Abstract:
The present invention relates generally to devices and methods for retrieving or manipulating objects within a lumen. More specifically, embodiments of the invention relate to devices and methods for retrieving or manipulating medical devices from a body lumen. One embodiment of the present invention provides a novel and improved retrieval snare and method of fabricating and using the same. The snare includes a snare wire, having a distal end and a proximal end, for use in the human anatomy, such as but not limited to blood vessels, pulmonary airways, reproductive anatomy, gastrointestinal anatomy, and organs such as the kidneys or lungs. The device enables a user to capture a foreign object located within the human anatomy, grasp said object in a controlled manner, and retrieve and remove said object from the human anatomy.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/586,683, filed Jan. 13, 2012 and entitled “Retrieval Snare Device and Method”, which is herein incorporated by reference in its entirety. 
     
    
     INCORPORATION BY REFERENCE 
       [0002]    All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. 
         [0003]    The following patents and patent applications are herein incorporated by reference in their entirety: U.S. patent application Ser. No. 11/969,827 titled, “ENDOLUMINAL FILTER WITH FIXATION” filed on Jan. 4, 2009. 
       FIELD 
       [0004]    Embodiments of the invention relate generally to devices and methods for retrieving or manipulating objects within a lumen. More specifically, embodiments of the invention relate to devices and methods for retrieving or manipulating medical devices from a body lumen. 
       BACKGROUND 
       [0005]    Embolic protection is utilized throughout the vasculature to prevent the potentially fatal passage of embolic material in the bloodstream to smaller vessels where it can obstruct blood flow. The dislodgement of embolic material is often associated with procedures which open blood vessels to restore natural blood flow such as stenting, angioplasty, arthrectomy, endarterectomy or thrombectomy. Used as an adjunct to these procedures, embolic protection devices trap debris and provide a means for removal for the body. 
         [0006]    One widely used embolic protection application is the placement of filtration means in the vena cava. Vena cava filters (VCF) prevent the passage of thrombus from the deep veins of the legs into the blood stream and ultimately to the lungs. This condition is known as deep vein thrombosis (DVT), which can cause a potentially fatal condition known as pulmonary embolism (PE). 
         [0007]    The next advancement in filters added the element of recoverability. Retrievable filters were designed to allow removal from the patient subsequent to initial placement. These filters can incorporate retrieval features that can be grasped and/or secured by a retrieval device, such as a snare based retrieval device. Grasping the retrieval feature using a snare generally requires the user to manipulate the snare over the retrieval feature, which can be difficult due to a variety of factors, such as retrieval feature geometry and location within the lumen, the structure and properties of the snare, and ability to visualize the retrieval feature and/or snare using a real-time visualization technique such as fluoroscopy. 
         [0008]    Accordingly, it would be desirable to have an improved retrieval device that would facilitate engagement with a retrieval feature on a device making retrieval and/or manipulation of the device easier and faster to complete. 
       SUMMARY OF THE DISCLOSURE 
       [0009]    The present invention relates generally to devices and methods for retrieving or manipulating objects within a lumen. More specifically, embodiments of the invention relate to devices and methods for retrieving or manipulating medical devices from a body lumen. 
         [0010]    One embodiment of the present invention provides a novel and improved retrieval snare and method of fabricating and using the same. The snare includes a snare wire, having a distal end and a proximal end, for use in the human anatomy, such as but not limited to blood vessels, pulmonary airways, reproductive anatomy, gastrointestinal anatomy, and organs such as the kidneys or lungs. The device enables a user to capture a foreign object located within the human anatomy, grasp said object in a controlled manner, and retrieve and remove said object from the human anatomy. Examples of foreign objects which might be removed from the human anatomy include implants such as stents, guidewires, sheaths, filters, and valves, and organic objects such as kidney stones or calcified emboli. Other areas where embodiments of the snare can be used include, for example, removal and/or repositioning of distal protection devices that are used in a variety of medical procedures such as carotid stenting and percutaneous aortic valve replacement; and abdominal aortic aneurysm and thoracic aortic aneurysm devices. For example, a snare can be used to capture a vena cava filter and pull it into a retrieval sheath for removal from the patient. The snare is advanced through one or more retrieval sheaths, up to the site of a deployed filter. The snare is then deployed into the vessel, and engaged with the filter. Finally, the snare is held under tension while the sheath is advanced over said filter, collapsing it into the ID of said sheath. Another example is the use of a snare to grasp and extract loose kidney stones from a patient&#39;s kidneys. The snare is advanced through one or more sheaths, up to the site of the loose kidney stone. The snare is then deployed and engaged with the stone. Next, the snare is pulled into the sheath, drawing the stone into the distal ID of said sheath. 
         [0011]    In some embodiments, a device for retrieving an object from a lumen is provided. The device includes a sheath configured to fit within the lumen, the sheath having a proximal end and a distal end. A snare can be disposed within the sheath. The snare can have a shaft with a longitudinal axis, a proximal end and a distal end and a plurality of loop elements in connection with the distal end of the shaft. The plurality of loop elements can have a collapsed configuration within the sheath and at least one deployed configuration outside the sheath. The plurality of loop elements can be configured to be deployed through an opening at the distal end of the sheath. The at least one deployed configuration can include a fully deployed configuration in which the plurality of loop elements are deployed in a propeller-like configuration. 
         [0012]    In some embodiments, the first sheath includes a flexible distal tip portion that is configured to invert when the object is withdrawn into the sheath. 
         [0013]    In some embodiments, a plurality of sheaths includes flexible distal tip portions that are configured to invert when the object is withdrawn into the sheaths. 
         [0014]    In some embodiments, the plurality of loop elements in the fully deployed configuration are angled less than 90 degrees with respect to the longitudinal axis of the shaft such that the plurality of loop elements has an axial reach both proximal and distal the distal end of the shaft. 
         [0015]    In some embodiments, each of the plurality of loop elements includes at least one shape memory wire and one radiopaque wire. 
         [0016]    In some embodiments, the shape memory wire is made of a nickel titanium alloy and the radiopaque wire is made of platinum. 
         [0017]    In some embodiments, the loop elements in the fully deployed configuration are arranged to form a circle geometry when viewed along the longitudinal axis. 
         [0018]    In some embodiments, the object being retrieved by the device is a filter having a retrieval element and a support member, and wherein the axial reach of the loop elements in the fully deployed configuration is less than the distance between the retrieval element and the support member. 
         [0019]    In some embodiments, the proximal portion of the sheath and the proximal portion of the shaft are connected with a snap fitting. 
         [0020]    In some embodiments, the proximal portion of the outer sheath and the proximal portion of the inner sheath are connected with a snap fitting. 
         [0021]    In some embodiments, the device further includes an outer sheath, wherein the sheath is disposed within the outer sheath. 
         [0022]    In some embodiments, the outer sheath has greater column strength than the inner sheath. 
         [0023]    In some embodiments, the loop elements have a plurality of deployment configurations, and wherein the proximal portion of the shaft includes a plurality of indicators that correspond to the plurality of deployment configurations. 
         [0024]    In some embodiments, the plurality of indicators includes a plurality of detents. 
         [0025]    In some embodiments, the proximal portion of the sheath includes a first tactile identifier and the proximal portion of the shaft includes a second tactile identifier, wherein the first tactile identifier is different from the second tactile identifier. 
         [0026]    In some embodiments, the at least one deployed configuration includes an initial deployed configuration in which the plurality of loop elements are deployed substantially transversely with respect to the longitudinal axis. 
         [0027]    In some embodiments, the plurality of loop elements is deployed in a clover leaf configuration in the initial deployed configuration. 
         [0028]    In some embodiments, the at least one deployed configuration includes an intermediate deployed configuration in which the plurality of loop elements are deployed substantially axially with respect to the longitudinal axis. 
