Abstract:
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.

Description:
This is a continuation of application Ser. No. 10/400,003, filed Mar. 26, 2003, now U.S. Pat. No. 6,964,673 which is a continuation of application Ser. No. 09/679,911, filed Oct. 5, 2000, now U.S. Pat. No. 6,676,682, which is a continuation of application Ser. No. 09/421,138, filed Oct. 19, 1999, now U.S. Pat. No. 6,165,200, which is a continuation of application Ser. No. 09/287,217, filed Apr. 5, 1999, now U.S. Pat. No. 6,027,520, which is a continuation of application Ser. No. 09/022,510, filed Feb. 12, 1998, now U.S. Pat. No. 5,910,154, which is a continuation of application Ser. No. 08/852,867, filed May 8, 1997, now U.S. Pat. No. 5,911,734. Each of the above applications is hereby expressly and fully incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to treating plaque deposits and occlusions within major blood vessels, more particularly to an apparatus and method for preventing detachment of mobile aortic plaque within the ascending aorta, the aortic arch, or the carotid arteries, and to an apparatus and method for providing a stent and a filter in a percutaneous catheter for treating occlusions within the carotid arteries. 
     BACKGROUND OF THE INVENTION 
     Several procedures are now used to open stenosed or occluded blood vessels in a patient caused by the deposit of plaque or other material on the walls of the blood vessels. Angioplasty, for example, is a widely known procedure wherein an inflatable balloon is introduced into the occluded region. The balloon is inflated, dilating the occlusion, and thereby increasing intraluminal diameter. Plaque material may be inadvertently dislodged during angioplasty, and this material is then free to travel downstream, possibly lodging within another portion of the blood vessel or possibly reaching a vital organ, causing damage to the patient. 
     In another procedure, stenosis within arteries and other blood vessels is treated by permanently or temporarily introducing a stent into the stenosed region to open the lumen of the vessel. The stent typically comprises a substantially cylindrical tube or mesh sleeve made from such materials as stainless steel or nitinol. The design of the material permits the diameter of the stent to be radially expanded, while still providing sufficient rigidity such that the stent maintains its shape once it has been enlarged to a desired size. 
     Generally, a stent having a length longer than the target region is selected and is disposed on a catheter prior to use. The catheter typically has a flexible balloon, near its distal end, designed to inflate to a desired size when subjected to internal pressure. The stent is mounted to the catheter and compressed over the balloon, typically by hand, to assure that the stent does not move as it passes through the blood vessel to the desired location within the patient. Alternatively, self-expanding stents may also be used. 
     The stent is typically introduced into the desired blood vessel using known percutaneous methods. The catheter, having the stent securely crimped thereon, is directed to the region of the blood vessel being treated. The catheter is positioned such that the stent is centered across the stenosed region. The balloon is inflated, typically by introducing gas or fluid such as saline solution, through a lumen in the catheter communicating with the balloon. Balloon inflation causes the stent to expand radially, thereby engaging the stenosed material. As the stent expands, the material is forced outward, dilating the lumen of the blood vessel. 
     Due to substantial rigidity of the stent material, the stent retains its expanded shape, providing an open passage for blood flow. The balloon is then deflated and the catheter withdrawn. 
     Because the stent is often constructed from a mesh material, the stent typically compresses longitudinally as it expands radially. Stenotic material trapped between the stent and the vessel wall may extend into the openings in the mesh and may be sheared off by this longitudinal compression to create embolic debris free. When this material travels downstream, it can cause serious complications. For example loose embolic material released within the ascending aorta, the aortic arch, or the carotid arteries may travel downstream to the brain, possibly causing stroke, which can lead to permanent injuries or even death of the patient. 
     Thus, there is a need for an apparatus and method for delivering a stent into an arterial occlusion which substantially reduces the risk of embolic material escaping to the vessel and causing a blockage at a downstream location. There is also an apparatus and method for substantially preventing detachment of plaque deposited on the walls of the ascending aorta, the aortic arch, the descending aorta, and the carotid arteries. In addition, there is a need for an apparatus and method to substantially contain loose embolic material within the aorta and the carotid arteries during an interventional procedure, preventing it from reaching the brain. 
