referring to fig1 to 13 there is illustrated an embolic protection device as described in our wo - a - 9923976 indicated generally by the reference number 100 . the device 100 has a guidewire 101 with a proximal end 102 and a distal end 103 . a tubular sleeve 104 is slidably mounted on the guidewire 101 . a collapsible filter 105 is mounted on the sleeve 104 , the filter 105 being movable between a collapsed stored position against the sleeve 104 and an expanded position as shown in the drawings extended outwardly of the sleeve 104 for deployment in a blood vessel . the sleeve 104 is slidable on the guidewire 101 between a pair of spaced - apart end stops , namely an inner stop 106 and an outer stop which in this case is formed by a spring tip 107 at the distal end 103 of the guidewire 101 . the filter 105 comprises a filter body 110 mounted over a collapsible support frame 111 . the filter body 110 is mounted to the sleeve 104 at each end , the body 110 being rigidly attached to a proximal end 112 of the sleeve 104 and the body 110 being attached to a collar 115 which is slidable along a distal end 114 of the sleeve 104 . thus the distal end of the body 110 is longitudinally slidable along the sleeve 104 . the support frame 111 is also fixed at the proximal end 112 of the sleeve 104 . a distal end 116 of the support frame 111 is not attached to the sleeve 104 and is thus also free to move longitudinally along the sleeve 104 to facilitate collapsing the support frame 111 against the sleeve 104 . the support frame 111 is such that it is naturally expanded as shown in the drawings and can be collapsed inwardly against the sleeve 104 for loading in a catheter 118 or the like . the filter body 105 has large proximal inlet openings 117 and small distal outlet openings 119 . the proximal inlet openings 117 allow blood and embolic material to enter the filter body , while , the distal outlet openings 119 allow through passage of blood but retain undesired embolic material within the filter body . an olive guide 120 is mounted at a distal end of the sleeve 104 and has a cylindrical central portion 121 with tapered ends 122 , 123 . the distal end 122 may be an arrowhead configuration for smooth transition between the catheter and olive surfaces . the support frame 111 is shaped to provide a circumferential groove 125 in the filter body 110 . if the filter is too large for a vessel , the body may crease and this groove 125 ensures any crease does not propagate along the filter . enlarged openings are provided at a proximal end of the filter body 110 to allow ingress of blood and embolic material into an interior of the body 110 . in use , the filter 105 is mounted in a collapsed state within a distal end of the catheter 118 and delivered to a deployment site . when the filter is correctly positioned the catheter 118 is retracted allowing the support frame 111 to expand expanding the filter body 110 across the vessel in which the filter is mounted . blood and emboli can enter the enlarged openings at a proximal end of the filter body 110 . the blood will pass through the filter body , however , the openings or pores in the filter body are sized so as to retain the embolic material . after use , a retrieval catheter 18 is delivered along the guidewire 101 and slid over the filter 105 engaging the proximal inlet end 112 first to close the openings and then gradually collapsing the filter body against the sleeve 104 as the catheter 118 advances over the filter 105 . once the filter 105 is fully loaded in the catheter 118 , it can then be withdrawn . it will be noted that a proximal end of the filter is fixed and a distal end of the filter is longitudinally movable along the sleeve to facilitate collapsing of the filter body . further , the catheter engages the proximal end of the filter body first thus closing the filter body inlet and preventing escape of embolic material from the filter body as the filter body is being collapsed . the outer filter body 110 is preferably of a resilient biocompatible elastomeric material . the material may be a polyurethane based material . there are a series of commercially available polyurethane materials that may be suitable . these are typically based on polyether or polycarbonate or silicone macroglycols together with diisocyanate and a diol or diamine or alkanolamine or water chain extender . examples of these are described in ep - a - 461 , 375 and u . s . pat . no . 5 , 621 , 065 . in addition , polyurethane elastomers manufactured from polycarbonate polyols as describe u . s . pat . no . 