         [0029]    In some embodiments, a method for capturing an object in a lumen defined by a lumen wall is provided. The method includes advancing a sheath within the lumen, the sheath having a proximal end and a distal end, until the distal end of the sheath is proximal the object; deploying a plurality of loop elements of a snare out of the distal end of the sheath in a propeller-like configuration; and capturing a portion of the object with at least one of the plurality of loop elements. 
         [0030]    In some embodiments, the method further includes withdrawing the loop elements in a proximal direction to engage the portion of the object. 
         [0031]    In some embodiments, the method further includes rotating the loop elements to engage the portion of the object. 
         [0032]    In some embodiments, the method further includes retracting the portion of the object within the sheath. 
         [0033]    In some embodiments, the method further includes advancing an outer sheath over the object. 
         [0034]    In some embodiments, the method further includes advancing the snare to a full deployment detent on the snare. 
         [0035]    In some embodiments, the method further includes visualizing the snare in the lumen using fluoroscopy. 
         [0036]    In some embodiments, the method further includes decoupling a snap fitting holding together the sheath and the snare. 
         [0037]    In some embodiments, the method further includes decoupling a snap fitting holding together the outer sheath and the inner sheath. 
         [0038]    In some embodiments, a device for retrieving an object from a lumen is provided. The device can include a sheath configured to fit within the lumen, the sheath having a proximal end, a distal end and a radiopaque marker offset from the distal end. A snare can be disposed within the sheath, the snare having a shaft with a longitudinal axis, a proximal end and a distal end and a plurality of loop elements in connection with the distal end of the shaft. The plurality of loop elements can have a collapsed configuration within the sheath and at least one deployed configuration outside the sheath. The plurality of loop elements can be configured to be deployed through an opening at the distal end of the sheath. At least one deployed configuration can include an initial deployed configuration in which the plurality of loop elements is deployed substantially transversely with respect to the longitudinal axis. 
         [0039]    In some embodiments, the plurality of loop elements are deployed in a clover leaf configuration in the initial deployed configuration. 
         [0040]    In some embodiments, the plurality of loop elements are deployed in an elliptical or oblong configuration in the fully deployed configuration. 
         [0041]    In some embodiments, the at least one deployed configuration includes a fully deployed configuration in which the plurality of loop elements are deployed in substantially circular configuration. 
         [0042]    In some embodiments, the radiopaque marker is offset about 3 to 5 mm from the distal end of the sheath. 
         [0043]    In some embodiments, a specific radiopaque marker pattern is disposed on each of the loop elements to enable visual differentiation of each loop element fluoroscopically. For example, each loop element can have a different number of radiopaque markers. 
         [0044]    In some embodiments, a method for capturing an object in a lumen defined by a lumen wall is provided. The method includes advancing a sheath within the lumen, the sheath having a proximal end and a distal end, until the distal end of the sheath is proximal the object; deploying a plurality of loop elements of a snare out of the distal end of the sheath until the loop elements achieve substantially full apposition with the circumference of the lumen wall; and capturing a portion of the object with at least one of the plurality of loop elements. 
         [0045]    In some embodiments, the method further includes aligning a radiopaque marker offset from the distal end of the sheath with a radiopaque feature of the object. 
         [0046]    In some embodiments, the radiopaque feature of the object is a retrieval element. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0047]    The novel features of the invention are set forth with particularity in the claims that follow. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which: 
           [0048]      FIG. 1A  is an axial view of the distal end of one embodiment of the snare device, showing the loop elements which substantially form a complete circle about the axis of the shaft. The edges of each loop overlap adjacent loops to ensure a substantially continuous circular pattern. 
           [0049]      FIG. 1B  is a side perspective view of the snare device shown in  FIG. 1A , showing the loop elements such that the plurality of loop elements has an axial reach both proximal and distal the distal end of the shaft. 
           [0050]      FIG. 1C  is a side cross-sectional view of a stowed snare within both an outer sheath and an inner sheath. 
           [0051]      FIGS. 1D-1F  illustrate the various deployment stages of the loop elements of one embodiment of the snare.  FIGS. 1D and 1E  illustrate an initial deployment stage of the loop elements, while  FIG. 1F  illustrates an intermediate deployment stage of the loop elements. 
           [0052]      FIGS. 1G and 1H  illustrate the flexible distal tip portion of the sheath with a deployed snare ( FIG. 1G ) and a partially stowed snare ( FIG. 1H ). 
           [0053]      FIGS. 1I-1J  illustrate snare embodiments having two loop elements with a substantially elliptical or oblong fully deployed configuration. 
           [0054]      FIGS. 1K-1M  illustrate snare embodiments having two loop elements with a substantially elliptical or oblong fully deployed configuration and a loop collapse facilitator. 
           [0055]      FIGS. 1N-1Q  illustrate the stages of deployment of an embodiment of a snare with two loop elements. 
           [0056]      FIG. 1R  illustrates a snare embodiment having two loop elements with a substantially elliptical or oblong fully deployed configuration, and a plurality of radiopaque markers disposed on each loop in different patterns, to differentiate each loop element fluoroscopically. 
           [0057]      FIG. 1S  is a side view of a snare embodiment having two loop elements with a substantially elliptical or oblong fully deployed configuration, showing the loop elements having both a distal and proximal reach. 
           [0058]      FIG. 1T  illustrates a snare embodiment having four loop elements in a substantially circular fully deployed configuration, and a plurality of radiopaque markers disposed on each loop in different patterns, to differentiate each loop element fluoroscopically. 
           [0059]      FIG. 1U  illustrates another snare embodiment having two loop elements with a substantially elliptical or oblong fully deployed configuration and a loop collapse facilitator. 
           [0060]      FIG. 2A  is an end view of an embodiment of a single loop element, using a single nitinol wire wrapped with a single radiopaque platinum wire. 
           [0061]      FIG. 2B  is a perspective view of the single loop element shown in  FIG. 2A . 
           [0062]      FIG. 3A  is a side view of another embodiment of a single loop on the end of a snare device, to illustrate the relative geometry of the loop elements. 
           [0063]      FIG. 3B  is an end view of the single loop shown in  FIG. 3A . 
           [0064]      FIG. 4  is an end view of a loop element and a hypo tube, to illustrate the D shape or pie shape geometry of the loop element features. 
           [0065]      FIG. 5A  is an end view of an embodiment of a single loop element, using a plurality of wires which are twisted together to form a strand. 
           [0066]      FIG. 5B  is a close up view of a portion of the single loop element strand shown in  FIG. 5A . 
           [0067]      FIG. 6A  illustrates an embodiment of a single loop element, using a plurality of wires which are braided together to form a strand. 
           [0068]      FIG. 6B  illustrates a close up view of a portion of the single loop element strand shown in  FIG. 6A . 
           [0069]      FIG. 7  is a side view of an embodiment of a snare device using single wire loop elements, and a steel hypo tube which attaches the loops to the shaft via a crimp process. 
           [0070]      FIG. 8  is a close up view of the snare device shown in  FIG. 7 , further illustrating the steel hypo tube which attaches the loops to the shaft via a crimp process. 
           [0071]      FIG. 9  is a perspective view of the snare device shown in  FIG. 7 . 
           [0072]      FIG. 10  is an end view of the snare device shown in  FIG. 7 . The view illustrates how the loops overlap laterally, with the outer perimeter forming a circular shape. 
           [0073]      FIG. 10A  is an end view of another embodiment of a snare device. The view illustrates how the loop elements are twisted together laterally, with the outer perimeter forming a circular shape. 
           [0074]      FIG. 11  is a side view of an embodiment of a snare assembly, where the loop elements are attached to the shaft element with a wire coil. 
           [0075]      FIG. 12  is a side view of an embodiment of the shaft, hypo tube, and a single loop element for illustrative purposes. The actual snare device can have a plurality of loop elements. The view illustrates an embodiment of the loop element wherein the angle of the radius portion of the loop element is typically about 45 degrees from the central axis of the hypo tube component. 
