Abstract:
A method of implanting a vessel filter by a femoral approach comprising the steps of providing a sheath with a pusher and the vessel filter positioned therein and providing a sheath centering structure movable within the sheath. The centering structure has a distal portion expandable from a collapsed position within the sheath to an expanded position outside the sheath. The steps further include inserting the sheath into the vessel, moving the centering structure with respect to the sheath to enable the centering structure to move from the collapsed position to the expanded position to move a distal tip of the sheath away from a vessel wall and to a more centered position, and subsequently exposing the vessel filter from the sheath to enable the filter to move from a collapsed position to an expanded position. An implantation system is also provided.

Description:
PRIORITY CLAIM 
       [0001]    This application claims priority from provisional application Ser. No. 61/988,051, filed on May 2, 2014, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    This application relates to a vascular filter and more particularly to a method of inserting a vein filter into the vessel. 
         [0004]    2. Background of Related Art 
         [0005]    Passage of blood clots to the lungs is known as pulmonary embolism. These clots typically originate in the veins of the lower limbs and can migrate through the vascular system to the lungs where they can obstruct blood flow and therefore interfere with oxygenation of the blood. Pulmonary embolisms can also cause shock and even death. 
         [0006]    In some instances, blood thinning medication, e.g. anticoagulants such as Heparin, or sodium warfarin can be given to the patient. These medications, however, have limited use since they may not be able to be administered to patients after surgery or stroke or given to patients with high risk of internal bleeding. Also, this medication approach is not always effective in preventing recurring blood clots. 
         [0007]    To avoid invasive surgery, less invasive surgical techniques involving placement of a mechanical barrier in the inferior vena cava have been developed. These barriers are in the form of filters and are typically inserted through either the femoral vein in the patient&#39;s leg or the right jugular vein in the patient&#39;s neck or arm under local anesthesia. The filters are then advanced intravascularly to the inferior vena cava where they are expanded to block migration of the blood clots from the lower portion of the body to the heart and lungs. 
         [0008]    These prior filters take various forms. One type of filter is composed of coiled wires such as disclosed in U.S. Pat. Nos. 5,893,869 and 6,059,825. Another type of filter consists of legs with free ends having anchors for embedding in the vessel wall to hold the filter. These filters are disclosed, for example, in U.S. Pat. Nos. 4,688,553, 4,781,173, 4,832,055, and 5,059,205, 5,984,947 and 6,007,558. Another type of filter is disclosed in U.S. Pat. No. 6,214,025 consisting of wires twisted together to form a cylindrical anchoring portion conforming to the inner vessel wall surface to exert a radial force and a conical filtering portion. 
         [0009]    Commonly assigned U.S. Pat. No. 7,704,266 (the “266 patent”) and U.S. Pat. No. 8,162,972 (the “972 patent”), the entire contents of both of which are incorporated herein by reference, disclose other forms of vein filters. These filters can be permanently implanted or removed minimally invasively, e.g. intravascularly. 
         [0010]    The methods of placement of the filter described in the &#39;274 and &#39;972 patents are effective. However, in certain patients, the vena cava is not straight, but is curved and/or more tortuous. Although the filters of the &#39;274 patent and &#39;972 patents can be placed effectively in such vena cava, it would be advantageous to provide a delivery method and apparatus to even better accommodate these curved anatomies. 
         [0011]    Additionally, the better centered the filter, the easier the subsequent removal of the filter. This is due to the fact that if the retrieval end (cranial end) of the filter is against the vessel wall when placed, access to the retrieval end could be difficult. Also, additional tissue ingrowth could occur over the cranial end which could increase the difficulty of removal. 
         [0012]    Prior art attempts to center the filter include modifications to the filter itself to provide centering structure. Not only does this complicate the filter design but could require the length of the filter to be increased. Such increased length can be disadvantageous due to limited space in the inferior vena cava. 
         [0013]    Commonly assigned Patent Publication No. 2009/0143813 (Ser. No. 12/288,217, filed Oct. 17, 2008) discloses an attempt to center the filter without modifying the filter. In this patent publication, the delivery system is modified to provide for more centered placement of the filter by moving the delivery sheath opening toward a center of the vessel by use of a curved pusher. Although in certain applications this method has been effective, sometimes the user does not properly perform the technique and therefore the filter is not centered upon delivery. 
