Patent Publication Number: US-2021186700-A1

Title: Vascular valve prosthesis

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 16/007,471, filed Jun. 13, 2018, entitled, “VASCULAR VALVE PROSTHESIS,” which is a continuation-in-part of U.S. application Ser. No. 15/247,523, filed Aug. 25, 2016, entitled, “VENOUS VALVE PROSTHESIS,” now U.S. Pat. No. 10,231,838, issued Mar. 19, 2019, which claims priority to U.S. Provisional Application Nos. 62/209,351, filed Aug. 25, 2015 and 62/356,337, filed Jun. 29, 2016, both entitled, “VENOUS VALVE PROSTHESIS.” This application also claims the benefit of U.S. Provisional Patent Application Nos.: 62/518,859, filed Jun. 13, 2017, entitled, “VENOUS VALVE PROSTHESIS DEVICE AND METHOD;” and 62/610,338, filed Dec. 26, 2017, entitled, “NEUTRAL DENSITY BALL VALVE.” The above-referenced applications are hereby incorporated by reference in their entireties into the present application. 
    
    
     TECHNICAL FIELD 
     This application relates generally to the field of medical devices. More specifically, the application relates to prosthetic valve implant devices, systems and methods for implantation within the vasculature. 
     BACKGROUND 
     Veins in the human body are weak-walled blood vessels that carry blood under low pressures back to the heart from the extremities. To help move the blood toward the heart, most frequently against the force of gravity, veins have one-way valves, which open in the direction of forward-moving blood flow and close to prevent backflow of blood. When these valves become compromised, the veins cannot function properly. Venous disease due to incompetent venous valves is a prevalent clinical problem. In the U.S., 20 million patients demonstrate chronic venous insufficiency, with swelling, pain, and/or ulceration of the affected extremity. An additional 74 million patients exhibit the dilation and deformity of varicose veins. 
     Various approaches have been advanced for addressing the clinical problem of poorly functioning venous valves. Mauch et al. (U.S. Pat. No. 7,955,346) teach a percutaneous method for creating venous valves from native vein tissue. Laufer et al. (U.S. Pat. No. 5,810,847) describe catheter placement of a clip appliance onto the cusp of a valve to restore the function of incompetent lower extremity venous valves. Multiple designs for implantable venous valves have also been described. These designs involve implantable prosthetic valves that mimic the patient&#39;s natural (autologous) valves; that is, the implants use pliable leaflet or flap valves to restore unidirectional venous flow. Examples of such implantable venous valves are described by Acosta et al. (U.S. Pat. No. 8,246,676), Shaolian et al. (U.S. Pat. No. 6,299,637), and Thompson (U.S. Pat. No. 8,377,115), for example. 
     In order to mimic native human peripheral venous valves, leaflet or flap valves are formed of extremely thin membrane material, to allow the valve to open properly for return flow to occur in the low pressure venous system, while still providing proper sealing and avoiding valvular insufficiency. Prosthetic membrane or flap valves are prone to failure, due to tearing from repeated opening and closing of the leaflets, permanent closure due to thrombosis and cell adhesion to the prosthetic leaflets, or leaflet inversion and incompetence over time. Currently available replacement venous valves, whether artificial or transplanted tissue valves, also often cause problems with thrombosis (clotting) during long term valve implantation. 
     Therefore, it would be advantageous to have improved implantable venous valve devices. It would desirable, for example, to have a prosthetic venous valve that would prevent and/or accommodate for the occurrence of thrombosis or cell adhesion to the valve components during long term valve implantation. Ideally, the improved prosthetic valve would be relatively easy to implant and would address at least some of the challenges of currently available valve implants discussed above. 
     BRIEF SUMMARY 
     The embodiments described herein are directed to implantable, prosthetic vascular valve devices, systems and methods for their use. Typically, the vascular valve implants described herein are used in veins, to replace or do the work of faulty or nonexistent venous valves. However, the implants may be used in arteries or other structures in the human body, such as heart valves or other body lumens that might benefit from a prosthetic valve. Thus, the description herein of venous valve implants may also be applied to arteries and other structures. 
     In many embodiments, the valve prosthesis device includes a ball valve mechanism to help facilitate blood flow through a vein, artery or other body lumen. The ball valve embodiments generally include an anchoring mechanism, a ball disposed within the anchoring mechanism, and a valve seat against which the ball rests to prevent backflow of blood in a retrograde fashion through the valve. The ball valves also include some type of ball retention mechanism, which prevents the ball from leaving the prosthetic and floating away in the direction of the blood flow. In some embodiments, the mechanism is some kind of blocking member (or members). In other embodiments, the mechanism is some kind of tether. In either case, the ball moves back and forth within the lumen of the anchoring mechanism, between an open position, in which blood flows through the valve and around the ball, and a closed position, in which the ball seats on the valve seat and prevents backflow of blood through the valve. A number of different embodiments of this implantable valve prosthetic device, as well as methods for delivering the device, are described herein. 
     The vascular valve prosthesis systems described herein generally include a delivery catheter. During placement of an implantable vascular valve prosthesis, it is desirable to minimize the diameter of the delivery catheter used to deploy the valve, to facilitate intravenous access and prosthesis insertion. A smaller diameter delivery catheter is desirable, because it may be inserted into a vein using a smaller puncture hole, and because it decreases trauma to the venous endothelium during advancement and manipulation of the catheter. On the other hand, it is desirable to maximize the diameter of the ball used in the venous valve, as a larger diameter ball may be paired with a valve seat containing a larger diameter valve orifice, to decrease flow resistance through the valve. Enhancing flow characteristics through the valve is important, in order to avoid thrombus (clot) formation in the valve, which may cause valve occlusion. According to various embodiments, the ball within the prosthetic valve may be collapsible/expandable (or “non-rigid”), so that it will change from a smaller diameter configuration during delivery to a larger diameter configuration following implantation. Other embodiments include different or additional mechanisms for preventing clot formation, as will be described further below. 
     In one aspect of the present application, a venous valve prosthetic implant for treating a vein includes a tubular, expandable anchoring frame, a valve seat formed at or near the middle of the anchoring frame, an expandable ball disposed within the lumen of the anchoring frame, and a ball retention tether attached to the expandable ball and to the valve seat and/or the anchoring frame. The anchoring member may be a stent that extends from a proximal end to a distal end of the implant and forms a lumen from the proximal end to the distal end. The anchoring frame may include a cylindrical proximal portion at the proximal end, a cylindrical distal portion at the distal end, an inwardly angled inlet portion between the cylindrical proximal portion and a middle of the anchoring frame, and an inwardly angled outlet portion between the cylindrical distal portion and the middle of the anchoring frame. The expandable ball expands from a compressed configuration for delivery into the vein through a delivery catheter to an expanded configuration outside the delivery catheter. The expandable ball in the expanded configuration moves between an open position, in which the expandable ball is located apart from the valve seat, to allow forward flow of blood through the implant, and a closed position, in which the expandable ball contacts the valve seat to prevent backflow of blood through the implant. 
