fig1 is a fragmentary section through a human body from left to right and illustrates a medical procedure of installing the thrombosis filter in the inferior vena cava and removal of the filter by percutaneously entering the venous system at the jugular vein and withdrawing the filter . this illustrates the body 10 with a cutaway portion 12 that exposes a portion of the vascular system . the femoral vein 14 leads to the external iliac vein 16 . the common iliac vein 18 leads to the inferior vena cava 20 . as illustrated at the cutaway section 22 , a filter 24 is dispersed within the inferior vena cava and is held in place by the structure that will be described . as shown , a catheter tube is inserted at incision 28 into the venous system . as it extends toward heart 30 , it reaches the inferior vena cava 20 and the filter 24 is deployed . the distal end 32 of the catheter structure 26 is shown after deployment of the filter 24 . for withdrawal or removal of filter 24 , a recovery mechanism ( 36 ) is inserted in the jugular vein 38 at incision 40 and passes through an atrium of heart 30 until its distal end 42 enters the inferior vena cava 20 . the recovery mechanism is not shown in detail in this figure , but will be described in detail below . fig2 is a side cutaway view of a filter in a relaxed position . the filter 44 has a plurality of shaped filtering elements 46 , each having a mounting end 48 and a wall engaging end 50 . projections 52 have a length sufficient to engage an associated vein wall ( not shown ) while being short enough so the vein will not be pierced . connecting structure 54 has a frustum shaped end 56 that fixedly attaches the mounting ends 48 . structure 54 defines a longitudinal cavity 58 within which mounting member 60 is slidably retained . a plurality of flexible anchoring struts 62 are mounted on mounting member 60 and project outwardly to wall engaging surfaces 64 . projections 66 function to position and hold the filter 44 in position when engaged to an inner vein wall . a hooking element 68 is affixed to mandrel 70 . an end 72 of mandrel 70 is affixed within the connecting structure 56 . a tubular member 74 has one end affixed to a pushing structure 76 and a second end 78 mounted in the mounting member 60 . tubing 74 surrounds a mandrel 70 and is coaxially aligned therewith . in the relaxed state , the length l 1 from projection 52 to projection 66 is in the order of 2 . 0 inches . the length l 2 of the joining member 54 is about 0 . 4 inch . the tip - to - tip length l 3 is in the order of 1 . 25 inches , and the projection - to - projection distance l 4 is in the order of 1 . 2 inches . various configurations and geometries will be described below , it being understood that when deployed , the filtering portion shown at dashed line 78 will function to restrict the flow of blood clots or thrombosis when blood is flowing in the direction of arrows 80 . at the same time , positioning and holding portion 82 will restrict longitudinal and transverse movement of the filter 44 within the associated lumen or vein . holding portion 82 preferably centers the device within the lumen . fig3 is a partial perspective view of the vein engaging end of a filter leg member . the end member 50 has a generally curved structure and is flattened to a desired dimension such that the under surface 84 will slidably engage an associated vein wall . the thickness is selected for the desired flexibility . an outward projection 52 is arranged for engaging the vein wall . a similar configuration is utilized for the anchoring elements . fig4 is a side view of a ribbon wire leg member . the filter member 46 has the mounting end 48 positioned at a predetermined angle to the longitudinal arrangement of the member 46 . at its other end , the curved portion 84 deflects in the opposite direction and has projection 52 . fig5 is a cross - sectional view taken at line 5 — 5 in fig4 . in one configuration , the flat wire has a thickness t 1 of about 0 . 006 inch and a width w 1 of about 0 . 026 inch . it is , of course , understood that differences in thickness relative to width will effect the flexibility of the element . fig6 is a side view of a round leg member . again , the leg member has a deflection 48 ′ and has an upper thickness t 2 that can be in the order of 0 . 016 inch . the lower portion has a reduced cross section with a thickness t 3 in the order of about 0 . 