         [0014]    Therefore, it would be advantageous to improve centered delivery of a filter within the vessel by modifications of the filter delivery system, rather than the filter itself, and which can provide a more reliable and consistent technique for centered placement. 
       SUMMARY 
       [0015]    The present invention provides a method of implanting a vein filter to facilitate centering of the filter at the surgical site. The present invention also provides a method of delivering the filter in a manner to facilitate later removal of the filter from the vessel. This is achieved by providing an expandable centering member as part of the delivery system which is preferably movable with respect to the pusher utilized for deploying the filter in the vessel. 
         [0016]    In one aspect, the present invention provides a method of implanting a vessel filter in a vessel by a femoral approach comprising the steps of:
       providing a sheath having a distal tip and having a filter pusher and vessel filter positioned therein;   providing a sheath centering structure within the sheath and movable with respect to the sheath, the centering structure having a distal portion expandable from a collapsed position within the sheath to an expanded position outside the sheath;   inserting the sheath into the vessel;   moving the centering structure with respect to the sheath to enable the centering structure to move from the collapsed position to the expanded position to move the distal tip of the sheath away from a vessel wall and to a more centered position within the vessel; and   subsequently exposing the vessel filter from the sheath to enable the filter to move from a collapsed condition to an expanded condition within the vessel.       
 
         [0022]    In some embodiments, the method includes the step of advancing the sheath through the femoral vein into the vena cava. 
         [0023]    In some embodiments, the pusher includes a lumen extending therein, and the centering structure includes a wire, the wire movable within the lumen of the pusher and through the filter. The pusher can have a stepped portion forming a shoulder to support the filter and the vessel filter can be mounted on the pusher within the sheath. 
         [0024]    In some embodiments, the centering structure includes a plurality of wires extending from an apex and terminating in free ends; in other embodiments, the centering structure includes a plurality of wires extending from an apex and joined at terminal ends. In some embodiments, the centering structure includes a plurality of wires bowing radially outwardly in the expanded configuration. 
         [0025]    In some embodiments, the step of subsequently exposing the filter includes the step of moving the pusher and/or sheath relative to each other. 
         [0026]    The method can further include the step of removing the vein filter from the vessel. 
         [0027]    In accordance with another aspect, an implantation system for a vascular implant is provided comprising a sheath having a longitudinal axis, a lumen formed therein and a distal opening. A pusher is positioned within the sheath in contact with the vascular implant to deliver the implant from the sheath, the implant moving from a reduced profile position within the sheath to an expanded placement position when exposed from the sheath. The implant is configured for deployment through the distal opening in the sheath for implantation in a patient&#39;s body. A centering structure includes an elongated portion and a plurality of arms extending from a distal portion of the elongated portion, the arms movable from a reduced profile position to an expanded position to move the sheath away from the vessel wall to a more centered position, and the centering structure is movable relative to the pusher. 
         [0028]    In some embodiments, the pusher comprises a lumen and the centering structure is slidably positioned within the pusher. In some embodiments, the pusher includes a stepped portion forming a shoulder to support the implant. 
         [0029]    Preferably, the centering structure is movable independent of the pusher and is movable through the implant. 
         [0030]    In some embodiments, the arms of the centering structure are joined at an apex and terminate in free ends; in other embodiments, the arms are joined at proximal and distal ends to form a basket like structure. 
         [0031]    In some embodiments, the implant comprises a vessel filter, the filter moving to the expanded position when deployed from the sheath. 
         [0032]    In accordance with another aspect, the present invention provides in combination, a delivery sheath, a filter, a pusher and a centering structure. The delivery sheath has a lumen therein dimensioned to receive the filter, the filter positioned within the sheath and configured for deployment through a distal opening in the sheath for implantation in a patient&#39;s body. The pusher is slidably positioned with respect to the sheath and engages the filter for deployment of the filter from the sheath. The centering structure is slidably positioned with respect to the filter, pusher and sheath, and has an expandable distal portion to aid centering of the sheath and thus centering of the filter upon delivery of the filter from the delivery sheath. 