           [0076]      FIG. 13  is a side view of an alternate embodiment of the snare device where the shaft is made from a twisted strand, and the loop elements form a circular shape in a single plane 90 degrees from the axis of the shaft. 
           [0077]      FIG. 14  is a horizontal isometric view of the alternate embodiment shown in  FIG. 13 , illustrating the flat circular shape of the outer perimeter of the snare loops. 
           [0078]      FIG. 15  is a frontal angled view of the alternate embodiment shown in  FIG. 13 , illustrating the circular shape of the snare outer perimeter, as well as the straight portions of each loop overlapping the adjacent loop to form a closed circle with no gaps about the perimeter. 
           [0079]      FIGS. 16-19  illustrate embodiments of methods of using any of the snares  10  disclosed herein. 
           [0080]      FIGS. 20-22  illustrate embodiments of a snap fitting that can be used with the snare. 
       
    
    
     DETAILED DESCRIPTION 
       [0081]    As illustrated in  FIGS. 1A and 1B , an embodiment of a retrieval device  10 , such as a snare, includes a primary or main shaft  12 , having a distal end  14  and a proximal end  16 . At the distal end  14  of the shaft  12  is a plurality of loop elements  18 . In some embodiments, the device  10  can typically have at least two loop elements  18 , but can have three or more loop elements  18 . These loop elements  18  are attached proximally to the distal end  14  of the shaft  12  via a hypo tube component  20 , and can be free and independent at their distal-most ends. In other embodiments, the distal ends of the loop elements  18  can be fastened or connected to adjacent loop elements using, for example, loop connectors, as described in more detail below. The loops  18  can be of a polymeric or metallic material, and are typically radiopaque and flexible. 
         [0082]    The loop elements  18  can have a region of overlap  31 , with a span L 1 , between the adjacent loop elements. In some embodiments, L 1  can be less than about 5, 10, 15, 20, 25, 30, 35, 40 or 45 degrees. In some embodiments, L 1  can be between about 0 to 45 degrees, or about 0 to 15 degrees. The span of radial or circumferential coverage by each loop element  18  can be defined by the angle α between the two spoke elements  30  of the loop element  18 , as shown in  FIG. 1A  and  FIG. 4 . In some embodiments, angle α depends on the number of loop elements  18  and the amount of loop element overlap, L 1 . For example, in some embodiments, angle α can be determined approximately by dividing 360 degrees by the number of loop elements and then adding the amount of overlap, L 1 . Thus, for a four loop element snare embodiment with 10 degrees of overlap between each loop element, angle α equals approximately 100 degrees. For a two loop element snare embodiment with 10 degrees of overlap, angle α equals about 190 degrees. In other embodiments, the radial or circumferential coverage of the loop elements can be different while still providing complete radial or circumferential coverage. For example, in a four loop element embodiment with 10 degrees overlap, two loop elements can have an angle α of about 130 degrees while the other two loop elements can have an angle α of about 70 degrees. 
         [0083]    The shape and flexibility of the loop elements  18  allows them to collapse and/or fold down easily into, for example, a 7Fr or smaller sheath catheter  22  during loading of the device  10  into the sheath  22  and/or during deployment of the device  10  from the sheath  22  and retraction of the device  10  into the sheath  22 , as illustrated in  FIG. 1C . In some embodiments, an additional outer sheath  36  can be used to provide additional column strength. In some embodiments, the outer sheath  36  can be a braided sheath, while the inner sheath  22  can be a coiled sheath, which can be more flexible that the braided sheath. The outer sheath  36  can be used with any of the embodiments disclosed herein. 
         [0084]    In some embodiments, as illustrated in  FIGS. 1G and 1H , the sheath  22 , which can be used in a single sheath embodiment or as an inner sheath in a double sheath embodiment, can have a soft, flexible and elastic distal tip portion  32  that can expand over a foreign object, such as a filter  40 , that is being pulled into the sheath  22 . In addition, the flexible distal tip portion  32  can evert when the foreign object and/or deployed loop elements  18  are retracted back into the sheath  22 . When the flexible distal tip portion  32  inverts, it can form a ramp-like structure that facilitates the retraction of the filter  40  and the loop elements  18  back into the sheath  22 . The main portion  34  of the sheath  22  can have stiffer column strength than the flexible distal tip portion  32  in order to tolerate the relatively high levels of force that can be generated while pulling out embedded filters with the device  10 . In some embodiments, as mentioned above, an outer sheath can be used to provide additional column strength if needed. 
         [0085]    In some embodiments, the distal tip portion  32  of the sheath  22  can be radiopaque and/or include a radiopaque marker. For example, in some embodiments, the polymer forming the distal tip portion  32  can be doped with radiopaque elements or compounds, such as barium, tantalum, tungsten, palladium, platinum or iridium based compounds or elements. Alternatively or in addition to the radiopaque doping, a single or plurality of radiopaque markers, such as a radiopaque marker band made of the radiopaque elements or compounds described herein, can be incorporated into the distal tip portion  32 . In some embodiments, the radiopaque marker band can be offset approximately 1-10 mm, or about 3-mm from the distal end of the sheath  22 , so as to not interfere with the elasticity and eversion of the distal tip portion  32  during the capture process. The radiopaque doping and/or marker allow the operator to visualize the location of the distal tip portion  32  of the sheath  22  during insertion, advancement, and positioning of the sheath  22  near the foreign object within the lumen. This allows the operator to accurately and precisely advance and position the tip of sheath  22  to the foreign object. In some embodiments where an outer sheath is combined with the retrieval sheath, each sheath can employ different radiopaque marker patterns to allow the operator to differentiate between the two sheaths fluoroscopically. 
         [0086]    In addition, the marker offset can also function as an alignment feature which aids the operator in positioning the distal end of the sheath  22  in the proper location relative to the foreign object to be retrieved. For example, the foreign object can be a filter  40  with a frame  52 , a plurality of anchors  50  on the frame  40  and a retrieval element  42  as illustrated in  FIGS. 16-19 . In some embodiments, deployment of the loop elements  18  is ideally distal the retrieval element  42  but proximal the anchor  50  closest to the retrieval element  42 , which can be achieved be lining up the marker band  54  with an element or feature on the filter  40 , such as the retrieval element  42 , for example. The distance d between the retrieval element  42  and the anchor  50  can serve as a design constraint for loop element  18  deployments, where the loop elements  18  can be designed to deploy with an axial reach of less than the distance d between the retrieval element  42  and the anchor  50  or other feature on the filter  40 .  FIGS. 16-19  are more fully described below. 
         [0087]    In some embodiments, the shaft  12  is straight and can be made of polymeric or metallic material, for example. The shaft  12  can be made of a solid design such as a wire, but can alternatively be hollow to facilitate passage of secondary devices through a lumen in the shaft  12 . The shaft  12  can be of a single wire or element, but can also be constructed of a plurality of wires or elements which can be braided, twisted or stranded into a single shaft  12 . The shaft  12  provides a means by which the user can advance, manipulate, and retract the distal end  14  of the device to capture and remove a foreign object from the human body. Typically, the user manipulates the device  10  at the proximal end  16 , which is typically outside of the human anatomy. By manipulating the shaft  12 , the motion is translated to the distal end  14  of the device  10 , which in turn causes the loop elements  18  to move within the human anatomy. This motion allows the loop elements  18  to catch on the foreign object to be removed from the body. Consequently, the shaft  12  can be designed to have sufficient stiffness, flexibility, pushability and torqueability to accomplish the functions described herein. In some embodiments, a single wire shaft can provide sufficient stiffness, flexibility, pushability and torqueability. In other embodiments, a multiple wire shaft can provide sufficient stiffness, flexibility, pushability and torqueability. 
