PATENT ABSTRACT
A sheath comprises an elastomeric tube having a self-expanding scaffold coupled to a wall. The scaffold can expand to a diameter larger than the tube diameter to provide an enlarged distal opening. An aspiration catheter has a balloon and an aspiration port so that occlusive material can be removed from a blood vessel by drawing the balloon through the vessel while simultaneously aspirating through the port.

PATENT DESCRIPTION
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of application Ser. No. 13/035,755, filed on Feb. 25, 2011, which claims priority to provisional application Ser. No. 61/309,389, filed on Mar. 1, 2010 and provisional application Ser. No. 61/385,637, filed on Sep. 23, 2010. The entire contents of the priority applications are hereby incorporated by reference and made a part of this disclosure. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to medical devices and methods. More particularly, the present invention relates to apparatus for accessing vascular lumens and methods for clearing vascular lumens of occlusive materials. 
         [0004]    Removing occlusive materials from the vasculature and other body lumens is the objective of many medical procedures. Obstructive materials in the vasculature include plaque, thrombus, embolus, clots, and fatty deposits. To remove such occlusive materials, catheters may be inserted into the occluded artery or vein for opening or removing the occlusive material. Of particular interest to the present invention, procedures commonly referred to as thrombectomy or embolectomy use a balloon-tipped catheter which is inserted into a blood vessel, either percutaneously or via a surgical cut down, where the balloon is advanced to a position distal to the obstructing material. After inflating the balloon, the catheter is drawn proximally to dislodge the material and remove it from the blood vessel. In some instances, a second sheath or catheter is introduced coaxially over the balloon-tipped catheter in order to apply suction and help remove the occlusive material before it is drawn out of the blood vessel. 
         [0005]    When performing such thrombectomy or embolectomy procedures, the balloon-tipped catheters and other auxiliary tools may be introduced through a sheath which is positioned through a percutaneous tissue tract to allow access to the blood vessel. In addition, other auxiliary sheaths and tubular catheters may be employed and other aspects of the thrombectomy, embolectomy, or other vascular procedures. 
         [0006]    While very effective, thrombectomy and embolectomy procedures sometimes have difficulty dislodging and removing certain occlusive materials from certain types of vessels. For example, the use of thrombectomy for removing plaque, clot and other occlusive buildups in arterio-venous grafts (AVG&#39;s) and arterio-venous fistulas (AVF&#39;s) can be particularly problematic. For example, a plug of occlusive materials frequently forms at the anastomosis site between the artery and vein, or artery and graft, and can be very difficult to remove. Moreover, the access sheaths and capture devices used in such procedures are not always optimal. 
         [0007]    For these reasons, it would be desirable to provide improved methods and apparatus for performing thrombectomy and embolectomy procedures. It would be particularly desirable if such catheters and devices could improve the capture of clot, plaque, and other occlusive materials from AVG&#39;s and AVF&#39;s. Improved sheaths and other auxiliary devices for performing those procedures and others would also be desirable. At least some of these objectives will be met by the inventions described below. 
         [0008]    2. Description of the Background Art 
         [0009]    Thrombectomy devices employing aspiration are described in U.S. Pat. No. 6,292,633; U.S. 2002/0169436; U.S. Pat. No. 7,141,045; U.S. Pat. No. 7,033,344; U.S. Pat. No. 6,544,276; U.S. Pat. No. 7,578,830; U.S. Pat. No. 6,695,858; U.S. Pat. No. 6,210,370; U.S. Pat. No. 5,102,415; and U.S. Pat. No. 5,092,839. Catheters and sheaths having self-expanding regions are described in U.S. 2010/0131000; U.S. 2007/0135832; U.S. Pat. No. 7,799,046; U.S. Pat. No. 7,410,491; U.S. Pat. No. 6,511,492; U.S. Pat. No. 6,159,230; and U.S. Pat. No. 5,971,938. 
       SUMMARY OF THE INVENTION 
       [0010]    One embodiment of the present radially collapsible and expandable sheath is configured for introducing an intravascular device into a patient&#39;s vasculature through a percutaneous access site. The sheath comprises an elongate, elastomeric, tubular casing including an inner layer and an outer layer defining an annular space therebetween. The casing has a distal end. The sheath further comprises an elongate wire. At least a portion of the wire occupies the annular space and forms a helix around the casing inner layer. The helix includes a plurality of coils. A distally directed force applied to the wire decreases a pitch between adjacent ones of the coils and radially expands the helix and the casing. A proximally directed force applied to the wire increases the pitch between adjacent ones of the coils and radially contracts the helix and the casing. 
         [0011]    One embodiment of the present radially collapsible and expandable intravascular device is configured for removing a thrombus from a patient&#39;s vasculature through a percutaneous access site. The device comprises an elongate tubular catheter having a distal end. The device further comprises an elongate, elastomeric, tubular casing surrounding at least a portion of the catheter. The casing is secured to the catheter at or near the catheter distal end. The device further comprises an elongate wire. At least a portion of the wire occupies a space between the catheter and the casing and forms a helix around the catheter. The helix includes a plurality of coils. A distally directed force applied to the wire decreases a pitch between adjacent ones of the coils and radially expands the helix and the casing. A proximally directed force applied to the wire increases the pitch between adjacent ones of the coils and radially contracts the helix and the casing. 
         [0012]    One embodiment comprises a system for removing a thrombus from a patient&#39;s vasculature through a percutaneous access site. The system includes the sheath described above in combination with the thrombus collection device described above. 
         [0013]    One embodiment of the present methods for emplacing a radially collapsible and expandable sheath into a patient&#39;s vasculature through a percutaneous access site comprises a sheath including an elongate, elastomeric, tubular casing including an inner layer and an outer layer defining an annular space therebetween. The sheath further comprises an elongate wire, at least a portion of the wire occupying the annular space and forming a helix around the casing inner layer, the helix including a plurality of coils. The method comprises puncturing the patient&#39;s skin and vasculature with a catheter delivery needle in order to dispose a catheter within the patient&#39;s vasculature with a proximal end of the catheter protruding from the percutaneous access site. The method further comprises withdrawing the delivery needle. The method further comprises introducing the sheath, in a collapsed state, into the vasculature through a hollow lumen of the catheter. The method further comprises applying a distally directed force to the wire to decrease a pitch between adjacent ones of the coils and radially expand the helix and the casing so that the casing contacts interior walls of the vasculature. In certain embodiments, the method may further comprise applying a proximally directed force to the wire to increase a pitch between adjacent ones of the coils and radially collapse the helix and the casing. 
         [0014]    One embodiment of the present methods for extracting a thrombus from a patient&#39;s vasculature through a percutaneous access site using a radially collapsible and expandable thrombus collection device comprises the device including an elongate tubular catheter having a distal end, an elongate, elastomeric, tubular casing surrounding at least a portion of the catheter. The device further comprises an elongate wire, at least a portion of the wire occupying a space between the catheter and the casing and forming a helix around the catheter, the helix including a plurality of coils. The method comprises emplacing a percutaneous introducer sheath into the patient&#39;s vasculature. The method further comprises introducing the thrombus collection device, in a collapsed state, by passing it through the sheath and into the patient&#39;s vasculature. The method further comprises advancing the device through the patient&#39;s vasculature toward a location of the thrombus by applying a distally directed force to a portion of the catheter that protrudes from the percutaneous access site. The method further comprises continuing to apply the distally directed force to push a distal end of the device through the thrombus. The method further comprises advancing the device through the thrombus until the casing has completely passed through the thrombus. The method further comprises expanding the wire and the casing by applying a distally directed force to the wire while holding the catheter stationary until at least a proximal end of the casing contacts an interior diameter of the vasculature. The method further comprises drawing the device back through the vasculature by applying a proximally directed force to the catheter while holding the wire stationary with respect to the catheter to maintain the casing in its expanded state. The method further comprises collecting the thrombus and trapping it within the space between the casing and the catheter as the device is drawn back. The method further comprises continuing to pull back on the catheter until the thrombus collection device reaches the distal end of the sheath. The method further comprises drawing the device through the sheath, together with the collected thrombus, until the device and the thrombus are completely extracted from the patient; and withdrawing the sheath from the percutaneous access site. 
         [0015]    Another embodiment of the present methods for extracting a thrombus from a patient&#39;s vasculature through a percutaneous access site using a radially collapsible and expandable sheath and a radially collapsible and expandable thrombus collection device comprises the sheath including an elongate, elastomeric, tubular casing including an inner layer and an outer layer defining an annular space therebetween. The sheath further comprises an elongate wire, at least a portion of the sheath wire occupying the annular space and forming a helix around the casing inner layer, the sheath helix including a plurality of coils. The thrombus collection device includes an elongate tubular catheter having a distal end, an elongate, elastomeric, tubular casing surrounding at least a portion of the catheter, and an elongate wire. At least a portion of the device wire occupies a space between the catheter and the device casing and forms a helix around the catheter, the device helix including a plurality of coils. The method comprises puncturing the patient&#39;s skin and vasculature with a catheter delivery needle in order to dispose a delivery catheter within the patient&#39;s vasculature with a proximal end of the delivery catheter protruding from the percutaneous access site. The method further comprises withdrawing the delivery needle. The method further comprises introducing the sheath, in a collapsed state, into the vasculature through a hollow lumen of the delivery catheter. The method further comprises applying a distally directed force to the sheath wire to decrease a pitch between adjacent ones of the sheath coils and radially expand the sheath helix and the sheath casing so that the sheath casing contacts interior walls of the vasculature. The method further comprises introducing the thrombus collection device, in a collapsed state, by passing it through the sheath and into the patient&#39;s vasculature. The method further comprises advancing the device through the patient&#39;s vasculature toward a location of the thrombus by applying a distally directed force to a portion of the device catheter that protrudes from the percutaneous access site. The method further comprises continuing to apply the distally directed force to push a distal end of the device through the thrombus. The method further comprises advancing the device through the thrombus until the device casing has completely passed through the thrombus. The method further comprises expanding the device wire and the device casing by applying a distally directed force to the device wire while holding the device catheter stationary until at least a proximal end of the device casing contacts an interior diameter of the vasculature. The method further comprises drawing the device back through the vasculature by applying a proximally directed force to the device catheter while holding the device wire stationary with respect to the device catheter to maintain the device casing in its expanded state. The method further comprises collecting the thrombus and trapping it within the space between the device casing and the device catheter as the device is drawn back. The method further comprises continuing to pull back on the device catheter until the thrombus collection device reaches the distal end of the sheath. The method further comprises drawing the device through the sheath, together with the collected thrombus, until the device and the thrombus are completely extracted from the patient. The method further comprises applying a proximally directed force to the sheath wire to increase a pitch between adjacent ones of the sheath coils and radially collapse the sheath helix and the sheath casing. The method further comprises withdrawing the sheath from the percutaneous access site. 