         [0033]    In some embodiments, the centering structure is slidable within a lumen of the pusher. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    Preferred embodiment(s) of the present disclosure are described herein with reference to the drawings wherein: 
           [0035]      FIG. 1  is a perspective view of one embodiment of a filter shown in a collapsed delivery position; 
           [0036]      FIG. 2  is a perspective view of the filter of  FIG. 1  shown in an expanded position; 
           [0037]      FIG. 3  is a side view of the delivery sheath (catheter) being inserted into the vena cava of a patient (via a femoral approach); 
           [0038]      FIG. 4  is a side view of the delivery sheath shown in contact with the wall of the vessel which occurs in certain instances of use, and the filter pusher shown advanced from the catheter; 
           [0039]      FIG. 5  is a side view illustrating the centering wires of a first embodiment of the centering structure of the present invention, the centering structure exposed from the delivery sheath to center the distal opening of the delivery catheter; 
           [0040]      FIG. 5A  is an enlarged longitudinal cross-sectional view taken along line  5 A- 5 A of  FIG. 5 ; 
           [0041]      FIG. 5B  is a perspective view of the centering structure of  FIG. 5 : 
           [0042]      FIG. 6  is a side view similar to  FIG. 5  showing the filter partially exposed from the delivery sheath but not yet expanded; 
           [0043]      FIG. 7A  is a side view similar to  FIG. 6  illustrating the filter fully deployed from the delivery sheath and in the expanded position; 
           [0044]      FIG. 7B  is a view similar to  FIG. 7A  showing partial withdrawal of the centering wires into the filter pusher after full deployment of the filter; 
           [0045]      FIG. 7C  is an enlarged view of the area of detail designated in  FIG. 7A ; 
           [0046]      FIG. 8  is a side view similar to  FIG. 7B  illustrating the centering wires withdrawn into the delivery sheath; 
           [0047]      FIG. 9  is a side view similar to  FIG. 8  illustrating the delivery sheath withdrawn and the filter substantially centered in the vessel in an expanded position; 
           [0048]      FIG. 10A  is a side view similar to  FIG. 6  illustrating an alternate embodiment of a centering structure of the present invention in the form of a basket, the centering structure shown in the expanded configuration and the filter show partially exposed from the delivery sheath but not yet expanded; 
           [0049]      FIG. 10B  is a side view similar to  FIG. 10A  showing the filter fully deployed from the delivery sheath and in the expanded position; 
           [0050]      FIG. 10C  is a perspective view of the centering structure of  FIG. 10A ; 
           [0051]      FIG. 11A  is a perspective view of an alternate embodiment of the pusher and centering mechanism of the present invention, the centering mechanism shown in the retracted position; 
           [0052]      FIG. 11B  is a view similar to  FIG. 11A  showing the centering mechanism advanced from the pusher; 
           [0053]      FIG. 12A  is a perspective view of another alternate embodiment of the pusher and centering mechanism of the present invention, the centering mechanism shown in the retracted position; 
           [0054]      FIG. 12B  is a view similar to  FIG. 12A  showing the centering mechanism advanced from the pusher; and 
           [0055]      FIG. 13  is a flow chart showing the method steps of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0056]    Turning now to the drawings, wherein like reference numerals identify similar or like components throughout the several views, a method of implanting vein filters is disclosed. The filter is inserted via a femoral approach. In commonly assigned U.S. Pat. Nos. 7,704,266 and 8,162,972, the entire contents of each of which are incorporated herein by reference, various embodiments of filters are described with various structures. The delivery system of the present invention can be used to insert the filters disclosed in these patents as well as used to insert other filters. 
         [0057]    As is common, the term “proximal” used herein refers to the part closer to the user, e.g., surgeon, and the term “distal” refers to the part further from the user. Thus, for example, the distal opening of the delivery sheath is the part further from the user as the proximal end extends from the patient&#39;s body for manipulation by the user. 
