Recoilable thrombosis filtering device and method

A thrombosis filter which can be securely affixed at a selected location in the vascular system of a patient and removed when no longer required. An embodiment of the thrombosis filter includes a plurality of struts formed of a shape memory material. A change in temperature can cause the struts to extend and engage a wall of a blood vessel.

FIELD OF THE INVENTION

The present invention relates generally to filters for use inside blood vessels. More particularly, the present invention relates to thrombus filters which can be securely affixed at a selected location in the vascular system and removed when no longer required.

BACKGROUND OF THE INVENTION

There are a number of situations in the practice of medicine when it becomes desirable for a physician to place a filter in the vascular system of a patient. One of the most common applications for vascular filters is the treatment of Deep Venous Thrombosis (DVT). Deep Venous Thrombosis patients experience clotting of blood in the large veins of the lower portions of the body. These patients are constantly at risk of a clot breaking free and traveling via the inferior vena cava to the heart and lungs. This process is known as pulmonary embolization. Pulmonary embolization can frequently be fatal, for example when a large blood clot interferes with the life-sustaining pumping action of the heart. If a blood clot passes through the heart it will be pumped into the lungs and may cause a blockage in the pulmonary arteries. A blockage of this type in the lungs will interfere with the oxygenation of the blood causing shock or death.

Pulmonary embolization may be successfully prevented by the appropriate placement of a thrombus filter in the vascular system of a patient's body. Placement of the filter may be accomplished by performing a laparotomy with the patient under general anesthesia. However, intravenous insertion is often the preferred method of placing a thrombus filter in a patient's vascular system.

Intravenous insertion of a thrombus filter is less invasive and it requires only a local anesthetic. In this procedure, the thrombus filter is collapsed within a delivery catheter. The delivery catheter is introduced into the patients vascular system at a point which is convenient to the physician. The delivery catheter is then fed further into the vascular system until it reaches a desirable location for filter placement. The thrombus filter is then released into the blood vessel from the delivery catheter.

In the treatment of Deep Venous Thrombosis, a thrombus filter is placed in the inferior vena cava of a patient. The inferior vena cava is a large vessel which returns blood to the heart from the lower part of the body. The inferior vena cava may be accessed through the patient's femoral vein.

Thrombus filters may be placed in other locations when treating other conditions. For example, if blood clots are expected to approach the heart and lungs from the upper portion of the body, a thrombus filter may be positioned in the superior vena cava. The superior vena cava is a large vessel which returns blood to the heart from the upper part of the body. The superior vena cava may by accessed through the jugular vein, located in the patient's neck.

Once placed inside a blood vessel, a thrombus filter acts to catch and hold blood clots. The flow of blood around the captured clots allows the body's lysing process to dissolve the clots.

SUMMARY OF THE INVENTION

The present invention pertains to a thrombosis filter which can be securely affixed at a selected location in the vascular system of a patient and removed when no longer required. In a first embodiment, the thrombosis filter includes a strut formation, a wire formation, and a body portion. The body portion includes a plurality of apertures. The strut formation includes a plurality of struts each having a fixed end and a free end. The fixed ends of the struts are each fixably attached to the body portion of the thrombus filter inside the apertures; one strut radiating from each aperture.

The wire formation is comprised of a plurality of wires. Each wire has a fixed end and a free end. The fixed ends of the wires are fixably attached to the body portion of the thrombus filter. The struts radiate away from the proximal end of the body portion in a proximal direction such that the strut formation is generally conical in shape. Likewise, the wires radiate away from the distal end of the body portion in a distal direction such that the wire formation is generally conical in shape.

When the thrombosis filter is disposed in a blood vessel, the wire formation acts to capture blood clots. The generally conical shape of the wire formation serves to urge captured blood clots toward the center of the blood flow. The flow of blood around the captured clots allows the body's natural lysing process to dissolve the clots. The struts are formed of a shape memory material. At about body temperature, the struts assume an extended shape and engage the walls of the blood vessel. At a selected temperature, other than body temperature, the struts assume a contracted shape. This contracted shape causes the struts to contract inside the apertures of the body portion.