         [0088]    In some embodiments, a hypo tube  20  attaches the loop elements  18  to the shaft  12 . The hypo tube  20  has an inner diameter and an outer diameter, and is typically sized such that the shaft  12  and all of the loop elements  18  can fit within the inner diameter of the hypo tube  20 . The inner diameter is sized such that there is adequate interference between the hypo tube  20  and the shaft  12  and the loop elements  18 , so that the hypo tube  20  can be swaged or crimped circumferentially, mechanically locking the loop elements  18  and shaft  12  together. Additionally, the hypo tube can be radially shaped into a non-circular shape, such as but not limited to a hexagon or square or other rectilinear shape, to further facilitate mechanical fit and locking of said shaft  12  and loop elements  18 . In some embodiments, the length of the hypo tube  20  is about at least two times its outer diameter, but can be as short as one times its outer diameter, or as long as twenty times its outer diameter. The loop elements  18  can also be attached to the shaft  12  via welding, soldering, capturing within a coil, or potting within a polymeric or rigid adhesive form, for example. 
         [0089]    In some embodiments, the loop elements  18  have a geometric shape which allows them to deploy in a staged manner, where the shape and effective diameter of the snare  10  is dependent upon how far the snare  10  is deployed out of the sheath  22 . In a first deployment stage as shown in  FIG. 1D , the loops  18  are initially deployed from the sheath  22  and expand, each with a semi-circular shape, a semi-oval shape, or semi-oblong shape, for example, and the effective diameter of the snare  10  is smaller than the effective diameter when the snare  10  is fully deployed. In some embodiments such as a four loop elements  18  embodiment, the snare geometry in the first deployment stage resembles a cloverleaf shape. In some embodiments, as illustrated in  FIG. 1E , the cloverleaf shaped loops  18  extend substantially transversely from the shaft  12  and sheath  22 . In a second deployment stage as shown in  FIG. 1F , the loops  18  extend further from the sheath  22 . In some embodiments, in the second deployment stage the loops  18  extend both transversely and axially from the distal end  24  of the sheath  22 , thereby providing the snare  10  with extended axial reach in this configuration. In a third deployment stage as illustrated in  FIG. 1A , the loops  18  fully expand, reaching the full effective diameter of the snare  10 . The snare  10  geometry in the third deployment stage can resemble a substantially complete circle, when viewed along the longitudinal axis of the snare  10  to yield an end view as shown in  FIG. 1A , with spoke elements that lead from the circle towards the central hypo tube attachment point. The circle geometry created by the radial edge portions of the loop elements  18  eliminates or reduces gaps between the loop elements  18 , which can make it easier for the operator to engage a retrieval element on a foreign object with the snare  10 , especially when the retrieval element is located near or around the periphery of the lumen. 
         [0090]    To facilitate engagement of the loop elements  18  with the retrieval element, the loop elements  18 , when fully deployed, can be sized to conform approximately to the inner diameter of the lumen in which the foreign object is located. This allows full or substantially full apposition between the loop elements  18  and the full circumference of the lumen wall, which enhances the ability of the snare  10  to capture the retrieving element. In some embodiments, the geometry of the fully deployed loop elements  18  can be substantially elliptical, oval or oblong in order to conform to a lumen with a substantially elliptical, oval or oblong cross-sectional geometry. In these embodiments, the major axis of the elliptical or oblong geometry can be sized to conform approximately to the inner diameter of the lumen in which the foreign object is located. In general terms, the geometry of the fully deployed loop elements  18  can substantially match the geometry of the lumen. 
         [0091]    For example, the vena cava may have a generally elliptical or oblong cross-sectional geometry. For use in the vena cava, a snare  10  with loop elements  18  having a substantially elliptical or oblong fully deployed configuration can be used advantageously, as shown in  FIGS. 1I-1M , which illustrate snare  10  embodiments having two loop elements  18 . In other embodiments, more than two loop elements  18 , such as 3, 4 or more loop elements, can be used. By matching the geometry of the deployed loop elements  18  with the geometry of the lumen, full circumferential apposition with the lumen wall can be more readily achieved. In addition, an elliptical or oblong snare  10 , which can have a major axis and a minor axis, can be used in lumens having a wide range of sizes because the major axis of the snare can be rotated to provide greater wall to wall reach when needed. Additionally, the loop elements  18  can exhibit both distal and proximal reach, by forming the shape of said loops with a proximally biased curve  58 , as shown in  FIG. 1S . In some embodiments, the distal reach, D 3 , is up to about 10 mm, and the proximal reach, D 4 , is up to about 10 mm, where distal reach and proximal reach are in reference to the distal end of the shaft  12 . In other embodiments, D 3  and D 4  can be greater than or less than the values recited above. 
         [0092]    In some embodiments, each individual loop element  18  can employ a single or plurality of radiopaque markers  56 , such that each loop element  18  has a different quantity of radiopaque markers  56 , or a different pattern of radiopaque markers  56 , to allow the operator to visually differentiate and identify each loop element  18  fluoroscopically, as shown in  FIGS. 1R and 1T . For example, as illustrated in  FIG. 1R , one loop element  18  has a single radiopaque marker  56  while the other loop element  18  has two radiopaque markers  56 . Similarly, in  FIG. 1T , the first loop element  18  has one radiopaque marker  56 ; the second loop element  18  has two radiopaque markers  56 ; the third loop element  18  has three radiopaque markers  56 ; and the fourth loop element  18  has four radiopaque markers  56 . 
         [0093]    In some embodiments, the loop elements  18  can be attached or connected together using a variety of techniques, as illustrated in  FIGS. 1I and 1J . For example, the loop elements  18  can be connected together by loop connectors  19  which can be made from a piece of wire, metal, plastic or polymer that can be wrapped, twisted, crimped, molded or formed around the two loop elements  18  at, for example, crossover junctions between the loop elements  18 . Other techniques for connecting the loop elements  18  together can be used, such as welding or applying adhesives. Additionally, the spoke portions  30  can be twisted together to attach the loop elements  18  together, as shown in  FIG. 10A . For example, the spoke portions  30  of adjacent loop elements  18  can be twisted together. Attaching or connecting the loop elements  18  together can reduce the likelihood of unwanted or unintentional loop eversion or loop displacement that can occur during loop deployment, loop manipulation within the lumen and loop retraction. 
         [0094]    In some embodiments, the loop elements  18  can include a single or plurality of loop collapse facilitator  23  features, as shown in  FIGS. 1K-1M , that facilitates collapse of the loop elements  18  when the loop elements  18  are retracted back into the sheath  22  or when the sheath  22  is advanced over the loop elements  18 . The loop collapse facilitator  23  can be a preformed crimp or fold in the loop element  18  that serves as a collapse or folding point for the loop element  18  and therefore initiates or facilitates collapse of the loop element  18  when compressive forces are applied to the loop element  18 . In some embodiments, each loop element  18  can have at least one loop collapse facilitator  23 . 
         [0095]    In addition, the loop collapse facilitator  23  can be oriented in a variety ways. For example, the loop collapse facilitators  23  can be pointed or extend either in a distal direction, as shown in  FIG. 1K  or a proximal direction (not shown), such that the circumference of the loop elements  18  in the deployed configuration when viewed axially remains in the same shape, such as elliptical, oval or oblong, as compared to embodiments without the loop collapse facilitators  23 , as shown in  FIG. 1I . In other embodiments, the loop collapse facilitators  23  can be pointed or extend radially inwards as shown in  FIGS. 1L and 1M , such that the circumference of the loop elements  18  in the deployed configuration when viewed axially remains in substantially the same shape, such as elliptical, oval or oblong, as compared to embodiments without the loop collapse facilitators  23 , as shown in  FIG. 1L . In other embodiments, the loop collapse facilitators  23  can be pointed or extend radially inwards as shown in the dotted lines in  FIGS. 1L and 1M , such that the circumference of the loop elements  18  in the deployed configuration when viewed axially still remains substantially the same shape, such as elliptical, oval or oblong, but also includes a radially inward indentation, which can be arcuate and taper to a point that extends radially inwards. The size of the indentation can be controlled by the size of the loop collapse facilitator  23  as well as the shape of the taper, as illustrated by the dotted lines and solid lines representing the loop collapse facilitator in  FIGS. 1L and 1M . In some embodiments, the loop collapse facilitator  23  can be oriented both distally or proximally as well as radially. In some embodiments, the loop collapse facilitator  23  can employ a loop geometry which provides a hinge point to allow the loop element  18  to fold down and collapse with low force, as shown in  FIG. 1U . 