         [0016]    Another embodiment of the present introducer sheaths is configured for introducing an intravascular device into a patient&#39;s vasculature through a percutaneous access site. The sheath is elongate, tubular, and defines a sheath lumen. The sheath comprises a medial neck portion that flares outwardly to a wider bell portion at a distal end. The distal end of the bell portion is open. The neck portion and the bell portion comprise a compliant material. The bell portion of the sheath includes a wire that is encased within the compliant material. The wire supports the compliant material, maintaining the bell portion in its expanded shape when the sheath is unstressed. At a proximal end, the sheath includes a flush port that enables fluid to be injected and/or aspirated from the sheath lumen. Once deployed within the vasculature, a hemostasis valve at the proximal end of the sheath resists outflow of bodily fluids through the sheath. 
         [0017]    One of the present embodiments comprises a deployment apparatus for an introducer sheath. The deployment apparatus includes a tubular dilator that is a rigid or semi-rigid component configured to guide the deployment apparatus through a skin puncture and through the vasculature. The dilator includes a proximal handle, a conically shaped distal tip, and defines a lumen that extends between the proximal and distal ends. The lumen is configured to receive a guide wire to facilitate introduction of the dilator into a patient. The introducer sheath is disposed coaxially about the outside of the dilator. An outer sheath is disposed coaxially about the outside of the introducer sheath. The outer sheath radially compresses the bell portion, which facilitates introduction of the sheath into the patient. The outer sheath is a tearaway sheath that can be torn by hand. 
         [0018]    Another embodiment of the present methods comprises a method for deploying an introducer sheath in a patient&#39;s vasculature at a percutaneous access site using a deployment apparatus. The access site is prepared by puncturing the skin, any underlying tissue, and the vasculature with a needle. The operator then introduces a guide wire through the lumen of the needle, and withdraws the needle. The method further comprises the operator introducing the deployment apparatus into the vasculature through the puncture site using the guide wire. The operator advances the apparatus through the puncture site and the vasculature until a bell portion of the sheath is located entirely within the vasculature and a neck portion traverses the puncture site. The operator next removes a tearaway outer sheath from the deployment apparatus and pulls the outer sheath through the puncture site. The operator then removes a dilator of the apparatus. 
         [0019]    Another embodiment of the present intravascular devices is configured for removing a thrombus from a patient&#39;s vasculature through a percutaneous access site. The device comprises an aspiration catheter including an elongate body having a balloon at its distal end. The catheter body comprises a flexible material having sufficient rigidity to facilitate guiding the catheter through the vasculature from the proximal end. The body defines two radially spaced lumens that are not in fluid communication with one another. The first lumen is an aspiration lumen that extends from an aspiration connector at the proximal end of the catheter to a plurality of aspiration openings toward the distal end of the catheter. The second lumen is an inflation lumen that extends from an inflation connector at the proximal end of the catheter to the balloon toward the distal end of the catheter. The aspiration lumen has a larger diameter than the inflation lumen, and is configured for passage of thrombus. 
         [0020]    Another embodiment of the present methods comprises a method for percutaneously removing a thrombus from a patient&#39;s vasculature. The method comprises introducing an aspiration catheter into a patient&#39;s vasculature through an introducer sheath. The aspiration catheter is then advanced distally through the sheath, the vasculature, and the thrombus until a balloon of the catheter is disposed on the far side of the thrombus. A guide wire may be used to advance the catheter. The method further comprises connecting a syringe filled with inflation liquid to an inflation connector of the catheter. The operator depresses the syringe plunger to force the inflation liquid into the balloon through an inflation lumen. The operator inflates the balloon until it presses against the interior walls of the vasculature on the far side of the thrombus. The operator moves a stopcock to a position to prevent liquid flow through the inflation connector and disconnects the syringe from the stopcock. The operator removes the thrombus from the vasculature by using a combination of suction through the aspiration openings, and proximal movement of the inflated balloon across the thrombus. To do so, the operator connects a Luer stopcock to an aspiration connector and an empty syringe to the stopcock. To generate suction, the operator draws back on the syringe plunger with the stopcock in the closed position and then locks the plunger. The operator then draws the catheter out of the vasculature while simultaneously moving the stopcock to the open position, thereby exposing the vacuum in the syringe barrel to the aspiration lumen, generating suction that pulls pieces of the thrombus into the aspiration lumen through the aspiration openings. The operator continues to pull back on the aspiration catheter until all or substantially all of the thrombus has been pulled into the sheath. The operator then continues to pull back on the aspiration catheter to force the thrombus out of the vasculature through the sheath. 
         [0021]    Thus, in a first aspect of the present invention, a sheath comprises a tubular body having a proximal, a distal end, and an axial passage therethrough. The tubular body is formed at least partially from an elastomeric material so that it can be collapsed, be expanded to a fully open configuration where it has an open diameter, and be further expanded beyond the open diameter by applying a radially outward force to an internal surface of the tubular body. The sheath further comprises a self-expanding scaffold coupled to at least a portion of the tubular body. The self-expanding scaffold also has a collapsed configuration, an expanded diameter when free from external constraint, and a super-expanded diameter or width when subject to a radially outward inner force. The expanded diameter of the self-expanding scaffold will be at least as large as the open diameter of the tubular body, optionally being larger. In this way, the scaffold will be able to open the tubular body. For example, the scaffold could be present only at the distal end of the tubular body so that said distal end will remain open while the remainder of the tubular body could remain in a collapsed configuration. 
         [0022]    Optionally, the sheath will further comprise a shaft extending from the proximal end of the tubular body. In many instances, the shaft will comprise an extension of the scaffold. For example, the scaffold may be in the form of a helical coil where the shaft is an integral extension of the coil. That is, the shaft and coil may be formed from a single wire, filament, bundle or other structure where only a distal portion of the structure is formed into the coil to act as the scaffold while the remaining proximal portion of the structure can act as the shaft. 
         [0023]    In most instances, the scaffold will have a cylindrical geometry when expanded, but in other instances the scaffold may have a tapered geometry when expanded. For example, the scaffold may be configured so that it tapers to a more narrow configuration in the distal direction. In such instances, the scaffold can form the tubular body into a capturing element for withdrawing clot. 
         [0024]    In still other embodiments, the sheath may further comprise a catheter body where the sheath and scaffold are disposed over a distal end of the catheter body. Optionally, a shaft of the sheath may then extend through a lumen of the catheter body to allow selective opening and closing of the sheath over the catheter by translating the shaft forwardly or distally. 
         [0025]    In specific embodiments, the self-expanding scaffold may be embedded in a wall of the sheath. Alternatively, the self-expanding scaffold may be secured to an inner or outer surface of a wall of the sheath. In a still further alternative embodiment, the self-expanding scaffold may be disposed in an annular space formed or created in a wall of the sheath so that the scaffold can foreshorten as it expands without constricting or deforming the wall (other than any radial expansion that may occur). 
         [0026]    The sheath will have dimensions typical for medical sheaths. Typically, the tubular body will have an expanded diameter in the range from 3 Fr. to 24 Fr., the self-expanding scaffold will have a diameter in the range from 3 Fr. to 38 Fr. and the sheath will have a length in the range from 10 cm to 200 cm. 
         [0027]    In a further aspect of the present invention, methods for aspirating occlusive material from a patient&#39;s vasculature comprise providing a catheter including a shaft, an expandable member at a distal end of the shaft, and an aspiration port on the shaft proximal to the expandable member. The aspiration port is connected to an aspiration lumen extending to a proximal end of the shaft. The catheter is introduced to a blood vessel (including implanted grafts and created fistulas) so that the expandable member lies on a distal side of the occlusive material. The expandable member is then expanded, and the catheter is drawn proximal while aspirating through the lumen end port to remove the occlusive material from the vessel. The methods of the present invention may be used in any blood vessel, but will find particular use with peripheral blood vessels, arterio-venous grafts, arterio-venous fistulas, and the like. 
