Patent Publication Number: US-2007112371-A1

Title: Embolic protection filter having compact collapsed dimensions and method of making same

Description:
FIELD OF THE INVENTION  
      The invention relates generally to intraluminal distal protection devices for capturing particulate in the vessels of a patient. More particularly, the invention relates to a filter for capturing emboli in a blood vessel during an interventional vascular procedure.  
     BACKGROUND OF THE INVENTION  
      Catheters have long been used for the treatment of diseases of the cardiovascular system, such as treatment or removal of stenosis. For example, in a percutaneous transluminal coronary angioplasty (PTCA) procedure, a catheter is used to insert a balloon into a patient&#39;s cardiovascular system, position the balloon at a desired treatment location, inflate the balloon, and remove the balloon from the patient. Another example is the placement of a prosthetic stent in the body on a permanent or semi-permanent basis to support weakened or diseased vascular walls to avoid closure or rupture thereof.  
      These non-surgical interventional procedures often avoid the necessity of major surgical operations. However, one common problem associated with these procedures is the potential release of atherosclerotic or thrombotic debris into the bloodstream that can embolize distal vasculature and cause significant health problems to the patient. For example, during deployment of a stent, it is possible for the metal struts of the stent to cut into the stenosis and shear off pieces of plaque which become embolic debris that can travel downstream and lodge somewhere in the patient&#39;s vascular system. Further, particles of clot or plaque material can sometimes dislodge from the stenosis during a balloon angioplasty procedure and become released into the bloodstream.  
      Medical devices have been developed to attempt to deal with the problem created when debris or fragments enter the circulatory system during vessel treatment. One technique includes the placement of a filter or trap downstream from the treatment site to capture embolic debris before it reaches the smaller blood vessels downstream. A filter placed in the patient&#39;s vasculature before or during treatment of the vascular lesion can collect embolic debris in the bloodstream.  
      It is known to attach an expandable filter to a distal end of a guidewire or guidewire-like member that allows the filtering device to be placed in the patient&#39;s vasculature. The guidewire allows the physician to steer the filter to a location downstream from the area of treatment. Once the guidewire is in proper position in the vasculature, the embolic filter can be deployed to capture embolic debris. Some embolic filtering devices utilize a restraining sheath to maintain a self-expanding filter in a collapsed configuration. Once the restraining sheath is retracted by the physician withdrawing the proximal end of the sheath extending outside the patient&#39;s body, the expandable filter will attempt to transform itself into its fully expanded configuration. The restraining sheath can then be removed from the guidewire allowing the guidewire to be used by the physician to deliver interventional devices, such as a balloon angioplasty catheter or a stent delivery catheter, into the area of treatment. After the interventional procedure is completed, a recovery sheath can be delivered over the guidewire using over-the-wire techniques to collapse the expanded filter (with the trapped embolic debris) for removal from the patient&#39;s vasculature. Both the delivery sheath and recovery sheath should be relatively flexible to track over the guide wire and to avoid straightening the body vessel once in place.  
      Another distal protection device known in the art includes a filter mounted on a distal portion of a hollow guidewire or tube. A moveable core wire is used to open and close the filter. The filter is coupled at a proximal end to the tube and at a distal end to the core wire. With the physician manipulating a proximal portion of the device outside the patient&#39;s body, pulling on the core wire while pushing on the tube draws the ends of the filter toward each other, causing the filter framework between the ends to expand outward into contact with the vessel wall. Filter mesh material is mounted to the filter framework. To collapse the filter, the procedure is reversed, i.e., pulling the tube proximally while pushing the core wire distally to force the filter ends apart. A sheath catheter may be additionally used as a retrieval catheter at the end of the interventional procedure to reduce the profile of the “push-pull” filter, as due to the embolic particles collected, the filter may still be in a somewhat expanded state. The retrieval catheter may be used to further collapse the filter and/or smooth the profile thereof, so that the filter guidewire may pass through the treatment area without disturbing any stents or otherwise interfering with the treated vessel.  