006 inch . fig7 is a cross - sectional view taken at line 7 — 7 in fig6 . it illustrates the extent of deflection of portion 48 ′. fig8 is a plan view of a serpentine shaped leg member . as illustrated , serpentine section 86 is provided to yield an improved filtering function when used in combination with other filter members . fig9 is a plan view of a spiral shaped leg member . in this alternative embodiment , a spiral portion 88 is utilized to enhance the filtering operation . fig1 is a partial perspective view taken at line 10 — 10 in fig9 . it illustrates the spiral portion 88 . the design of serpentine portion 86 or spiral portion 88 will be selected in accordance with the number of the filter elements used , the overall size of the filter 44 , the attributes of the lumen in which it will be installed , and the flow of blood being filtered . fig1 is a side cutaway view of a filter positioned in a lumen about to be engaged for removal . it will be noted that the positioning portion 82 and the filtering portion 78 have their respective members deflected within the confines of vein 90 . as deflected , the curved engaging portions 50 are brought in contact with the inner wall 90 , as are contact portions 64 of the positioning portion 82 . this arrangement provides for the vein walls 90 to provide adequate tension on the positioning portion 82 and the filtering portion 78 to cause the projections 52 and 66 to engage the inner wall without piercing the inner wall . a filter recovery mechanism 92 is inserted in the direction of arrow 94 until a grasping mechanism 96 is brought in proximity to hooking element 68 . snare 96 is a looped cord or wire that can be externally manipulated to engage mandrel 70 behind the hooking element 68 . in one configuration , the hooking element 68 and the grasping mechanism 96 can be constructed of materials that can be tracked fluoroscopically . fig1 is a side cutaway view of a filter positioned in a lumen having the positioning portion collapsed for removal . when the extensible gripping device 96 engages members 68 , it can be utilized to hold member 68 in a relatively fixed longitudinal position . when thus arranged , actuating device 98 is moved in the direction of arrow 100 to engage element 76 to thereby force tube 74 to move along mandrel 70 and cause the positioning portion 82 to collapse . mounting element 60 is moved within cavity 58 to effect the collapse , and cause the positioning elements to be substantially parallel aligned along the longitudinal axis . fig1 is a side cutaway view of a filter positioned in a lumen having the positioning portion enclosed within a recovery mechanism . once the positioning portion 82 has been collapsed , outer shield 102 is moved in the direction of arrow 104 while the gripping device is held steady . when thus positioned , the outer shield 102 is positioned at end 106 to engage the filtering elements 78 . fig1 is a side cutaway view of a filter positioned within a lumen having the entire filter enclosed within a recovery mechanism and ready for removal . once the positioning portion 82 is enclosed within outer shield 102 , pressure can be applied to the gripping member 96 for moving the gripping member in the direction of arrow 108 . when thus moved , the outer shield 102 is held firm and end 106 functions to collapse filtering portion 78 such that it can be withdrawn within the confines of outer shield 102 . when fully withdrawn within the recovery mechanism 92 , the relatively stiff portion of the recovery mechanism 92 has a length l 5 of about 2 . 77 inches . fig1 is a side cutaway view of another embodiment of a filter in a relaxed position . elements having similar functions will have a similar reference numeral designation . in this embodiment , filtering portion 78 is mounted in mounting structure 110 enjoining member 54 . this configuration eliminates the frustum element 56 and provides additional strength at this structure . a hook 112 replaces the button element 68 . pushing element 76 of fig2 is replaced by a pushing frustum element 114 . this frustum configuration provides an improved blood flow and minimizes turbulence . further , it gives a larger dimension along mandrel 70 such that there is minimization of the tendency to tilt as it is being moved forward as previously described . in this embodiment , dimensions l 2 , l 3 , and l 4 are similar to those described with regard to fig2 . the projection - to - projection length l 6 is in the order of 2 . 1 inches , while the tip - to - tip length l 7 is in the order of about 2 . 22 inches . finally , the over - all relaxed length of the filter is designated l 8 , and is about 2 . 