         [0028]    In the preferred embodiments, the catheter will consist of only a single balloon at a distal end of the catheter shaft and further preferably will consist of only a single aspiration port located proximally of the balloon, typically at a distance from 5 mm to 3 cm. Usually, the drawing and aspiration steps are performed simultaneously and are able together to remove substantially all the occlusive material. In other instances, however, some portion of the occlusive material will be drawn proximally without being aspirated through the port and lumen and will be removed from the vessel, graft, or fistula through an access sheath and/or a capturing catheter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]      FIG. 1  is a cross-sectional end view of one embodiment of the present radially collapsible and expandable introducer sheath, taken along the line  1 - 1  in  FIG. 3 , and illustrating the sheath in a collapsed state; 
           [0030]      FIG. 2  is a cross-sectional side view of the sheath of  FIG. 1 , taken along the line  2 - 2  in  FIG. 3 ; 
           [0031]      FIG. 3  is an end/side perspective view of the sheath of  FIG. 1 ; 
           [0032]      FIG. 4  is a cross-sectional side view of the sheath of  FIG. 1 , taken along the line  4 - 4  in  FIG. 5 , and illustrating the sheath in an expanded state; 
           [0033]      FIG. 5  is an end/side perspective view of the sheath of  FIG. 4 ; 
           [0034]      FIG. 6  is a partial cross-sectional side view of the sheath of  FIGS. 1-5  disposed in a patient&#39;s vasculature at a percutaneous access site; 
           [0035]      FIG. 7  is a side elevation view of one embodiment of the present collapsible and expandable thrombus collection device, illustrating the device in a collapsed state; 
           [0036]      FIG. 8  is an end/side perspective view of the device of  FIG. 7 ; 
           [0037]      FIG. 9  is a side elevation view of the device of  FIG. 7 , illustrating the device in an expanded state; 
           [0038]      FIG. 10  is an end/side perspective view of the device of  FIG. 9 ; 
           [0039]      FIG. 11  is a partial cross-sectional side view of the sheath of  FIGS. 1-6  in combination with the device of  FIGS. 7-10 ; 
           [0040]      FIG. 12  is a partial cross-sectional side view of the device of  FIGS. 7-10  disposed in a patient&#39;s vasculature during a thrombectomy procedure; 
           [0041]      FIG. 13  is a partial cross-sectional side view of the device of  FIGS. 7-10  disposed in a patient&#39;s vasculature during a thrombectomy procedure; 
           [0042]      FIG. 14  is a partial cross-sectional side view of the device of  FIGS. 7-10  disposed in a patient&#39;s vasculature during a thrombectomy procedure; 
           [0043]      FIG. 15  is a partial cross-sectional side view of the device of  FIGS. 7-10  disposed in a patient&#39;s vasculature during a thrombectomy procedure; 
           [0044]      FIG. 16  is a cross-sectional side view of another embodiment of the present radially collapsible and expandable introducer sheath; 
           [0045]      FIG. 17  is a cross-sectional side view of another embodiment of the present radially collapsible and expandable thrombus collection device; 
           [0046]      FIG. 18  is a side elevation view of another embodiment of the present introducer sheath; 
           [0047]      FIG. 19  is a side elevation view of one embodiment of a deployment apparatus for the introducer sheath of  FIG. 18 ; 
           [0048]      FIG. 20  is a side cross-sectional view of the deployment apparatus of  FIG. 19 ; 
           [0049]      FIGS. 21-24  are side elevation views of one embodiment of steps for deploying the introducer sheath of  FIG. 18  in a patient&#39;s vasculature at a percutaneous access site; 
           [0050]      FIG. 25  is a side elevation view of one embodiment of the present thrombus collection device having aspiration ports; 
           [0051]      FIG. 26  is a cross-sectional end view of the thrombus collection device of  FIG. 25 , taken along the line  26 - 26  in  FIG. 25 ; 
           [0052]      FIGS. 27 and 28  are side elevation views of the proximal portions and distal portions, respectively, of the introducer sheath of  FIG. 18  and the thrombus collection device of  FIG. 25  during one step of a percutaneous thrombus collection procedure; 
           [0053]      FIGS. 29 and 30  are side elevation views of the proximal portions and distal portions, respectively, of the introducer sheath of  FIG. 18  and the thrombus collection device of  FIG. 25  during another step of a percutaneous thrombus collection procedure; 
           [0054]      FIGS. 31 and 32  are side elevation views of the proximal portions and distal portions, respectively, of the introducer sheath of  FIG. 18  and the thrombus collection device of  FIG. 25  during another step of a percutaneous thrombus collection procedure; 
           [0055]      FIGS. 33 and 34  are side elevation views of the proximal portions and distal portions, respectively, of the introducer sheath of  FIG. 18  and the thrombus collection device of  FIG. 25  during another step of a percutaneous thrombus collection procedure; 
           [0056]      FIG. 35  is a side elevation view of the introducer sheath of  FIG. 18  after withdrawal from a patient&#39;s vasculature during another step of a percutaneous thrombus collection procedure; 
           [0057]      FIG. 36  is a side elevation view of another embodiment of the present thrombus collection device having aspiration ports; 
           [0058]      FIG. 37  is a side elevation view of the introducer sheath of  FIG. 18  and a Fogarty balloon catheter disposed in a patient&#39;s vasculature during a percutaneous thrombus collection procedure; 
           [0059]      FIG. 38  is a side elevation view of the introducer sheath of  FIG. 18  and the thrombus collection device of  FIGS. 7-10  disposed in a patient&#39;s vasculature during a percutaneous thrombus collection procedure; and 
           [0060]      FIG. 39  is a side elevation view of a standard balloon catheter introducer sheath and the aspiration catheter of  FIG. 25  disposed in a patient&#39;s vasculature during a percutaneous thrombus collection procedure. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0061]    The following detailed description describes the present embodiments with reference to the drawings. In the drawings, reference numbers label elements of the present embodiments. These reference numbers are reproduced below in connection with the discussion of the corresponding drawing features. The various embodiments of the present introducer sheaths, thrombus collection devices and associated methods now will be discussed in detail. These embodiments include the introducer sheaths and thrombus collection devices shown in the accompanying drawings, which are for illustrative purposes only. 
         [0062]    Some embodiments of the present introducer sheaths, thrombus collection devices and associated methods are described below with reference to the figures. These figures, and their written descriptions, indicate that certain components of the apparatus are formed integrally, and certain other components are formed as separate pieces. Components shown and described herein as being formed integrally may in alternative embodiments be formed as separate pieces. Components shown and described herein as being formed as separate pieces may in alternative embodiments be formed integrally. Further, as used herein the term integral describes a single unitary piece. 
         [0063]      FIGS. 1-6  illustrate one embodiment of the present radially collapsible and expandable sheath  20 . As shown in  FIG. 6 , the sheath  20  is configured for passage into a patient&#39;s vasculature  22  (e.g. in a vein or artery, an arterio-venous fistula (AVF) or arterio-venous graft (AVG), or alternatively in a non-vascular location such as the peritoneal cavity or other bodily cavities or hollow anatomical structures) through an opening  24  at a percutaneous access site  26 . Once deployed as shown in  FIG. 6 , the sheath  20  can be used as a conduit for introducing one or more intravascular devices into the patient&#39;s vasculature  22 . For example, and as discussed further below, in one embodiment the sheath  20  can be used to introduce a thrombectomy device. 
         [0064]      FIGS. 1-3  illustrate the sheath  20  in a collapsed or contracted state.  FIGS. 4 and 5  illustrate the sheath  20  in an expanded state. An operator may readily expand and contract the sheath  20  in the radial direction to increase or decrease its internal diameter  28 ,  28 ′, respectively. For example, the internal diameter  28 ,  28 ′ may be increased for the passage of intravascular devices, and decreased to promote hemostasis at the percutaneous access site  26 , as discussed further below. 
         [0065]    With reference to  FIGS. 1-3 , the sheath  20  comprises an elongate, elastomeric, tubular casing  30 . As shown in the cross-sectional views of  FIGS. 1 and 2 , the tubular casing  30  includes an inner layer  32  and an outer layer  34 . The layers  32 ,  34  define an annular space  36  between them. The annular space  36  receives a portion of an elongate wire  38  that an operator may manipulate to expand and contract the casing  30 , as described in detail below. 
         [0066]    With particular reference to  FIG. 2 , a distal end  40  of the wire  38  is disposed within the annular space  36  at or near a distal end  42  of the casing  30 . In one embodiment, the distal end  40  of the wire  38  may be secured to the casing  30 . In an alternative embodiment, the distal end  40  of the wire  38  may be freely movable with respect to the inner layer  32  and the outer layer  34 . The distal end  40  of the wire  38  may include a blunt cap (not shown) to reduce the likelihood of the wire  38  puncturing the elastomeric casing  30 . 
         [0067]    Proximal of the wire  38  distal end  40 , the wire  38  forms a helix  44 . The helix  44  includes a plurality of coils  46  that wrap around the casing inner layer  32  beneath the casing outer layer  34 . The helix  44  extends to a proximal end  48  of the casing  30  where the wire  38  extends through an opening  50  in the casing  30 . As indicated by the break lines in  FIGS. 2 and 3 , the wire  38  may have any desired length extending proximally of the casing  30 . As explained in further detail below, an operator may manipulate the proximal end of the wire  38  to force more of the wire  38  into the annular space  36  through the opening  50 , or to withdraw some of the wire  38  from the annular space  36  through the opening  50 . This manipulation expands and contracts the helix  44  and the casing  30 , as described below. 
         [0068]    As described above, the casing  30  may comprise a compliant material. As used herein, the term compliant should be understood to include at least the following properties: flexibility, elasticity, and collapsibility/expandability. Further, because the casing  30  is configured for use internally, the material is preferably biocompatible. Example materials for the casing  30  include silicone film, polyisoprene, TECOTHANE®, PELLETHANE®, and other materials having similar properties. 
         [0069]    The wire  38  preferably comprises a material that is flexible but incompressible. Further, because the wire  38  is configured for use internally, the material is preferably biocompatible. Example materials for the wire  38  include nickel-titanium (NiTi) alloys, stainless steel, polyether ether ketone (PEEK) and other materials having similar properties. 
         [0070]    Again,  FIGS. 1-3  illustrate the sheath  20  in a collapsed or contracted state. In this state, a relatively small portion of the wire  38  is disposed within the annular space  36 . However, when the flexible but incompressible wire  38  is subjected to a compressive force applied proximally of the casing  30 , wire  38  is forced into the annular space  36  through the opening  50  where the wire  38  enters the casing  30 . As more wire  38  enters the annular space  36 , the wire  38  forms tighter and more closely-spaced coils  46  within the helix  44 , with the coils  46  having increasingly larger diameters, as shown in  FIGS. 4 and 5 . The elastomeric nature of the casing  30  makes it readily expandable in the radial direction as the wire  38  forces it outward. Similarly, when the wire  38  is subjected to a tensile force applied proximally of the opening  50 , the coils  46  within the helix  44  relax and spread apart as wire  38  is drawn out of the opening  50 . Again, the elastomeric nature of the casing  30  makes it readily contractible in the radial direction as the radial support provided by the wire  38  diminishes. 
         [0071]    In the illustrated embodiment, the wire  38  is freely slidable within the annular space  36  with respect to the inner layer  32  and the outer layer  34 . Thus, as the wire  38  is forced into the annular space  36  through the opening  50 , the helix  44  slides against the inner and outer layers  32 ,  34  to enable the casing  30  to expand without forming pleats between adjacent coils  46 . The expanded sheath  20  thus presents a relatively smooth inner diameter  28 ′ for easy passage of intravascular devices. However, in alternative embodiments the wire  38  may be secured to the casing  30  at one or more locations. 
