Patent Publication Number: US-2007118079-A1

Title: Medical devices and related systems and methods

Description:
TECHNICAL FIELD  
      This invention relates to medical devices and related methods.  
     BACKGROUND  
      Systems are known for delivering medical devices, such as stents, into a body lumen. Often, such systems include a proximal portion that remains outside the body during use and a distal portion that is disposed within the body during use. The proximal portion typically includes a handle that is held by an operator of the system (e.g., a physician) during use, and the distal portion can include an outer tube surrounding an inner tube with a stent positioned between the inner and outer tubes. Generally, the operator of the system positions the distal portion within the lumen at a desired location. For example, the operator can position the distal portion so that the stent is adjacent an occlusion. The operator can then retract the outer tube to allow the stent to engage the occlusion and/or the lumen wall. After implanting the stent, the operator can remove the distal portion of the system from the lumen.  
     SUMMARY  
      In general, the invention relates to systems that are configured to hold an elongate element (e.g., a guide wire) in a fixed position relative to an inner member (e.g., a catheter). The invention also relates to methods of using such systems. The systems can, for example, be used to treat an occluded body vessel (e.g., blood vessel) and/or to deliver an endoprosthesis (e.g., a stent) within the body vessel.  
      In one aspect of the invention, a system includes an inner member having a lumen that extends longitudinally through the inner member such that an elongate element (e.g., a guide wire) can be disposed within the lumen. A holding device is generally secured to the inner member (e.g., secured to a handle that is attached to the inner member) and includes a mechanism (e.g., a spring loaded member, an inflatable member, a clamp, a magnet) that is configured to hold the elongate element in a fixed position relative to the inner member. The inner member is generally surrounded by a retractable outer member (e.g., a sheath), and an endoprosthesis (e.g., a stent) is generally disposed between the inner member and the outer member.  
      To treat the occluded body vessel, the system can be inserted into the body vessel such that the portion of the inner member about which the endoprosthesis is located is positioned within the occluded region of the vessel. Upon being positioned as desired within the occluded region of the vessel, the holding device can be activated to fix the elongate element relative to the inner member. The outer member can then be retracted such that the endoprosthesis is delivered within the vessel.  
      In some embodiments, the system is configured to be switched between a first position in which the elongate element is substantially fixed relative to the inner member and a second position in which the elongate element is free to move relative to the member.  
      In certain embodiments, the inner member includes a first region that is more compliant than a second region. In such embodiments, the holding device can be configured to deform the first region such that the first region contacts the elongate element disposed in the lumen. The contact between the elongate element and the first region can fix the elongate element relative to the inner member.  
      In some embodiments, the holding device is configured to directly contact the elongate element. The contact between the holding device (e.g., a member of the holding device) and the elongate element can fix the elongate element relative to the inner member.  
      In certain embodiments, the holding device is configured to hold the elongate element in a fixed position relative to the inner member using magnetic force.  
      Embodiments may include one or more of the following advantages.  
      In certain embodiments, the elongate element is substantially prevented from moving relative to the inner member. Fixing the elongate element relative to the inner member can help to improve the precision with which a procedure can be performed within the body vessel. It can, for example, help to improve the precision with which the endoprosthesis can be deployed within the body vessel.  
      In some embodiments, the holding device is positioned near a handle (e.g., in the handle) of the system. This can help to enable the system to be operated by a single user (e.g., by a single physician).  
      In certain embodiments, a manually operable mechanism (e.g., a push button) is connected to the holding device. The manually operable mechanism can be manipulated (e.g., pushed) to activate the holding device in order to fix the elongate element relative to the inner member or to free the elongate element for movement relative to the inner member. In some embodiments, the holding device and the manually operable mechanism are disposed within the handle, which allows the user to activate the holding device while grasping the handle. In certain embodiments, the user can simultaneously grasp the handle and activate the holding device with a single hand. This can allow the user to perform other functions with his or her free hand, such as retracting the outer member.  
      In some embodiments, the manually operable mechanism can improve the user&#39;s control of the resistance provided to the elongate element. In certain embodiments, for example, tactile feedback may be provided to the hand of the user via the manually operable mechanism, which can help the user to determine whether a desirable amount of friction or resistance is being provided to the elongate element.  