         [0058]    Turning initially to  FIGS. 5A and 7A , the filter delivery system  10  of the present invention has a delivery catheter or sheath  20  forming the outermost tube, a filter pusher  30  and a centering structure or centering mechanism  40  (or  140 ). For clarity, the centering structure  40  is not shown in  FIG. 5A . 
         [0059]    Delivery sheath (catheter)  20  has a distal tip  24  and a distal opening  26  at distal portion  22  ( FIG. 3 ). In a preferred embodiment, the sheath  20  can be composed of a Pebax material with a stainless steel braid embedded in the wall to increase its rigidity. A PTFE liner or coating is preferably provided on the inner surface of the sheath. Other materials and compositions are also contemplated. The sheath can have a hub (not shown) at a proximal portion for connection of a tube to allow for injection of cold saline, if desired, as described in the &#39;266 patent which can be provided to maintain the filter in a relatively softer condition as it is in the martensitic state within the sheath. The tubing can also be utilized to inject other fluids. 
         [0060]    The filter pusher  30  has a distal tip  32  and a lumen  34  extending therethrough (see  FIG. 5A ). At a distal portion, but spaced proximally from the distal tip  32 , a step is formed to create a shoulder  38  to abut and support a filter thereon. The pusher  30  is in contact with the filter  100  by the abutment of the shoulder  38  and filter and deploys the filter  100  either by distal movement of the pusher  30  to advance the filter  100  from the sheath  20 , by proximal movement of the sheath  20  to expose the filter  100 , or by movement of both the pusher  30  distally and the sheath  20  proximally. In either event, such relative movement of the pusher  30  and sheath  20  exposes the filter  100  so it can move from its collapsed reduced profile delivery position or condition (see  FIG. 1 ) contained with the sheath  20  to its expanded position or condition ( FIGS. 2 and 7A ) exposed from the sheath  20  to contact the vessel wall. 
         [0061]    The pusher  30  can be formed from a tube. In a preferred embodiment, the pusher  30  can be formed of Pebax material. The centering wires can be composed of stainless steel. Other materials and compositions of the pusher and wires are contemplated. A wire protruding beyond the distal end of the pusher  30  also can serve as a guidewire. The wire can also help keep the vessel engaging hooks of the filter separated during insertion. A marker band or other indicia can be provided to provide a visual indication of when the filter is at the distal end of the sheath (when the markings are adjacent a proximal end of a filter cartridge). Note in some embodiments, the centering wire can be attached to a hub of the pusher for slidable movement, e.g., by a control knob, such as in the embodiment described below. 
         [0062]    The centering structure is designated by generally by reference numeral  40  and has a distal portion  42  and a proximal portion extending outside the body for manipulation by the user. Distal portion  42  includes a plurality of centering arms  44 , joined at apex  46 , bowing radially outwardly and terminating in free ends  48  ( FIGS. 5B and 7A ). In a preferred embodiment, three centering arms  44  are provided, however, a fewer or greater number of arms can alternatively be provided. The centering structure  40  is slidably positioned within lumen  34  of the filter pusher  30  and therefore moves, e.g., slides, relative to the pusher  30 , sheath  20  and filter  100 . That is, the centering structure  40  is movable from a retracted (collapsed) position within the delivery sheath  20  to an extended (advanced) position where the distal portion  42  extends beyond the distal tip  24  of sheath  20  for movement from a collapsed to an expanded position. 
         [0063]    In one embodiment, the centering structure  40  is formed by a series of wires, e.g., an elongated wire  43  with centering arms  44  formed of separate wires and attached to a distal portion of the wire  43  at apex  46  such as by welding, crimping, soldering, bonding or other known methods. Alternatively, the elongated wire  43  can form one of the centering arms and then additional centering arms  44  can be attached to a region of the elongated wire  43  slightly proximal of its distal tip (as in the location of apex  46 ). The centering structure can alternatively be formed integrally from a monolithic wire or hypotube. The one piece structure can be laser cut and shape set. 
