Patent Publication Number: US-2021169494-A1

Title: Use of peripheral embolization device for secondary treatment

Description:
INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS 
     This application claims priority benefit under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 62/944953, filed Dec. 6, 2019, titled “USE OF A PERIPHERAL EMBOLIZATION DEVICE FOR THE DELIVERY OF AGENTS,” which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Field 
     The present disclosure generally relates to apparatuses and methods for delivering therapeutic agents or advancing a treatment instrument through an embolization device. 
     Description of the Related Art 
     When a therapeutic agent is delivered to the body, the therapeutic agent is systemically distributed through the body by blood circulation. As a result, suboptimal concentrations of the therapeutic agent may reach the target site. A majority of the therapeutic agent will accumulate in healthy tissue, which may have detrimental effects. There remains a need for solutions to targeted drug delivery. 
     SUMMARY 
     Peripheral occlusion devices delivered over-the-wire, as described herein, provide physicians with accurate, stent-like delivery of the occlusion device in the vessel. Such occlusion devices take advantage of natural hemodynamic forces to provide immediate, focal, and stable occlusions. A single delivery system may be used to deliver both the peripheral occlusion device and a therapeutic agent. In addition to the delivering therapeutic agents, the inner body of the delivery system can serve as a working channel for complimentary medical devices such as steerable ablation needles. 
     Certain aspects of the disclosure are directed toward improved methods of providing targeted drug delivery. The improved methods increase the amount of therapeutic agent that reaches the target site. The improved methods also prevent reflux during infusion, thereby preventing the therapeutic agent from accumulating in healthy tissue. 
     Certain methods of delivering a therapeutic agent may include advancing a delivery system to a vessel, for example over a guidewire or through an access catheter. The delivery system may include an outer body and an inner body disposed within the outer body. The delivery system may carry an implantable occlusion device between the inner body and the outer body. For example, the occlusion device may be carried by the inner body and/or radially restrained between the inner body and the outer body. The method may include at least partially deploying, which may be less than fully deploying, the implantable occlusion device from the outer body of the delivery system. At least partially deploying the implantable occlusion device may include moving the inner body relative to the outer body, which may include retracting the outer body or advancing the inner body. The method may include delivering therapeutic agent from the inner body of the delivery system. For example, the therapeutic agent may be released from the opening at the distal most end of the inner body. The therapeutic agent may be delivered from the guidewire lumen of the inner body or a lumen separate from the guidewire lumen. Delivery of the therapeutic agent may occur prior to deploying any portion of the occlusion device from the outer body, prior to fully deploying the occlusion device from the outer body, and/or after fully deploying the occlusion device from the outer body. The therapeutic agent may be delivered in a single dose or in multiple doses at different time points during the procedure. The therapeutic agent may be delivered from the inner body of the delivery system, while the inner body carries or extends through an opening of the implantable occlusion device, for example extending through a guidewire opening in the neck portion of the implantable occlusion device. The therapeutic agent may be delivered upstream or downstream, with respect to blood flow, of the implantable occlusion device. Prior to delivering the therapeutic agent, the guidewire may be withdrawn from the delivery system. The method may include releasing the implantable occlusion device from the delivery system, for example by releasing the implantable occlusion device from the outer body and/or withdrawing the inner body from the implantable occlusion device. 
     Certain methods are directed toward providing a secondary treatment near an implantable occlusion device. The method may include using a common delivery system to deliver the occlusion device and provide the secondary treatment near the occlusion device. The secondary treatment may be provided downstream or upstream, with respect to blood flow, of the implantable occlusion device. The method may include advancing a delivery system to the vessel, for example over a guidewire or through an access catheter. The delivery system may include an outer body and an inner body disposed within the outer body. The inner body may include a working lumen extending therethrough. The working lumen may be the same lumen as the guidewire lumen or separate from the guidewire lumen. The delivery system may carry the implantable occlusion device between the inner body and the outer body. For example, the occlusion device may be carried by the inner body and/or radially restrained between the inner body and the outer body. The method may include at least partially deploying the implantable occlusion device from the outer body of the delivery system. The method may include advancing a treatment instrument through the working lumen of the inner body. The treatment instrument may be an ablation device, for example a steerable ablation needle. The treatment instrument may be advanced through the working lumen, while the inner body extends through an opening of the implantable occlusion device, for example a guidewire opening in the neck portion. The treatment instrument may be advanced relative to the inner body prior to deploying any portion of the implantable occlusion device, after at least partially deploying the implantable occlusion device, or after fully deploying the implantable occlusion device. The method may include providing the secondary treatment, for example ablation therapy, at the target site using the treatment instrument. The secondary treatment may be provided prior to deploying any portion the implantable occlusion device, after at least partially deploying the implantable occlusion device, or after fully deploying the implantable occlusion device. The treatment instrument may provide the treatment upstream or downstream, with respect to blood flow, of the implantable occlusion device. In some methods, the secondary treatment may be ablation therapy. The method may include releasing the implantable occlusion device from the delivery system, for example by releasing the implantable occlusion device from the outer body and/or withdrawing the inner body from the implantable occlusion device. For purposes of summarizing the disclosure, certain aspects, advantages, and features of the inventions have been described herein. It is to be understood that not necessarily any or all such advantages are achieved in accordance with any particular embodiment of the inventions disclosed herein. No aspects of this disclosure are essential or indispensable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments are depicted in the accompanying drawings for illustrative purposes, and should in no way be interpreted as limiting the scope of the embodiments. Furthermore, various features of different disclosed embodiments can be combined to form additional embodiments, which are part of this disclosure. 
         FIG. 1A  illustrates a delivery system for delivering an occlusion device. 
         FIG. 1A-1  illustrates an enlarged view of a distal portion of the delivery system shown in  FIG. 1A . 
         FIG. 1B-1  illustrates an embodiment of an outer catheter that can be used with the delivery system shown in  FIG. 1A . 
         FIG. 1B-2  illustrates an enlarged view of the working length of the outer catheter shown in  FIG. 1B-1 . 
         FIG. 1B-3  illustrates an embodiment of an inner catheter that can be used with the delivery system shown in  FIGS. 1A . 
         FIG. 1B-4  illustrates an enlarged view of a distal portion of the inner catheter shown in  FIG. 1B-3  through line  1 B- 3 - 1 B- 3 . 
         FIG. 1C-1  illustrates an embodiment of a delivery system having a pusher interlock assembly in a locked configuration. 
         FIG. 1C-2  illustrates the pusher interlock assembly shown in  FIG. 1C-1  in an unlocked configuration. 
         FIG. 1C-3  illustrates an embodiment of an occlusion device having a portion of the pusher interlock assembly shown in  FIG. 1C-1  and detached from the delivery system. 
         FIG. 1D-1  illustrates another embodiment of a delivery system having a threaded interlock assembly. 
         FIG. 1D-2  illustrates an enlarged view of the threaded interlock assembly through line  1 D- 2  shown in  FIG. 1D-1 . 
         FIG. 1E-1  illustrates another embodiment of a delivery system having an interlock catheter. 
         FIG. 1E-2  illustrates an enlarged view of a portion of the delivery system shown in  FIG. 1E-1  taken through line  1 E- 2  to  1 E- 4  with the interlock assembly in a locked configuration. 
         FIG. 1E-3  illustrates an enlarged view of a portion of the delivery system shown in  FIG. 1E-1  taken through line  1 E- 2  to  1 E- 4  with the interlock assembly in an unlocked configuration. 
         FIG. 1E-4  illustrates an enlarged view of a portion of the delivery system shown in  FIG. 1E-1  taken through line  1 E- 2  to  1 E- 4  with the occlusion device detached. 
         FIG. 1E-5  illustrates a cross-section of  FIG. 1E-2  taken through line  1 E- 5  to  1 E- 5  without the occlusion device. 
         FIG. 1E-6  illustrates a cross-section of  FIG. 1E-4  taken through line  1 E- 6  to  1 E- 6 . 
         FIG. 2A  illustrates another embodiment of a delivery system. 
         FIG. 2B  illustrates an enlarged view of a distal portion of the delivery system shown in  FIG. 2A  through line B prior to deployment. 
         FIG. 2C  illustrates the distal portion of the delivery system shown in  FIG. 2A  with the distal lobe of the occlusion device partially deployed. 
         FIG. 2CC  illustrates an enlarged cross-section of the distal portion shown in  FIG. 2C  taken through line CC. 
         FIG. 2D  illustrates the distal portion of the delivery system shown in  FIG. 2A  with the distal lobe of the occlusion device fully deployed. 
         FIG. 2DD  illustrates an enlarged cross-section of the distal portion shown in  FIG. 2D  taken through line DD. 
         FIG. 2E  illustrates the distal portion of the delivery system shown in  FIG. 2A  with the distal lobe of the occlusion device partially retracted. 
         FIG. 2EE  illustrates a cross-section of the distal portion shown in  FIG. 2E  taken through line EE. 
         FIG. 2F  illustrates the distal portion of the delivery system shown in  FIG. 2A  with a majority of the occlusion device deployed. 
         FIG. 2FF  illustrates a cross-section of the distal portion shown in  FIG. 2F  taken through line FF. 
         FIG. 2G  illustrates the distal portion of the delivery system shown in  FIG. 2A  with the occlusion device fully deployed. 
         FIG. 2H  illustrates a cross-section of the occlusion device shown in  FIG. 2G  with the inner catheter partially retracted. 
         FIG. 2HH  illustrates an enlarged view a tubular membrane portion of the occlusion device shown in  FIG. 2H  taken through line HH. 
         FIG. 2I  illustrates a cross-section of the occlusion device shown in  FIG. 2H  with the inner catheter further retracted. 
         FIG. 2II  illustrates an enlarged view of the tubular membrane portion of the occlusion device shown in  FIG. 21  taken through line II. 
         FIG. 2J  illustrates a cross-section of the occlusion device shown in  FIG. 2I  with the inner catheter further retracted. 
         FIG. 2JJ  illustrates an enlarged view of the tubular membrane portion of the occlusion device shown in  FIG. 2J  taken through line JJ. 
         FIG. 2K  illustrates a cross-section of the occlusion device shown in Figure JJ with the delivery system fully withdrawn from the occlusion device. 
         FIG. 2L  illustrates the inner catheter of the delivery system shown in  FIG. 2A . 
         FIG. 2M  illustrates an enlarged view of a distal portion of the inner catheter shown in  FIG. 2L . 
         FIG. 2N  illustrates a cross-section of a distal portion through line  2 N of the outer catheter shown in  FIG. 2M . 
         FIG. 2O  illustrates the outer catheter of the delivery system shown in  FIG. 2A  for contrast dye injection. 
         FIG. 2P  illustrates an enlarged view of a working length of the outer catheter shown in  FIG. 20 . 
         FIG. 2Q  illustrates another deployment system having an interlock attachment member interfacing with an occlusion device. 
         FIG. 2R  illustrates another deployment system having an interlock attachment member released from the occlusion device. 
         FIG. 2S  illustrates an embodiment of a delivery system for delivering an occlusion device having a test balloon. 
         FIGS. 3A-3F  illustrate another delivery system and an occlusion device having a tapered proximal end. 
         FIGS. 4A-4F  illustrate yet another delivery system and a generally cylindrical occlusion device. 
         FIG. 4G  illustrates an enlarged view of the occlusion device shown in  FIGS. 4A-4F . 
         FIGS. 5A-5F  illustrate a delivery system and another generally cylindrical occlusion device. 
         FIG. 5G  illustrates an enlarged view of the occlusion device shown in  FIGS. 5A-5F . 
         FIG. 6  illustrates a partially covered, hourglass-shaped occlusion device. 
         FIG. 7A  illustrates a partially covered occlusion device having tapered ends. 
         FIG. 7B  illustrates a fully covered occlusion device having tapered ends. 
         FIG. 8  illustrates an expandable structure having a non-uniform diameter. 
         FIG. 9A  illustrates another expandable structure having tapered ends. 
         FIGS. 9B-9C  illustrate the expandable structure in  FIG. 9A  partially covered with a cover. 
         FIG. 10A  illustrates a fully covered occlusion device having a first, closed end portion and a second, opened end portion. 
         FIG. 10B  illustrates a partially covered occlusion device having a first, closed end portion and a second, opened end portion. 
         FIGS. 11A-11C  illustrate different views of an occlusion device having a drumhead and a cover. 
         FIG. 12A  illustrates an embodiment of an occlusion device having an asymmetrical hourglass shape. 
         FIG. 13A  illustrates another embodiment of an hourglass-shaped occlusion device in an expanded configuration with a portion of the membrane removed to show the tubular portion of the membrane. 
         FIG. 13B  illustrates the occlusion device shown in  FIG. 13A  in an unexpanded configuration. 
         FIG. 14A  illustrates yet another embodiment of an occlusion device. 
         FIG. 14B  illustrates a cross-section of the occlusion device shown in  FIG. 14A . 
         FIG. 14C  is an image of a proximal end view of the occlusion device shown in  FIG. 14A  in a closed configuration. 
         FIGS. 15A to 15D  illustrate a method of delivering a therapeutic agent downstream of the occlusion device. 
         FIGS. 16A to 16D  illustrate a method of providing a secondary treatment downstream of the occlusion device. 
     
    
    
     DETAILED DESCRIPTION 
     The following discussion is presented to enable a person skilled in the art to make and use one or more embodiments of the invention. The general principles described herein may be applied to embodiments and applications other than those detailed below without departing from the spirit and scope of the invention. Therefore the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed or suggested herein. 
       FIGS. 1A and 1A-1  illustrate an exemplary delivery system  100  for delivering any of the occlusion devices illustrated herein. The delivery system  100  can include an outer catheter  110  and an inner catheter  120  extending through the outer catheter  110 . Although primarily described in the context of an intravascular embolic deployment catheter with a single central lumen, catheters of the present invention can readily be modified to incorporate additional structures, such as permanent or removable column strength enhancing mandrels, two or more lumen such as to permit drug or irrigant infusion or aspiration or radiation delivery or to supply inflation media to an inflatable balloon, or combinations of these features, as will be readily apparent to one of skill in the art in view of the disclosure herein. 
     The catheters and occlusion devices disclosed herein may readily be adapted for use throughout the body wherever it may be desirable to introduce an occluder. For example, occlusion devices may be deployed throughout the coronary and peripheral vasculature, neurovasculature, the gastrointestinal tract, the urethra, ureters, Fallopian tubes, and other lumens and potential lumens, as well. 
     Generally, the occlusion devices described herein can be delivered via a low profile outer catheter  110  (e.g., having an outer diameter from about  2 . 8  F (0.93 mm) to about 6 F (2.0 mm), typically from about 3 F (1.0 mm) to about 5 F (1.67 mm, preferably less than about 5 F (1.67 mm), such as about 4.7 F (1.57 mm)). Further, the occlusion devices described herein can be delivered over a guide wire having a diameter of at least about 0.010 inches and/or less than or equal to about 0.02 inches to facilitate trackability of the delivery catheter, while still utilizing a low profile delivery catheter. For example, the guide wire can have a diameter of about 0.01 inches, 0.014 inches, or about 0.018 inches. 
     The outer catheter  110  can generally include an elongate tubular body  116  extending between a proximal end  112  and a distal end  114 . The length of the tubular body  116  depends upon the desired application. For example, lengths in the area of from about 120 cm to about 140 cm or more are typical for use in femoral access percutaneous transluminal coronary applications. Further, the outer catheter  110  should have sufficient working length to reach the target vessel. The minimum working length for these applications can be at least about 75 cm about 90 cm, or at least about 100 cm, but no more than about 175 cm. Intracranial or other applications may call for a different catheter shaft length depending upon the vascular access site, as will be understood in the art. Deployment catheters adapted for intracranial applications generally have a total length in the range from 60 cm to 250 cm, usually from about 135 cm to about 175 cm. 
     In general, neurovascular devices may be deployable from catheters having a length of at least about 120 cm or 125 cm or greater, to allow access to the carotid artery bifurcation and above. Devices configured for coronary or peripheral applications may have shorter delivery catheters and other dimensional modifications as are understood in the art. 
     The catheters of the present invention may be composed of any of a variety of biologically compatible polymeric resins having suitable characteristics when formed into the tubular catheter body segments. Exemplary materials include polyvinyl chloride, polyethers, polyamides, polyethylenes, polyurethanes, a polycarbonate blend, copolymers thereof, and the like. Optionally, the tubular body may be reinforced with a metal or polymeric braid or other conventional reinforcing layer. 
     The catheter material should be selected such that the delivery system demonstrates acceptable trackability and deployment forces to enable access to the target vessel and delivery of the implant to the target vascular. Further, the material of the outer catheter  110  should be sufficient to maintain its integrity during flushing and hemostasis. For example, the outer catheter  110  should be able to resist a pressure of at least about  45  psi/min. 
     Further, the outer catheter  110  must have sufficient structural integrity (e.g., column strength or “pushability”) to permit the outer catheter  110  to be advanced to distal locations without buckling or undesirable bending of the tubular body  116 . The ability of the outer catheter  110  to transmit torque may also be desirable, such as to avoid kinking upon rotation, to assist in steering. The outer catheter  110 , and particularly the distal portion, may be provided with any of a variety of torque and/or column strength enhancing structures. For example, axially extending stiffening wires, spiral wrapped support layers, and/or braided or woven reinforcement filaments may be built into or layered on the tubular body  116 . 
     The delivery system  100  and its variants described herein are capable of penetrating the target vessel by at least 4 cm, such as between about 4 cm and 6 cm, for example, at least 5 cm, or preferably at least about 5.5 cm as determined by the Trackability Protocol described below. 
     The proximal portion of the outer catheter  110  may have a shore hardness in the range from 50 D to 100 D, often being about 70 D to 80 D. Usually, the proximal portion of the outer catheter  110  will have a flexural modulus from 20,000 psi to 1,000,000 psi, preferably from 100,000 psi to 600,000 psi. The distal portion of the outer catheter  110  will be sufficiently flexible and supple so that it may navigate the patient&#39;s distal vasculature. In highly flexible embodiments, the shore hardness of the distal portion may be in the range from about 20 A to about 100 A, and the flexural modulus for the distal portion may be from about 50 psi to about 15,000 psi. 
     The outer catheter  110  may be produced in accordance with any of a variety of known techniques for manufacturing interventional catheter bodies, such as by extrusion of appropriate biocompatible polymeric materials. At least a proximal portion or all of the length of outer catheter  110  may comprise a polymeric or metal spring coil, solid walled hypodermic needle tubing, or braided reinforced wall, as is known in the microcatheter arts. 
     The proximal end  112  of outer catheter  110  can include a manifold  118  having one or more access ports as is known in the art. Generally, the manifold  118  can include a guidewire port. Additional access ports may be provided as needed, depending upon the functional capabilities of the catheter. The manifold  118  can be compatible with luer connections from related accessories. Further, the manifold  118  may be injection molded from any of a variety of medical grade plastics, or formed in accordance with other techniques known in the art. 
     Manifold  118  can also include a control (not shown), for controlling deployment of the occlusion device. The control may take any of a variety of forms depending upon the mechanical structure of the support. For example, the control can include a slider switch, which can connect to the inner catheter  120 . Distal axial advancement of the slider switch can produce an axial advance of the connected feature. When the occlusion device advances from the distal end of the outer catheter  110 , the occlusion device can move from the reduced diameter to the enlarged diameter. 
     Any of a variety of controls may be utilized, including switches, levers, rotatable knobs, pull/push wires, and others that will be apparent to those of skill in the art in view of the disclosure herein. 
