of these devices on the lesion is captured before the expandable filter is removed from the patient &# 39 ; s vessel . the percutaneous instrument is then withdrawn from the vessel over the guidewire . a sheath is introduced into the vessel over the guidewire and advanced until the sheath covers the expandable filter . the guidewire and sheath are then removed from the vessel . human aortic anatomy is depicted in fig2 . during cardiac surgery , bypass cannula 243 is inserted in the ascending aorta and either balloon occlusion or an aortic cross - clamp is installed upstream of the entry point for cannula 243 . the steps in a cardiac procedure are described in barbut et al ., u . s . application ser . no . 08 / 842 , 727 , filed apr . 16 , 1997 , and the level of debris dislodgment is described in barbut et al ., “ cerebral emboli detected during bypass surgery are associated with clamp removal ,” stroke , 25 ( 12 ): 2398 - 2402 ( 1994 ), which is incorporated herein by reference in its entirety . fig2 demonstrates that the decoupling of the filter from the bypass cannula presents several avenues for filter deployment . as discussed in maahs , u . s . pat . no . 5 , 846 , 260 , incorporated herein by reference , a modular filter may be deployed through cannula 243 either upstream 244 or downstream 245 . in accordance with the present disclosure , a filter may be deployed upstream of the innominate artery within the aorta by using a filter guidewire which is inserted at 240 through a femoral artery approach . alternatively , filter guidewire may be inserted through route 241 by entry into the left subclavian artery or by route 242 by entry through the right subclavian artery , both of which are accessible through the arms . the filter guidewire disclosed herein permits these and any other routes for accessing the ascending aorta and aortic arch for blood filtration . in another embodiment , a generalized filter guidewire is depicted in fig2 . fig2 shows guidewire 40 having sleeve 250 disposed thereabout . sleeve 250 includes longitudinally slitted region 251 which is designed to radially expand when compressed longitudinally . thus , when the distal end of sleeve 250 is pulled proximally , the slitted region 251 buckles radially outwardly as shown in fig2 a to provide a form of eggbeater filter . the expanded cage thus formed may optionally include mesh 52 draped over a distal portion , a proximal portion , or both . in use , a stent catheter , such as those previously described , is used in a retrograde application , preferably to prevent the detachment of mobile aortic plaque deposits within the ascending aorta , the aortic arch , or the descending aorta . preferably , the stent catheter is provided with a filter assembly , such as that just described , attached to the catheter proximal of the stent . alternatively , a stent catheter without any filter device , may also be used . the stent catheter is percutaneously introduced into the patient and directed to the desired region . preferably , the catheter is inserted into a femoral artery and directed into the aorta , or is introduced into a carotid artery and directed down into the aorta . the stent is centered across the region which includes one or more mobile aortic deposits . if a filter assembly is provided on the catheter , it is expanded to its enlarged condition before the stent is deployed in order to ensure that any material inadvertently dislodged is captured by the filter . alternatively , a sheath having a guidewire and filter assembly similar to those previously described may be separately percutaneously introduced downstream of the region being treated , and opened to its enlarged condition . the stent balloon is inflated , expanding the stent to engage the deposits . the stent forces the deposits against the wall of the aorta , trapping them . when the balloon is deflated , the stent substantially maintains its inflated cross - section , substantially permanently containing the deposits and forming a portion of the lumen of the vessel . alternatively , a self - expanding stent may be delivered , using a sheath over the stent catheter as previously described . once the stent has been deployed , the filter assembly is closed , and the stent catheter is withdrawn using conventional methods . unlike the earlier embodiments described , this method of entrapping aortic plaque is for a purpose other than to increase luminal diameter . that is , mobile aortic deposits are being substantially permanently contained beneath the stent to protect a patient from the risk of embolization caused by later detachment of plaque . of particular concern are the ascending aorta and the aortic arch . loose embolic material in these vessels presents a serious risk of entering the carotid arteries and traveling to the brain , causing serious health problems or possibly even death . permanently deploying a stent into such regions substantially reduces the likelihood of embolic material subsequently coming loose within a patient , and allows treatment without expensive intrusive surgery to remove the plaque . while the invention is susceptible to various modifications , and alternative forms , specific examples thereof have been shown in the drawings and are herein described in detail . it should be understood , however , that the invention is not to be limited to the particular forms or methods disclosed , but to the contrary , the invention is to cover all modifications , equivalents and alternatives falling within the spirit and scope of the appended claims .
the invention provides a nested tubing cannula which comprises outer and inner elongate tubular members , both having a proximal end , a distal end , and a lumen therebetween . the inner tubular member is sealed at its distal end and is nested substantially coaxially within the lumen of the outer tubular member , so that the gap between the inner and the outer tubular member defines a second lumen whereas the first lumen is the lumen of the inner tubular member . a tubular sleeve is disposed coaxially between the inner and outer tubular members . a balloon is mounted on a distal region of the outer tubular member and is in communication with the first lumen . the cannula further comprises a port proximal or distal the balloon occluder and is in communication with the second lumen . methods for making the devices herein are disclosed .