      In certain embodiments, the holding device can be locked in at least one of a first position in which the elongate element is substantially fixed relative to the inner member and a second position in which the elongate element is free to move longitudinally relative to the inner member. The locking of the holding device can increase the efficiency with which the user can operate the system.  
      Other aspects, features, and advantages are in the description, the drawings, and the claims. 
    
    
     DESCRIPTION OF DRAWINGS  
       FIG. 1  is a cross-sectional view of an embodiment of a medical system including a spring loaded member in a locked configuration.  
       FIG. 2  is a cross-sectional view of the medical system of  FIG. 1  in an unlocked configuration.  
       FIGS. 3-5  illustrate an embodiment of a method of using the medical system of  FIGS. 1 and 2 .  
       FIG. 6  is a cross-sectional view of an embodiment of a medical system including an inflatable member in an unlocked configuration.  
       FIG. 7  is a cross-sectional view of the medical system of  FIG. 6  in a locked configuration.  
       FIG. 8  is a cross-sectional view of an embodiment of a medical system including multiple inflatable members in an unlocked configuration.  
       FIG. 9  is a cross-sectional view of the medical system of  FIG. 8  in a locked configuration.  
       FIG. 10  illustrates an embodiment of an inner member of a medical system.  
       FIG. 11  is a cross-sectional view of an embodiment of a medical system including an inflatable member at a distal portion of the system, the system being in a locked configuration.  
       FIG. 12  is a cross-sectional view of the medical system of  FIG. 11  in an unlocked configuration.  
       FIG. 13  is a cross-sectional view of an embodiment of a medical system including a clamp in an unlocked configuration.  
       FIG. 14  is a cross-sectional view of the medical system of  FIG. 13  in a locked configuration.  
       FIG. 15  is a cross-sectional view of an embodiment of a medical system including a magnet in a locked configuration.  
       FIG. 16  is a cross-sectional view of the medical system of  FIG. 15  in an unlocked configuration.  
       FIG. 17  is a partial side view of an embodiment of a rapid exchange catheter system. 
    
    
      Like reference symbols in the various drawings indicate like elements.  
     DETAILED DESCRIPTION  
      In general, systems include a member (e.g., a catheter) with a lumen extending through the member. The systems are generally configured so that, when an elongate element (e.g., a guide wire) is disposed within the lumen, the elongate element can be held in a substantially fixed position relative to the member. In some embodiments, the systems are configured to be switched between a first position in which the elongate element is substantially fixed relative to the member and a second position in which the elongate element is free to move relative to the member. Examples of such systems are described below.  
      Referring to  FIGS. 1 and 2 , a system  100  includes an inner member (e.g., a catheter)  110  having a relatively compliant region  135  positioned between two relatively rigid regions  130 . Relatively compliant region  135  and relatively rigid regions  130  can be attached to one another using any of various techniques, such as co-extrusion, thermal bonding, adhesive bonding, and/or mechanical attachments. A lumen  125  extends along the longitudinal axis of inner member  110  from a proximal end  111  of inner member  110  to a distal end  113  of inner member  110 . An outer member (e.g., a sheath)  115  surrounds inner member  110  and extends to distal end  113  of inner member  110 . An endoporosthesis (e.g., a self-expanding stent)  120  is disposed adjacent a distal region  117  of inner member  110  between inner member  110  and outer member  115 . Outer member  115 , while surrounding endoprosthesis  120 , can prevent endoprosthesis  120  from expanding.  
      A handle  105  is secured to a proximal region of inner member  110 . Handle  105  can, for example, be secured to inner member  110  using any of various attachment techniques, such as adhesive attachment techniques and/or mechanical attachment techniques.  
      Handle  105  includes a holding mechanism  140 . Holding mechanism  140  can be operated to switch system  100  between a locked configuration (e.g., a configuration in which a guide wire  170  extending through lumen  125  is fixed relative to inner member  110 ) and an unlocked configuration (e.g., a configuration in which guide wire  170  extending through lumen  125  is free to move relative to inner member  110 ). Holding mechanism  140  includes a beam  145  that is free at its distal end and is attached to an activation button  155  at its proximal end. A contact member  165  extends from the distal end of beam  145 . Contact member  165  includes a pointed tip  167 . A spring  150  links button  155  to handle  105  (e.g., to an inner housing wall of handle  105 ). Spring  150  can, for example, be fixed at its bottom end to handle  105  and can be fixed at its top end to button  155 . Button  155  is configured so that it can be moved in and out of handle  105 . Button  155  includes a head  156  attached to a stem  157 . Stem  157  is sized to fit through an aperture  158  formed in handle  105 , while head  156  is larger than aperture  158  such that head  156  is prevented from passing through aperture  158  and remains outside of handle  105 . Spring  150  can provide resistance to the inward and/or outward movement of button  155 . As button  155  is actuated, it causes beam  145  to pivot about a fulcrum  160 , which is fixed to handle  105  between the proximal and distal ends of beam  145 .  