         [0072]    As shown in  FIGS. 2 and 4 , the inner and outer layers  32 ,  34  of the casing  30  preferably converge at the proximal end  52 , and at the distal end  42 , thereby sealing the proximal and distal ends  42 ,  52  of the annular space  36 . The inner and outer layers  32 ,  34  may, for example, be formed integrally. The sealed proximal end  52  of the annular space  36  facilitates controlled insertion and withdrawal of the wire  38  through the opening  50 . The sealed distal end  42  of the annular space  36  resists movement of the wire  38  distally out of the annular space  36 . The sealed distal end  42  can also form a smooth, atraumatic leading edge of the casing  30  to facilitate transport of material into the distal opening of the sheath  20  while avoiding injury to blood vessel walls or other nearby anatomy. 
         [0073]      FIG. 6  illustrates the sheath  20  positioned in a patient&#39;s vasculature  22  through an opening  24  at a percutaneous access site  26 . The sheath  20  may be deployed in this configuration using, for example, a catheter (not shown). An operator may puncture the patient&#39;s skin  54  and vasculature  22  with a catheter delivery needle (not shown) in order to dispose the catheter within the patient&#39;s vasculature  22  with a proximal end of the catheter protruding from the percutaneous access site  26 , e.g. via the Seldinger technique or any other suitable access technique. The operator may then introduce the sheath  20  into the vasculature  22  through the catheter lumen and then withdraw the catheter over the sheath  20 , leaving the sheath  20  in the state shown in  FIG. 6 . Alternatively, the operator can insert the sheath  20  over a guidewire emplaced via the Seldinger technique. For ease of insertion, the operator would typically introduce the sheath  20  in its collapsed state ( FIGS. 1-3 ). Upon emplacement, the operator may thereafter expand the sheath  20  to the configuration shown in  FIG. 6  so that it achieves wall-to-wall apposition with the interior walls  56  of the vasculature  22 . The operator expands the sheath  20  by applying a distally directed force to the wire  38  as described above. Further expansion of the sheath  20  may facilitate removing thrombus from the vasculature  22 , as explained further below. 
         [0074]    Once the sheath  20  is emplaced as shown in  FIG. 6 , it is configured to provide an access path to the vasculature  22  for various intravascular devices. In one procedure described below, the sheath  20  is used to introduce a device for removing a thrombus. The sheath  20  can be used as an introducer for any type of intravascular device. The example described below is not limiting. 
         [0075]    The expandable and contractible nature of the sheath  20  allows it to accommodate devices of various sizes. For example, the sheath  20  may be expanded to such an extent that it also radially expands the vasculature  22 , allowing for passage of a particularly large device or thrombus. Further, when another device is not disposed through the interior of the sheath  20 , the sheath  20  may be contracted to tighten the percutaneous access opening  24 . This contraction aids hemostasis, reducing the tendency of blood to flow outward from the percutaneous access opening  24 . The contraction can occur “automatically” without requiring action by the operator, resulting from the natural compliance and collapsibility of the sheath. The subcutaneous tissues surrounding the sheath  20  can exert sufficient pressure on the sheath  20  to contract the sheath and/or force it closed entirely, or otherwise force the sheath walls into close contact with any object(s) in the sheath lumen. When the intravascular procedure is complete, the operator may contract the sheath  20  and withdraw it from the percutaneous access opening  24 . The operator contracts the sheath  20  by applying a proximally directed force to the wire  38  as described above. 
         [0076]      FIGS. 7-10  illustrate one embodiment of the present radially collapsible and expandable thrombus collection device  60 . As described further below, the device  60  is configured to be inserted into a patient&#39;s vasculature through an introducer sheath that passes through an opening at a percutaneous access site. When inserted in a collapsed state, the device  60  can be advanced past the thrombus, expanded, and then drawn back to pull the thrombus away from the interior of the vasculature and trap the thrombus within the device  60 . As the expanded device  60  is withdrawn further, it pulls the thrombus proximally through the introducer sheath until it eventually exits the vasculature through the percutaneous opening. This procedure is described further below. 
         [0077]      FIGS. 7 and 8  illustrate the device  60  in a collapsed or contracted state.  FIGS. 9 and 10  illustrate the device  60  in an expanded state. An operator may readily expand and contract the device  60  in the radial direction to increase or decrease its external diameter. For example, the external diameter may be decreased to enable the device  60  to pass freely through the introducer sheath. Once deployed in the vasculature, the external diameter may be increased to contact the interior diameter of the vasculature, thereby matching the diameter of a thrombus. 
         [0078]    With reference to  FIGS. 7 and 8 , the thrombus collection device  60  comprises an elongate, elastomeric, tubular casing  62 . As shown in the side elevation view of  FIG. 7 , the tubular casing  62  extends over a tubular catheter  64  from a distal end  66  of the catheter  64  to a point distal of an opening  68  in the sidewall of the catheter  64 . A space between the catheter  64  and the casing  62  receives a portion of an elongate wire  70  that an operator may manipulate to expand and contract the casing  62 , as described in detail below. While  FIG. 7  is not a cross-sectional view, the catheter  64  and the wire  70  are shown beneath the casing  62  for clarity. 
         [0079]    With continued reference to  FIG. 7 , a distal end  72  of the wire  70  is disposed at or near a distal end  66  of the catheter  64 . For clarity, a distal portion  74  of the wire  70  that is positioned on the far side of the catheter  64  is shown in hidden lines. In one embodiment, the distal end  72  of the wire  70  may be secured to the catheter  64 . In an alternative embodiment, the distal end  72  of the wire  70  may be freely movable with respect to the catheter  64  and the casing  62 . The distal end  72  of the wire  70  may include a blunt cap (not shown) to reduce the likelihood of the wire  70  puncturing the elastomeric casing  62 . 
         [0080]    Proximal of the wire distal end  72 , the wire  70  forms a helix  76 . The helix  76  includes a plurality of coils  78  that wrap around the catheter  64  beneath the casing  62 . The wire  70  extends past a proximal end  80  of the casing  62  and then through the opening  68  in the catheter  64 . The wire  70  extends through the interior of the catheter  64  proximal of the opening  68 , exiting through a proximal end of the catheter lumen. In an alternative embodiment, the catheter  64  may omit the opening  68 , so that the wire  70  is always disposed externally of the catheter  64 . Further, the wire  70  may have any desired length extending proximally of the casing  62  and/or catheter  64 . As explained in further detail below, an operator may manipulate the proximal end of the wire  70  to force the wire  70  to expand and contract radially in a fashion similar to that described above with respect to the sheath  20 . 
         [0081]    The casing  62  and the wire  70  preferably comprise material properties corresponding to those described above with respect to the casing  30  and the wire  38  of the sheath  20 . Further, the example materials described with respect to the sheath  20  can also be implemented in the present thrombus collection device  60 . 
         [0082]    The catheter  64  preferably comprises a material that is flexible but rigid enough to support the casing  62  and the wire  70  as the device  60  is inserted into a patient&#39;s vasculature through an introducer sheath, and also rigid enough to support the casing  62  and the wire  70  as those components radially expand and contract. Further, because the catheter  64  is configured for use internally, the material is preferably biocompatible. Example materials for the catheter  64  include various thermoplastics such as polyimide, fluorinated ethylene propylene (FEP), PEBAX, and other materials having similar properties. 
         [0083]    Again,  FIGS. 7 and 8  illustrate the device  60  in a collapsed or contracted state. In this state, the wire  70  includes a relatively straight portion  82  extending between the opening in the catheter  64 , and a helical portion distal of the straight portion  82 . However, when the flexible but incompressible wire  70  is subjected to a compressive force applied proximally of the opening  68 , the wire  70  is forced distally in the space between the casing  62  and the catheter  64 . As the wire  70  moves distally, it forms tighter coils  78  within the helix  76 , with the coils  78  having increasingly larger diameters, as shown in  FIGS. 9 and 10 . The elastomeric nature of the casing  62  makes it readily expandable in the radial direction as the wire  70  forces it outward. The expanded casing  62  presents a wide proximal opening  84  to the space between the casing  62  and the catheter  64 . Similarly, when the wire  70  is subjected to a tensile force applied proximally of the opening  68 , the coils  78  within the helix  76  relax as wire  70  is pulled proximally, collapsing the wire  70  and the casing  62  and narrowing the proximal opening  84 . Again, the elastomeric nature of the casing  62  makes it readily contractible in the radial direction as the radial support provided by the wire  70  diminishes. 
         [0084]    In one embodiment, the wire  70  is freely slidable within the space between the casing  62  and the catheter  64 . Thus, as the wire  70  is forced distally, additional wire  70  is forced into the space between the casing  62  and the catheter  64 . The helix  76  slides against the casing  62  and the catheter  64  as it expands radially to enable the casing  62  to expand without forming pleats between adjacent coils  78 . The expanded sheath thus presents a relatively smooth outer diameter for easy passage of the device  60  within the patient&#39;s vasculature. However, in alternative embodiments the wire  70  may be secured to the casing  62  at one or more locations, such as at the proximal end  80  of the casing  62 . 
         [0085]    As shown in  FIGS. 9 and 10 , the illustrated embodiment of the thrombus collection device  60  expands to form a substantially conical shape, or any other suitable shape, including any tapering shape with a proximal open end and a smaller, closed distal end. To achieve this expanded shape, the casing  62  may, for example, be secured to the catheter  64  at one or more locations along a straight line that traces the outer surface of the catheter  64 . In the illustrated embodiment, this line is along the lower side  86  of the catheter  64 . Because the casing  62  is attached to the catheter  64 , as the wire  70  is forced distally under an applied force the wire  70  and the casing  62  are constrained against expansion on the side  86  of the catheter  64  where the casing  62  is attached, causing the casing  62  to assume a generally conical or elongate conical shape as it expands. The conical expanded shape achieves advantages for thrombus collection, as described in further detail below. 
         [0086]      FIGS. 11-15  illustrate one method of using the thrombus collection device  60  of  FIGS. 7-10  to perform a thrombectomy. As shown in  FIG. 11 , the thrombus collection device  60  may be combined with the sheath  20  of  FIGS. 1-6  to form a system  88  for performing a thrombectomy. However, the present thrombus collection device  60  may be used with any introducer sheath. Thus, the present sheath  20  and thrombus collection device  60  are each usable separately, or in combination. 