     Some embodiments may further include a material disposed over at least part of the anchoring frame. For example, the material may be made of at least one substance, such as but not limited to polymers, hyaluronic acid, heparin and anticoagulant agents. The anchoring frame may optionally include multiple outward facing protrusions the proximal portion, apart from the proximal end, and/or the distal portion, apart from the distal end. The multiple outward facing protrusions may be barbs, hooks, U-shaped protrusions, V-shaped protrusions or the like. In some embodiments, each of the multiple outward facing protrusions forms an angle with an adjacent portion of the anchoring frame of between 25 degrees and 45 degrees. In some embodiments, the valve seat is a ring attached to at least one of an inner surface or an outer surface of the anchoring member. Alternatively, the valve seat may be formed of material used to make the anchoring frame or of material used to coat or cover the anchoring frame. 
     In some embodiments, the expandable ball is a solid, compressible foam ball. Such embodiments may optionally further include at least one weight embedded within the ball. Alternatively, the expandable ball may include an elastic shell and a filler substance inside the elastic shell. For example, the filler substance may be air, a gel or a fluid. Some embodiments include at least one weight inside the elastic shell. Optionally, the filler substance may be a curable substance that hardens when cured. In some embodiments, the filler substance is a spiral-cut, elastic, hollow sphere. In some embodiments, the expandable ball includes an aperture through which the ball retention tether is passed. In some embodiments, the expandable ball has a density of less than 2.5 grams per square centimeter. the ball retention tether is attached to the valve seat, wherein the tether and the valve seat form a filling lumen, and wherein the valve seat is accessible through a filling port to pass a filler substance through the valve seat and the tether to fill the expandable ball. In some embodiments, the expandable ball has a density of no greater than 1.06 grams per square centimeter, and the tether is elastic, to pull the ball toward the valve seat to prevent backflow of blood through the implant. 
     In some embodiments, the inlet portion and the outlet portion each form an angle, relative to a longitudinal axis of the implant, of between 15 degrees and 35 degrees. In some embodiments, the ball retention tether has a length of between 0.5 millimeters and 10 millimeters. In some embodiments, the ball retention tether is long enough to allow the expandable ball to be positioned outside of the distal end of the anchoring frame. In various embodiments, the expandable ball may be made of a material such as but not limited to thermoplastic polyurethane, elastomeric thermoplastic polyurethane, PVC, Polyethylene, polycarbonate, PEEK, ultem, PEI, polypropylene, polysulfone, FEP, PTFE, coated hollow heavy metal or combinations thereof. 
     In another aspect of the present application, a venous valve prosthetic implant system for treating a vein includes an implant, according to any of the aspects and embodiments described above, and a delivery device. The delivery device includes an elongate, flexible catheter body and a deployment plunger disposed within the catheter body for pushing the implant out of the catheter body. 
     In some embodiments, the deployment plunger includes a curing member for curing a curable material of which the expandable ball is at least partially made. For example, the curing member may be configured to emit a curing agent, such as but not limited to heat, light, electricity, sound waves, or a chemical mixture. In some embodiments, the delivery device further includes an inflation tube disposed within the catheter body, where the inflation tube includes a distal end configured to enter an aperture in the expandable ball to inflate the expandable ball. In some embodiments, the inflation tube further includes a curing member configured to emit a curing agent. In alternative embodiments, the delivery device may further include an inflation attachment configured for passing fluid through a lumen in at least one of the valve seat or the ball retention tether to inflate the expandable ball. 
     Optionally, the system may further include a ball extraction device configured to extract the expandable ball from the implant. In one embodiment, the ball extraction device includes a grasper for grasping the expandable ball and a cutter for cutting a tether attaching the expandable ball to at least one of the anchoring frame or the valve seat. In some embodiments, the ball extraction device is configured to pass through the catheter body of the delivery device. The delivery device may also optionally include at least one orientation indicator for indicating an orientation of the implant within the catheter body. 
     In another aspect of the present disclosure, a method for implanting a venous valve prosthetic implant in a vein or other blood vessel first involves advancing a delivery catheter containing the implant into the vein. The method next involves retracting a catheter body of the delivery catheter and/or advancing a deployment plunger of the delivery catheter, to cause the implant to exit a distal end of the delivery catheter. Then, a tubular stent anchoring member and a ball disposed inside the anchoring member are expanded, within the vein and outside of the delivery catheter. The anchoring member, when expanded, contacts an inner wall of the vein to maintain the implant within the vein. The ball, when expanded, moves between an open position, in which the ball is positioned to allow forward flow of blood through the implant, and a closed position, in which the ball contacts a valve seat, to prevent backflow of blood through the implant. Lastly, the method involves removing the delivery catheter from the vein. 
     In some embodiments, expanding the anchoring member and the ball involves releasing the anchoring member and the ball from constraint within the catheter body, and both the anchoring member and the ball are made of at least one shape memory material. Some embodiments may further include using the delivery catheter to cure a curable material of which the ball is at least partially made. This curing may involve emitting a curing agent, such as heat, light, electricity, sound waves, or a chemical mixture. 
     In some embodiments, the method further involves advancing an inflation tube out of the catheter body of the delivery catheter, where a distal end of the inflation tube is positioned through an aperture of the ball, and inflating the ball, using the inflation tube. In various embodiments, the ball may be inflated with air, a fluid, a gel or an elastic, hollow sphere. In some embodiments, inflating the ball involves using an inflation attachment of the delivery catheter to pass fluid through a lumen in a valve seat and/or a ball retention tether of the implant. In some embodiments, the method also includes orienting the implant with the catheter body, using at least one orientation feature on at least one of the implant, the catheter body or a handle coupled with the catheter body. 
     Optionally, the method may also include extracting the ball from the implant, using a ball extraction device. For example, extracting the ball may involve grasping the ball with a grasper of the extraction device and cutting a tether attached to the ball, using a cutter of the extraction device. 