      When system  100  is in a locked position, as shown in  FIG. 1 , spring  150  is expanded, which forces button  155  and the proximal end of beam  145  outward (e.g., away from inner member  110 ). As a result, the distal end of beam  145  and contact member  165  are forced inward (e.g., toward inner member  110 ), causing contact member  165  to contact an outer surface of region  135 . The rotational force applied to beam  145  by spring  150  causes contact member  165  to deform region  135  of inner member  110 , causing the wall of region  135  to press against guide wire  170 . The pressure applied to guide wire  170  by the wall of region  135  can help to reduce (e.g., prevent) the ability of guide wire  170  to move longitudinally within lumen  125 .  
      When system  100  is in an unlocked position, as shown in  FIG. 2 , button  155  is depressed and spring  150  is compressed between button  155  and handle  105 . As compared to the locked position of  FIG. 1 , the proximal end of beam  145  is positioned nearer the outer surface of inner member  110  and the distal end of beam  145  is positioned farther from the outer surface inner member  110  (e.g., out of contact with the outer surface of inner member  110 ). Consequently, region  135  of inner member  110  is substantially undeformed and guide wire  170  is free to move longitudinally within lumen  125 .  
       FIGS. 3-5  describe an exemplary method of using system  100 . Referring to  FIG. 3 , guide wire  170  can be inserted into a body vessel (e.g., a blood vessel)  175  of a subject. A distal portion  101  of system  100  can then be inserted over guide wire  170  into body vessel  175 . While inserting distal portion  101  of system  100  into body vessel  175 , the user can depress button  155  so that inner member  110  is free to slide over guide wire  170  without substantial resistance. The user can, for example, depress button  155  with a finger or thumb of the hand in which handle  105  is grasped. Guide wire  170  can help to track or guide distal portion  101  of system  100  as it is pushed through body vessel  175 .  
      The user can continue to insert distal portion  101  of system  100  into body vessel  175  until distal region  117  of inner member  110  (e.g., the region about which endoprosthesis  120  is located) is positioned within a target region (e.g., an occluded region)  180  of body vessel  175 . Once distal region  117  of inner member  110  is positioned within target region  180  of body vessel  175 , as shown in  FIG. 4 , the user can release button  155  to place system  100  in the locked position such that guide wire  170  becomes fixed relative to inner member  110 .  
      Referring to  FIG. 5 , after fixing guide wire  170  relative to inner member  110 , the user can retract outer member  115  to deploy endoprosthesis  120 . Because guide wire  170  is fixed relative to inner member  110  while deploying endoprosthesis  120 , proximal and/or distal movement of inner member  110  resulting from the retraction of outer member  115  can be reduced (e.g., substantially prevented). It is believed that friction between inner member  110  and guide wire  170  in regions distal to the point at which region  135  is pressed against guide wire  170  can prevent reactionary forces associated with retraction of outer member  115  and/or potentional energy associated with any slack within inner member  110  from moving inner member  110  relative to guide wire  170 . Consequently, it is believed that the precision with which endoprosthesis  120  can be deployed within body vessel  175  can be improved.  
      After deploying endoprosthesis  120  within body vessel  175 , distal portion  101  of system  100  can be removed from body vessel  175 . System  100  can be held in an unlocked position while removing distal portion  101  from body vessel  175  so that guide wire  170  can remain within body vessel  175  as distal portion  101  is removed. Alternatively, system  100  can be held in a locked position while removing distal portion  101  from body vessel  175  so that guide wire  170  can be simultaneously removed from body vessel  175 .  
      Relatively rigid regions  130  are generally less compliant than region  135 . In certain embodiments, regions  130  are harder than region  135 . Regions  130  can, for example, have a hardness of about 60 D to about 90 D (e.g., about 70 D to about 80 D), and region  135  can have a hardness of about 50 A to about 70 A (e.g., about 55 A to about 65 A).  
