Abstract:
A delivery apparatus for a lumen occlusion device includes a pusher configured for releasably coupling with and pushing and pulling a proximal end of the occlusion device in a distal or proximal direction and a distal control wire capable of releasably coupling with the distal end and the proximal end of the occlusion device. The control wire may be configured for moving the distal end of the occlusion device in both proximal and distal directions allowing precise simultaneous control of both proximal and distal ends of the occlusion device. Control of both ends provides for placing the occlusion device in tension during delivery through a delivery catheter, thereby reducing delivery forces, achieving greater compaction of the occlusion device in the lumen, and precisely locating both distal and proximal ends of the occlusion device within the lumen.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Ser. No. 61/591,119 filed on Jan. 26, 2012 and U.S. Provisional Application Ser. No. 61/681,507 filed on Aug. 9, 2012, both of which are incorporated by reference herein in their entirety for all purposes. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This technology was developed with sponsorship by the National Science Foundation&#39;s AAA Endograft PII/IIB Grant No. 0823015 and the U.S. federal government has certain rights to this technology. 
    
    
     TECHNICAL FIELD 
     The present description relates generally to implantable devices for therapeutic treatment, and more particularly to an apparatus for endoluminally delivering a device for vascular occlusion. 
     BACKGROUND 
     During many clinical procedures, a physician requires the reduction or complete stoppage of blood flow to a target region of the patient&#39;s body to achieve therapeutic benefit. A variety of devices are available to provide occlusion of blood vasculature including embolic coils, metal-mesh vascular plugs, beads, particles, and glues. Interventional radiologists and vascular surgeons (and similar medical specialists) draw from these choices based upon the specific need and confidence of a rapid and effective occlusion given the attributes and deficiencies of each of these options. These devices may be used to occlude vasculature in situations, for example, requiring treatment of arteriovenous malformations (AVMs), traumatic fistulae, some aneurysm repair, uterine fibroid, and tumor embolization. For these clinical treatments, the blood flow through a target section of a blood vessel must be stopped. The device is introduced into the blood vessel through a sterile delivery catheter or sheath using common percutaneous access outside the body. The delivered, artificial device, induces an initial reduction of blood flow through a simple mechanical blockage which in turn triggers the body&#39;s natural clotting process to form a more complete blockage comprised of the thrombus adhered to the device. 
     Current exemplary embolic coils are made from biocompatible materials, and provide a biodurable, stable blockage of blood flow. The coils anchor to the vessel wall through radial compliance pressing onto the vessel wall surface. Coils must be suitably anchored to avoid migrating downstream under the forces of the blood flow, which can be significant in larger vasculature. Embolic coils are often shaped for flexibility through the use of a primary coiling, and for achieving a “coil pack” within the vessel through the use of a secondary, sometimes complex, three dimensional shape. The coil pack appears as a relatively random crossing and intertwining of the coil within the vessel. After slowing the blood flow, over time, a clot forms around the embolic coil, and blood flow through the section is completely blocked. 
     Typical embolic coils are formed using two major steps: 1) a wire of platinum or other bio-compatible material is wound into a spring, forming what is commonly referred to as a primary coil; and 2) the primary coil is in turn wound around a mandrel having a more complex shape and then subjected to high heat (e.g., heat setting) to yield a secondary coil. The secondary coil thus is a coiled wire of complex-shape or, if helical, a larger curl diameter. Coils can also be provided in other secondary shapes, such as those having multiple helical curl diameters, and in tapered helical shapes with one end employing a large curl diameter and the other end a small curl diameter. These metal coils are straightened, within their elastic bending limit, so as to be advanced into a delivery catheter and pushed down the catheter by a guide wire, pusher, or a detachable pre-attached pusher, until expelled into the vessel. Often, polymeric fibers are applied to the metallic coils in order to increase a thrombus response in addition to providing a scaffolding for thrombi to adhere to and be retained on the coil. 
     Embolic coils are sized to fit within the inner lumen of a catheter or sheath to be delivered to the target occlusion site individually and sequentially. Typically, a physician will use multiple coils to occlude a single vessel and in some cases, especially for larger blood vessels (above 5 mm or so), the physician may use a significant number coils to achieve cessation of blood flow. To complete an occlusion procedure with embolic coils, the physician must sequentially reload the catheter with several individual coils until he/she has determined that the occlusion is sufficient. The physician typically determines whether sufficient coils have been deployed by assessing the level of occlusion of the vessel flow, e.g., by using contrast media in concert with typical medical imaging techniques. This “place and assess” method can extend the medical procedure time, expose the patient to increased levels of contrast agent, and increase radiation exposure to both the patient and the physician through extensive imaging. 
     Embolic coils are also known for challenges in achieving precise vascular placement. Many of these coils are simply pushed out of the end of a delivery catheter. The final coil pack location is dependent upon whether the coil has been properly sized prior to deployment or whether the coil was properly anchored into a side vessel/branch as prescribed by several of the coil manufacturers for greater confidence in the coil pack&#39;s final position. Both of these techniques require a high level of physician skill if there is a desire to accurately position both the distal and proximal faces of the coil pack in a vessel using sequential, pushable coils. Some of the coil manufacturers provide a detachable coil that, once properly placed, can be released from a delivery control wire at the user&#39;s discretion. If the coil is not in the preferred location, it can be retracted and replaced if needed to achieve better position. However, only the proximal end of the coil is attached to this control wire resulting in only indirect control of the position of the coil pack&#39;s distal face. 
     Using coils for embolization can present other unique challenges. Voids in the coil pack, developed either during the procedure or post operatively, can cause channels and resulting blood flow in an unintended area. This condition is typically referred to as recanalization. Depending upon the significance of the condition, e.g., internal hemorrhage, retreatment or surgical intervention may be necessary. The ability to quickly and reliably develop a consistently dense coil pack in a vessel is a key to a successful vascular occlusion product. 
     Also, embolic coils can be easily misplaced. Embolic coils may either be injected through a delivery catheter with a syringe filled with saline, pushed by an independent guide wire, or deployed with a detachable pusher that is only connected to the coil via its proximal end. The coil pack shape is dependent upon the successful placement of the initial coil. Therefore, coils can easily be misplaced, should the initial coil not land correctly or be slightly undersized to the target vessel and slip beyond the target location. As such, embolic coil packs are known for a high propensity of being elongated in overall size. While these devices have been employed clinically for years, coils reflect significant challenges when attempting to embolize in a very precise or limited section of vasculature. 
     Metal mesh vascular plug devices have also been developed and commercialized to achieve vascular occlusion. These devices achieve occlusion with a single deployment using a metal mesh to provide mechanical flow blockage and, after some time, a thrombus forms and a complete occlusion results. When deployed, these devices appear like metal mesh balloons or baskets, with one or more lobes contacting the vascular wall, but with defined proximal and distal faces. With occlusion occurring after a single device deployment, these products address many of the deficiencies of embolic coils. However, due to the porosity of the mesh basket and the lack of the polymeric fibers used in coils, the metal mesh plugs have been shown to take longer to achieve occlusion than a properly placed embolic coil pack. 
     Further, these metal mesh devices are relatively stiff due to their construction and have limited ability to traverse the sharp turns found in catheters that have been placed in a highly tortuous vascular path. The mesh is collapsed into a narrow tube-like shape for introduction and deployment through a delivery catheter or sheath before expanding into the balloon-like shape upon deployment. This narrow tube-like shape allows the device to be delivered in the central lumen of small catheters or sheaths similar to coils. However, when the mesh is collapsed, it elongates and becomes a fairly rigid tubular structure. So while being capable of entry into a small delivery catheter, it has a limited ability to traverse the sharp turns found in highly tortuous paths to the target vessel. Subsequently, the advantages of a single occlusion device are offset by the slow occlusion performance and limited application to occlusion target sites that have non-tortuous access. 
     The information included in this Background section, including any references cited herein and any description or discussion thereof, is included for technical reference purposes only and is not to be regarded subject matter by which the scope of the claims is to be bound. 
     SUMMARY 
     In one embodiment a delivery apparatus for distal and proximal control of a vascular or lumen occlusion device is disclosed. Example applications for the vascular occlusion device include, but are not limited to, the occlusion of peripheral vasculature, occlusion of cerebral aneurysms, and the occlusion of parent vessels to cerebral aneurysms. An exemplary occlusion device controlled by the delivery apparatus includes a plurality of coil members, with each member defining a proximal end and a distal end. The occlusion device also includes a proximal retaining feature coupled to the proximal ends of the plurality of coil members and a distal retaining feature coupled to the distal ends of the plurality of coil members. The proximal and distal retaining features may each be a nubbin (e.g., a homogenous section formed by the coil material, adhesive, etc.). The delivery apparatus may include a pusher configured for moving the proximal retaining feature in a distal direction, or both proximal and distal directions, and a distal control wire releasably coupled to the distal retaining feature. The distal control wire may be configured for moving the distal retaining feature in both proximal and distal directions. 
     In some embodiments, the occlusion device may be delivered within the vasculature by the delivery apparatus within a delivery catheter. In additional embodiments, the distal control wire extends through the proximal retaining feature and the pusher, which may both move freely relative to the distal control wire and the distal retaining feature. In further embodiments, the distal control wire may be decoupled from the distal retaining feature by applying a force on the wire in a proximal direction that is greater than a minimum threshold force. 
