the invention provides an embolic protection system which has a number of features which allows the system to be used in placing a guide catheter proximal to lesion as per standard practice and advance any suitable guidewire across the lesion . a load filter is loaded into the delivery catheter in such a way as to provide a lumen through the loaded device through which the guidewire will pass . the loaded device is advanced over the guidewire and across the lesion . the filter is deployed from the delivery catheter and the delivery catheter is removed . the filter remains stable in the vessel without any user control . standard interventional procedures ( angioplasty , stent etc . . . . ) can be performed . the guidewire may be replaced by simply removing the initial wire and advancing a replacement wire through the guide catheter , across the lesion and through the filter . the filter may be retrieved by advancing a retrieval catheter over the guidewire and up to the filter . an inner member of the retrieval catheter may be engaged with the filter . then outer retrieval sheath is advanced to collapse the filter and retrieve . the guidewire may be left in place if desired . referring to the drawings and initially to fig1 there is illustrated an embolic protection filter 1 according to the invention , the filter 1 being suitable for deployment in a vasculature to filter undesired embolic material from the blood stream flowing through the vasculature . the filter 1 comprises a collapsible filter body 2 which in this case is supported by a collapsible filter support frame 3 . in this case the filter support is mounted on an inner tube 8 . the filter body 2 has an inlet end 4 and an outlet end 5 . the inlet end 4 has one or more , and in this a single , large inlet opening 6 which are sized to allow blood and embolic material enter the filter body 2 . the outlet end 5 has a plurality of small outlet openings 7 which are sized to allow through passage of blood but to retain undesired embolic material within the filter body 2 . in this way , the filter 1 captures and safely retains any undesired embolic material in the blood stream within the filter body 2 while facilitating continued flow of blood through the vascular system . emboli are thus prevented from flowing further downstream through the vascular system , which could otherwise have potentially catastrophic results . the relatively large inlet opening 6 provide for the possibility of aspirating embolic material from within the filter body 2 . this may be particularly advantageous if it is desired to leave the filter 1 in place in a vasculature for a long period of time , for example overnight , to assist in vascular recovery . the filter body 2 may have a low - friction outer layer , for example a hydrophilic coating , to minimise frictional resistance during deployment and retrieval of the filter 1 , and the filter body 2 may be of an oriented polymeric material , as described in international patent application no . pct / ie01 / 00087 , the relevant contents of which are incorporated herein by reference . the inner tube 8 has a guidewire lumen 12 therethrough for passing the filter 1 over a guidewire 10 . a guidewire 10 can pass through the filter , however , in the deployed configuration the filter is independent of the guidewire . thus , the guidewire can be moved independently of the filter without any associated movement of the filter . the arrangement allows relatively large radial forces to be exerted on the vascular wall without the risk of abrasion causes by movement of the deployed filter . in this way damage to the endothelium can be avoided . the filter 1 is movable between a low - profile , collapsed configuration for movement through the vasculature , and an outwardly extended configuration for deployment in the vasculature in apposition with the vasculature wall . in the outwardly extended configuration , the filter body 2 is supported in an expanded position by the filter support 3 so as to maximise the internal volume of the filter body 2 to capture and safely retain as much embolic material as possible . the filter support 3 supports the filter body 2 in the outwardly extended configuration in apposition with the vasculature wall to prevent blood flow bypassing the filter 1 between the filter body 2 and the vasculature wall . the support frame in this case defines a proximal support hoop 15 which is connected to the tubular member 8 by a support arm 16 . the support 3 in this case also comprises a number of axially extending portions 17 which assist in providing body support to the filter in a vessel and assist in preventing rotation of the filter when deployed in the deployed configuration . the support may be of wire and may also comprise one or more stabilising hoops ( s ) 18 . in this case the tubular member 8 terminates proximally of the distal end 5 of the filter . this has a number of advantages . it facilitates recrossing of the filter 1 with a guidewire and the distal free end of the tubular member 8 may be readily snared for snaring and / or retrieval of the filter when it is desired to remove the filter from the vasculature . in the outwardly extended configuration , the filter support 3 exerts an outward radial force on the filter body 2 and the vasculature wall which results in a frictional force between the filter body 2 and the vasculature wall sufficient to retain the filter 1 in position against substantial longitudinal movement . in the invention the filter will not rotate or collapse in the absence of guidewire support . conventional filters are coupled ( directly or indirectly ) to a wire — this wire enhances the stability of the filter . this invention describes a filter which will remain fully open and opposed to the vessel wall in the absence of any support from a guidewire . this is achieved by using a support frame which does not allow rotation in the vessel lumen . in general , a frame which lies in only one plane cannot remain apposed to the vessel wall without support from the guidewire . the design of the system is such that the filter must do considerable work to move longitudinally . in order to ensure that the filter is retained in position the filter apposition force generates a frictional force between the filter and the vessel . the frictional force generated by the filter is dependent on the contact area , the apposition force generated by the filter and the coefficient of static friction between the filter and the vessel . locating the filter using frictional forces alone is a worst - case analysis as it does not include the effect of tapered vessels . these will increase the apposition force generated by the filter as it moves distally into a lumen of decreasing diameter . the radial apposition force of the filter support 3 is sufficient to retain the deployed filter 1 in position in the vasculature against substantial longitudinal movement , even if the guidewire , over which the filter 1 is delivered , is moved . no step , abutment or other stop means is required on the guidewire to prevent the filter 1 from migrating downstream in the vasculature . in this manner , the invention enables an interventional procedure to be performed using a standard guidewire . this enhances clinician freedom by enabling a clinician to choose the most appropriate medical guidewire for a particular interventional procedure , and / or a particular patient anatomy . in the case of a filter which has an integral tubular member the tubular member defines a lumen through which a guidewire can pass . in the invention such a guidewire passageway may be provided by a component of the delivery system such as a portion of a deployment pusher . alternatively , the tubular member may be a separate component which is removed after the guidewire has passed through the filter . thus , the member defining a guidewire pathway through the filter may be a movable or removable component . referring to fig2 to 16 there are illustrated various steps in the use of an embolic protection device during an interventional procedure . various steps in the method will be described and it will be appreciated that the various steps and the features of the various apparatus used in the method may be used independently of one another , for example in the methods and apparatus of other aspects of the invention . the filter does not necessarily itself have a predetermined lumen for passage of a guidewire . at various stages a lumen is defined when such a lumen is required . on loading of a filter 20 into a delivery catheter 21 a guidewire lumen is defined ( fig2 ) which is used for delivery of the filter 20 over a pre - positioned guidewire 10 ( fig3 ). the lumen - defining member 22 may be removed ( fig3 ) and the filter is advanced to and deployed distal to a treatment location in the vasculature ( fig4 and 5 ). various procedures may be carried out such as balloon angioplasty and stenting ( fig6 and 7 ). the filter may be retrieved into a retrieval catheter 25 ( fig1 to 15 ) and the filter removed . in this case the filter 20 comprises a filter body supported in the deployed configuration by a support frame 3 defining a large proximal opening 6 and having a snaring engaging element in the form of a hook 26 . in use , the filter is loaded into a delivery catheter l 6 by inserting a tubular element 22 through the filter . the delivery catheter may be threaded onto a pre - deployed bare guidewire 10 , the tubular element 22 guiding the guidewire 10 through the filter 20 at the distal end of the delivery catheter 21 . once the guidewire 10 has entered the delivery catheter 21 proximal to the filter 20 the tubular element 22 may be removed . to facilitate this , the tubular element may be of c - shape in transverse cross section . the delivery catheter 21 is then advanced over the guidewire 10 to a location which is