5 , 254 , 622 ( szycher ) are also suitable . the filter material may also be a biostable polycarbonate urethane article example of which may be prepared by reaction of an isocyanate , a chain extend and a polycarbonate copolymer polyol of alkyl carbonates . this material described in our wo - a - 9924084 . the filter material may be manufactured from a block and cut into a desired shape . however the filter is preferably formed by dipping a rod of desired geometry into a solution of the material which coats the rod . the rod is then dissolved . the final geometry of the filter may be determined in the dipping step or the final geometry may be achieved in a finishing operation . typically the finishing operations involve processes such as mechanical machining operations , laser machining or chemical machining . the filter body is of hollow construction and is formed as described above by dipping a rod in a solution of polymeric material to coat the rod . the rod is then dissolved , leaving a hollow body polymeric material . the rod may be of an acrylic material which is dissolved by a suitable solvent such as acetone . the polymeric body thus formed is machined to the shape illustrated in fig1 to 13 . the final machined filter body comprises an inlet or proximal portion 210 with a proximal neck 212 , and outlet or distal portion 213 with a distal neck 214 , and an intermediate portion 215 between the proximal and distal portions . the inlet holes 117 are provided in the proximal portion 210 which allow the blood and embolic material to flow into the filter body . in this case the proximal portion 210 is of generally conical shape to maximise the hole size . the intermediate portion 215 is also hollow and in this case is of generally cylindrical construction . this is important in ensuring more than simple point contact with the surrounding blood vessel . the cylindrical structure allows the filter body to come into soft contact with the blood vessel to avoid damaging the vessel wall . the intermediate portion 215 is provided with a radial stiffening means , in this case in the form of a radial strengthening ring or rim 220 . the ring 220 provides localised stiffening of the filter body without stiffening the material in contact with the vessel . such an arrangement provides appropriate structural strength so that line apposition of the filter body to the vessel wall is achieved . it is expected that other geometries of stiffening means will achieve a similar result . the tubular intermediate portion 215 is also important in maintaining the stability of the filter body in situ to retain captured emboli and to ensure that flow around the filter is minimised . for optimum stability we have found that the ratio of the axial length of the intermediate portion 215 of the filter body to the diameter of the intermediate portion 215 is preferably at least 0 . 5 and ideally greater than 1 . 0 . the collapsible support frame 111 has four foldable arms 290 which are collapsed for deployment and upon release extend outwardly to expand the filter body 110 . the support frame 111 can be manufactured from a range of metallic or polymeric components such as a shape memory alloy like nitinol or a shape memory polymer or a shaped stainless steel or metal with similar properties that will recover from the deformation sufficiently to initiate opening of the filter body 110 . the support frame may be formed as illustrated in fig1 by machining slots in a tube 291 of shape memory alloy such as nitinol . on machining , the unslotted distal end of the tube forms a distal collar 293 and the unslotted proximal end of the tube forms a proximal collar 294 . in use , the distal collar 293 is slidably moveable along the tubular sleeve 104 which in turn is slidably mounted on the guidewire 101 for deployment and retrieval . the proximal collar 294 is fixed relative to the tubular sleeve 104 . to load the filter the sub assembly of the support frame and filter body is pulled back into the catheter 118 to engage the distal stop 107 . the support arms 290 are hinged inwardly and the distal collar 293 moves forward along the tubular sleeve 104 . as the support arms 290 enter the catheter 118 the filter body 110 stretches as the filter body collar 115 slides along the tubular sleeve 104 proximal to the olive 120 . on deployment , the catheter 118 is retracted proximally along the guidewire 101 initially bringing the collapsed filter assembly with it until it engages the proximal stop 106 . the catheter sleeve then begins to pull off the filter , freeing the support arms 290 to initiate opening of the filter body to appose the vessel wall . for retrieval , a retrieval catheter is introduced by sliding it over the guidewire 101 until it is positioned at the proximal end of the filter body and support frame . pulling the guidewire 101 will initially engage the distal stop 107 with the filter element and begin to pull it into the retrieval catheter . the initial travel into the delivery catheter acts to close the proximal openings of the filter element , thus entrapping the embolic load . as the filter continues to be pulled back the filter body and the support frame are enveloped in the retrieval catheter . the collapsed filter may then be removed from the patient . referring to fig1 and 15 there is illustrated a medical guidewire assembly according to one