         [0064]    The wires of the centering structure can be made of shape memory material such as Nitinol. In this manner, the wires are collapsed into a low profile position where the arms  44  are substantially aligned with a longitudinal axis of the delivery sheath  20  for delivery. When advanced from the sheath  20 , the centering wires are exposed and return to their shape memorized expanded configuration (position) of  FIG. 5 . Alternatively, they can be composed of spring material such as, stainless steel, and biased to an expanded position. Additionally, as an alternative, the centering wires could be moved to an expanded position when exposed from the sheath by an actuating mechanism, e.g., by actuating a wire or cable which when pulled bows the arms  44 . 
         [0065]    Note in the expanded position, the apex  46  can be exposed; alternatively the apex  46  can remain within the confines of the sheath  20  or pusher  30 . 
         [0066]    As shown, when the centering wires expand, they have a transverse dimension sufficiently large to contact, preferentially circumferentially, the wall of the vessel, thereby keeping the delivery sheath  20  and distal tip  32  of the pusher  30  substantially centered within the vessel. It should be appreciated that the term “substantially centered” as used herein includes exactly centered within the vessel as well as slightly off center such as at an angle of up to about 30 degrees with respect to the longitudinal axis of the vessel, but preferably smaller. By keeping this angle closer to zero, centering of the delivery sheath distal tip  24  and distal opening  26 , and therefore the filter  100  when delivered, can better be achieved. 
         [0067]    An alternate embodiment of the centering structure is illustrated in  FIGS. 10A-10C . The delivery sheath and filter pusher of  FIG. 10A  are identical to that of the embodiment of  FIGS. 1-9 , and therefore for brevity are not described in detail again. In short, filter pusher  130  is identical to filter pusher  30  and includes a distal tip and a shoulder (not shown) identical to shoulder  38 . Delivery sheath or catheter  120  is identical to delivery sheath  20  and includes a distal tip  122  and a distal opening  124  for exit of the filter  100 , identical to distal tip  22  and opening  24  of delivery sheath  20 . 
         [0068]    Centering structure  140  differs from centering structure  40  in that it is a closed loop design. More specifically, distal portion  142  includes a plurality of centering arms  144 , joined at proximal apex  146  and at distal converging region  147 . The connection at distal region  147  provides more structural integrity. Centering arms  144  bow radially outwardly between their proximal and distal fixed points. In a preferred embodiment, three centering arms  144  are provided, however, a fewer or greater number of arms can alternatively be provided. The centering structure  140  is slidably positioned within a lumen of the filter pusher  130  (similar to lumen  34  of pusher  30 ) and therefore moves, e.g., slides, relative to the pusher  130 , sheath  120  and filter  100 . That is, the centering structure  140  is movable from a retracted position within the delivery sheath  120  to an extended (advanced) or exposed position where it extends beyond the distal tip of sheath  120  for movement from a collapsed position to the expanded position of  FIGS. 10A and 10B . 
         [0069]    In one embodiment, the centering structure is formed by a series of wires, e.g., an elongated wire  143  ( FIG. 10C ) with centering arms  144  formed of separate wires and attached to a distal portion of the wire  143  at apex  146  such as by welding, crimping, soldering, bonding or other known methods. The arms  144  are also attached at distal converging region  147  by welding, crimping, bonding, soldering or other known methods. Alternatively, the elongated wire  143  can form one of the centering arms and then additional centering arms  144  are attached to a region of the elongated wire  143  slightly proximal of the distal tip (as in the location of apex  146 ) and at the distal tips (as in distal region  147 ). The centering structure  140  can alternatively be formed integrally from a monolithic wire or hypotube. The one piece structure can be laser cut and shape set. 
         [0070]    The wires of the centering structure can be made of shape memory material. In this manner, the wires are collapsed into a low profile position where the arms  144  are substantially aligned with a longitudinal axis of the delivery sheath  120  for delivery. When advanced from the sheath  120 , the wires are exposed and return to their shape memorized expanded configuration (position) of  FIGS. 10A and 10B . Alternately, they can be composed of spring material such as stainless steel, and biased to an expanded position. Note in the expanded position, the proximal apex  146  can be exposed; alternatively the apex  146  can remain within the confines of the sheath  120  or pusher  130 . An actuation mechanism, e.g., a wire or cable, can alternatively be used, e.g., pulled, to bow the arms  144  when exposed. 