     The outer catheter  110  can define a lumen through which the inner catheter  120  can move axially. The inner catheter  120  can include a proximal end  122  and a distal end  124 . Similar to the outer catheter  110 , the inner catheter  120  can include a manifold  126  disposed at the proximal end  122  of the inner catheter  120 . The manifold  126  can be configured to control movement of the inner catheter  120 , deployment of the occlusion device, and/or fluid flow through the inner catheter  120 . The inner catheter  120  should be sufficiently long to deliver the occlusion device out of the distal end  114  of the outer catheter  110 . Further, the inner catheter  120  can include a material exhibiting any of the material properties described in connection with the outer catheter  110 . 
     The inner catheter  120  can define a lumen through which a conventional guide wire can move axially. In an alternate configuration, the outer catheter  110  can include a second lumen having a guide wire axially movable therein. In either scenario, the guide wire lumen should be sufficiently large to accommodate a guide wire  128  having a diameter between about 0.25 mm and about 0.5 mm. As shown in  FIG. 1A , the guide wire  128  can include a hub  130  disposed at a proximal end of the guide wire  128 . 
     Avoiding a tight fit between the guide wire  128  and inside diameter of guidewire lumen enhances the slideability of the delivery system  100  over the guidewire. In ultra-small diameter catheter designs, it may be desirable to coat the outside surface of the guidewire  128  and/or the inside surface of the inner catheter  120  with a lubricous coating to minimize friction as the inner catheter  120  is axially moved with respect to the guidewire  128 . A variety of coatings may be utilized, such as Parylene, Teflon, silicone rubber, polyimide-polytetrafluoroethylene composite materials, or others known in the art and suitable depending upon the material of the guidewire or inner tubular wall. 
     The delivery system  100  can include different features depending on whether the occlusion device is self-expanding or balloon expandable. For example, if the occlusion device is balloon expandable, the inner catheter  120  can carry the occlusion device on a balloon (not shown). 
     For example, if the occlusion device is self-expanding, the occlusion device can be constrained by a distal portion of the outer catheter  110 , and the inner catheter  120  can push the occlusion device out from the distal end  114  of the catheter  110 . As another example, as shown in  FIG. 3F , the delivery system  100  can include a support tube  134  axially disposed between the outer catheter  110  and the inner catheter  120 . The support tube  134  can move axially to push the occlusion device off the inner catheter  120 . The force necessary to push the occlusion device off the inner catheter  120  can be less than or equal to about 5 N, for example, within about 0.25 N of about 4.5 N or within about 0.25 N of about 4.0 N. 
     Other conventional mechanisms can be used to release the occlusion device, including, but not limited to, a ratcheting mechanism, an electrolytically erodible attachment, involuted deployment, a threaded attachment, or other torque releasing attachment. 
     In some situations, it may be necessary to resheath the occlusion device to deliver the occlusion device to the target vessel. The delivery system  100  can be configured to resheath and reposition the occlusion device after deployment, but before release. Prior to release, the inner catheter  120  can be retracted to pull the occlusion device back into the outer catheter  110 . The retraction force necessary to retract the occlusion device should be less than or equal to about 5 N, for example, between about 3 N and about 4 N, or between about 3.5 N and about 4.5 N. The interlock interference feature can have a dimension between about 0.15 mm and about 0.25 mm, for example, within about 0.02 mm of about 0.2 mm. 
     The delivery system  100  may further comprise other components, such as radiopaque fillers, colorants, reinforcing materials, reinforcement layers, such as braids and helical reinforcement elements, or the like. In particular, at least the proximal portion may be reinforced in order to enhance its column strength and torqueability while preferably limiting its wall thickness and outside diameter. Further, radiopaque markers may be positioned on the inner and/or outer catheters  120 ,  110  to monitor the delivery system  100  during the procedure. 
     Fluoroscopic guidance can be used to monitor the delivery of the occlusion device. For example, the delivery system can include radiopaque features that allow for their fluoroscopic visualization during delivery, deployment, and/or retraction. Usually, the delivery system can include marker bands or coiled wires disposed along one or more of the outer catheter  110 , inner catheter  120 , and the guide wire  128 . The bands or coils can include a minimum thickness of at least about 0.02 mm and a minimum length of about 0.5 mm. Suitable marker bands can be produced from any number of a variety of materials, including platinum, gold, tantalum, and tungsten/rhenium alloy. Preferably, the radiopaque metal band will be recessed in an annular channel formed in the tubular body. 
       FIGS. 1B-1 and 1B-2  illustrate a possible embodiment the outer catheter  110  of the delivery system. The outer catheter permits contrast dye to be injected through the delivery system and can be used to determine the position of the occlusion device before detaching the occlusion device from the delivery system. 
     The outer catheter  110  can have a working length of about  120  cm or any other suitable working length described above. An internal diameter of the outer catheter  110  can be less than or equal to about 0.10 inches, such as about 0.05 inches. The distal end  114  of the outer catheter  110  can have a reduced diameter between about 0.02 inches and about 0.04 inches. The outer catheter  110  can include a plurality of openings  121  (e.g., at least two, five, six, eight, or more openings) disposed near a distal end  114  of the outer catheter  110 , such that contrast dye can be released near the proximal side of the occlusion device. The placement of the openings  121  can remove the pressure of the contrast on the occlusion device to mitigate the likelihood of damaging the occlusion device prior to deployment (see  FIG. 1B-2 ). For instance, the distal most opening  121 ′ can be positioned less than or equal to about  2 . 0  inches from the distal end  114  or at a location that is between about 1.5% and 2.5% of the working length of the catheter from the distal end  114 . The plurality of openings  121  can be positioned in a helical configuration spanning less than or equal to about 0.5 inches measured in an axial direction (e.g., about 0.3 inches, about 0.35 inches, or about 0.4 inches). Further, the plurality of holes  121  can be equally, axially spaced apart (e.g., less than about 0.10 inches, such as about 0.05 inches). In some embodiments, the contrast flow rate can be at least about 2 cc/second or at least about 5 cc/second under an infusion pressure of no more than about 500 psi, preferably no more than about 250 psi as measured under the Injection Protocol described herein. For example, the contrast flow rate can between about 2 cc/second and 5 cc/second under infusion pressures between about 100 psi and 200 psi or between about 100 psi and 150 psi, such as about 2.0 or 2.3 cc/min. Additionally, the openings  121  provide a sufficient flow rate to prevent the buildup of pressure distal to the openings  121  such that the occlusion device is not inadvertently deployed simply by injecting contrast. The flow rate through the openings  121  prevents a distal pressure higher than 50 psi when a 200 psi infusion pressure is applied or a distal pressure of no more than 10 psi. 
       FIGS. 1B-3 and 1B-4  illustrate a possible embodiment of the inner catheter  120 . The inner catheter  120  can include a manifold  126  that provides access to a lumen of the inner catheter  120 . Further, the inner catheter  120  can include a pusher member  123 . When the delivery system is assembled, the occlusion device can be positioned between the distal end  124  and the pusher member  123  of the inner catheter  120 . The pusher member  123  can be used to push the occlusion device out of the outer catheter  110 . As shown in  FIG. 1B-4 , the inner catheter  120  can also include a radiopaque marker  125  disposed near the distal end  124  of the inner catheter  120 , so the user can monitor placement of the occlusion device. 
     It can be clinically desirable to assess the performance of the occlusion device prior to releasing the occlusion device from the delivery system  100 . Thus, in some embodiments, as shown in  FIGS. 1C-1 to 1C-3 , the delivery system  100   c  (including one or more features of the delivery system  100 ) and the occlusion device  140  can include an interlock assembly  150  that allows the occlusion device  140  to be resheathed or repositioned. The interlock assembly  150  can removably secure the inner catheter  120   c  to the occlusion device  140 . In some examples, the occlusion device  140  can resemble  1500  any of the occlusion devices described below. 
     The interlock assembly  150  can include one or more resilient members  152  and a corresponding number of recesses  154  (e.g., channels or grooves). As shown in  FIG. 1C-3 , the interlock assembly  150  can include a first resilient member  152   a  and a second resilient member  152   b;  however, more resilient members can be utilized (e.g., three or four). The resilient members  152  can extend from one of a reduced diameter portion (e.g., a proximal end  142 ) of the occlusion device  140  or a distal end of the inner catheter  120   c,  and the recesses  154  can be disposed on the other of the reduced diameter portion (e.g., the proximal end  142 ) of the occlusion device  140  or the distal portion  156  of the inner catheter  120   c.  When the recesses  154  are disposed on the distal portion  156  of the inner catheter  120   c,  a diameter of the distal end portion  156  can be greater than a remaining portion of the inner catheter  120   c  and less than or equal to a diameter of the proximal end  142  of the occlusion device  140  (see  FIG. 1C-1 ). For example, as shown in  FIG. 1C-1 , the resilient members  152  can extend proximally from a proximal end  142  of the occlusion device  140 , and the recesses  154  can be disposed at the distal end portion  156  of the inner catheter  120   c.    
     As shown in  FIG. 1C-3 , the resilient members  152  can be biased toward an outward extending position. Further, the resilient members  152  can each have a Z-shape, such that a first end of a resilient member  152  is axially displaced from a second end of the resilient member  152 . In certain variants, the resilient members  152  can have a T-shape, a lollipop shape, a Christmas tree shape, or any other suitable shape, which provides at least a first interference surface for engaging with a second complementary interference surface to releasably retain the occlusion device on the catheter. 
     Additionally, the shape of the recesses  154  can generally correspond to the shape of the resilient members  152 , such that when the resilient members  152  are constrained within the outer catheter  110   c,  the resilient members  152  can engage the corresponding recesses  154 . 
     The interlock assembly  150  maintains the inner catheter  120   c  and the occlusion device  140  in a locked configuration (see  FIG. 1C-1 ) until the resilient members  152  are pushed beyond the distal end  114   c  of the catheter body  110   c  (see  FIG. 1C-2 ). When the resilient members  152  are pushed beyond the distal end  114   c  of the catheter  110   c,  the resilient members  152  move back to the outward extending position, thereby releasing the occlusion device  140  from the inner catheter  120   c  (see  FIG. 1C-3 ). Advantageously, the interlock assembly  150  allows the occlusion device  140  to be resheathed and repositioned so long as the resilient members  152  do not extend beyond the distal end  114   c  of the catheter  110   c.  Further, the interlock assembly  150  requires no additional movable members for actuation, which has a number of benefits, including, but not limited to, a reduced profile delivery system, a more flexible delivery system, fewer components for manufacturing, and fewer steps during the procedure. 
       FIGS. 1D-1 and 1D-2  illustrate another embodiment of an interlock assembly  170  that can be used with delivery system  100   d  (including one or more features of the delivery system  100 ). The interlock assembly  170  can include a first threaded region  172  at a reduced diameter portion (e.g., a proximal portion  162 ) of an occlusion device  160  and a second, corresponding threaded region  174  at a distal portion  156  of the inner catheter  120   d.  For example, as shown in  FIG. 1D-2 , the first threaded region  172  can be disposed around an interior surface of the proximal portion  162  of the occlusion device  160 , and the second region  174  can be disposed around an exterior surface of the distal end portion  176 . An outer diameter of the distal portion  176  can be less than an interior diameter of the proximal portion  162  of the occlusion device  160 , such that the second threaded region  174  can threadably engage the first threaded region  172 . 
     The interlock assembly  170  can maintain the inner catheter  120   d  and the occlusion device  160  in a locked configuration (see  FIG. 1D-2 ) until the inner catheter  120   d  is rotated counterclockwise and unscrewed from the occlusion device  160 . Advantageously, the interlock assembly  170  allows the occlusion device  160  to be resheathed and repositioned so long as the inner catheter  120   d  remains threadably engaged with the occlusion device  160 . Further, the interlock assembly  170  requires no additional movable members for actuation, which has a number of benefits, including, but not limited to, a reduced profile delivery system, a more flexible delivery system, fewer components for manufacturing, and fewer steps during the procedure. 
     With reference to  FIGS. 1E-1 to 1E-6 , another illustrative embodiment of a delivery system is shown. Portions of the delivery system  100   e  resemble the delivery system  100  discussed above. Accordingly, numerals used to identify features of the delivery system  100  include an “e” to identify like features of the delivery system  100   e  (e.g., the outer catheter  110   e  can resemble the outer catheter  110 ). 
     As shown in  FIG. 1E-1 , the delivery system  100   e  can include an interlock catheter  101   e  extending through the outer catheter  110   e.  The interlock catheter  101  can include an outer pusher  188   e  and an inner pusher  186   e  (see  FIGS. 1E-5 and 1E-6 ). Further, a hemostasis valve  103   e  can form a seal between the outer catheter  110   e  and the interlock catheter  101   e.  For purposes of illustration, the delivery system  100   e  is described in connection with the occlusion device  1500  (described in further detail below); however, the delivery system  100   e  can be used with other occlusion devices, such as the occlusion device  1500 . 
     Additionally, the interlock catheter  100   e  and the occlusion device  1500  can include an interlock assembly  180   e.  The interlock assembly  180   e  can include a key ring  182   e  that can be secured to a distal portion of the outer pusher  188   e.  As shown in  FIG. 1E-2 , an inner diameter of the key ring  182   e  can be greater than an outer diameter of the distal portion of the outer pusher  188   e,  such that the key ring  182   e  can be secured over the distal portion of the outer pusher  188   e.  Further, one or more locking tabs  183   e  (e.g., two, three, or four) can extend from a distal end of the key ring  182   e.  The locking tabs  183   e  can be biased inward toward the inner pusher  186   e.  Additionally, as shown in  FIG. 1E-1 , the locking tabs  183   e  can have a generally lollipop shape. Although, in other embodiments, the locking tab  183   e  can have a T-shape, Z-shape, Christmas Tree shape, or any other suitable shape. 
     The interlock assembly  180   e  can also include a locking drum  184   e  that is coaxial with the outer pusher  188   e  (see  FIGS. 1E-5 and 1E-6 ). The locking drum  184   e  can be secured to the inner pusher  186   e,  and thus advanceable relative to the outer pusher  188   e.  To secure the interlock catheter  101   e  to the occlusion device  1500 , the inner pusher  186   e  is advanced until the locking drum  184   e  pushes the locking tabs  183   e  outward into a corresponding interlock feature  1518  on a reduced diameter portion (e.g., a proximal collar  1516 ) of the occlusion device  1500  (see  FIGS. 1E-2 and 1E-5 ). In this locked configuration, the occlusion device  1500  can be advanced through the outer catheter  110   e  using the interlock catheter  101   e.    
     To release the occlusion device  1500  from the outer pusher  188   e,  the inner pusher  186   e  is advanced further until a proximal end of the locking drum  184   e  is distal to the locking tabs  183   e  (see  FIG. 1E-3 ). In this configuration, the locking tabs  183   e  can return to the inward extending position such that the occlusion device  1500  can be detached from the outer pusher  188   e  (see  FIGS. 1E-4 and 1E-6 ). Advantageously, the interlock assembly  180   e  allows the occlusion device  1500  to be resheathed and repositioned so long as the outer pusher  188  is secured to the occlusion device  1500 . 
       FIGS. 2A to 2K  illustrate a method of using another embodiment of a delivery system  200  having an interlocking attachment member  231  that interfaces with an occlusion device O. Portions of the delivery system  200  resemble the delivery system  100  discussed above. Accordingly, numerals used to identify features of the delivery system  100  are incremented by a factor of “100” to identify like features of the delivery system  200  (e.g., the outer catheter  210  can resemble the outer catheter  110 ). 
     Generally, the delivery system  200  can include an inner catheter  220  adapted to advance an occlusion device O (e.g., an hourglass-shaped occlusion device as described below) through the outer catheter  210  and into the target vessel (see  FIG. 2A ). The inner catheter  220  can include an interlocking attachment member  231  that enables the clinician to advance and retract the occlusion device O, so long as the proximal end of the occlusion device O remains constrained within the outer catheter  210  and interfaces within the interlocking attachment member  231  (see  FIGS. 2L and 2M ). When the proximal end of the occlusion device O is advanced distally of the distal end  214  of the outer catheter  210 , the proximal end of the occlusion device O expands and releases from the interlocking attachment member  231  (see  FIG. 2G ). Advantageously, the interlocking attachment member  231  enables the clinician to assess the performance of the occlusion device O prior to releasing the occlusion device O from the delivery system  200 . 
       FIGS. 2A and 2B  illustrates a fully assembled delivery system  200  with the inner catheter  220  extending through the outer catheter  210 . To begin deployment, the distal lobe of the occlusion device D can be deployed. The occlusion device O can be deployed by advancing the inner catheter  220  relative to the outer catheter  210  (see  FIGS. 2C and 2D ). With only the distal lobe of the occlusion device D deployed, contrast injection can be delivered to confirm the position of the occlusion device O. Since the distal lobe of the occlusion device D is uncovered (e.g., bare metal struts), the occlusion device O does not occlude flow of the dye. As shown in  FIGS. 2CC and 2DD , as the inner catheter  220  is advanced, a distal face of the interlock attachment member  231  interfaces with the occlusion device O at a location distal to the proximal end of the occlusion device O, such that the interlock attachment member  231  urges the occlusion device O in a distal direction. 
     If the distal lobe D is improperly positioned, the inner catheter  220  can be retracted to retract the occlusion device O (see  FIG. 2E ). As shown in  FIG. 2EE , as the inner catheter is retracted, a proximal face of the interlock attachment member  231  interfaces with the occlusion device O (e.g., proximal hooks of the occlusion device O), such that the interlock attachment  231  urges the occlusion device O in a proximal direction. 
     Once the distal lobe  1202   e  of the occlusion device  1200   e  is properly position, the remaining portion of the occlusion device can be deployed (see  FIGS. 2F and 2G ). Next, the inner catheter  220  can be retracted relative to the outer catheter  210  (see FIG. H). As shown in  FIG. 2HH , a proximal face of the ramp  229  is larger than an end portion E of the tubular membrane portion of the occlusion device T (e.g., a larger diameter or larger surface area). Consequently, as the inner catheter  220  is further withdrawn, the ramp  229  forces the tubular portion T to invert (see  FIGS. 2I and 2II ), such that a proximal portion of the tubular membrane portion T that is within the proximal lobe P begins to fold over a remaining portion of the tubular membrane portion T. Viewed another way, an inner surface of the tubular portion T becomes an external surface of the tubular portion T. During the inversion process, the tubular portion T moves from being positioned within the distal lobe D (see  FIGS. 2H and 2HH ) to being positioned within the proximal lobe P (see FIG.  2 J and  2 JJ). Viewed another way, the tubular portion T moves from being external to a membrane cover M (see  FIG. 2H and 2HH ) to being positioned within the membrane cover M (see  FIG. 2J and 2JJ ). When the inner catheter  220  is fully removed from the occlusion device O (see  FIG. 2K ), the tubular portion T closes like a valve to prevent blood from flowing through the tubular portion T. The tubular portion T has sufficiently low collapse resistance such that when the delivery system  200 ′ (and guidewire, if present) is removed, the tubular portion T collapses (e.g., kinks, folds, buckles, flops over, or likewise) into a closed position. 
       FIGS. 2L to 2N  illustrate the outer catheter  210  of the delivery system  200 . The outer catheter  200  permits contrast dye to be injected through the delivery system  200  and can be used to determine the position of the occlusion device before detaching the occlusion device from the delivery system  200 . 
     The outer catheter  210  can have a working length of about  120  cm or any other suitable working length described above. An internal diameter of the outer catheter  210  can be less than or equal to about 0.10 inches, such as about 0.05 inches. A distal portion of the outer catheter  210  can be bulbous shaped if a marker band  225  is embedded within the outer catheter  210  (see  FIG. 2N ). As shown in  FIG. 2N , the outer catheter  210  can include at least three concentric layers, e.g., an inner layer  210 ′, an intermediate layer  210 ″, and an outer layer  210 ′″. The outer layer  210 ′″ can be constructed from Pebax or other medical grade polymer materials. The intermediate layer  210 ″ can be a stainless steel braid to reinforce the outer catheter  210 . The inner layer  210 ′ can be constructed from PTFE or other suitable medical grade polymer materials. If present, the radiopaque marker  225  can be embedded radially between the outer layer  210 ′″ and the intermediate layer  210 ″. 