68 inches . fig1 is an end view of a joining member taken at line 16 — 16 in fig1 . it illustrates the housing 54 mounting positioning elements 62 , which number four in this configuration , surrounding mandrel 70 which passes therethrough . this figure is expanded and is not in scale . fig1 is an end view of a joining member taken at line 17 — 17 in fig1 . it illustrates the mounting member 110 which is mounted in the connecting housing 54 , and shows six mounting ends 48 of the filtering members . mandrel 70 is affixed in the mounting member 110 . again , this figure is in a different scale to that of fig1 . fig1 is a side cutaway view of yet another embodiment of a filter in a relaxed position . in this embodiment , the mounting element 60 is fixedly mounted within channel 58 substantially adjacent to mounting member 110 . the mounting ends 78 of positioning struts 62 are restrained by the outer limits of housing 54 . a hook 112 is fixedly mounted to mandrel 70 which in turn is secured in mounting element 110 . in this embodiment , housing 54 is shorter than the embodiment illustrated in fig2 and has a length l 9 of about 0 . 265 inch . the overall length l 10 from a projection - to - projection is in the order of 1 . 85 inches , and the length l 11 from the end of mounting member 110 to the filtering portion 78 projections is in the order of 1 . 27 inches . the relaxed spacing of the filtering portion l 12 is in the order of 1 . 2 inches . the releasing and collapsing of the anchoring elements 62 in this embodiment will be described below . fig1 is a side cutaway of the filter of fig1 positioned in a lumen . as shown , positioning portion 82 engages the inner vein wall 90 , as does the filtering portion 78 . when thus contained , the diameter of the lumen or vein l 13 is in the order of 0 . 866 inch . when installed , the overall length l 14 is in the order of 2 . 25 inches , while the tip projection - to - projection length l 15 is in the order of 2 . 11 inches . fig2 is a side cutaway of the filter of fig1 engaged for removal . in this embodiment , a recovery mechanism 120 has a gripping device 122 for engaging hook 112 . when thus engaged , the gripping device can be held firmly externally , and the outer shield 124 extended in the direction of arrow 126 to engage the legs 62 of positioning portion 82 . outer shield 24 can include a funnel shaped end to assist in directing the filter into the recovery mechanism 120 . fig2 is a side cutaway of the filter of fig1 with the positioning portion enclosed within a recovery mechanism . as shown , the recovery mechanism 120 has had the outer shield 124 moved farther in the direction of arrow 126 such that positioning struts 62 have been bent back upon themselves and are within outer shield 124 . as thus positioned , struts 62 are substantially parallel to each other and aligned along the longitudinal axis of the filter and the recovery mechanism 120 . when the positioning portion is thus collapsed and retracted , the outer shield 124 is held stationary and the gripping device 122 is moved in the direction of arrow 128 for drawing the filtering portion 78 into outer shield 124 . when the filtering portion 78 is fully withdrawn within outer shield 124 , the recovery mechanism 120 can be withdrawn from the body . fig2 a - 22e illustrate the deflection and retraction of a flexible anchor member of the type used with the filter of fig1 . in fig2 a , a flexible anchor member 62 is in a holding position on the inner wall of vein 90 . as force is applied in the direction of arrow 130 to the portion of flexible anchor member 62 by the outer shield 124 ( see , fig2 ), the tip 64 and the protrusion 66 are started in a direction to be released from the inner wall 90 . in fig2 b , the force has been applied at arrow 130 to start deflection of flexible anchor member 62 . at this juncture , the protrusion 66 has been removed from inner wall 90 and the tip 64 has started to slide along the inner wall . anchor member 62 can have a predetermined region of greater flexibility to control the location of the deflection caused by the force supplied at arrow 130 . in fig2 c , the force applied at arrow 130 has deflected flexible anchor member 62 such that the end 64 is merely moving along the inner wall surface 90 . in fig2 d , there is an illustration that the force applied in the direction of arrow 130 has proceeded to a point where flexible anchor member 62 has started to bend back upon itself , and the tip 64 is out of contact with the inner wall of vein 90 . finally , in fig2 e , it is shown that force applied