distal of a treatment site . the filter 20 is deployed by pushing it out from the distal end of the delivery catheter , for example by using a pusher . the filter is then in the deployed open configuration distal to a treatment location ( fig5 ). various procedures may be carried out at the treatment location , and embolic material released during the treatment procedures being captured in the filter . the treatment procedures may include deployment of a stent 29 from a stent delivery catheter threaded over the guidewire 10 . when it is desired to retrieve the filter a retrieval catheter 25 is delivered over the guidewire 10 . the retrieval catheter 25 may be a snare catheter or a separate snare catheter may be delivered through the retrieval catheter . the snare may comprise a lasso 30 or the like which engages the snaring hook 26 of the filter support frame . the guidewire 10 may then be withdrawn or left in place . in certain circumstances the guidewire 10 could be retracted , or even removed completely ( fig8 ), without disturbing the position of the deployed filter in the vasculature . another guidewire 10 a may be advanced through the filter ( fig9 and 10 ). this may be particularly advantageous in the case of certain interventional procedures , for example in coronary applications as will be described in more detail below . the support 3 may be configured to distribute the outward radial force over a relatively large area of the vasculature wall to minimise local stress distributions . many different designs of filter may be used such that on deployment , the filter applies a local radial force to the vasculature to substantially prevent movement of the filter relative to the vasculature in the deployed configuration . in the deployed configuration the filter is anchored to the vasculature . in some cases the filter comprises a filter body and a filter support frame to support the filter in the deployed configuration . the support frame and / or the filter body may comprise the anchor . the anchor may comprise a plurality of anchor elements which may be spaced - apart circumferentially around the filter when the filter is in the deployed configuration . referring to fig1 the filter frame includes a proximal support hoop 31 with radially projecting vessel indentors or stabilisers 32 to prevent longitudinal movement of the filter in the vessel . the frame may include a snaring feature 33 which may have a radiopaque marker 34 . referring to fig1 and 19 the vessel indentors or stabilisers 32 may also provide convenient attachment locations for attachment of tethers 35 . the tethers 35 may be interconnected at the proximal end by a connector 36 which may be radiopaque for ease of location to snare the filter for retrieval . referring to fig2 the filter may have an enlarged lip 37 at the proximal end for engagement in a vessel to anchor the filter in a desired position . referring to fig2 and 22 there is illustrated another filter which is apposed in a vessel . the filter has a retrieval mechanism somewhat like a closed drawstring arrangement with a mesh - like structure 38 , when deployed , which may be engaged by the distal tip 39 of a centering catheter ( or any suitable snare ) for collapsing the filter and drawing it into a retrieval catheter 40 . another filter frame is illustrated in fig2 to 26 . the frame has a proximal hoop 41 and distally projecting arm 42 . x denotes terminations of the bifilar type to facilitate wrap - down of the filter as illustrated in fig2 and 25 . thus , the parking space occupied by the filter is optimised . in the deployed configuration in a vessel as schematically illustrated in fig2 the filter apposes the vessel wall and rotation and translation of the filter in relation to the vasculature is prevented . in general , the filter applies sufficient radial force to remain stable in a vessel when in the deployed configuration . in addition , the filter remains correctly orientated even without a guidewire in place . some filters of this type are illustrated in fig2 to 31 . in fig2 the filter 43 has body support . in fig2 the filter 44 has stabilising arms 45 . the filter of fig2 is in the form of a hoop 46 with a number of inflection points 47 . there may be four or more such inflection points as illustrated . in fig3 the filter has two axially spaced - apart support hoops 48 which are interconnected by connecting arms 49 . the filter of fig3 has two offset hoops 50 . any of these filters may be connected to a central tubular member by a rigid member ( s ) and / or by a tether ( s ). many more arrangements with support in more than one place are envisaged . the filter 51 of fig3 has body support provided by a nitinol tube or wire . to retrieve the filter 710 , any suitable means , such as the hooked retrieval catheter ( fig2 ), or the looped retrieval catheter ( fig2 ) may be used , in a manner similar to that described previously with reference to fig2 and 243 . referring to fig3 to 39 there is illustrated a delivery catheter 200 which may be used with a filter of the invention . this catheter is described in detail in our co - pending u . s . ser . no . 10 / 180 , 980 , the relevant contents of which are incorporated herein by reference . the delivery catheter 200 comprises a catheter body 202 which extends between a proximal end 203 and a distal end 204 , a restraining sheath 210 at the distal end 204 of the catheter body 202 , and an elongate actuator , which is provided in this case in the form of a stainless steel wire 209 . the catheter body 202 comprises a proximal hypotube portion 205 and a radially offset distal spring pusher 206 . as illustrated in fig3 and 35 , the pusher 106 is fixedly attached to the hypotube 205 in a side - by - side overlapping arrangement with the proximal end of the pusher 206 located proximally of the distal end of the hypotube 205 . the pusher 206 has a guidewire lumen 16 extending through the pusher 206 with an opening 217 at the proximal end of the lumen 216 for passage of a guidewire 222 through the lumen 216 and out through the proximal guidewire opening 217 ( fig3 ). the delivery catheter 200 is thus configured to be passed over the guidewire 22 in a rapid - exchange manner . the pusher 206 tapers proximally inwardly at the opening 217 for a smooth crossing profile . when assembled , the hypotube 205 and the pusher 206 are located substantially side - by - side . this side - by - side assembly of the hypotube 205 relative to the pusher 206 enables the guidewire 222 to exit through the proximal guidewire opening 217 smoothly and substantially parallel to the longitudinal axis of the catheter 200 . in particular , the passage of the guidewire 222 through the proximal guidewire opening 217 does not increase the overall profile of the catheter 200 . a connector shaft 212 is fixed to the sheath 210 with the shaft 212 extending proximally over the pusher 206 towards the distal end of the hypotube 205 . the proximal end of the sheath 210 overlaps the distal end of the shaft 212 , and a marker band 213 is located at the distal end of the shaft 212 between the shaft 212 and the sheath 210 . the actuator wire 209 extends distally through an actuator lumen 232 in the hypotube 205 , out of the actuator lumen 232 at the distal end of the hypotube 205 , externally along the pusher 6 to the proximal end of the shaft 212 . the wire 209 is attached to the exterior surface of the shaft 212 , for example by bonding . by attaching the wire 209 to the exterior of the shaft 212 , this arrangement provides for more space within the pusher lumen 216 for guidewire passage . in addition , attachment of the actuator wire 209 to the exterior of the shaft 212 is an easier step to achieve from a manufacturing viewpoint than attachment to the interior of the relatively long shaft 12 . the restraining sheath 210 and the connector shaft 212 are movable in a sliding manner relative to the catheter body 202 . when the sheath 210 extends distally of a distal end of the spring pusher 206 , the sheath 210 defines an internal reception space 211 , as illustrated in fig3 to 38 . a collapsed embolic protection filter 301 may be received within the reception space 211 , where the filter 231 will be restrained by the sheath 210 in a low - profile configuration during delivery to a desired site in a vasculature . a suitable material for the sheath 210 is polyethyleneterephthalate ( pet ). the distal end of the shaft 212 is flared outwardly ( fig3 ). during delivery of the filter 231 , the distal end of the pusher 206 is spaced proximally of the distal end of the shaft 212 , and the proximal end of an inner tubular member 236 of the filter is partially inserted into the flared shaft 212 . this arrangement provides a bridge in stiffness between the relatively stiff shaft 212 and the relatively stiff inner tubular member 236 of the filter 231 . thus the possibility of buckling of the relatively flexible sheath 10 is minimised . the distal end of the pusher 206 is engagable with the inner tubular member 236 of the filter 231 upon retraction of the sheath 210 to deploy the filter 231 out of the reception space 211 . as illustrated in fig3 , at the proximal end 203 of the catheter 200 a distal handle 208 is provided for gripping the catheter body 202 and a proximal handle 214 is provided for gripping the actuator wire 209 . the distal handle 208 is injection moulded over the hypotube 205 and the proximal handle 214 is crimped to the proximal end of the wire 209 . the handles 208 , 214 are movable relative to one another in a telescoping manner with the proximal handle 214 sliding within the distal handle 208 . movement of the handles 208 , 214 is limited by means of stop means . abutment of an outward annular protrusion 233 on the proximal handle 214 against the proximal end of the distal handle 208 prevents further movement of the proximal