Various techniques can be used to alter the temperature of the struts causing them to retract. Suitable techniques for warming the thrombosis filter include applying electromagnetic energy to a portion of the thrombosis filter (e.g. laser light delivered by an optical fiber), and inducing an electrical current through a portion of the thrombosis filter. In a preferred embodiment, the struts are cooled by introducing a relatively cool fluid into the blood vessel proximate the thrombosis filter. After the struts are retracted, the thrombosis filter can be readily pulled into the lumen of a removal catheter.

A second embodiment of the thrombosis filter includes a generally cylindrical anchoring portion and a generally conical filtering portion terminating at a body member. The filtering portion includes a plurality of elongated strands. The strands of the filtering portion are arranged in an interwoven pattern to create cells. The interwoven pattern of strands enables the filtering portion to trap or capture blood clots. The conical shape of the filtering portion urges captured blood clots toward the center of the blood flow. The flow of blood around the captured blood clots allows the body's natural lysing process to dissolve the clots.

The strands extend beyond the filtering portion to create the anchoring portion. The strands are formed from a shape memory alloy. The shape memory alloy construction of the thrombosis filter allows it to change shape in response to a change in temperature. At about body temperature, the thrombosis filter assumes an extended shape. At a selected temperature other than body temperature, the thrombosis filter assumes a contracted shape. When the thrombosis filter assumes a contracted shape the anchor portion of the thrombosis filter disengages the walls of the blood vessel. When it is desirable for the thrombosis filter to be removed from a blood vessel, a physician may selectively heat or cool the thrombosis filter causing it to assume the contracted shape. Various techniques can be used to change the temperature of the thrombosis filter. In a preferred embodiment, the thrombosis filter is cooled by introducing a relatively cold fluid into the blood vessel proximate the thrombosis filter. Once the thrombosis filter assumes a contracted shape, it may be pulled in the lumen of a removal catheter.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description should be read with reference to the drawings, in which like elements in different drawings are numbered identically. The drawings which are not-necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention.

Examples of constructions, materials, dimensions, and manufacturing processes are provided for selected elements. All other elements employ that which is known to those of skill in the field of the invention. Those skilled in the art will recognize that many of the examples provided have suitable alternatives which may be utilized.

Reference is now made to the drawings, in which like numbers refer to like elements throughout.FIG. 1is a plan view of a thrombosis filter20positioned in a lumen21of a blood vessel22. Blood vessel22includes walls23which define lumen21. The main components of thrombosis filter20are a body portion24, a strut formation26and a wire formation28.

Body portion24includes a plurality of apertures30. Strut formation26includes a plurality of struts32each having a fixed end34, and a free end36. Fixed ends34of struts32are each fixedly attached to body portion24inside apertures30; one strut32radiating from each aperture30.

Wire formation28is comprised of a plurality of wires37. Each wire37has a fixed end38and a free end40. Fixed ends38of wires37are fixedly attached to body portion24.

Wire37may include a plurality of bends46disposed between free end40and fixed end38. Free end40of each wire37includes an anchor50. Likewise, each strut32includes an anchor52. InFIG. 1, anchors50and52are pictured as sharp projections or barbs. It should be understood that anchors50and52may be comprised of other means for anchoring without departing from the spirit or scope of this invention.

Body portion24includes a proximal end60and a distal end62. A coupling member64is fixedly attached to proximal end60of body portion24.

Struts32radiate away from proximal end60of body portion24in a proximal direction. Such that strut formation26is generally conical in shape. Likewise, wires37radiate away from distal end62of body portion24in a distal direction such that wire formation28is generally conical in shape.

When thrombosis filter20is disposed in a blood vessel, wire formation28acts to trap, or capture blood clots. The generally conical shape of wire formation28serves to urge captured blood clots toward the center of the blood flow. The flow of blood around the captured blood clots allows the body's natural lysing process to dissolve the clots.

Struts32act as opposing wall contacting members and serve to position thrombosis filter20in the center of lumen21of blood vessel22shown with hidden lines in FIG.1. Likewise, wires37act as opposing wall contacting members and serve to position thrombosis filter20in the center of lumen21of blood vessel22. Anchors52of struts32generally oppose anchors50of wires37. These opposing anchors50and52serve to maintain the position of thrombosis filter20, preventing it from migrating upstream or downstream in blood vessel22. In the embodiment shown inFIG. 1anchors50and52include a plurality of sharp projections which penetrate the walls of blood vessel22.