     The outer catheter  210  can include a plurality of openings  221  (e.g., at least two, five, six, eight, or more openings) disposed near a distal end  114   h  of the outer catheter  210 , such that contrast dye can be released near the proximal side of the occlusion device (see  FIG. 2M ). The placement of the openings  221  can remove the pressure of the contrast on the occlusion device to mitigate the likelihood of damaging the occlusion device prior to deployment. For instance, the distal most opening  221 ′ can be positioned less than or equal to about 2.0 inches from the distal end  114   h  or at a location that is between about 1.5% and 2.5% of the working length from the distal end  114   h.  The plurality of openings  221  can be positioned in a helical configuration spanning less than or equal to about 0.5 inches measured in an axial direction (e.g., about 0.3 inches, about 0.35 inches, or about 0.4 inches). Further, the plurality of holes  221  can be equally, axially spaced apart (e.g., less than about 0.10 inches, such as about 0.05 inches). The contrast flow rate can be at least about 2 cc/second or at least about 5 cc/second under an infusion pressure of no more than about 500 psi, preferably no more than about 250 psi as measured under the Injection Protocol described herein. For example, the contrast flow rate can between about 2 cc/second and 5 cc/second under infusion pressures between about 100 psi and 200 psi or between about 100 psi and 150 psi, such as about 2.0 or 2.3 cc/min. Additionally, the openings  221  provide a sufficient flow rate to prevent the buildup of pressure distal to the openings  221  such that the occlusion device is not inadvertently deployed simply by injecting contrast. The flow rate through the openings  221  prevents a distal pressure higher than 50 psi when a 200 psi infusion pressure is applied or a distal pressure of no more than 10 psi. 
       FIGS. 20 and 2P  illustrate the inner catheter  220  of the delivery system  200 . The inner tubular body  220  has a proximal end  222  and a distal end  224 . A proximal hub  226  can be positioned at the proximal end  222  of the inner catheter  220  to provide access to a lumen of the inner catheter  220 . A pusher tip  227  can be positioned at the distal end  224  of the inner catheter  220 . The pusher tip  227  can be tapered at a distal and/or a proximal portion of the pusher tip  227 , with a uniform diameter section therebetween. If the pusher tip  227  and the inner catheter  220  are separate components, a radiopaque marker  225  can be positioned radially between the pusher tip  227  and the inner catheter  220 . 
     As shown in  FIG. 2P , a distal ramp  229  can be positioned proximal to the pusher tip  227 . The distal ramp  229  can be tapered in a distal direction. As explained in further detail below, when the delivery system  200  is used with an hourglass-shaped occlusion device having a tubular membrane portion (as described below), the ramp  229  can invert a tubular section of an occlusion membrane as the inner catheter  220  is retracted through the occlusion device. 
     As mentioned above, the delivery system  200  can include an interlocking attachment member  231  positioned proximal to the distal ramp  229 . As shown in  FIG. 2P , the interlocking attachment member  231  can be ring-shaped. The interlocking attachment member  231  can interface with an occlusion device having proximal hooks, barbs, or the like (see e.g., occlusion device  1200   e ). The proximal hooks of the occlusion device can interface with the interlocking attachment member  231  so long as the proximal end of the occlusion device remains constrained within the outer catheter  210 . The outer catheter  210  constrains the proximal end of the occlusion device, thereby allowing the occlusion device to interface with the interlocking attachment member  231 . 
     The length of the proximal hooks of the occlusion device and the length of the interlocking attachment member  231  can be optimized to provide a controlled amount of axial clearance in between proximal hooks of the occlusion device and the interlocking attachment member  231  (see  FIGS. 2DD and 2EE ). When the inner catheter  220  advances the occlusion device distally, the interlocking attachment member  231  pushes on a portion of the occlusion device distal to the proximal end of the occlusion device but does not engage the proximal hooks of the occlusion device (see  FIG. 2DD ). The axial clearance enables the proximal end of the occlusion device to expand when advanced out of the outer catheter  210 . Prior to the proximal end of the occlusion device being advanced distally of the distal end of the outer catheter  210 , retracting the inner catheter  220  causes the interlocking attachment member  231  to engage the proximal hooks and retract the occlusion device (see  FIG. 2EE ). 
     As shown in  FIG. 2P , a proximal coupler  233  can be positioned proximal to the interlocking attachment member  231 . The proximal coupler  233  can be tapered in a proximal direction. The proximal coupler  233  can prevent the occlusion device from moving proximally prior to deployment. 
       FIGS. 2Q and 2R  illustrate another delivery system  200 ′. Portions of the delivery system  200 ′ resemble the delivery system  200  discussed above. Accordingly, numerals used to identify features of the delivery system  200  are include an apostrophe (′) to identify like features of the delivery system  200 ′ (e.g., the outer catheter  210 ′ can resemble the outer catheter  210 ). 
     The interlock attachment member  231 ′ can have a number of longitudinally extending grooves  240 ′ (indentations, openings, or the like) circumferentially positioned around the interlock attachment member  231 ′. These grooves  240 ′ are shaped to receive a neck portion  244 ′ of a marker  242 ′ (see  FIG. 2Q ). 
     As shown in  FIG. 2R , at least a proximal lobe P of the occlusion device O can include a number of markers  242 ′. Each of these markers  242 ′ can include an aperture  246 ′ (eyelet, opening, or the like) and a neck portion  244 ′. These markers  242 ′ can be press-fit onto the strut endings of the proximal lobe P. The markers  242 ′ can be radiopaque to facilitate visualization of the occlusion device O. 
     The method of delivering the occlusion device O is similar to the method described in  FIGS. 2A to 2K . Prior to full release (see  FIG. 2Q ), the occlusion device O can be retracted and repositioned. The occlusion device O is configured to interface with the interlock attachment member  231 ′ until a proximal end of the occlusion device O has been released from the delivery system  200 ′ (see  FIG. 2R ). 
     The occlusion devices described herein can include an expandable structure configured to move between an unexpanded or constrained configuration and an expanded or unconstrained or enlarged configuration. The expandable structure can include any of a number of medical grade materials, including, but not limited to, polymers (e.g., PET) or non-ferrous metals (e.g., nitinol, stainless steel, or cobalt chrome). 
     The expansion ratio of the expandable structure should be sufficiently large such that the occlusion device is capable of compressing to a minimum size suitable for delivery through a catheter having an outer diameter of  6  F (i.e., 2.0 mm) or less, thereby minimizing trauma to the vessel during delivery. Further, the expansion ratio should be sufficiently large such that a single, expanded occlusion device is capable of preventing substantially all fluid from flowing past the occlusion device in vessel range of different sized target vessels. Although, additional occlusion devices (e.g., two or three) can be delivered depending on clinical judgment. 
     The expandable structure can be configured to include an expansion ratio that is at least about 3:1, at least about 5:1, preferably at least about 7:1, and more preferably at least about 8:1. In some examples, the expansion ratio can be about 7:1 or about 8:1. In other words, a diameter of the expandable structure in the expanded configuration can be at least about three times, at least about five times, preferably at least about seven times, and more preferably at least about eight times, a diameter of the expandable structure in the unexpanded configuration. For example, the diameter of the expandable structure in the expanded configuration can be between about three times and about nine times greater, preferably at least about seven times greater, than the diameter of the expandable structure in the unexpanded configuration. In some examples, the diameter of the expandable structure can be at least about seven times or about eight times greater than a diameter of the expandable structure in the unexpanded configuration. 
     As described above, the delivery system preferably has a sufficiently small diameter to avoid causing damage to the vessel wall during delivery. Therefore, the occlusion device should be configured for delivery through a catheter having an outer diameter that is less than 7 F (2.3 mm), preferably less than 6 F (2.0 mm), for example 5 F (1.67 mm), 4 F (1.33 mm), or 3 F (1.0 mm). In the unexpanded configuration, the occlusion device can include an outer diameter that is less than or equal to about 2 mm or less than or equal to about 1.75 mm, preferably less than or equal to about 1.5 mm. For example, the outer diameter of the occlusion device in the unexpanded configuration can be within about 0.5 mm, or within about 0.25 mm, of about 1.25 mm. Further, a length of the occlusion device in the unexpanded configuration can be less than or equal to about 3 cm or less than or equal to about 2.5 cm, for example, within about 0.5 cm of about 2 cm. 
     As explained in further detail below, the expandable structure can include one or more strands braided to form the expandable structure. Each strand can include a diameter between about 0.025 mm and about 0.05 mm. In the unexpanded configuration, the braided expandable structure can include a pore size of no more than about 1.5 sq. mm, preferably no more than about 1.25 sq. mm, for example, within about 0.25 sq. mm of about 1.0 sq. mm. Further, in the unexpanded configuration, the braided strands can form intersecting angles between about 70 degrees and about 130 degrees, for example, between about 70 degrees and 90 degrees, between about 80 degrees and about 100 degrees, between about 90 degrees and about 110 degrees, between about 100 degrees and about 120 degrees, or between about 110 degrees and about 130 degrees. 
     An expanded diameter of the expandable structure can vary depending on the application of the occlusion devices. For example, the diameter can vary depending on whether the occlusion device is delivered within a renal vessel, a cardiovascular vessel, a pulmonary vessel, a neurovascular vessel, or otherwise. In any of these vessels, the expanded configuration must have an acceptable diameter, length, and radial outward forces to maintain proper vessel wall apposition and resist migration. In some implementations, the aspect ratio between the expanded diameter and the expanded length can be less than or equal to about 1:1, such as 1:2, or the length can be proportionally longer depending on the desired application. 
     In the unconstrained expanded configuration, a maximum diameter of the occlusion device can be between about 1.0 to about 1.5 times or more a diameter of the target site in a vessel. In some applications, the occlusion device can expand to a diameter between about 5.0 mm and about 11 mm, for example, within about 0.5 mm of each of about 6.0 mm, 7.0 mm, 8.0 mm, 9.0 mm, or 10.0 mm. In some applications, the expanded diameter can be between about 4.0 mm and about 6.0 mm, for example, within about 0.5 mm of about 4.5 mm. In other applications, the expanded diameter can be between about 2.0 mm and about 3.0 mm, for example, within about 0.25 mm of about 2.5 mm. 
     For example, in neurovascular applications, the expanded diameter can be between about 1.5 mm and about 4.0 mm, for example, within about 0.5 mm of each of about 2.0 mm, 2.5 mm, 3.0 mm, or 3.0 mm. Each of these occlusion devices can be delivered through a catheter having an internal diameter of less than or equal to about 0.7 mm (0.027″). The expansion ratio can be at least about 5:1, for example, between about 5:1 and 5.5:1 or between about 5.5:1 and about 6:1, such as about 5.8:1. 
     In some peripheral applications, the expanded diameter can be between about 4.0 mm and about 6.0 mm, for example, within about 0.25 mm of each of about 4.25 mm, 4.5 mm, 4.75 mm, 5.0 mm, 5.25 mm, 5.5 mm, or 5.75 mm. Each of these occlusion devices can be delivered through a catheter having an internal diameter of no more than about 1.0 mm (0.038″). The expansion ratio can be at least about 5:1, preferably at least about 6:1, for example, between about 6:1 and about 7:1, such as about 6.2:1. 
     In other peripheral applications, the expanded diameter can be between about 7.0 mm and about 12.0 mm, for example, within 0.5 mm of each of about 7.5 mm, 8.0 mm, 8.5 mm, 9.0 mm, 9.5 mm, 10.0 mm, 10.5 mm, 11.0 mm, or 11.5 mm. Each of these occlusion devices can be delivered through a catheter having an outer diameter of less than or equal to about 2.0 mm, for example, between about 1.5 mm and about 2.0 mm (e.g., 1.67 mm (5 F)). 
     The expanded length should be between about 0.5 times and about 1.5 times the diameter of the target vessel, or greater depending on the desired performance. In some applications, the expanded length can be between about 2.5 mm to about 7.5 mm, for example, between about 4.0 mm to about 6.0 mm, or within about 0.5 mm of about 5.0 mm. In some applications, the expanded length can be between about 2.0 mm to about 6.0 mm, for example, between about 3.0 mm and about 5.0 mm, or within about 0.5 mm of about 4.5 mm. In some applications, the expanded length can be between about 1.0 mm and about 3.0 mm, for example, within about 0.5 mm of about 2.5 mm. 
     In some applications, the expanded lengths can vary from 1 cm to 5 cm (e.g., from 1 cm to 4 cm, from 2 cm to 5 cm, from 2 cm to 4 cm, overlapping ranges thereof, 1 cm, 1.5 cm, 2 cm. 2.5 cm, 3 cm, 3.5 cm, 4 cm, 4.5 cm, 5 cm), and the expansion diameter can vary from 1 mm to 6 mm (e.g., from 1 mm to 4 mm, from 2 mm to 6 mm, from 3 mm to 5 mm, overlapping ranges thereof, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm) depending on the vessel to be addressed. In some applications, the expandable structure can be configured to expand to diameters larger than 5 mm (e.g., 6 mm, 7 mm, 8 mm, 9 mm, 10 mm) or less than 2 mm (e.g., 1.8 mm, 1.6 mm, 1.4 mm, 1.2 mm, 1.0 mm). 
     As shown in at least  FIGS. 7A to 10B , in some instances, one or both ends of the occlusion device can be tapered. A proximal end which tapers down in diameter in the proximal direction can be useful to facilitate retraction. For example, an angle of a proximal tapered end can be less than or equal to about 45 degrees, for example, between about 15 degrees and about 30 degrees or between about 30 degrees and about 45 degrees. 
     Clinically, it can be desirable for the occlusion device to exert sufficient radial outward pressure to maintain proper vessel wall apposition and resist migration of the occlusion device after deployment. The occlusion device can have an average COP across a diameter between about 2.5 mm and about 8.0 mm (e.g., a diameter between about 3.0 mm and about 8.0 mm) of between about 20 mmHg and about 250 mmHg, such as between about 30 mmHg and about 140 mmHg, between about 30 mm Hg and 80 mmHg, between about between about 70 mmHg and 100 mmHg, between about 90 mmHg and 120 mmHg, or between about 100 mmHg and 140 mmHg. The occlusion devices described herein can exert a radial outward pressure between about 30 mmHg and about 50 mmHg, for example, between about 30 mmHg and about 40 mmHg, between about 35 mmHg and about 45 mmHg, or between about 40 mmHg and about 50 mmHg at the diameter of an intended target site in a vessel. In some instances, a proximal end of the occlusion device can include features to cause radial outward force to increase at the center of the occlusion device without traumatizing the vessel. The radial outward force at the center of the occlusion device can increase by up to 20 mmHg, for example, between about 10 mmHg to about 15 mmHg, or between about 15 mmHg and about 20 mmHg. 
     The expandable structure should include a wall pattern configured to facilitate proper vessel wall apposition and resist migration after delivery. At the same time, the wall pattern preferably permits the occlusion device to be collapsed inside the delivery system without negatively impacting trackability and accurate deployment. In general, the wall pattern can include struts that run diagonal or perpendicular to blood flow to maintain proper vessel wall apposition and resist migration. For example, the occlusion device can include a wall pattern configured such that a backpressure generated from the blood flow can help stabilize the occlusion device without causing trauma to the vessel wall. In some instances, the wall pattern can be substantially uniform along an entire length of the expandable structure. In some instances, the wall pattern can vary between the first and second end portions and the middle portion. In some instances, the density of the wall pattern can vary across the length of the occlusion device, for example, the pore size of the occlusion device can gradually increase across the length of the occlusion device or towards both ends from the center. 
     In any of these wall patterns, the pore size should be sufficiently large to maintain proper vessel wall apposition and resist migration. For example, the expanded average pore size can be greater than or equal to about 0.75 sq. mm, for example, within about 0.25 sq. mm of about 1.0 sq. mm, within about 0.5 sq. mm of about 1.25 sq. mm, or within about 0.5 sq. mm. of about 4.5 sq. mm. 
     Other methods for reducing migration can include incorporating one or more anchors, such as barbs, hooks, or likewise, along any portion of the occlusion device, preferably an uncovered bare strut portion, such as the middle portion or one of two end lobes of the occlusion device. 
     As another example, if the occlusion device is braided, the occlusion device can include one or more exposed strands or strand ends. The braided occlusion device can include one or more strands each having strand ends. At least some of those strand ends can remain exposed and can be configured to anchor the occlusion device to the vessel wall. 
     In other words, at least some of the strand ends can be secured to another of the strand ends, looped backed and secured to the same strand, or otherwise transformed to an atraumatic end, while at least some other of the strand ends can remain unsecured and can be configured to anchor the occlusion device to the vessel wall. These unsecured strand ends can be disposed anywhere along the occlusion device, for example, at least at one of the first and second end portions. 
     It can also be desirable to encourage endothelial growth or the formation of blood clots to ensure the permanency of the occlusion device. For example, the occlusion device can be coated with a substance to promote endothelial growth or the formation of clots. In some instances, the occlusion device can be coated with a chemical sclerosing agent. In some instances, the occlusion device can be coated with a liquid embolic (e.g., cohesives (i.e., Onyx) or adhesives (i.e. n-BCA). 
     The occlusion device can be configured to occlude substantially all fluid flow through a vessel using a single occluder, although multiple occlusion devices can be delivered. Further, the single occluder can be configured to immediately occlude fluid flow through the vessel using a single occluder (e.g., upon expansion). Substantial occlusion can include occluding at least about 80%, at least about 85%, at least about 90%, at least about 95%, or at least about 98% of fluid flow through the vessel. 
     As described below, the occlusion device can include a cover at least partially covering the expandable structure. The cover can include a cover material including, but not limited to, PTFE, PET, silicone, latex, TecoThane, nylon, PET, Carbothane (Bionate), fluoropolymers, SIBS, TecoFlex, Pellethane, Kynar, or PLGA. 
     The cover should be substantially impermeable to blood with a biostability for at least about two weeks. Preferably, the permeability is less than about 0.1 mL/sq. cm/min. In some instances, the cover can include a pore size of less than or equal to about 0.075 sq. mm. In some instances, the cover has less than or equal to about 20 percent open area, less than or equal to about 15 percent open area, or within about 2 percent of each of about 10 percent, 12 percent, 14 percent, 16 percent, or 18 percent. Further, the cover should include sufficient elasticity and lubricity to permit the occlusion device to be deployed in catheters having An outer diameter of less than or equal to about 6 F (2.0 mm) or less than or equal to about 5 F (1.67 mm)and expand to a diameter at least about 2.5 mm and/or less than or equal to about 8.0 mm. In some instances, the cover can be electronically charged or chemically modified to promote thrombogenicity. However, the covering material may be coated with a material to inhibit thrombus formation temporarily (i.e. hydrophilic coating) so that the device can be retracted and repositioned prior to final placement. In addition, the cover should have sufficient tensile strength to resist yielding, stretching, or breaking under at least normal blood pressures. For example, the cover should be able to withstand pressures of at least about 140 mmHg, preferably at least about 160 mmHg. 
     The length of the fibers creating the covering material allows the elongation of the covering material to far greater with less force (0.25-0.75×) than that of the native cover materials described above of the same thickness. The length of the fibers can be between about 5 microns and about 25 microns, such as within about 5 microns of each of about 10 microns, 15 microns, or 20 microns, although greater lengths may be used depending on desired parameters. These lengths permit the elongate of the cover material to at least two times greater. In some cases, the elongation is between about two times greater and about five times greater, for example, about three times greater or about four times greater. This elongation occurs with less than or equal to about 75 percent, less than or equal to about 50 percent, or even about 25 percent of the force necessary for native cover materials described above having the same thickness (e.g., between about 10 and about 30 microns). 