         [0096]      FIGS. 1N-1Q  illustrate the stages of deployment of an embodiment of a snare  10  with two loop elements  18 . As shown in  FIG. 1N , during the initial or first deployment stage, the loop elements  18  extend axially out of the sheath  22 , thereby providing axial reach to the snare  10  in this configuration, which is suitable as described herein for guide wire retrieval, for example. In a second deployment stage, the loop elements  18  change from an axial orientation to a transverse or radial orientation, as shown in  FIG. 10 , in which the snare  10  has little or minimal axial reach. In the third or full deployment stage, as illustrated in  FIGS. 1P and 1Q , the loop elements  18  are fully deployed, forming a circumference that is shaped to conform to the shape of the lumen, such as circular, elliptical, oval, oblong, or any other suitable shape, as illustrated in  FIGS. 1I-1M . In the third deployment stage, the snare  10  can have some axial reach and full radial reach which can be configured to provide full circumferential apposition with the lumen wall. The axial reach in the third deployment stage can be increased or decreased to enhance capture of the foreign object, such as a filter, as described herein. 
         [0097]    The diameters of the wires can be 0.002″-0.007″ each. The wires can be tightly wound together, and then formed into a loop element  18  of the desired shape. The loop element  18  outer radiused edge portion  26  can be angled such that the span of the radiused edge portion  26  is at angle of between about 45 degrees and 90 degrees, relative to the axis of the shaft  12 . 
         [0098]    The loop element  18  of one embodiment, as illustrated in  FIGS. 2A and 2B  is made of at least two wires, which are tightly gathered in a twisted configuration, where at least one of the wires is a shape memory nickel titanium wire, and at least one of the wires is of a radiopaque platinum wire. In some embodiments, the twisted configuration can be advantageous over the braided configuration, when a specific stiffness property of the loop elements  18  is desired, by varying the number of wires and wire diameter used in the strand. In some embodiments, the loop element  18  includes 2 shape memory nickel titanium wires and two radiopaque platinum wires. Other materials can be used in place of the nickel titanium and/or radiopaque platinum wires. For example, the nickel titanium alloy, such as Nitinol, can be replaced with a stainless steel wire or polymeric wire. In addition, the radiopaque wire can be replaced with another radiopaque material, such as a platinum-iridium wire, a palladium wire, a gold wire, a tantalum wire, a tantalum-tungsten wire, and the like. In addition, these radiopaque materials can be incorporated into polymeric materials directly or a modified form, such as a salt for example. The radiopaque materials can be bonded or attached to the non-opaque wire in a variety of ways, including wrapping or braiding the radiopaque wire with the non-radiopaque wire together, or by attaching marker bands to the non-radiopaque wire, or by cladding the non-radiopaque wire with the radiopaque material, for example. In many embodiments, the use of various radiopaque markers can be used to indicate the relative location and orientation of the deployed snare  10  in the target area. 
         [0099]      FIGS. 3A and 3B  depict a view of one embodiment, where just one loop element  18  is shown attached to the shaft  12  for the sake of clarity. The embodiment shown in  FIGS. 3A and 3B  can have a plurality of loop elements  18 , such as two, three, or four loop elements  18 , or more than four loop elements  18  as described herein. A snare  10  with more loop elements  18  will have more spoke portions  30  that can engage with the foreign object, which may aid in retrieval of the foreign object. However, an increased number of loop elements  18  may obscure real-time imaging of the snare elements and foreign object, making it more difficult for the operator to correctly identify all the loop elements  18  on the screen, which may interfere with efficient manipulation of the snare  10 . In addition, a snare  10  with too many loop elements  18  can end up having a larger compressed diameter due to the many loop elements  18  that are attached to the shaft  12  via, for example, a hypo tube  20  swage connection, as discussed below. As more loop elements  18  are swaged to the hypo tube  20 , the diameter of the hypo tube  20  increases in order to accommodate the additional loop elements  20 . Increasing the compressed diameter of the snare  10  is generally undesirable for many minimally invasive techniques with which the snare  10  can be used because a larger device requires a larger percutaneous incision, which increases the pain and recovery time for the patient. 
         [0100]    In contrast, in some embodiments a snare  10  with fewer loop elements  18 , such as two loop elements  18 , can be more easily visualized using real time imaging techniques, thereby allowing the operator to accurately identify each loop element  18  and therefore efficiently manipulate the position and orientation of the snare with respect to the foreign object. The two loop element embodiment, as discussed above, can still be capable of achieving complete or substantial circumferential apposition with the lumen wall. In some embodiments with too few loop elements  18 , such as a single loop element, the single loop element can be too floppy, and a floppy loop element  18  can be difficult to precisely manipulate and position, making grasping a small retrieval element on a foreign object more difficult. 
         [0101]      FIGS. 3A and 3B  illustrate the shape of the loop element  18  from two angles; a transverse side view in  FIG. 3A  and a front axial view in  FIG. 3B . The shaft  12  can be attached to the hypo tube  20  via swaging. The hypo tube  20  can also be swaged to the loop element  18 . The loop element  18  can be made from a strand of four wires, two Nitinol wires and two platinum wires. 
         [0102]      FIG. 4  is an axial view of an embodiment of a loop element  18  and a hypo tube  20 . The shape of the loop element  18  includes a radiused edge portion  26  which shares its radial center with the center axis of the hypo tube  20 . The radiused edge portion  26  is bounded at each end by a radiused corner feature  28 , which transitions the radiused edge portion  26  into two straight spoke portions  30 . These straight spoke portions  30  are typically the radius length from the central axis of the hypo tube  20  to the radiused edge portion  26  of the loop element  18 . In some embodiments, the straight spoke portions  30  are set at an angle α of approximately 90 degrees, and radiate from the central axis of the hypo tube  20  to the outer radius of the radiused edge portion  26  of the loop element  18 . 
         [0103]    The loop elements  18  have a geometry that enables them to catch easily on foreign objects in the human anatomy. In some embodiments as shown in  FIG. 4 , the loop element  18  has a “D” shape which resembles a pie slice with rounded corners, when viewed axially along the device axis. This D shape includes a radiused edge portion  26 , which shares a radial center with the axis of the shaft of the device. The radiused edge portion  26  is bounded at either end by a radiused corner portion  28  which transitions the radiused edge portion  26  into two straight spoke portions  30 . In some embodiments, the radiused corner portion  28  bends about 90 degrees towards the central axis of the shaft  12 . 
         [0104]    In some embodiments, the two straight spoke portions  30 , which radiate from the central axis of the hypo tube to the outer radius of the radiused edge portion  26 , are set at an angle α of about 90 degrees, for a snare  10  with four loop elements  18 . In some embodiments, the angle α between the two straight spoke portions  30  can be less than 90 degrees when, for example, the snare  10  has more than four loop elements  18 , such as an angle of about 60 degrees for a snare  10  with six loop elements  18 , or an angle of about 72 degrees for a snare  10  with 5 loop elements. To generalize, in some embodiments, the angle in degrees between the straight spoke portions  30  can be determined by dividing 360 by the number of loop elements  18  in the snare  10 . This results in a configuration where the loop elements  18  cover an entire circle of space when viewed along the axial axis. Therefore, in an embodiment of the snare  10  with three loop elements  18 , the angle between the two straight spoke 30 portions can be about 120 degrees. In some embodiments, the angle α between the straight spoke portions  30  can be greater than as determined using the formula set forth above, which results in an overlap of portions of the loop elements  18  with adjacent loop elements  18 . In some embodiments, the angle between the two straight spoke 30 portions is greater than the value calculated in the formula set forth above, where an angle of about 5 to 15 degrees ensures that there is minimal or no gap about the perimeter of the snare, to form a closed circle. 