     These and other aspects and embodiments are described in further detail below, in reference to the attached drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are side views of a vascular prosthetic valve implant, according to one embodiment; 
         FIGS. 2A-2C  are front and side views of three different shapes of balls for a vascular prosthetic valve implant, according to three alternative embodiments; 
         FIGS. 3A and 3B  are side views of an expandable anchoring frame of a vascular prosthetic valve implant in its configuration before shaping ( FIG. 3A ) and after shaping ( FIG. 3B ), according to one embodiment; 
         FIGS. 4A and 4B  are side and front views, respectively, of a vascular prosthetic valve implant, according to one embodiment; 
         FIG. 5  is a side view of a vascular prosthetic valve implant having a V-shaped ball retaining member, according to one embodiment; 
         FIG. 6  is a side view of a vascular prosthetic valve implant having a tether, according to one embodiment; 
         FIGS. 7A and 7B  are side views of a vascular prosthetic valve implant system, illustrating delivery of the implant out of the delivery device, according to one embodiment; 
         FIG. 8  is a view of a compressible foam ball of a vascular prosthetic valve implant, according to one embodiment; 
         FIG. 9  is a view of an elastic, filled ball of a vascular prosthetic valve implant, according to one embodiment; 
         FIG. 10  is a view of an air filled ball with an internal weight, of a vascular prosthetic valve implant, according to one embodiment; 
         FIGS. 11A and 11B  are side views illustrating a method for delivering a vascular prosthetic valve implant and inflating an elastic ball of the implant, according to one embodiment; 
         FIG. 11C  is a front view of the dual lumen inflation catheter of  FIGS. 11A and 11B ; 
         FIGS. 12A-12E  are side views illustrating a method for inflating an elastic ball of a vascular prosthetic valve implant, according to one embodiment; 
         FIGS. 13A-13D  are side views illustrating a method for delivering a vascular prosthetic valve implant into a blood vessel, according to one embodiment; 
         FIG. 14A  is a cross-sectional view of a ball of a vascular prosthetic valve implant, which includes a hollow sphere filler, according to one embodiment; 
         FIG. 14B  is a view of the hollow sphere filler of  FIG. 14A ; 
         FIG. 14C  is a view of the hollow sphere of  FIGS. 14A and 14B  stretched out; 
         FIG. 14D  is a side view of a catheter delivering the stretched out hollow sphere into the shell of the ball of  FIG. 14A ; 
         FIG. 15  is multiple views of a ball of a vascular prosthetic valve implant configured as a stretchable shell with a spring ball retainer, according to one embodiment; 
         FIGS. 16A and 16B  are side views, illustrating a system and method for delivering a vascular prosthetic valve implant, according to one embodiment; 
         FIGS. 17A and 17B  are side views, illustrating a system and method for delivering a vascular prosthetic valve implant, according to an alternative embodiment; 
         FIG. 18  is a side view, illustrating a system and method for delivering a vascular prosthetic valve implant, according to another alternative embodiment; 
         FIGS. 19A and 19B  are side views of two embodiments of a vascular valve prosthetic implant having an internal ring valve seat ( FIG. 19A ) and an external ring valve seat ( FIG. 19B ), according to two alternative embodiments; 
         FIG. 20  is several views of a vascular prosthetic valve implant with an asymmetric expandable anchoring frame, according to one embodiment; 
         FIG. 21  is several views of a vascular prosthetic valve implant with an asymmetric expandable anchoring frame, according to an alternative embodiment; 
         FIG. 22  is a side view of a vascular prosthetic valve implant with a V-shaped tether, according to one embodiment; 
         FIG. 23  is a side view of a vascular prosthetic valve implant with a two-piece tether, according to an alternative embodiment; 
         FIG. 24  is a side view of a vascular prosthetic valve implant with a two-piece tether, according to another alternative embodiment; 
         FIG. 25  is a side view of a vascular prosthetic valve implant illustrating areas of shear stress within the implant; 
         FIG. 26  is a side view of a vascular prosthetic valve implant with a short tether, according to one embodiment; 
         FIG. 27  is a side view of a vascular prosthetic valve implant with a long tether, according to one embodiment; 
         FIG. 28  is a side view of a vascular prosthetic valve implant with a long ended expandable anchoring frame, according to one embodiment; 
         FIG. 29  is a side view of a vascular prosthetic valve implant illustrating outlet angles within the implant; 
         FIG. 30  is a side view of a vascular prosthetic valve implant, implanted in a vein at the location of a native venous valve, according to one embodiment; 
         FIGS. 31A-31C  are side, front and side views, respectively, of a vascular prosthetic valve implant with a flap valve ball retaining member, according to one embodiment; 
         FIG. 32  is a side view of an expandable anchoring frame of a vascular prosthetic valve implant, having barbs protruding outward in locations separate from the ends of the frame, according to one embodiment; 
         FIG. 33  is a side view of an expandable anchoring frame of a vascular prosthetic valve implant, having V-shaped protrusions protruding outward in locations separate from the ends of the frame, according to one embodiment; 
         FIGS. 34A-34C  are side view of an a system and method for removing a ball from an implanted vascular prosthetic valve implant, according to one embodiment; 
         FIGS. 35A and 35B  are side views of a vascular prosthetic valve implant with a single leaf flap valve, according to one embodiment; 
         FIGS. 36A and 36B  are side views of a vascular prosthetic valve implant with a single leaf flap valve, according to one embodiment; 
         FIGS. 37A and 37B  are side views of a vascular prosthetic valve implant with a tether, illustrating the effects of gravity on the ball of the implant; 
         FIG. 38  is a side view of a vascular prosthetic valve implant with an anchoring member with a central round portion, according to one embodiment; 
         FIGS. 39A and 39B  are side views of a ball without and with a tether, respectively, of a vascular prosthetic valve implant, according to one embodiment; 
         FIG. 40  is a side view of a ball and a tether of a vascular prosthetic valve implant, according to an alternative embodiment; 
         FIG. 41  is a side view of a ball and a tether of a vascular prosthetic valve implant, according to another alternative embodiment; and 
         FIGS. 42A and 42B  are side views of a vascular prosthetic valve implant with a ball having a central rod, according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     This application describes various embodiments and features of a device, system, and method involving a vascular valve prosthesis for implantation in a blood vessel to improve function of the blood vessel. In many cases, the vascular valve prosthesis is used in human veins, to help treat venous insufficiency. In alternative embodiments, however, the valve prosthesis may be used in arteries, other locations in the body, such as heart valves or other body lumens, and/or it may be used in animals. Therefore, although the following description focuses on use of the valve prosthesis in veins, this should not be interpreted as limiting the scope of the claims. 
     Many of the embodiments described herein are of a vascular ball valve prosthesis, as opposed to prior art leaflet or flap valve approaches. The assignee of the present application described a number of embodiments of ball valve prostheses in U.S. Patent Application Pub. No. 2017/0056175, titled “Venous Valve Prosthesis” (hereinafter referred to as “the Venous Valve Prosthesis application”), filed Aug. 25, 2016, the full disclosure of which is hereby incorporated into this application. As mentioned above, some potential challenges with a vascular ball valve include: (1) being able to compress the valve prosthesis into a small-diameter catheter for delivery while also allowing for good flow dynamics through the valve once implanted, (2) preventing clot formation on the ball or other parts of the prosthetic valve, and (3) preventing migration of the valve prosthesis within the vein, due to the increasing diameter of veins as they approach the heart. The embodiments described below address these challenges. 
     Referring now to  FIGS. 1A and 1B , in one embodiment, a prosthetic venous valve implant  10  may include an anchoring member  12  (or “anchor frame”), such as a self-expanding, stent-like frame, for anchoring the implant  10  within a vein. The anchoring member  12  may have a first end  14  (sometimes referred to herein as an “upstream end”), a second end  16  (sometimes referred to herein as a “downstream end”), and a middle valve portion  13 . Although not labeled  FIGS. 1A and 1B , portions of the anchoring member  12  that lie between the first end  14  and the middle valve portion  13  and between the second end  16  and the middle valve portion  13  may be referred to as an “upstream portion” and a “downstream portion,” respectively, of the anchoring member  12 . In many embodiments, there is no clear delineation or demarcation between the various portions of the anchoring member  12 , and these descriptive terms are used for explanatory purposes only and should not be interpreted as limiting the scope of the invention. 