Struts32and wires37may all be fabricated from wire with a circular, rectangular or other cross section. For example, straight wires37may be comprised of 0.018″ diameter wire. Stainless steel, titanium, and nickel titanium alloy have all been found to be acceptable materials for wires37.

Struts32are formed from a shape-memory material. The shape-memory material of struts32may be a shape-memory polymer, or a shape-memory alloy. Suitable shape memory materials are commercially available from Memry Technologies (Brookfield, Conn.), TiNi Alloy Company (San Leandro, Calif.), and Shape Memory Applications (Sunnyvale, Calif.). In a preferred embodiment, struts32are comprised of an alloy of titanium and nickel known in the art as Nitinol.

The shape-memory material construction of struts32enable struts32to change shape in response to a change in temperature. At about body temperature, struts32assume an extended shape as shown in FIG.1. At a selected temperature other than body temperature, struts32assume a contracted shape as shown in FIG.2.

InFIG. 2, struts32have partially contracted inside apertures30of body portion to24. As a result of the contraction of struts32, anchors52have retracted from walls23of blood vessel22.

Various techniques can be used to alter the temperature of struts32. Suitable techniques for warming struts32include applying electromagnetic energy to body portion24(e.g. laser light delivered by an optical fiber), and applying electrical energy to thrombosis filter20(e.g. inducing a current through struts32).

A process which may be used to remove thrombosis filter20from lumen21of blood vessel22is illustrated inFIG. 3. Aremoval catheter110with a lumen112and a distal end114is disposed in lumen21of blood vessel22. Removal catheter10enters the patients vascular system at a point which is readily accessible to the physician. Once in the vascular system, removal catheter110is urged forward until distal end114is proximate thrombosis filter20. For example, if thrombosis filter20is located in the inferior vena cava of a patients vascular system, removal catheter110may enter the vascular system at the femoral vein. Alternately, if thrombosis filter20is located in the superior vena cava of a patients vascular system, removal catheter110may enter the vascular system at the jugular vein. In either case, the filter removal procedure is minimally invasive, and does not require general anesthesia.

An elongated retrieval member116including a distal end118and a proximal end120(not shown) is disposed in lumen112of removal catheter110. InFIG. 3, distal end118of retrieval member116has been releasibly mated to coupling member64of thrombosis filter20. Proximal end120of elongated retrieval member116protrudes beyond the proximal end of removal catheter110. Both removal catheter110and retrieval member116extend outside the body of the patient.

When distal end114of removal catheter110reaches a position proximate thrombosis filter20, the temperature of struts32is altered, causing them to retract. With struts32in a retracted position, thrombosis filter20may be readily pulled into lumen112of removal catheter110by applying a pulling force to proximal end120of retrieval member116. This pulling force is transferred via retrieval member116to thrombosis filter20. The pulling force applied to retrieval member116of thrombosis filter20pulls anchors50of wires37out of blood vessel22.

As shown ifFIG. 3, pulling thrombosis filter20into lumen112of removal catheter110causes wires37to collapse causing wire formation28to transform from a generally conical shape toward a generally cylindrical shape. With wires37in a collapsed position, thrombosis filter20may be pulled completely into lumen112of removal catheter110. Once thrombosis filter20is inside lumen112; removal catheter110may be withdrawn from blood vessel22.

FIG. 4is a plan view of a second embodiment of a thrombosis filter400, disposed in a blood vessel450. Blood vessel450includes a lumen452defined by blood vessel walls454. Thrombosis filter400includes a generally cylindrical anchoring portion402, and a generally conical filtering portion404terminating at a body member406. Filtering portion404includes a plurality of elongated struts or strands410. Strands410of filtering portion404are arranged in an interwoven pattern to create cells412. The interwoven pattern of strands410enables filtering portion404to trap, or capture blood clots. The conical shape of filtering, portion404urges captured blood clots toward the center of the blood flow. The flow of blood around the captured blood clots allows the to body's natural lysing process to dissolve the clots.