handle 214 distally relative to the distal handle 208 . engagement of a shoulder 234 on the proximal handle 214 with an inward annular protrusion 235 on the distal handle 208 prevents further movement of the proximal handle 214 proximally relative to the distal handle 208 . a releasable safety clip 237 is provided to maintain the handles 208 , 214 fixed relative to one another . when the catheter 200 is assembled the sheath 10 is directly connected to the proximal handle 214 , and the pusher 206 is directly connected to the distal handle 208 . movement of the proximal handle 214 proximally relative to the distal handle 208 moves the wire 209 , the connector shaft 212 and the sheath 210 proximally relative to the pusher 206 to facilitate deployment of the filter 231 from within the reception space 211 . the delivery catheter 200 may be used to deliver the embolic protection filter 231 through a vasculature and to deploy the embolic protection filter 231 downstream of a stenosed region in the vasculature to prevent potentially harmful emboli , which may be released into the blood stream during treatment of the stenosis , such as by a stenting procedure , from migrating further through the vascular system . referring to fig4 to 54 the use of the delivery catheter 200 will now be described in relation to a filter 301 of the invention which has tubular member 306 with a distal end that is spaced proximally from the distal end of the filter . such as arrangement facilitates removal replacement of a guidewire and can also be readily snared and retrieved as described herein . in use , a loading device 310 is partially inserted into the reception space 211 of the sheath 210 . a pushing device 311 is then threaded through the tubular member 306 of the filter 301 and extended into the reception space 211 , as illustrated in fig4 . by moving the pushing device 311 proximally , an engagement stop 312 on the pushing device 311 engages the distal end of the tubular member 306 and the filter 301 is moved towards the loading device 310 ( fig1 ). continued proximal movement of the pushing device 311 pushes the filter 301 through the loading device 310 , thereby collapsing the filter 301 , and into the reception space 11 ( fig4 ). the catheter 200 with the collapsed filter 301 received within the reception space 11 are then moved together proximally away from the loading device 310 ( fig4 ). the method of collapsing the filter 301 and loading the filter 301 into the reception space 211 is similar to that described in international patent application number pct / ie01 / 00052 , the relevant contents of which are incorporated herein by reference . next the guidewire 222 is inserted into a vasculature 315 and advanced through the vasculature 315 until the guidewire 222 has crossed a site of interest in the vasculature 315 ( fig4 ). a typical site of interest is a stenosed or diseased region 316 of the vasculature 315 . the delivery catheter 200 is then threaded over the guidewire 222 by inserting the proximal end of the guidewire 222 into the guidewire lumen 216 at the distal end of the pusher 206 , through the lumen 216 , and out of the lumen 216 through the proximal guidewire opening 217 . the catheter 200 is advanced over the guidewire 222 in a rapid - exchange manner until the reception space 211 is located downstream of the stenosis 316 ( fig4 ). to deploy the filter 301 at the desired site in the vasculature 315 downstream of the stenosis 316 , the proximal handle 14 is moved proximally while holding the distal handle 208 fixed , thereby causing the pull wire 209 and the connector shaft 212 to be pulled proximally . because the connector shaft 212 is attached to the sheath 210 , the sheath 210 also moves proximally while the pusher 206 does not move . in this way , the collapsed filter 301 is uncovered by the sheath 10 while the distal end of the pusher 206 abuts the proximal end of the tubular member 306 of the filter 301 . the delivery catheter 200 thus enables the self - expanding filter 301 to expand outwardly to a deployed configuration . the distal end of the pusher 6 acts as an abutment for a controlled , accurate deployment of the filter 301 at the desired site in the vasculature 315 . when the filter 230 has been fully deployed at the desired site in the vasculature 315 , the delivery catheter 200 is withdrawn from the vasculature 315 over the guidewire 222 in a rapid - exchange manner to leave the deployed filter 301 in place in the vasculature 315 ( fig4 ). various procedures can be carried out using the guidewire such as an angioplasty using a balloon 320 ( fig4 ) or a stenting procedure with a stent 321 ( fig5 ). on completion of the procedures a retrieval device such as a retrieval catheter 325 or snare may be used to retrieve the filter ( fig5 to 53 ). the guidewire 222 may be left in place or removed . in fig5 to 57 there is illustrated another delivery catheter 600 according to the invention , which is similar to the delivery catheter 200 and similar elements are assigned the same reference numerals . in this case the distal end of the shaft 212 is not flared outwardly , and the proximal end of the inner tubular member 306 is not inserted into the shaft 212 , during delivery of the embolic protection filter 610 . instead a bridging sleeve 601 is provided mounted around the shaft 212 distally of the marker band 213 , as illustrated in fig5 . the sleeve 601 extends distally of the distal end of the shaft 212 , such that the proximal end of the inner tubular member 306 of the filter 610 may be partially inserted into the sleeve 601 during delivery of the filter 610 ( fig5 ). this arrangement provides a bridge in stiffness between the relatively stiff shaft 212 and the relatively stiff inner tubular member 306 of the filter 610 . thus the possibility of buckling of the relatively flexible sheath 210 is minimised . it is noted that the filter 610 of fig5 ( a ) to 57 ( c ) is of a different configuration to the filter described previously . in particular the inner tubular member 306 of the filter 610 does not have any step formations or protrusions at the proximal end of the inner tubular member 306 . the delivery catheter of the invention is also suitable for over - the - wire exchange over a guidewire . the rapid exchange configuration is not essential . referring to fig5 to 61 there is illustrated one means of temporarily providing a tubular lumen in a filter to facilitate delivery of the filter to a desired location . in this case an introducer tool is in the form of a c - shaped tubular member 60 with a distal peel - back feature 61 . the tool is inserted into the distal end of the filter 62 as illustrated in fig5 . the filter is loaded into a distal pod 63 of a delivery catheter 64 ( fig5 ) and the distal end of the delivery catheter 64 is threaded over the proximal end of a deployed guidewire 65 . when the guidewire has passed through the filter the introducer may be pulled away and removed as illustrated in fig6 . in another arrangement illustrated in fig6 to 65 the delivery catheter 70 may itself be provided with a member 71 defining a temporary tubular member for a guidewire . the tubular member may also function as a pusher . in one case once the guidewire has traversed the filter 62 the tubular member 71 may be positioned proximal of the filter during delivery and deployment ( fig6 to 65 ). in another case ( fig6 to 68 ) the tubular member 71 may extend through the filter up to the stage when the delivery catheter is being withdrawn . the pusher 71 may pass through the centre ( fig7 and 72 ) of the filter or may run beside the filter ( fig6 and 70 ). in fig7 and 74 , there is illustrated another embolic protection filter 520 according to the invention . in the case of filter 520 , the guidewire lumen 521 through the filter 520 is defined by two telescoping tubes 522 , 523 . the proximal tube 522 is fixed to the filter 520 at the proximal end of the filter 520 , and the distal tube 523 is fixed to the filter 520 at the distal end of the filter 520 . in the deployed configuration of fig7 , the distal tube 523 telescopes proximally over the proximal tube 522 so that the overall parking space of the filter 520 in a vasculature is minimised . in addition the distal tube 523 is spaced distally of the guidewire aperture 112 to facilitate crossing of the filter 520 with a guidewire without requiring the guidewire to be threaded through the tubes 522 , 523 . in the collapsed configuration of fig7 , the distal tube 523 telescopes distally over the proximal tube 522 so that the guidewire lumen 521 is defined through the entire length of the filter 520 when collapsed , for example in a pod 524 of a delivery catheter 525 . the invention also envisages the use of a delivery catheter 650 , as illustrated in fig7 to 89 , which is particularly suitable for delivering an embolic protection filter 651 , as illustrated in fig7 , the filter 651 not having an inner tubular member to define a guidewire lumen through the filter 651 . the delivery catheter 650 comprises an outer tubular member 652 , and an inner tubular member 653 , the inner tubular member 653 being movable distally relative to the outer tubular member 652 from a delivery configuration ( fig7 ) to a deployment configuration ( fig7 ). in the delivery configuration , the catheter 650 defines a reception space 654 for receiving the filter 651 in a collapsed configuration , as illustrated in fig7 . when the inner tubular member 653 is moved distally relative to the outer tubular member 652 , the filter 651 is pushed distally out of the reception space 654 by means of an engagement between a shoulder 655 of the inner tubular member 653 and the collapsed filter 651 . the invention provides features to enable a guidewire to be repositioned across the filter . it may be necessary to be able to replace the guidewire if the wire