      In some embodiments, the wall of region  135  is thinner than the walls of regions  130 . The wall of region  135  can, for example, be about 0.005 inch to about 0.010 inch (about 0.127 millimeter to about 0.254 millimeter) thinner than the walls of regions  130 . In some embodiments, the wall of region  135  has a thickness of about 0.004 inch to about 0.008 inch (about 0.102 millimeter to about 0.203 millimeter). The thinness of the wall of region  135  relative to the wall of regions  130  can help to make region  135  more compliant than regions  130 .  
      Regions  130  can include one or more materials that are capable of withstanding forces associated with inserting inner member  110  into body vessel  175 . In some embodiments, regions  130  include one or more polyamides (e.g., Vestamid®), polyetheretherketones (PEEKs), polyether block amides (e.g., Pebax®), polytetrafluoroethylenes (e.g., Teflon®), polyether-block co-polyamide polymers (e.g., Pebax®), copolyester elastomers (e.g., Arnitel® copolyester elastomers), thermoplastic polyester elastomers (e.g., Hytrel®), thermoplastic polyurethane elastomers (e.g., Pellethane™), polyeolefins (e.g., Marlex® polyethylene, Marlex® polypropylene), high-density polyethylenes (HDPEs), low-density polyethylenes (LDPEs), and/or polyimides.  
      Region  135  can include one or more resilient materials. In certain embodiments, region  135  includes one or more silicones, polyurethane elastomers (e.g., Pellethane®), thermoplastic rubbers (e.g., Alcryn®), rubbers, styrenic block copolymers (SBCs) (e.g., Kraton®), and urethanes.  
      Beam  145  of holding device  140  can be formed of one or more materials that are capable of deforming region  135 . Beam  145  is generally less compliant than region  135  so that beam  145  can deform region  135  without becoming substantially deformed itself. Examples of materials from which beam  145  can be formed include stainless steel, thermoplastic, and thermoset materials.  
      Spring  150  can include any of various types of springs, such as compression springs, coil springs, and leaf springs. In some embodiments, spring  150  has a spring force of about two pounds or greater (e.g., about three pounds or greater, about four pounds or greater) and/or about five pounds or less (e.g., about four pounds or less, about three pounds or less). Spring  150  can include one or more materials, such as steel (e.g., stainless steel) and/or plastic.  
      As an alternative or in addition to using a spring to apply a force to button  155  and beam  145 , other types of devices can be used. For example, elastic bands can be used to elastically connect beam  145  to inner member  110  (e.g., to compliant region  135  of inner member  110 ).  
      Handle  105  can be formed of one or more relatively rigid materials. The rigidity of handle  105  can help to provide a stable structure to which one or more of the components of holding device  140  (e.g., spring  150  and fulcrum  160  of holding device  140 ) can be supported. Examples of materials from which handle  105  can be formed include thermoplastics (e.g., Acrylonitrile Butadiene Styrene (ABS), polycarbonate).  
      Endoprosthesis  120  is generally a self-expanding stent. Examples of materials from which endoprosthesis  120  can be formed include shape memory materials, such as nitinol, silver-cadmium (Ag—Cd), gold-cadmium (Au—Cd), gold-copper-zinc (Au—Cu—Zn), copper-aluminum-nickel (Cu—Al—Ni), copper-gold-zinc (Cu—Au—Zn), copper-zinc/(Cu—Zn), copper-zinc-aluminum (Cu—Zn—Al), copper-zinc-tin (Cu—Zn—Sn), copper-zinc-xenon (Cu—Zn—Xe), iron beryllium (Fe 3 Be), iron platinum (Fe 3 Pt), indium-thallium (In—Tl), iron-manganese (Fe—Mn), nickel-titanium-vanadium (Ni—Ti—V), iron-nickel-titanium-cobalt (Fe—Ni—Ti—Co) and copper-tin (Cu—Sn). For yet additional shape memory alloys, see, for example, Schetsky, L. McDonald, “Shape Memory Alloys”,  Encyclopedia of Chemical Technology  (3rd ed.), John Wiley &amp; Sons, 1982, vol. 20. pp. 726-736.  