      However, regardless of how a distal protection filter is expanded during a procedure, i.e., sheath delivered or by use of a push-pull mechanism, a crossing profile of the collapsed filter is to be at a minimum to reduce interference between the filter and other interventional devices or in-placed stents. As well, a compact filter profile is beneficial in crossing severely narrowed areas of vascular stenosis. Furthermore, it is advantageous for a filter to have a short or compact collapsed length, which allows the filter to be utilized in vessels that have minimal space distal to a stenosis. Thus, what is needed is a filter that achieves a reduced profile and/or a compact collapsed length without sacrificing the strength and stability needed for effective embolic capture and retention.  
     BRIEF SUMMARY OF THE INVENTION  
      The present invention is a filter for collecting debris in a body lumen. The filter is constructed of an outer tubular member having a first spiral cut along a length thereof and an inner tubular member having a second spiral cut along a length thereof. The first spiral cut and the second spiral cut have opposite chirality, such that the first spiral cut is a right-handed helix and the second spiral cut is a left-handed helix. In an alternate embodiment, the first spiral cut may be a left-handed helix and the second spiral cut a right-handed helix without departing from the scope of the invention. The inner tubular member is coaxially positioned within the outer tubular member to situate the second spiral cut within the first spiral cut, such that when the filter is in an expanded configuration filter openings are defined by intersections between the first and second spiral cuts. The pitch of the first and second spiral cuts may be varied as the cuts extend distally. The pitch may also be decreased as the cuts extend distally to obtain filter openings in a proximal portion of the filter that are larger than filter openings in a distal portion of the filter. In another embodiment, the pitch of the first and second spiral cuts may be held constant over the proximal portions of the inner and outer tubular members and decreased over the distal portions of the inner and outer tubular members to obtain filter openings in a proximal portion of the filter that are larger than filter openings in a distal portion of the filter.  
      At least one of the inner or outer tubular members is preferably made from a metallic material, such as stainless steel, nitinol, or a cobalt-chromium super alloy. Accordingly, the filter may be heat treated in an expanded or a collapsed configuration to retain its shape. In another embodiment, the outer tubular member may be made from a polymeric material, such as polyethylene block amide copolymer, polyvinyl chloride, polyethylene, polyethylene terephthalate, polyamide, or polyimide. In another embodiment, each of the inner and outer tubular members is a metallic hypotube.  
      A method of making an embolic filter is also disclosed. The method includes cutting a left-handed helix in a section of outer tubing, cutting a right-handed helix in a section of inner tubing, and slidably inserting the inner tubing into the outer tubing, such that the right-handed helical cut is disposed within the left-handed helical cut. The steps of helically cutting the inner and outer tubing may include varying the pitch of the cuts, such as to gradually decrease the pitch of the cuts as they extend distally. In one embodiment, the method includes securing the distal end of the outer tubing to the distal end of the inner tubing and rotating the proximal end of the inner tube in one direction while rotating the proximal end of the outer tube in an opposite direction to expand the first and second helical cuts into the form of an expanded filter subassembly. The expanded filter subassembly is then heat treated in the expanded configuration to set the size and shape of the filter and the filter openings. In another embodiment, the inner and outer tube subassembly is longitudinally stretched to create elastically deformable open coils. A filter-shaped mandrel is then inserted between the coils to be positioned within the inner and outer tube subassembly. The coils are then arranged around the mandrel and heat treated to set the size and shape of the filter and the filter openings in the expanded filter configuration.  
      A method according to the present invention may also include selecting metallic hypodermic tubing for at least one of the inner and outer tubes, or for each of the inner and outer tubes. In another embodiment, polymeric tubing may be selected for the outer tube, and a shape memory alloy may be selected for the inner tube. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
      The foregoing and other features and advantages of the invention will be apparent from the following description of the invention as illustrated in the accompanying drawings. The accompanying drawings, which are incorporated herein and form a part of the specification, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. The drawings are not to scale.  