         [0105]    In some embodiments, from a transverse view, the large radiused edge portion  26  of the loop element  18  can be angled between about 90 degrees and about 30 degrees relative to the axis of the shaft  12  of the device  10 , as shown in  FIG. 12 . This edge can also be substantially or exactly 90 degrees from the shaft axis, forming a flat, single plane circle when viewed transversely, as shown in  FIG. 13 . 
         [0106]    In other embodiments, from a transverse view, the large radiused edge portion  26  of the loop element  18  can be angled at an angle β that is from about 5 to 45 degrees relative to the longitudinal axis L of the shaft  12  of the device  10 , as shown in  FIGS. 3A and 12 . Such a configuration where the radiused edge portion  26  is angled less than 90 degrees results in a propeller like configuration where the loop element  18  has a pitch and axial reach both proximal and distal the end of the shaft  12  and/or sheath  22 . As illustrated in  FIG. 12 , the loop element  18  has a portion proximal to the distal most portion of the shaft and a portion distal to the distal most portion of the shaft, as shown by the dotted line which divides loop element  18  into the proximal portion  18 A and the distal portion  18 B. In addition, the propeller configuration can result in the opening of the loop elements  18  being oriented in both a plane transverse to the snare axis and a plane parallel to the snare axis. 
         [0107]    In these embodiments, the axial deployment length at full deployment of the loop elements  18  is relatively short when compared to some prior art devices which resemble the intermediate deployment configuration illustrated in  FIG. 1F  for some embodiments. A long axial deployment length can be beneficial in some situations, such as capturing a guide wire that is oriented generally transversely to the snare  10 , or capturing a retrieval element on a foreign object when the retrieval element is located at or near the center of the lumen. A short axial deployment length can be beneficial in other situations, such as capturing a retrieval element that is located at or near the periphery of the lumen. In some embodiments, loop elements  18  with a long axial deployment length can inadvertently capture structural elements on the foreign object, such as frame anchors on a filter, rather than the retrieval element which is specifically designed to be engaged by the snare. When a structural element such as a frame anchor is captured instead of the retrieval element, the filter may not be able to be withdrawn into the sheath  22  and be removed. In addition, the loop elements  18  may get tangled up with the frame anchors and other structural elements more easily when the axial length is long. This can be a problem with some prior art devices, such as the EN Snare® retrieval device, which has a long axial reach. For at least these reasons, a short deployment length can be advantageous over a long deployment length in certain situations. In some embodiments, the axial deployment length of the loop elements  18  can be less than the distance between the retrieval element and the support member or anchor of the filter, thereby reducing the likelihood that the loop elements  18  will inadvertently engage the anchors on the support members. In some embodiments, the axial deployment length of the loop elements  18  can be less than the distance between the retrieval element and the support member crossover or the material capture structure of the filter. In some embodiments, the axial deployment length of the loop elements  18  can be less than the distance between the retrieval element and any structure on the filter in which the loop elements can get entangled with or that interfere with the function of the loop elements  18 . 
         [0108]    In addition to the axial deployment length, loop elements of prior art devices lack substantially complete circumferential apposition with the vessel wall, which makes it difficult to retrieve objects near the periphery of the blood vessel lumen. In contrast, embodiments of the snare disclosed herein achieve substantially complete circumferential apposition which facilitates retrieval of objections, such as retrieval elements on filters, that are located near the periphery of the blood vessel lumen. 
         [0109]      FIGS. 5A and 5B  illustrates an embodiment of a loop element  18  made of four round wires, which are tightly gathered in a twisted configuration, where two of the wires are of shape memory nickel titanium wire, and two of the wires are of a radiopaque platinum wire. The diameters of the wires can be about 0.004″ each. The wires are tightly wound together, and then formed into a loop shape. In some embodiments, the loop outer radius is angled such that the span of the radius is at angle of between about 45 degrees and 90 degrees, relative to the axis of the shaft.  FIGS. 6A and 6B  illustrates a similar embodiment of a loop element  18  made of four wires, except that the wires are braided together rather than twisted together to form the loop element  18 . 
         [0110]    One alternate embodiment of the device  10 , illustrated in  FIGS. 7-10 , includes a series of loop element structures  18  mounted in a substantially circular geometry when viewed along the longitudinal axis. In some embodiments, the loop elements  18  extend substantially transversely with respect to the longitudinal axis. In some embodiments, the outer circular perimeter defined by the loop elements  18  is substantially continuous and does not have gaps. In some embodiments, the overlap  31  between the loop elements  18  is as described above for FIG.  1 A, where the overlap  31  covers a pie shaped region that extends from the outer circumference of the loop elements to the center where the loop elements are attached to the shaft. In other embodiments, the overlap  31  between the loop elements  18  can change as the loop elements  18  are further extended out of the sheath. For example, as shown in  FIG. 10 , the loop elements  18  can have an overlap  31  that occurs over approximately the middle to distal portion of the loop elements  18 . As illustrated in  FIG. 10 , the overlap  31  begins at crossover points  33  between the spokes  30  of the loop elements  18 . In some embodiments, as the loop elements  18  are retracted back into the sheath, the crossover points  33  move closer towards the center, until the crossover points merge into the center, resulting in an overlap configuration similar to that illustrated in  FIG. 1A . In addition to the variable overlap regions, the embodiment illustrated in  FIG. 10  has interior gap portions  35  between the loop elements. These interior gap portions  35  extend radially inwards from the crossover points  33 , and can decrease in size and disappear as the loop elements  18  are retracted back into the sheath. In these embodiments, the loop elements  18  can have a radial span that can be defined by the angle α, and an overlap with a span L 1 , similar to that described above for  FIG. 1A . In these embodiments and in others, the overlap portions can also act as additional snaring portions which increase the likelihood that a portion of the device engages the object to be retrieved. 
         [0111]    In some embodiments, the loop elements  18  can be attached to a shaft  12  via a swaged or crimped hypo tube  20 . These loop elements  18  can be made of two or more wires, including at least one Nitinol wire and at least one platinum wire. As illustrated in  FIGS. 7-10 , in some embodiments the most distal part of the device  10  can be the loop elements  18  because the device  10  does not have a distally extending control member that can be found in some prior art devices, such as the grasping device disclosed in U.S. Pat. No. 7,753,918. In some embodiments, the presence of a control member may interfere with retrieval of the foreign object, such as a filter, by getting entangled with the filter, making it advantageous for some embodiments to not have a distally extending control member. In some embodiments, the loop elements  18  can be angled or have a pitch with respect to the longitudinal axis. 
         [0112]      FIG. 11  illustrates another embodiment of the snare  10  where the loop elements  18  are attached to the shaft  12  with a wire coil  21 . In some embodiments, the wire coil  21  can be a separate wire that can be wrapped around the proximal portions of the loop elements  18 . In other embodiments, the proximal portions of the loop elements  18  can be wrapped around the distal end of the shaft  12  in order to form the wire coil  21 . As additionally shown in  FIG. 11 , the loop elements  18  can extend axially, or in other words, have an axial depth, D 1 , that can be between about 1 to 10 mm. This axial reach allows loop elements  18  to effect capture of an object, such as a retrieval element of a filter, via rotation about the longitudinal axis of the snare. In some embodiments, the axial depth, D 1 , is less than the distance between a retrieval element on a filter and the closest anchor to the retrieval element, as further described below. 