     The disclosed vascular or lumen occlusion apparatus (or system) allows for controlling both the proximal and distal ends of the occlusion device, thereby enhancing the delivery, placement, packing density, and anchoring of the occlusion device within a vessel, which are key characteristics of a successful embolic procedure. Existing single coil devices, whether pushable or detachable (i.e., where the occlusion devices are held/detached from only their proximal end), rely on the curl or shape of the coil members to control the distal position of the occlusion device and are typically anchored to the closest or immediate vessel wall upon exiting the delivery catheter. During and after deployment of the occlusion device, the coil members may migrate downstream (distally) to an unintended location along the vessel. 
     The disclosed delivery apparatus allows for controlling the distal end throughout the delivery of the occlusion device in the delivery catheter, as well as during deployment of the device in the vessel. This allows the attending physician to maintain the occlusion device in a specific position relative to the delivery catheter until the point of release, resulting in more accurate placement of the occlusion device during the occlusion procedure and avoiding misplacement of the occlusion device within the lumen. 
     The distal end control provided by the disclosed delivery apparatus may further allow for more effective compression of the coil members between the distal and proximal retaining ends, resulting in the formation of a higher density coil pack. For example, the disclosed apparatus allows the attending physician to maintain the position of the distal end of the occlusion device while pushing the proximal end, thereby compressing the coil members between the proximal and distal ends. Alternatively, the distal end of the occlusion device may further be pulled in a proximal direction via the wire to further compress in the coil members. The disclosed occlusion apparatus thereby allows for better compression of the coil members, resulting in a higher-density coil pack with increased flow blockage and anchoring properties. 
     The disclosed delivery apparatus further allows for retaining the proximal end of the occlusion device with the pusher until it is specifically released by the physician. In other words, the apparatus allows the physician to control the position of the proximal end of the occlusion device as it is delivered through the catheter and during deployment. This feature provides multiple advantages. For example, it allows for positioning coil members in slight tension between the proximal and distal ends, thereby preventing bunching of the coil members as they are moved through the delivery catheter before deployment into the lumen, as well as preventing buckling of the individual coil members. Accordingly, damage to the coils during delivery of the occlusion device through the catheter is avoided and the force to pass the device through the delivery catheter is reduced. 
     The proximal control provided by the disclosed delivery apparatus further allows for repositioning of the occlusion device during the occlusion procedure. For example, the physician may retract a partially deployed occlusion device back into the delivery catheter, as well as remove a partially deployed occlusion device from the vessel without retracting it back into the delivery catheter. This feature serves to reduce the potential for leaving a misplaced occlusion device within the vessel, which may lead to other medical complications or require surgical intervention to correct. 
     The proximal and distal control provided by the disclosed delivery apparatus may be similarly beneficial if the occlusion device was a single coil device, and regardless of material, e.g., metals (stainless steel, platinum, nitinol), traditional polymers/plastics (thermoplastic or thermoset resins), shape memory polymers, or a combination of these. It can be seen that the benefits of such a delivery apparatus may also be applicable for use with devices for occlusion of any number of types of biological lumens, e.g., arterial and venous vasculature, reproductive tracts (e.g., fallopian tubes), lung and air passageways (including lung lobe resection), digestive organs (esophagus, stomach, intestines, bile ducts and other passageways in the biliary tree, etc.), left atrial appendages, patent foramen ovales, and so forth. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. A more extensive presentation of relevant features, details, utilities, and advantages are provided in the following written description of various embodiments of the inventive subject matter and illustrated in the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The details of the subject matter set forth herein, both as to its structure and operation, may be apparent by study of the accompanying figures. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the subject matter. Moreover, all illustrations are intended to convey concepts, where relative sizes, shapes and other detailed attributes may be illustrated schematically rather than literally or precisely. 
         FIG. 1A  is a schematic side view of a distal end of an example embodiment of a vascular occlusion apparatus in a first stage, before deployment of the occlusion device. 
         FIG. 1B  is a schematic cross-sectional view of the distal end of the vascular occlusion apparatus shown in  FIG. 1A . 
         FIG. 2A  is a schematic side view of the distal end of the vascular occlusion apparatus shown in  FIG. 1A  in a second stage, in which the distal retaining feature is advanced past the distal end of the delivery catheter. 
         FIG. 2B  is a schematic side view in cross section of the distal end of the vascular occlusion apparatus shown in  FIG. 1A  in a third stage, in which a coil pack is formed. 
         FIG. 3A  is a schematic side view in cross section of the distal end of the vascular occlusion apparatus shown in  FIG. 1A  in a fourth stage, in which the distal control wire is disconnected from the distal retaining feature. 
         FIG. 3B  is a schematic side view in cross section of the distal end of the vascular occlusion apparatus shown in  FIG. 1A  in a fifth stage, in which the occlusion device is released into the vessel. 
         FIG. 4  is a schematic side view in cross section of an alternative embodiment of a distal end of a vascular occlusion apparatus with a distal control wire having an enlarged section to aid in retention of the proximal control wire. 
         FIG. 5  is a schematic side view in cross section of a distal end of another embodiment of a vascular occlusion apparatus with an additional lock wire interfacing with the ball on the end of the distal control wire. 
         FIG. 6  is a schematic side view in cross section of a distal end of another embodiment of a vascular occlusion apparatus with an additional lock wire and a proximal control wire extending proximally through the delivery catheter ex vivo. 
         FIG. 7A  is a schematic isometric view of an alternate embodiment of a retention structure in the form of an elastomeric O-ring for retaining the distal end of the distal control wire within a distal engagement feature. 
         FIG. 7B  is a schematic side view in cross section of the O-ring retention structure of  FIG. 7A  within the distal engagement feature. 
         FIG. 8  is a schematic isometric view of another embodiment of a retention structure in the form of a C-clip for retaining the distal end of the distal control wire within a distal engagement feature. 
         FIG. 9  is a schematic isometric view of another embodiment of a retention structure in the form of a star washer for retaining the distal end of the distal control wire within a distal engagement feature. 
         FIG. 10  is a schematic isometric view in partial cross section of a further embodiment of a retention structure in the form of a slot bounded by parallel wires or posts for retaining the distal end of the distal control wire within a distal engagement feature. 
         FIG. 11  is a schematic isometric view of another embodiment of a retention structure based upon rotational position in the form of a keyhole for retaining the distal end of the distal control wire having a key feature within a distal engagement feature. 
         FIGS. 12A-B  are perspective views of an exemplary embodiment of a distal retaining feature used in conjunction with an exemplary embodiment of the occlusion apparatus. 
         FIG. 13A  is a perspective view of an exemplary embodiment of a proximal retaining feature. 
         FIG. 13B  is a perspective and partial cross-sectional view of the exemplary embodiment of the proximal retaining feature of  FIG. 13A  used in conjunction with an exemplary embodiment of the occlusion apparatus. 
         FIG. 13C  is a side view of an exemplary embodiment of the occlusion apparatus during release of the implant. 
         FIG. 13D  is a perspective and partial cross-sectional view of an embodiment of a proximal retaining feature used in conjunction with another exemplary embodiment of the occlusion apparatus. 
         FIG. 14A  is a perspective view of another exemplary embodiment of a proximal retaining feature. 
         FIG. 14B  is a side and partial cross-sectional view of another embodiment of the proximal retaining feature of  FIG. 14A  used in conjunction with another exemplary embodiment of the occlusion apparatus. 
         FIG. 15  is a perspective view of another exemplary embodiment of a proximal retaining feature. 
         FIG. 16A  is a side view of an exemplary embodiment of a stent in a radially expanded state. 
         FIG. 16B  is a partial side view of the embodiment of the stent of  FIG. 16B  in a radially compressed state. 
         FIG. 16C  is a side-by-side comparison of exemplary lobes from the embodiment of the stent of  FIG. 16A . 
         FIG. 16D  is an end-on view of an exemplary embodiment of a stent delivery system. 
         FIG. 17  is a side view of an exemplary embodiment of an embolic cage release system. 
     
    
    
     DETAILED DESCRIPTION 
     This detailed description sets forth numerous embodiments of an occlusion apparatus. It should be noted that all features, elements, materials, components, functions, and steps described with respect to any embodiment of this occlusion apparatus (and methods of using and making the apparatus) are intended to be freely combinable and substitutable with those from any other embodiment. If a certain feature, element, component, function, or step is described with respect to only one embodiment, then it should be understood that that feature, element, material, component, function, or step can be used with every other embodiment described herein unless explicitly stated otherwise. This paragraph therefore serves as antecedent basis and written support for the introduction of claims, at any time, that combine features, elements, materials, components, functions, and steps from different embodiments, or that substitute features, elements, materials, components, functions, and steps from one embodiment with those of another, even if the following description does not explicitly state, in a particular instance, that such combinations or substitutions are possible. 
     Vascular sections targeted for occlusion may present with some anatomical variability. Therefore, a clinically acceptable vascular occlusion device is flexible and adaptive to the structure it is filling while anchoring without inducing significant pressure on the vessel wall to avoid migration under the influence of the blood flow. It should be noted that all example embodiments of occlusion implant devices described herein can be used with all embodiments of the delivery apparatus of portion of a delivery apparatus, unless explicitly stated otherwise. A delivery apparatus may deliver an occlusion device into a vessel or lumen wherein the occlusion device is constructed of one or a series of (preferably parallel) coil members. For instance, in one embodiment, the occlusion device has seven coil members and fits in a sheath (or delivery catheter) that has an approximately 5 French (Fr) inner diameter (ID). In another embodiment for a sheath ID larger than 5 Fr, the occlusion device has more than seven coil members (e.g., 8, 9, 10, etc.). In yet another embodiment for a sheath ID less than 5 Fr, the occlusion device has less than seven coil members (e.g., 1, 2, 3, 4, 5, or 6). It should be noted that this is only an example and that devices for larger than 5 Fr IDs may have seven or less coil members and devices for smaller than 5 Fr IDs may have seven or more coil members. 