         [0071]    As shown, when the wires expand, the have a transverse dimension sufficiently large to contact the wall of the vessel, thereby keeping the delivery sheath  120  and distal tip  122  of pusher  120  substantially centered within the vessel. Substantially centered as noted above includes exactly centered as well as slightly off center such as at an angle of up to 30 degrees with respect to the longitudinal axis, but preferably smaller. By keeping this angle closer to zero, centering of the opening of the delivery sheath  120 , and therefore the filter  100  when delivered, can better be achieved. 
         [0072]      FIGS. 11A-12B  illustrate alternate embodiments wherein the centering structure is attached to the pusher. In the foregoing embodiments, the centering mechanism is unattached to the pusher and slid within a lumen of the pusher. In the embodiments of  FIGS. 11A-12B  the centering mechanism is attached at a proximal end to the pusher and is slid within the lumen of the pusher between retracted and advanced positions. 
         [0073]    Turning to the embodiment of  FIGS. 11A and 11B , filter pusher  230  has a proximal portion  232  and a distal portion  234 . A centering mechanism  240  is slidingly received within a lumen of the pusher  230  for movement between a retracted position wherein the distal portion of the centering structure  240  is contained within the confines of the pusher  230  in a collapsed position and an extended exposed position ( FIG. 11B ) wherein the distal portion of the centering structure  240  is exposed from the pusher  230  to move to the expanded position. The centering structure  240  shown includes a series of wires with free ends as in the embodiment of  FIG. 5 . Alternatively, the centering structure can be in the form of a basket or closed loop as in the structure of  FIG. 10A . Hub or handle  242  of centering mechanism  240  is grasped by the user and moved toward the hub or handle  236  of filter pusher  230  to advance the centering structure  240  with respect to the pusher  230  and sheath within which the pusher  230  is located. The centering wires are thereby slidably attached to the pusher  230 , for example, within a plurality of channel guides in hub  236 , each dimensioned to receive one of the centering wires. Alternatively, a single channel guide can be provided to receive only one of the centering wires, e.g., the central wire. In either event, the centering mechanism is attached (connected) to the pusher mechanism for slidable movement therein. 
         [0074]    In the embodiment of  FIGS. 12A ,  12 B, filter pusher  260  has a proximal portion  262  and a distal portion  264 . A centering mechanism  270  is slidingly received within a lumen of the pusher  260  for movement between a retracted position wherein the distal portion of the centering structure is contained within the confines of the pusher  260  in a collapsed position and an extended exposed position ( FIG. 12B ) wherein the distal portion of the centering structure  270  is exposed from the pusher  260  to move to the expanded position. The centering structure  270  shown includes a series of wires with free ends as in the embodiment of  FIG. 5 . Alternatively, the centering structure  270  can be in the form of a basket or closed loop as in the structure of  FIG. 10A . Actuator  274  moves within elongated slot  265  of hub or handle  266  of pusher  260 . The actuator  274  is attached to the centering structure  270  and is moved distally within the slot  265  to advance the centering structure  270  with respect to the pusher  260  and sheath in which the pusher  260  is positioned. 
         [0075]    The centering structures described herein are self-expanding, e.g., composed of a shape memory material that automatically returns to the expanded position of  FIG. 7A ,  10 A,  11 B or  12 B when exposed from the pusher and sheath. It is also contemplated that the structure can be controllably expanded with wires, cable or structure which can be actuated to expand the centering structure. In any of these versions, exposure from the confines of the walls of the pusher and/or sheath enables expansion of the centering structure. 
         [0076]    The use of the filter implantation system will now be described. It should be understood that the method of use will be described in conjunction with the centering structure  40  of  FIGS. 2-9 , it being understood that the centering structure of  FIGS. 10A-10C  would be utilized in an identical manner. The centering structures of  FIGS. 11A-12B  would also be used in similar manner, the difference being that the centering structure is slidably attached to the pusher, e.g., via a channel guide or a slot in the hub/handle, as it slides within the pusher lumen rather than being a separate component. Also, the delivery system  10  is shown delivering filter  100  of  FIGS. 1 and 2 , it being understood that other filters can be delivered with the delivery system of the present application. 