Strands410extend beyond filtering portion404into anchoring portion402. Strands410are formed from a shape-memory material. The shape-memory material of strands410may be a shape-memory polymer or a shape memory metal. Suitable shape memory materials are commercially available from Memry Technologies (Brookfield, Conn.), TiNi Alloy Company (San Leandro, Calif.), and Shape Memory Applications (Sunnyvale, Calif.). In a preferred embodiment, strands410are comprised of an alloy of titanium and nickel known in the art as Nitinol.

The term “strands”, as used in describing strands410should not be mistaken as limiting strands410to elements having a circular cross section. The cross section of strands410may be any number of shapes. For example, the cross section of strands410could be rectangular, elliptical, etc. Embodiments of the present invention have been envisioned in which strands410are comprised of laser cut elements.

The shape-memory alloy construction of strands410enable thrombosis filter400to change shape in response to a chance in temperature. InFIG. 4, thrombosis filter400is shown in an extended shape420. Thrombosis filter400assumes extended shape420when strands410are generally at about body temperature. A contracted shape430is shown with phantom lines in FIG.4. Thrombosis filter400assumes contracted shape430when strands410are at a selected temperature other than body temperature.

When it is desirable for thrombosis filter400to be removed from a blood vessel, a physician may selectively heat or cool thrombosis filter400causing it to assume contracted shape430. When thrombosis filter400assumes contracted shape430, anchoring portion402retracts away from walls454of blood vessel450.

Various techniques may be utilized to change the temperature of thrombosis filter400. Suitable techniques for warming thrombosis filter400include applying electromagnetic energy to body member406(e.g. laser light delivered by an optical fiber), and applying electrical energy to thrombosis filter400(e.g. inducing a current through strands410). In a preferred cooling method, the thrombosis filter is cooled by introducing a relatively cold fluid into the body proximate the thrombosis filter.

Thrombosis filter400may be removed from lumen452of blood vessel450utilizing a method similar to the one described for the previous embodiment. A removal catheter is positioned in lumen452of blood vessel450so that the distal end of the removal catheter is proximate thrombosis filter400.

Embodiments of the present invention are possible in which portions of the thrombosis filter are coated with a coating material. Embodiment of the present invention have been envisioned in which the coating material prevents tissue growth proximate the filter to facilitate subsequent disengagement of the filter. Embodiment of the present invention have also been envisioned in which the coating material comprises a non-stick material to facilitate subsequent disengagement of the filter. These envisioned coating materials may be utilized with the various embodiments disclosed herein.

The removal catheter may enter the patients vascular system at a point which is readily accessible to the physician. Once in the vascular system, the removal catheter is urged forward until its distal end is proximate thrombosis filter400. For example, if thrombosis filter400is located in the inferior vena cava of a patients vascular system, the removal catheter may enter the vascular system at the femoral vein. Alternately, if thrombosis filter400is located in the superior vena cava of a patients vascular system, the removal catheter may enter the vascular system at the jugular vein. In either case, the filter removal procedure is minimally invasive, and usually does not require general anesthesia.

An elongated retrieval member is disposed in the lumen of the retrieval catheter. The distal end of the elongated retrieval member is releasably mated to a coupling member440which is fixedly attached to body member406of thrombosis filter400.

A presently preferred method includes the step of altering the temperature of strands410. When the temperature of strands410is altered, they change shape, causing thrombosis filter400to retract from extended position420to contracted position430. The change in shape causes anchor portion402to disengage walls454of blood vessel450

With anchor portion402disengaged from walls454of blood vessel450, thrombosis filter400may be readily pulled into the lumen of the retrieval catheter. The pulling force is applied to thrombosis filter400by pulling on the proximal end of the elongated retrieval member which has been joined to coupling member440.

FIG. 5is a plan view illustrating thrombosis filter400taken from line A—A shown in FIG.4. Thrombosis filter400is disposed in lumen452of blood vessel450. Thrombosis filter400includes filtering portion404. Filtering portion404includes strands410which are arranged in an interwoven pattern to create cells412. The interwoven pattern of strands410enables filtering portion404to trap, or capture blood clots. The conical shape of filtering portion404urges captured blood clots toward the center of the blood flow. The flow of blood around the captured blood clots allows the body's natural lysing process to dissolve the clots.