in the direction of arrow 130 by the outer shield 124 as bent flexible anchor member 62 back upon itself , such that the outer shield can pass over it . fig2 is a side view of yet another embodiment of a retrievable filter in accordance with the present invention . the filter as shown in fig2 is in a relaxed , uncompressed state . the filter of fig2 is substantially similar to that of fig1 - 22 , except as the description below may vary from that of the embodiment of fig1 described above . the filter of fig2 includes a plurality of filtering elements 146 having wall engaging ends 150 . wall engaging ends 150 as shown in this embodiment are curved to present a rounded convex face to a vessel wall . collectively filtering elements 146 form a filter portion or array 178 . disposed distally of filter array 178 are a plurality of legs or anchoring struts 162 . anchoring struts 162 have proximal and distal ends . a typical distal end is shown in fig2 in detail . the filter also includes a hook 212 to aid in removal of the filter from a vessel . an enjoining member 154 joins filter array 178 , struts 162 proximate their proximal ends and hook 212 together . struts 162 preferably are formed in a ribbon shape , wherein the thickness of the ribbon is shown in fig2 and the width is perpendicular to the thickness , i . e ., directly into the paper . fig2 is a detailed view of the distal end of a strut 162 . the distal end includes a sharpened portion 166 and a pad portion 164 extending distally beyond sharpened portion 164 . sharpened portion 164 is sufficiently sharp to penetrate a vessel wall . pad portion 164 similarly to strut 162 , preferably has a ribbon shape wherein the thickness is shown in fig2 and the width is perpendicular to the thickness , i . e ., directly into the paper . as can be seen in fig2 , the thickness of pad portion 164 decreases distally . the decrease in pad thickness 164 can create an increase in flexibility of pad portion 164 distally . a similar increase in flexibility distally along pad portion 164 can be created by varying the material characteristics of pad 164 . pad portion 164 is preferably flexible enough not to puncture the vessel wall , i . e ., the pad portion 164 is preferably atraumatic . in a preferred embodiment of the present invention , the length of sharp portion 164 is between about 2 to 6 millimeters and the length of pad portion 162 is between about 4 to 20 millimeters . in a preferred embodiment , pad portion 164 is more than twice as long as sharp portion 164 . fig2 and 26 show the filter of fig2 disposed in a vessel a during normal use . the direction of blood flow is shown by arrows b . the removal of the filter would be in the direction indicated by arrow c by way of hook 212 . filter elements 146 are shown moderately compressed in comparison to their relaxed state shown in fig2 . as shown in fig2 , sharp portion 166 is penetrating the wall of the vessel a and pad portion 164 is generally parallel to the wall of vessel a . fig2 and 28 show the filter of fig2 in the process of being removed from vessel a in the direction indicated by arrow c . as the filter is withdrawn using the same procedure as that of the filter of fig1 , struts 162 will deform generally as shown in fig2 a - 22e . strut 162 as shown in fig2 is in the approximate position of strut 62 in fig2 b . as the process continues , strut 162 will assume generally the position shown in fig2 e . the ultimate removal of the filter will be accomplished as described with respect to the filter of fig1 above . fig2 is a detailed view of the distal end of strut 162 as shown in fig2 . although the configuration of strut 162 in fig2 is similar to that of strut 62 in fig2 b , it can be appreciated that the length of pad portion 164 relative to sharpened portion 166 is substantially greater than element 64 is to element 66 of fig2 b , respectively . as can be appreciated the increased length and increasing flexibility of pad portion 164 distally provides an effective cantilever for retracting sharp portion 166 from the wall of vessel a . fig2 is a side view of yet another embodiment of filter 200 in accordance with the present invention disposed within a vessel a . filter 200 has a longitudinal axis d . blood or fluid flow in vessel a is shown in the direction indicated by arrows b . filter 200 includes flexible struts 202 generally extending in the first direction along axis d from a hub 204 , while diverging from axis d . a first end of strut 202 is coupled to hub 204 . second end 206 of strut 202 is preferably