       FIG. 1  is an illustration of a filter system in accordance with an embodiment of the present invention deployed within a blood vessel.  
       FIG. 2  is an illustration of a filter system in accordance with an embodiment of the present invention deployed within the coronary arterial anatomy.  
       FIG. 3  is a perspective view of a portion of a distal protection device in accordance with the present invention.  
       FIG. 3A  is an enlarged cross-sectional view of the device of  FIG. 3  taken along the line A-A.  
       FIGS. 4A-4E  illustrate a method of making a filter in accordance with an embodiment of the present invention.  
       FIGS. 5A-5D  illustrate another method of making a filter in accordance with an embodiment of the present invention.  
       FIG. 6  is a sectional view of a distal portion of a distal protection device in accordance with another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Specific embodiments of the present invention are now described with reference to the figures, wherein like reference numbers indicate identical or functionally similar elements. The terms “distal” and “proximal” are used in the following description with respect to a position or direction relative to the treating clinician. “Distal” or “distally” are a position distant from or in a direction away from the clinician. “Proximal” and “proximally” are a position near or in a direction toward the clinician.  
      The present invention is a temporary distal protection device for use on a filter guidewire in minimally invasive procedures, such as vascular interventions or other procedures, where the practitioner desires to capture embolic material that may be dislodged during the procedure. With reference to  FIGS. 1 and 2 , deployment of balloon expandable stent  130  is accomplished by threading catheter  125  through the vascular system of the patient until stent  130  is located within a stenosis at predetermined treatment site  115 . Once positioned, balloon  111  of catheter  125  is inflated to expand stent  130  against the vascular wall to maintain the opening. Stent deployment can be performed following treatments such as angioplasty, or during initial balloon dilation of the treatment site, which is referred to as primary stenting.  
      Catheter  125  is typically guided to treatment site  115  by a guidewire. In cases where the target stenosis is located in tortuous vessels that are remote from the vascular access point, such as with the coronary arteries  117  as shown in  FIG. 2 , a steerable guidewire is commonly used. According to an embodiment of the present invention, a filter guidewire generally designated as  120  guides catheter  125  to treatment site  115  and includes distally disposed filter  100  to collect embolic debris that may be generated during the procedure.  
      The present invention is directed to a distal protection device, viz., temporary embolic filter  100 , which has a reduced profile in its collapsed configuration or state. In the embodiment shown in  FIG. 3 , filter guidewire  120  includes a hollow proximal shaft  320  in sliding relationship with core wire  318 . Embolic filter  100  is axially secured at its proximal end  302  to a distal portion of proximal shaft  320  and at its distal end  304  to core wire  318 . Filter ends  302 ,  304  may be spot welded, laser welded or secured using a bonding sleeve or adhesive to proximal shaft  320  or core wire  318 , respectively, as would be apparent to one skilled in the relevant art.  FIG. 3A  is a sectional view of a distal portion of filter guidewire  120 , taken along line A-A.  FIG. 6  illustrates an alternate arrangement for joining filter distal end  304  to core wire  318 . In this embodiment, filter distal end  604  is affixed to a cylindrical collar or bearing  638 , such that core wire  618  may rotate relative to filter  600 . Filter distal end  604  is held in its axial position relative to core wire  618 , proximally by stop  628  and distally by flexible tip  608 .  
      Core wire  318  may be made from a metal, such as nitinol, or a stainless steel wire. In an embodiment of the present invention (not shown), core wire  318  may be tapered at its distal end and/or be comprised of one or more core wire sections. Core wire  318  may be ground down and have several diameters in its profile in order to provide a stiffness transition. Core wire  318  has a proximal end (not shown) that extends outside of the patient from a proximal end (not shown) of proximal shaft  320 . Core wire  318  also has coiled portion  308  with windings that extend from distal end  304  of filter  100 . Coiled portion  308  may be a separate component from core wire  318 , such as a flexible coil spring  608  shown in  FIG. 6  that is formed from a round or flat coil of stainless steel and/or one of various radiopaque alloys such as platinum, as is well known to those of skill in the art of medical guidewires.  