FIG. 6is a plan view of an additional embodiment of a thrombosis filter500. In the embodiment ofFIG. 6, thrombus filter500includes a body portion502and a plurality of spokes506. Spokes506each have a joined end508and a free end.510. Joined end508of each spoke506is fixedly attached to body portion502. Spokes506radiate outwardly from body portion502such that thrombus filter500is generally conical in shape. An anchor member512is disposed proximate the free end510of each spoke506.

Thrombosis filter500also includes a ring520which is disposed proximate free ends510of spokes506. In the embodiment ofFIG. 6, each spoke506is fixed to ring520. Those of skill in the art will appreciate that many methods may be used to fix ring520to Spokes506. Examples of methods which may be Suitable in some applications include welding, brazing, soldering, and the use of adhesives. Other embodiments of thrombus filter500are possible, in which ring520mechanically engages spokes506. For example, spokes506may include holes, slots, or eyes. In this exemplary embodiment, ring520may be threaded through the holes, slots, or eyes of spokes506.

As shown inFIG. 6, ring520of thrombus filter500includes a plurality of bends522. In a presently preferred embodiment, ring520is comprised of a shape memory alloy. Suitable shape memory alloys are commercially available from Memry Technologies (Brookfield, Conn.), TiNi Alloy Company (San Leandro, Calif.), and Shape Memory Applications (Sunnyvale, Calif.). In a presently most preferred embodiment, ring520is comprised of an alloy of titanium and nickel known in the art as Nitinol.

When thrombus filter500is released in a blood vessel, spokes506expand outward so that free ends510of spokes506contact the walls of the blood vessel. The geometry of anchor members512results in localized contact between the thrombus filter and the blood vessel walls. Anchor members512become imbedded in the walls of the blood vessel proximate these points of initial contact.

FIG. 7is a plan view of a thrombus filter500in an expanded state. Thrombus filter500of the embodiment shown inFIGS. 6 and 7includes an insulating layer524substantially covering thrombus filter500including body portion502, spokes506, and anchor members512. A number of materials have been found to be suitable for use in insulating layer524, these materials include fluoropolytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), polyvinylchloride (PVC), and polyurethane. A number of manufacturing processes may be used to create insulating layer524. For example, a portion of insulating layer524may be made up of sections of shrink tubing. The shrink tubing sections may be positioned over the spokes then shrunk by the application of heat. A spray process may also be used to apply insulating layer524to thrombus filter500. For example, spraying PTFE solids in a suitable solvent carrier is a process which has been found suitable for this application.

Another material which may be used to fabricate insulating layer524is a thermoplastic generically known as parylene. There are a variety of polymers based on para-xylylene. These polymers are typically placed onto a substrate by vapor phase polymerization of the monomer. Parylene N coatings are produced by vaporization of a di(P-xylylene)dimer, pyrollization, and condensation of the vapor to produce a polymer that is maintained at comparatively lower temperature. In addition to parylene-N, parylene-C is derived from di(monochloro-P-xylylene) and parylene-D is derived from di(dichloro-P-xylylene). There are a variety of known ways to apply parylene to substrates.

It should be understood that insulating layer524may include apertures, when these apertures are necessary to create an electrical circuit. The significance of these apertures and insulating layer524will be made clear in the discussion which follows.

FIG. 8is a diagrammatic view illustrating a process which may be used to remove a thrombus filter600from the body of a patient. In the embodiment ofFIG. 7, thrombus filter600includes a body portion602and a plurality of spokes606. Spokes606each have a joined end608and a free end610. Joined end608of each spoke606is fixedly attached to body portion602. In a presently preferred embodiment, body portion602is comprised of a non-conductive material so that body portion602does not form a path for electric current between spokes606.

Thrombosis filter600also includes a ring620which is disposed proximate free ends610of spokes606. In a presently preferred embodiment, ring620is electrically coupled to spokes606. Also in a presently preferred embodiment, ring620is comprised of a shape memory alloy. Suitable shape memory alloys are commercially available from Memry Technologies (Brookfield, Conn.), TiNi Alloy Company (San Leandro, Calif.), and Shape Memory Applications (Sunnyvale, Calif.). In a presently most preferred embodiment, ring620is comprised of an alloy of titanium and nickel known in the art as Nitinol.