     For the sake of clarity, it should also be noted that the occlusion device (e.g., proximal and distal hubs, coil members, etc.) can be fabricated from any metallic material (e.g., stainless steel, platinum, nitinol and other nickel-titanium alloys, and so forth), polymeric material (e.g., PEEK, plastics (thermoplastic or thermoset resins), shape memory polymers, and so forth), or a combination of both. 
     The coil members may be delivered simultaneously to form a coil pack to occlude a vascular target. The occlusion device may be used, for example, for occluding an artery or vein, to block blood flow within a vessel supplying blood to or from the liver (hepatic artery), kidney (renal artery), spleen (splenic artery) or intestines (mesenteric artery), but not limited to these applications. Occlusion devices may also be used for occlusion of other biological lumens, for example, reproductive tracts (e.g., fallopian tubes), lung and air passageways (including lung lobe resection), digestive organs (esophagus, stomach, intestines, bile ducts and other passageways in the biliary tree, etc.), left atrial appendages, patent foramen ovales, and so forth. 
     A delivery apparatus that delivers the occlusion device into a vessel or other biological lumen may include a distal control wire for controlling a distal end of the occlusion device and a pusher or a separate proximal control wire for manipulating the proximal end of the occlusion device. The coil members of the occlusion device may be joined together at the distal end to provide greater control of the resulting coil pack, reduce the potential for errant coils to extend downstream in the vessel, and facilitate the ability to utilize a distal control wire. The distal retaining feature may be releasably coupled to the distal control wire, which allows the distal retaining feature to be controlled during delivery of the vascular occlusion device and to be released at the proper time within the vessel. The coil members of the occlusion device may be joined together at the proximal end to provide greater control of the occlusion device during delivery, provide greater control of the resulting coil pack, reduce the potential for errant coils to prolapse upstream adjacent to the catheter in the lumen, and facilitate the ability to utilize a pusher that is releasably coupled to the proximal end of the occlusion device. The proximal retaining feature may be releasably coupled to the pusher, which pushes the proximal retaining feature through the catheter. The disclosed design, which allows for both proximal and distal end control of the vascular or lumen occlusion device, helps reduce the delivery force and guide the occlusion device into proper placement in the lumen, and further allows for better compression of the coil members to form a higher density coil pack. 
       FIGS. 1A and 1B  illustrate an occlusion apparatus  100  in a first preliminary stage, before deployment of an occlusion device. As is shown, the occlusion apparatus  100  may include an occlusion device  108 , a pusher  104 , a proximal coupling wire  156 , and a distal control wire  106  that are housed within a sheath or delivery catheter  102 . The occlusion device  108  may include a plurality of coil members  114  which are joined at their respective proximal and distal ends  123 ,  125  by a proximal retaining feature  110  and a distal retaining feature  112 , which are each shown here to be configured as hubs. As shown in  FIGS. 1A and 1B , the coil members  114  are in an elongated, predeployment state for delivery through the catheter  102 . The pusher  104  may engage the proximal end of the proximal retaining feature  110  to push the proximal retaining feature  110  in a distal direction through the delivery catheter  102 . 
     In one embodiment, a short segment of wire with a ball end feature, i.e., the proximal coupling wire  156  with a lock ball  154 , is attached to the distal end of the pusher  104  within a sidewall of an internal passage  122  defined within the pusher  104 . The proximal retaining feature  110  provides an internal passage  120  with a larger diameter section providing a retention chamber  152  in which the lock ball  154  of the proximal coupling wire  156  resides after assembly. Both the proximal coupling wire  156  and the distal control wire  106  pass through the internal passage  120  in the proximal retaining feature  110 . With both wires  106 ,  156  passing through the internal passage  120 , the proximal lock ball  154  is inhibited from pulling free of the retention chamber  152  within the proximal retaining feature  110 . Upon detachment, detailed below, the distal control wire  106  is retracted through the proximal retaining feature  110 . With the distal control wire  106  completely withdrawn, there is sufficient clearance for the proximal coupling wire  156  and lock ball  154  to release from the retention chamber  152  in the proximal retaining feature  110 . 
     The distal control wire  106  may be releasably coupled to the distal retaining feature  112  such that the distal retaining feature  112  is positioned by the physician and then held approximately 1.5 to 2 cm past the distal end of the delivery catheter  102 . In one embodiment, the distal control wire  106  may be a metal wire, such as a stainless steel or nitinol wire. As best shown in  FIG. 1B , the distal control wire  106  may extend from the proximal end of the distal retaining feature  112  through internal passages  120 ,  122  defined by the proximal retaining feature  110  and the pusher  104 , respectively. The distal control wire  106  may or may not contact the proximal retaining feature  110  and pusher  104 , which are allowed to move freely in proximal and distal directions relative to the distal wire  106  and the connected distal retaining feature  112 . 
     In some embodiments, the proximal and distal retaining features  110 ,  112  may be a molded nubbin or other structure that permanently joins the respective proximal and distal ends of the coil members  114 . In another exemplary embodiment, the ends of the coil members may be permanently held together via a metal band, tie, wrap, or crimp. The retaining features  110 ,  112  of the occlusion device  100  may be made from other biocompatible materials, for example polyetheretherkeytone (PEEK), to provide high dimensional capabilities for the precision openings and access channels and may be bonded to the molded nubbin or exposed ends of the joined coil member  114 . Other embodiments may utilize other configurations of retaining features  110 ,  112 . For example, the proximal and distal ends  123 ,  125  may be bonded together by an adhesive, and the distal end of the wire  106  may be embedded in the adhesive joining the coil members  114  together. In another exemplary embodiment, the proximal and distal ends  123 ,  125  may be housed within a compressive cap and the distal end of the control wire  106  held therein by friction fit. A combination of two or more of each of these aforementioned options is also possible. 
     Referring to  FIG. 1B , the distal retaining feature  112  may be configured to hold a stopper element  118 , which may be dislodged from the distal retaining feature  112  through the application of a threshold force in the distal direction. The stopper element  118  (e.g. a stainless steel or Nitinol ball) may be joined to the distal end of the control wire  106  or, alternatively, the distal end of the control wire may be enlarged with respect to the control wire&#39;s shaft. In some embodiments, the distal retaining feature  112  may define or house an engagement feature  116  at or within a proximal end of the distal retaining feature  112  that engages the outer surface of the stopper element  118  to retain the stopper element  118  within the distal retaining feature  112 . For example, the engagement feature  116  may have a narrow opening or access channel  150  through which the control wire  106  passes. The diameter of the outer surface of the stopper element  118  may be slightly larger than the diameter of the access channel  150 . The access channel  150  may be somewhat pliable and the stopper element  118  can be dislodged from the distal retaining feature  112  by pulling the control wire  106  with sufficient force (i.e., the threshold force) to pull the stopper element  118  through the access channel  150  to overcome the engagement feature  116 . Pulling the control wire  106  with less force than the threshold force will move the distal retaining feature  112  proximally or distally, but will not disconnect the control wire  106  from the distal retaining feature  112 . In an alternate embodiment, the control wire  106  may disconnect from the stopper element  118  at the threshold force and the stopper element  118  may remain in the engagement feature  116  while the control wire  106  is withdrawn. In yet another embodiment, the stopper element  118  may be deformable, elastic, or pliable, such that it will change its shape and pass through the narrow opening or access channel  150  upon the application of the threshold force. 
     In other embodiments, the distal control wire  106  may be otherwise releasably joined to the distal retaining feature  112 . For example, the distal end of the distal control wire  106  may be attached to the distal retaining feature  112  using an adhesive, and the distal control wire  106  may be dislodged from the wire  106  by applying sufficient force  138  in the proximal direction to break the adhesive bonds. Alternatively, the distal control wire  106  may be embedded in the distal retaining feature  112  and held therein by compression and friction, and the control wire  106  may be dislodged by applying a minimum threshold force required to remove the control wire  106  from the distal retaining feature  112 . In an alternate embodiment, the distal end of the control wire  106  may be formed of a fiber, a weakened area, or smaller gauge of wire, and may be broken, such that the distal end of the distal control wire  106  remains within the distal retaining feature  112  as it is deployed in the vessel. Another embodiment may utilize a releasable clamp on the proximal end of the distal control wire  106  to releasably join the control wire  106  to the distal retaining feature  112 . 
       FIG. 2A  illustrates the apparatus  100  shown in  FIGS. 1A and 1B  in a second stage, in which the occlusion apparatus  100  is first inserted into vessel  124  deployed from the delivery catheter  102 . In this stage, the proximal retaining feature  110  is advanced along the control wire  106  in a distal direction (represented by arrow  130 ) towards the distal end of the catheter  102 . As discussed above, the proximal retaining feature  110  may be moved by the pusher  104  housed in the delivery catheter  102 . The distal retaining feature  112  is simultaneously moved in a distal direction away from the catheter  102 . As discussed above, the distal retaining feature  112  may be moved by pushing and pulling the control wire  106 . During this second stage, the physician may move the distal retaining feature  112  in both proximal and distal directions (represented by bi-directional arrow  132 ) by manipulating the proximal end of the control wire  106 , so long as the force applied to the stopper element  118  is not sufficient to dislodge the stopper element  118  from the distal retaining feature  112 . The distal retaining feature  112  may be maintained at a constant separation distance from the proximal retaining feature  110  via the control wire  106  during travel through the catheter  102  such that the coil members  114  retain their linear (e.g., generally straight) shape, may be placed under slight tension, and are oriented in a substantially parallel configuration to minimize delivery friction and force. This feature allows for deployment of coil structures that may not have sufficient tensile strength in an elongated form to navigate a catheter  102  without buckling and possibly getting stuck. 