     Optionally, as illustrated in  FIG. 1B , all or a portion of the anchoring member  12  may be coated or otherwise covered with a material or membrane  26 , to help direct blood flow through the implant  10  and prevent blood from flowing through the wall of the anchoring member  12  in the coated portion. In some embodiments, the membrane  26  may be made of or coated with an anticoagulant substance. In alternative embodiments, however, the anchoring member  12  may include no membrane or coating material. This may be possible, for example, in embodiments that expand sufficiently that the native vein wall itself acts as a wall, so that blood is conducted by the vein wall itself. In general, the anchoring member  12  is configured to anchor the valve implant  10  to the luminal surface of the vein. 
     The venous valve implant  10  may also include a tubular frame  20 , which is housed within the anchoring member  12 , and a ball  28  housed within the tubular frame  20 . Attached to, or integrally formed with, the tubular frame  20  are a valve seat  18 , a retention member  22 , and multiple through-holes  24 , through which blood is free to exit the tubular frame  20 . In some embodiments, the tubular frame  20 , valve seat  18 , retention member  22  and ball  28  may be referred to as the “valve portion” of the implant device  10 , which is housed within the anchoring member  12 . 
     In alternative embodiments, which will be described further below, the prosthetic venous valve implant may include fewer parts than in the valve implant  10  of  FIGS. 1A and 1B . For example, alternative embodiments do not include a tubular frame. These embodiments may simply include a valve seat attached directly a self-expanding stent anchoring member, a ball, and a ball retention feature, such as a tether or a constraining portion of the anchoring member. Other embodiments may include additional components or features, such as retaining barbs on an anchoring member. A number of these alternative embodiments and features are described in greater detail below. 
     The ball  28 , embodiments of which will be described further below, may be collapsible (or “compressible” or “flexible”), to help allow the valve implant  10  to be compressed and loaded into a small diameter delivery catheter. The density of the ball  28 , in some embodiments, may be equal to, approximately equal to, or slightly greater than the average density of venous blood (or arterial blood in other embodiments), so the valve functions with both a low opening pressure and a low closing pressure. For example, in some embodiments, the ball  28  may have a density of between about 1.06 grams per cubic centimeter (approximately the density of blood) and about 2.5 grams per cubic centimeter, or more specifically between about 0.9 and about 2.5 grams per cubic centimeter, or even more specifically, between about 0.9 and about 2.0 grams per cubic centimeter. In alternative embodiments, the density of the ball  28  may fall outside these ranges, such as between about 0.1 grams per cubic centimeter and about 5 grams per cubic centimeter. Various additional ranges of densities for the ball  28  include, but are not limited to between 0.96 and 1.16 grams per cubic centimeter, between 0.7 and 1.42 grams per cubic centimeter, between 0.1 and 1.06 grams per cubic centimeter, between 0.5 and 1.06 grams per cubic centimeter, between 1.06 and 2.5 grams per cubic centimeter, and between 1.06 and 2.0 grams per cubic centimeter. 
     In various embodiments, the ball  28  may be constructed of any of a number of suitable materials, including but not limited to PTFE (polytetrafluoroethylene), silicone rubber, silastic rubber, silicone, stainless steel, Teflon, thermoplastic polyurethane, elastomeric thermoplastic polyurethane, PVC, Polyethylene, polycarbonate, PEEK, ultem, PEI, polypropylene, polysulfone, FEP, coated hollow heavy metal or any combination thereof. Optionally, an anti-coagulant agent, such as heparin, or another coating, such as hyaluronic acid, may be bonded to the surface of the ball  28 . The valve seat  18  may be formed of toroidal elastomer, silicone rubber, or other material. 
     In various alternative embodiments, the ball  28  may have any suitable shape, size, surface feature(s) or the like. In its simplest form, for example, the ball  28  may be spherical and solid. Alternatively, and with reference now to  FIGS. 2A-2C , a ball incorporated into a prosthetic valve implant of the present disclosure may have any of a number of alternative shapes, such as ovoid, oblong, asymmetrical, etc. In  FIGS. 2A-2C , the left hand view is a front view, and the right hand view is a side view. As illustrated in  FIG. 2A , a ball  240  according to one embodiment may have a shape  242 , when viewed from the side, of a cylinder with a pointed end. As illustrated in  FIG. 2B , a ball  244  according to another embodiment may have a shape  246 , when viewed from the side, of a rhombus. As illustrated in  FIG. 2C , a ball  248  according to yet another embodiment may have a shape  250 , when viewed from the side, of a cylinder with a rounded end. Any other shape may be used, according to alternative embodiments. In some embodiments, the ball  28  may have an outer shell and an inner core, and these two parts may be made of different substances. In some embodiments, the inner core may be made of a liquid substance, and in some embodiments the liquid may be injected through the outer shell to fill the core. The substance may be an anticoagulant or other drug or therapeutic substance and may leak out of one or more holes in the shell in some embodiments. The ball  28  may also have surface features, such as dimples, grooves, indents, pockets or the like. In embodiments, for example, surface features may facilitate the flow of blood around the ball  28 . Again, these and other embodiments of the ball  28  will be described more fully below. 
     With reference now to  FIGS. 3A and 3B , the anchoring member  12  (or “anchoring frame”) is illustrated in further detail. In various embodiments, the anchoring member  12  may be formed as a stent-like lattice structure  30 , (or sometimes referred to herein simply as a “stent”), with open portions  32  within the lattice. The anchoring member  12  is typically self-expanding, but in alternative embodiments it may be expandable, such as with a balloon catheter. In some embodiments, all or a portion of the self-expanding anchoring frame  12  may be coated, to render it impervious to blood flow. (In other words, so that blood flows through the lumen of the anchoring member  12  and not through the open portions  32 .) The anchoring member  12  may be a frame constructed of an engineered polymer (i.e., PEEK, Polypropylene, PTFE, etc.), stainless steel, or a superelastic metal, such as Nitinol. For example, a Nitinol tube may be laser cut in a lattice pattern  30  to form the anchoring member  12 . 
     As illustrated in  FIG. 3B , in some embodiments, the middle valve portion  13  of the anchoring member  12  may either not expand or may expand less than (to a smaller diameter than) an upstream portion  15  and a downstream portion  17  of the anchoring member  12 . The upstream portion  15  and downstream portion  17  may be expanded, for example, to between 1 mm and 30 mm, and the middle valve portion  13  may be between 1 mm and 30 mm. More specifically, some embodiments may have an upstream portion  15  and a downstream portion  17  that expand to between 10 mm and 20 mm, and a middle valve portion  13  that may be between 2 mm and 10 mm. The length of the anchoring member  12  may be between 1 mm and 200 mm, with some embodiments between 20 mm to 40 mm. The first end  14  and the second end  16  of the anchoring member  12  may have multiple apices, which, when expanded, anchor the anchoring member  12  to the inner wall of the vein. The anchoring member  12  may be heated above its transition temperature and quenched, to place it in its austenitic, self-expanding state. 