         [0077]    In use, once the sheath  20  and dilator (not shown) are inserted through the femoral vein and advanced through the iliac vein into the inferior vena cava, the dilator is removed. Due to the anatomy of the particular patient&#39;s vena cava C, the sheath  20  may end up off center such as against the vessel wall V such that distal opening is close to the vessel wall (see  FIG. 4 ). If the filter  100  was then delivered from the sheath  20 , it would not be centered on delivery. In accordance with the present invention, the advancement of the centering structure of the present invention moves the distal end  22  and distal opening  24  of the delivery sheath  20  away from a position adjacent or tangent to the vessel wall V so the distal opening  24  of sheath  20  is more centered in the vessel, thus better ensuring the filter  100  will be initially placed in a more centered position. 
         [0078]    Note that during intravascular insertion of the sheath  20  into the vena cava C, filter pusher  30 , filter  100  and centering structure  40  positioned therein are fully covered by sheath  20  so as not to be exposed ( FIG. 3 ). With reference to  FIGS. 4-9 , and to the flow chart of  FIG. 13 , after the sheath  20  is advanced adjacent the vena cava, the pusher  30  is advanced distally within the delivery sheath  20  to advance the filter  100  distally adjacent a distal end of the sheath  20 ; however, the filter  100  remains within the delivery sheath  20  with a distal region of the pusher  30  exposed as shown in  FIG. 4 . 
         [0079]    Next, the centering structure  40  is advanced distally from the sheath  20  ( FIG. 5 ), sliding distally within lumen  34  of pusher  30 . When the centering arms  44  are exposed from the sheath  20 , they move to the expanded configuration as they return to the shape memorized shape. The centering arms  44  ensure the distal opening  24  of sheath  20  is moved away from the vessel wall V, which can be appreciated by comparing  FIGS. 4 and 5 . In this substantially centered position of the distal tip  22  of sheath  20 , the filter  100  is now ready for delivery to the vessel. 
         [0080]    The filter  100  is exposed from the sheath  20  ( FIG. 6 ) either by distal advancement of the pusher  30 , retraction of the sheath  20 , or movement of both the pusher  30  distally and sheath  20  proximally. When the filter  100  is fully exposed ( FIG. 7A ), it returns to its shape memory position, with the vessel engaging hooks  172  engaging the vessel wall V to secure the filter  100 . Note that before fully deployed as in the position of  FIG. 6 , the user can easily alter the position of placement of the filter  100  by adjusting the longitudinal (i.e., distal or proximal) position by movement of the components. 
         [0081]    Once the filter  100  is fully deployed in the vessel, the centering structure  40  is then retracted proximally by the user, and the centering arms  44  are thereby collapsed within the lumen  34  of the pusher  30  as it is withdrawn through the pusher  30  and into the sheath  20  ( FIG. 8 ). Once the centering structure  40  is withdrawn, the pusher  30  is retracted proximally within the sheath  20  and the components are removed from the vascular system, leaving the filter  100  in place as shown in  FIG. 9 . 
         [0082]    Note the Figures illustrate filter  100  identical to the filter of U.S. Pat. No. 8,162,972 incorporated by reference above as one example of a filter that can be utilized with the delivery system of the present invention Thus, filter  100  is preferably formed from a single tube, and is preferably composed of shape memory material such as Nitinol. A plurality of cutouts are formed in the filter  100 , preferably by laser cutting, although other techniques are contemplated to thereby form struts  114 . 
         [0083]    Filter  100 , as shown in the expanded configuration of  FIG. 2 , has a filter portion (section)  123  and a mounting portion (section)  130 . As shown, filter  100  is generally bell-shaped in configuration. Filter  100  has a flared region and a converging region  121  at the filtering portion  123 . The transverse dimension of the filter at the flared (or mounting/anchoring) portion (region)  130  is greater than the transverse dimension at filtering portion (region)  123 . Elongated struts  114  are spaced apart as shown and extend at an angle away from the longitudinal axis of the filer  110  to provide a flare. 