     After the occlusion device  108  has been extended beyond the delivery catheter  102  a prescribed distance as controlled by the physician, the distal control wire  106  may be restricted from further movement, thereby holding the distal retaining feature  112  of the occlusion device  108  in a stable position. Deployment of the occlusion device  108  continues by further advancing the pusher  104 . 
     A comparison of the device  100  in  FIG. 2A  with the device  100  in  FIGS. 1A and 1B  shows that the distance between the proximal and distal retaining features  110 ,  112  decreases in the second stage as the coil members  114  begin to curl at the distal end upon deployment.  FIG. 2B  illustrates the apparatus  100  in a third stage, in which both the proximal and distal retaining features  110 ,  112  are in the vessel  124  and a coil pack  126  is formed. A comparison of  FIG. 2B  with  FIG. 2A  reveals that the pusher  104  has advanced the proximal retaining feature  110  along the control wire  106  past the distal end of the catheter  102 , while the distal retaining feature  112  is maintained in the same position within the vessel  104  as in the second stage (shown in  FIG. 2A ), further decreasing the distance between the proximal and distal retaining features  110 ,  112 . During this stage, the coil members  114  deploy and change from an elongated form to a curled form, and are further compressed, thereby forming a dense coil pack  126  between the proximal and distal retaining features  110 ,  112 . As discussed above, maintaining the distal retaining feature  112  in a fixed position may allow for better compression of the coil members  114  against the distal retaining feature  112  as the pusher  104  is advanced towards the distal retaining feature  112 , thereby increasing the density and outward radial force of the resulting coil pack  126  which increases flow blockage and therefore reduces occlusion time. Similar to the second stage shown in  FIG. 2A , at the physician&#39;s discretion, the distal retaining feature  112  may still be moved in both proximal and distal directions  132  as shown in  FIG. 2B  by manipulating the proximal end of the control wire  106  ex vivo, allowing the attending physician to accurately position the occlusion device  108  during the occlusion procedure such that it will be anchored in an appropriate location within the vessel  124 . 
     At this third stage, in which the distal retaining feature  112  is still connected to the control wire  106 , the physician can freely retract a partially deployed occlusion device back into the delivery catheter  102 , if necessary, by pulling the pusher  104  and the proximal control wire  156  in a proximal direction, drawing the coiling members  114  back into the delivery catheter  102 . The entire occlusion device  108  may be retracted until the distal control wire  106  and the distal retaining feature  112  are retracted back into the catheter  102 . This reduces the potential for having to leave a misplaced occlusion device  108  within the vessel  124 , which may lead to other medical complications or require surgical intervention to correct. Alternatively, the physician may choose to remove the partially deployed occlusion device  108  from the vessel  124  without retracting into the catheter  102  by simply removing the occlusion device  108  and the delivery catheter  102  simultaneously while the occlusion device  108  remains connected to the proximal coupling wire  156  and/or the distal control wire  106  within the proximal and distal retaining features  110 ,  112 , respectively. 
       FIG. 3A  illustrates the apparatus  100  in a fourth stage, in which the stopper element  118  is dislodged from the engagement feature  116  of the distal retaining feature  112 . As discussed above, removal of the stopper element  118  may require an application of a threshold force in the proximal direction (represented by arrow  138 ) on the control wire  106  that is sufficient to overcome any compression, adhesion, or frictional forces applied by the engagement feature  116  on the surface of the stopper element  118 . Applying a force that is smaller than the threshold force will serve to move the distal retaining feature  112  in a proximal or distal direction (represented by arrow  132  in  FIGS. 2A and 2B ), as described above with respect to  FIGS. 2A and 2B . 
     The stopper element  118  may have a spherical shape, as shown, or may have some other low friction shape which does not have sharp corners or edges which might catch and potentially damage the coil members  108  defining the coil pack  126  as it is withdrawn. As described above in other embodiments, the control wire  106  may disengage from the stopper element  118  or otherwise separate from the distal retaining feature  112  and be withdrawn through the coil pack  126  and into the catheter  102 . 
       FIG. 3B  illustrates the occlusion apparatus  100  in a fifth stage, in which the occlusion device  108  has been released within the vessel  124 . As is shown, the stopper element  118  is pulled in a proximal direction (represented by arrow  140 ) via the control wire  106  and drawn through the coil pack  126  and the passage  120  defined by the proximal retaining feature  110  back into the catheter  102 . In this stage, the control wire  106  and stopper element  118  are completely disconnected from the occlusion device  108 , which is anchored within the vessel  124 . Once the stopper element  118  passes through the proximal retaining feature  110  and is retracted into the passage  122  defined by the pusher element  104 , the lock ball  154  and proximal control wire  156  are released from the proximal retaining feature  110 . The pusher element  104  and the catheter  102  may then be removed from the lumen  124 . 
       FIG. 4  illustrates an alternative embodiment of an occlusion apparatus  400  in a preliminary stage, before deployment of the occlusion device  108 . As in previous embodiments, the occlusion apparatus  400  may include the occlusion device  108 , a pusher  104 , a proximal coupling wire  156 , and a distal control wire  106  that are housed within a sheath or delivery catheter  102 . The occlusion device  108  may include a plurality of coil members  114  which are joined at their respective proximal and distal ends  123 ,  125  by a proximal retaining feature  110  and a distal retaining feature  112 . As in the prior embodiment, a short segment of wire with a ball end feature, i.e., the proximal coupling wire  156  with a lock ball  154 , is shown attached to the distal end of the pusher  104  within a sidewall of an internal passage  122  defined within the pusher  104 . The proximal retaining feature  110  provides an internal passage  120  with a larger diameter section providing a retention chamber  152  in which the lock ball  154  of the proximal coupling wire  156  resides after assembly. Both the proximal coupling wire  156  and the distal control wire  106  pass through the internal passage  120  in the proximal retaining feature  110 . In another embodiment, the proximal coupling wire  156  may be attached to the end of the pusher  104 . 
     In this embodiment, the distal control wire  106  may have a stepped diameter with a proximal portion  160  being of a larger diameter than a distal portion  162  of the distal control wire  106  attached to the lock ball  118 . During deployment, the proximal portion  160  may extend beyond the end of the pusher  104  to an intermediate point within the occlusion device  108 . With both wires  106 ,  156  passing through the internal passage  120 , the proximal lock ball  154  is inhibited from pulling free of the retention chamber  152  within the proximal retaining feature  110 . The thicker proximal portion  160  of the distal control wire  106  is adjacent to the proximal lock ball  154  to help ensure that the proximal lock ball  154  maintains the engagement with the proximal retaining feature  110  of the occlusion device  108 . When the distal control wire  106  is pulled proximally, the thicker proximal portion  160  is pulled past the proximal lock ball  154 . The length of the thinner distal portion  162  of the distal control wire  106  may be chosen such that the thicker proximal portion  160  remains in contact with the proximal lock ball  154  for a significant portion of the linear contraction of the occlusion device  108  as the coil members  114  coil to ensure that the proximal end of the occlusion device  108  remains in place and the proximal lock ball  154  does not release too early. 
     The precision dimensions of the components may be designed to allow the proximal lock ball  154  to disengage from the retention chamber  152  in the proximal retaining feature  110  as the thinner distal portion  162  passes by the proximal lock ball  154  (i.e., the retention chamber  152  is designed such that there is enough clearance for the distal portion  162  of the distal control wire  106  and the proximal lock ball  154  to exit the proximal retaining feature  110 ). Thus, with the proximal lock ball  154  removed, it is easier (i.e., a lower force is required) for the distal lock ball  118  to pass through the proximal retaining feature  110  because it does not have to pass the proximal lock ball  154 . 
       FIG. 5  illustrates another alternative embodiment of an occlusion apparatus  500  in a preliminary stage, before deployment of the occlusion device  108 . As in previous embodiments, the occlusion apparatus  500  may include the occlusion device  108 , a pusher  104 , a proximal coupling wire  156 , and a distal control wire  106  that are housed within a sheath or delivery catheter  102 . The occlusion device  108  may include a plurality of coil members  114  which are joined at their respective proximal and distal ends  123 ,  125  by a proximal retaining feature  110  and a distal retaining feature  112 . As in the prior embodiments, a short segment of wire with a ball end feature, i.e., the proximal coupling wire  156  with a lock ball  154 , is attached to the distal end of the pusher  104 . The proximal retaining feature  110  provides an internal passage  120  with a larger diameter section providing a retention chamber  152  in which the lock ball  154  of the proximal coupling wire  156  resides after assembly. Both the proximal coupling wire  156  and the distal control wire  106  pass through the internal passage  120  in the proximal retaining feature  110 . 
     In this embodiment, a lock wire  164  is used in conjunction with the distal control wire  106 . The lock wire  164  may extend (or be coextensive) with the distal control wire  106  from a delivery control system located proximally ex vivo to the termination in the distal retaining feature  112 . Both the distal control wire  106  and the lock wire  164  are thus controlled by the physician. When the lock wire  164  is in place within the distal retaining feature  112 , there is insufficient clearance through the access channel  150  for the lock ball  118  to pass, i.e., the lock ball  118  is retained by an interference fit. Additionally, the combined diameters of the distal control wire  106  and the lock wire  164  adjacent to the proximal lock ball  154  help ensure that the proximal lock ball  154  maintains the engagement with the proximal retaining feature  110  of the occlusion device  108 . 