     SUMMARY OF THE INVENTION 
     The present invention provides an apparatus and method for preventing embolic material from escaping a site of intervention within the aorta, the carotid arteries, and other arteries generally, thereafter causing damage to vital organs, such as the brain. More particularly, the present invention involves an apparatus and method for introducing a stent into a region of a major blood vessel within the human body having plaque deposits, such as the ascending aorta, the descending aorta, aortic arch, common carotid artery, external and internal carotid arteries, brachiocephalic trunk, middle cerebral artery, anterior cerebral artery, posterior cerebral artery, vertebral artery, basilar artery, subclavian artery, brachial artery, axillary artery, iliac artery, renal artery, femoral artery, popliteal artery, celiac artery, superior mesenteric artery, inferior mesenteric artery, anterior tibial artery, and posterior tibial artery, thereby opening occlusions and/or preventing embolic material from breaking free within the blood vessel. 
     In a first embodiment, the invention includes a guidewire having an expandable filter attached to it, and a stent catheter. The catheter has an inflatable balloon mounted on or near its distal end, and an inflation lumen extending through the catheter between a proximal region of the catheter and the balloon. A stent is provided on the outer surface of the catheter, substantially engaging the balloon. Generally, the stent comprises an expandable substantially rigid tube, sheet, wire or spring, but preferably a cylindrical mesh sleeve. See Palmaz, U.S. Pat. No. 4,733,665, incorporated herein by reference. 
     Alternatively, the stent may be a self-expanding sleeve, preferably from nitinol. In this case, the stent catheter does not require an inflatable balloon. Instead the stent is compressed over the catheter and a sheath or outer catheter is directed over the stent to hold it in the compressed condition until time of deployment. 
     The guidewire has a filter assembly attached at or near its distal end, which includes an expansion frame which is adapted to open from a contracted condition to an enlarged condition. Filter material, typically a fine mesh, is attached to the expansion frame to filter undesirable embolic material from blood. 
     The guidewire with the expansion frame in its contracted condition is provided through a sheath or cannula, or preferably is included directly in the stent catheter. The catheter typically has a second lumen extending from its proximal region to its distal end into which the guidewire is introduced. The filter assembly on the distal end of the guidewire is then available to be extended beyond the distal end of the catheter for use during stent delivery. 
     The device is typically used to introduce a stent into a stenosed or occluded region of a patient, preferably within the carotid arteries. The catheter is introduced percutaneously into a blood vessel and is directed through the blood vessel to the desired region. If the filter device is provided in a separate sheath, the sheath is percutaneously inserted into the blood vessel downstream of the region being treated, and is fixed in position. 
     The filter assembly is introduced into the blood vessel, and the expansion frame is opened to its enlarged condition, extending the filter mesh substantially across the blood vessel until the filter mesh substantially engages the walls of the vessel. 
     The catheter is inserted through the region being treated until the stent is centered across the plaque deposited on the walls of the blood vessel. Fluid, preferably saline solution, is introduced through the inflation lumen, inflating the balloon, and expanding the stent radially outwardly to engage the plaque. The stent pushes the plaque away from the region, dilating the vessel. The balloon is deflated, and the catheter is withdrawn from the region and out of the patient. The stent remains substantially permanently in place, opening the vessel and trapping the plaque beneath the stent. 
     When the stenosed region is opened, embolic material may break loose from the wall of the vessel, but will encounter the filter mesh and be captured therein, rather than traveling on to lodge itself elsewhere in the body. After the stent is delivered, the expansion frame is closed, containing any material captured in the filter mesh. The filter assembly is withdrawn back into the sheath or the catheter itself, which is then removed from the body. 
     If a self-expanding stent is used, the stent catheter with the compressed stent thereon is inserted into a sheath, which restrains the stent in a compressed condition. The catheter is introduced into the patient&#39;s blood vessel and directed to the target region. Once the stent is localized across the stenosed region and the filter assembly is in position, the sheath is drawn proximally in relation to the catheter. This exposes the stent, which expands to engage the wall of the blood vessel, opening the lumen. The filter assembly is then closed and the catheter withdrawn from the patient. 