became accidentally withdrawn by the user during the procedure . it may then be necessary to replace the wire in order to access the lesion with other devices such as a balloon or stent catheter or even the filter retrieval catheter . merely advancing a wire up to the filter is unlikely to provide sufficient support in all cases . guidewire replacement may also be needed if the user desires to use a wire with different properties during the procedure . for example a very torqueable wire may be ideal for initially accessing and crossing the lesion , and may have adequate support to enable the filter to be delivered and deployed , but may not have sufficient support to enable a stiffer stent delivery system to reach the lesion . the invention facilitates removal of the first wire and replacement with a more supportive guidewire to facilitate use of the stent delivery system . this may be achieved without having to use an additional exchange catheter . this invention describes a filter which comprises a guidewire recrossing feature , wherein this feature may comprise some or all of a guiding funnel , a pathway and a blood restrictor . a guiding funnel is used as this operation will be performed “ blind ”. in general , it would be difficult to replace a guidewire through a tubular lumen while the filter is in the patient . in the invention the guidewire may be passed through the distal filter neck . the distal cone of the filter will act as a guiding channel . however the guidewire tip is very flexible — if it is to open a “ valve ” or blood restrictor it will need to have good push . in order to provide this push it is necessary to restrain the guidewire tip within a relatively narrow channel — this channel is provided by the filter neck . a restrictor may be provided to prevent any loss of embolic material while the first guidewire was absent — during which period the neck of the filter would be an open hole if no restrictor were present . this restrictor is intended simply to close and prevent blood flow in the absence of a guidewire . once there is no blood flow through the filter neck embolic material will not collect there and will not restrict the passage of the second guidewire . various guideways may be provided for a guidewire to assist crossing of a filter . referring to fig7 to 81 the pathway may be provided around the filter , for example in a side channel 80 . a radiopaque feature 81 may be provided on the filter to guide a user to the passageway . alternatively the pathway may be through the filter to a single exit 82 ( fig8 ), a separate exit 83 ( fig8 ) or through the same exit 84 using a shortened tubular member 85 illustrated in fig8 and described in more detail herein . in these cases the guidewire passage / hole may be sealed to prevent passage of embolic therethrough as will be described in more detail below . referring now to fig8 to 92 , there is illustrated another embolic protection filter 50 according to the invention . the filter 150 comprises a receiver to guide a docking device into association with the filter 150 . in this case , the receiver is configured to guide a guidewire , such as the guidewire 130 , into the guidewire lumen 112 . the receiver is provided by a funnel 151 which diverges outwardly proximally , the funnel 151 being mounted to the filter 150 to extend proximally of the inlet end of the filter 150 . in this specification , the term funnel will be understood to mean any orifice with a cross - sectional area that decreases with distance . the funnel 151 may comprise a collapsible funnel body in the form of a membrane 152 , which in this case is supported by a collapsible funnel support , in the form of a plurality of support fingers 153 . the fingers 153 are pivotally mounted to the filter 50 and are biased to move the filter membrane 152 from a collapsed configuration for movement through the vasculature , to an outwardly extended configuration for guiding the guidewire 130 , as illustrated in fig8 . the funnel 151 may be of a radiopaque material . the funnel 151 may be used to guide the guidewire 130 along a pathway that enables the guidewire 130 to cross the filter 150 . the funnel 151 allows the procedure of leading the small diameter guidewire 130 through the small diameter guidewire lumen of the filter 150 to be performed more easily by guiding the tip of the guidewire 130 towards the proximal end of the guidewire lumen 158 . use of the funnel 151 is particularly beneficial in the case where it is desired to lead the guidewire 130 through the guidewire lumen while the filter 150 is deployed in the vasculature , as illustrated in fig8 to 89 . the funnel 151 enables a clinician to accurately and quickly thread the guidewire 130 through the guidewire lumen without risk of puncturing the filter body or of disturbing the filter 50 from its deployed position in the vasculature in apposition with the wall of the vasculature . the filter 150 further comprises at least one , and in this case two , seals 160 , 161 to seal the guidewire lumen 158 to prevent embolic material from passing through the guidewire lumen 158 , when the filter 150 is in use in the vasculature . the seals 160 , 161 are self - closing . in this case one seal 160 located at the proximal end of the filter 150 , and the other seal 161 located at the distal end of the filter 150 . the proximal seal 160 may be in the form of a tubular member of a soft membrane material . the guidewire lumen 158 extends through the tubular seal 160 and the seal 160 is closable down to seal the guidewire lumen 158 . the distal seal 61 is in the form of a tubular member with two or more , and in this case seven , circumferentially overlapping flaps , as illustrated in fig9 . this seal 161 is also closable down to seal the guidewire lumen 158 . it will be appreciated that the guidewire lumen 158 can be provided as any suitable passageway through the filter 150 . the guidewire lumen 158 does not have to be located along the central axis of the filter 150 . the guidewire lumen 158 may be radially offset from the longitudinal axis of the filter 150 . when the guidewire 30 is extended through the guidewire lumen 158 , the seals 160 , 161 self - close around the guidewire 130 to prevent emboli flowing through the guidewire lumen 158 . upon removal of the guidewire 130 from the guidewire lumen 158 while the filter 150 is deployed in the vasculature , the seals 160 , 161 self - close down to completely close off the guidewire lumen 158 . in this manner , the seals 160 , 161 ensure that no blood flow potentially carrying harmful embolic material can pass through the guidewire lumen 158 . all blood flows into the filter body through the inlet openings and out of the filter body through the small outlet openings , thereby trapping and safely retaining the undesired embolic material within the filter 150 . after an embolic protection filter has been delivered over a guidewire and deployed in a vasculature , it is not always possible to withdraw the guidewire from the vasculature before collapsing and withdrawing the filter from the vasculature . however in some cases it may be necessary to withdraw the guidewire over which the filter was delivered while leaving the filter deployed in the vasculature . when a high torque guidewire is used to facilitate filter delivery and deployment , and a stiffer guidewire is subsequently used to provide additional support during delivery and deployment of a stent ; when a guide catheter has prolapsed ; when a guidewire is withdrawn into a guide catheter to accelerate rate of resolution of a spasm . when this need does arise , the filter 50 of the invention may be used to filter potentially harmful emboli from a vasculature when the guidewire is withdrawn , while the filter remains deployed in the vasculature , as illustrated in fig9 to 110 . a first guidewire 130 is introduced into and advanced through the vasculature 121 to cross the treatment location 122 ( fig9 ), and the filter 150 is delivered through the vasculature 121 and deployed distally of the treatment location 122 ( fig9 to 97 ), in a manner similar to that described previously . in the outwardly extended configuration , the deployed filter 150 is retained in position in the vasculature 121 against substantial longitudinal movement by the radial apposition force of the filter body against the wall of the vasculature 121 . the first guidewire 130 can thus be withdrawn from the guidewire lumen of the filter 150 , and completely withdrawn from the vasculature 121 without disturbing the outwardly extended configuration of the filter 150 in the vasculature 121 . the deployed filter 150 is retained in position in the vasculature 121 against substantial longitudinal movement by means of the radial apposition force exerted by the filter support on the filter body and the vasculature wall , as described previously . a second guidewire 140 is then introduced into the vasculature 121 and advanced through the vasculature 121 until the second guidewire 140 crosses the desired treatment location 122 . the tip of the second guidewire 140 is guided towards the proximal end of the guidewire lumen by engagement of the guidewire tip with the funnel 151 , and the second guidewire 140 is then lead through the guidewire lumen . a stent 136 may then be delivered through the vasculature 121 , and deployed at the treatment location 122 using the stent delivery catheter 135 . in this case , the stent delivery catheter 135 passes over the second guidewire 140 . after completion of the interventional procedure , the retrieval catheter 120 is advanced to cross the stent 136 and the treatment location 122 , and the tip 125 is engaged with the filter 150 . as the tip 125 passes through the funnel 151 , the funnel 151 is caused to collapse down to the collapsed configuration . the filter 150 is then collapsed and retrieved into the