     When time for detachment, the lock wire  164  may be retracted proximally and removed from the distal retaining feature  112 . Further, in this embodiment, there is no need for the access channel  150  to be a precision dimension component; the diameter of the access channel  150  may actually be slightly larger than the diameter of the distal lock ball  118 , thereby allowing the distal lock ball  118  to easily exit the distal retaining feature  112  without additional force. Depending upon the cross-sectional dimensions of the lock wire  164  and the distal control wire  106 , the proximal lock ball  154  may remain in place in the proximal retaining feature  110  after the lock wire  164  is retracted through the proximal retaining feature  110  or the proximal lock ball  154  may dislodge from the proximal retaining feature  110  once the lock wire  164  is retracted through the proximal retaining feature  110 . In the former case, the occlusion device  108  will remain attached to the pusher  104  until the distal lock ball  118  passes by the proximal lock ball  154  in the retention chamber  152 . In the latter case, once the lock wire  164  exits the proximal retaining feature  110 , the precision dimensions of the components may be designed to allow the proximal lock ball  154  to disengage from the retention chamber  152  as there is enough clearance for the proximal lock ball  154  to exit the proximal retaining feature  110  adjacent the distal control wire  106 . Again, if the proximal lock ball  154  is removed first, it may be easier for the distal lock ball  118  to pass through the proximal retaining feature  110  because it does not have to pass the proximal lock ball  154 . Further, the physician may thus be provided greater control over when the proximal end of occlusion device  108  is released from the pusher  104 . 
       FIG. 6  illustrates a further embodiment of an occlusion apparatus  600  in a preliminary stage, before deployment of the occlusion device  108 . As in previous embodiments, the occlusion apparatus  600  may include the occlusion device  108 , a pusher  104 , a proximal coupling wire  158 , and a distal control wire  106  that are housed within a sheath or delivery catheter  102  or, in the case of wires  158  and  106 , may be housed within the pusher  104 . The occlusion device  108  may include a plurality of coil members  114  which are joined at their respective proximal and distal ends  123 ,  125  by a proximal retaining feature  110  and a distal retaining feature  112 . Unlike the prior embodiments, the proximal coupling wire  158  is not attached to the pusher  104 , but instead extends all the way through the delivery catheter  102 . The lock ball  154  is attached to the distal end of the proximal coupling wire  158 . The proximal retaining feature  110  provides an internal passage  120  with a larger diameter section providing a retention chamber  152  in which the lock ball  154  of the proximal coupling wire  158  resides after assembly. Both the proximal coupling wire  158  and the distal control wire  106  pass through the internal passage  120  in the proximal retaining feature  110 . 
     In this embodiment, the lock wire  164  is also used in conjunction with the distal control wire  106  in the same manner as previously described with respect to  FIG. 5 . Thus, all three wires, the distal control wire  106 , the lock wire  164 , and the proximal coupling wire  158  may extend (or be coextensive) with the distal control wire  106  from a delivery control system ex vivo for control by the physician. When the lock wire  164  is in place within the distal retaining feature  112 , there is insufficient clearance through the access channel  150  for the lock ball  118  to pass. Additionally, the combined diameters of the distal control wire  106  and the lock wire  164  adjacent to the proximal lock ball  154  help ensure that the proximal lock ball  154  maintains the engagement with the proximal retaining feature  110  of the occlusion device  108 . It may be noted that the proximal control wire  158  of this embodiment may be substituted for the proximal control wire  156  attached to the pusher  104  in prior embodiments. 
     When time for detachment, the lock wire  164  may be retracted proximally and removed from the distal retaining feature  112 . Further, in this embodiment, there is no need for the access channel  150  to be a precision dimension component; the diameter of the access channel  150  may actually be slightly larger than the diameter of the distal lock ball  118 , thereby allowing the distal lock ball  118  to easily exit the distal retaining feature  112  without additional force. Depending upon the cross-sectional dimensions of the lock wire  164  and the distal control wire  106 , the proximal lock ball  154  may remain in place in the proximal retaining feature  110  after the lock wire  164  is retracted through the proximal retaining feature  110  or the proximal lock ball  154  may dislodge from the proximal retaining feature  110  once the lock wire  164  is retracted through the proximal retaining feature  110 . In the former case, the occlusion device  108  will remain attached to the pusher  104  until the distal lock ball  118  passes by the proximal lock ball  154  in the retention chamber  152 . In the latter case, once the lock wire  164  exits the proximal retaining feature  110 , the precision dimensions of the components may be designed to allow the physician to retract the proximal control wire and disengage the proximal lock ball  154  from the retention chamber  152  as there is enough clearance for the proximal lock ball  154  to exit the proximal retaining feature  110  adjacent the distal control wire  106 . Again, if the proximal lock ball  154  is removed first, it may be easier for the distal lock ball  118  to pass through the proximal retaining feature  110  because it does not have to pass the proximal lock ball  154 . Further, the physician may thus be provided greater control over when the proximal end of occlusion device  108  is released from the pusher  104 . 
       FIGS. 7A and 7B  depict an alternate exemplary implementation of an interface structure between the distal control wire  106  and the engagement feature  116  in the distal retaining feature  112 . In this embodiment, instead of using a precision aperture for the access channel  150 , the diameter of the access channel  150  is oversized to allow clearance around the lock ball  118 . To provide the desired force for release of the distal control wire  106  from the distal retaining feature  112 , an elastomeric O-ring  170  may be used. The O-ring  170  may be positioned within the engagement feature  116  and around the distal control wire  106 . The outer diameter of the O-ring  170  is larger than the diameter of the access channel  150 , thereby preventing the O-ring  170  from exiting the engagement feature  116 . The inner diameter of the O-ring  170  is smaller than the diameter of the lock ball  118  on the control wire  106  so that the distal lock ball  118  is retained within the engagement feature  116 . The size of the inner diameter, the wall thickness, and the material properties (e.g., hardness, modulus of elasticity) of the O-ring  170  may be chosen in conjunction with the size of the access channel  150  to provide for the O-ring  170  to radially expand under a specific force to allow the lock ball  118  to pass through the O-ring  170  for release of the distal control wire  106  from the distal retaining feature  112 . As an alternative to an O-ring, a section of tubing can be used. 
     In order to assemble the device, the distal control wire  106  can be inserted into the distal retaining feature  112  through the access channel  150 , and the O-ring or tubing can then be placed around the distal control wire  106 , for instance, through a gap (or window) in the distal retaining feature  112  such as described with respect to  FIG. 12A . The stopper element  118  can then be coupled to the distal terminus of the distal control wire  106  to lock the wire in place with respect to the distal retaining feature  112 , at which point the gap (or window) can be optionally covered (such as with an insert) or otherwise blocked or filled in. 
       FIG. 8  depicts another exemplary implementation of an interface structure between the distal control wire  106  and the engagement feature  116  in the distal retaining feature  112 . In this embodiment, a precision aperture for the access channel  150  is also not required and the diameter of the access channel  150  may be oversized to allow clearance around the lock ball  118 . To provide the desired force control for release of the distal control wire  106  from the distal retaining feature  112 , a C-clip or split washer (or ring)  172  defining a gap  174  in the circumference of the split washer  172  may be used. The split washer  172  may be positioned within the engagement feature  116  and around the distal control wire  106 . The outer diameter of the split washer  172  is larger than the diameter of the access channel  150 , thereby preventing the split washer  172  from exiting the engagement feature  116 . The inner diameter of the split washer  172  is smaller than the diameter of the lock ball  118  on the control wire  106  so that the distal lock ball  118  is retained within the engagement feature  116 . The size of the inner diameter, the width of the gap  174 , and the material properties (e.g., tensile and shear strength of metal, plastic, or other material used to form the) of the split washer  172  may be chosen in conjunction with the size of the access channel  150  to provide for the split washer  172  to bend and widen the gap  174  under a specific force to allow the lock ball  118  to pass through the split washer  172  for release of the distal control wire  106  from the distal retaining feature  112 . 
       FIG. 9  depicts a further exemplary implementation of an interface structure between the distal control wire  106  and the engagement feature  116  in the distal retaining feature  112 . In this embodiment, a precision aperture for the access channel  150  is not required and the diameter of the access channel  150  may be oversized to allow clearance around the lock ball  118 . To provide the desired force control for release of the distal control wire  106  from the distal retaining feature  112 , a star washer (or ring)  176  having a plurality of tabs  178  extending radially inward from a ring portion  180  into an aperture  182  of the star washer  176  may be used. The star washer  176  may be positioned within the engagement feature  116  and around the distal control wire  106 . The outer diameter of the star washer  176  is larger than the diameter of the access channel  150 , thereby preventing the star washer  176  from exiting the engagement feature  116 . The inner diameter of the star washer  176  measured from the ends of the tabs  178  is smaller than the diameter of the lock ball  118  on the control wire  106  so that the distal lock ball  118  is retained within the engagement feature  116 . The size of the inner diameter and the material properties (e.g., tensile and shear strength of metal, plastic, or other material used to form the star washer  176 ) of the star washer  176  may be chosen in conjunction with the size of the access channel  150  to provide for the tabs  178  of the star washer  176  to bend and widen the aperture  182  under a specific force to allow the lock ball  118  to pass through the star washer  176  for release of the distal control wire  106  from the distal retaining feature  112 . 