embodiment of the invention . a filter 31 is mounted on a guidewire 30 and projecting from the distal end of the guidewire 30 is a guidewire tip 32 . the guidewire tip 32 is slidable in a bore 38 in a sleeve 39 of the filter 31 . when the filter 31 is being manoeuvred into place the guidewire tip 32 facilitates the manoeuvring of the filter device . by advancing and retracting the tip 32 relative to the filter assembly 31 it is possible to manoeuvre the guidewire tip 32 around various portions of the anatomy , for example , where it is particularly tortuous , or where the guidewire tip 32 has to cross lesions . the tip 32 can be partially retracted to give a stiffer tip , or can be fully retracted in the deployment position , fig1 . the guidewire 30 is slidable between a proximal guidewire limiting element 35 on the guidewire 30 and a filter limiting element 37 provided at a proximal end of the filter 31 . a stop defined by a shoulder 36 of the tip 32 is engagable against the limiting element 37 . the proximal limiting element 35 and the filter limiting element 37 are of a relatively stiff material , such that upon engagement of the filter 31 with the proximal limiting element 35 , or the shoulder 36 with the filter limiting element 37 , the limiting elements 35 , 37 do not deform . in this way the movement of the filter 31 relative to the guidewire tip 32 is accurately controlled . one or both of the limiting elements 35 , 37 may be of a compliant material . this feature will assist in ensuring that the flexibility of the filter is not affected by the limiting elements . referring to fig1 and 17 there is illustrated a medical guidewire assembly including a filter 42 , which is similar to the filter 31 of fig1 and 15 , and the same reference numerals are used to denote similar elements in fig1 and 17 . in this case the guidewire 30 is slidable between a proximal limiting element 35 on the guidewire 30 and a filter limiting element 40 positioned intermediate the proximal and distal ends of the filter 42 . a distal stop defined by a shoulder 36 of the tip 32 is engagable against the filter limiting element 40 . referring to fig1 to 20 there is illustrated a medical guidewire assembly including a filter 50 , which is similar to filters 31 and 42 of fig1 to 17 , and the same reference numerals are used to denote similar elements in fig1 to 20 . in this arrangement a guidewire limiting element 51 is rigidly fixed to the guidewire 30 proximal of the tip 32 , the filter 50 being mounted on the guidewire 30 so that the limiting element 51 is intermediate the proximal and distal ends of the filter 50 . the guidewire 30 is slidable between a distal limiting element defined by a proximal shoulder 53 of the filter 50 which is engagable against the guidewire limiting element 51 , and a proximal limiting element defined by a distal shoulder 52 of the filter 50 which is engagable against the guidewire limiting element 51 . in this arrangement there is no obstruction to advancement of another medical device over the guidewire 30 to approach the filter 50 from the proximal direction . referring to fig2 to 23 in an alternative embodiment of the invention , the guidewire limiting element 51 is slidably mounted within a recess 53 provided on the guidewire 30 , the movement of the limiting element 51 relative to the guidewire 30 being limited between a proximal stop provided by a shoulder 55 of the recess and a distal stop provided by a shoulder 54 provided by the guidewire tip 32 . this arrangement provides an even greater degree of freedom for movement of the guidewire 30 relative to the filter . the filter may be placed over or beyond the distal guidewire tip . thus , the invention facilitates the optimal placement of a filter device in the limited vasculature space available . other medical devices may be advanced over the guidewire to approach the filter from the proximal direction without obstruction . such devices may be for use in performing angioplasty procedures , stenting and the like . ready access is also provided to perform emergency procedures such as snaring of a medical device or part , and lysis for treatment of a blood clot . it will be appreciated that while the invention has been described in relation to an embolic protection device it may also be applied to medial guidewire assemblies for placement of other medical devices . the invention is not limited to the embodiments hereinbefore described which may be varied in both construction and detail .
a medical guidewire assembly comprises a guidewire having a flexible tip . a medical device such as a collapsible filter for use as an embolic protection device is mounted on the guidewire . the filter is advanced through a body lumen with the guidewire tip extending distally . at a first location the filter is advanced relative to the tip to a location which is distally advanced from the first location . placement of the filter in an optimal distal location is thereby achieved .