         [0087]    With reference to  FIG. 11 , a process for extracting a thrombus begins with the operator emplacing the sheath  20  as described above with respect to  FIG. 6 . The operator can then expand the sheath  20  by applying a distally directed force to the sheath wire  38 . With the sheath  20  expanded, the operator introduces the thrombus collection device  60  by passing it through the expanded sheath  20  and into the patient&#39;s vasculature  22 , as shown in  FIG. 11 . To aid introduction, the operator would typically introduce the thrombus collection device  60  in its collapsed state ( FIGS. 7 and 8 ).  FIG. 11 , however, illustrates the device wire  70  and the device casing  62  in their expanded states for clarity. Once the device  60  has been introduced into the vasculature  22 , the operator may collapse the sheath  20  by applying a proximally directed force to its wire  38 . In the collapsed state, the sheath  20  advantageously promotes hemostasis at the percutaneous access site  26  by allowing the percutaneous puncture  24  to reduce in size. The collapsed sheath  20 , however, still provides an adequate inside diameter to enable the thrombus collection device  60  to be manipulated within the vasculature  22 . The step of collapsing the sheath  20  is optional. 
         [0088]    With reference to  FIG. 12 , the operator advances the device  60  through the patient&#39;s vasculature  22  toward the location of the thrombus  90 . The operator may advance the device  60  by applying a distally directed force to the portion of the catheter  64  that protrudes from the percutaneous access site  26 . The operator may use a guide wire (not shown) and/or imaging, such as ultrasound, to assist in guiding the device  60  through the vasculature  22  to the thrombus  90 . 
         [0089]    When the thrombus collection device  60  reaches the thrombus  90 , as shown in  FIG. 13 , the operator continues applying distally directed force to push the distal end  66  of the device  60  through the thrombus  90 . The present thrombus collection device  60  is configured to collect acute thrombi, which typically have a gelatin-like consistency. The operator may thus typically pass the device  60  through the thrombus  90  without substantial difficulty. The moderate rigidity of the catheter  64  and the low profile of the device  60  aid in penetrating the thrombus  90 . 
         [0090]    The operator continues advancing the device  60  through the thrombus  90  until the device casing  62  has completely passed through the thrombus  90 . The operator then expands the device wire  70  and the device casing  62  as shown in  FIG. 14 . The operator expands the device wire  70  and the device casing  62  by applying a distally directed force to the device wire  70  while holding the catheter  64  stationary. The operator may expand the device wire  70  and the device casing  62  until achieving wall-to-wall apposition with the interior diameter  56  of the vasculature. The operator may use imaging and/or tactile feedback to determine when the device casing  62  is expanded to the desired amount. 
         [0091]    With the device casing  62  expanded and positioned distally of the thrombus  90 , the operator draws the device  60  back through the vasculature  22  by applying a proximally directed force to the catheter  64  while holding the device wire  70  stationary with respect to the catheter to maintain the device casing  62  in its expanded state. As the expanded device  60  is pulled proximally, the proximal opening  84  of the device casing  62  collects the thrombus  90  and traps it within the space between the device casing  62  and the catheter  64 , as shown in  FIG. 15 . The operator continues to pull back on the catheter  64  until the thrombus collection device  60  reaches the distal end  42  of the sheath  20 , as shown in  FIG. 11 . Again, the operator may use imaging to determine the location of the thrombus collection device  60 . As illustrated, in  FIGS. 12-15 , the operator may advantageously advance the device  60  through the thrombus  90  such that the line  86  along which the device casing  62  is attached to the catheter  64  faces the interior wall  56  of the vasculature  22 . Thus, when the conical device casing  62  is expanded, its proximal opening  84  is positioned to completely engulf the thrombus  90  when pulled back. 
         [0092]    When the thrombus collection device  60  reaches the distal end  42  of the sheath  20 , as shown in  FIG. 11 , the operator draws the device  60  through the sheath  20 , together with the collected thrombus  90 , until the device  60  and the thrombus  90  are completely extracted from the patient. To aid in extraction, the operator would typically expand the sheath  20  prior to withdrawing the device  60  so that the sheath  20  may better accommodate the expanded device  60 . The sheath  20  may advantageously be expanded over a wide range, so that it can for example be expanded to contact the interior diameter  56  of the vasculature  22 , and be expanded even farther to radially expand the vasculature  22 . This increased expansion is advantageous for withdrawing the thrombus collection device  60 , as the thrombus collection device  60  may sometimes be expanded during withdrawal to a diameter that is substantially equal to the interior diameter of the vasculature  22 . Optionally, the operator can rely upon the natural expandability of the sheath  20 , rather than or in addition to manual expansion of the sheath, to expand the sheath  20  in response to the introduction of a large-diameter object (e.g. the device  60  containing a relatively large portion of thrombus) into the sheath lumen. Upon withdrawing the thrombus collection device  60 , the operator may thereafter collapse the sheath  20  and also withdraw it from the percutaneous access site  26 . Just before or during withdrawal of the device  60 , the operator can pull the device wire  70  proximally so that the wire  70  serves as a clamp or drawstring that holds the collected thrombus in the casing  62  or wire coils more securely during withdrawal. 
         [0093]    In an alternative embodiment of the sheath  20 ′, the sheath wire  38 ′ may not be coiled around the inner layer  32 ′ when the sheath  20 ′ is in the collapsed state. For example,  FIG. 16  shows an alternative sheath  20 ′ in which the sheath wire  38 ′ extends substantially straight from the opening  50 ′ to the distal end  42 ′ of the sheath casing  30 ′. Similarly, in an alternative embodiment of the thrombus collection device  60 ′, the device wire  70 ′ may not be coiled around the catheter  64 ′ when the device casing  62 ′ is in the collapsed state. For example,  FIG. 17  shows an alternative thrombus collection device  60 ′ in which the device wire  70 ′ extends substantially straight along the catheter  64 ′ from the opening  68 ′ to the distal end  66 ′ of the catheter  64 ′. In both embodiments of  FIGS. 16 and 17 , the wire  38 ′,  70 ′ coils around the inner layer  32 ′/catheter  64 ′ in response to a distally directed force applied to the wire  38 ′,  70 ′, substantially as described above with respect to the foregoing embodiments. 
         [0094]    As illustrated above, the present embodiments of the radially collapsible and expandable sheath  20  advantageously provide an introducer sheath that can be adjusted to accommodate intravascular devices of various sizes. The sheath  20  is simple in construction, including only two pieces (the casing  30  and the wire  38 ) in certain embodiments. The sheath  20  is easily adjustable in radial dimension through the application of pushing or pulling force to the wire  38 . The sheath  20  can expand radially on its own in response to movement of a large object into the sheath, such as a large intravascular device or a device carrying a relatively large amount of thrombus. In the latter case, this property of the sheath facilitates removal of large thrombi without need for macerating the thrombi or treating them with a thrombolytic agent before moving them through the sheath. The sheath  20  can be expanded within the vasculature to radially expand the vasculature. When collapsed, the portion of the sheath  20  extending through the percutaneous access opening promotes hemostasis by allowing the opening to partially or completely collapse. 
         [0095]    As also illustrated above, the present embodiments of the radially collapsible and expandable thrombus collection device  60  advantageously provide a collection device that can be collapsed to a low profile for easy introduction to the vasculature through a sheath, and easy penetration of the thrombus. When the collapsed device  60  is advanced past the thrombus, it can be expanded to match the interior diameter of the vasculature and pulled back to entrain the thrombus. It is optional to macerate the thrombus or to soften it with a thrombolytic prior to extraction. The proximal opening of the casing, supported by the wire, simply pulls the thrombus away from the vasculature wall and traps it within the casing. This embodiment is particularly useful for removing thrombi that repeatedly form in arterio-venous fistulas (AVF) of hemodialysis patients. The thrombus collection device  60  enables removal of the thrombi without the need for repeated surgical cut downs. Several devices  60  can be provided in a package or kit for use within a single procedure, e.g. when thrombus is to be removed in several stages each calling for a separate device  60 . 
         [0096]    As also illustrated above, the present embodiments of the radially collapsible and expandable sheath  20  can be combined with the present embodiments of the radially collapsible and expandable thrombus collection device  60  to form a system  88  ( FIG. 11 ) for performing a thrombectomy. The system  88  achieves the combined advantages of each component of the system  88 . Those of ordinary skill in the art will appreciate, however, that both the sheath  20  and the thrombus collection device  60  are usable separately. 
         [0097]      FIG. 18  illustrates another embodiment of the present introducer sheaths. The sheath  100  is tubular, and includes a medial neck portion  102 . At a distal end, the neck portion  102  flares outwardly to a wider bell portion  104 . The distal end  106  of the bell portion  104  is open. 
         [0098]    The neck portion  102  and the bell portion  104  may comprise a compliant material. As used herein, the term compliant should be understood to include at least the following properties: flexibility, elasticity, and collapsibility/expandability. Further, because the sheath  100  is configured for use internally, the material is preferably biocompatible. Example materials for the sheath  100  include silicone film, polyisoprene, TECOTHANE®, PELLETHANE®, and other materials having similar properties. The compliant sheath material is advantageously kink resistant and capable of folding upon itself. 
         [0099]    In one embodiment, the sheath  100  comprises HT-310 synthetic polyisoprene having a thickness of approximately 3-4.5 mils. A length of the bell portion  104  is approximately 26 mm, as measured from the distal end  106  to the transition point  108  between the bell portion  104  and the flared portion  110 . A diameter of the bell portion  104  is approximately 10 mm. A length of the neck portion  102  is approximately 34 mm, as measured from the proximal end  112  to the transition point  114  between the neck portion  102  and the flared portion  110 . A diameter of the neck portion  102  is approximately 7 mm. A length of the flared portion  110  is approximately 10 mm. The foregoing material and dimensions are merely one example, and are not limiting. 