retrieval catheter 120 and withdrawn from the vasculature 121 . upon collapse of the filter 1 , the apposition of the filter with the vasculature 121 is released . the filter 150 ensures any embolic material generated during the interventional procedure is captured and safely removed from the vasculature 121 . the second guidewire 140 may be of a different diameter , or have different material properties to the first guidewire 130 . it may thus be easier or more suitable for the clinician to advance the stent delivery catheter 35 over the second guidewire 140 rather than over the first guidewire 130 . for example , it is sometimes the case that a high torque guidewire 130 is used to facilitate filter delivery and deployment , and a stiffer guidewire 140 is used subsequently to provide additional support during delivery and deployment of a stent . in some cases , it may be necessary or desirable to withdraw the second guidewire 140 from the filter 150 and the treatment location 122 after deployment of the stent 136 , and then to advance a third guidewire through the vasculature 121 to the filter , the retrieval catheter 120 then being advanced over the third guidewire to retrieve the filter 150 . this invention enables such a procedure to be carried out . furthermore withdrawing a guidewire into a guide catheter may accelerate the resolution of spasm and reduce the risk of ischaemia . referring to fig1 to 114 , there is illustrated another retrieval catheter according to the invention , which is similar to the retrieval catheter of fig1 to 192 . in this case , the catheter body 23 defines a guidewire lumen 151 radially offset from the coupling member 24 . the guidewire lumen 151 extends through only part of the catheter body 23 to facilitate passage of the catheter body 23 over a guidewire , such as the guidewire 140 , in a rapid exchange manner . in use , the retrieval catheter 150 may be used to retrieve the filter 1 deployed in the vasculature 21 . in one possible procedure , the second guidewire 140 is not led through the guidewire lumen 12 of the filter 1 . instead the second guidewire 140 is advanced until the guidewire 140 has crossed the treatment location and the guidewire tip is proximally of the filter 1 ( fig1 ). the filter 1 is then retrieved into the catheter body 23 . during this procedure the retrieval catheter 150 may be advanced distally off the end of the guidewire 140 . fig1 illustrates another filter 170 according to the invention . in this case , the funnel 151 is mounted to the filter 170 distally of the inlet end of the filter 170 , so that the funnel 151 is located at least partially within the filter 170 . it will be appreciated that the receiver may be detachably mounted to the filter . for example , the receiver may be mounted to the filter after deployment in a vasculature , and / or may be detached from the filter before retrieval of the filter from a vasculature . in addition , the receiver may be radially offset from the longitudinal axis of the filter . referring to fig1 and 117 , there is illustrated another filter 180 according to the invention . the funnel is provided , in the case of filter 180 , by sloping walls 181 of the filter body at the inlet end . as the guidewire 130 is advanced to the filter 180 , the tip of the guidewire 130 meets the sloping walls 181 of the filter body and is guided distally inwardly towards the proximal end of the guidewire lumen . in this manner , the sloping walls 181 enable the guidewire 130 to be easily and quickly threaded into the guidewire lumen . the angle of inclination α of these sloping walls 181 can be altered , as indicated in fig1 , to suit the characteristics of the interventional procedure , and / or the vasculature , and / or the guidewire . the large inlet openings enable substantially unrestricted flow into the filter body , and the sloping walls 81 may be radiopaque material to aid guidewire passage . fig1 illustrates a further filter 190 according to the invention . in this case , the filter 190 has a guidewire aperture 192 for passing the filter 190 over the guidewire 130 , and the filter 190 has a single , large inlet opening 191 at the inlet end of the filter 190 . the single , large inlet opening 191 provides no resistance to blood flow into the filter body . the sloping walls 192 at the outlet end of the filter 190 provides the funnel , in this case , to guide the guidewire 130 towards the guidewire aperture 192 . it will be appreciated that the outlet openings are smaller , in this case , than the guidewire diameter , thus the guidewire 130 does not snag or pass through the outlet openings but instead the guidewire 130 is guided distally inwardly to the guidewire aperture 192 . the filter 90 may have a guidewire aperture 112 for passing the filter 90 over the guidewire 30 , and the filter 90 has a single , large inlet opening 91 at the inlet end 4 of the filter 90 . the single , large inlet opening 91 provides no resistance to blood flow into the filter body 2 . the sloping walls 190 at the outlet end of the filter 190 provides the funnel , in this case , to guide the guidewire 130 towards the guidewire aperture 192 , as illustrated in fig1 and 120 . it will be appreciated that the outlet openings are smaller , in this case , than the guidewire diameter , thus the guidewire 130 does not snag or pass through the outlet openings but instead the guidewire 30 is guided distally inwardly to the guidewire aperture 192 . as illustrated in fig1 to 121 the filter 190 further comprises a distal seal at the guidewire aperture 192 in the form of an elastomeric self - sealing valve 400 . the valve 400 has co - operating flaps which meet centrally to close off the guidewire aperture 192 when the guidewire is not extended through the aperture 192 , as illustrated in fig1 and 121 . as the guidewire is pushed through the guidewire aperture 192 , the flaps of the valve 400 are forced apart to permit passage of the guidewire 130 , as illustrated in fig1 . it will be appreciated that the valve 400 could alternatively be provided in the form of four , two , or any other number of co - operating flaps . referring to fig1 to 127 the guidewire exit hole may be sealed with a thin flexible membrane 401 which can withstand any pressure differential across the filter but can be deformed by the guidewire tip to open the seal / membrane . various options are possible such as those illustrated in fig1 to 126 . another option is to provide a seal in the form of an invertible flexible tube 402 . the tube may have slits 403 for additional flexibility . fig1 shows an initial guidewire in position , fig1 shows the wire removed and the tube collapsed , sealing the hole . in fig1 a new wire is shown being advanced through the filter , the advancing of the wire pushing the tube out of the filter neck and forming a seal with the new wire as illustrated in fig1 . the tube may be slits or slots for added flexibility as illustrated in fig1 . the guidewire exit hole may also be sealed by a flap valve or the like . referring to fig1 to 135 a closure flap 410 is hingedly connected to the filter 411 by a curved lever 412 . the hinge point 413 is stepped back proximally from the flap 410 so that the pressure drop across the flap 410 does not cause the flap 410 to open . the flap 410 is opened against the biasing of the lever 412 on insertion of a guidewire 415 as illustrated in fig1 and 135 . it will be appreciated that the hinge may have a range of different constructions . for example , as illustrated in fig1 a hinge 416 may be provided by a flattened wire or a hinge 417 may be formed by a narrowing of the lever as illustrated in fig1 . in another embodiment illustrated in fig1 to 140 a distal end 420 of a filter may have a flattened neck section 421 which normally seals a guidewire aperture 422 but which can be opened to facilitate passage of a wire 423 . a further embodiment is illustrated in fig1 to 143 in which the filter distal guidewire aperture has a foam - like insert 425 with slits to facilitate deformation of the foam as a guidewire 426 is inserted whilst still maintaining a sealing engagement with the guidewire 426 . in the invention the retrieval device grips and retrieves the filter . conventional filters are retrieved by using the guidewire to engage with the filter . this invention describes a retrieval device with one member which engages with and restrains the filter while a second member may envelop the filter . the retrieval device may function in the absence of a guidewire so that the filter can be retrieved even if the user has removed the guidewire and failed to replace it . this retrieval process may involve three stages : 1 ) engage with the filter , 2 ) decouple filter from vessel , 3 ) retrieve the filter . alternatively the retrieval may involve two stages : 1 ) engage with the filter , 2 ) retrieve the filter . the retrieval process is simple and reliable . the snare ( or loop or lasso ) designs described provide one of the most reliable and versatile methods . there is preferably a feature on the filter with which this snare will engage easily . this feature and the snare loop are preferably radiopaque for ease of visibility and positioning . for example a large radiopaque ball ( or shepherds crook ) inside the filter may be pulled proximal to the filter when snared and wrapped down . referring in particular to fig1 to 146 , there is illustrated a retrieval catheter 620 according to the invention . the retrieval catheter 620 is suitable for retrieving a filter , deployed in a vasculature 621 distally of a treatment location 622 , such as a region of stenosis . the catheter 620 comprises an outer catheter body 623 and a coaxial inner coupling member 624 , the coupling member 624 having means for coupling to the filter especially a filter deployed in the vasculature 621 to be retrieved . the coupling