     Referring again to  FIG. 1B , in some embodiments, some or all of the open areas  32  of the lattice  30  may be closed off via the membrane  26 , which may be a thin layer of silicone rubber or a covering membrane such as PET (polyethylene teraphthalate), PTFE, Nylon, hyaluronic acid or other material. In some embodiments, the membrane  26  may have anticoagulant properties and may thus be referred to herein as an “anticoagulant membrane,” but the anticoagulant properties are not required. The membrane  26  may also be referred to in this application as a “hemostatic membrane,” because it prevents or helps prevent blood from flowing through the openings  32  in the wall of the anchoring member  12 . The membrane  26  may cover the inlet and/or outlet sections of the anchoring member  12  and may thus, when the anchoring member  12  is expanded, form a seal against the inner vein wall, to prevent leakage around the outside of the anchoring member  12 . Sealing may also be facilitated by adding short barbs  34  onto the apices first end  14  (or “inlet” or “upstream” end). In various alternative embodiments, barbs  34  may be included on the second end  16 , on both the first and second ends  14 ,  16 , on the middle valve portion  13 , or on any combination thereof. The first end  14  of the implant  10 , with the membrane  26 , may form a circumferential linear seal against the inner surface of the vein, facilitated by the barbs  34  protruding into the vein wall. The edge of the membrane  26  may also be thickened with respect to the remainder of the membrane  26 , to enhance its sealing capability. 
     One advantage of the self-expanding venous valve prosthesis  10  is its sealing mechanism, which incorporates a significantly more substantial valve structure—the moveable ball  28  that seats onto the ring of the valve seat  18 . Other advantages include the self-expanding frame/anchoring member  12  that distends the vein wall upon deployment, to prevent valve migration, maximize flow-through area, and minimize sheath size for introducing the device  10  and the impermeable covering  26 . Use of a ball valve instead of super-thin membranes or leaflets imparts longevity to the implant  10 . Due to the larger size and greater mass of the ball  28 , compared to thin leaflets, and due to the greater excursion of a rolling ball  28  upon opening and closing of the valve, a ball valve will avoid at least some of the sealing and fatigue problems encountered with thin membrane and leaflet valves. Another advantage of the venous valve implant device  10  is that it is able to clean itself, at least in part, as the ball  28  rolls back and forth and thus cleans off the inner surface of the anchoring member  12 , the valve seat  18  and/or the retention member  22 . To provide adequate excursion of the rolling ball  28  for the purpose of self-cleaning the device  10 , the distance between the valve seat  18  and the retention member  22  may be about two to four times greater than the diameter of the ball  28 . In alternative embodiments, this distance may be longer or shorter, such as about 1.5 to about five times greater than the diameter of the ball  28 , for example. As the ball  28  moves back and forth, it rubs against the inside of the ball valve frame  20 , dislodging potential adherent cells and thrombus. In embodiments described further below that do not include a tubular frame  20 , the ball  28  may instead clean an inner surface of the anchoring member  12 . 
     Referring now to  FIGS. 4A and 4B , in another embodiment, a venous valve prosthesis  160  may include an anchoring member  162  (or “anchoring frame”), with a first end  164 , a second end  166 , and a middle valve portion  163 . Inside the anchoring member  162  are a ball  170 , a valve seat  168  and a ball retention member  172 . In this embodiment, there is no inner tubular frame. Instead, the first and second ends  164 ,  166  of the anchoring member  162  expand to anchor the implant  160  within a vein, and the middle valve portion  163  maintains a smaller diameter and acts as a substantially tubular holder for the ball  170 . As discussed above, the anchoring frame  162  may be made of continuous superelastic material, such as Nitinol, which may be entirely or partially coated in a material, such as PTFE, silicone, or hyaluronic acid. This coating funnels blood through the central valve component. The ball retention member  172  may include multiple pieces of crossing suture, which extend across the lumen of the implant in any suitable pattern or configuration. The entire implant  160  may be compressible (ball  170 , valve seat  168 , anchoring frame  162 , ball retention member  172 ), so that it can be packed into a small delivery catheter to facilitate ease of implantation. Any valve seat, ball, anchor feature such as barbs, or retainer embodiment described in this application may be used in this embodiment. External compression and/or a ferromagnetic ball and externally placed magnet may also be applied with this embodiment, for clearance of clot. Removal of the entire device  160 , or just the ball  170 , is also possible. The same deployment funnel may be mated with the proximal end of the prosthesis  160 , using the graspers or small scissors to cut the retention member  172 , and using graspers or suction to remove the ball  170  from the valve  160 . 
     In some embodiments, the ball  170  may have a ball diameter such that the distance between the valve seat  168  and the ball retention member  172  is between two times and four times greater than the ball diameter. The ball diameter may also be sized such that the ball  170  contacts an inner surface of the middle valve portion  163  as the ball  170  travels back and forth between the valve seat  168  and the ball retention member  172 , so that contact between the ball  170  and the middle valve portion  163  is able to dislodge substances that form on or cling to the middle valve portion  163 . This sizing of the ball  170  and the diameter of the middle valve portion  163  thus may impart a “self-cleaning” ability to the implant device  160 . For example, in some embodiments, the ball  170  may have a diameter of between 0.5 mm and 30 mm. More specifically, in some embodiments, the ball  170  may have a diameter between 1 mm and 8 mm. 
     The valve seat  168  may be formed of toroidal elastomer, silicone rubber, Nitinol, or any other material. In some embodiments, the valve seat  168  and the anchoring frame  162  may be made of the same material, such as Nitinol in one embodiment. The valve seat  168  may be rigid (e.g., stainless steel, Nitinol, or polycarbonate) or flexible/collapsible (e.g., silicone), to facilitate packing into a smaller delivery sheath. In some embodiments, an inner surface of the valve seat  168  may be coated in the same continuous material lining of the anchoring member  162 , to limit or prevent luminal or blood exposure. The valve seat  168  may expand to a diameter greater than that of the delivery sheath and/or vein wall to maximize flow-through area. The valve seat  168  may be permanent or replaceable. 