      Guide wire  170  can be formed of a relatively flexible material, which can help to allow guide wire  170  to be navigated through tortuous regions of vessels. Guide wire  170  can, for example, be formed of one or more metals (e.g., stainless steels, nitinol) and/or polymeric materials (e.g., polyamides, nylons). Examples of other materials from which guide wire  170  can be formed are described in U.S. Pat. No. 6,436,056 issued to Wang et al., which is incorporated by reference herein.  
      While embodiments of spring loaded holding devices have been described, other types of holding devices can alternatively or additionally be used. Referring to  FIG. 6 , for example, a system  200  includes a holding device  240  having an inflatable member (e.g., a balloon)  245  that is fluidly connected to a fluid pump  255 . Inflatable member  245  is positioned adjacent region  135  of inner member  110 . An inflation lumen  250  connects fluid pump  255  to inflatable member  245 . Inflation lumen  250  can be integrally formed within handle  105 . Alternatively or additionally, inflation lumen  245  can include tubing disposed within handle  105 . Fluid pump  255  is positioned (e.g., attached) at a proximal end  106  of handle  105 . The positioning of fluid pump  255  in close proximity to handle  105  can help to allow the user of system  200  to operate fluid pump  255  while grasping handle  105 .  
      When inflatable member  245  is deflated, as shown in  FIG. 6 , region  135  is substantially undeformed and guide wire  170  is free to move longitudinally within lumen  125 . In order to longitudinally fix guide wire  170  relative to inner member  110 , inflatable member  245  can be inflated, as shown in  FIG. 7 . Inflatable member  245  can be inflated by pumping an inflation fluid (e.g., saline) from fluid pump  255  through inflation lumen  250  to inflatable member  245 . The inflation of inflatable member  245  can deform region  135 , which can compress guide wire  170  between opposite sides of region  135 . The compression of guide wire  170  between opposite sides of region  135  can substantially prevent guide wire  170  from moving longitudinally within lumen  125 .  
      Fluid pump  255  can include one or more devices capable of transferring the inflation fluid to inflatable member  245 . Examples of such devices include syringes and biflators. In some embodiments, fluid pump  255  is manually operable. In certain embodiments, for example, fluid pump  255  can be actuated by depression of the user&#39;s thumb or finger, which can enable inflation of inflatable member  245  while simultaneously grasping handle  105 .  
      While fluid pump  255  has been described as being positioned at proximal end  106  of handle  105 , fluid pump  255  can alternatively or additionally be located at other positions. In certain embodiments, for example, fluid pump  255  is disposed within handle  105 . In some embodiments, fluid pump  255  is detached from handle  105 .  
      While inflatable member  245  has been described as a balloon, other types of inflatable members can alternatively or additionally be used. Examples of other types of inflatable members include inflatable cuffs.  
      Inflatable member  245  can be formed of one or more distensible materials. Examples of materials from which inflatable member  245  can be formed include polyurethanes and block copolymers, such as polyamide-polyether block copolymers or amide-tetramethylene glycol copolymers. Examples include the Pebax® (a polyamide/polyether/polyester block copolymer) family of polymers, e.g., Pebax® 70D, 72D, 2533, 5533, 6333, 7033, or 7233 (available from Elf AtoChem, Philadelphia, Pa.). Other examples include nylons, such as aliphatic nylons, for example, Vestamid L2101F, Nylon 11 (Elf Atochem), Nylon 6 (Allied Signal), Nylon 6/10 (BASF), Nylon 6/12 (Ashley Polymers), or Nylon 12. Additional examples of nylons include aromatic nylons, such as Grivory (EMS) and Nylon MXD-6. Other nylons and/or combinations of nylons can be used. Still other examples include polybutylene terephthalate (PBT), such as Celanex® (available from Ticona, Summit, N.J.), polyester/ether block copolymers such as Arnitel® (available from DSM, Erionspilla, Ind.), e.g., Arnitel® EM740, aromatic amides such as Trogamid (PA6-3-T, Degussa), and thermoplastic elastomers such as Hytrel® (Dupont de Nemours, Wilmington, Del.).  
      While the inflation fluid has been described as saline, other types of fluids can be used. Examples of inflation fluids include liquids (e.g., saline, contrast solution, water) and gases (e.g., inert gases, such as air).  
      While embodiments of holding devices have been described in which the holding device is configured to compress or deform region  135  at a single location (e.g., at the top of region  135 ), the holding device can alternatively or additionally be configured to compress or deform region  135  at multiple locations. The holding device can, for example, include multiple members that are spaced around the circumference of region  135 . Alternatively or additionally, multiple members can be longitudinally spaced along region  135 .  