      In another embodiment of the present invention, proximal shaft  320  may be constructed of multiple shaft components of varying flexibility to provide a gradual transition in flexibility as the shaft extends distally. Such a shaft arrangement is disclosed in U.S. Pat. No. 6,706,055, which is incorporated by reference herein in its entirety. In addition, a liner or axial bearings (not shown) as disclosed in the &#39;055 patent may be utilized between core wire  318  and proximal shaft  320  in order to facilitate sliding movement there between during expansion and collapse of filter  100 . In another embodiment, proximal shaft  320  may be a hollow tube enabling filtering device  120  to also function as a medical guidewire.  
      As illustrated in  FIGS. 3 and 3 A, embolic filter  100  includes a thin-walled, outer tubular member  314  surrounding a thin-walled, inner tubular member  316 . When filter  100  is in its expanded configuration, filter openings  310 ,  312  are defined by the intersections of spiral cuts, as described below. Proximal filter openings  310  are larger than distal filter openings  312 . Accordingly, proximal filter openings  310  are of a shape and size for receiving particulate debris there through, and distal filter openings  312  are sized for collecting embolic debris within filter  100  while permitting fluid to flow there through, such as blood flow sufficient for perfusion of body tissues. Optionally, radiopaque markers (not shown) may be placed on proximal and distal ends  302 ,  304  of filter  100  to aid in fluoroscopic observation during manipulation thereof. Filter  100  is sized and shaped such that when it is fully deployed, its greatest expanded diameter at approximately the midpoint of the filter will contact the inner surface of the blood vessel wall into which it is placed. The inner surface contact is preferably maintained over a substantial portion of the expanded circumference to prevent any emboli from escaping past filter  100 .  
       FIGS. 4A-4E  illustrate a method of making filter  100  in accordance with an embodiment of the present invention. In  FIG. 4A , a first, outer tube  424  having proximal end  430  and distal end  432  is selected of wall thickness and outer diameter to form expanded filter  100 . A variable pitch spiral cut  425  is made in first tube  424 , such that the pitch of the cut decreases as the cut extends from proximal end  430  to distal end  432 . Spiral cut  425  may be a single, dual, or multi-helix. In this embodiment, a single, right-handed, spiral cut  425  is illustrated in  FIG. 4A . The cut may be made by laser, water jet, electric discharge machine (EDM), or by any other suitable method known to one of skill in the art of making medical devices. Pitch is defined herein as the axial distance between the ends of one complete (360°) turn of a spiral cut. Spiral cuts, according to the invention, may be narrow slits that are spread open during elongation of the cut tube or expansion of the filter to form filter openings. Alternatively, spiral cutting may remove more material to form relatively broader slots. Coils or helical struts comprise the tube material that remains after spiral cuts, slits or slots are made are.  
      In  FIG. 4B  a second, inner tube  426  having proximal end  434  and distal end  436  is selected with an outer diameter that is slightly less than an inner diameter of first tube  424 , such that an outer surface of second tube  426  will slide on an inner surface of first tube  424  during assembly. A variable pitch spiral cut  427  is made in second tube  426 , such that the pitch of the cut decreases as the cut extends from proximal end  434  to distal end  436 . Spiral cut  427  may be a single, dual, or multi-helix. In this embodiment, a single, left-handed spiral cut  427  is illustrated in  FIG. 4B . It should be understood that inner tube cut  427  could be a right-handed spiral cut and outer tube cut  425  could be a left-handed spiral cut without departing from the scope of the present invention.  