         [0100]    The bell portion  104  of the sheath  100  includes a wire  116  that is encased within the compliant material. Unlike the sheath  20  described above and illustrated in  FIGS. 1-6 , the wire  116  is not movable relative to the compliant sheath material. The sheath  100  may, for example, be made by overmolding the compliant sheath material over the wire  116 . The resulting structure keeps the wire  116  in the desired position along the length of the bell portion  104 . 
         [0101]    The wire  116  extends around the circumference of the bell portion  104  along a path that repeatedly doubles back and forth in the direction of the longitudinal axis A of the sheath  100 . As measured in the direction of the longitudinal axis A, the wire  116  extends over approximately half the length of the bell portion  104  from the distal end  106  thereof to approximately the center thereof. As illustrated, however, a narrow band  118  of the bell portion  104  extends beyond the wire  116  at the distal end  106 . A length of this band  118 , as measured in the direction of the longitudinal axis A, may be approximately 1 mm in one embodiment. 
         [0102]    The wire  116  supports the compliant material, maintaining the bell portion  104  in its expanded shape when the sheath  100  is unstressed. The wire  116  comprises a material that is flexible but incompressible. Further, because the wire  116  is configured for use internally, the material is preferably biocompatible. Example materials for the wire  116  include nickel-titanium (NiTi) alloys, stainless steel, polyether ether ketone (PEEK) and other materials having similar properties. 
         [0103]    At a proximal end  120 , the sheath  100  includes a flush port  122 . The flush port  122  includes a tubular portion  124  that is coaxial with the neck portion  102  and the bell portion  104 . Together, the tubular portion  124 , the neck portion  102  and the bell portion  104  define an interior lumen, or sheath lumen (not shown). A port  126  extends radially from the tubular portion  124 . The port  126  defines a port lumen (not shown) that is in fluid communication with the sheath lumen. The port  126  is conically shaped, tapering down to a smaller diameter with increasing distance from the tubular portion  124 . A medial portion of the port  126  includes an annular bulge  128  where the exterior diameter of the port  126  is increased. The port  126  is configured to receive standard medical tubing  130  in a liquid tight friction fit with the tubing  130  extending around the outside of the bulge  128 . An end of the tubing  130  spaced from the port  126  includes a connector  132 . In the illustrated embodiment, the illustrated connector  132  is a female Luer connector  132 . A conical distal end  134  of the connector  132  is received within the tubing  130  in a liquid tight friction fit. The connector  132  includes a stopcock  136  that enables flow through the connector  132  to be selectively blocked. The flush port  122  enables fluid to be injected and/or aspirated from the sheath lumen. For example, a syringe (not shown) may be connected to the connector  132 , and fluid may be injected or aspirated by depressing or drawing back on the syringe plunger. 
         [0104]    The introducer sheath  100  of  FIG. 18  is configured for passage into a patient&#39;s vasculature (e.g. in a vein or artery, an arterio-venous fistula (AVF) or arterio-venous graft (AVG), or alternatively in a non-vascular location such as the peritoneal cavity or other bodily cavities or hollow anatomical structures) through an opening at a percutaneous access site. Once deployed, the sheath  100  can be used as a conduit for introducing one or more intravascular devices into the patient&#39;s vasculature. For example, and as discussed further below, in one embodiment the sheath  100  can be used to introduce a thrombectomy device.  FIG. 18  illustrates the introducer sheath  100  in an unstressed, or expanded, configuration. The compliant portions of the introducer sheath  100  are configured to be radially compressed for ease of introduction into the vasculature, as described below. Once deployed within the vasculature, a hemostasis valve  138  at the proximal end of the sheath  100  ( FIG. 20 ) resists outflow of bodily fluids through the sheath  100 . The hemostasis valve  138  is shaped substantially as a disk, and is located within the tubular portion  124  at the proximal end  120  thereof. The valve  138  may, for example, comprise a foam material. The valve  138  forms a seal around the exterior of a tubular dilator  140 , which is described below. 
         [0105]      FIGS. 19 and 20  illustrate one embodiment of a deployment apparatus  142  for the introducer sheath  100  of  FIG. 18 . With reference to the cross-sectional view of  FIG. 20 , the deployment apparatus  142  includes a tubular dilator  140 , which may also be referred to as a hypotube  140 . The dilator  140  is a rigid or semi-rigid component configured to guide the deployment apparatus  142  through a skin puncture and through the vasculature, as described in further detail below. The dilator  140  includes a proximal handle  144 , a conically shaped distal tip  146 , and defines a lumen  148  that extends between the proximal and distal ends. The handle  144  is shaped as a round knob. The lumen  148  extends through the handle  144  and through the distal tip  146 . The lumen is configured to receive a guide wire (not shown) to facilitate introduction of the dilator  140  into a patient, as described in detail below. 
         [0106]    With continued reference to  FIG. 20 , the introducer sheath  100  of  FIG. 18  is disposed coaxially about the outside of the dilator  140 , and an outer sheath  150  is disposed coaxially about the outside of the introducer sheath  100 . The outer sheath  150  has an inner diameter that is approximately equal to an outer diameter of the neck portion  102  of the introducer sheath  100 , but less than the outer diameter of the bell portion  104  of the introducer sheath  100 . The outer sheath  150  thus radially compresses the bell portion  104 , which facilitates introduction of the sheath  100  into the patient. In certain embodiments, the outer sheath  150  comprises a non-elastic material so that the radially compressed bell portion  104  does not induce expansion of the outer sheath  150 . 
         [0107]    The outer sheath  150 , however, is a tearaway sheath. Thus, it comprises a material that can be torn by hand. Example materials include polytetrafluoroethylene (PTFE) and materials having similar properties. The outer sheath  150  includes a proximal handle  152  that extends radially away from the outer sheath  150  at a location just distal of the tubular portion  124  of the introducer sheath  100 . As discussed further below, the operator may remove the outer sheath  150  by grasping the handle  152  and pulling it proximally while holding the introducer sheath  100  and the dilator  140  steady. The outer sheath  150  material tears away from the deployment apparatus  142  as it is withdrawn from the percutaneous access site. Once the outer sheath  150  is removed, the bell portion  104  of the introducer sheath  100  expands to its unstressed condition, subject to any stresses applied by the patient&#39;s vasculature. 
         [0108]      FIGS. 21-24  illustrate one embodiment of a method for deploying the introducer sheath  100  of  FIG. 18  in a patient&#39;s vasculature  154  at a percutaneous access site  156  using the deployment apparatus  142  of  FIGS. 19 and 20 . The access site  156  may be prepared by puncturing the skin  158 , any underlying tissue  160 , and the vasculature  154  with a needle  162 , as shown in  FIG. 21 . The operator then introduces a guide wire  164  through the lumen of the needle  162 , and withdraws the needle  162 . 
         [0109]    With reference to  FIG. 22 , the operator introduces the deployment apparatus  142  into the vasculature  154  through the puncture site  156  using the guide wire  164 . The operator threads the guide wire  164  into the dilator lumen  148  ( FIG. 20 ) from the distal end  146  and advances the deployment apparatus  142  through the puncture site  156 . In some embodiments the dilator  140  is a rigid component that provides sufficient column strength to facilitate tissue puncturing and/or penetration. However, in alternative embodiments the dilator  140  includes sufficient flexibility to facilitate navigating tortuous vasculature  154 . The conically shaped distal tip  146  of the dilator  140  facilitates passage of the deployment apparatus  142  through the patient&#39;s tissue  160  ( FIG. 21 ) and into the vasculature  154 . 
         [0110]    With reference to  FIGS. 22 and 23 , after penetrating the vasculature  154  the deployment apparatus  142  is advanced through the vasculature  154  until the handle portion  152  of the outer sheath  150  approaches the puncture site  156 . In this position, the introducer sheath  100  is located such that the bell portion  104  is located entirely within the vasculature  154  and the neck portion  102  traverses the puncture site  156 . The hemostasis valve  138  ( FIG. 20 ) within the introducer sheath  100  resists outflow of blood through the annular space defined by the interior of the sheath  100  and the exterior of the dilator  140 . The dilator  140  may also include a hemostasis valve (not shown) to resist outflow of blood through the dilator lumen  148 . 
         [0111]    With reference to  FIG. 23 , the operator next removes the outer sheath  150  from the deployment apparatus  142 . As indicated above, the outer sheath  150  is a tearaway sheath. Thus, to remove the outer sheath  150 , the operator grasps the handle  152  and pulls it proximally while holding the introducer sheath  100  and the dilator  140  steady. The operator may, for example, grasp the outer sheath handle  152  with one hand and the dilator handle  144  with the other hand. The outer sheath  150  tears away from the remainder of the deployment apparatus  142  and pulls through the puncture site  156 . 
         [0112]    With reference to  FIGS. 23 and 24 , the operator draws the entire outer sheath  150  out of the body through the puncture site  156 . Upon removal of the outer sheath  150 , the compressive force applied to the introducer sheath  100  by the outer sheath  150  is no longer present. The bell portion  104  of the introducer sheath  100  thus expands as the stored energy in the wire  116  is released.  FIG. 24  illustrates the introducer sheath  100  in its expanded state within the vasculature  154 . Depending upon the relative dimensions of the introducer sheath  100  and the vasculature  154 , the vasculature  154  may constrain the expansion of the introducer sheath  100  somewhat so that it does not achieve the fully relaxed state that it would outside the body. Skin  158  and underlying tissue  160  further constrain expansion of the neck portion  102  where it traverses the puncture site  156 . 
         [0113]    With reference to  FIGS. 23 and 24 , after removing the outer sheath  150  the operator next removes the dilator  140 . To remove the dilator  140 , the operator draws back on the proximal handle  144 . During withdrawal, the operator may optionally apply digital pressure at the puncture site  156  in order to prevent the introducer sheath  100  from being withdrawn together with the dilator  140  due to friction between those two components where they are squeezed by the elastic skin  158  at the puncture site  156 . With the dilator  140  completely removed, the introducer sheath  100  is disposed within the vasculature  154  through the puncture site  156  as shown in  FIG. 24 . The tubular portion  124  is disposed exteriorly of the body, the bell portion  104  is disposed within the vasculature  154 , and the neck portion  102  traverses the skin  158  and tissue  160  therebetween. Advantageously, the compliant nature of the neck portion  102  promotes hemostasis at the puncture site  156  by allowing the elastic skin  158  to collapse around the puncture. The compliant neck  102  further speeds hemostasis at the end of a procedure, because the skin  158  and underlying tissue  160  do not remain stretched for an extended period. The hemostasis valve  138  within the proximal end  120  of the introducer sheath  100  ( FIG. 20 ) further promotes hemostasis at the puncture site  156 . When the dilator  140  is withdrawn, the hemostasis valve  138  may close to seal the opening formerly occupied by the dilator  140 . The valve  138  may reopen as additional apparatus is introduced into the vasculature  154  through the sheath  100 . However, the valve  138  preferably forms a seal around any such apparatus. 