     The filter assembly has a number of preferred forms. For example, the expansion frame may comprise a plurality of struts or arms attached to and extending distally from the distal end of the guidewire. The struts are connected to each other at each end and have an intermediate region which is biased to expand radially. Filter mesh is attached typically between the intermediate region and the distal ends of the struts, thereby defining a substantially hemispherical or conical shaped filter assembly. 
     To allow the filter assembly to be inserted into the lumen of the sheath, the intermediate region of the expansion frame is compressed. When the filter assembly is ready to be introduced into a blood vessel, the guidewire is pushed distally. The expansion frame exits the lumen, and the struts automatically open radially. This expands the filter mesh to substantially traverse the vessel. After the stent is delivered, the guidewire is pulled proximally to withdraw the filter assembly. The struts contact the wall of the filter lumen, forcing them to compress, closing the frame as the filter assembly is pulled into the sheath. 
     In another embodiment, the expansion frame includes a plurality of struts attached to the distal end of the sheath. The struts extend distally from the sheath and attach to the distal end of the guidewire which is exposed beyond the sheath. At an intermediate region, the struts are notched or otherwise biased to fold out radially. Filter mesh is attached to the struts between the intermediate region and the distal end of the guidewire. 
     The filter assembly is directed into position in the blood vessel, either exposed on the end of the sheath or preferably within a second sheath which is withdrawn partially to expose the filter assembly. With the sheath fixed, the guidewire is pulled proximally. This compresses the struts, causing them to bend or buckle at the intermediate region and move radially outwardly, expanding the filter mesh across the blood vessel. After use, the guidewire is pushed distally, pulling the struts back down and closing the filter mesh. 
     In an alternative to this embodiment, the struts attached to the distal end of the sheath and to the distal end of the guidewire are biased to expand radially at an intermediate region. The filter mesh is attached to the struts between the intermediate region and the distal end of the guidewire. Prior to introduction into a patient, the guidewire is rotated torsionally in relation to the sheath, twisting the struts axially around the guidewire and compressing the filter mesh. Once in position in the blood vessel, the guidewire is rotated in the opposite direction, unwinding the struts. The struts expand radially, opening the filter mesh. After use, the guidewire is rotated once again, twisting the struts and closing the filter mesh for removal. 
     In yet another embodiment, the filter assembly comprises a plurality of substantially cylindrical compressible sponge-like devices attached in series to the guidewire. The devices have an uncompressed diameter substantially the same as the open regions of the blood vessel. They are sufficiently porous to allow blood to pass freely through them but to entrap undesirable substantially larger particles, such as loose embolic material. 
     The devices are compressed into the lumen of the sheath prior to use. Once in position, they are introduced into the blood vessel by pushing the guidewire distally. The devices enter the vessel and expand to their uncompressed size, substantially engaging the walls of the blood vessel. After use, the guidewire is pulled proximally, forcing the devices against the distal end of the sheath and compressing them back into the lumen. 
     In a second embodiment, a stent catheter and filter assembly are also provided. Unlike the previous embodiments, the filter assembly is not primarily mechanically operated, but is instead, generally fluid operated. Typically, the stent catheter includes a second balloon on or near the distal end of the catheter. A second inflation lumen extends through the catheter from the proximal region of the catheter to the balloon. The balloon is part of the expansion frame or alternatively merely activates the expansion frame, opening the filter assembly to the enlarged condition for use and closing it after being used. 
     In one form, the balloon has an annular shape. Filter mesh is attached around the perimeter of the balloon, creating a conical or hemispherical-shaped filter assembly. A flexible lumen extends between the balloon and the inflation lumen within the catheter. Optionally, retaining wires are connected symmetrically between the balloon and the catheter, thereby holding the balloon substantially in a desired relationship to the catheter. 