      Second tube  426  is then slidably inserted within first tube  424 , such that spiral cut  427  is situated within spiral cut  425  creating tubular subassembly  438 , as shown in longitudinal cross-section in  FIG. 4C . Tubular subassembly  438  is longitudinally stretched (see opposed force vector arrows) to open the spiral cuts thereby creating elastically deformable coils. A filter shaped mandrel, such as mandrel  440  shown in  FIG. 4D , is then inserted between the coils to be positioned within the inner and outer tube subassembly  438 . The coils are then arranged around mandrel  440  such that spiral cuts  425 ,  427  spread open and intersect with each other to form proximal and distal filter openings  310 ,  312  of filter  100 , as shown in  FIG. 4E . Filter openings  310 ,  312  may also be described as interstices between the coils or struts formed by spiral cuts  425 ,  427 . A heat treatment is performed to set the size and shape of filter  100  and filter openings  310 ,  312  in the expanded filter configuration. Mandrel  440  is then removed by enlarging an opening  310  or  312  sufficiently to accommodate the removal without plastically deforming the filter. At any step after first and second tubes  424 ,  426  are nested together, they may be fixedly attached one to another at their proximal and distal ends by any suitable method known in the art of constructing medical devices.  
      In an embodiment of the present invention, both first and second tubes  424 ,  426  are comprised of a thin-walled, tubular structure of a metallic material, such as stainless steel, nitinol, or a cobalt-chromium super alloy. Such metallic tubing is commonly referred to as hypodermic tubing or a hypotube. Metallic tubing formed from other alloys, as disclosed in U.S. Pat. No. 6,168,571, which is incorporated by reference herein in its entirety, may also be used in the tubing of the present invention. When either of first or second tubes  424 ,  426  is made from a heat-treatable alloy, the filter subassembly is shaped into the configuration shown in  FIG. 4E  and, preferably, heat treated to set the filter shape, and particularly the various sizes of filter openings  310 ,  312  to form self-expanding filter  100 .  
      In a second embodiment, second inner tube  426  is made from a metal alloy and first outer tube  424  is comprised of tubing made from a thermoplastic material such as polyethylene block amide copolymer, polyvinyl chloride, polyethylene, polyethylene terephthalate, polyamide, or a thermoset polymer such as polyimide. In this embodiment, inner tube  426  is arranged by itself around mandrel  440  in the configuration shown in  FIG. 4E  and is heat treated at a temperature suitable to set the filter shape in inner tube  426 . If pre-shaped inner tube  426  alone has sufficient stiffness to provide structural support for filter  100 , then mandrel  440  can be removed after the first heat treating step by sufficiently expanding one of the turns in spiral cut  427 . Then, outer tube  424  is arranged about pre-shaped inner tube  426  to make tube subassembly  438 . Finally, first and second tubes  424 ,  426  are fixedly attached one to another at their proximal and distal ends to create filter  100 .  
      Optionally, if outer tube  424  in the second embodiment comprises a thermoplastic material, then subassembly  438  can be heat treated at a temperature suitable to set the filter shape in outer tube  424 . The temperature for such a second heat treating step would be lower than the temperature of the first heat treating step due to the differences in thermal properties between themoplastics and metals. The second heat treating step can be performed with or without mandrel  440  supporting the assembly of tubes  424  and  426 , depending on the radial strength provided by pre-shaped inner tube  426 . If used, mandrel  440  is removed by enlarging an opening  310  or  312  sufficiently to accommodate removing the mandrel without plastically deforming the filter, as described in the previous example. The second embodiment can have a lower collapsed profile than the all-metal embodiment described above because plastic outer tube  424 , i.e. polyimide, can be thinner than metal inner tube  426 .  