         [0084]    The struts  114  of filter  1010  terminate in hooks  172 . In some embodiments, some struts can terminate in a hook larger than the hook of other struts. In some embodiments, the struts  114  can terminate in alternating larger and smaller hooks such that every other strut  114  would terminate in a small hook and the other struts (in between) would terminate in a larger hook. The penetrating tips  176  of hooks  172  penetrate the tissue to retain the filter, preferably temporarily, and point toward the cranial end of the filter. 
         [0085]    The six filter struts or strut portions  114  extend longitudinally and then curve outwardly from tubular portion  118 , extend radially therefrom and divide into two connecting filter struts or strut portions  114   a ,  114   b  (preferably of equal width, although differing dimensions are contemplated) that angle way from each other (in different directions) to extend to the connecting strut portion of an adjacent strut  114 . Thus, connecting strut portion  114   a  of one strut  114  interconnects with the connecting strut portion  114   b  of an adjacent strut at joining region  114   d . This forms closed geometric shapes  125 , preferably substantially diamond shaped in configuration. For clarity, not all of the identical parts are labeled in the drawings. 
         [0086]    In the illustrated embodiment, preferably six struts are provided forming twelve interconnecting struts; however a different number of struts and closed geometric shapes can be provided. Note that although all six struts  114  are shown interconnected, it is also contemplated that fewer than all the struts can be interconnected. Also, the strut width can vary as described with respect to the filters disclosed in the &#39;972 patent. 
         [0087]    After convergence of strut portions  114   a ,  114   b  at joining region  114   d , it transitions into elongated mounting strut portions  114   c  which form the flared mounting or anchoring region  130 . The length of the strut portions  114   c  in the anchoring region  130  can vary, with increased/decreased length increasing the flexibility/rigidity of the struts. The thickness of the strut portions can also vary to affect flexibility/rigidity. 
         [0088]    The tubular portion  118  is preferably in the form of a retrieval hook  192 . In an alternate embodiment, instead of a retrieval hook  102 , a ball or groove can be provided engageable by the retrieval snare (not shown) for retrieval of the filter. 
         [0089]    Note that the tubular region  118  has a lumen  119  therethrough (see  FIG. 7C ) through which the filter pusher  30  can extend in the collapsed and in the expanded position of the filter  100 . Thus, as shown in  FIG. 7C , the centering structure  40  (or  140 ,  240  or  270 ), which extends through the pusher  30 , would likewise extend through the tubular portion  118 . In the collapsed position of the filter of  FIG. 1 , the pusher  30  would likewise extend through the lumen of the tubular portion  118 , and the centering structure  40  (or  140 ,  240 , or  270 ) would also extend through the lumen  119  of the tubular portion  118 . 
         [0090]    After exposure of the filter  100  by advancing the pusher  30  to eject the filter  100  or retracting the sheath  20  with the pusher  30  held stationary, or relative movement of both the pusher  30  and sheath  20 , the pusher  30  and sheath  20  are removed, enabling the filter  100  to expand from its collapsed position of  FIG. 1  and leaving the filter in place in the vena cava. 
         [0091]    If it is later desired to remove the filter, the retrieval methods for the filter which are illustrated and described in detail in the &#39;972 patent, such as a retrieval snare, can be utilized. 
         [0092]    If the filter  100  is more centered in the vessel, the retrieval snare is better adapted to access and engage (grasp) the retrieval region, e.g., the retrieval hook  192 , of the filter  100 . Also, if placement is more centered, removal can be easier because there will be less tissue ingrowth at the retrieval region. 
         [0093]    Although described for inserting a vessel filter, the pusher and sheath can be utilized to insert other implants, including vascular implants such as a stent or valve. 
         [0094]    While the above description contains many specifics, those specifics should not be construed as limitations on the scope of the disclosure, but merely as exemplifications of preferred embodiments thereof. Those skilled in the art will envision many other possible variations that are within the scope and spirit of the disclosure as defined by the claims appended hereto.