     It can be desirable for the cover to include a thickness that is sufficiently large to resist perforation during and after delivery, but sufficiently thin to minimize the diameter of the occlusion device in the unexpanded configuration and the diameter of the delivery device. Preferably, the thickness of the cover is less than or equal to about 30 microns, for example, within about 5 microns of each of about 15 microns, 20 microns, or 25 microns. 
     The cover can surround at least a portion of the expandable structure. The surrounded portion of the expandable structure should be sufficiently large to prevent fluid from flowing past the occlusion device when the occlusion device is expanded in the vessel. For example, the cover can surround the entire circumference of a covered portion of the expandable structure. Further, the cover can surround the expandable structure such that at least one end of the occlusion device is substantially closed. As shown in  FIGS. 9B  and  9 C, the cover may only surround one of the first or second end portions of the expandable structure. In some instances, a length of the covered portion can be between about approximately 15 percent and about 35 percent of a diameter of the target vessel or the expanded occlusion device, for example, approximately 25 percent of a diameter of the target vessel or the expanded occlusion device. In other examples, as shown in at least  FIG. 7A , the cover can surround the first end portion and the second end portion of the expandable structure, but leave a middle portion uncovered. In yet other examples, as shown in at least  FIG. 7B , the cover can surround substantially the entire expandable structure. 
     In some clinical scenarios, it can be more desirable to cover only a portion of the expandable structure, such that at least the middle portion remains uncovered. The exposed wall pattern of the expandable structure can help maintain proper vessel wall apposition and resist migration of the occlusion device. 
     The expandable structure can be coated with the cover using an electrospinning process. Electrospinning refers generally to processes involving the expulsion of flowable material from one or more orifices, and the material forming fibers are subsequently deposited on a collector. Examples of flowable materials include dispersions, solutions, suspensions, liquids, molten or semi-molten material, and other fluid or semi-fluid materials. In some instances, the rotational spinning processes are completed in the absence of an electric field. For example, electrospinning can include loading a polymer solution or dispersion, including any of the cover materials described herein, into a cup or spinneret configured with orifices on the outside circumference of the spinneret. The spinneret is then rotated, causing (through a combination of centrifugal and hydrostatic forces, for example) the flowable material to be expelled from the orifices. The material may then form a “jet” or “stream” extending from the orifice, with drag forces tending to cause the stream of material to elongate into a small diameter fiber. The fibers may then be deposited on a collection apparatus. Further information regarding electrospinning can be found in U.S. Publication No. 2013/0190856, filed Mar. 13, 2013, and U.S. Publication No. 2013/0184810, filed Jan. 15, 2013, which are hereby incorporated by reference in their entirety. 
     To facilitate occlusion of the target vessel site, the occlusion device in an over the wire embodiment should include a sufficiently small residual guide wire hole after deployment or a valve for occluding the guidewire opening. After full deployment, the occlusion device should include a residual guidewire hole having a diameter of less than or equal to about 0.25 mm. However, prior to deployment, the guide wire hole must be sufficiently large in both the unexpanded and expanded configuration to accommodate a standard guide wire having a diameter of at least about 0.25 mm, preferably at least about 0.4 mm. 
     Any of the occlusion devices described herein can include a number of radiopaque features that permit the fluoroscopic visualization of the occlusion device during one or more of delivery, deployment, post-deployment, and retraction. The marker bands can be positioned along the expandable structure. The marker bands can have a thickness of at least about 0.01 mm and a length of at least about 0.1 mm. Suitable marker bands can be produced from any number of a variety of materials, including platinum, gold, tantalum, and tungsten/rhenium alloy. 
     Turning to the figures,  FIGS. 3A-3F  illustrate the delivery system including any of the features of the delivery system  100  shown in  FIGS. 1A and 1B . The delivery system can be used to deliver the occlusion device  300 . As shown in the figures, the occlusion device can include a braided expandable structure having a tulip shape (e.g., laser cut with a woven pattern or braided from a plurality of strands). In other words, a diameter of a first end portion  302  can be smaller than a diameter of a second end portion  304 . Further, a diameter of the middle portion  306  can be greater than the diameter of the first end portion  302 , but smaller than the diameter of the second end portion  304 . The diameter can gradually decrease from the second end portion  304  to the first end portion  302 . 
     As shown in  FIG. 3D , the occlusion device  300  can include a cover  308  surrounding at least the first end portion  302 . The cover  308  can surround the entire circumference of the first end portion  302  and close the first end such that fluid cannot flow through the first end portion  302 . In some instances, the cover  308  can surround at least 20 percent of a length of the expandable structure, for example, between about 20 percent and about 40 percent or between about 30 percent and about 50 percent of the length of the expandable structure. Although, in other embodiments, the cover  308  can surround substantially the entire expandable structure, leaving a second end opened or substantially closed. 
     As shown in  FIG. 3F , the occlusion device  300  can include a central hub  310  for engaging the inner catheter  120  prior to delivery. If the occlusion device  300  is formed from a plurality of braided wire strands, the central hub can also be configured to secure the strand ends of the braided wire strands. Although the occlusion device  300  is described with the central hub  310 , a central hub  310  is not necessary, and the inner catheter  120  may carry the occlusion device  300  without the central hub  310 . Further, if the occlusion device  300  is formed from a plurality of braided wire strands, the braided wire strands can be heat-treated to maintain the position of the heated strands, or the strand ends can be secured to each other. 
       FIGS. 4A-4G  illustrate the delivery system including any of the features of the delivery system  100  shown in  FIGS. 1A and 1B . The delivery system can be used to deliver the occlusion device  400 . As shown in the figures, the occlusion device can include a braided expandable structure having a substantially cylindrical or barrel shape (e.g., laser cut with a woven pattern or braided from a plurality of strands). In other words, a diameter of a first end portion  402  can substantially the same as a diameter of a second end portion  404 . In some instances, a diameter of the middle portion  406  can substantially the same as the diameters of the first end portion  402  and the second end portion  404 . In other instances, a diameter of the middle portion  406  can be no more than about 25 percent larger, or no more than about 10 percent larger, than the diameters of the first and second end portions  402 ,  404 . 
     The occlusion device  400  can include a diamond wall pattern across the length of the occlusion device. As shown in  FIG. 4D , the first and second end portions  402 ,  404  can include a different wall pattern than the middle portion  406 . For example, the percentage of open area of the first and second end portions  402 ,  404  can be greater than the percentage of open area of the middle portion  406 . Although, in other examples, the wall pattern can be substantially the same across a length of the occlusion device  400 . 
     The first and second ends can each include a diamond pattern. Further, each end can include an inner band  412  of strand portions and an outer band  414  of strand portions. Each band  412 ,  414  can form the same number of apexes and form a diamond pattern therebetween. The inner band  412  can define a guide wire opening  416  at the center of the inner band  412 , through which a guide wire can pass. 
     The occlusion device  400  can include a cover surrounding at least one of the first and second end portions  402 ,  404 . The cover can surround the entire circumference of the first end portion  402  and/or second end portion  404  and substantially close the first and/or second ends such that fluid cannot flow through the covered end(s). In some instances, the cover can surround substantially the entire occlusion device  400 . As shown in  FIG. 4G , the cover portion  408   a  can surround the first end portion  402  and the cover portion  408   b  can cover the second end portion  404 , thereby substantially closing both the first and second ends. In some instances, each cover portion  408   a,    408   b  can surround at least 20 percent of a length of the occlusion device  400 , for example, between about 20 percent and about 40 percent or between about 30 percent and about 50 percent. 
       FIGS. 5A-5G  illustrate the delivery system including any of the features of the delivery system  100  shown in  FIGS. 1A and 1B . The delivery system can be used to deliver the occlusion device  500 . As shown in the figures, the occlusion device can include a braided expandable structure having a substantially cylindrical or barrel shape (e.g., laser cut with a woven pattern or braided from a plurality of strands). In other words, a diameter of a first end portion  502  can be substantially the same as a diameter of a second end portion  504 . In some instances, a diameter of the middle portion  506  can substantially the same as the diameter of the first end portion  502  the second end portion  504 . In other instances, a diameter of the middle portion  506  can be no more than about 25 percent larger, or no more than about 10 percent larger, than the diameters of the first and second end portions  502 ,  504 . 
     Similar to the occlusion device  400 , the occlusion device  500  can include a diamond wall pattern across the length of the occlusion device. As shown in  FIG. 5D , the wall pattern can be substantially the same across a length of the occlusion device  500 . However, in other examples, the first and second end portions  502 ,  504  can include a different wall pattern than the middle portion  506 . For example, the percentage of open area of the first and second end portions  502 ,  504  can be greater than the percentage of open area of the middle portion  506 . 
     The first and second ends can each include a diamond pattern. As shown in  FIGS. 5F and 5G , each end can include a band  518  of circumferentially disposed diamonds. The band  518  can define a guide wire hole  516  at the center of the inner band, through which a guide wire can pass. 
     The occlusion device  500  can include a cover surrounding at least one of the first and second end portions  502 ,  504 . The cover can surround the entire circumference of the first end portion  502  and/or second end portion  504  and substantially close the first and/or second ends such that fluid cannot flow through the covered end(s). In some instances, the cover can surround substantially the entire occlusion device  400 . As shown in  FIG. 5G , the cover portion  508   a  can surround the first end portion  502 , and the cover portion  508   b  can cover the second end portion  504 , thereby substantially closing both the first and second ends. In some instances, each cover portion  508   a,    508   b  can surround at least 20 percent of a length of the expandable structure, for example, between about 20 percent and about 40 percent or between about 30 percent and about 50 percent. 
       FIG. 6  illustrates an occlusion device  600  having a braided expandable structure (e.g., laser cut with a woven pattern or braided from a plurality of strands). The expandable structure can include a substantially hourglass shape. In other words, a diameter of a first end portion  602  can be substantially the same as a diameter of a second end portion  604 . Further, a diameter of the middle portion  606  can be substantially smaller than the diameters of the first and second end portions  602 ,  604 . In some instances, the diameter of the middle portion  606  can be at least about 50 percent, at least about 60 percent, at least about 70 percent, at least about 80 percent, or at least about 90 percent smaller than the diameters of the first and second end portions  602 ,  604 . The middle portion  606  can define a guide wire passage large enough for a conventional guide wire to pass. 
     The occlusion device  600  can include a cover surrounding the outside surface or the inside surface on at least one of the first and second lobes or end portions  602 ,  604 . The cover can surround the entire circumference of the first end portion  602  and/or second end portion  604 . In some instances, the cover can surround substantially the entire occlusion device  600 . As shown in  FIG. 6 , the cover  608  can surround the second end portion  604 . In some instances, each cover  608  can surround at least 25 percent of a length of the expandable structure, for example, between about 40 percent and about 60 percent of the length of the expandable structure, such as about 50 percent of the length of the expandable structure. 
       FIGS. 7A-7B  illustrate the occlusion device  700 . As shown in the figures, the occlusion device  700  can include a braided, elongate expandable structure (e.g., laser cut with a woven pattern or braided from a plurality of strands). As shown in the figures, the expandable structure can define a diamond wall pattern along a length of the expandable structure. Further, the expandable structure can include tapered first and second end portions  702 ,  704 . The first and second end portions  702 ,  704  can each define a guide wire hole large enough to permit a conventional guide wire to pass through the occlusion device. 
     A diameter of a middle portion  706  can be greater than a diameter of a first end portion  702  and a diameter of a second end portion  704 . The diameter of the middle portion  706  can be no more than about 60 percent, 50 percent, or 40 percent larger than the diameters of the first and second end portions  702 ,  704 . In some instances, the middle portion  706  can be at least as long as the first and second end portions  702 ,  704  combined. 
     The occlusion device  700  can include a cover surrounding at least one of the first and second end portions  702 ,  704 . The cover can surround the entire circumference of the first end portion  702  and/or second end portion  704  and substantially close the first and/or second ends such that fluid cannot flow through the covered end(s). As shown in  FIG. 7A , the cover portion  708   a  can surround the first end portion  702 , and the cover portion  708 b can cover the second end portion  704 , thereby substantially closing both the first and second ends. In some instances, each cover portion  708   a,    708   b  can surround at least 10 percent of a length of the expandable structure, for example, between about 10 percent and about 20 percent or between about 20 percent and about 30 percent. In some instances, as shown in  FIG. 7B , the cover  708   c  can surround substantially the entire occlusion device  700 . 
       FIG. 8  illustrates an occlusion device  800  formed from one or more strands woven to form an expandable structure. The expandable structure can include a first portion  802 , a second portion  804 , and a middle portion  806  therebetween. The first and second end portions  802 ,  804  can include tapered ends. Further, the first and second end portions  802 ,  804  can each include a smallest diameter that is at least large enough to permit a conventional guide wire to pass through. 
     The middle portion  806  can include a diameter that is substantially larger than a diameter of the first and second end portions  802 ,  804 . For example, the diameter of the middle portion  806  can be at least about 50 percent or at least about 75 percent larger than a diameter of the first and second end portions  802 ,  804 . In some instances, the diameter of the middle portion  806  can be between about 60 percent and 80 percent larger or between about 70 percent and about 90 percent larger. Further, as shown in  FIG. 8 , the middle portion  806  can include a non-uniform diameter; for example, the middle portion  806  can be generally rounded to form a bulbous shape. 
     Although not shown, the occlusion device  800  can include a cover surrounding at least one of the first and second end portions  802 ,  804 . The cover can surround the entire circumference of the first end portion  802  and/or second end portion  804  and substantially close the first and/or second ends such that fluid cannot flow through the covered end(s). In some instances, each cover portion can surround at least 10 percent of a length of the expandable structure, for example, between about 10 percent and about 20 percent or between about 20 percent and about 30 percent. In some instances, the cover can surround substantially the entire occlusion device  800 . 
       FIG. 9A  illustrates an occlusion device  900  formed from one or more strands woven to form an expandable structure. The expandable structure can include a first portion  902 , a second portion  904 , and a middle portion  906  therebetween. The first and second end portions  902 ,  904  can include tapered ends. Further, the first and second end portions  902 ,  904  each include a smallest diameter that is at least large enough to permit a conventional guide wire to pass through. 
     The middle portion  906  can include a diameter that is substantially larger than a diameter of the first and second end portions  902 ,  904 . For example, the diameter of the middle portion  906  can be at least about 50 percent, or at least about 75 percent larger than a diameter of the first and second end portions  902 ,  904 . In some instances, the diameter of the middle portion  906  can be between about 60 percent and 80 percent larger or between about 70 percent and about 90 percent larger. Further, as shown in  FIG. 9 , the middle portion  906  can include a substantially uniform diameter. 
     The occlusion device  900  can include a cover  908  surrounding at least one of the first and second end portions  902 ,  904 . The cover  908  can surround the entire circumference of the first end portion  902  and/or second end portion  904  and substantially close the first and/or second ends such that fluid cannot flow through the covered end(s). In some instances, each cover portion can surround at least 10 percent of a length of the expandable structure, for example, between about 10 percent and about 20 percent or between about 20 percent and about 30 percent. As shown in the figures, the cover  908  surrounds the first end portion  902 . However, in some instances, the cover can surround the second end portion  904  or substantially the entire occlusion device  900 . 
       FIGS. 10A-10B  illustrate the occlusion device  1000 . As shown in the figures, the expandable structures can define a diamond wall pattern along a length of the expandable structure. Further, the expandable structure can include tapered first end portion  1002  and an opened second end portion  1004 . Although the first end portion  1002  is tapered, the first end portion  1002  still defines a guide wire hole large enough to permit a conventional guide wire to pass through the occlusion device. A diameter of a middle portion  1006  can be substantially the same as a diameter of the second end portion  1004 . 
     As shown in  FIG. 10B , the occlusion device  1000  can include a cover  1008  surrounding at least the first end portion  1002 . The cover  1008  can surround the entire circumference of the first end portion  1002  such that fluid cannot flow through the covered end. In some instances, the cover  1008  can surround at least 10 percent of a length of the expandable structure, for example, between about 10 percent and about 20 percent or between about 20 percent and about 30 percent. As shown in  FIG. 10A , the cover  1008  can surround substantially the entire expandable structure. 
       FIGS. 11A-11C  illustrate another exemplary embodiment of an occlusion device  1100 . As shown in the figures, the occlusion device  1000  can include a substantially uniform diameter. The occlusion device  1100  also defines a substantially uniform diamond wall pattern along a length of the occlusion device  1100 . 
     As shown in  FIG. 11C , the occlusion device  1100  can include a drumhead  1120  disposed within the first end portion  1102 . The drumhead  1120  can be configured to close the first end  1102  such that fluid is prevented from flowing through the occlusion device  1100 . 
     Further, the occlusion device  1100  can include a cover  1108  surrounding at least a portion of the occlusion device  1100 . For instance, the cover  1108  can cover the drumhead  1120 , or, as shown in  FIGS. 11A-11C , the cover  1108  can surround at least the middle portion  1106  and the second end portion  1104 . Although, depending on the desired performance of the cover  1108 , the cover  1108  can extend along different lengths of the occlusion device. In some scenarios, it may be desirable to have greater overlap between the cover  1108  and the frame to adequately anchor the cover  1108  to the frame. For example, the cover  1108  can extend along at least about 50 percent, as at least about 60 percent, at least about 70 percent, at least about 80 percent, or at least about 90 percent of the length of the occlusion device  1100 . In some examples, the cover  1108  extends along substantially the entire length of the occlusion device  1100 . In other scenarios, it may be desirable to leave a higher percentage of the frame uncovered to facilitate endothelialization, for example, across less than about 50 percent, less than about 40 percent, less than about 30 percent, or less than about 20 percent of the length of the occlusion device  1100 . Preferably, to achieve both endothelialization and sufficient overlap, the cover  1108  should extend across at least about 25 percent of the length of the frame and no more than about 50 percent of the length of the frame, for example, within about 5 percent of each of about 30 percent, 35 percent, 40 percent, or 45 percent. 
     Although certain embodiments have been described herein within respect to the illustrated expandable structures, the occlusion devices described herein can include differently shaped or differently formed expandable structures. For example, the expandable structure can be substantially conical, coiled, or any other conventional stent shape. As another example, the expandable structure can include a laser cut frame. In some instances, the frame can include a first closed end and a second opened end. The percentage of open area of the second opened end can be greater than the percentage of open area of the first closed end. 
     The specific examples described above in connection with  FIGS. 3A-11C  are for illustrative purposes only and should not be construed as limiting. Any combination of the configuration, shape, or wall pattern of the expandable structure can be combined with any type or amount of covering described herein. 
     Further, any of the features of the occlusion devices (e.g., expansion ratio, shapes, dimensions, materials, covers, etc.) disclosed herein can be accomplished in a stent, having two open ends and a central lumen to maintain vascular patency and permit perfusion. 
       FIGS. 12A and 12F  illustrate an occlusion device  1200   a  having a first lobe or end portion  1202   a,  a second lobe or end portion  1204   a,  and a central or neck portion  1205   a  extending between the first and second end portions  1202   a,    1204   a.  The first end portion  1202   a  can generally refer to the distal end portion or the anchor portion of the occlusion device  1200   a  and the second end portion  1204   a  can generally refer to the proximal end portion or the occlusive portion of the occlusion device  1200   a  when the occlusion device  1200   a  is introduced into the patient. As described in further detail below, the second end portion  1204   a  can be coated such that the second end portion  1204   a  provides occlusion, while the first end portion  1202   a  maintains an open cell structure to anchor the occlusion device  1200   a  and permit lateral flow. Further, the open cell structure of the first end portion  1202   a  enables the clinician to partially deploy the occlusion device  1200   a  against the wall of the vessel (e.g., just the first end portion  1202   a ) and confirm the position of the occlusion device  1200   a  by injecting contrast (e.g., by using delivery system  200 ) without materially impeding flow or raising hydrostatic pressure. In contrast, if a mechanically occlusive element were partially deployed, the mechanically occlusive element would impede flow and raise hydrostatic pressure. 
