turning now to the drawings , wherein like reference numerals identify similar or like components throughout the several views , a method for retrieving vein filters utilizing a femoral approach is described . in co - pending commonly assigned patent application ser . no . 10 / 899 , 429 , filed jul . 12 , 2004 , various embodiments of filters are described with various structures , e . g . hooks , to facilitate removal . the &# 39 ; 429 application also describes retrieval of the filter through the catheter . being that the retrieval structure of the filters is at the cranial end , the method of the present invention provides a way to retrieve those filters from the inferior vena cava , as well as other filters with retrieval hook or structure on the cranial end , utilizing a femoral approach . turning initially to fig1 , the retrieval catheter or sheath 10 of the present invention has a body 12 and a distal tip 14 . the distal tip 14 has a curved shape as shown in fig2 ( the straightened shape is shown in phantom ). the curved shape is the normal condition of the catheter tip 14 and the curve shown is about 180 degree turn although other curves are also contemplated . the curved catheter tip 14 is sufficiently flexible to be straightened by insertion of dilator 20 through lumen 16 as shown in fig1 . the retrieval method is illustrated by the method steps of fig3 - 14 . after insertion of the guidewire 30 through the right femoral vein “ f ” ( or alternatively the left ), the guidewire 30 is maneuvered past the cranial end 54 of filter 50 . retrieval catheter 10 , with dilator 20 positioned therein , is then inserted through the femoral vein “ f ” and advanced through the iliac veins into the inferior vena cava . ( tubing 104 and valve assembly 106 enable saline injection described below .) that is , dilator 20 is positioned in the lumen 16 of the retrieval catheter 10 during insertion to move and maintain the tip 14 in the substantially straightened position ( or more straightened position ) to enable advancement of the catheter through the vascular system . retrieval catheter 10 and dilator 20 are inserted over guidewire 30 past the caudal end 52 of the filter 50 and beyond the cranial end 54 as shown in fig5 . dilator 20 ( and guidewire 30 ) is then withdrawn as shown by the arrow in fig6 , which enables the distal tip 14 of catheter 10 to return to its normal more curved configuration . in this curved configuration , the distal opening 18 of catheter 10 faces the cranial end of the filter and is maneuvered so opening 18 is above the hook 56 of filter 50 . it could also be placed to substantially align with the hook . snare catheter 40 is inserted through the lumen 16 of the retrieval catheter 10 , as shown by the arrow of fig7 , and extends around the curved distal tip 14 of catheter 10 as shown in fig8 and 9 , exiting distal opening 18 . the snare 42 , movably positioned in a lumen of the snare catheter 40 , is placed around hook 56 of filter 50 , and then tightened around the hook as shown in fig1 , by retraction of the snare wire to grasp the filter . once tightened , the catheter 10 is preferably moved distally ( shown in phantom ) in the direction of the arrow of fig1 to disengage the filter retention hooks 58 from the vessel wall . to facilitate such distal advancement and hook disengagement , a wire can be used as shown in the alternate embodiment of fig1 a . in this embodiment , catheter 10 ′ has a side opening 15 through which wire 17 extends from the catheter lumen , either the lumen for the snare or another lumen adjacent to the snare lumen . this stiffening wire 17 is pushed forward along with the retrieval catheter 10 ′ to help move the catheter distally by providing additional force on the catheter . once the filter retention hooks 58 are disengaged from the vessel wall , the snare catheter 40 is withdrawn , pulling the filter 50 into the retrieval catheter 10 as shown in fig1 . the snare catheter 40 and filter 50 are then removed through the proximal end of the catheter 10 . next , the dilator 20 , preferably with guidewire 30 , is reinserted through the catheter lumen 16 ( fig1 ) to straighten the distal tip 14 ( or move it to more straightened position ). the retrieval catheter 10 , with the straightened tip , along with the dilator 20 and guidewire 30 , are then withdrawn from the body in the direction of the arrow of fig1 . fig1 a and 17b illustrate an alternate retrieval catheter . retrieval catheter or sheath 110 has a substantially straight tip 114 and distal opening 118 . the tip portion 115 of catheter 110 has a first hardness and the intermediate portion 117 ( or portion proximal of tip portion 115 ) has a second hardness greater than the first hardness . a dilator or stylet 120 has a curved tip 122 . the dilator 120 has a third hardness greater than the first hardness of the tip portion 115 but less than the second hardness of the intermediate portion 117 . when the dilator 120 is inserted in the catheter 110 and the tip 122 is in the intermediate portion 117 , the tip is restrained in a more straightened position due to the greater hardness of portion 117 . when the dilator 120 is further inserted so the tip 122 is in the tip portion 115 , it is enabled to return to its normally curved position since its hardness is greater than that of tip portion 115 , thereby forcing the distal tip 114 of retrieval catheter 110 into a more curved position as shown in fig1 b . thus , in use , after insertion of the guidewire as described above , retrieval catheter 110 , with dilator 120 positioned partially therein , is inserted through the femoral vein “ f ” and advanced through the iliac arteries into the inferior vena cava . retrieval catheter 110 and dilator 120 are inserted over the guidewire past the caudal end 52 of the filter 50 and beyond the cranial end 54 . ( alternatively , the dilator 120 can be inserted into catheter 110 after the catheter is inserted ). dilator 120 is then fully inserted into the catheter 110 ( and the guidewire withdrawn either prior to or after full insertion ) to force the distal tip 114 of catheter 110 to its curved configuration . in this more curved configuration , the distal opening 118 of catheter 110 faces the cranial end of the filter and preferably is maneuvered so opening 18 is above the hook 56 of filter 50 . snare catheter 40 is inserted through the lumen of the dilator 120 and extends around curved tip 122 of dilator 120 and curved distal tip 114 of catheter 110 , exiting the distal opening of the dilator and the distal opening 118 of the catheter 110 . the snare 42 is placed around hook 56 of filter 50 , and then tightened as described above . once tightened , the catheter 10 is preferably moved distally , also as described above , to disengage the filter retention hooks 58 from the vessel wall . after the filter 50 is withdrawn , the dilator 120 is retracted to straighten the tip of catheter 110 . fig1 a shows an example of a filter that could be withdrawn using the retrieval method of the present invention . the filter 50 is shown in the expanded placement configuration . it should be appreciated that other filters , including those described in the &# 39 ; 429 application , could be retrieved using the femoral approach method described herein . the filter 50 ( and other filters described therein ) can be inserted through the jugular vein in the neck of the patient or through the femoral vein in the leg of the patient or the arm . the filters can also be placed in the superior vena cava . filter 50 is preferably made from a shape memory nitinol tube and has a flared region 57 and a converging region 51 at the filtering region 59 . filtering region 59 has six struts 61 ( only some of which are labeled for clarity ) curving outwardly from tubular portion 64 . each filter strut or strut portion 61 extends radially from tubular portion 64 and divides into two connecting filter struts or strut portions 61 a , 61 b ( preferably of equal width ) that angle way from each other ( in different directions ) to extend to the connecting strut portion of an adjacent strut 61 . after convergence of strut portions 61 a , 61 b at joining region 61 d , it transitions into elongated mounting strut portions 61 c which form flared mounting or anchoring region 57 . the struts 61 terminate in hooks 58 , of two different sizes as described in the &# 39 ; 429 application . hooks 58 include a series of teeth 58 a ( fig1 b ) to engage the vessel wall to provide additional retention to prevent movement of the implanted filter in the caudal direction . a heel 59 extends past the hook to function as a stop to prevent the filter strut portions from going through the vessel wall . the tubular portion 64 is preferably in the form of a retrieval hook as described in the &# 39 ; 429 application . hook 56 has a curved hook 72 at the proximalmost end which is configured to receive a retrieval snare or other retrieval device . a portion of the wall of the hook 56 is cut out to expose the annular interior surface 74 . the interior surface 74 accommodates a portion of a tubular snare sheath . that is , the outer wall of the snare sheath ( tube ) can partially fit within the cut out region . this enhances removal as the snare pulls the filter hook into collinear arrangement with the sheath tube . engagement of the retrieval hook 56 and its retraction into the snare sheath or tube , including the collinear arrangement are described in detail and shown in fig1 h - 13n of the &# 39 ; 429 application . when the filter 50 is pulled into the retrieval sheath 10 it is collapsed for removal . fig1 shows an alternate embodiment of a retrieval hook 170 having a longer hook 172 to increase the snare engagement area and provide a more closed area to retain the snare . fig1 and 19 illustrate alternative cranial ends of the filter which can be achieved using the method of the present invention . in fig1 , a rounded dome - shaped tip 210 can be engaged by a grasping device to retrieve the filter . the grasping device can be inserted around the curved catheter tip in the same manner as described above for the snare retrieval device . in fig1 , a notch 222 is formed in dome - shaped tip 220 to receive a retrieval snare or other grasping device inserted through the curved retrieval catheter ( sheath ) tip . to facilitate removal of the filter from the vessel , cold saline can be injected onto the implanted filter to change the temperature of the filter to move it to a relatively softer condition to facilitate the filter being drawn in to the retrieval sheath . that is , injection of cold saline will cause the filter to approach its softer martensitic state , bringing the filter to a more flexible condition . the flexible condition facilitates the collapse and withdrawal of the filter into the retrieval sheath by decreasing the frictional contact between the filter and the inner surface of the retrieval sheath . while the above description contains many specifics , those specifics should not be construed as limitations on the scope of the disclosure , but merely as exemplifications of preferred embodiments thereof . those skilled in the art will envision many other possible variations that are within the scope and spirit of the disclosure as defined by the claims appended hereto .
a method of removing an implanted vessel filter by a femoral approach comprising the steps of providing a catheter with a curved tip , inserting a straightening device into the catheter to move the catheter tip from a curved position to a more straightened position , advancing the catheter tip through the femoral vein and past a cranial end of the filter , withdrawing the straightening device to enable the catheter tip to return to the curved condition , and inserting a filter grasping device though the catheter and a curved catheter tip to exit a distal portion to grasp the filter .