     As mentioned above, the anchoring member  162  may be a self-expanding or balloon expandable anchoring frame, having a stent-like lattice structure. In this embodiment, the first or upstream end  164  and the second or downstream end  166  expand to greater diameters than the middle valve portion  163  of the anchoring member  162 . The two ends  164 ,  166  typically dilate a vein or other vessel into which they are implanted. In some embodiments, the middle valve portion  163  also expands upon delivery to a diameter sufficient to dilate the vein. In some embodiments, the implant  160  also includes a material, membrane or coating (not illustrated), disposed over part of the anchoring member  162 . This coating may act as a hemostatic barrier that funnels blood through the central lumen of the device  160 . The coating may consist of a hemostatic material, such as a polymer (e.g. PTFE, silicone, PET, nylon, or hyaluronic acid), and may further be infused or bonded with heparin, hyaluronic acid, or other agent. The hemostatic membrane covering the inlet and/or outlet sections of the anchoring frame  162  can seal against the inner vein wall to prevent or reduce leakage around the outside of the implant  160 . Additionally, the extreme downstream end  166  may expand to a slightly larger diameter than an immediately adjacent downstream portion, thus forming a wider expandable portion, which may also be uncovered/uncoated and may act as multiple anti-migration tips when the anchoring member  162  is expanded. These tips may help prevent downstream migration of the implant  160  within a vein. Optionally, some embodiments may include additional anti-migration barbs on the anchoring frame  162 . 
     The anchoring member  162  may be a frame constructed of an engineered polymer (i.e., PEEK, Polypropylene, PTFE, etc.), stainless steel, or a superelastic metal, such as Nitinol. A Nitinol tube may be laser cut in a lattice pattern, and its proximal and distal sections (or “downstream and upstream sections,” respectively) may be expanded, while the middle valve portion  163  may be retained in a smaller diameter. In some embodiments, the proximal and distal sections of anchoring member  162  may be expanded to between 0.1 mm and 100 mm. More specifically, some embodiments may have proximal and distal sections expanded to between 10 mm and 20 mm. In some embodiments, the length of the anchoring member  162  may be between 1 mm and 200 mm, with some embodiments between 20 mm to 40 mm. In some embodiments, the central narrowed middle valve portion  163  may have a diameter between 1 mm and 100 mm, and a length between 0.1 mm and 100 mm. More specifically, in some embodiments the middle valve portion  163  may have an outer diameter between 3 mm and 20 mm, and a length between 5 mm and 15 mm. The anchoring member  162  may be self-expandable from a collapsed configuration, for delivery through a delivery catheter, and have an expanded configuration upon release from the delivery catheter. Alternatively, the anchoring frame  162  may be balloon expandable. The upstream end  164  and the downstream end  166  of the anchoring frame  162  may be sized to dilate the vein when the implant  160  is implanted in the vein. The middle valve portion  163  of the anchoring frame may also be sized to dilate the vein when the implant  160  is implanted in the vein. The middle valve portion  163  may have a mostly straight configuration, as in  FIG. 4A , or may have an hourglass shape. 
       FIGS. 5 and 6  illustrate two additional alternative embodiments of a prosthetic venous valve implant. In the embodiment of  FIG. 5 , the venous valve implant  260  includes an anchoring member  262 , a ball  264 , a valve seat  266 , and a retention member  268 . In this embodiment, the retention member  268  is an expandable wire anchor, attached to the ball  264 . The expandable wire anchor retention member  268  may be made of a shape-memory material, for loading into a delivery catheter, and it includes a first end attached to the ball  264  and a V-shaped end opposite the ball  264 . The V-shaped end is large enough, when expanded, to not fit through the valve seat  266 , thus preventing the ball  264  from passing out of the valve implant  260  in the downstream direction. The end of the retention member  268  attached to the ball  264  may be attached via adhesive, by being passed into or through an aperture in the ball  264  and then being tied, by being welded to the ball  264 , or by any other suitable means. In alternative embodiments, the V-shaped end may have other shapes. The valve implant  260  may include any of the features described above, such as a material disposed over all or part of the anchoring member  262 , a collapsible valve seat  266 , barbs protruding from the anchoring member  262  and/or the like. 
     In the embodiment of  FIG. 6 , the implant  270  includes an anchoring member  272 , a ball  274 , a valve seat  276 , and a retention member  278 . In this embodiment, the retention member  278  is a tether, attaching the ball  274  to the valve seat  276 . The retention member  278  may be made of suture, wire such as Nitinol, an elastic material or the like. Again, the tether retention member  278  stops the ball  274  from passing out of the valve implant  270  in the downstream direction. The end of the retention member  278  attached to the ball  274  may be attached via adhesive, by being passed into or through an aperture in the ball  274  and then being tied, by being welded to the ball  274 , or by any other suitable means. The opposite end of the tether retention member  278  may be attached to the valve seat  276 , as shown, to the anchoring member  272 , or both. The valve implant  270  may include any of the features described above, such as a material disposed over all or part of the anchoring member  272 , a collapsible valve seat  276 , barbs protruding from the anchoring member  272  and/or the like. Either of these two retention members  268 ,  278  may be applied in other embodiments described herein. 
       FIGS. 7A and 7B  are diagrammatic illustrations of one embodiment of a vascular ball valve prosthetic system  100 , which includes the prosthetic vascular valve  102  (or “implant”) itself and a delivery catheter  120  for delivering the prosthetic valve  102  to its target location in a vein (or alternatively in an artery).  FIGS. 7A and 7B , as well as many of the remaining figures in this application, include diagrammatic representations of different embodiments of a vascular prosthetic valve and a delivery catheter for delivering the valve into a vein (or other blood vessel in other embodiments). In any of these illustrated embodiments, the prosthetic valve may be the same as, or similar to, any of the embodiments described above, in reference to  FIGS. 1A-6 , or any of the embodiments described in any of the references previously incorporated by reference. Any features, elements or components described for the valve prosthesis embodiments described above or described in any of the references previously incorporated by reference may be applied to the embodiments that follow. Therefore, the size, shape and features of the embodiments described via diagrammatic illustrations should not be limited by the nature of the illustrations themselves. 
     Returning to  FIGS. 7A and 7B ,  FIG. 7A  illustrates the prosthetic valve  102  in a collapsed or compressed configuration, within the delivery catheter  120 , and  FIG. 7B  shows the prosthetic valve  102  in an expanded configuration, outside the delivery catheter  120  (as it might look inside a vein). In this embodiment, the prosthetic valve  102  includes an expandable anchoring frame  104  (or “anchoring member”), which includes a wide proximal portion  112 , a wide distal portion  116  and a narrower middle portion  114 . The narrower middle portion  114  includes an inwardly angled proximal portion, between the wide proximal portion  112  and the middle of the anchoring frame  104 , and an inwardly angled distal portion, between the wide distal portion  116  and the middle of the anchoring frame  104 . The valve  102  also includes a valve seat  106  attached to the middle of the anchoring member  104 , a ball  108 , and a tether  110  attached at one end to the valve seat  106  (and/or the anchoring frame  104  in alternative embodiments) and at an opposite end to the ball  108 . The delivery catheter  120  includes a tubular catheter body  122  and a deployment plunger  124  slidably disposed inside the catheter body  122 . In some embodiments, a light source (not visible) may be disposed inside, or at the distal end of, the plunger  124 , to emit light  126 , which will be described further below. 