     As shown in  FIG. 12A , the diameter of the central portion  1205   a  can be less than a diameter of the first or second end portions  1202   a,    1204   a,  e.g., the occlusion device  1200   a  can have a generally hourglass shape (see  FIG. 12A ). For example, the diameter D 1  of the central portion  1205   a  can be between about 5% and about 25% of the diameter D 2  of the first or second end portions  1202   a ,  1204   a , preferably less than or equal to about 15%, or less than or equal to about 10% of the diameter D 2  of the first or second end portions  1202   a,    1504 . 
     The occlusion device  1200   a  can be asymmetrical about a transverse axis T-T of the occlusion device  1200   a  in the expanded and/or unexpanded configurations (see  FIG. 12A ). For example, in the expanded configuration, the occlusion device  1200   a  can be asymmetrical about a transverse axis T-T. 
     As shown in  FIG. 12A , a uniform portion  1204   a ′ of the second end portion  1204   a  can have a generally uniform diameter (e.g., cylindrical) and a tapered portion  1204   a ″ of the second end portion  1204   a  can taper towards the central portion  1205   a.  The tapered portion  1204   a ″ of the second end portion  1204   a  can form an angle α between about 45 degrees and about 75 degrees, between about 55 degrees and about 65 degrees, preferably about 60 degrees with respect to the longitudinal axis. 
     Similarly, a uniform portion  1202   a ′ (e.g., cylindrical) of the first end portion  1202   a  can have a generally uniform diameter and a tapered portion  1202   a ″ of the first end portion  1202   a  can taper toward the central portion  1205   a.  The tapered portion  1202   a ″ of the first end portion  1202   a  can form an angle β. Angle β can be substantially the same as angle α. 
     Even if the angle of the tapered portions  1202   a ″,  1204   a ″ is substantially the same, an angle γ can be different from an angle δ relative to the longitudinal axis. The angle γ can be measured from a line extending through a transition point T 1  (between the tapered portion  1204   a ″ and the cylindrical portions  1204   a ′) and the axial center C of the occlusion device  1200   a . The angle δ can be measured from a line extending through a transition point T 2  (between the tapered portion  1202   a ″ and the cylindrical portions  1202   a ′) and the axial center C of the occlusion device  1200   a . Angle δ can be less than angle γ to reduce the force necessary to retract the first end portion  1202   a  into the delivery system. 
     As illustrated in  FIG. 13B , each of the proximal (covered)  1204   e  and distal (typically bare strut)  1202   e  lobes are connected to the central hub  1205   e ′ by a plurality of struts  1210   e  which incline radially outwardly in their respective directions away from the hub  1205   e ′. In the illustrated embodiment, a shallower distal lobe strut  1280   e  launch angle between the curved axis of the strut and the longitudinal axis of the implant is clinically desirable because it provides a ramped surface that facilitates easy resheathing of the deployed distal lobe of the implant as it is pulled proximally back into the tubular deployment catheter. Preferably, the expanded implant is bilaterally asymmetrical, with the proximal struts  1282   e  exhibiting a steeper launch angle from the hub. This enables the implant to reach the fully expanded diameter of the proximal lobe  1204   e  over the shortest possible axial length. Thus, the shallow launch angle distal struts  1280   e  and steeper launch angle proximal struts  1282   e  optimize retrievability of the partially deployed implant while at the same time minimizes overall implant length. The wall pattern of the implant may in one embodiment exhibit bilateral symmetry in the collapsed configuration but expands to demonstrate the bilateral asymmetry described above due to a preset shape in the Nitinol or other shape memory material of the frame. 
     The distal struts  1280   e  are concave outwardly in a side elevational view, defining a generally trumpet shaped or flared configuration. The curvature of the struts  1280   e  as they leave the hub  1205   e ′ and incline radially outwardly do not necessarily have a constant radius of curvature, but can be considered to conform to a best fit circle A having a constant radius (see  FIG. 13B ). The radius is generally at least about 25%, in some embodiments at least about 30% or 35% or more of the unconstrained diameter of the expanded distal lobe  1202   e.  For example, in an implant having an unconstrained distal lobe diameter of about 10 mm, the radius is generally within the range of from about 2.5 mm to about 5.5 mm, and in some embodiments between about 3 mm and 5 mm, or approximately 4 mm. 
     The proximal lobe struts  1282   e  can have a steeper launch angle to enable the proximal lobe  1202   e  to reach full diameter over a short axial distance from the hub. Thus, the radius of circle B which best fits the launch geometry of the proximal struts is generally less than about 25%, preferably less than about 20% or 15% or less of the expanded diameter of the proximal lobe  1202   e,  depending upon the physical properties and dimensions of the strut material (see  FIG. 13B ). 
     The best fit circles A, B described above will preferably be located against the strut such that it is approximately symmetrical about the midpoint of the arc of the struts that define the concave outwardly concave curvature section. Thus, the midpoint of the arc in the distal strut  1280   e  illustrated in  FIG. 13B  is a greater radial distance from the longitudinal axis of the implant than is the midpoint of the arc in the proximal strut  1282   e  due to the proximal strut transitioning from the arc to a substantially linear shoulder which extends out to the generally cylindrical body of the proximal lobe. 
     As shown in  FIG. 12A , a length Li of the second end portion  1204   a  (including the tapered portion  1204   a ″ and generally uniform portion  1204   a ′) can be greater than a length L 2  of the first end portion  1202   a  (including the tapered portion  1202   a ″ and generally uniform portion  1202   a ′). For example, L 2  can be between about 25% and about 75% of L 1 , such as between about 50% and about 60%. Forces directed at a concave surface of the second end portion  1204   a  can provide a radially outward directed force to push the second end portion  1204   a  open and increase radial outward forces acting on the occlusion device  1200   a  and the vessel wall, when the occlusive concave side is facing an upstream direction with respect to blood flow in the vessel. The occlusive lobe (e.g., the second end portion  1204   a ) also places the hub under axial compression, which increases the radial force on the bare metal strut lobe (e.g., the first end portion  1202   a ). In certain aspects, the length of the second end portion Li can be about the same as a diameter of the second end portion  1204   a.  This ensures that the second end portion  1204   a  does not rotate perpendicular to an axis of the vessel and ensures that other anti-migration features remain properly aligned and positioned. 
     A length L 3  of the uniform portion  1204   a ′ of the second end portion  1204   a  can be longer than a length L 4  of the uniform portion  1202   a ′ of the first end portion  1202   a ′ (see  FIG. 12A ). For example, in the unconstrained configuration, the uniform portion  1204   a ′ can include a greater number of circumferential rings R 1 , R 2 , R 3  of open cells  1212   a  than the uniform portion  1202   a ′. For example, the uniform portion  1204   a ′ can include three circumferential rings R 1 , R 2 , R 3  of open cells  1212   a,  while the uniform portion  1202   a ′ can include one circumferential ring R 4  of open cells  1212   a . A size of an open cell  1212   a  in circumferential ring R 1  can be substantially the same size as the size of an open cell  1212   a  in circumferential ring R 4 . In the constrained configuration, the second end portion  1204   a  can include a greater number of circumferential rings of struts than the first end portion. For example, the second end portion  1204   a  can include six circumferential rings C 1 , C 2 , C 3 , C 4 , C 5 , C 6 , of struts  1210   a,  while the first end portion  1202   a  can include four circumferential rings C 7 , C 8 , C 9 , C 10  of struts  1210   a.    
     The occlusion device  1200   a  can have an aspect ratio less than or equal to about 2:1 (unconstrained length to unconstrained lobe diameter), such as between about 1:1 and about 2:1 or between about 1.5:1 and about 2:1. An unconstrained length of the occlusion device  1200   a  can be between about 10 mm and about 25 mm, in some implementations from about 15 mm to about 22 mm. The first end portion  1202   a  having an unconstrained length of less than about 50% of a length of the occlusion device  1200   a  (e.g., when the unconstrained length is 20 mm, the length of the proximal portion is less than about 10 mm), less than about 40% of a length of the occlusion device  1200   a  (e.g., when the unconstrained length is 20 mm, the length of the proximal portion is less than about 8 mm), or less than about 30% of a length of the occlusion device  1200   a  (e.g., when the unconstrained length is 20 mm, the length of the proximal portion is less than about 6 mm). An unconstrained expanded diameter of the occlusion device  1200   a  can be between about 5 mm and about 15 mm, such as about 10 mm. 
     The occlusion device  1200   a  can include an expandable frame  1206   a  and a membrane  1208   a  carried by the expandable frame  1206   a.  The expandable frame  1206   a  can define a lumen therethrough to facilitate delivery of the occlusion device  1200   a  over a guide wire (e.g., a 0.018-inch guidewire). Further, the expandable frame  1206   a  can have a wall thickness of less than or equal to about 0.003 inches, such as about 0.002 inches. 
     The expandable frame  1206   a  can be at least partially covered by a thin membrane  1208   a  (e.g., between about 10 microns and about 30 microns thick). The membrane  1208   a  should be sufficiently thick to facilitate occlusion, while still minimizing the profile of the collapsed occlusion device  1200   a.  Possible materials for the membrane  1208   a  can include PTFE, PET, silicone, latex, TecoThane, nylon, PET, Carbothane (Bionate), fluoropolymers, SIBS, TecoFlex, Pellethane, Kynar, or PLGA. 
     The membrane  1208   a  can be applied to the expandable frame  1206 a in a manner that encapsulates at least some of the struts  1210   a,  such that the membrane  1208   a  is present along either or both an interior surface and an exterior surface of the expandable frame  1206   a.  Possible methods of applying the membrane  1208   a  are described in further detail below. 
     The membrane  1208   a  can cover at least one end of the expandable frame  1206   a  and extend across at least a partial length of the expandable frame  1206   a.  In some embodiments, the membrane  1208   a  at least coats a portion of the occlusion device  1200   a  that is concave to the direction of the blood flow, which can be more occlusive and resist more migration than occlusion devices that only coat a surface convex to the direction of the blood flow or coat the entire occlusion device or coat the entire occlusion device. For example, the membrane  1208   a  can cover at least a portion of or the entire the second end portion  1204 a and the first end portion  1202   a  can be a bare frame. When the bare first end portion  1202   a  is deployed before the covered second end portion  1204   a,  the bare first end portion  1202   a  can at least partially anchor the occlusion device  1200   a  in the vessel and allow visualization before deploying the covered second end portion  1204   a,  which facilitates precise placement of the occlusion device  1200   a.    
     When the covered second end portion  1204   a  is upstream (i.e., anatomically proximal) from the bare first end portion  1202   a,  the increase in arterial pressure at the second end portion  1204   a  increases the radially outward forces directed toward the membrane  1208   a,  which helps the occlusion device  1200   a  resist migration. A higher blood pressure difference between the proximal and distal ends of the occlusion device  1200   a  will cause higher outward forces. Further, when the covered second end portion  1204   a  is upstream from the bare first end portion  1202   a,  forward pressure from blood flow acts on the central portion  1205   a.  After the occlusion device  1200   a  expands, forces acting on the central portion  1205   a  cause the tapered portion  1202   a ″ of the first end portion  1202   a  (e.g., struts closer to or adjacent to the central portion  1205   a ) to collapse (e.g., bend inward), which causes the uniform portion  1202   a ′ (e.g., struts closer to or at a distal end of the occlusion device) to move outward and further anchor the first end portion  1202   a  in the vessel. 
     Additionally, the membrane  1208   a  can be positioned on portions of the expandable frame  1206   a  on which hydraulic pressure will force the expandable frame  1206   a  outward. In some embodiments, portions of the expandable frame  1206 a where the hydraulic pressure would force the expandable frame  1206   a  inward are not coated. 
     The membrane  1208   a  can extend to form a thin extended tubular section of coating  1250   a  through which the guidewire (e.g., a 0.018″ guidewire) can be introduced. The thin tube  1250   a  can extend through the first end portion  1202   a  or the second end portion  1204   a.  As described in further detail below, the thin tube  1250   a  can be configured to invert from a position extending through the first end portion  1202   a  such as during deployment to a position extending through the second end portion  1204   a  following deployment. The thin tube  1250   a  can extend across less than or equal to about 85% (e.g., between about 75% and about 85%), less than or equal to about 75%, less than or equal to about 60%, or less than or equal to about 50% of the length of the second end portion  1204   a.  In use, the thin tube  1250   a  can have sufficiently low collapse resistance such that blood pressure will cause the thin tube  1250   a  to collapse (e.g., kink, fold, buckle, flop over, or likewise) when the guidewire is removed. The thin tube  1250   a  acts like a valve (e.g., a duckbill valve) to occlude the guidewire lumen  1252   a  and aid in the capture and formation of clots. The tube  1250   a  may be formed integrally with the formation of the membrane, during the spin coating process. Alternatively, the tube  1250   a  may be separately formed and attached to the hub and/or membrane using suitable adhesives, solvent bonding, heat bonding, or other techniques known in the art. Alternatively, one, two, or more flaps or leaflets may be provided, to occlude the guidewire opening following removal of the guidewire, preferably on the upstream blood flow side of the hub. 
     After the occlusion device  1200   a  has been deployed, the occlusion device  1200   a  can resist migration (e.g., migrate less than about 5.0 mm from the deployed position, preferably less than about 4.0 mm, or less than about 2.0 mm) for at least 10 minutes under pressures of at least about 100 mmHg and/or less than or equal to about 300 mmHg, for example, between about 100 mmHg and 150 mmHg, between about 150 mmHg and about 300 mmHg, between about 200 mmHg and about 300 mmHg, between about 250 mmHg and about 300 mmHg, such as about 270 mmHg, as determined by the Migration Protocol described below. 
     In at least a straight 8 mm vessel or curved 8 mm vessel with a 20 mm radius to centerline of vessel, the structure of the deployed occlusion device  1200   a  permits the device to resist migration under at least average blood pressure (e.g., 120 mmHg) according to the Migration Protocol described below. In at least a straight 8 mm vessel or curved 8 mm vessel with a 20 mm radius to centerline of vessel, under retrograde venous deployment conditions, the structure of the deployed occlusion device  1200   a  permits the device to resist migration under at least 7 mmHg of pressure according to the Migration Protocol described below. Migration is defined as continuous movement of the embolic device or movement of the proximal end of the embolic device by greater than 5 mm from the initial location. 
     When the occlusion device  1200   a  is deployed in the vessel, the occlusion device  1200   a  can occlude at least about 80% of blood flow within 30 seconds, at least about 90% of blood flow within about 3 minutes, and/or about 100% of blood flow within about five minutes, without reliance on biological processes. Because of the mechanical mechanism of occlusion, performance is the same whether or not the patient has been anticoagulated (e.g., heparin, aspirin, warfarin, Plavix, etc.). In some implementations, the occlusion device  1200   a  can achieve complete occlusion within about two minutes or within about one minute. Using the Occlusion Protocol described below, the occlusion device  1200   a  can limit the flow rate through a vessel to no more than about 200 cc/min at 20 mmHg, such as to between about 50 cc/min and about 150 cc/min, preferably less than about 130 cc/min, less than about 100 cc/min at 20 mmHg or less than about 65 cc/min at 20 mmHg within about five minutes. Further, the occlusion device  1200   a  can limit the flow rate through a vessel to no more than about 400 cc/min at 60 mmHg or no more than about 330 cc/min at 60 mmHg, such as to between about 150 cc/min and about 250 cc/min, preferably less than or equal to about 175 cc/min at 60 mmHg within about five minutes. The occlusion device  1200   a  can limit the flow rate through a vessel to about no more than 600 cc/min at about 100 mmHg or 430 cc/min at 100 mmHg, such as to between about 200 mmHg and about 250 mmHg, preferably less than about 225 cc/min at about 100 mmHg within about five minutes. 
     In at least a 3 mm curved vessel with a 7.5 mm radius to centerline of vessel or a 8 mm vessel with a 20 mm radius to centerline of vessel, using the Occlusion Protocol described below, the occlusion device  1200   a  will permit a maximum flow rate of 130 cc/min at 20 mmHg (e.g., a maximum flow rate of 70 cc/min at 20 mmHg or 40 cc/min at 20 mmHg), 330 cc/min at 60 mmHg (e.g., a maximum flow rate of 175 cc/min at 60 mmHg or 125 cc/min at 60 mmHg), or 430 cc at 100 mmHg (e.g., a maximum flow rate of 315 cc/min at 100 mmHg or 185 cc/min at 100 mmHg) after about one minute. In at least a 3 mm curved vessel with a 7.5 mm radius to centerline of vessel or an 8 mm vessel with a 20 mm radius to centerline of vessel, under retrograde venous deployment conditions, using the Occlusion Protocol described below, the occlusion device  1200   a  will permit a maximum flow rate of 130 cc/min at 20 mmHg after about one minute. 
     The occlusion device  1200   a  has an expansion ratio of at least about 5:1. The expansion ratio of the occlusion device  1200   a  allows the occlusion device  1200   a  to treat different sized vessels between about 2.5 mm and about 8.0 mm. For example, the same occlusion device  1200   a  that can occlude a 2.5 mm vessel can occlude a 6.0 mm vessel. 
     The expansion ratio of the occlusion device  1200   a  can be between about 5:1 to about 10:1, such as at least about 5:1, at least about 6:1, at least about 7:1, at least about 8:1, or at least about 9:1. In some implementations, the expansion ratio can be at least about 10:1. In other words, a diameter of the occlusion device  1200   a  in the expanded configuration can be between about five times and about ten times greater than the diameter of the occlusion device  1200   a  in the unexpanded configuration, such as at least about five times, at least about six times, at least about seven times, at least about eight times, or at least about nine times. In some implementations, the diameter of the expanded configuration can be at least about ten times greater than the diameter of the unexpanded configuration. The expansion ratio of the occlusion device  1200   a  is sufficiently large such that the occlusion device  1200   a  is capable of compressing to a minimum size suitable for delivery through a catheter having a diameter of less than about 5 F, thereby minimizing trauma to the vessel during delivery. Further, the expansion ratio of the occlusion device  1200   a  is sufficiently large that a single, expanded occlusion device is capable of preventing substantially all fluid from flowing past the occlusion device in the target vessel. Generally, the expansion ratio of each lobe is equal to the ratio of the hub to the lobe in an unconstrained expansion. 
     A single occlusion device  1200   a  can be used to treat a wide range of vessel diameters. For example, the occlusion device  1200   a  can have an expansion range when delivered from a lumen having an internal diameter of at least about 2.0 mm up to at least about 8.0 mm or 10.0 mm or more, such as at least about 3.0 mm, at least about 4.0 mm, or at least about 5.0 mm. For instance, a single occlusion device  1200   a  can treat vessels having a diameter between about 2.5 mm and about 8.0 mm, or between about 3.0 mm and 7.0 mm. Using a single occlusion device  1200   a  to treat a wide range of vessels can be desirable to reduce the total stock of occlusion devices that must be kept on hand, and the ability to occlude large vessels with a single occlusion device  1200   a  can reduce costs. 
     Further, the single occlusion device  1200   a  having an expansion range of at least about 2.0 mm, 4.0 mm, or more, and also exhibits less than 20 percent elongation when moving from the unexpanded configuration to the expanded configuration, preferably less than about 15 percent. Minimizing elongation can help ensure accurate positioning of the occlusion device  1200   a.    