       FIGS. 8 and 9  illustrate an example of a system  200 A with a holding device  240 A that includes multiple members  245  and  245 A. As shown, inflatable members  245  and  245 A are positioned on opposite sides of region  135 . Similar to inflatable member  245 , inflatable member  245 A is fluidly connected to fluid pump  255  via an inflation lumen  250 A. When inflatable members  245  and  245 A are inflated, as shown in  FIG. 9 , guide wire  170  is compressed between opposite walls of region  135 .  
      While various embodiments of holding devices have been described, other types of holding devices that are capable of deforming region  135  can alternatively or additionally be used. Examples of other types of holding devices include clamps, Touhy-Borst valves, and EAP rings.  
      While relatively compliant region  135  of the embodiments above extends around the entire circumference of the inner member, other configurations are possible. In some embodiments, region  135  extends about only a portion of the circumference of the inner member. As shown in  FIG. 10 , for example, region  135  extends along a top portion of the inner member. Consequently, a guide wire can be compressed between region  135  and the portion of relatively rigid region  130  opposite region  135 . This arrangement can help to reduce (e.g., prevent) deformation of the opposite side wall of the inner member while region  135  is deformed by the holding device. Consequently, the force with which guide wire  170  is compressed within lumen  125  can be increased.  
      While the embodiments above describe deforming region  135  in order to secure guide wire  170  relative to inner member  110 , other techniques can be used. In certain embodiments, for example, holding devices can be arranged to contact (e.g., compress) the guide wire directly. For example, as shown in  FIGS. 11 and 12 , a system  300  includes a holding device  340  positioned at the proximal end of handle  105 . Holding device  340  includes a clamp  345  that can be secured to handle  105  using any of various techniques. Clamp  345  can, for example, be thermally bonded, adhesively bonded, and/or mechanically attached to handle  105 .  
      During use, the user can activate holding device  340  so that clamp  345  compresses guide wire  170 , as shown in  FIG. 11 . Consequently, guide wire  170  can be prevented from moving longitudinally relative to inner member  110 . The user can also deactivate holding device  340  so that clamp  345  is released from contact with guide wire  170 , as shown in  FIG. 12 . As a result, guide wire  170  is free to move longitudinally within lumen  125 .  
      While holding device  340  has been described as including a clamp, it should be understood that any of the other types of holding devices described herein can alternatively or additionally be used to compress guide wire  170 . For example, a spring loaded member and/or an inflatable member can similarly be arranged to contact guide wire  170  directly in order to hold guide wire longitudinally fix guide wire  170  relative to inner member  110 .  
      While the embodiments above describe holding devices that are positioned near the proximal end of the system (e.g., near handle  105 ), holding devices or members of holding devices can alternatively or additionally be positioned nearer the distal end of the system. Referring to  FIGS. 13 and 14 , for example, a system  400  includes a holding device  440 , which includes a ring-shaped inflatable member  445  positioned near a distal region  417  of an inner member  410 . Inflatable member  445  is positioned between a proximal portion  411  and a distal portion  413  of inner member  410 . Inflatable member  445  can be joined to proximal and distal portions  411  and  413  using any of various techniques, such as thermal bonding, adhesive bonding, and/or mechanical attachment techniques. Inflatable member  445  is fluidly connected to fluid pump  255  by inflation lumens  450 . Inflation lumens  450  can be formed within catheter  410 . Alternatively or additionally, inflation lumens  450  can include one or more tubes extending along inner member  410 . Upon inflating inflatable member  445 , guide wire  170  is compressed between inner surfaces of inflatable member  445 . This compressive force can help to prevent guide wire  170  from moving longitudinally relative to inner member  110 .  
      While the embodiments described above include holding devices that are configured to deform region  135  and/or compress guide wire  170 , other types of holding devices can alternatively or additionally be used. Referring to  FIGS. 15 and 16 , for example, a system  500  includes a holding device  540  that uses magnetic force to fix guide wire  170  relative to inner member  110 . System  500  is similar to system  100  discussed above. However, holding device  540  includes a magnet  565  at the distal end of beam  145 . Magnet  565  can be formed of one or more magnetic materials. Examples of magnetic materials include iron and cobalt. Any of various other magnetic materials can alternatively or additionally be used.  