       FIG. 10  depicts an additional exemplary implementation of an interface structure between the distal control wire  106  and the engagement feature  116  in the distal retaining feature  112 . In this embodiment, a precision aperture for the access channel  150  is again not required and the diameter of the access channel  150  may be oversized to allow clearance around the lock ball  118 . To provide the desired force control for release of the distal control wire  106  from the distal retaining feature  112 , a pair of parallel bars  186   a/b  may be used. The bars  186   a/b  may be positioned within the engagement feature  116  and on opposing sides of the distal control wire  106 . In one exemplary embodiment, the parallel bars  186   a/b  may be formed of two short sections of wire embedded in a sidewall  184  of the engagement feature  116 , in the exemplary embodiment shown in  FIG. 10  appearing as chords of the circular cross section of the cylindrical sidewall  184  of the engagement feature  116 . In another exemplary embodiment, the parallel bars  186   a/b  may be formed as two integrally molded bars extending as chords of the circular cross section of the cylindrical sidewall  184 . It may be appreciated that in other embodiments, more than two bars could be provided, e.g., three forming a triangle, four forming a square, etc. The width of the gap  188  between the bars  186   a/b  is smaller than the diameter of the lock ball  118  on the control wire  106  so that the distal lock ball  118  is retained within the engagement feature  116 . The width of the gap  188 , the thickness of the bars  186   a/b , the number of bars  186   a/b , and the material properties (e.g., tensile and shear strength) of the metal, plastic, or other material used to form the bars  188   a/b  may be chosen to provide for the bars  186   a/b  to bend apart and widen the gap  188  under a specific force to allow the lock ball  118  to pass between the bars  188   a/b  for release of the distal control wire  106  from the distal retaining feature  112 . 
     In designing structures for retention of the lock ball  118  in the engagement feature  116 , several performance factors may be taken into consideration. One factor may be the force the particular retention mechanism withstands when holding the distal (or proximal) retainer when under load. In exemplary device designs for use with the devices disclosed herein, holding forces may be between 0.25 and 3 lbs. This range of force assures that the engagement feature  116  does not prematurely release the distal control wire  106  during deployment of the occlusion device. An additional factor to consider is the force required to retract the distal lock ball  118  from the engagement feature  116 . In exemplary implementations, this force may range from 0.25 to 5 lbs, depending on the absolute and relative dimensions of the components. Maintaining a narrow range and repeatable force for disposable devices such as those disclosed herein is challenging and requires highly precise dimensions, which are not always cost effective. Thus, the implementations shown in  FIGS. 7A-10  and other similar concepts allow the introduction of some additional dimensional flexibility in the design in order to reduce the precision required yet still produce a relatively narrow range of forces for release. For designs in which the retention and release force work in the same axis, the force to release may be somewhat higher than the retention force performance and that margin of difference between these forces should be repeatable as well. 
       FIG. 11  depicts an additional exemplary implementation of an interface structure between the distal control wire  106  and the engagement feature  116  in the distal retaining feature  112 . In this embodiment, no precision aperture for the access channel  150  is required. In this implementation, the distal end of the distal control wire is formed as a key  190  and the lumen of the access channel  150  is formed as a keyway  196 . Notably, the key hole design eliminates the release force issue discussed above. Instead of requiring a force to release the distal control wire  106  from the engagement feature  116 , this approach uses a different mechanism. During placement of the occlusion device, the distal control wire  106  is oriented by the physician such that the key  190  on the distal end of the distal control wire  106  interfaces with or engages a shelf  194  or other surface defining the keyway  196  between the sidewalls  192  of the engagement feature  116 . In order to remove the distal control wire  106  from the distal retaining feature  112 , the physician must rotate the distal control wire  106  such that the key  190  aligns with the complementary keyway opening  196  in the engagement feature  116 . When the key  190  and the keyway  196  are aligned, the key  190  passes through the keyway  196  in the access channel  150  allowing the distal control wire  106  to be released from the engagement feature in the distal retaining feature  112 . 
       FIGS. 12A-B  depict an additional exemplary embodiment of a distal retaining feature  112  of the occlusion device  108 . In this embodiment, the distal retaining feature  112  is configured as a hub having a head portion  202  and proximally located stem portion  204 . The stem portion  204  has a relatively smaller latitudinal dimension (or width) than the head portion  202  to accommodate attachment of the coil members  114  as shown in  FIG. 12B . In this embodiment, the proximal end  203  of the head portion  202  steps immediately outward from the narrower stem portion  204 , although a sloping or gradual transition can be used. The distal ends  125  of the coil members  114  can be coupled directly to the stem sidewall  205  such that the distal terminus of each coil member  114  is adjacent (or abutting) the proximal end  203  of the head portion  202 . Techniques for attachment include the use of, e.g., adhesive, thermal bonding, a crimp, wrap, tie, or band, and other methods available to those of ordinary skill in the art. 
     Both the head portion  202  and the stem portion  204  preferably have cylindrical (or substantially cylindrical) bodies, with the head portion  202  having an atraumatic dome  206 . Other shapes can be used for the head portion  202  and the stem portion  204 , such as ones having elliptical, polygonal, and/or asymmetrical cross sections, to name a few. The atraumatic dome  206  is hemispherical in shape, but other atraumatic configurations can be used as well. 
     As shown in  FIG. 12A , a sidewall  208  extends partially around the perimeter of the head portion  202  such that a gap (or opening)  210  is present. Both a retention chamber  153  (for housing the stopper element  118 ) and the access channel  150  (that permits passage of the distal control wire  106 ) can be seen through this gap  210 . 
     In one embodiment, the gap  210  can be used to facilitate the assembly process by permitting insertion of the stopper element  118  (having a larger lateral dimension than the access channel  150 ) through the gap  210  and into the retention chamber  153 , where the stopper element  118  can then be coupled with the distal control wire  106  to form the arrangement depicted in  FIG. 12B . A sidewall insert  212  (shown in  FIG. 12B ) can then be placed into the gap  210  and fixed to the head portion  202  (e.g., by adhesive or thermal bonding) in order to fully house, or encapsulate, the stopper element  118  within the retention chamber  153 . This can protect against the entry of bodily fluids or other objects that may inhibit proper release of the distal retention feature  112 . 
     In another embodiment, the gap  110  can permit the insertion, into the retention chamber  153 , of any of the elements (e.g.,  170 ,  172 ,  180 ,  184 ,  194 ) for resisting passage of the distal control wire  106  that are described with respect to  FIGS. 7A-11 . In these embodiments, the stopper element  118  will preferably have a lateral dimension that is less than that of the access channel  150 , although it can be greater as well. 
     The sidewall insert  212  preferably has an outer surface that is shaped to match, or conform to, the outer surface of the head portion  202 . The sidewall insert  212  can also be radiopaque, or have enhanced radiopacity as compared to the rest of head portion  202 , which could be advantageous when the head portion  202  is fabricated from a polymer lacking pronounced radiopacity (e.g., PEEK). The sidewall insert  212  can be made radiopaque in a number of ways, such as by fabricating the insert  212  out of a radiopaque material (e.g., platinum, gold, tantalum, and alloys based on these materials) or by fabricating insert  212  out of the same material as the head portion  202  and then coupling a radiopaque material thereto. Of course, any other part of the distal retaining feature  112  can be made radiopaque if so desired. 
     Turning now to the opposite end of the implant,  FIGS. 13A-B  depict another exemplary embodiment of the proximal retaining feature  110 . Here, similar to the previous embodiment, the proximal retaining feature  110  is configured as a hub having both a head portion  222  and, in this case, a distally located stem portion  224 , which has a relatively smaller latitudinal dimension (or width) than the head portion  222  to accommodate attachment of the proximal ends  123  of the coil members  114  (not shown). In this embodiment, the distal end  223  of the head portion  222  steps immediately outward from the narrower stem portion  224 , although a sloping or gradual transition can be used. The proximal ends  123  of the coil members  114  (again, not shown) can be coupled directly to the stem sidewall  225  such that the proximal terminus of each coil member  114  is adjacent (or abutting) the base  223 . The same techniques for attachment can be used as described in the previous embodiment. 
     Both the head portion  222  and the stem portion  224  preferably have cylindrical (or substantially cylindrical) bodies, with the head portion  222  having one or more lateral (side) windows  226 . Other shapes can be used for the head portion  222  and the stem portion  224 , such as ones having elliptical, polygonal, and/or asymmetric cross sections, to name a few. 
     Here, the head portion  222  has a single window (or opening)  226  opposite the proximally extending sidewall (or strut)  227 . The window  226  can be alternatively described as a gap in the sidewall of the proximal retaining feature  110 . The proximal end  228  of the head portion  222  is in the form of a lip or plate-like cover. An access channel  120 - 1  extends through the proximal end  228  and continues, as access channel  120 - 2 , through the main body of the head portion  222  so as to accommodate passage of the distal control wire  106  therethrough. The periphery (or edge) of the head portion proximal end  223  has an end-on profile that is generally circular with one side truncated such that it has a generally straight edge  230  akin to a chord of a circle. This edge  230  is located radially closer to the longitudinal axis  231  of the proximal retaining feature  110  than is the side surface of the more distally located main body of the head portion  222 , and accommodates passage of an engagement element over the edge  230  and into the side window  226 . 