     In the expanded state, the occlusion device  1200   a  can have an unconstrained diameter that is between about 30% and about 50% larger than the vessel diameter. For vessels sized between about 2.0 mm and about 8.5 mm in diameter, the diameter of the expanded occlusion device  1200   a  can be at least about 2.6 mm and/or less than or equal to about 12.75 mm, e.g., between about 9 mm and about 11 mm, such as about 10 mm. 
     The occlusion device  1200   a  may provide a chronic outward pressure (“COP”). As used herein, COP is the radial pressure (expressed in terms of mmHg) necessary to maintain stability of the occlusion device in a vessel under normal physiological blood pressure (i.e., about 135 mmHg). Radial forces used to determine the following COP values were based on data collected using the Migration Protocol described below. Further, the calculation of the COP assumes that the occlusion device  1200   a  forms a complete seal, and thus the flow rate equals zero and shear forces equal zero. The calculation also assumes that the occlusion device  1200   a  is rigid, and thus the normal force due to transfer of hydraulic force to the vessel wall equals zero. 
     Using these assumptions, the occlusion device can provide a COP between about 20 mmHg and about 250 mmHg, such as between about 30 mmHg and about 140 mmHg, between about 30 mm Hg and 80 mmHg, between about between about 70 mmHg and 100 mmHg, between about 90 mmHg and 120 mmHg, or between about 100 mmHg and 140 mmHg., for vessels having a diameter between about 3 mm and about 8 mm under a physiological pressure of about 135 mmHg, preferably between about 20 N/mm 2  (2.67 kPa) and about 50 N/mm 2  (6.67 kPa). For example, the occlusion device  1200   a  can provide about 48 mmHg (6.4 kPa) of radial pressure in a 7 mm vessel with a physiological pressure of about 135 mmHg pressure when the length of the contact area between an exemplary embodiment of the occlusion device  1200   a  and the vessel wall is about 12.5 mm (e.g., L 1 =4.5 mm, L 2 =8.0 mm). The occlusion device  1200   a  can provide about 20 mmHg (2.67 kPa) of radial pressure in a 7 mm vessel with a physiological pressure of about 135 mmHg pressure when the length of the contact area is about 30.0 mm, the entire length of an exemplary embodiment of the occlusion device  1200   a.  The latter calculation assumes that a thrombus will form and that the occlusion device  1200   a  will transfer radial force through the thrombus and across the entire length of the occlusion device  1200   a.    
       FIGS. 13A and 13B  illustrate another hourglass-shaped occlusion device  1200   e  having the same general structure and properties as occlusion device  1200   a.  In generally, the occlusion device  1200   e  is adapted to move between a constrained configuration ( FIG. 13B ) and an unconstrained configuration ( FIG. 13A ). The occlusion device  1200   e  can have any number of the characteristics (e.g., dimensions, construction, performance, etc.) as the occlusion device  1200   a  except as described below. 
     Similar to the occlusion device  1200   a,  as shown in  FIG. 13A , the occlusion device  1200   e  can have a first lobe or end portion  1202   e,  a second lobe or end portion  1204   e,  and a central or neck portion  1205   e  extending between the first and second end portions  1202   e,    1204   e.  The first end portion  1202   e  can generally refer to the distal end portion, the downstream portion, or the anchor portion of the occlusion device  1200   e  and the second end portion  1204   e  can generally refer to the proximal end portion, the upstream portion, or the occlusive portion of the occlusion device  1200   e  when the occlusion device  1200   e  is introduced into the patient. The second end portion  1204   e  can be coated such that the second end portion  1204   e  provides occlusion, while the first end portion  1202   e  maintains an open cell structure to anchor the occlusion device  1200   e  and permit lateral flow. Further, the open cell structure of the first end portion  1202   e  enables the clinician to partially deploy the occlusion device  1200   e  against the wall of the vessel (e.g., just the first end portion  1202   e ) and confirm the position of the occlusion device  1200   a  by injecting contrast (e.g., by using delivery system  200 ) without materially impeding flow or raising hydrostatic pressure. In contrast, if a mechanically occlusive element were partially deployed, the mechanically occlusive element would impede flow and raise hydrostatic pressure. 
     As shown in  FIG. 13A , the diameter of the central portion  1205   e  can be less than a diameter of the first or second end portions  1202   e,    1204   e,  e.g., the occlusion device  1200   e  can have a generally hourglass shape (see  FIG. 13A ). For example, the diameter D 1  of the central portion  1205   e  can be between about 5% and about 25% of the diameter D 2  of the first or second end portions  1202   a,    1504 , preferably less than or equal to about 15%, or between about 10% and about 15% of the diameter D 2  of the first or second end portions  1202   e,    1204   e.  The diameter of the hub can be substantially equal to the diameter of the proximal and distal lobes when in the collapsed configuration. 
     As shown in  FIG. 13A , the occlusion device  1200   e  can be asymmetrical about a transverse axis T-T of the occlusion device  1200   a  in the expanded. As shown in  FIG. 13B , in an constrained position, the length L 1  of the first end portion  1202   e  can be substantially the same as the length L 2  of the second end portion  1204   e . For example, in the constrained configuration, the second end portion  1204   e  can include the same number of circumferential rings as the first end portion, such as six rings C 1 , C 2 , C 3 , C 4 , C 5 , C 6 , of struts  1210   e  (or four or five or more) in the first end portion  1202   e  and six rings C 7 , C 8 , C 9 , C 10 , C 11 , C 12 , of struts  1210   e  (or four or five or more) in the second end portion  1204   e . 
     However, as shown in  FIG. 13A , in the unconstrained position, the length L 3  of the generally uniform portion  1204   e ′ of the second end portion  1204   e  can be less than the length L 4  of the generally uniform portion  1202   e′  of the first end portion  1202   e . For example, L 3  can span about two circumferential rings R 4 , R 5  or less than three full circumferential rings of open cells  1212   e,  while L 4  can span about three full circumferential rings R 1 , R 2 , R 3  of open cells  1212   e . Although the first end portion  1202   e  and the second end portion  1204   e  have the same length in the unconstrained configuration, the first end portion  1202   e  and the second end portion  1204   e  to expand into different configurations. A size of an open cell  1212   e  in circumferential ring R 1  can be substantially the same size as the size of an open cell  1212   e  in circumferential ring R 4 . 
     As shown in  FIG. 13A , the angle α of the tapered portion  1204   a ″ or angle β of the tapered portion  1202   a ″ can be between about 45 degrees and about 75 degrees, between about 55 degrees and about 65 degrees, preferably about 60 degrees with respect to the longitudinal axis. The angle α can be substantially the same as angle β. 
     However, even if the angle of the tapered portions  1202   e ″,  1204   e ″ is substantially the same, an angle γ can be different from an angle δ relative to the longitudinal axis. The angle γ can be measured from a line extending through a transition point (between the tapered portion  1204   e ″ and the cylindrical portions  1204   e ′) and the axial center of the occlusion device  1200   e.  The angle δ can be measured from a line extending through a transition point (between the tapered portion  1202   e ″ and the cylindrical portions  1202   a ′) and the axial center of the occlusion device  1200   e.  Angle δ can be less than angle γ to reduce the force necessary to retract the first end portion  1202   e  into the delivery system. 
     During the manufacturing process, after the hypotube is laser cut, two different sized mandrels are inserted into the occlusion device  1200   e.  A first mandrel having a desired shape of the first end portion  1202   e  can be inserted through a distal end of the occlusion device  1200   e  and a second mandrel having a desired shape of the second end portion  1204   e  can be inserted through a proximal end of the occlusion device  1200   e.  The first mandrel can be locked together with the second mandrel. With the occlusion device  1200   e  loaded on the first and second mandrels, the occlusion device  1200   e  can be heat treated to the shape described herein. 
     The occlusion device  1200   e  can have an aspect ratio less than or equal to about 2:1 (unconstrained length to unconstrained lobe diameter), such as between about 1:1 and about 2:1 or between about 1.5:1 and about 2:1. An unconstrained length of the occlusion device  1200   e  can be between about 10 mm and about 25 mm, in some implementations from about 15 mm to about 22 mm. The first end portion  1202   e  having an unconstrained length of less than about 50% of a length of the occlusion device  1200   e  (e.g., when the unconstrained length is 20 mm, the length of the proximal portion is less than about 10 mm), less than about 40% of a length of the occlusion device  1200   e  (e.g., when the unconstrained length is 20 mm, the length of the proximal portion is less than about 8 mm), or less than about 30% of a length of the occlusion device  1200   e  (e.g., when the unconstrained length is 20 mm, the length of the proximal portion is less than about 6 mm). An unconstrained expanded diameter of the occlusion device  1200   e  can be between about 5 mm and about 15 mm, such as about 10 mm. 
     The occlusion device  1200   e  can include an expandable frame  1206   e  and a membrane  1208   e  (not shown) carried by the expandable frame  1206   e  (see  FIG. 13A ). The expandable frame  1206   e  can define a lumen G therethrough to facilitate delivery of the occlusion device  1200   e  over a guide wire (e.g., a 0.018 inch guidewire). Further, the expandable frame  1206   e  can have a wall thickness of less than or equal to about 0.003 inches, such as about 0.002 inches. 
     The first end portions and the second end portions  1202   e,    1204   e  of the expandable frame  1206   e  can include a plurality of interconnected struts  1210   e  that can be laser cut from a Nitinol hypotube. At least a portion of the central portion  1205   e  can be a bare hypotube section  1205   e ′ (e.g., uncut). 
     A length of each strut  1210   e  can generally vary from an end of the occlusion device  1200   e  toward the central portion  1205   e  of the occlusion device  1200   e.  For example, a length of each strut  1210   e  can generally increase from one or both ends of the occlusion device  1200   e  to a central portion  1205   e  of the occlusion device (e.g., from about 0.05 cm at the proximal and distal ends to about 0.25 cm at the central portion  1205   e ). For example, a length of a strut closest to the center can be about 150% of a length of a strut closest to an end of the occlusion device  1200   e.  For example, a length of a strut closest to the center of the occlusion device can be about 0.09 inches and a length of a strut closest to an end of the occlusion device can be about 0.06 inches. 
     As an example, a first ring of struts R 1  can have an axial length that is about 115% of a length of a second, adjacent ring of struts R 2 . For example, a first ring of struts R 1  can have an axial length of about 0.0910 inches and a second ring of struts R 2  can have an axial length of about 0.0785 inches. A second ring of struts R 2  can have an axial length that is about 112% of a length of a third, adjacent ring of struts R 3 . For example, a second ring of struts R 2  can have an axial length of about 0.0785 inches and a third ring of struts R 3  can have an axial length of about 0.0700 inches. A third ring of struts R 3  can have an axial length that is about 113% of a length of a fourth, adjacent ring of struts R 4 . For example, a third ring of struts R 3  can have an axial length of about 0.0700 inches and a second ring of struts R 2  can have an axial length of about 0.0620 inches. A fourth ring of struts R 4  can have an axial length that is about the same as a fifth adjacent ring of struts R 5 . For example, a fourth ring of struts R 4  and a fifth ring of struts R 5  can have an axial length of about 0.0.0620 inches. A fifth ring of struts R 5  can have an axial length that is about 103% of a length of a sixth, adjacent ring of struts R 6 . For example, a fifth ring of struts R 5  can have an axial length of about 0.0620 inches and a sixth ring of struts R 6  can have an axial length of about 0.06 inches. 
     A thickness in a circumferential direction of each strut  1210   e  can generally vary from an end of the occlusion device  1200   e  toward the central portion  1205   e  of the occlusion device  1200   e.  For example, a thickness of each strut  1200   e  can generally decrease from one or both ends of the occlusion device toward the central portion  1205   e  of the occlusion device  1200   e.  Varying the lengths and thicknesses of the struts can evenly distribute force across the occlusion device  1200   e,  which can decrease the chronic outward pressure the occlusion device  1200   e  exerts on the vessel or decrease the total length of the occlusion device  1200   e.  In the constrained configuration, a diameter of the occlusion device  1200   e  can decrease from the ends of the occlusion device  1200   e  toward the central portion  1205   e  of the occlusion device  1200   e.  For example, there can be a gradual decrease in diameter at an intermediate portion of the first end portion  1202   e  and an intermediate portion of the second end portion  1204   e.  The intermediate portions can be positioned the same distance from a center of the occlusion device  1200   e.  The intermediate portions can extend across a same axial length of the occlusion device  1200   e.  For example, each of the intermediate portions can extend across about less than 5 percent of an axial length of the entire length of the occlusion device  1200   e,  such as about three percent. The intermediate portions can begin at a position about 20 percent to about 40 percent of the axial length from an end of the occlusion device, such as between about 20 percent and about 30 percent or between about 30 percent and about 40 percent. Although the profile of the occlusion device  1200   e  can be symmetrical in the constrained position, as described above, the first and second end portions  1202   e,    1204   e  can expand into different configurations (see  FIG. 13A ). 
     When the occlusion device  1200   e  is deployed using the delivery system  200  (described above), the angle θ of the proximal hooks  1217   e  of the occlusion device  1200   e  can be optimized to maintain engagement between the occlusion device  1200   e  and the interlocking attachment member  231  during retraction (described above). For example, the angle θ can be between about 60 degrees and about 90 degrees, such as about 75 degrees. 
     When expanded, the ratio of strut width/thickness causes the struts and the hooks to twist approximately 90 degrees. Twisting the hooks allows for a relatively “tall” hook while keeping the embolic strut thickness low to provide a greater profile for secure fixation. 
     Similar to the occlusion device  1200   a,  the expandable frame  1206   e  can be at least partially covered by a thin membrane (partially removed to show tubular section  1250   e ) (e.g., between about 10 microns and about 30 microns thick) (see  FIG. 13A ). The membrane should be sufficiently thick to facilitate occlusion, while still minimizing the profile of the collapsed occlusion device  1200   e.  Possible materials for the membrane can include PTFE, PET, silicone, latex, TecoThane, nylon, PET, Carbothane (Bionate), fluoropolymers (e.g., PVDF), SIBS, TecoFlex, Pellethane, Kynar, or PLGA. 
     As described below, the membrane (not shown) can be applied to the expandable frame  1206   e  in a manner that encapsulates at least some of the struts  1210   e,  such that the membrane  1208   e  is present along either or both an interior surface and an exterior surface of the expandable frame  1206   e.  Possible methods of applying the membrane  1208   e  are described in further detail below. 
     The membrane can cover a portion of the occlusion device  1200   e  that is concave to the direction of the blood flow, which can be more occlusive and resist more migration than occlusion devices that only coat a surface convex to the direction of the blood flow or coat the entire occlusion device or coat the entire occlusion device. For example, the membrane  1208   e  can cover at least a portion of or the entire the second end portion  1204   e  and the first end portion  1202   e  can be a bare frame. When the bare first end portion  1202   e  is deployed before the covered second end portion  1204   e,  the bare first end portion  1202   e  can at least partially anchor the occlusion device  1200   e  in the vessel and allow visualization before deploying the covered second end portion  1204   e,  which facilitates precise placement of the occlusion device  1200   e.    
     The membrane can extend to form a thin extended tubular section of coating  1250   e  through which the guidewire (e.g., a 0.018″ guidewire) can be introduced (see  FIGS. 13A ). The thin tube  1250   e  acts like a valve (e.g., a duckbill valve) to occlude the guidewire lumen  1252   e  and aid in the capture and formation of clots. An end portion  1251   e  of the thin tube  1250   e  can have a reduced diameter compared to a remaining portion of the thin tube  1250   e  to facilitate the closing of the valve. The thin tube  1250   e  can include a portion  1253   e  that tapers toward the reduced diameter end portion  1251   e.    
     The central portion  1205   e  enables the occlusion device  1200   e  to bend around approximately a 90 degree bend at a vessel bifurcation according to the Trackability Protocol described below (e.g., in a simulated 3 mm vessel having a 7.5 mm radius to centerline of vessel or in a simulated 8 mm vessel having a 20 mm radius to centerline of vessel). The central portion  1205   e  can include flexibility features to increase the flexibility of the occlusion device  1200   e.  For example, the thickness of the struts  1210   e  near or at the central portion  1205   e  can be less than the thickness of the struts  1210   e  near or at the ends of the occlusion device  1200   e.    
       FIGS. 14A-14C  illustrate another embodiment of a vascular occlusion device. The vascular occlusion device can have any of the features recited in the above-mentioned vascular occlusion devices. 
     As shown in  FIG. 14A , the vascular occlusion device  1400  can include an expandable frame  1406 . The expandable frame  1406  can include an upstream lobe  1404  and a downstream lobe  1402  separated by a neck portion  1405 . The upstream lobe  1404  is sometimes referred to herein as an upstream portion, a proximal portion, proximal lobe, occlusive portion, or likewise. The downstream lobe  1402  is sometimes referred to herein as a downstream portion, a distal portion, a distal lobe, anchoring portion, or likewise. The neck portion  1405  is sometimes referred to herein as a central portion or likewise. 
     The upstream lobe  1404  can include a concave configuration that is concave in a direction opposite or away from a concave configuration of the downstream lobe  1402 . As shown in  FIG. 14A , the expandable frame can be generally asymmetric in that the upstream lobe  1404  can be longer in a longitudinal direction than the downstream lobe  1402 . Although, in other configurations, the downstream lobe  1402  can be longer than the upstream lobe  1404  or the expandable frame  1406  can be generally symmetrical in that the upstream lobe  1404  and the downstream lobe  1402  can be about the same length. 
     The neck portion  1405  can be expandable and/or flexible. For example, as shown in  FIG. 14A , the neck portion  1405  can include a cell structure enables expansion. Different configurations of neck portions that facilitate expansion and/or flexibility are described in more detail in U.S. Publication No. 2015/0039017, titled “METHODS AND DEVICES FOR ENDOVASCULAR EMBOLIZATION,” which is hereby incorporated by reference in its entirety herein. In other configurations, the neck portion  1405  may not be expandable and may, for example, be formed by a section of hypotube or other tubular structure. The neck portion  1405  can include a guidewire opening or other through-hole that provides access between the downstream lobe  1402  and the upstream lobe  1404 . 
     At least the upstream lobe  1404  of the frame  1406  can carry a covering  1408  (also referred to herein as a cover or a membrane). As shown in  FIG. 14A , the covering  1408  can be carried entirely by (e.g., supported by or likewise) the upstream lobe  1404 . However, in other configurations at least a portion of the covering  1408  may be carried by the downstream lobe  1402  and/or the neck portion  1405 . 
     The covering  1408  can include a tubular portion  1450  having a lumen at least partially aligned with the guidewire opening of the neck portion  1405 . The tubular portion  1450  can be configured to transition between an open configuration in which the tubular portion  1450  is configured to receive a guidewire and a closed configuration in which the tubular portion  1450  is configured to occlude blood flow therethrough, e.g., by collapsing inward and/or by folding over. 
     The tubular portion  1450  can be integrally formed with a remaining portion of the covering  1408 . Although, in other configurations, the tubular portion  1450  may be separately formed and attached to the remaining portion of the covering  1408  and/or frame  1406 . 
     As shown in  FIG. 14B , the tubular portion  1450  can include a reinforced portion  1450   a  anchored at its distal end with respect to the expandable frame  1406  and a free portion  1450   b  extending proximally into upstream lob  1404 . The reinforced portion  1450   a  can extend along a majority of a length of the tubular portion  1450  from the distal end in a proximal direction. For example, the reinforced portion  1450   a  can extend along between about 50% and about 75% of a length of the tubular portion  1450 , between about 60% and about 85% of a length of the tubular portion  1450 , or more. The reinforced portion  1450   a  can be integrally formed with the free portion  1450   b.  However, in other configurations, the reinforced portion  1450   a  and the free portion  1450   b  may be separately formed and attached to each other. For example, the free portion  1450   b  may be a valve that is separately attached to a tubular reinforced portion  1450   a.  The valve may be an elastomeric valve, such as a duckbill valve or an umbrella valve, or the valve may be a metal valve, such as a nitinol spring clip. 