      When spring  150  is expanded, as shown in  FIG. 15 , magnet  565  rests against an outer surface of inner member  110 . The magnetic force produced by magnet  565  can help to prevent guide wire  170  from moving longitudinally within lumen  125  relative to inner member  110 . Upon depressing button  155 , which compresses spring  150 , magnet  565  is moved away from inner member  110  and guide wire  170 . As a result, the magnetic force acting on guide wire  170  is weaker and guide wire  170  can move longitudinally within lumen  125 .  
      In certain embodiments, holding device  540  includes multiple magnets. The magnets can, for example, be arranged at spaced apart locations along the length of inner member  110 . Alternatively or additionally, the magnets can be radially spaced about inner member  110 .  
      As an alternative to or in addition to using one or more magnets to create a magnetic force about inner member  110 , a conductive member (e.g., a copper wire) configured to carry an electrical current can be positioned around inner member  110 . The conductive member can be electrically connected to a power source. During use of the system, the user can activate the power source to cause an electric current to flow through the conductive member, which can create a magnetic field around the inner member. This magnetic field can help to prevent the guide wire  170  from moving longitudinally relative to inner member  110 .  
      While various embodiments have been described above, other embodiments are possible.  
      As an example, while many of the embodiments above describe systems that are generally in a locked configuration and can be unlocked by activating the holding device, the systems can alternatively be configured such that they are generally unlocked and can be locked by activating the holding device. Similarly, those systems that have been described as generally being in an unlocked configuration but being capable of being locked by activating the holding device can alternatively be configured such that they are generally in a locked configuration and are capable of being unlocked by activating the holding device.  
      As a further example, while the embodiments above describe a inner member having a relatively rigid region and a relatively compliant region, in some embodiments, substantially the entire inner member has substantially the same compliance (e.g., substantially the entire inner member is relatively compliant or substantially the entire inner member is relatively rigid).  
      As an additional example, while the embodiments above describe endoprosthesis  120  as a self-expanding stent, other types of endoprostheses can alternatively or additionally be used. In certain embodiments, for example, endoprosthesis  120  is a balloon-expandable stent. In such embodiments, the inner member on which endoprosthesis  120  is carried can be a balloon catheter. Other examples of endoprostheses include stent-grafts and filters (e.g., arterial filters and venous filters).  
      As another example, while over-the-wire systems have been described, other types of systems, such as rapid exchange systems, can alternatively or additionally be used. Referring to  FIG. 17 , for example, a system  600  includes a rapid exchange catheter  610 . A handle  605  is secured to catheter  610 , and includes a holding device  640 . Holding device  640  includes a resilient tab  645  that is attached to a housing of handle  605  at its bottom edge  641  and is free at its top edge  642 . Resilient tab  645  can be formed of one or more resilient materials such as silicones and thermoplastic rubbers.  
      During use of system  600 , guide wire  170  can be inserted into a body vessel and then a distal portion of system  600  can be guided over guide wire  170  until positioned within a target region of the vessel. Unlike over-the-wire systems, guide wire  170  is not generally contained within handle  105 . During use, however, guide wire  170  can be positioned between resilient tab  645  and handle  105 . When no force is applied by the user to resilient tab  645 , guide wire is free to move longitudinally. To fix guide wire  170  relative to handle  105  (and to catheter  610 ), the user can press (e.g., with his or her thumb) resilient tab  645  against guide wire  170  such that guide wire  170  is compressed between resilient tab  645  and handle  105 . As an alternative to or in addition to resilient tab  645 , any of the various other types of holding devices described herein can be used.  
      As a further example, while the systems of the embodiments above include endoprostheses, the systems can alternatively or additionally be equipped with other devices, such as laser ablation tools and inflatable balloons.  
      As an additional example, while the embodiments above show the systems being used in blood vessels of a subject, the systems can alternatively or additionally be used within any of various other body vessels or cavities of a subject. For example, the systems can be used within pulmonary vessels, gastrointestinal vessels, urinary vessels, reproductive vessels, biliary vessels, lymphatic vessels, the thoracic cavity (e.g., the heart, the lungs, the trachea, the esophagus, large blood vessels), the abdominal cavity (e.g., the gastrointestinal tract, the kidneys), the pelvic cavity (e.g., the urogenital system, the rectum), and the cranial cavity (e.g., the brain, vertebral canal).  
      Other embodiments are in the claims.