     When deflated, the balloon substantially engages the periphery of the catheter, holding the filter mesh closed and allowing the catheter to be directed to the desired location. Once the catheter is in position, the balloon is inflated. The balloon expands radially until it engages the walls of the blood vessel, the filter mesh thereby substantially traversing the vessel. After use, the balloon is deflated until it once again engages the perimeter of the catheter, thereby trapping any embolic material between the filter mesh and the outer wall of the catheter. 
     Alternatively, the balloon of this embodiment may be provided on the catheter proximal of the stent for retrograde use. In this case, the filter mesh is extended between the balloon and the outer surface of the catheter, instead of having a closed end. 
     In a third embodiment of the present invention, a method is provided in which a stent catheter is used to prevent the detachment of mobile aortic deposits within the ascending aorta, the aortic arch or the carotid arteries, either with or without an expandable filter assembly. A stent catheter, as previously described, is provided having an inflatable balloon and a stent thereon, or alternatively a self-expanding stent and a retaining sheath. The catheter is percutaneously introduced into a blood vessel and is directed to a region having mobile aortic plaque deposits, preferably a portion of the ascending aorta or the aortic arch. 
     The stent is positioned across the desired region, and the balloon is inflated. This expands the stent to engage the plaque deposits and the walls of the blood vessel, thereby trapping the plaque deposits. The balloon is deflated, and the catheter is removed from the blood vessel. Alternatively if a self-expanding stent is used, the sheath is partially withdrawn proximally, and the stent is exposed, allowing it to expand. The stent substantially retains its expanded configuration, thereby containing the plaque beneath the stent and preventing the plaque from subsequently detaching from the region and traveling downstream. 
     Optionally, a filter device similar to those already described may be introduced at a location downstream of the treated region. The filter device may be provided in a sheath which is inserted percutaneously into the blood vessel. Preferably, however, a filter device is attached to the stent catheter at a location proximal to the stent. Instead of attaching the filter assembly to a guidewire, it is connected directly to the outer surface of the catheter proximal to the stent. A sheath or cannula is typically provided over the catheter to cover the filter assembly. 
     Once the catheter is in position within the vessel, the sheath is withdrawn proximally, the filter assembly is exposed and is expanded to its enlarged condition. In a preferred form, the expansion frame includes biased struts similar to the those described above, such that when the filter assembly is exposed, the struts automatically expand radially, and filter mesh attached to the struts is opened. After the stent is deployed, the sheath is moved proximally, covering the expansion frame and compressing the struts back into the contracted condition. The catheter and sheath are then withdrawn from the patient. 
     Thus, an object of the present invention is to provide an apparatus and method for substantially preventing mobile aortic plaque deposited within the ascending aorta, the aortic arch, or the carotid arteries from detaching and traveling to undesired regions of the body. 
     Another object is to provide an apparatus and method for treating stenosed or occluded regions within the carotid arteries. 
     An additional object is to provide an apparatus and method for introducing a stent to treat a stenosed or occluded region of the carotid arteries which substantially captures any embolic material released during the procedure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the invention, and to show how it may be carried into effect, reference will be made, by way of example, to the accompanying drawings, in which: 
         FIG. 1  is a longitudinal view of an embodiment being inserted into a blood vessel, namely a stent catheter in a stenosed region and a filter device downstream of the region. 
         FIG. 2  is a longitudinal view of another embodiment, showing the filter device included in the stent catheter. 
         FIG. 3  is a longitudinal view of an embodiment of the filter assembly in its enlarged condition within a blood vessel. 
         FIGS. 4A ,  4 B and  4 C show a longitudinal view of an embodiment of the filter assembly in a contracted condition, a partially expanded condition, and an enlarged condition respectively within a blood vessel. 
         FIGS. 5A ,  5 B and  5 C show a longitudinal view of another embodiment of the filter device in a contracted condition, a partially opened condition, and an enlarged condition across a blood vessel respectively. 
         FIGS. 6A and 6B  are longitudinal views, showing the orientation of the filter mesh in an antegrade approach to a stenosed region and in a retrograde approach respectively. 
         FIG. 7  is a longitudinal view of another embodiment of the filter assembly. 
         FIGS. 8A and 8B  are longitudinal views of another embodiment of the filter assembly, showing the filter mesh without gripping hairs and with gripping hairs respectively. 