         [0114]    The introducer sheath  100  described above may advantageously be used to introduce a wide variety of instruments into a patient&#39;s vasculature  154 . For example, the introducer sheath  100  may be used to introduce a thrombus collection device. Various examples of thrombus collection procedures using the present embodiments are described below. 
         [0115]      FIGS. 25 and 26  illustrate an aspiration catheter  166 , which is another embodiment of the present thrombus collection devices. With reference to  FIG. 25 , the catheter  166  includes an elongate body  168  having a balloon  170  at its distal end  172 . The catheter body  168  comprises a flexible material that is configured for navigating tortuous vasculature. However, the catheter body  168  material includes sufficient rigidity to facilitate guiding the catheter  166  through the vasculature from the proximal end  174 . Example materials for the catheter body  168  include polyether block amide (PEBAX®) and materials having similar properties. 
         [0116]      FIG. 26  illustrates a cross-sectional view of the catheter body  168 . The body  168  defines two radially spaced lumens  176 ,  178  that are not in fluid communication with one another. The first lumen  176  is an aspiration lumen  176  that extends from an aspiration connector  180  ( FIG. 25 ) at the proximal end  174  of the catheter  166  to a plurality of aspiration openings  182  toward the distal end  172  of the catheter  166 . The second lumen  178  is an inflation lumen  178  that extends from an inflation connector  184  at the proximal end  174  of the catheter  166  to the balloon  170  toward the distal end  172  of the catheter  166 . The aspiration lumen  176  has a larger diameter than the inflation lumen  178 , and is configured for passage of thrombus, as described below. In one embodiment, the catheter body  168  may have a diameter of 6 Fr, while the aspiration lumen  176  may have a diameter of 0.055″. 
         [0117]    In certain embodiments, the aspiration lumen  176  may further extend to the distal end  172 , which is open but sealed by a valve (not shown). The valve enables a guide wire (not shown) to pass to facilitate introduction of the catheter  166  into the vasculature. However, upon withdrawal of the guide wire the valve seals to resist flow into or out of the distal end  172  of the aspiration lumen  176 . 
         [0118]    With reference to  FIG. 25 , the aspiration connector  180  and the inflation connector  184  extend proximally from a Y-shaped body  186 . The body  186  includes a main conduit  188  that extends inline with the catheter body  168 . The aspiration connector  180  extends proximally from the main conduit  188 , inline therewith. The body  186  further includes a branch conduit  190  that extends at an angle from the body  186 . The inflation connector  184  extends proximally from the branch conduit  190 , inline therewith. In the illustrated embodiment, both connectors  180 ,  184  comprise a female Luer connector including an external thread  192 . In alternative embodiments different types of connectors could be substituted. In certain embodiments, either or both of the connectors  180 ,  184  may include a stopcock (not shown) for selectively halting liquid flow through the connector(s)  180 ,  184 . 
         [0119]    The Y-shaped body  186  and the connectors  180 ,  184  may be formed as a single piece or as multiple pieces. These portions are preferably formed from a rigid medical grade plastic. For example, these portions may comprise polycarbonate, acrylic, polypropylene, styrene, or any other suitable plastic material. 
         [0120]    With continued reference to  FIG. 25 , and as indicated above, the aspiration catheter  166  includes a plurality of aspiration openings  182  toward the distal end  172 . Three openings are shown, but other embodiments may include any number of openings  182 , including only a single opening  182 . The aspiration openings  182  are in fluid communication with the aspiration connector  180  through the aspiration lumen  176 . During a thrombus collection procedure, a syringe (not shown) may be connected to the aspiration connector  180 . Drawing back upon a plunger of the syringe creates suction at the aspiration openings  182 . The suction can be used to draw pieces of the thrombus into the aspiration lumen  176  for removal from the vasculature. This process is described more fully below. 
         [0121]    The aspiration catheter  166  further includes a balloon  170  toward the distal end  172 . The balloon  170  is shown in a partially inflated state for illustration. The balloon  170  is sealed at its proximal end  194  and distal end  196  to the catheter body  168 . An inflation port (not shown) passes through the wall of the catheter body  168  within the balloon  170 . The interior of the balloon  170  is in fluid communication with the inflation lumen  178  through the inflation port. During a thrombus collection procedure, a syringe (not shown) may be connected to the inflation connector  184 . The balloon  170  may be inflated by depressing the syringe plunger to force a fluid through the inflation lumen  178  and into the balloon  170 . The balloon  170  may be deflated by drawing the syringe plunger back to evacuate the fluid from the balloon  170 . For intravascular procedures, the inflation fluid is preferably a non-toxic liquid, such as saline. Thus, as used herein the terms inflate and deflate are to be construed broadly enough to include using a liquid as the inflation agent. 
         [0122]    As described above, the aspiration catheter  166  shown in  FIGS. 25 and 26  is configured for percutaneously removing a thrombus from a patient&#39;s vasculature.  FIGS. 27-35  illustrate one example of such a procedure. In  FIGS. 27-34 , each drawing sheet illustrates the proximal portions (odd numbered figures) of the introducer sheath  100  and the aspiration catheter  166  and the distal portions (even numbered figures) as they appear during the same step of the procedure. In other words,  FIGS. 27 and 28  illustrate different portions of the apparatus during the same step of the procedure,  FIGS. 29 and 30  illustrate different portions of the apparatus during a subsequent step of the procedure, etc. 
         [0123]    With reference to  FIGS. 27 and 28 , the aspiration catheter  166  is introduced into the vasculature  154  through the introducer sheath  100  described above with respect to  FIGS. 18-24 . The introducer sheath  100  may be deployed according to the method described above with respect to  FIGS. 21-24 . The aspiration catheter  166  is then advanced distally through the sheath  100 , the vasculature  154 , and the thrombus  198  until the balloon  170  is disposed on the far side of the thrombus  198  ( FIG. 28 ). A guide wire  164  extending through the aspiration lumen  176  may be used to advance the catheter  166 . As shown, the catheter  166  is advanced with the balloon  170  in the deflated state for ease of passage through the sheath  100 , the vasculature  154  and the thrombus  198 . The conically shaped distal tip  172  further facilitates passage of the catheter  166 , especially through the constricted portion of the sheath  100  that traverses the puncture site, and through the thrombus  198 . 
         [0124]    With reference to  FIGS. 29 and 30 , when the catheter  166  has advanced sufficiently that the balloon  170  is disposed on the far side of the thrombus  198 , the operator connects a syringe  200  ( FIG. 29 ) filled with inflation liquid to the inflation connector  184 . As shown, a Luer stopcock  202  may be connected between the syringe  200  and the inflation connector  184 . The operator depresses the syringe plunger  204  to force the inflation liquid into the balloon  170  through the inflation lumen  178 . The operator inflates the balloon  170  until it presses against the interior walls of the vasculature  154  on the far side of the thrombus  198  ( FIG. 30 ). If the stopcock  202  is not provided, the operator maintains the syringe  200  connected to the inflation connector  184  in order to maintain the inflation pressure within the balloon  170 . However, if the stopcock  202  is provided, the operator moves the stopcock  202  to a position to prevent liquid flow through the inflation connector  184 . The operator may then disconnect the syringe  200  from the stopcock  202 , which may make it easier for the operator to perform subsequent steps of the procedure. 
         [0125]    With reference to  FIGS. 31 and 32 , the operator removes the thrombus  198  from the vasculature  154  by using a combination of suction through the aspiration openings  182 , and proximal movement of the inflated balloon  170  across the thrombus  198 . These actions may occur simultaneously, or in succession, or alternatingly. The following discussion describes a method for applying suction simultaneously while drawing the inflated balloon  170  across the thrombus  198 . This illustrated method is only one of many possibilities for removing the thrombus  198 , and is not intended to be limiting. 
         [0126]    With reference to  FIG. 31 , the operator connects a Luer stopcock  202  to the aspiration connector  180  and an empty syringe  206  to the stopcock  202 . If a guide wire  164  was used to advance the catheter  166 , it is removed prior to connection of the syringe  206 . The syringe  206  is configured so that the plunger  208  can be drawn back to create a vacuum within the barrel  210  and the plunger  208  locked to maintain the vacuum. One such syringe is sold under the trade name VACLOK®. To generate suction, the operator draws back on the syringe plunger  208  with the stopcock  202  in the closed position and then locks the plunger  208 . The operator then draws the catheter  166  out of the vasculature  154  while simultaneously moving the stopcock  202  to the open position. Moving the stopcock  202  to the open position exposes the vacuum in the syringe barrel  210  to the aspiration lumen  178 , generating suction that pulls pieces of the thrombus  198  into the aspiration lumen  176  through the aspiration openings  182 . The aspiration openings  182  thus advantageously assist in collecting the thrombus  198  both by tearing away pieces of thrombus  198  from the larger whole, and by vacuuming up any loose pieces of thrombus  198 . Some of these pieces of thrombus  198  may be sucked into the syringe  206 , as shown in  FIG. 31 . 
         [0127]    Because the operator draws the catheter  166  out of the vasculature  154  simultaneously while generating suction at the aspiration openings  182 , the aspiration openings  182  are more likely to be exposed to all portions of the thrombus  198  as the openings  182  are drawn across the thrombus  198 , as shown in  FIG. 32 . The suction is thus more likely to remove more of the thrombus  198  than if the catheter  166  remains stationary while the vacuum is applied. In certain embodiments, the aspiration openings  182  may be located within the thrombus  198  at the point in the procedure where the operator opens the stopcock  202 . In alternative embodiments, some or all of the openings  182  may be disposed proximally and/or distally of the thrombus  198  at this point in the procedure. 