     Many of the features and aspects of the implant  102  are described more fully in the Venous Valve Prosthesis Application, which was previously incorporated by reference. In various embodiments, the anchoring frame  104  is formed as an expandable stent. The anchoring frame  104  is a one-piece structure that extends from one end of the implant  102  to the opposite end of the implant  102 . The anchoring frame  104  may have any suitable size and shape, some variations of which will be shown and described further below. The anchoring frame  104  may be made of any expandable or self-expanding material and is configured, when expanded, to anchor the implant  102  within the vein being treated. The anchoring frame  104  may be made of any shape-memory metal or polymer, for example, such as Nitinol. In some embodiments, at least a portion of the anchoring frame  104  is coated or covered with a material that may be fully or partially impermeable to blood. Examples of such materials include polymers, hyaluronic acid, heparin and/or anticoagulant agents. 
     In use, the delivery catheter  120  is advanced into the target vein with the prosthetic valve  102  loaded in the catheter body  122  ( FIG. 7A ). Once in the appropriate vessel location, the catheter body  122  may be retracted relative to the deployment plunger  124  to cause the valve  102  to exit the catheter body  122  ( FIG. 7B ). Alternatively, the plunger  124  may be advanced, while the catheter body  122  is held immobile, or a combination of advancement of the plunger  124  and retraction of the catheter body  122  may be employed. Once released, the anchoring member  104  expands to anchor against the blood vessel inner wall. As the anchoring member  104  expands during and after deployment, the compressive force it places on the expandable ball  108  in the compressed configuration inside the catheter body  122  is removed. The ball  108  thus expands to assume its default spherical shape. In some embodiments, as illustrated in  FIG. 7B , the deployment plunger  124  may emit light  126  to cure a curable substance of which the ball  108  is at least partially made. The curing process may make the ball  108  harder or more resistant to compression, thus preventing it from accidentally squeezing through one end of the anchoring member  104  after deployment. In alternative embodiments, the ball  108  may be cured via other methods, such as but not limited to the application of sound, heat or electricity to the ball  108 . In other embodiments, curing is not used. 
     The embodiment illustrated in  FIGS. 7A and 7B  may be referred to as a self-expanding embodiment, in that the anchoring member  104 , the ball  108  and the valve seat  110  all self-expand from a compressed, delivery configuration to an expanded, deployed configuration. In alternative embodiments, one or more of these three components (the anchoring member  104 , the ball  108  and the valve seat  110 ) may be expandable but not self-expanding. For example, the anchoring member and the valve seat  110 , in one embodiment, may be expanded with the use of a balloon catheter or other expanding device. Although this increases complexity of the delivery and deployment procedure, it may be part of some alternative embodiments. Unless stated otherwise, however, the embodiments described herein are assumed to be self-expanding and thus the anchoring member  104 , the ball  108  and/or the valve seat  110  self-expand when released from constraint within the delivery catheter  120 . 
     The expandable ball  108  has a number of different alternative embodiments, some of which are described below. Generally speaking, the various embodiments of the expandable ball  108  may be categorized as either self-expanding or expandable. The self-expanding embodiments of the ball  108  are made at least partially of a resilient or shape-memory material, such as a compressible foam, an elastic shell filled with gel or fluid, or other embodiments, some of which are described below. The expandable (non-self-expanding) embodiments of the ball  108  typically involve some kind of inflation or other expansion mechanism, as described further below. 
     The valve seat  106  in the embodiment of  FIGS. 7A and 7B  is compressible, as evident from comparing the two figures, and it may have any of the materials and characteristics described above for valve seats. For example, the valve seat  106  may be formed of silicone rubber, a flexible polymer, such as Viton, a shape-memory metal, such as Nitinol, or any other suitable material. It may be insert-molded into or otherwise attached to an inner surface and/or an outer surface of the anchoring member  104 . 
     Referring to  FIGS. 8-10 , three different embodiments of a compressible ball for a vascular prosthetic valve are illustrated. In each embodiment, the compressibility of the ball allows it to reside within the compressible anchoring frame of the vascular valve prosthesis in an elongated configuration and then expand to a spherical geometry following valve deployment in the vein. 
     In one embodiment, depicted in  FIG. 8 , a vascular valve prosthesis ball  300  may be constructed of closed cell polymeric foam, such as polyurethane foam. The foam ball  300  may be stored inside the valve anchoring frame and delivery catheter in a compressed condition, and expand to a spherical configuration following valve deployment. Optionally, the foam material may be covered in a shell of another material, such as PTFE, silicone, or the like, which acts as a barrier between blood and the foam material. As mentioned previously, in various embodiments, the ball  300  may have any of a number of suitable densities, which may be greater than, equal to or less than the density of blood. The various density ranges and ball materials are listed above and thus are not repeated here. 
     As illustrated in  FIG. 9 , an alternative embodiment of a compressible ball  310  may include a hollow spherical shell  312  constructed of an elastic material, such as silicone rubber or polyurethane, filled with a filler substance  314 , which may be a fluid, gel or air. The filler substance  314  may be selected such that the overall density of the ball  310  is slightly higher than the density of blood, such that gravity causes the ball  310  to rest against the valve seat to close the valve, but a low forward pressure is sufficient to open the valve, resulting in a low cracking pressure of the valve. 
     As illustrated in  FIG. 10 , in another alternative embodiment, the ball  322  may also include an elastic shell  322 , in this case filled with air, but also including a small diameter inner weight  324 , constructed of material such as stainless steel. The dimensions of the inner weight  324  may be selected to give the ball  320  a desired overall density. Upon movement of the ball  320  towards and away from the valve seat, the weight  324  drops within the ball  320 , causing the ball  320  to rotate in an asymmetrical fashion within the valve frame. The asymmetrical contact of the ball  320  against the valve frame may help prevent cell and thrombus adhesion to the ball  320  and thus may help prevent valve occlusion. 
     In other alternative embodiments, the ball of a vascular valve prosthesis may be constructed of, or filled with, any other suitable combination of foam, fluid, gel, gas, or solid. The combination of filler materials may be selected such that the overall density of the ball is slightly higher than the density of blood. It may further be formed such that it has asymmetrically distributed weight or altered shape that encourages ongoing ball movement and limits stagnation. Further, the material may be selected such that it solidifies or cures around the temperature of blood. This would allow the ball to deform while being compacted for delivery, but subsequently expand and then solidify after deployment once in the presence of blood. Any of the various compressible ball embodiments described in relation to  FIGS. 8-10  or in any other figures may be used in any of the vascular valve prosthesis embodiments described herein. 