means is provided , in this case , by an arrow - head shaped tip 625 on the coupling member 624 . the tip 625 has two male fingers 626 for engagement with two corresponding female recesses 627 on the filter 1 . the male fingers 626 are moveable between a low - profile configuration and an outwardly protruding configuration for engagement with the filter . in this case , the fingers 626 are of a resilient material , and are biased towards the outwardly protruding configuration . during introduction of the retrieval catheter 620 through the vasculature 621 , the tip 625 protrudes only partially distally of the distal end of the catheter body 623 , so that the resilient fingers 626 are maintained in the low - profile configuration . the protruding tip 625 prevents snagging of the open mouth of the catheter body 623 against any protruding parts of the vasculature wall . in addition the tip 625 tapers distally inwardly for a smooth crossing profile . when the retrieval catheter 620 has crossed the treatment location 622 , the coupling member 624 is moved distally relative to the catheter body 623 , to release the resilient fingers 626 to move to the outwardly protruding configuration . the coupling member 624 is then moved further distally into the filter until the fingers 626 engage with the recesses 627 of the filter . the recesses 627 may be defined in a more pronounced manner by providing inwardly protruding steps or abutments on the proximal end of the filter support against which the fingers 626 may engage . the catheter body 623 is next moved distally relative to the engaged filter 1 by maintaining the position of the coupling member 624 , the distal end of the catheter body 623 is engaged with the proximal end of the filter body , the catheter body 623 is further advanced and thus the coupled filter 1 is collapsed down releasing the apposition force and is retrieved into the catheter body 623 . when the collapsed filter 1 has been fully retrieved into the catheter body 623 , the retrieval catheter 620 is withdrawn with the filter 1 from the vasculature 621 . the coupling member 624 of the retrieval catheter 620 enables a deployed medical device , such as the filter 1 , to be retrieved into the retrieval catheter 620 with any retained embolic material within the filter 1 without requiring a step , or a clamp or any special stop features on the guidewire . thus the retrieval catheter 620 enables the filter 1 to be used in combination with any standard guidewire . in addition , it is not necessary to retract the guidewire to facilitate retrieval of the filter 1 . in certain circumstances if the guidewire was withdrawn from the deployed filter 1 it would still be possible to retrieve the filter 1 using the retrieval catheter of the invention . this could speed up the overall procedure . also in some cases it may be difficult to recross the filter 1 with a guidewire . furthermore by obviating the need to recross the filter 1 with a guidewire , the possibility of a spasm being caused is minimised . fig1 to 165 illustrate the embolic protection filter 1 and the retrieval catheter 620 according to the invention , in use . a guidewire 630 is introduced into and advanced through the vasculature 621 until the guidewire 630 crosses the desired treatment location 622 . a delivery catheter 631 is then used to deliver the embolic protection filter 1 through the vasculature 621 over the guidewire 630 , the filter 1 being housed within a distal pod 632 of the delivery catheter 631 in the collapsed configuration . the filter 1 may in one case be loaded into a delivery catheter 631 as described in international patent applications nos . pct / ie01 / 00052 and pct / ie01 / 00053 , the relevant contents of which are incorporated herein by reference . it will be appreciated that other loading alternatives are also possible . when the distal pod 632 has been advanced to a desired site distal to the treatment location 622 , the pod 632 is moved proximally relative to an inner pusher to deploy the filter 1 out of the pod 632 into the outwardly extended configuration , as described in further detail in international patent applications nos . pct / ie01 / 00052 and pct / ie01 / 00053 . after complete deployment of the filer 1 , the delivery catheter 631 is withdrawn from the vasculature 621 ( fig1 ). in the outwardly extended configuration the filter 1 is in apposition with the vasculature 621 , thereby preventing blood flow from bypassing the filter 1 between the filter 1 and the vasculature 621 . the radial apposition force of the filter support against the filter body and the wall of the vasculature 621 retains the filter 1 in position against substantial longitudinal movement , even if the guidewire 630 is moved or indeed removed . in this way the filter 1 is prevented from migrating downstream in the vasculature 621 . an interventional procedure is then carried out at the treatment location 622 . in the case illustrated , the interventional procedure is a stenting procedure using a self - expanding stent . however , a range of procedures are possible as alternatives to , or in addition to stenting , for example a balloon angioplasty procedure , a balloon - expandable stenting procedure , an atherectomy procedure , a lysis . a stent delivery catheter 635 is used to deliver a stent , such as a self expanding stent 636 , through the vasculature 621 , the stent 636 being held in a collapsed configuration by a restraining sheath 637 of the stent delivery catheter 635 . when the stent delivery catheter 635 has been advanced to the treatment location 622 , the sheath 637 is moved proximally relative to an inner body 638 of the catheter 635 to facilitate deployment of the stent 636 at the treatment location 622 . after complete deployment of the stent 636 , the stent delivery catheter 635 is withdrawn from the vasculature 621 , leaving the deployed filter 1 and the deployed stent 636 in the vasculature 621 . any embolic material generated during delivery or deployment of the stent 636 , or during withdrawal of the stent delivery catheter 639 is captured and safely retained in the deployed filter 1 . after completion of the interventional procedure , the retrieval catheter 620 is introduced into the vasculature 621 , and advanced through the vasculature 621 until the stent 636 and the treatment location 622 have been crossed . the filter 1 is simultaneously collapsed and retrieved into the catheter body 623 of the retrieval catheter 620 and with it the captured embolic material , by engaging the tip 625 with the filter 1 , and then advancing the catheter body 623 distally over the coupling member 624 and the engaged filter 1 . upon collapse of the filter 1 , the apposition of the filter 1 with the vasculature 621 is released . when the filter 1 has been fully collapsed and retrieved into the retrieval catheter 620 , the retrieval catheter 620 with the collapsed filter 1 and retained emboli therein are withdrawn from the vasculature 621 , leaving the deployed stent 636 in place at the treatment location 622 in the vasculature 621 . in this way , the filter 1 may be used to capture and safely remove any embolic material which has been generated during the interventional procedure . an expandable balloon may be provided on the filter to enhance the outward radial force on the vasculature wall to retain the filter in position against substantial longitudinal movement . in use , the balloon may be inflated after deployment at the desired site in the vasculature to effectively anchor the filter in position . the balloon may be subsequently deflated before retrieval of the filter . fig1 and 165 illustrate another embolic protection filter 300 according to the invention . the filter 300 comprises a capture tether 301 which extends externally of the filter body 2 from a proximal ring 302 , to which the tether 301 is fixed , to a distal capture hoop 303 . the capture hoop 303 is located around the distal core at the outlet end 5 of the filter 300 when the filter 300 is in the outwardly extended configuration , as illustrated in fig1 . the capture hoop 303 is slidable over the filter body . to collapse and retrieve the filter 300 into the retrieval catheter 20 , the coupling member 24 engages the capture tether 301 and causes the capture hoop 303 to move proximally . the coupling member 24 may be engaged with the capture tether 301 using a hook , or loop , or any other suitable coupling means , as described previously . in this manner the filter 300 is compressed for retrieval into the catheter body 23 , as illustrated in fig1 . the coupling means may alternatively be provided by a male member in the form of a hook 700 , as illustrated in fig1 for hooking around a receiver on the filter 1 . the hook 700 may be used to couple the coupling member 24 to any suitably configured embolic protection filter . for example , an embolic protection filter 710 , illustrated in fig1 and 169 , has a tether arm 711 at a proximal end of the filter 710 around which the hook 700 may be extended to couple the deployed filter 710 with the coupling member 24 and thereby facilitate retrieval of the filter 710 into the catheter body 23 . fig1 to 173 illustrate further embolic protection devices 720 , 725 , 730 according to the invention . the filter 720 of fig1 has three tether arms 721 which extend radially inwardly from the filter body 2 to meet at a central point 722 . the hook 700 may be extended around any one of the tether arms 721 to couple the coupling member 24 to the filter 720 . this tether arrangement enables the filter 720 to be retrieved with a central , axial pull force . in the filter 725 of fig1 , the three tether arms 726 extend radially inwardly and distally to the central point 727 . in this manner the central point 727 is stepped back distally from the single , large inlet opening 6 to minimise the possibility