the following description of the preferred embodiments of the present invention is intended to be merely illustrative in nature , and as such , is not intended to limit in any way the present invention , its application , or uses . numerous modifications may be made by those skilled in the art without departing from the true spirit and scope of the invention . for example , the preferred embodiments of the present invention are shown in use in a vein but may also be used in other body passages . now referring to fig1 - 3 , a preferred embodiment of a medical filter of the present invention is shown and indicated generally by the numeral 10 . filter 10 is made of a resilient material which tends to expand to the form illustrated in fig1 but can be compressed to a smaller diameter form as shown in fig2 where filter 10 is shown inside a suitable delivery catheter 12 . fig3 shows filter 10 in place in a vein . filter 10 has a body 14 which extends generally along the longitudinal axis of filter 10 and which carries a plurality of radially and axially extending struts 16 and 18 . struts 16 combine to define a first filter basket 20 and struts 18 combine to define a second filter basket 22 . a first collar 24 with retrieval hook 26 attached thereto is located at one longitudinal end of filter 10 . a second collar 28 with retrieval hook 30 attached thereto is located at the other longitudinal end of filter 10 . filter 10 is symmetric in form although it will be appreciated by those skilled in the art that asymmetric forms of filter 10 are within the broad scope of the present invention . for example filter 10 may have more or less struts 16 than struts 18 and filter 10 may have a retrieval hook at one end but not the other end thereof . it is , however , preferred that filter 10 is symmetrical and has retrieval hooks at both ends to allow it to be retrieved using a snare either from a femoral or jugular approach . each strut 16 is attached to body 14 at a first end 32 thereof and is formed so as to extend , when not compressed , first generally axially along body 14 and then after bend 34 generally radially outwardly from body 14 for a distance slightly greater than the radius of a vena cava of intended use . the end portion 36 of each strut 16 is bent back slightly towards body 14 so that end 38 of strut 16 is radially inward with respect to bend radius 40 . filter 10 may be made of any suitable material using a variety of methods . nitinol and stainless steel are examples of suitable materials but other materials may be used so long as the material has the desired characteristics of strength , resilience , flexibility , biocompatibility and endurance and is suitable for the particular manufacturing technique employed . it is , of course , required that the material employed be capable of expanding to the desired shape upon ejection from the delivery catheter . thus , the material must also be sufficiently resilient to accomplish both compression in the delivery catheter and expansion upon ejection from the catheter . suitable methods of manufacture include cutting a pattern into a tube to enable expansion of the tube into the desired body and struts . another suitable method is forming the struts and body from separate strips or wires and then joining the respective parts together by suitable methods which are well known in the art . having described the structure of filter 10 , a preferred embodiment of the present invention , further understanding of the unique character and advantages of the present invention will be had by an understanding of its use . now referring to fig2 - 6 , filter 10 is intended to be initially deployed in the lumen 50 of a delivery catheter 12 as shown in fig3 . insertion of filter 10 into delivery catheter 12 can be by any conventional method including by simply pushing filter 10 into the lumen at the distal end of a delivery catheter . alternatively , filter 10 may be inserted into the proximal end of a delivery catheter and pushed by means of a push wire or the like to the distal end of the catheter . emplacement of filter 10 is illustrated in fig4 . as shown in fig4 , delivery catheter 12 carrying radially compressed filter 10 in lumen 52 at distal end 54 of catheter 12 is inserted along body vessel 56 in a patient until distal end 54 is near the desired site for treatment . catheter 12 may be inserted using either a femoral approach or a jugular approach . a push wire ( not shown in the figures ) may be used to eject filter from lumen 52 by pushing filter 10 in the direction indicated by arrow 58 . as filter 10 is ejected , arms 16 expand radially outwardly until bend radius 40 of arm 16 contacts wall 60 of vessel 56 . after arms 16 are deployed , delivery catheter 12 is withdrawn slightly in the direction indicated in fig4 by arrow 62 whereupon filter 10 is completely ejected from lumen 52 and arms 18 expand into contacting relationship with wall 60 of vessel 56 and assume an operative filtering position within vessel 56 as is best illustrated in fig5 . once emplaced in a body passage such as a vein and now referring to fig2 , filter 10 has struts 16 and 18 with ends 38 positioned proximal to wall 60 of vessel 56 but spaced therefrom so as to avoid piercing