     An example embodiment of such an engagement element is depicted in  FIG. 13B . Here, the engagement element  230  engages with the distal control wire  106  and prevents the proximal end of the occlusion device  108  from moving with respect to the distal end of the pusher  204 . Retraction of the distal terminus of the control wire  106  proximally past the engagement element  230  disengages the element  230  and permits complete release of the occlusion device  108 . 
     The engagement element  230  can be configured as (or with) a loop that can reliably maintain engagement with the distal control wire  106 , for instance, with one side of the loop passing or extending around the control wire  106  so as to substantially or completely surround the control wire  106 . The system can be configured such that the loop encircles only the control wire  106 . The engagement element  230  can act as a tether and can be formed from wire, ribbon, a filament, or suture and can be composed of nitinol, stainless steel, polymers, and the like. 
     In  FIG. 13B , the engagement element  230  is a flexible loop formed from a single wire body doubled back upon itself. The wire loop is preferably fabricated from nitinol and heat treated so as to retain its shape (i.e., preset or preformed). In the shape depicted here, both termini  231 - 1  and  231 - 2  of the wire body are proximally located within a lumen  240  of the pusher  104 , and the legs  232 - 1  and  232 - 2  of the wire body extend in a substantially longitudinal direction over the proximal end  228  of the head portion  222 . At that location, the legs  232 - 1  and  232 - 2  bend into an orientation transverse to the longitudinal axis  231  such that they extend in a substantially latitudinal direction and come together to form loop  233  around the distal control wire  106  (between access channels  120 - 1  and  120 - 2 ). It should be noted that one or more legs can be used. 
     A proximal portion  234  of the wire body is preferably securely coupled (i.e., fixed or anchored) within the lumen  240  such that the wire body, as a whole, cannot slide in relation to the pusher  104 . In the embodiment of  FIGS. 13A-B , the proximal portion  234  includes the legs  232 - 1  and  232 - 2 . The proximal portion  234  can be fixed within the lumen  240  using, e.g., mechanical means or adhesive. Alternatively, the proximal portion  234  can be embedded or encapsulated in the pusher sidewall during a fusion process. The proximal portion  234  can also be coupled directly to the outer surface of the pusher sidewall, such as with adhesive or a mechanical band, tie, or crimp, which can also be radiopaque (see the embodiment described with respect to  FIG. 17 ). Preferably, the proximal portion  234  does not extend along the entire length of the pusher  104  so as not to, for example, reduce the flexibility of the pusher  104  or hinder the ability of the catheter to navigate tortuous vasculature. 
     A distal portion  238  of the engagement element  230  is flexible so as to bend between the transverse orientation shown in  FIG. 13B  and a substantially longitudinal orientation shown in  FIG. 13C . After the terminus of the distal control wire  106  is retracted past the engagement element  230 , the occlusion device  108  is no longer attached to the pusher  104 . Proximal retraction of the pusher  104  pulls the distal portion  238  of the engagement element  230  against the proximal end  228  of the occlusion device  108  and causes the distal portion  238  to deflect from the transverse orientation to the substantially longitudinal orientation (e.g., by approximately 90 degrees). 
     This distal portion  238  of the engagement element  230  (including the bend) is preferably substantially flexible such that it deflects readily upon retraction of the pusher  104 . This keeps the looped wire body from catching or hanging up on the proximal end  230  of the occlusion device  108 , thereby preventing the application of a torque (or angular momentum) to the occlusion device  108  or dislodging the proximal end  228  of the occlusion device  108  from the primary coil pack. 
     In order to assist deflection of the distal portion  238  and provide a low friction release mechanism, the proximal retaining feature  110  can be configured with a sloped surface (e.g., slide or ramp), that allows the distal portion  238  to more easily transition out of the window region  226 .  FIG. 13D  depicts an exemplary embodiment having a slide  239 . Here, the slide  239  has a constant angle of about 45 degrees. Steeper or shallower angles can be used, as can angles that vary along the length of the proximal retaining feature  110 . The slide  239  is oriented such that the proximal end portion  228  of the proximal retaining feature  110  is thicker (in the longitudinal direction) on the side that is adjacent strut  227  and thinner on the side that is adjacent the window  226 . In addition to providing the slide  239 , or as an alternative, the engagement element  230  can be biased such that the distal portion  238  automatically transitions towards the substantially longitudinal orientation as the implant is released from the pusher. 
     The proximal retaining feature  110  can also be configured with more than one window  226  to accommodate multiple engagement elements  230 .  FIGS. 14A-B  depict an exemplary embodiment of the proximal retaining feature  110  having two side windows  226 - 1  and  226 - 2  separated by struts  227 - 1  and  227 - 2 . The side windows  226 - 1  and  226 - 2  are preferably located symmetrically, i.e., laterally opposing each other at the same position along the longitudinal axis of the retaining feature  110 , to allow for uniformity during the release procedure. Likewise, as shown in  FIG. 14B , the engagement elements  230 - 1  and  230 - 2  would preferably be positioned in symmetrical locations on the pusher  104  and would each extend into a different window  226 - 1  and  226 - 2 , respectively. From there the elements  230 - 1  and  230 - 2  extend over the distal control wire  106  from opposite directions, with one element  230 - 1  lying directly beneath the other element  230 - 2 . A configuration where the elements  230  are not lying next to each other but are gapped apart is also possible, although that is a less symmetrical arrangement. 
     In the case of three engagement elements  230 , the center of each window  226  would preferably be located 120 degrees apart with the engagement elements  230  coupled to the pusher  104  in locations corresponding to those of the windows  226 . In any of these multi-window embodiments, and as shown in  FIG. 14B , the proximal end  228  of the retaining feature  110  can have a truncated edge  230  located proximal to each window  226  to allow for passage of the engagement element  230  without increasing the overall device profile. 
       FIG. 15  depicts another exemplary embodiment of the proximal retaining feature  110 . Here, the stem portion  224  includes a flared (or barbed) end  244  with a pronounced ridge  245 . The ridge resembles a serration and increases the surface friction between the coil members  114  (not shown) and the stem portion  224  itself, to reduce the likelihood that the coil members will detach. Multiple such flares can be used along the length of the stem portion  224 . Also, other features that enhance the surface friction can be used such as a textured or abrasive surface, multiple grooves (or recessions), and the like. 
     It should also be noted that in this and the other embodiments described herein, the stem portion (e.g.,  204 ,  224 ) can be omitted altogether. This can be particularly useful with an implant having only a single coil, in which case the single coil is attached directly to the head portion (or main body) of the hubs. 
     The embodiments of the proximal retaining feature  110 , especially those described with respect to  FIGS. 12A-15 , are suitable for use as a proximal release system for other types of medical implants and delivery systems as well.  FIGS. 16A-D  depict an exemplary embodiment of a stent  300  (suitable for use as a coronary or neuro-stent (e.g., for ischemia or neck-bridging), with or without a graft, etc.). Stent  300  is shown in a radially expanded state in  FIG. 16A  and in a radially compressed state in  FIG. 16B . Stent  300  includes multiple interconnecting elastic struts  301  with expandable open cells  302  formed therebetween. Where struts  301  intersect at the proximal end  305  of the stent are four independently movable crowns  303 - 1  through  303 - 4 . Proximal to each crown  303 - 1  through  303 - 4  is a lobe (or extension)  304 - 1  through  304 - 4 , respectively. Each of the lobes  304  has an eyelet therein. Two of the lobes,  304 - 1  and  304 - 3 , each have radiopaque (e.g., Pt) markers  307 - 1  and  307 - 3  fixed within the eyelets and the other two lobes,  304 - 2  and  304 - 4 , have open eyelets,  306 - 2  and  306 - 4 , through which an engagement element can pass. It should be noted that usage of the terms “crown” and “lobe” herein are not intended to be mutually exclusive in all contexts. 
     Four independently movable crowns  303 - 5  through  303 - 8  are also present on the distal end  314 . A radiopaque marker  309 - 1  through  309 - 4  is crimped, bonded, welded, or otherwise coupled to each of the distal crowns  303 - 5  through  303 - 8 , respectively. In this embodiment, each marker  309 - 1  through  309 - 4  is in the form of a sleeve placed over top the (preferably) elongate strut-like crowns  303 - 5  through  303 - 8 . Each sleeve  309 - 1  through  309 - 4  can have either an open or a closed distal terminus. Although the stent in  FIG. 16A  has a different type of radiopaque marker at each end, the different types can be used on either end and mixed as desired. 
     The overall device  300  is preferably constructed by cutting, etching, or otherwise forming the struts, cells, crowns, and eyelets in a hypotube fabricated from nitinol, other nickel titanium alloys, stainless steel, or the like. This can be done with a hypotube having a diameter corresponding to the stent in either the compressed state, the expanded state, or an intermediate state between the two. The various radiopaque markers are then coupled (e.g., adhesively bonded, welded, crimped, wrapped, tied, or otherwise secured) to the device body, followed by a heat treatment of the device so that it is biased towards its expanded state, which requires first expanding the hypotube if it is initially formed in a compressed or intermediate state. 
       FIG. 16C  shows two lobes  304 - 2  and  304 - 3  in a side-by-side comparison as if the stent  300  was unrolled into a planar state. Lobe  304 - 2  with the open eyelet  306 - 2  has a relatively greater lateral dimension along the common axis  308  than lobe  304 - 3 . This configuration allows a sufficiently large opening  306 - 2  through which the engagement element can pass, while at the same time allowing for the presence of a radiopaque marker  307 - 3  within the narrower space of the adjacent eyelet  306 - 3 . 