sharpened and barbed to engage with the wall of vessel a . filter 200 also includes a strut retraction member 208 . strut retraction member 208 includes a plurality of retraction loops 210 extending from retraction member hub 212 generally in the second direction along axis d . each of loops 210 preferably loops around a strut 202 . a tether connector 214 extends from hub 212 in the first direction along axis d . a telescoping connector 216 connects hub 204 and retraction member hub 212 . various elements of filter 200 such as struts 202 or loops 210 may be formed from nitinol , stainless steel or other biocompatible materials . one skilled in the art would appreciate that the materials described above with respect to the other filter embodiments could advantageously be applied to construct the embodiment 200 as well . fig3 is an end view of filter 200 shown within vessel a . in the illustrated embodiment of filter 200 there are six struts 202 and loops 210 . fig3 is a side view of the filter of fig2 to which a tether 218 having a loop 220 is attached to tether connector 214 . tether 218 is disposed within a catheter 222 having an outer tubular member 224 and an inner tubular member 226 . assuming that , for example , filter 220 is disposed in the inferior vena cava , catheter 222 may be advanced to the filter from a femoral vein access point . outer tube 224 and inner tube 226 are preferably formed from biocompatible materials including polymers known to those skilled in the art . the materials must be of sufficient strength and rigidity or flexibility to accomplish the procedure described below . fig3 is a side view of the filter of fig2 wherein the retraction member 208 is being pulled in the first direction such that loops 210 are advancing along and engaging struts 202 . fig3 is a side view of filter 200 of fig2 wherein inner tube 226 of catheter 222 has been brought into engagement with loops 210 . in dashed lines , inner tube 226 is shown being advanced in a second direction over loops 210 such that struts 202 are brought from a first position engaging the walls of vessel a to a second position adjacent axis d of filter 200 . fig3 is a side view of filter 200 shown in fig2 . in fig3 struts 202 are shown disposed in the second position . second ends 206 of struts 202 have been brought into contact with the distal end of inner tube 226 . fig3 is a side view of filter 200 of fig2 in which filter 200 has been withdrawn into outer tube 224 of catheter 222 . filter 200 could now be removed from the patient through outer tube 224 , or filter 200 and catheter 222 could be simultaneously removed from the patient . it can be appreciated that performing the steps of removal process in reverse would provide a method of placing filter 200 in vessel a as shown in fig2 . in a preferred method , however , hubs 204 and 212 would be spaced as shown in fig2 prior to placement in catheter 222 . after deployment of filter 200 , as shown in fig2 , tether 218 and catheter 222 can be removed from the patient such that filter 200 may remain in place for an extended period of time . from the foregoing , it is understood that various configurations and selection of materials will provide suitable removable filter structures that may be utilized in conformance with the inventive concepts described herein . in general , it is understood that the materials must be suitable for implantation in a human body and will remain intact without adding contaminants to the blood stream . the selection of materials will also determine the flexibility and resiliency of the various members . the various components of the filter can be constructed of a class of elastic materials including nitinol , stainless steel , platinum , tungsten , titanium , and chromium alloys . the shaping and bonding structures are those available in the construction of thrombosis filters of the class described . having described the various embodiments and methods of the invention in conjunction with the drawings , it can be seen that the various stated purposes and objectives have been achieved , and that various modifications and extensions will be apparent to those skilled in the art while remaining within the spirit and scope of the invention . accordingly , what is intended to be protected by letters patent is set forth in the appended claims .
a recoverable thrombosis filter that can be implanted and securely positioned within a vein at a desired location , and can be recovered through an endovenous route even after formation of neointima hyperplasia , is disclosed .