     The tubular portion  1450  can extend in an upstream direction and at least partially through the upstream lobe  1404 , such that the free portion  1450   b  extends upstream of the reinforced portion  1450   a  (see  FIG. 14B ). As explained further below, the tubular portion  1450  can extend in the upstream direction prior to deployment and post-deployment. Although, in other configurations, the tubular portion  1450  may extend in the downstream direction prior to deployment and in the upstream direction post-deployment, or vice versa. 
     A wall thickness of at least a distal portion of the reinforced portion  1450   a  can be at least 2× (or at least 3×, 4×, 5×, or more) greater than a minimum wall thickness of the free portion  1450   b.  The wall thickness of each of the reinforced portion  1450   a  and the free portion  1450   b  can be generally uniform along a length of that portion. The transition in wall thickness between the anchored portion and the free portion can be a stepped transition. However, in other configurations, the change in thickness can be gradual. The thicker wall of the reinforced portion  1450   a  can prevent inversion of the tubular portion  1450  at least at pressures of at least about: 20 mmHg, 50 mmHg, 80 mmHg, 120 mmHg, or 150 mmHg. The thinner wall portion of the free portion  1450   b  can facilitate closure or occlusion of the free portion  1450   b  at least at pressures of less than or equal to about 150 mmHg, 120 mmHg, 80 mmHg, 50 mmHg, or 20 mmHg. 
     To further prevent inversion at the reinforced portion  1450   a  and/or facilitate closure or occlusion of the free portion  1450   b,  an average density of the wall of the reinforced portion  1450   a  can be greater than an average density of the wall of the free portion  1450   b,  e.g., at least about 5× greater, 8× greater, or 10× greater. In some configurations, the reinforced portion  1450   a  and the free portion  1450   b  can differ in other respects. For example, the reinforced portion  1450   a  can be non-porous, while the free portion  1450   b  can be porous. As another example, the reinforced portion  1450   a  can be substantially homogenous, while the free portion  1450   b  is not homogenous. 
     The tubular portion  1450  can be tapered such as from a larger diameter to a smaller diameter in the upstream direction and across at least a majority of a length, substantially the entire length, or the entire length of the tubular portion  1450 . As shown in  FIG. 14B , the tubular portion  1450  can be generally tapered from the anchor portion  1450   a  to the free portion  1450   b.  The tubular portion  1450  can be tapered at an angle of less than about: 15 degrees, 10 degrees, or 5 degrees, such as between about 0 degrees and about 4 degrees. 
     A diameter of the tubular portion  1450  can be between about 0.04″ and about 0.08″ at the downstream end and between about 0.03″ and about 0.05″ at the upstream end. A length of the tubular portion  1450  in the longitudinal direction can be between about 0.31″ and about 0.35″. A ratio between a length of the tubular portion  1450  and a length of the upstream lobe  1404  can be between about 1:2 and about 3:2. For example, the length of the tubular portion  1450  can be about the same as the axial length of the upstream lobe  1404 . As another example, the length of the tubular portion  1450  can be at least about 50% or at least about 75% of the length of the upstream lobe, or greater than the length of the upstream lobe  1404 , such that an end of the tubular portion  1450  extends outward of an open end of the upstream lobe  1404 . 
     As mentioned above, the covering  1408  can be carried by at least the interior surface, exterior surface, or both the interior and exterior surface of the upstream lobe  1404 . The covering  1408  can extend from a junction  1407  between the neck portion  1405  to the open end of the upstream lobe  1404 . The covering  1408  can include a first portion  1408   a  extending from the junction  1407  to a shoulder portion  1409  of the upstream lobe  1404  and a second portion  1408   b  extending from the shoulder portion  1409  toward or to the open end of the upstream lobe  1404 . The first portion  1408   a  and the second portion  1408   b  can be porous or woven to provide flexibility and prevent tearing when the expandable structure  1406  expands. The expansion ratio can be at least about: 5:1, 6:1, 7:1, or more. A wall thickness of the first portion  1408   a  can be thicker than a wall thickness of the second portion  1408   b  and/or a wall thickness of the reinforced portion  1450   a,  e.g., at least about 3×, 5×, or 10× thicker. 
     Although the above described occlusion device  1400  is described with a tubular portion  1450  that may fold over to occlude blood flow or include a valve that occludes blood flow through the tubular portion  1450 , the occlusion device and/or delivery system may include alternative or additional features to facilitate closure of the tubular portion  1450  (if present) or other guidewire lumen or opening. 
     In some embodiments, the occlusion device  1400  may include a valve instead of the tubular portion  1450 . The valve can be configured to occlude the guidewire opening in the neck portion  1405  when the guidewire is removed. The valve may be an elastomeric valve, such as a duckbill valve or an umbrella valve, or the valve may be a metal valve, such as a nitinol spring clip. 
     In some embodiments, the neck portion  1450  may be pre-deformed to a closed configuration (e.g., to occlude the guidewire opening). Prior to delivering the occlusion device  1400 , the occlusion device  1400  can be loaded into the delivery system with an elongate support tube or other tubular structure extending through the neck portion  1450 . The support tube can maintain the guidewire opening in an open configuration so the occlusion device  1400  can be advanced over a guidewire. When the elongate support tube is removed, the neck portion can collapse to the pre-deformed, closed configuration. For example, with a nitinol frame, the neck portion  1450  can be heat set to a closed configuration. 
     In some embodiments, the occlusion device  1400  may include an inflatable member within the tubular portion  1450  or the neck portion  1405 . After the occlusion device  1400  has been delivered to the target site, the inflatable member may be inflated to occlude the tubular portion  1450  or neck portion  1405 . The delivery system may include an inflation lumen to inflate the inflatable member after the guidewire is removed. 
     In some embodiments, the guidewire or elongate support tube extending through the guidewire opening may support (e.g., external to the guidewire or elongate support tube) a plug or other occluding element distal to the occlusion device  1400 . After the occlusion device  1400  has been delivered to the target site, the guidewire or elongate support tube may be retracted. As the plug reaches the tubular portion  1450  or guidewire opening, the plug can be deposited to occlude the tubular portion  1450  or guidewire opening and removed from the guidewire or elongate support tube. 
     Although the embodiment shown in  FIGS. 14A-14C  is described with respect to an expandable frame having downstream and upstream lobes  1402 ,  1404  with opposing concave configurations, any features of the covering  1408  can be used with any of the expandable frame structures described herein or in U.S. Publication No. 2015/0039017, titled “METHODS AND DEVICES FOR ENDOVASCULAR EMBOLIZATION,” which is hereby incorporated by reference in its entirety. For example, the covering  1408 , with or without the tubular portion  1450 , can be applied to an expandable frame in which the concave configurations of an upstream portion and a downstream portion face each other (see e.g.,  FIGS. 9A-9C ). The expandable frame may include guidewire openings at either end of the expandable frame, such that the expandable frame may be delivered over a guidewire. The covering  1408  can be supported by the downstream and/or the upstream portion. Any of the alternative features described above for occluding a guidewire lumen or opening in the neck portion  1405  of occlusion device  1400  may also be used to occlude guidewire openings in the alternative frame configurations. 
     Any of the alternative frame configurations may also include an inner tubular structure extending through the expandable frame that serves as a guidewire lumen. The inner tubular structure may be occluded using any of features described above. For example, the inner tubular structure may be pre-deformed to a collapsed configuration. The delivery system can include an elongate support tube or tubular structure that maintains the inner tubular structure in an open configuration during delivery. When the inner tubular structure is removed, the inner tubular structure can collapse to the pre-deformed, closed configuration. 
     The occlusion device  1400  can be deployed using any of the delivery systems described herein or in U.S. Publication No.  2015 / 0039017 , titled “METHODS AND DEVICES FOR ENDOVASCULAR EMBOLIZATION,” which is hereby incorporated by reference in its entirety. 
     In use, the delivery system may be advanced over a guidewire and into a target vessel. The delivery system may carry the occlusion device  1400  in a collapsed configuration by extending a support shaft longitudinally through the occlusion device and/or by interfacing with markers  1442  of the occlusion device. As shown in  FIG. 14A , one or more markers  1442  may be positioned at proximal or distal end of the device, e.g., the markers  1442  may be press-fit onto the strut endings of the expandable frame  1406 . The markers  1442  may have eyelets or any other feature described in U.S. Publication No. 2015/0039017, titled “METHODS AND DEVICES FOR ENDOVASCULAR EMBOLIZATION,” which is hereby incorporated by reference in its entirety herein. These markers  1442  may be radiopaque and provide visual guidance of the ends of the expandable frame  1406 . These markers  1442  may form an interference fit with an interference feature of the delivery system. 
     While the delivery system is being advanced to the target vessel, the tubular portion  1450  extends upstream and through the upstream lobe  1404  with the guidewire extending through the tubular portion  1450 . When the occlusion device  1400  is properly positioned, the occlusion device  1400  can be expanded by retracting an outer sheath and/or by advancing the support shaft to remove the radial restraint. Depending on the delivery system, if the occlusion device  1400  is improperly positioned, it may be possible to re-collapse the occlusion device  1400 . For example, if the markers  1442  at a proximal end of the occlusion device  1400  form an interference fit with an interference feature of the delivery system. The occlusion device  1400  may be proximally retracted back into the delivery sheath. The occlusion device  1400  may be re-collapsed so long as the markers  1442  have not been released from the interference feature. 
     After the occlusion device has been released, the delivery system and the guidewire may be withdrawn. As the guidewire is removed from the tubular portion  1450 , the tubular portion  1450  continues to extend in the upstream direction and through the upstream lobe  1404 . Once the guidewire is removed, the tubular portion  1450  transitions from an open configuration with a thru-lumen to a closed configuration in response to arterial pressure in which the tubular portion  1450  occludes blood flow at pressures of at least about: 20 mmHg, 50 mmHg, 80 mmHg, 120 mmHg, 150 mmHg, or ranges inbetween. For example, as shown in  FIG. 14C , the tubular portion  1450  may occlude blood flow by collapsing the free portion  1450   b.  A wall thickness of the free portion  1450   b  is sufficiently thin that the walls of the free portion  1450   b  collapse inward to occlude the tubular portion. 
     Additionally or alternatively, the tubular portion  1450  may fold over, e.g., at a position between an anchored end and a free end of the tubular portion  1450 , to further occlude blood flow through the tubular portion  1450 . 
     In an alternative configuration, the delivery system may be advanced over a guidewire without advancing the occlusion device over the guidewire. For example, the delivery system may include an outer catheter with a single lumen. When the delivery system is advanced over the guidewire, the guidewire is positioned radially outward of the occlusion device or radially between the occlusion device and the outer catheter when the occlusion device is positioned at a distal portion of the outer catheter. As another example, the delivery system may include an outer catheter with at least two lumens. The guidewire may extend through a first lumen, while the occlusion device is advanced through or positioned in a second lumen. Radiopacity 
     As shown in  FIG. 12A , a tubular marker  1214   a  can be positioned around a central portion  1205   a,  such that the expanded first and second end portions  1202   a,    1204   a  prevent migration of the tubular marker  1214   a.    
     The shape of the expandable frame fully constrains the tubular marker without crimping the marker to the frame, which reduces stress applied to the underlying frame. Further, since the diameter of the tubular markers is no greater than the outer diameter of the occlusion device, the tubular markers do not increase the delivery profile of the occlusion device. In certain aspects, a coating can be applied over the tubular markers. 
     In some embodiments, at least one radiopaque marker (e.g., two, three, or four) can be positioned (e.g., crimped, press-fit) on at least one end of the expandable frame. For example, one radiopaque marker  1214 ′ can be positioned at the second end portion  1204 ′ of the occlusion device  1200   a ′, and another radiopaque marker can be positioned at the second end portion of the occlusion device (not shown). Positioning these markers on the ends of an occlusion device having expanding ends (e.g., occlusion device  1200   a - 1 ) facilitates visualization of the occlusion device moving between the compressed and expanded configurations.  FIGS. 2Q and 2R  illustrate another occlusion device O having markers  242 ′ press-fit onto strut endings of the occlusion device O. The markers  242 ′ can include an aperture  246 ′ and a neck portion  244 ′ (e.g., a lollipop shape) to facilitate certain retraction capabilities, as described above. 
     In some embodiments, a fine radiopaque powder can be added to the membrane material to make the entire coating visible. Integrating the radiopaque marker into the coating eliminates the manufacturing step of having to secure a marker to the occlusion device. Alternatively, the fine radiopaque powder can be painted onto the occlusion device or the occlusion device can be dipped into the radiopaque powder. 
     Methods of Coating the Expandable Frame 
     In any of the occlusion devices described above, a membrane can be deposited at least substantially uniformly using an electrospinning process. Further, using an electrospinning process, the porosity can be controlled of the membrane can be controlled to achieve different properties. For example, the membrane can be formed having sufficient tensile strength to resist yielding, stretching, or breaking under at least normal blood pressures, preferably at least about 140 mmHg or 160 mmHg. Further, the fibers forming the membrane can have a cross-sectional diameter between about 5 microns and about 25 microns, such that the membrane can be elongated at least about two to five times greater with 25%-75% less force than that of the native material having the same thickness. An average pore size can be less than or equal to about 100 microns or less than or equal to about 50 microns. Additionally, the coated occlusion device can weigh less than or equal to about 1 gram, preferably less than or equal to about 0.6 grams. 
     In general, the expandable frame can be coated by applying a dissolved polymer onto the expandable frame to encapsulate at least some of the struts or strands. The membrane material can be heated to form a viscous liquid solution that is placed in a syringe. The membrane material can be advanced by a piston or plunger through a nozzle having one or more outlets, where the material flows out onto a rotating mandrel as fine fibers. The fine fibers can form a fibrous mat or covering of biocompatible covering material on the rotating mandrel. As the membrane material cools, the fibers solidify, and adjacent, contacting fibers are sintered to one another. Controlling the number of layers of fiber that are applied to the rotating mandrel provides control over the porosity of membrane. 
     The method can include providing a mandrel in the shape of the expandable frame. Optionally, portions of the mandrel can be masked to outline the form of an inner coating. Thereafter, an inner coating can be applied to the mandrel using an electrospinning process. When the inner coating is complete, the expandable frame can be positioned over the inner coating, such that the expandable frame is in intimate contact with the inner coating. If portions of the expandable frame are intended to remain uncovered, those uncovered portions can be masked before application of the outer coating. For example, the expandable frame can be masked by loading uncovered portions of the expandable frame into a tube. The outer coating can adhere to the inner coating to from a single coating that encapsulates at least some of struts or strand portions. 
     Depending on the membrane material, application of the inner coating to the membrane may be unnecessary. For example, if the membrane includes Kynar, a single outer coating can be applied to the expandable frame without the use of a mandrel. The single outer coating can flow around the struts or strands to encapsulate and adhere to the struts or strands. Application of the outer coating alone can also be useful for occlusion device designs that may be difficult to position on a mandrel. 
     The suitability of the membrane can be determined using a number of factors. For example, when visually inspecting the membrane, the membrane should not include any cuts, tears, or large gaps. Further, for at least a Kynar membrane, the membrane should be white or opaque, which suggests that the membrane has a porosity and that the membrane is sufficiently flexible. As another example, the coated occlusion device should allow less than or equal to about 200 cc/min at 20 mmHg, such as to between about 50 cc/min and about 150 cc/min, preferably less than about 130 cc/min, less than about 100 cc/min at 20 mmHg or less than about 65 cc/min at 20 mmHg within about five minutes. Further, the occlusion device  1200   a  can limit the flow rate through a vessel to no more than about 400 cc/min at 60 mmHg or no more than about 330 cc/min at 60 mmHg, such as to between about 150 cc/min and about 250 cc/min, preferably less than or equal to about 175 cc/min at 60 mmHg within about five minutes. The occlusion device  1200   a  can limit the flow rate through a vessel to about no more than 600 cc/min at about 100 mmHg or 430 cc/min at 100 mmHg, such as to between about 200 mmHg and about 250 mmHg, preferably less than about 225 cc/min at about 100 mmHg within about five minutes, according to the Occlusion Protocol described below. Additionally, the force to load the coated occlusion device should be less than or equal to about 0.5 lbs. 
     In some embodiments, the mandrel can have a thin, elongated section that extends through the center of the occlusion device. When the membrane  1208   a  is formed, the coating can be applied to the elongated section to produce a thin extended tubular section of coating  1250   a  through which the guide wire (e.g., a 0.018″ guidewire) can be introduced (see  13 A). Further, depending on the membrane material, the elongated inner mandrel can help eliminate irregular buildup of coating on the mandrel. The elongated mandrel can also aids in reducing stray charges from carrying the coating away from the mandrel. 
     In any of the embodiments disclosed herein configured for over the wire delivery, a small (e.g., approximately 0.020″) aperture will remain in the membrane following removal of the guide wire. Occlusion will be primarily mechanical due to the membrane, but a small blood flow through the guidewire aperture will gradually stop via natural biological mechanisms. It may be desirable to achieve rapid, essentially completely mechanical occlusion, which can be done by mechanically patching the aperture. This can be accomplished in any of a variety of ways, by placing an occluder across the aperture. The occluder may take the form of a flap of material attached to the membrane of frame or a plug that is forced by blood flow into or across the opening following retraction of the guidewire. 
     Method of Delivering an Occlusion Device 
     The occlusion devices described herein can be advanced to the target vessel using any of the delivery systems described herein. In use, the access to the vasculature can be provided using conventional techniques through an incision on a peripheral artery, such as right femoral artery, left femoral artery, right radial artery, left radial artery, right brachial artery, left brachial artery, right axillary artery, left axillary artery, right subclavian artery, or left subclavian artery. An incision can also be made on right carotid artery or left carotid artery in emergencies. 
     The guide wire  128  (e.g., 0.018″ guidewire or smaller) can be delivered to the target vessel. Thereafter, the delivery system  100 ,  200  can be delivered over the guide wire  128  to the target vessel with sufficient trackability as defined herein. The outer catheter  110 ,  210  (e.g.,  5 F or smaller) and the inner catheter  120 ,  220  can be delivered together with the occlusion device pre-loaded into the delivery system  100 ,  200 . Alternatively, the outer catheter  110 ,  210  can be delivered first, followed by the inner catheter  120 ,  220  carrying the occlusion device. Once the delivery system  100 ,  200  has been delivered to the target vessel, the inner catheter  120 ,  220  can move axially until the occlusion device extends from the distal end  114 ,  224  of the outer catheter  110 ,  220 , as shown in  FIG. 3A . In some embodiments, the outer catheter  110 ,  210  can include features shown in  FIGS. 1B-1 or 2N  to delivery contrast dye and monitor performance of the occlusion device. In some instances, after the performance assessment, it may be necessary to resheath and reposition the occlusion device to position the occlusion device accurately. 
     The occlusion device can be released from the delivery system  100 ,  200  using any of the techniques described above or any other conventional technique (see e.g.,  FIGS. 2A to 2K  and related discussion). Alternatively, as shown in  FIGS. 3D-3F , the support tube  134  can move axially to push the occlusion device off the inner catheter  120 . Alternatively, the delivery system  100  may utilize any of the interlock assemblies  150 ,  170 , or  180  described herein. 
     As described above, in some embodiments, the occlusion device can include one opened end and one closed end (e.g., covered, structurally closed, or otherwise blocked). In some instances, the closed end can be downstream from the opened end. Preferably, the closed end would be on the upstream end of the device. This would have the tendency to minimize “wind-socking” of the device due to blood flow forces and would permit the open downstream end to act as an anchor. Blood pressure on the occluded upstream end would have the effect of foreshortening the device frame, which would secondarily cause an expansion of the distal end accentuating the anchoring force of the device. This effect is particularly evident in a braided frame in which the downstream end is open. 