         [0113]    Another alternate embodiment, as illustrated in  FIGS. 13-15 , utilizes a twisted strand shaft  12  made of four 0.010″ Nitinol wires. This shaft  12  is attached to twisted strand loops elements  18  using a hypo tube  20  using silver solder, for example. After full deployment, the loop elements  18  form a substantially circular geometry which is in a single plane typically 90 degrees from the axis of the shaft  12 . In some embodiments, as illustrated, the loop elements  18  extend both transversely and axially with respect to the longitudinal axis of the shaft  12 , forming a cone-like structure with a circular base defined by the distal edge portions of the loop elements  18 . The axial reach, D 2 , or extension of the circular portion past the distal end of the shaft can vary and can depend on and be less than, for example, the distance between the retrieval element and a particular filter structure, such as an anchor, support member, support member crossover, or material capture structure of the filter, as further described herein. The axial reach, D 2 , can be between about 1 to 10 mm. In addition, the loop elements  18  can a region of overlap  31  and can have a radial or circumferential span defined by the angle α, as described above with reference to  FIGS. 1A and 4 . 
         [0114]    In some embodiments, this design offers several key features and capabilities, for example: 
         [0115]    1. Loop Design 
         [0116]    The design of the loop elements allows for deployment in different size lumens, and can conform to variations in lumen anatomy such as tapering, curvature, and angulations. This conformance feature can also enable the device to achieve full radial apposition with the target lumen regardless of lumen diameter or circularity. The loop configuration allows the device to catch a foreign object no matter where the object is located within the luminal space, since the loops reach full radial apposition within the lumen. The design of the elements allows the snare to fit into a very small guiding sheath, facilitating navigation through tortuous anatomies. The angled design of the loop radius allows the device to have axial reach both distal and proximal to the point where the loops are attached to the shaft, enabling the loops to locate foreign objects with minimal forward and backward axial manipulation of the device by the user. The non-angled design of the loop radius allows the device to have a flat, single plane circle geometry, enabling the loops to locate foreign objects with which may be against the vessel wall or partially embedded in the vessel wall. The loops can be made radiopaque, which allows visualization of the loop under fluoroscopy. Additionally, each individual loop element can employ a single or plurality of radiopaque markers such that each loop element has a different quantity of radiopaque markers, or a different pattern of radiopaque markers, to allow the operator to visually differentiate and identify each loop element fluoroscopically. 
         [0117]    2. Shaft Design 
         [0118]    The diameter and mechanical properties of the shaft, such as tensile strength, stiffness and/or elasticity, allows the user to manipulate the loops easily, by transferring axial and torsional motion from the proximal end of the device down to the distal end of the device. The diameter of the shaft allows for it to fit within a small diameter guiding sheath. The diameter of the shaft provides tensile support and strength to allow for high forces that may be required for removing a foreign object from the human anatomy. The shaft can be either solid or hollow, allowing the passage of devices, such as a guidewire, through the shaft. The shaft can be of a single element such as a wire, or a construction of a plurality of elements which are braided or stranded together. The shaft can be of a radiopaque material, to facilitate fluoroscopic visualization. 
         [0119]    3. Hypo Tube Design 
         [0120]    The inner diameter of the hypo tube allows the loop wires and shaft wire to fit snugly within the inner diameter, to facilitate mechanical swaging, soldering, or crimping of said hypo tube, mechanically locking the elements together. The outer diameter of the hypo tube provides adequate wall thickness to allow mechanical swaging or crimping of the hypo tube to provide a strong mechanical attachment, without cracking the hypo tube. The hypo tube can be of a radiopaque material, to facilitate fluoroscopic visualization. Additionally, the hypo tube can be radially shaped into a non-circular shape, such as but not limited to a hexagon or square or rectilinear shape, to further facilitate mechanical fit and locking of the shaft and loop elements. 
         [0121]    In some embodiments, the fundamental design elements which achieve these features include, for example: (1) a plurality of loop elements, which are attached to a shaft via a hypo tube; (2) loops which are designed to be flexible and radiopaque; (3) loops which can be collapsed within a guiding catheter, and deployed outside of the guiding catheter; (4) loops which can reach full circular apposition within the luminal space in a human body; (5) loops which are attached to a shaft distally, which extend laterally towards the wall of the vessel of a human body; (6) loops which are angled relative to the axis of the shaft, typically less than 91 degrees and typically greater than 1 degrees; (7) loops which employ an attachment that is typically a crimped or swaged hypo tube; (8) a shaft which is attached to the loops; (9) a shaft having a diameter allows it to fit within a small diameter guiding catheter; (10) a shaft which can be either solid or hollow; (11) a shaft made of a material which can be polymeric, or can be of a metal such as but not limited to nickel titanium; and (12) a shaft having a length designed to enable the user to position the loops at a desired location to remove a foreign object from a human body. 
         [0122]    In some embodiments, the snare device  10  is designed for placement into a guiding sheath  22 , being advanced through said sheath  22 , deploying near a foreign object located within the human anatomy, capturing said object, and removing the object from the human anatomy. The shape of the loop elements  18  allows them to conform to the diameter of the vessel in which they are deployed into, allowing easier capture of the foreign body with less manipulation. 
         [0123]    The device  10  enables a user to capture a foreign object located within the human anatomy, grasp said object in a controlled manner, and retrieve and remove said object from the human anatomy. Examples of foreign objects which might be removed from the human anatomy include implants such as stents, filters, and valves, and organic objects such as kidney stones or calcified emboli. For example, a snare  10  can be used to capture a vena cava filter and pull it into a retrieval sheath  22  for removal from the patient. 
         [0124]      FIGS. 16-19  illustrate embodiments of methods of using any of the snares  10  disclosed herein. As shown in  FIG. 16 , the snare  10  can be advanced through one or more retrieval sheaths  22  and up to the site of a deployed filter  40 , which, for example, can be located within the lumen  46  of a blood vessel  48 . In some embodiments, the snare  10  can be pre-loaded into a sheath  22  which can be inserted into the patient via a minimally invasive procedure, such as a percutaneous insertion technique. In some embodiments, the distal end  24  of the sheath  22  can be advanced to or proximally to the retrieval element  42  of the filter  40 . In some embodiments, the distal end  24  of the sheath  22  is advanced just past, i.e. just distal, the retrieval element  42 , taking care to avoid advancing the distal end  24  into the other elements of the filter  40 , such as the filter portion  44  or anchors  50  on the filter frame  52 , which would indicate that the distal end  24  had been advanced too far. In some embodiments, the distal end  24  is advanced to a location distal the retrieval element  42  and proximal the anchors  50  closest the retrieval element  42 . In some embodiments, the sheath  22  includes a radiopaque marker  54  located near the distal end  24  of the sheath  22  that facilitates alignment of the distal end  24  with respect to the filter  40 . For example, the operator can align the radiopaque marker on the sheath  22  with the radiopaque retrieval element  42  of the filter  40  under fluoroscopy, which results in the distal end  24  of the sheath being correctly positioned for loop element  18  deployment, which in some embodiments as described herein is located between the retrieval element  42  and the anchor  50  closest to the retrieval element. 
         [0125]    As illustrated in  FIG. 17 , the snare  10  is then deployed into the vessel  48 . As described above, deployment of the snare  10  can include three deployment phases. In some embodiments, deployment of the snare  10  can include less than three deployment phases, such as one or two deployment phases, while in other embodiments, deployment of the snare  10  can include more than three deployment phases.  FIG. 17  illustrates full deployment of the snare  10  into the vessel  48  with the loop elements  18  in a propeller-like configuration that provides some axial reach both proximal and distal to the distal end  24  of the sheath  22 . In some embodiments, the axial reach in the distal direction can be less than the distance d between the retrieval element  42  and anchor  50 , thereby reducing the likelihood that the loop elements  18  become entangled with or caught on the anchor elements  50  of the filter during loop element  18  deployment and manipulation. In some embodiments, the distance d can be between about 5 to 20 mm The region between the retrieval element  42  and the anchor  50  forms a zone of action in which the loop elements  18  can be deployed and manipulated to effect capture of the retrieval element  42 . In some embodiments, the loop elements  18  can have a pitch like the blades of a propeller such that the openings of the loop elements  18  are oriented in both a plane transverse to the snare  10  axis and a plane parallel to the snare axis. This allows the loop elements  18  to capture the retrieval element  42  either by moving the loop elements  18  axially in a proximal or distal direction or by rotating the loop elements  18  about the snare axis. In some embodiments, the loop elements  18  are deployed distal the retrieval element  42  and proximal the support member of the filter, such that the loop elements  18  achieve substantial apposition with the full circumference of the lumen wall, which is advantageous for capturing retrieval elements located near the periphery of the lumen. The deployed loop elements  18  can be withdrawn or retracted proximally to engage the retrieval element. 