InFIG. 8, thrombus filter600is disposed within a lumen632of a blood vessel630. A removal catheter640is also disposed within lumen632of blood vessel630. A distal end644of removal catheter640is disposed proximate thrombus filter600. Removal catheter also includes a lumen642and a proximal end646.

A first electrical conductor650and a second electrical conductor660are disposed inside lumen642of removal catheter640. First electrical conductor650includes a proximal end654and a distal end652. Second electrical conductor660includes a proximal end664and a distal end662.

As in the previous embodiment, thrombus filter600includes a insulating layer624. In the embodiment ofFIG. 8, distal end652of first electrical conductor650has penetrated insulating layer624of thrombus filter600to form an electrical connection with a first spoke616. Likewise, distal end662of second electrical conductor660has penetrated insulating layer624of thrombus filter600to form an electrical connection with a second-spoke618.

A number of methods may be suitable for forming the electrical connection between the distal ends of the electrical conductors and the spokes. For example, a needle electrode may be disposed at distal ends652,662of electrical conductors650,660respectively. The needle electrodes could penetrate insulating layer524and make electrical contact with the spokes. An easily deformable material such as silicone rubber or foam rubber could be disposed around the needle electrode to insulate the electrical connection.

Proximal end654of first electrical conductor650and proximal end664of second electrical conductor660are both electrically coupled to a power supply670. Power supply670is used to selectively apply a voltage differential between first electrical conductor650and second electrical conductor660.

In the embodiment ofFIG. 8, a circuit path between first spoke616and second spoke618comprises ring620. In a presently preferred embodiment, current must travel through ring620in order to pass from first spoke616to second spoke618. The voltage differential created by power supply670induces a current flow through ring620. The flow of current through ring620causes the temperature of ring620to be altered. When the temperature of ring620is altered, ring620assumes a contracted position as shown in FIG.9.

FIG. 9, is a diagrammatic view of the thrombus filter ofFIG. 8with ring620in a contracted position. As shown inFIG. 9, the contraction of ring620causes anchors612to disengage the walls of blood vessel630. Once anchors612are disengaged from the walls of blood vessel630, thrombus filter600may be pulled into lumen642of removal catheter640.

FIG. 10is a diagrammatic view illustrating an additional process which may be used to remove a thrombus filter700from the body of a patient. In the embodiment ofFIG. 10, thrombus filter700includes a body portion702and a plurality of spokes706. Spokes706each have a joined end708and a free end710. Joined end708of each spoke706is fixedly attached to body portion702. In a presently preferred embodiment, of thrombus filter700, body portion702is electrically insulated from the plurality of spokes706with the exception of a first spoke0.716. In this presently preferred embodiment, body portion702is electrically coupled to first spoke716.

Thrombosis filter700also includes a ring720which is disposed proximate free ends710of spokes706. In a presently preferred embodiment, ring720is electrically coupled to first spoke716. Also in a presently preferred embodiment, ring720is comprised of a shape memory alloy. Suitable shape memory alloys are commercially available from Memry Technologies (Brookfield, Conn.), TiNi Alloy Company (San Leandro, Calif.), and Shape Memory Applications (Sunnyvale, Calif.). In a presently most preferred embodiment, ring720is comprised of an alloy of titanium and nickel known in the art as Nitinol.

InFIG. 10, thrombus filter700is disposed within a lumen732of a blood vessel730. A removal catheter740is also disposed within lumen732of blood vessel730. A distal end744of removal catheter740is disposed proximate thrombus filter700. Removal catheter also includes a lumen742, a proximal end746, and a ring electrode780disposed proximate the distal end thereof.

A first electrical conductor750and a second electrical conductor760are disposed inside lumen742of removal catheter740. First electrical conductor750includes a proximal end754and a distal end752. Second electrical conductor760includes a proximal end764and a distal end762.

As shown inFIG. 10, distal end762of second electrical conductor760is coupled to ring electrode780. Distal end752of first electrical conductor750is coupled to body portion702of thrombus filter700. As in the previous embodiment, thrombus filter700includes a insulating layer724.