      In accordance with the present invention, the pitch of spiral cuts  425 ,  427  may be varied at a constant or variable rate, depending on the desired final size of proximal and distal openings  310 ,  312 . In one embodiment, the pitch may be held constant over the proximal portions of the length of first and second tubes  424 ,  426 , and varied over the distal portions to achieve the desired opening sizes for a particular filter. Alternatively, the pitch may be held constant at a first pitch over the proximal portions of the length of first and second tubes  424 ,  426 , and held constant at a second, smaller pitch over the distal portions.  
      In  FIG. 3 , filter  100  is shown in the deployed configuration. Filter  100  is transformable between its deployed, i.e., expanded, and collapsed configurations by relative movement between its ends. In the embodiment of  FIG. 3 , filter  100  is collapsed by distally advancing core wire  318  with respect to proximal shaft portion  320  to move filter distal end  304  away from filter proximal end  302 . Filter  100  is returned to its deployed state by pulling core wire  318  proximally relative to hollow tube  320  to bring filter ends  302 ,  304  closer together, thereby allowing filter  100  to regain its expanded configuration. In further embodiments, a filter guidewire mechanism similar to that shown in any of the filter guidewires disclosed in U.S. Pat. Nos. 6,706,055, 6,818,006 and 6,866,677, which are incorporated by reference herein in their entireties, may be modified for use with filter  100 .  
      Alternatively, a filter in accordance with the present invention may be deployed and/or retrieved via a sheath catheter, such as by the method and apparatus disclosed in U.S. Pat. Nos. 6,059,814 and 6,346,116, which are incorporated by reference herein in their entireties. Further, the transformation of the filter may be impelled by external mechanical means alone or by self-shaping memory (either self-expanding or self-collapsing) within the filter materials. Preferably, filter  100  is self-expanding, meaning it has a mechanical memory to return to the expanded, or deployed configuration. As previously discussed, such mechanical memory can be imparted to the metallic tubing comprising filter  100  by thermal treatment to achieve a spring temper in stainless steel, for example, or to set a shape memory in a susceptible metal alloy, such as nitinol. Yet another method of transforming a filter in accordance with the invention between deployed and collapsed configurations is described infra with respect to  FIG. 5D .  
       FIGS. 5A-5D  illustrate a method of making filter  500  in accordance with another embodiment of the present invention. In  FIG. 5A , a first, outer tube  524  having proximal end  530  and distal end  532  is selected with suitable dimensions to form expanded filter  500 . A variable pitch spiral cut  525  is made in first tube  524 . Spiral cut  525  may be a single, dual, or multi-helix. In this embodiment, a right-handed spiral cut  525  is illustrated in  FIG. 5A . In  FIG. 5B  a second, inner tube  526  having proximal end  534  and distal end  536  is selected with an outer diameter that is slightly less than an inner diameter of first tube  524 , such that an outer surface of second tube  526  will slide on or within an inner surface of first tube  524  during assembly. A variable pitch spiral cut  527  is made in second tube  526 . Spiral cut  527  may be a single, dual, or multi-helix. In this embodiment, a left-handed spiral cut  527  is illustrated in  FIG. 5B , such that spiral cuts  525 ,  527  have opposite chirality. As in the first embodiment, it should be understood that inner tube cut  527  could be a right-handed spiral cut and outer tube cut  525  could be a left-handed spiral cut without departing from the scope of the present invention.  
      Inner tube  526  is then inserted within outer tube  524 , such that spiral cut  527  is situated within spiral cut  525 , creating tubular subassembly  538 , as represented in  FIG. 5C . Filter distal end  504  is then formed by fixedly attaching first tube distal end  532  to second tube distal end  536  by any suitable method known in the art of constructing medical devices. The proximal ends  530 ,  534  are then rotated in opposite directions relative to one another, as indicated by counterclockwise and clockwise arrows A and B in  FIG. 5C , to untwist or unwind first and second tubes  524 ,  526 , thus radially expanding helical cuts  525 ,  527  and the coils or struts formed thereby into the expanded configuration of filter  500 , as shown in  FIG. 5D . In the expanded configuration of filter  500 , filter openings  510 ,  512  are formed by the intersections of spread-open spiral cuts  525 ,  527 . Filter openings  510 ,  512  may also be described as interstices between the coils or struts formed by spiral cuts  525 ,  527 . If spiral cuts  525 ,  527  include varying pitch, as described above, then filter openings  512  can be larger than filter openings  510 . Filter  500  thus formed is self-collapsing and relies on the relative rotation of proximal ends  530 ,  534  of first and second tubes  524 ,  526  to be expanded.  