into vessel wall 60 and also to minimize any encapsulation by tissue growth . in operation , filter 10 provides a first filter basket 20 and a second filter basket 22 with basket openings facing each other so that the particular orientation of filter 10 with respect to flow of blood is not important . furthermore , filter 10 as retrieval hooks 26 and 20 at opposite ends so that filter 10 can be retrieved from either direction . while filter 10 is suitable for permanent placement in vessel 56 , filter 10 may be readily removed or retrieved from vessel 56 if retrieval is desired . as is shown in fig5 and 6 , the retrieval of filter 10 may be accomplished by means of a retrieval catheter 62 which may be inserted from either the femoral or jugular direction . after snaring retrieval hook 30 with snare 64 of retrieval catheter 62 , filter 10 is drawn into lumen 66 of retrieval catheter 62 as shown in fig5 whereupon struts 18 come into contact with distal end 68 of retrieval catheter 62 which contacting relationship urges the loose ends of struts 18 radially inwardly as shown in fig6 . pulling of filter 10 rightward as shown in fig5 results in struts 16 reversely bending to the positions shown in fig6 . further pulling of filter 10 into lumen 66 results in distal end 68 of retrieval catheter 62 coming into contact with struts 16 to urge struts 16 radially inwardly . struts 16 thus are inverted as they are bent by the force exerted by end 68 of retrieval catheter 62 in a leftward direction as viewed in the figures and are ultimately bent radially inwardly as shown in fig6 . because struts 16 and 18 have free ends 38 , they may be bent as shown in the figures to radially collapsed positions which can be compressed within lumen 66 for ready withdrawal from vessel 56 . now referring to fig7 , an alternative preferred embodiment of a filter of the present invention is shown and indicated generally by numeral 100 . filter 100 is similar in construction to filter 10 . but has a spine 114 with serpentine end rings 124 and 126 . both spine 114 and serpentine end rings 124 and 126 compress radially for insertion into the lumen of a delivery catheter but expand to a relatively greater radius when deployed as shown in fig8 . filter 100 is well adapted to be made from a tubular material by cutting the respective parts therefrom . retrieval of filter 100 is analogous to retrieval of filter 10 . fig8 shows another alternative embodiment of a filter of the present invention which is indicated generally by the numeral 200 . filter 200 is a cross - over design wherein struts 216 and 218 extend from spine 214 initially in a generally circumferential direction . fig9 shows filter 200 in a deployed state . filter 200 is substantially equivalent to filter 10 in filtering efficiency . and retrieval of filter 200 can be done in a manner analogous to retrieval of filter 10 . however , during retrieval , the somewhat circumferential orientation of struts 216 and 218 is advantageous because retrieval into the lumen of a retrieval catheter can be achieved with a greater bending radius of the struts as is illustrated in fig9 and 10 . this feature allows use of a lumen with a small diameter because the cross - over design minimizes the size of the filter during retrieval . the filter size of filter 10 during retrieval is determined by the bend radius of struts 16 . the filter size of filter 200 during retrieval is reduced by the difference between the bend radius of the strut and the diameter of the end ring . a filter made in accordance with the present invention is retrievable at any time following implantation and may be retrieved from either femoral or jugular approaches . the cross - over design of the preferred embodiment shown in fig8 further reduces the size of the filter during retrieval . the filter has the clot capture efficiency of a double - basket filter . while preferred embodiments of the present invention have been specifically described above , it will be appreciated by those skilled in the art that the present invention is subject to variations and modifications . for example , the filter may be cut from a single tube and have end rings which are integral , i . e ., one piece , with the spine and struts . the end rings may be tubular or cut into a serpentine pattern to allow the end rings to expandable to a larger diameter and subsequently compressible to a smaller diameter . this feature allows for very low profile filters when in the compressed state — an obvious advantage for insertion and removal . of course , the filter may be tube - based or wire based or a combination .
a retrievable medical filter which can be placed in a blood vessel or other body passage . the filter has improved structural features for enhancing its filter effectiveness and to facilitate its retrieval from the body passage . the filter has a longitudinal spine with struts extending from each longitudinal to form filter baskets . the ends of the spine to which the struts are attached may be rings with serpentine cuts in the rings to make them expandable . the struts can extend circumferentially as well as radially outwardly to provide a structure which can be radially compressed without bending the struts in a tight radius .