     The four crown stent  300  can then be reduced to a highly compressed radial state as shown in the cross-sectional view of  FIG. 16D . Here, the inner wall  311  of the delivery catheter is shown surrounding and preferably maintaining the stent  300  in the compressed state. A control wire  310  is slidably received within the inner lumen of the stent  300  and two engagement elements  312 - 1  and  312 - 2  are looped around the control wire  310  through the open eyelets  306 - 2  and  306 - 4 . A pusher (not shown) has an inner lumen that slidably receives the control wire  310 . The pusher would be fixed to the proximal ends of the engagement elements  312 - 1  and  312 - 2  in one of the manners described above. 
     After deployment of the stent  300  from within the catheter, the control wire  310  can be proximally retracted to release the engagement elements  312 - 1  and  312 - 2 , at which point the proximal end of the stent  300  can self-expand, pulling the loop elements  312 - 1  and  312 - 2  back through the eyelets  306 - 2  and  306 - 4 , and freeing the stent  300  from the pusher. While this embodiment has been described with respect to a four crown stent  300 , the alternating open eyelet and marker-bearing eyelet technique can be repeated in a stent with greater than four crowns to offer a stent release system with increased compactability. It should be noted that the stent  300  can be used with any embodiment of a proximal retaining feature described herein. 
     The proximal retaining features described herein can also be used with vena cava filters, aneurysm neck bridges, and embolic cages such as those described in U.S. Pat. No. 5,916,235 (“Apparatus and Method for the Use of Detachable Coils in Vascular Aneurysms and Body Cavities” naming Guglielmi), which is fully incorporated by reference herein for all purposes. 
       FIG. 17  is a side view depicting an exemplary embodiment of an embolic cage  400  having a distal hub  402  (housing a radiopaque marker) and a proximal hub  404 . The device  400  is preferably constructed by cutting, etching, or otherwise forming the device from, a hypotube. In this example, the hubs  402  and  404  remain in their tubular form and the remainder of the device has been expanded outward. The device can be constructed in a manner similar to that described with respect to  FIGS. 16A-B . 
     On the proximal side, two of the crowns  403 - 2  (obscured) and  403 - 4  are joined together at the proximal hub  404  and the remaining crowns  403 - 1  and  403 - 3  remain free. Similarly, on the distal side, two of the crowns  403 - 6  (obscured) and  403 - 8  are joined together at the distal hub  402  and the remaining crowns  403 - 5  and  403 - 7  remain free. (Having all of the proximal crowns connected to the proximal hub  404  would allow retrievability of the device  400  into the catheter, thereby enabling usage as a stentriever, in which case any number of one or more distal crowns  403  can couple to the distal hub  402 .) 
     In the embolic cage embodiment depicted here, the proximal hub  404  is open and allows for the passage of a control wire  405  therethrough. A pusher (or delivery catheter)  406  slidably receives the control wire  405  through an inner lumen. The pusher  406  is in contact with the terminus of the proximal hub  404  and an engagement element  408  is connected to the outer surface of the pusher  406  and held in place by an overlaid band  410 , which can be radiopaque. The engagement element  408  is sized small enough to extend distally just past the proximal hub  404  when the pusher  406  is in close contact. The control wire  405 , when extended moderately past the proximal hub  404 , will then hold the engagement element  408  taught and thereby couple the pusher  406  to the embolic cage  400 . At the desired time of release, the control wire  405  can be proximally retracted through the proximal hub  404  to free the looped engagement element  408 . It should be noted that the embolic cage  400  can be used with any embodiment of a proximal retaining feature described herein. 
     It should also be noted that the embodiments described with respect to  FIGS. 16A-17  can be used with coil-based occlusive implants having only one coil member or more than one coil member, and each coil member can be composed of a metal or a polymer. 
     The embodiments of the proximal retaining feature  110  described with respect to  FIGS. 12A-17  exhibit superior attributes over the prior art. This is particularly true in the context of treating cerebral aneurysms and occluding vasculature. For instance, in these embodiments the engagement element is secured directly to the pusher and made releasable from the implant. This ensures that the engagement element is not left behind in the patient&#39;s body. Reversing the engagement element such that it is secured to the implant and made releasable from the pusher would require leaving the engagement element behind, where it is essentially free to hang or dangle within the bloodstream, which can result in undesirable thrombus formation. For example, for an implant deployed within an aneurysm, the engagement element could extend through the aneurysm neck and into the parent vessel, where blood flow should remain unimpeded. Because the engagement element is in a hanging state, it is free to move and contact adjacent bodies or swing within the blood stream, thereby increasing the risk that a thrombus on the engagement element will become dislodged and embolize. 
     As another example, in the embodiments of  FIGS. 12A-17  the engagement element is secured to the pusher in a distal end region of the pusher and is not configured as, nor does it couple with, a pullwire that extends the length of the catheter to an accessible position outside of the patient&#39;s body. Such a pullwire configuration raises the complexity of the device as both the engagement element and the control wire must extend the entire length of the catheter. This could require the outer diameter of the catheter to be increased to fit the engagement element, which is undesirable (and in some cases not possible) in many applications. It could also force other components to be reduced in size, which, in turn, decreases the stress tolerances of those components, making the possibility of failure more likely. As already mentioned, the presence of the engagement element along the length of the catheter reduces that catheter&#39;s flexibility and increases the difficulty in navigating tortuous vasculature. It also requires the physician to perform an additional step in the release of the implant, increasing the time necessary to complete the procedure as well as the complexity of the procedure itself. If a proximal handle or control device is used (as it can be for all embodiments described herein), then that handle requires an additional actuator to control the pullwire. 
     Another attribute is the manner of attachment of the engagement element to the pusher, e.g., either embedded within the pusher wall or secured to the outer surface of the pusher. In these locations, the engagement element does not interfere with the sliding movement of other components through the open distal end of the pusher and, more importantly, the friction created by the sliding movement of other components (such as a core wire) does not urge the engagement element in the same direction as that sliding component. For instance, were the engagement element to extend through the open distal end of the pusher, distal movement of a core wire would pull or tug on the engagement element and could cause it to break free of the pusher. Conversely, proximal movement of the core wire could cause the engagement element to tighten around the core wire, impeding movement of the core wire and release of the implant. 
     Yet another attribute of certain embodiments is that the engagement element passes through a window in the sidewall of the proximal hub (as opposed to, e.g., over a strut or pin attached across a proximal end opening of the implant). For instance, in the embodiments of  FIGS. 14A-15 , the window is directly in the curved sidewall of the hub, with a substantial portion of the sidewall located proximal to the window. The size of this sidewall portion and its curvature increase its resistance to buckling as the engagement element transitions into the substantially transverse orientation. In the embodiments of  FIGS. 13A-B , the plate-like proximal end  228  of the hub is provided with ample support by the sidewall strut  227 . 
     A further attribute is that the control wire is not woven through the implant, which avoids the risk that the control wire will become inadvertently bound or stuck with respect to the implant. In many of the embodiments herein, the control wire can extend directly into the implant, e.g., without passing through the implant in a woven or interlaced manner. 
     Another attribute of certain embodiments is that the central (or inner) lumen of the pusher need only accommodate the control wire. In other words, the central lumen of the pusher can be adapted to slidably receive only the control wire, or the central lumen of the pusher can be filled (or substantially filled) with the control wire. This allows a minimization of pusher diameter, which in turn allows further reduction in the overall catheter diameter. 
     And yet another attribute of certain embodiments is the fact that the control wire is freely slidable with respect to the pusher and requires no threaded (or other locking) interface, such as those that require rotation to move the core wire proximally. Such interfaces are difficult to implement as a rotation applied at the proximal end of the core wire tends to cause the core wire to twist along its length, instead of inducing a corresponding rotation at the location of the threads. 
     The preceding paragraphs discussing the “attributes” of various embodiments in relation to the prior art should not be interpreted as a disavowal of claim scope, nor should they be used to define a claimed invention beyond the explicit language of the claim itself. 
     All directional references (e.g., proximal, distal, upper, lower, upward, downward, left, right, lateral, longitudinal, front, back, top, bottom, above, below, vertical, horizontal, radial, axial, clockwise, and counterclockwise) are only used for identification purposes to aid the reader&#39;s understanding of the present invention, and do not create limitations, particularly as to the position, orientation, or use of the invention. Connection references (e.g., attached, coupled, connected, and joined) are to be construed broadly and may include intermediate members between a collection of elements and relative movement between elements unless otherwise indicated. As such, connection references do not necessarily infer that two elements are directly connected and in fixed relation to each other. Non-limiting inclusive terms (e.g., comprising, including, and having) are to be construed as being open-ended, while limiting inclusive terms (e.g., consisting of) are to be construed as closed-ended. Also, the term “end” is used generally herein to include the terminus as well as the region of the structure adjacent to the terminus. As such, the terms “end region” and “terminus” have antecedent support in the specification by virtue of the contents of the figures and the multiple usages of the term “end” herein. The terms “end region” and “terminus” can thus be used in the claims included herewith or presented at a later date. The exemplary drawings are for purposes of illustration only and the dimensions, positions, order and relative sizes reflected in the drawings attached hereto may vary. 
     The above specification, examples and data provide a complete description of the structure and use of exemplary embodiments of the invention as defined in the claims. Although various embodiments of the claimed invention have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of the claimed invention. Other embodiments are therefore contemplated. It is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative only of particular embodiments and not limiting. Changes in detail or structure may be made without departing from the basic elements of the invention as defined in the following claims.