     In other embodiments, the occlusion device can include an hourglass design (see, e.g.,  FIG. 12A or 13A ). As described above, it can be preferable to deploy a bare, distal portion prior to deploying a covered, proximal portion. The bare end portion can at least partially anchor the occlusion device in the vessel before deploying the covered second end portion, which facilitates precise placement of the occlusion device. Further, when the covered end portion is upstream (i.e., proximal) from the bare end portion, the increase in arterial pressure at the proximal end increases the radially outward forces that can help the occlusion device resist migration. 
     In some instances, as shown in  FIG. 2S , the delivery system can include a test balloon  132 . Prior to deploying the occlusion device O, the test balloon  132  can be inflated through inflation lumen  134  to occlude the vessel temporarily. After the occlusion device O is delivered, the test balloon  132  can be deflated, and the delivery system can be withdrawn. 
     In certain variants, the occlusion device can be reinforced using other reinforcing devices or techniques. For example, one or more coils can be deployed within the expandable structure. As another example, the expandable structure can be reinforced with an occlusion balloon. In yet another example, the method can include ligation to close off the target vessel. 
     The performance characteristics of the present disclosure are verified using a series of in vitro test protocols, including: (1) Delivery, Deployment, and Retraction Test Protocol; (2) Acute Migration Test Protocol; (3) Occlusion Effectiveness Test Protocol; and (4) Contrast injection Test Protocol. The details of the test protocols are disclosed in U.S. patent application Ser. No. 14/449,037 to Cragg et al., the disclosure of which is hereby incorporated by reference in its entirety herein. Methods of Providing a Primary Occlusion Device and a Secondary Treatment 
     A common delivery system may be used to provide a primary treatment with an occlusion device and provide one or more secondary treatments, which may include delivering a therapeutic agent (see  FIGS. 15A to 15D ) or providing the secondary treatment with a treatment instrument (see  FIGS. 16A to 16D ). The occlusion device used in the primary treatment may include any of the features of the occlusion devices described above. Possible therapeutic agents include, but are not limited to, bland particles and/or beads, radioactive particles, drug eluting beads, liquids, gels, or otherwise. The secondary treatment may include embolic coils or ablation therapy. 
     As shown in  FIGS. 15A , the delivery system  1510  may include an outer body  1514  and an inner body  1512  with one or more through-lumens. The inner body  1512  may be disposed within the outer body  1514 . The one or more through-lumens may allow for tracking over a pre-placed guidewire, delivery of therapeutic agent, and/or deliver of a treatment instrument. The one or more through-lumens may also provide a passageway for contrast media to enable the clinical to visualize immediate occlusion during the procedure under fluoroscopy. In some implementations, the inner body  1512  may include a single lumen to provide each of these functions. In other implementations, the inner body  1512  may include multiple lumens, for example a guidewire lumen and a separate lumen for the delivery of therapeutic agent and/or advancement of a treatment instrument. 
     The occlusion device  1500  may be pre-loaded in the delivery system  1510  prior to introducing the delivery system  1510  into the patient. The occlusion device  1500  may be carried by the inner body  1512  in a position between the inner body  1512  and the outer body  1514 . The outer body  1514  may radially constrain or compress the occlusion device  1500 . The occlusion device  1500  may interface with the inner body  1512  using one or more interlocking features. The occlusion device  1500  may remain interlocked with the inner body  1512  until the entire occlusion device  1500  has been released from the outer body  1514 . 
     As shown in  FIGS. 15B to 15D , the occlusion device  1500  may include an expandable frame. The occlusion device  1500  may include a downstream portion  1502  and an upstream portion  1504 . The downstream portion  1502  may be configured to anchor the occlusion device  1500 . The upstream portion  1504  may be configured to provide occlusion. For example, the expandable frame may carry an occlusive membrane along at least a portion of the upstream portion  1504 . The downstream portion  1502  may be separated from the upstream portion  1504  by a neck portion  1505 . Although the occlusion device  1500  is described with respect to a downstream portion  1502  and an upstream portion  1504 , features of the downstream portion  1502  and the upstream portion  1504  are interchangeable. 
     The upstream portion  1504  may include a concave configuration that is concave in a direction opposite or away from a concave configuration of the downstream portion  1502 . The expandable frame may be generally asymmetric. For example, the upstream portion  1504  may be longer in a longitudinal direction than the downstream portion  1502 . In other configurations, the downstream portion  1502  may be longer than the upstream portion  1504 , or the expandable frame may be generally symmetrical in that the upstream portion  1504  and the downstream portion  1502  may be about the same length. 
     The neck portion  1505  may be expandable and/or flexible. For example, the neck portion  1505  may include a cell structure enables expansion. In other configurations, the neck portion  1505  may not be expandable. For example, the neck portion  1505  may be formed by a section of hypotube or other tubular structure. The occlusion device  1500  can include a guidewire opening or other through-hole, for example through the neck portion  1505  for access between the downstream portion  1502  and the upstream portion  1504 . 
     Similar to the occlusion device  1400 , the occlusive membrane may include a collapsible portion having a lumen at least partially aligned with the opening of the neck portion  1505 . The collapsible portion can be configured to transition between an open configuration in which the tubular portion is configured to receive a guidewire and a closed configuration in which the collapsible portion is configured to occlude blood flow therethrough, e.g., by collapsing inward and/or by folding over. The collapsible portion can extend in an upstream direction and at least partially through the upstream portion  1504 . In other configurations, the occlusion device  1500  may include a valve or other feature to occlude blood flow through the opening of the neck portion  1505 . 
     The occlusion device  1500  may include one or more radiopaque markers positioned at proximal or distal end of the device. These radiopaque markers may provide visual guidance of the ends of the expandable frame. 
     In use, the delivery system  1510  may be advanced into a target vessel (see  FIG. 15A ), for example over a guidewire or through an access catheter. The delivery system  1510  may carry the occlusion device  1500  by extending the inner body  1512  longitudinally through the occlusion device  1500  and/or by interfacing with the radiopaque markers on the occlusion device  1500 . The inner body  1512  may extend through an opening of the occlusion device  1500 . For example, the inner body  1512  may extend through the collapsible portion of the occlusive membrane in the upstream portion  1504 , through the opening of the neck portion  1505 , and through the downstream portion  1502 . The distal end of the inner body  1512  may extend distally beyond the downstream end of the occlusion device  1500 . 
     Once the delivery system  1510  reaches the vessel, the occlusion device  1500  can be at least partially deployed from the outer body  1514  of the delivery system  1510  (see  FIG. 15B ). The occlusion device  1500  may be expanded by retracting the outer body  1514  and/or by advancing the inner body  1512  to remove the radial restraint. As the occlusion device  1500  is released from the outer body  1514 , the downstream portion  1502  begins to expand. If the occlusion device  1500  is improperly positioned, it may be possible to re-collapse the occlusion device  1500  back into the outer body  1514 . As the upstream portion  1504  is released from the outer body  1514 , the upstream portion  1504  begins to expand (see  FIG. 15C ). During deployment, a distal end of the inner body  1512  may extend beyond the opening in the neck portion  1505  of the occlusion device  1500 . The distal end of the inner body  1512  may extend into the downstream portion  1502  of the occlusion device  1500  or distally of the downstream end of the occlusion device  1500 . 
     At any point during the procedure, a therapeutic agent  1520  (e.g., bland particles, beads, radioactive particles, and/or chemotherapy drug eluding beads) may be delivered from the through-lumen of the inner body  1512 . The therapeutic agent  1520  may be released from the opening at the distal end of the inner body  1512 . For example, the therapeutic agent  1520  may be delivered prior to deployment of the occlusion device  1500  (see  FIG. 15A ), after partial deployment of the occlusion device  1500  (see  FIG. 15B ), and/or after full deployment of the occlusion device  1500  (see  FIG. 15C ). As shown in  FIG. 15C , the therapeutic agent  1520  may be delivered from the through-lumen of the inner body  1512 , while the inner body  1512  extends through the occlusion device  1500 . Prior to delivering the therapeutic agent  1520 , the guidewire may be withdrawn from the inner body  1512  to increase fluid flow through the through-lumen of the inner body  1512 . The therapeutic agent  1520  may be delivered downstream of the opening in the neck portion  1505  of the occlusion device  1500 . The therapeutic agent  1520  may be delivered in the downstream portion  1502  of the occlusion device  1500  or distally of the downstream end of the occlusion device  1500 . Once the therapeutic agent  1520  has been released into the vessel, the therapeutic agent  1522  may remain generally in the region of delivery or travel downstream to a target site. Reflux of the therapeutic agent  1520  may be prevented by the upstream portion  1504  of the occlusion device  1500 . For example, reflux of therapeutic agent  1520  may be prevented by the downstream face of the occlusive membrane and/or the collapsible portion. Delivery of the therapeutic agent  1520  while the blood flow is arrested provides local delivery of the agent in a denser dose and prevents dilution of the agent as is experienced with systemic delivery. Delivery of the agent while flow is blocked can prevent the blockage of collateral blood flow. Embolization prevents distribution of therapeutic agent to non-target locations. 
     In some methods, embolic coils or other secondary treatment devices can be delivered to other locations prior to the delivery of therapeutic agents, for example downstream or upstream of the occlusion device  1500 . The secondary treatment device may restrict the therapeutic agent  1520  to a region between the secondary treatment device and the occlusion device  1500 . 
     After the occlusion device  1500  has been released from the outer body  1514  and the therapeutic agent  1520  has been released, the inner body  1512  may be withdrawn from the opening of the neck portion  1505  and/or the collapsible portion of the occlusive membrane (see  FIG. 15D ). As the inner body  1512  is withdrawn from the collapsible portion (or other valve structure), the collapsible portion collapses to occlude blood flow through the opening of the neck portion  1505 . After the inner body  1512  has been withdrawn from the occlusion device  1500 , it may be possible to reaccess an opening of the occlusion device  1500  during the same procedure or a separate procedure, particularly if there is a valve structure disposed in the neck portion  1505 . A tubular body may be advanced through the opening of the neck portion  1505  to deliver additional therapeutic agent. As illustrated, the therapeutic agent  1520  may be delivered downstream of the occlusion device  1500 , but in other methods, the therapeutic agent  1520  may be delivered upstream of the occlusion device  1500  after the inner body  1512  has been retracted from the occlusion device  1500 . After the inner body  1512  has been withdrawn, the entire delivery system  1510  may be withdrawn leaving the occlusion device  1500  in the vessel. 
     Examples of procedures that can utilize the above-described method include, but are not limited to, trans-arterial chemoembolization (TACE), drug-eluting bead chemoembolization (DEB-TACE), radioembolization (RE), and injection of sclerosants for embolization at the very small-vessel and tissue level. Liver cancer is one example of a disease where this device may be effective as the liver has two blood supplies. The portal vein feeds most of the liver cells. Cancer in the liver is fed by the hepatic artery. The occlusion device  1500  can be deployed in the hepatic artery to cut off the blood supply to the tumor and kill off the cancer cells. The healthy liver cells would still get their blood supply from the portal vein. Additional cancer treatment can be delivered to the tumor in the patient&#39;s liver by injecting an agent through the delivery system  1510  to a specific, localized site. This treatment will not be systemic since the blood flow is arrested by the occlusion device  1500 . 
       FIGS. 16A to 16D  illustrate a delivery system  1610  that may be used to deliver an implantable occlusion device  1600  and provide a secondary treatment using a treatment instrument  1622 . The delivery system  1610  and the occlusion device  1600  may include any of the features described above. The secondary treatment may be provided upstream or downstream of the occlusion device  1600 . As shown in  FIGS. 16A , the delivery system  1610  may include an inner body  1612  and an outer body  1614 . The occlusion device  1600  may be carried between the inner body  1612  and the outer body  1614 . The inner body  1612  may be used as a working channel for the treatment instrument  1622 . The treatment instrument  1622  may be an ablation device, for example a steerable ablation needle. 
     In use, the delivery system  1610  may be advanced into a target vessel (see  FIG. 16A ), for example over a guidewire or through an access catheter. The delivery system  1610  may carry the occlusion device  1600  in a collapsed configuration by extending the inner body  1612  longitudinally through an opening of the occlusion device  1600  and/or by interfacing with the radiopaque markers on the occlusion device  1600 . For example, the inner body  1612  may extend through the collapsible portion of the occlusive membrane in the upstream portion  1604 , through the opening of the neck portion  1605 , and through the downstream portion  1602 . 
     Once the delivery system  1610  reaches the vessel, the occlusion device  1600  can be at least partially deployed from the outer body  1614  of the delivery system  1610  (see  FIG. 16B ). The occlusion device  1600  may be expanded by retracting the outer body  1614  and/or by advancing the inner body  1612  to remove the radial restraint. As the occlusion device  1600  is released from the outer body  1614 , the downstream portion  1602  begins to expand. If the occlusion device  1600  is improperly positioned, it may be possible to re-collapse the occlusion device  1600  in the outer body  1614 . As the upstream portion  1604  is released from the outer body  1614 , the upstream portion  1604  begins to expand (see  FIG. 16C ). During deployment, a distal end of the inner body  1612  may extend beyond the opening in the neck portion  1605  of the occlusion device  1600 . The distal end of the inner body  1612  may extend into the downstream portion  1602  of the occlusion device  1600  or distally of the downstream end of the occlusion device  1600 . 
     At any point during the procedure, an end effector of a treatment instrument  1622  (e.g., an ablation device) may be advanced through the working channel of the inner body  1612 . The treatment instrument  1622  may be advanced through the working channel of the inner body  1612 , while the inner body  1612  extends through the opening of the neck portion  1605 . The end effector of the treatment instrument  1622  may be advanced distally of the downstream end of the occlusion device  1600 . The treatment instrument  1622  may be advanced distally of the occlusion device  1600  prior to deployment of the occlusion device  1600  (see  FIG. 16A ), after partial deployment of the occlusion device  1600  (see  FIG. 16B ), and/or after full deployment of the occlusion device  1600  (see  FIG. 16C ). The treatment instrument  1622  may perform a treatment prior to deployment of the occlusion device  1600  (see  FIG. 16A ), after partial deployment of the occlusion device  1600  (see  FIG. 16B ), and/or after full deployment of the occlusion device  1600  (see  FIG. 16C ). Treatment may be provided at one or more time points during a single procedure. Prior to advancing the treatment instrument  1622  through the occlusion device  1600 , the guidewire may be withdrawn from the inner body  1612 . 
     After the occlusion device  1600  has been released from the outer body  1614 , the inner body  1612  may be withdrawn from the opening of the neck portion  1605  and, if present, the collapsible portion of the occlusive membrane (see  FIG. 16D ). As the inner body  1612  is withdrawn from the collapsible portion (or other valve structure), the collapsible portion collapses to occlude blood flow through the opening of the neck portion  1605 . After the inner body  1612  has been withdrawn from the occlusion device  1600 , it may be possible to reaccess the opening of the occlusion device  1600  during the same procedure or a separate procedure, particularly if there is a valve structure disposed in the neck portion  1605 . A tubular body may be advanced through the opening of the neck portion  1605  to deliver additional therapeutic agent. As illustrated, the secondary treatment may be performed downstream of the occlusion device  1600 , but in other methods, the secondary treatment may be performed upstream of the occlusion device  1600  after the inner body  1612  has been withdrawn from the occlusion device  1600 . After the inner body  1612  has been withdrawn, the entire delivery system  1610  may be withdrawn leaving the occlusion device  1600  in the vessel. 
     In some implementations, the treatment instrument  1622  can be used to treat a tumor in combination with the occlusion device  1600  and/or the therapeutic agent  1620 . For example, the delivery system  1610  may be used to treat liver cancer. The occlusion device  1600  can be deployed in the hepatic artery to cut off the blood supply to the tumor and kill off the cancer cells. Additionally, the tumor may be treated with ablation therapy using an ablation needle. The ablation needle can be navigated through the inner body  1612  of the delivery system  1610 , which extends through the opening of the occlusion device  1600 , to provide ablation therapy downstream of the occlusion device  1600 . The ablation needle may include an end effector, such as an electrode for RF therapy or an antenna for microwave therapy, for treating a tumor downstream of the occlusion device. The combination of the occlusion device  1600  and the ablation therapy would improve the overall treatment of the tumor. 
     Terminology 
     Conditional language, such as “can,” “could,” “might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements, and/or steps. Thus, such conditional language is not generally intended to imply that features, elements, and/or steps are in any way required for one or more embodiments, whether these features, elements, and/or steps are included or are to be performed in any particular embodiment. 
     The terms “approximately,” “about,” and “substantially” as used herein represent an amount close to the stated amount that still performs a desired function or achieves a desired result. For example, depending on the context, the terms “approximately”, “about”, and “substantially” may refer to an amount that is within less than 10% of, within less than 5% of, within less than 1% of, within less than 0.1% of, and within less than 0.01% of the stated amount. 
     The ranges disclosed herein also encompass any and all overlap, sub-ranges, and combinations thereof. Language such as “up to,” “at least,” “greater than,” “less than,” “between” and the like includes the number recited. Numbers preceded by a term such as “about” or “approximately” include the recited numbers. For example, “about 3 mm” includes “3 mm.” 
     The ranges provided herein are set forth solely for illustrating typical device dimensions. The actual dimensions of a device constructed according to the principles of the present invention may obviously vary outside of the listed ranges without departing from those basic principles. For example, diameter outside of the preferred ranges may also be used, provided that the functional consequences of the diameter are acceptable for the intended purpose of the catheter. In particular, the lower limit of the diameter for any portion of catheter body  110  in a given application will be a function of the number of fluid or other functional lumen contained in the catheter, together with the acceptable minimum aspiration flow rate and collapse resistance. 
     Although certain embodiments and examples have been described herein, it will be understood by those skilled in the art that many aspects of the methods and devices shown and described in the present disclosure may be differently combined and/or modified to form still further embodiments or acceptable examples. All such modifications and variations are intended to be included herein within the scope of this disclosure. A wide variety of designs and approaches are possible. No feature, structure, or step disclosed herein is essential or indispensable. 
     Any methods disclosed herein need not be performed in the order recited. The methods disclosed herein include certain actions taken by a practitioner; however, they can also include any third-party instruction of those actions, either expressly or by implication. For example, actions such as “expanding an expandable structure” includes “instructing expansion of an expandable structure.” 
     Some embodiments have been described in connection with the accompanying drawings. However, it should be understood that the figures are not drawn to scale. Distances, angles, etc. are merely illustrative and do not necessarily bear an exact relationship to actual dimensions and layout of the devices illustrated. Components can be added, removed, and/or rearranged. Further, the disclosure herein of any particular feature, aspect, method, property, characteristic, quality, attribute, element, or the like in connection with various embodiments can be used in all other embodiments set forth herein. 
     Additionally, it will be recognized that any methods described herein may be practiced using any device suitable for performing the recited steps. 
     For purposes of this disclosure, certain aspects, advantages, and novel features are described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the disclosure may be embodied or carried out in a manner that achieves one advantage or a group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein. 
     Moreover, while illustrative embodiments have been described herein, the scope of any and all embodiments having equivalent elements, modifications, omissions, combinations (e.g., of aspects across various embodiments), adaptations and/or alterations as would be appreciated by those in the art based on the present disclosure. The limitations in the claims are to be interpreted broadly based on the language employed in the claims and not limited to the examples described in the present specification or during the prosecution of the application, which examples are to be construed as non-exclusive. Further, the actions of the disclosed processes and methods may be modified in any manner, including by reordering actions and/or inserting additional actions and/or deleting actions. It is intended, therefore, that the specification and examples be considered as illustrative only, with a true scope and spirit being indicated by the claims and their full scope of equivalents.