         FIG. 9  is a longitudinal view of another embodiment of the filter assembly including sponge-like devices. 
         FIG. 10  is a longitudinal view of another embodiment, namely a filter assembly attached to the outer surface of a stent catheter. 
         FIGS. 11A and 11B  show a filter assembly attached to the outer surface of a stent catheter, with a sheath retaining the filter assembly in the contracted condition, and with the filter assembly in the enlarged condition respectively. 
         FIGS. 12A and 12B  are longitudinal views of another embodiment including an inflatable filter assembly, shown in a contracted condition and an enlarged condition respectively. 
         FIG. 13  is a longitudinal view of an inflatable filter assembly attached to the catheter proximal of the stent shown in an enlarged condition. 
         FIG. 14  depicts a longitudinal view of a stent deployment device having a distal filter disposed within a carotid artery. 
         FIGS. 15 ,  15 A,  15 B,  15 C and  15 D show detailed longitudinal and cross-sectional views of a guidewire filter in accordance with the present invention. 
         FIGS. 16 ,  16 A,  16 B,  16 C and  16 D show longitudinal and cross-sectional views of an eggbeater filter in accordance with the present invention. 
         FIGS. 17 and 17A  show longitudinal views of a filter scroll in accordance with the present invention. 
         FIGS. 18 ,  18 A, and  18 B show longitudinal views of a filter catheter in accordance with the present invention. 
         FIG. 19  shows an alternate construction for an eggbeater filter as disclosed herein. 
         FIG. 20  shows a longitudinal view of an imaging guidewire having an eggbeater filter and restraining sheath. 
         FIG. 21  shows human aortic anatomy and depicts several routes for deployment of an aortic filter upstream of the carotid arteries. 
         FIG. 22  depicts a longitudinal view of a generalized filter guidewire. 
         FIGS. 23 and 23A  depict longitudinal views of a compressible, expansible sheath disposed over a guidewire in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Turning to  FIG. 1 , 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  FIG. 2 ). 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  FIG. 3 , 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  FIG. 3 ) 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 .mu.m, a thread diameter of 30-100 .mu.m, and a pore size of 60-100 .mu.m. 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  FIGS. 1 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  FIGS. 1 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  FIG. 14 , 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  FIG. 3 ), 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  FIG. 2 , 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  FIGS. 4A ,  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  FIG. 4A , 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  FIG. 4A , 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  FIG. 4B . 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  FIG. 4C . 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  FIGS. 5A ,  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  FIG. 5A , 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  FIG. 5B , 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  FIG. 5C . 
     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  FIG. 5A . 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  FIGS. 6A 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  FIG. 6A . 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  FIG. 6B , 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  FIGS. 6A 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. 
       FIG. 8A  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  FIG. 8B , 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. 
       FIG. 7  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,  FIG. 9  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  FIG. 10 , 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  FIG. 10 , 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  FIGS. 11A 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).  FIG. 11A  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  FIG. 11B . 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  FIGS. 12A 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  FIG. 12A , 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  FIG. 12B , 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  FIGS. 13A 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  FIG. 13A , 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  FIG. 13B , whereupon it substantially engages the walls  72  of the blood vessel  70 . 
     A detailed longitudinal view of a filter guidewire is shown in  FIG. 15 . 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  FIG. 15A . 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  5 F throughout segment  208 ,  4 F throughout segment  209 , and  3 F 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  FIGS. 16 ,  16 A.  16 B, and  16 C. With reference to  FIG. 16 , 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  8 F (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 5 viewed as limiting. 
       FIGS. 16A and 16B  depict the initial closing sequence at a cross-section through foam seal  214 .  FIG. 16C  depicts the final closing sequence. 
       FIGS. 17 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  FIGS. 18 ,  18 A, and  18 B. With reference to  FIG. 18 , 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  FIG. 18A .  FIG. 18B  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  FIG. 19 . 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  FIG. 20 . 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  FIG. 21 . 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.  FIG. 21  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  FIG. 22 .  FIG. 23  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  FIG. 23A  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.