In the embodiment ofFIG. 10, distal end752of first electrical conductor750has penetrated insulating layer724of thrombus filter700to form an electrical connection with body portion702. Also in the embodiment ofFIG. 10, insulating layer724includes an aperture790. Aperture790allows a portion of thrombus filter700to make electrical contact with the body of the patient. Those of skill in the art will appreciate that a number of embodiments of aperture790are possible without deviating from the spirit and scope of the present invention.

Proximal end754of first electrical conductor750and proximal end764of second electrical conductor760are both electrically coupled to a power supply770.

Power supply770is used to selectively apply a voltage differential between first electrical conductor750and second electrical conductor760.

In the embodiment ofFIG. 10, a circuit path between first electrical conductor750and second electrical conductor760comprises body portion702, first spoke716, ring720, aperture790, ring electrode780, and the body of the patient. Those of skill in the art will appreciate that many embodiments of the present invention are possible in which current flows through the body of the patient. For example, current may flow between ring electrode780and aperture790through the blood. By way of a second example, embodiments of the present invention have been envisioned in which ring electrode780is replaced with a conductive patch which may be applied to an area of exposed skin on the patients body. In this envisioned embodiment, the path of current flow through the patient will include tissue.

The voltage differential created by power supply770induces a current flow through ring720. The flow of current through ring720causes the temperature of ring720to be altered. When the temperature of ring720is altered, ring720assumes a contracted position as shown in FIG.11.

FIG. 11, is a diagrammatic view of the thrombus filter ofFIG. 10with ring720in a contracted position. As shown inFIG. 11, the contraction of ring720causes anchors712to disengage the walls of blood vessel730. Once anchors712are disengaged from the walls of blood vessel730, thrombus filter700may be pulled into lumen742of removal catheter740.

FIG. 12is a perspective view of an additional embodiment of a thrombosis filter800. Thrombus filter800includes a first hub802, a second hub804, and a plurality of ribs806extending between first hub802and second hub804. In the embodiment ofFIG. 12, thrombus filter800is shown in an expanded state. When thrombus filter800is in an expanded state, each rib806forms one or more bends808.

FIG. 13is a plan view of thrombosis filter800of FIG.12. First hub802and ribs806are visible in FIG.13. InFIG. 13it may be appreciated that ribs806extend radially away from first hub802when thrombosis filter800is in an expanded state.

FIG. 14is a plan view of thrombosis filter800in a contracted state. InFIG. 14it may be appreciated that ribs806are substantially flush with first hub802and second hub804when thrombosis filter800is in a contracted state. Thrombosis filter800may be formed by laser cutting a section of tubing to form ribs806. Methods in accordance with the present invention may be utilized to cause thrombosis filter800to contract from the expanded shape shown inFIGS. 12 and 13to the contracted shape shown in FIG.14.

FIG. 15is a plan view of an additional embodiment of a thrombosis filter820. Thrombosis filter820includes a base portion822and a plurality of branches824. In the embodiment ofFIG. 15, thrombosis filter820is shown in an expanded state. It may be appreciated that branches824radiate away from base portion822when thrombosis filter820is in an expanded state.

FIG. 16is a plan view of thrombosis filter820in a contracted state. InFIG. 16it may be appreciated that branches824do not appreciably extend in a radial direction beyond base portion822when thrombosis filter820is in a contracted state. Methods in accordance with the present invention may be utilized to cause thrombosis filter820to contract from the expanded shape shown inFIG. 15to the contracted shape shown in FIG.16. Thrombosis filter820may be formed by laser cutting a section of tubing to form branches824.

FIG. 17is a perspective view of an additional embodiment of a thrombosis filter840. Thrombosis filter840includes a body portion842. A plurality of legs844radiate away from body portion842forming a generally conical portion846of thrombosis filter840. Thrombosis filter840also includes a plurality of arms848. A portion of each arm is fixed to body portion842. Each arm extends radially away from body portion842. In the embodiment ofFIG. 17each arm includes a curve150. In the embodiment ofFIG. 17, thrombosis filter840is shown in an expanded state. Methods in accordance with the present invention may be utilized to cause thrombosis filter840to contract from the expanded shape shown inFIG. 17to a contracted shape.

Numerous advantages of the invention covered by this document have been set forth in the foregoing description. It will be understood, however, that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of parts without exceeding the scope of the invention. The inventions's scope is, of course, defined in the language in which the appended claims are expressed.