of embolic material becoming caught or hung up on the tether arms 726 . the filter 730 of fig1 has a central ring 332 to which the tether arms 331 are fixed . fig1 to 178 illustrate the embolic protection filter 710 , being retrieved into the catheter body 24 using grasping jaws 906 . in this case , the jaws 906 comprise serrated edges 750 to achieve a secure grasping of the tether arm 711 . in this manner , the filter 710 may be coupled to the coupling member 24 and retrieved into the catheter body 23 . the retrieval catheter 905 is withdrawn from the vasculature after retrieving the filter 710 leaving the guidewire 30 remaining in the vasculature . the tether arms of any of the above described embodiments may be mechanically attached at the central point , and / or at the central ring , and / or to the filter body 2 , for example by bonding , or welding , or brazing . alternatively the tether arms may be provided integral with the mesh / membrane of the filter body 2 . the tether arms could also be provided as a fibre from such a mesh . in the embolic protection filter 410 of fig1 the tether arm 411 is located within the filter 410 . to couple the coupling member 24 to the filter 410 , the hook 100 is extended into the filter 410 and hooked around the tether arm 411 . in the filter 413 of fig1 , two tether arms 412 are provided . it will be appreciated that any suitable number of tether arms may be provided at either end of an embolic protection filter , and / or within the filter . referring to fig1 and 182 , there is illustrated another embolic protection filter 500 according to the invention , which is similar to the filter 720 . in this case , the filter 500 comprises an inner tubular member 502 to which the three tether arms 501 are fixed . the tubular member 502 defines a guidewire lumen 503 therethrough for passing a guidewire 530 through the tubular member 502 ( fig1 ). the tubular member 502 extends through only part of the filter 500 . as illustrated in fig1 , this enables the guidewire 530 to cross the filter 500 without having to thread the guidewire 530 through the relatively small diameter guidewire lumen 503 . this configuration may be particularly advantageous when it is desired to cross the filter 500 with a guidewire while the filter 500 remains deployed in a vasculature . in this circumstance , the distal end cone of the filter body may act as a guide to guide the guidewire 530 through the guidewire aperture 112 . the tubular member 502 of the embolic protection filter 510 illustrated in fig1 also extends only partially through the filter 510 to facilitate crossing of the filter 510 with the guidewire 530 without requiring threading of the guidewire 530 through the tubular member 502 . it will be appreciated that any other suitable means for coupling the deployed filter 1 with the coupling member 24 of the retrieval catheter 20 may be employed to facilitate retrieval of the filter 1 into the catheter body 23 , for example the coupling member 24 may be provided with one or more female recesses for engagement with one or more corresponding male protrusions on the filter 1 . alternatively a female member on the coupling member 24 may be provided in the form of a loop 701 , as illustrated in fig1 , for looping around a male stub 702 protruding from the filter 1 . referring to fig1 to 189 there is illustrated another retrieval catheter 905 according to the invention . in this case , the coupling member 24 comprises a pair of jaws 906 at the distal end of the coupling member 24 . the jaws 906 are movable between an outwardly protruding configuration ( fig1 ) and a low - profile configuration ( fig1 ) to grasp the filter 1 . the jaws 906 are biased towards the low - profile configuration and may be moved outwardly by moving an inner elongate actuator 907 longitudinally distally relative to the jaws 906 to engage elbows 908 on the jaws 906 and thereby move the jaws 906 outwardly in a camming arrangement ( fig1 ). the jaws 906 define a recessed portion 909 a for co - operation with a protruding neck 909 b on the proximal end of the filter 1 during grasping of the filter 1 , as illustrated in fig1 . in use , the retrieval catheter 905 is advanced through the vasculature 21 in the low - profile configuration until the jaws 906 are proximally adjacent to the deployed filter 1 . the actuator 907 is then moved distally relative to the jaws 906 to cam the jaws 906 open , and the opened jaws 906 are advanced until the recessed portion 909 a of the jaws 906 are around the protruding neck 909 b of the filter 1 . by moving the actuator 907 proximally relative to the coupling member 24 the jaws 906 are released to move inwardly to grasp the filter 1 around the neck 909 b . the grasped filter 1 may then be retrieved into the catheter body 23 by moving the catheter body 23 distally relative to the coupling member 24 . it will be appreciated that the jaws 906 may grasp any suitable part of the filter 1 to facilitate retrieval . for example , the jaws 906 may grasp the filter 1 at the inlet openings 6 , as illustrated in fig1 and 189 . as illustrated in fig1 to 191 , the jaws 906 may alternatively be biased outwardly . during advancement of the retrieval catheter 905 through the vasculature 21 , the jaws 906 are restrained in the low - profile configuration by the catheter body 23 ( fig1 ). to move the jaws 906 outwardly , the coupling member 24 is moved distally relative to the catheter body 23 to release the jaws 906 to spring outwardly ( fig1 ). to subsequently move the jaws 906 inwardly when the recessed portion 909 a of the jaws 906 are around the protruding neck 909 b of the filter 1 , the catheter body 23 is moved distally relative to the coupling member 24 to engage the jaws 906 and move the jaws 906 inwardly to grasp the filter 1 around the neck 909 b . the filter 1 is then retrieved into the catheter body 23 by advancing the catheter body 23 further distally relative to the coupling member 24 and the grasped filter 1 ( fig1 ). alternatively , the coupling member 24 may have a magnetic tip 25 for magnetic coupling to an oppositely charged magnetic portion of the filter 1 . fig1 and 194 illustrate another retrieval catheter 940 according to the invention . in this case , the retrieval catheter 940 comprises a second coupling member 941 , which is movable relative to the first coupling member 24 . in this way , the second coupling member 941 may be used to axially elongate an element of the deployed filter 1 , such as the filter support frame 3 , to collapse the filter 1 to the low - profile configuration for retrieval into the catheter body 23 . in this case , the second coupling member 941 acts as a pusher and is movable distally relative to the tip 25 . by engaging the tip 25 with the filter support 3 and then moving the second coupling member 41 distally to engage a distal end 42 of the filter support 3 , the filter support 3 is axially elongated and the filter 1 is collapsed from the outwardly extended configuration of fig1 to the collapsed configuration . the collapsed filter 1 may then be retrieved by moving the catheter body 23 distally relative to the tip 25 and the engaged filter 1 . referring to fig1 to 201 there is illustrated another filter retrieval system of the invention . in this case a snare type retrieval is used for a filter 850 with a guidewire 851 extending through a tubular member 852 . the tubular member 852 has a projecting head portion 853 with an associated marker band 854 for engagement by a lasso or loop 855 delivered through a retrieval catheter 856 into which the filter is retrieved as illustrated . another embodiment is illustrated in fig2 to 206 which is used for retrieval of a filter 860 which does not have a tubular member . in this case the filter frame has a snare receiving projection 861 which is engaged by a snare lasso / loop 862 and the filter 860 is retrieved into a retrieval catheter 863 , as illustrated . fig2 to 212 illustrate an embodiment in which a filter 870 is used which has a partial tubular member 871 but the guidewire does not extend through the tubular member . this arrangement is similar to that of fig1 to 201 above and like parts are assigned the same reference numerals . the snare loop is in this case free of the guidewire and may be more easily manipulated . in both cases the snare loop may be rendered radiopaque to facilitate snaring with the filter for retrieval . further retrieval devices are illustrated in fig2 to 218 in which the retrieval devices have arms 950 which open out when an outer sheath 951 is retracted and thus create a large inlet mouth which can readily trap the filter frame , particularly if radiopaque features such as marker bonds are used . when the arms 950 are in position distal to the snare feature of the frame / filter the arms are closed again , for example by re - advancing a sheath 951 which collapses the arms 950 and traps tether feature 952 of the filter , for example behind a step or tooth on the arm ( s ). referring to fig2 to 224 the filter frame may have a retrieval feature such as a nodule 960 which may be engaged by a suitable snare such as a snare loop or lasso 961 which is then tightened or simply pulled back to collapse the frame and retrieve the filter . the centering tip 962 may be used to assist guiding of the snare loop . various alternative filter designs with an integral snare feature are possible . for example , in fig2 and 226 the filter frame has a projecting arm 970 which may be engaged by a snare . an expandable engagement member 971 may be used to catch a drawstring type arrangement 972 ( fig2 , 228 ) or to catch internal wires / tethers / fibers / strings of the filter ( fig2 , 230 ). referring to fig2 and 232 there is illustrated the size of a snare 990 to snare a filter 991 . the snare engagable features of the filter in this case are provided by indents 