         [0126]      FIGS. 18-19  illustrate the loop element  18  engaged with the retrieval element  42  of the filter  40  and the subsequent collapse of the filter  40  into the sheath  22 . After the retrieval element  42  is secured, the snare  10  is held under tension while the sheath  22  is advanced over the filter  40 , thereby collapsing the filter  40  into the ID of the sheath  22 . In some embodiments using both an inner sheath  22  and an outer sheath, the retrieval element  42 , and optionally a portion of the filter  40 , is first retracted or pulled into an inner sheath  22 , in order to secure the filter  40  to the snare  10  and to prevent or reduce unfurling of the tail portion of the filter  40 , before the outer sheath is advanced over the rest of the filter  40 . 
         [0127]    As the sheath  22  is advanced over the filter  40 , the flexible distal tip portion  32  of the sheath  22  can expand and invert over the filter  40 , providing a ramp in which the filter  40  can be drawn into the sheath  22 . In some embodiments, the inversion of the distal tip portion  32  can be initiated by contact with specific structures on the filter, such as the retrieval element and/or anchors on the filter frame. In some embodiments, the snare  10  can be retracted in the proximal direction while the sheath  22  is advanced in the distal direction to capture the filter  40  within the sheath  22 . In other embodiments, the snare  10  can be retracted in the proximal direction while the sheath  22  is held relatively immobile, i.e. neither advanced nor retracted, to capture the filter  40  within the sheath  22 . In some embodiments, the entire filter  40  can be retracted into or captured by the inner sheath. 
         [0128]    Another example is the use of a snare  10  to grasp and extract loose kidney stones from a patient&#39;s kidneys. The snare  10  is advanced through one or more sheaths  22 , up to the site of the loose kidney stone. The snare  10  is then deployed and engaged with the stone. Next, the snare  10  is pulled into the sheath  22 , or the sheath  22  advanced over the snare  10 , drawing the stone into the distal ID of said sheath  22 . 
         [0129]    As described above, the retrieval system can include a plurality of different components, such as a guide wire, a snare  10 , an inner sheath and an outer sheath  22 . The proximal ends of these components are generally located outside the patient&#39;s body so that the operator can manipulate each of the components by grasping the proximal portion of the components and moving the component in a proximal or distal direction. Often, the proximal portions or ends of the components are or can be reversibly secured or fixed to one another in a proximal handle portion, using a rotatable or twist fitting, such as a luer lock, for example. Because one hand of the operator is often used to manipulate the component, only one hand is free to disconnect or connect the fittings, which can be difficult to do for a rotatable luer lock fitting. In addition, the twisting or rotation of the twist fitting can lead to unintentional and undesired twisting or rotation of the snare device. 
         [0130]    Therefore, it would be advantageous to provide fittings that can more easily be manipulated with one hand, such as a snap fitting, as illustrated in  FIGS. 20-22 . The snap fitting  100  comprises a female connector  102  and a male connector  104 . In some embodiments, the female connector  102  can have a plurality of flexible latch portions  106  that define an opening  112  and enclose a receptacle  108  that is configured to receive the male connector  104 . For example, the female connector  102  can have 2, 3, 4 or more latch portions  106 . The distal end of each flexible latch portion  106  can include a retaining feature  110  that projects radially inwards and functions to secure the male connector  104  within the receptacle  108 . The male connector  104  comprises a distal portion  114  that is configured to fit through the opening  112  and within the receptacle  108 . The male connector  104  can also include a narrow stem portion  116  that has a diameter less than the diameter of the opening  112 . In some embodiments, the distal portion  114  and/or the latch portions  106  can be tapered towards the outer or inner edge in order to present an angled surface to the opening  112  that can aid in widening the opening  112  by pushing apart the latch portions  106 . 
         [0131]    These snap fittings  100  can be integrated into the proximal ends of the various components described herein, and well as other components that can be used with the retrieval system. Alternatively, the snap fittings  100  can be made into luer lock adaptors, or other connector adaptors such as screw adaptors, that allow the operator to convert a luer lock fitting, or other fitting, into a snap fitting, as illustrated in  FIGS. 20-22 . In some embodiments, the device can include an outer catheter with an outer catheter hub and an inner catheter with an inner catheter hub. The female connector  102  of the snap fitting  100  can include a locking feature  118 , such as a luer lock fitting, that allows it to reversibly attach to the inner catheter hub. The outer catheter hub can include the male connector  104 , which can be integrated into the outer catheter hub as illustrated, or can be reversibly attached as described above for the female connector  102 . In some embodiments, all the components are locked together during insertion. 
         [0132]    In some embodiments, the proximal gripping portions of the components can include an indicator that identifies which component the operator is gripping, thereby reducing the confusion that can occur in locating the corresponding proximal gripping portion for the desired component. In some embodiments, the gripping portion can include a visual indicator. For example, the different components can have color coded gripping portions, or can be labeled with, for example, an easily read symbol or the name of the component. In some embodiments, the gripping portion can include a tactile indicator that allows the operator to distinguish between the different components without having to look at the gripping portions, which allows the operator to maintain visual focus on more important matters, such as real-time imaging of the retrieval system within the patient provided through fluoroscopy. For example, one component can have a smooth gripping portion, another component can have a rough or knurled gripping portion, and another component can have a dimpled or ridged gripping portion. Each component can have a different tactile pattern to provide tactile contrast between the components. 
         [0133]    In some embodiments, the snare handle portion can include snare deployment indicators, such as detents, that allow the operator to easily identify and achieve the different stages of snare deployment described above. For example, the operator can deploy the snare using the snare handle until the snare handle reaches a first indicator, which signifies that the snare is deployed in the first deployment stage. The operator can then further deploy the snare using the snare handle until the snare handle reaches a second indicator, which signifies that the snare is deployed in the second or intermediate deployment stage. Then the operator can further deploy the snare using the snare handle until the snare handle reaches a third indicator, which signifies that the snare is fully deployed. In some embodiments, there is a snare deployment indicator for each stage of snare deployment. 
         [0134]    While described in various embodiments for retrieval of filters and other medical devices and objects, the sheath and snare designs may also be used to retrieve other filter devices, other embolic protection devices, and other objects. For example, filter devices and other devices described in commonly assigned, and concurrently filed U.S. Provisional Patent Application Ser. No. 61/586,661 (Attorney Docket Number 10253-701.102) is incorporated herein by reference in its entirety and for all purposes. 
         [0135]    It is understood that this disclosure, in many respects, is only illustrative of the numerous alternative filtering device embodiments of the present invention. Changes may be made in the details, particularly in matters of shape, size, material and arrangement of various filtering device components without exceeding the scope of the various embodiments of the invention. Those skilled in the art will appreciate that the exemplary embodiments and descriptions thereof are merely illustrative of the invention as a whole. While several principles of the invention are made clear in the exemplary embodiments described above, those skilled in the art will appreciate that modifications of the structure, arrangement, proportions, elements, materials and methods of use, may be utilized in the practice of the invention, and otherwise, which are particularly adapted to specific environments and operative requirements without departing from the scope of the invention. In addition, while certain features and elements have been described in connection with particular embodiments, those skilled in the art will appreciate that those features and elements can be combined with the other embodiments disclosed herein.