         [0128]    In addition to the vacuum action, pulling back on the aspiration catheter  166  pulls the balloon  170  against the distal side of the thrombus  198 , as shown in  FIG. 32 . The balloon  170 , which fills the circumference of the vasculature  154 , pulls the thrombus  198  away from the vasculature  154 . Portions of the thrombus  198  that are not sucked into the aspiration lumen  176  are drawn into the sheath  100  by the balloon  170 . 
         [0129]    With continued reference to  FIG. 32 , the operator continues to pull back on the aspiration catheter  166  until all or substantially all of the thrombus  198  has been pulled into the sheath  100 . The operator then continues to pull back on the aspiration catheter  166  in order to force the thrombus  198  out of the vasculature  154  through the sheath  100 . The balloon  170  is withdrawn through the percutaneous access site and into the portion of the sheath  100  that is disposed outside the body. The compliant material of the sheath  100  is advantageously able to expand as the inflated balloon  170  passes so that the balloon  170  can push the pieces of thrombus  198  out of the body. The compliant sheath  100  then collapses as the elastic skin at the puncture site constricts, advantageously facilitating hemostasis. With reference to  FIG. 33 , the thrombus  198  and balloon  170  are eventually pulled through the proximal end  120  of the introducer sheath  100 . The introducer sheath  100  may include a hinged proximal door  212  at the proximal end  120  that facilitates withdrawal of the inflated balloon  170 . 
         [0130]    After the thrombus  198  has been removed from the vasculature  154  the introducer sheath  100  remains in the vasculature  154  through the percutaneous access site. The sheath  100  advantageously maintains a path into the vasculature  154  so that a guide wire  164  ( FIG. 35 ) may be reinserted into the vasculature  154  as shown. It may be advantageous to reinsert a guide wire  164  so that the location of the removed thrombus  198  can be re-accessed. Repeat access may be desired so that the thrombus  198  removal procedure may be repeated or so that a stent may be placed, for example. After the guide wire  164  is reinserted, the introducer sheath  100  may be removed if desired, as shown in  FIG. 35 . 
         [0131]    The aspiration catheter  166  illustrated in  FIG. 25  includes three aspiration openings  182 . The present aspiration catheters may include any number of aspiration openings  182 . However, it has been found that three aspiration openings  182  achieve advantageous thrombus removal results. Further, providing more than one aspiration opening  182  advantageously maintains suction in the event that a first aspiration opening  182  becomes clogged. In the illustrated embodiments, each of the aspiration openings  182  on the catheter  166  has substantially the same diameter. However, in alternative embodiments the aspiration openings  182  could have varying diameters. For example, a diameter of the openings  182  may increase with increasing distance from the source of suction (the syringe  206  at the aspiration connector  180 ) in order to combat head losses across the openings  182 . 
         [0132]      FIG. 36  illustrates another embodiment of an aspiration catheter  214 . The catheter  214  of  FIG. 36  is similar to the catheter  166  of  FIG. 25 , except that it includes only two aspiration openings  182 , and the distal balloon  216  has a different shape. The balloon  216  of  FIG. 36  is shaped substantially as an arrowhead in profile. It includes a cone-shaped distal surface  218  and a proximal surface  220  shaped as an inverted cone. The inverted cone shape urges fluid to flow toward the centerline of the catheter  214  as the balloon  216  is pulled proximally. The flow direction carries thrombus particles toward the aspiration openings  182 , where they are more likely to be sucked into the aspiration lumen  176 . The balloon  216  thus increases the efficiency with which thrombus particles can be collected in the aspiration lumen  176 . 
         [0133]    As shown in  FIGS. 27-35 , the introducer sheath  100  of  FIG. 18  may be used to introduce the aspiration catheter  166  of  FIG. 25  into a patient&#39;s vasculature  154 . However, both the introducer sheath  100  and the aspiration catheter  166  can be used in a wide variety of procedures other than a percutaneous thrombus collection procedure. For example, the introducer sheath  100  and the aspiration catheter  166  can be used in non-vascular locations such as the peritoneal cavity or other bodily cavities or hollow anatomical structures. 
         [0134]    Further, both the introducer sheath  100  and the aspiration catheter  166  can be used with a wide variety of other apparatus. It should be understood that any of the apparatus described herein can be used separately, and/or in combination with any of the other apparatus described herein, and/or in combination with other apparatus not described herein. Several of these combinations are described below. It should be further understood that wherever the aspiration catheter  166  of  FIG. 25  is described, the aspiration catheter  214  of  FIG. 36  may be substituted therefore, wherever the sheath  100  of  FIG. 18  is described, the sheath  20  of  FIGS. 1-6  or the sheath  20 ′ of  FIG. 16  may be substituted therefore, and wherever the thrombus collection device  60  of  FIGS. 7-10  is described, the thrombus collection device  60 ′ of  FIG. 17  may be substituted therefore. 
         [0135]    With reference to  FIG. 37 , the introducer sheath  100  of  FIG. 18  can be used to introduce a standard Fogarty balloon catheter  222  into the vasculature  154 . Fogarty balloon catheters are well known, and will not be described in detail herein. The procedure for introducing the sheath  100  is as described above with respect to  FIGS. 21-24 , and the procedure for introducing the Fogarty catheter  222  is similar to the procedure described above with respect to  FIGS. 27 and 28 . 
         [0136]    With reference to  FIG. 38 , the introducer sheath  100  of  FIG. 18  can also be used to introduce the thrombus collection device  60  of  FIGS. 7-10  into the vasculature  154 . The procedure for introducing the sheath  100  is as described above with respect to  FIGS. 21-24 . The procedure for introducing the thrombus collection device  60  is described above with respect to  FIGS. 11-15 , except that the sheath  100  of  FIG. 18  is substituted for the sheath  20  of  FIGS. 1-6 . 
         [0137]    With reference to  FIG. 39 , the aspiration catheter  166  of  FIG. 25  can be introduced into the vasculature  154  through a standard balloon catheter introducer sheath  224 . Balloon catheter introducer sheaths are well known, and will not be described in detail herein. The procedure for introducing the sheath  224  is similar to the procedure described above with respect to  FIGS. 21-24 . The procedure for introducing the aspiration catheter  166  is described above with respect to  FIGS. 27 and 28 , except that the balloon catheter introducer sheath  224  is substituted for the sheath  100  of  FIG. 18 . 
         [0138]    While not illustrated herein, the introducer sheath  100  of  FIG. 18  and the aspiration catheter  166  of  FIG. 25  can also be used with other apparatus. For example, the sheath  20  of  FIGS. 1-6  can be used to introduce the aspiration catheter  166  of  FIG. 25  or the Fogarty balloon catheter  222  of  FIG. 37 . Further, the standard balloon catheter introducer sheath  224  of  FIG. 39  can be used to introduce the thrombus collection device  60  of  FIGS. 7-10 . 
         [0139]    As illustrated above, the present embodiments of the introducer sheath  100  and the aspiration catheter  166  offer numerous advantages. For example, with reference to the introducer sheath  100  of  FIG. 18 , the bell portion  104  expands upon deployment so that it contacts the interior walls of the vasculature  154  proximally of the thrombus  198  ( FIGS. 24 and 28 ). When a balloon  170  is then placed distally of the thrombus  198  and inflated, the thrombus  198  is isolated between the bell portion  104  and the balloon  170 . Since the bell portion  104  is open at its distal end  106 , drawing back the balloon  170  sweeps the thrombus  198  into the open mouth of the bell portion  104 . The removal process thus tends to reduce migration of thrombus  198 , and to collect a greater amount of the thrombus  198  as opposed to procedures not including a sheath having a wide, open distal end. 
         [0140]    The introducer sheath  100  of  FIG. 18  is also advantageously compliant. It is thus able to expand to allow the withdrawal of thrombus  198  and an inflated catheter balloon  170 . The sheath  100  thus enables a greater amount of thrombus  198  to be collected as compared to non-compliant sheaths  100 . For example, clot burdens in arterio-venous fistulas (AVF) tend to be large, making them hard to remove percutaneously. The expandable compliant sheath  100  is well suited for removing these types of thrombus  198 . Further, it is advantageous to remove the plug portion of a thrombus  198 . The plug (not shown) is a relatively hard portion of thrombus  198  at the anastomosis where the vein is sewn to the artery. The harder plug tends not to compress as it is withdrawn percutaneously. The expandable compliant sheath  100  is thus well suited for removing the plug. The compliant nature of the sheath  100  facilitates removal of large thrombi  198  and plugs without need for macerating the thrombi and plugs or treating them with a thrombolytic agent before moving them through the sheath  100 . 
         [0141]    The expandable sheath  100  further enables devices of varying sizes to pass through it, so that various devices can be used during a single procedure without having to exchange the sheath  100  for a differently sized one. The compliant sheath  100  is also able to contract to maintain hemostasis at the percutaneous access site  156  after the catheter  166  has been withdrawn. The compliant sheath  100  further speeds hemostasis at the end of a procedure, because the skin and underlying tissue do not remain stretched for an extended period. 
         [0142]    With reference to the aspiration catheter  166  of  FIG. 25 , the configuration of the catheter  166  advantageously provides push/pull inflation and aspiration. To inflate the balloon  170 , the operator need only connect a syringe  200  filled with inflation liquid and push the plunger  204 . To provide the suction force for thrombus aspiration, the operator need only connect an empty syringe  206 , draw back and lock the plunger  208 , then release the stopcock  202  while pulling on the catheter  166 . This push/pull inflation and aspiration provides mechanical stability that contributes to lesser incidence of user error. 
         [0143]    Both the introducer sheath  100  and the aspiration catheter  166  are also advantageously compatible with existing apparatus. As illustrated above, the introducer sheath  100  can be used to introduce a standard Fogarty balloon catheter  222 , and the aspiration catheter  166  can be introduced with a standard balloon catheter introducer sheath  224 . The introducer sheath  100  and the aspiration catheter  166  are thus easily adaptable to existing procedures that involve apparatus already familiar to those in the field.