      Optionally, a heat treatment may be performed on expanded tubular subassembly  538  to set a self-expanded size and shape of filter  500  and filter openings  510 ,  512 . In the self-expanding embodiment, the proximal ends  530 ,  534  are rotated in opposite directions that are reversed relative to arrows A and B in  FIG. 5C , to radially collapse filter  500  into the collapsed configuration. Both of the self-expanding and self-collapsing embodiments of filter  500  have an unexpanded, collapsed length that is substantially equal to the length of the expanded filter, allowing it to be used in procedures where insufficient space is available distal of the stenosis for positioning a filter having an elongated collapsed length.  
       FIG. 5D  illustrates filter  500 , without a core wire inserted, in its deployed configuration. Considered individually, either of spiral cut tubes  524  or  526  can be radially expanded or contracted by rotating one end with respect to the other. Tubes  524  and  526  require opposite end-to-end rotation for radial expansion because spiral cuts  525 ,  527  have opposite chirality, as described above. That is, a right-handed spiral can be expanded by rotating one end counterclockwise with respect to the other end, and a left-handed spiral can be expanded by rotating one end clockwise with respect to the other end. Alternatively, to contract tubes having oppositely chiral spirals, a right-handed spiral can be contracted by rotating one end clockwise with respect to the other end, and a left-handed spiral can be expanded by rotating one end counterclockwise with respect to the other end. Filter  500  is transformable between its deployed, i.e., expanded, and collapsed configurations by relative rotational movement between proximal ends  530 ,  534  of outer and inner tubes  524 ,  526 . As such, filter  500  is collapsed by rotating outer tube proximal end  530  clockwise and inner tube proximal end  534  counterclockwise. Filter  500  is returned to its deployed state by reversing the rotation of proximal ends  530 ,  534 , i.e., rotating outer tube proximal end  530  counterclockwise and inner tube proximal end  534  clockwise, thereby allowing filter  500  to regain its expanded configuration.  
      In an embodiment where outer and inner slotted tubes  524 ,  526  have unequal torsional stiffnesses, core wire  318  may be incorporated in the filter guidewire to provide rotational control of slotted tubes  524 ,  526 . With core wire  318  affixed within filter distal end  504 , outer tube proximal end  530  can be rotated with respect to core wire  318  to expand or collapse spiral cut  525 . Similarly, inner tube proximal end can be rotated with respect to core wire  318  to expand or collapse spiral cut  527 . Thus, by rotationally manipulating the proximal ends of core wire  318  and slotted tubes  524 ,  526  extending outside the patient, slotted tubes  524 ,  526  can be expanded or collapsed independently or simultaneously. For example, outer tube  524  can be rotationally expanded into the expanded configuration simultaneously or before inner tube  526  is expanded. Inner tube  526  can be rotationally collapsed simultaneously or before outer tube  524  is collapsed. For convenience, an accessory or tool (not shown) may be removably mounted to the proximal ends of core wire  318  and slotted tubes  524 ,  526  to aid in manually controlling and temporarily locking the relative rotational positions of the elements.  
      While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of illustration and example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the appended claims and their equivalents. It will also be understood that each feature of each embodiment discussed herein, and of each reference cited herein, can be used in combination with the features of any other embodiment. All patents and publications discussed herein are incorporated by reference herein in their entirety.