992 in the support arms over which the snare loop 990 is engaged . the snaring of a filter of any type is illustrated in fig2 to 237 . in this case the filter 995 is positioned distal to a stent 996 and a snare loop 997 is advanced through the stent to engage the filter as illustrated , allowing the filter to be at least partially collapsed for retrieval . in fig2 and 239 there is illustrated the snaring of a filter 1 as illustrated in fig1 using a snare loop 998 . a further embolic protection filter 700 according to the invention is illustrated in fig2 and 241 . the filter 700 comprises a collapsible filter support structure 701 and a collapsible filter body 702 . in the expanded , deployed configuration of fig2 , the support structure 701 does not have an inner tubular member to define a guidewire lumen for passing a guidewire 703 through . when the filter 700 is collapsed , the support structure collapses down into a smaller diameter tubular structure , as illustrated in fig2 . in this collapsed configuration , the support structure 701 defines the guidewire lumen for the guidewire 703 . in this manner the support structure 701 isolates the filter body 702 from the guidewire 703 , and thus prevents the filter body 702 from becoming fixed to the guidewire 703 during delivery or retrieval of the filter 700 . the filter 700 may be retrieved using any suitable means , such as the hooked retrieval catheter ( fig2 ), in a manner similar to that described previously or the hooped retrieval catheter ( fig2 ), in a manner similar to that described previously . if it is desired to remove the guidewire 703 from the filter 700 and recross the filter 700 with a second guidewire 704 , the guidewire 704 may be threaded through one of the relatively large inlet openings 705 instead of through the relatively small proximal collar 706 of the support structure 701 , as illustrated in fig2 . this enables a faster and more convenient means of recrossing the filter 700 . in addition , the distal collar 707 of the filter support structure 701 is spaced proximally of the distal end of the filter 700 to facilitate crossing of the filter 700 with the second guidewire 704 without requiring the guidewire 704 to be threaded through the distal collar 707 ( fig2 ). the filter 700 can be retrieved after crossing the filter 700 with the second guidewire 704 using any suitable means ( fig2 and 246 ). referring to fig2 and 248 , there is illustrated another embolic protection filter 710 according to the invention , which is similar to the embolic protection filter 700 of fig2 and 241 , and similar elements in fig2 and 248 are assigned the same reference numerals . the filter 710 is longitudinally shorter than the filter 700 . in addition the filter support structure 701 ends in an open distal mouth 711 in the filter 710 and no distal collar is provided in the filter 710 , as illustrated in fig2 . in the filter 710 , the filter body 702 is isolated from the guidewire 703 by the collapsed filter support structure 701 ( fig2 ), in a manner similar to that described previously with reference to fig2 . the filter 710 may be recrossed by the second guidewire 704 by threading the guidewire 704 through one of the relatively large inlet openings 705 ( fig2 ), in a manner similar to that described previously with reference to fig2 . referring to fig2 to 256 the position of the filter 1 in the vasculature 21 may be controlled by an abutment 200 on a guidewire 201 . by engaging the abutment 200 with an abutment surface on the filter 1 , the filter 1 is prevented from moving distally of the guidewire abutment 200 . in this manner , the position of the filter 1 in the vasculature 21 may be controlled , if necessary . the abutment 200 may be fixedly attached to the guidewire 201 by a suitable means , such as by crimping , before introducing the guidewire 201 into the vasculature 21 . alternatively the abutment 200 may be fixed to the guidewire 201 during deployment of the filter 1 . as illustrated in fig2 the filter 205 according to the invention may have a tether 206 fixed to the filter 205 , extending proximally of the filter 205 . the tether 206 may be used by a clinician to control the position of the filter 205 in the vasculature 21 from a location externally of the vasculature 21 . the tether 206 may be in the form of a wire , and may be of any suitable material . in use , the filter 205 may be deployed over a guidewire 207 . if appropriate or necessary , the guidewire 207 may then be withdrawn from the filter 205 and the vasculature 21 . the tether wire 206 may then be used as a platform for advancing further devices through the vasculature 21 , for example the retrieval catheter 20 . referring to fig2 to 260 , there is illustrated another embolic protection filter assembly 115 according to the invention . the assembly 115 comprises a filter and a receiver to guide the guidewire 30 into the guidewire lumen 12 . the receiver is provided , in this case , by an approach channel 116 for the guidewire 30 in the form of a lumen in a separate catheter 117 . the catheter 117 has one or more inflatable balloons 118 at the distal end of the catheter 117 . the shape and / or position of the balloons 118 is configured to ensure that the blood flow through the vasculature 21 will not be occluded upon inflation of the balloon ( s ) 118 . in one case , the catheter 117 has three balloons 118 spaced circumferentially around the catheter 117 , as illustrated in fig2 . in another case , the catheter 117 has four circumferentially spaced balloons 118 ( fig2 ). in use , the catheter 117 is introduced into the vasculature 21 and advanced through the vasculature 21 until the catheter distal end is proximally adjacent the filter 1 ( fig5 ). the balloon 118 is then inflated until the balloon 118 engages the wall of the vasculature 21 . by engaging the balloon 118 with the wall of the vasculature 21 , the catheter 117 is spaced from the wall of the vasculature 21 to assist in locating the catheter approach channel 116 centrally in the vasculature 21 . the guidewire 30 may then be introduced into the channel 116 and advanced through the catheter 117 . because the channel 116 is located centrally in the vasculature 21 , the guidewire 30 is guided into the guidewire lumen 12 of the filter 1 as it passes out of the distal end of the channel 116 . the balloon 118 may be deflated to a low profile configuration during introduction and withdrawal of the catheter 117 from the vasculature 21 . it will be appreciated that any number of seals may be provided to prevent embolic material passing through the guidewire lumen or the guidewire aperture , and the seals may be positioned at any suitable point along the guidewire lumen or the guidewire aperture . it will further be appreciated that the receiver may be configured to guide a docking device in the form of a coupling member , such as those described previously , towards the filter for coupling to the filter . in such a manner , the receiver may be used to assist retrieval of the filter . the coupling means may be achieved by numerous alternatives , for example male - female inter - engagement , or magnetic coupling , or hook and eyelet means . fig2 illustrates another retrieval catheter 600 according to the invention . the coupling member 24 , in this case , has a tubular extension part 601 which extends distally of the hooks 100 . in use , the tubular extension 601 may be extended through an embolic protection filter 602 to be retrieved , as illustrated in fig2 . the tubular extension 601 in this way defines the guidewire lumen 603 through the filter 602 through which a guidewire 604 may be passed . the retrieval catheter 600 is particularly suitable for retrieving filters , such as the filter 602 which do not have an inner tubular member to define a guidewire lumen through the filter 602 . filters which do not have an inner tubular member are liable to becoming fixed against the guidewire 604 when the filter is collapsed down . when this occurs it is no longer possible to retrieve the filter while the guidewire remains in situ in the vasculature . by defining the guidewire lumen 603 using the tubular extension 601 of the retrieval catheter 600 , this serves to isolate the collapsing filter 602 from the guidewire 604 , and thus prevents the filter 602 from becoming fixed to the guidewire 604 . the tubular extension 601 may be advanced to the distal end of the filter 602 before retrieving the filter 602 into the catheter body 23 , as illustrated in fig8 . alternatively the tubular extension 601 may be advanced until the tubular extension 601 is distally of the distal end of the filter 602 before retrieving the filter 602 into the catheter body 23 . the invention is not limited to the embodiments hereinbefore described , with reference to the accompanying drawings , which may be varied in construction and detail .
an embolic filter having a filter support frame with a collapsed and an expanded configuration and a collapsible filter body supported by the support frame . the filter body has inlet and outlet ends . the filter body includes a proximal section having a longitudinally extending cylindrical shape and a distal section having a longitudinally extending conical shape that tapers in the distal direction . the support frame includes a plurality of alternating first segments such that , when the support frame is in the expanded configuration , the alternating first segments circumferentially extend in a first zigzag path to support the proximal , cylindrically shaped section of the filter body . the support frame includes a plurality of alternating second segments such that , when the support frame is in the expanded configuration , the alternating second segments circumferentially extend in a second zigzag path to support the proximal , cylindrically shaped section of the filter body .