     Referring now to  FIGS. 11A and 11B , another embodiment of a vascular valve prosthesis system  350  includes an implantable prosthetic valve  352  and a delivery device  370 . The valve  352  includes an anchoring frame  354 , a valve seat  356 , a collapsible ball  358  and a tether  360  attaching the ball  358  to the valve seat  356 . The delivery device  370  includes a catheter body  372 , a deployment plunger  374  and an inflation catheter  376  attached to the ball  358 . The ball  358  may be an inflatable balloon (or “inflatable outer shell”), which is inflated with an inflation fluid. The fluid, in some embodiments, may be curable and thus hardens after curing. The inflatable balloon can exist in an un-inflated state during valve delivery ( FIG. 11A ), to be inflated with fluid, gel, or gas ( FIG. 11B ) and then, in some embodiments, cured after valve deployment. Alternatively, the balloon may be pre-filled with curable fluid, gel, or gas, which is then cured and solidifies after deployment. The fluid, gel, or gas may be cured by injecting a curing agent. It may be cured via heat, light (e.g., blue light or UV light), electricity, sound waves, chemical mixture, or other curing method. The curable fluid may be liquid silicone rubber, liquid polyurethane foam, an adhesive, such as epoxy or ultraviolet curing adhesive, or other curable material. 
       FIG. 11C  is a front, cross-sectional view of the inflation catheter  376  illustrated in  FIGS. 11A and 11B . In this embodiment, the inflation catheter  376  is a double-lumen catheter, with a light lumen  378  housing a fiber-optic cable to transmit light and an inflation lumen  380  used for fluid injection into the ball  358 . In alternative embodiments, the light lumen  378  may be used for any other curing devices and methods. 
       FIGS. 12A-12E  illustrate one embodiment of a method for inflating and curing the ball  358  using the inflation catheter  376 . Providing further detail, the inflation catheter includes an outer sheath that lies coaxially over the double lumen catheter body. The outer shell of the ball  358  includes a self-sealing valve that protrudes into the inside of the ball  358 , leaving a smooth surface on the outside of the ball  358  for proper sealing against the valve seat  356 . The self-sealing valve may be a cylindrical plug of elastomeric material with a collapsed central channel that is sealed to gas or fluid pressure within the balloon. 
     According to this method embodiment,  FIG. 12A  illustrates insertion of the catheter  376  into the self-sealing valve of the ball  358 . In  FIG. 12B , the ball  38  is then inflated with inflation fluid to a desired diameter, without detachment of the ball  358  from the catheter. In this embodiment, the ball  358  is inflated with light curing adhesive fluid via the fluid injection lumen  380  of the inflation catheter  376 . As in  FIG. 12C , following inflation of the ball  358  to the desired volume, light is transmitted via the fiber-optic cable lumen  378 , to solidify the fluid inside the ball  358 . In  FIG. 12D , detachment of the ball  358  is performed by pulling the catheter body of the inflation catheter  376  out of the ball  358  while the outer sheath of the inflation catheter  376  is held stationary to support the ball  358  during catheter withdrawal. Instead of a fiber-optic cable, the second channel could be used to transmit heat, sound waves, electricity, and/or a chemical that reacts with the chemical from the other channel to cure it. Finally, as in  FIG. 12E , the ball  358  is inflated, cured and detached from the inflation catheter  376 . 
     Referring back to  FIG. 11A , in alternative embodiments, the inflation catheter  376  (and/or a separate curing catheter) may be pre-attached to the ball  358  and loaded into the delivery device  370  with the ball  358  in its collapsed configuration. The inflation catheter  376  may then be used to inflate and cure the ball  358  after deployment out of the delivery device  370 . Alternatively, the ball  358  may be pre-filled with curable fluid and still be collapsible for delivery, so that the catheter  376  could instead be a single-lumen catheter designed for curing only (not inflation), via delivery of light, chemical, sound, etc. In either situation the fluid can be cured via heat, light, electricity, sound waves, chemical mixture, or other method, as described above. 
     Alternatively, the ball  358  could be made of a material or thickness that is less deformable once filled with any fluid, gel, or gas. The ball  358  could be left empty during loading and deployment to allow for a small catheter size, but after deployment filled with material using a catheter channel. This fluid does not need to be a curable fluid, but rather once sufficient fluid is injected into the ball  358 , the pressure causes it to retain its desired shape. 
       FIGS. 13A-13D  illustrate an alternative embodiment of a vascular prosthetic valve system  400 , including a prosthetic valve  402  and a delivery device  420 . As in previously described embodiments, the prosthetic valve  402  includes an anchoring frame  404 , a valve seat  406 , a collapsible ball  408  and a tether  410 . The delivery device  420  includes a catheter body  422 , a deployment plunger  424 , and an inflation attachment  426  attached to the deployment plunger  424 . The inflation attachment  426 , which in various embodiments may include one arm or multiple arms, extends over a portion of the anchoring frame  404  during delivery. The inflation attachment  426  has an inner lumen, which is in fluid communication with a lumen in the valve seat  406  and the tether  410 , which in turn leads into an interior of the ball  408 . Thus, inflation fluid may be passed through the inflation attachment  426 , the valve seat  406 , and the tether  410  to inflate the ball  408 . 
       FIG. 13A  shows the prosthetic valve  402  fully inside the delivery device  420  for delivery into the vein or other blood vessel. As shown in  FIG. 13B , the catheter body  422  may be retracted, allowing a first portion of the anchoring frame  404  to expand inside the vein. As illustrated in  FIG. 13C , inflation fluid may then be passed through the inflation attachment  426 , the valve seat  406 , and the tether  410  to inflate the ball  408 . Optionally, the ball  408  may be cured, using any of the curing methods listed above or any other suitable curing method. Then, as in  FIG. 13D , the inflation attachment  426  is retracted. As mentioned above, the inflation attachment  426  may have one arm or prong, or it may have multiple arms or prongs. One of the prongs, or multiple prongs, may have a single or double lumen, as described above. In a single lumen approach, fluid can be injected to distend the ball  408  to the desired shape where outward pressure is sufficient to prevent distortion and potential movement through the valve seat  406 . Alternatively, the ball  408  can be pre-filled with a curable agent. The single lumen can then be used to transmit a curing agent such as light. 
     Referring now to  FIGS. 14A-14D , in another embodiment, a collapsible/expandable ball  430  may include an outer shell  436  and a spiral cut elastic hollow sphere filler  432  that fills the inner cavity of the shell  436 . As illustrated in  FIG. 14C , the hollow sphere is made of a stretchable tube, which can be stretched for delivery through a delivery catheter ( FIG. 14D ) and then resumes its default spherical shape inside the shell  436  of the ball  430 . The hollow sphere  432  may be formed of a superelastic material, such as Nitinol alloy, cut to form a continuous strand. As an alternative, Nitinol wire may be formed into a spherical shape, heat treated and quenched in fluid to place it into an austenitic, superelastic phase. The stretched out wire may be advanced via a catheter into the shell, expanding the shell  436  and reforming into a sphere inside the shell  436 . Due to the higher forces exerted on the inside of the shell  436  as the superelastic strand or wire is advanced forward, the connection of the catheter to the self-sealing valve inside the shell  436  can be a positive mechanical joint, rather than a simple friction fit. The distal end of the catheter  434  may be externally threaded, and mate with internal threads on the inside of the self-sealing valve. 
     Referring now to  FIG. 15 , in one embodiment, a balloon  440  that is fluid filled, gel filled, or air filled may be placed in a stretched configuration for delivery, to decrease its diameter to fit within a delivery catheter. The stretched balloon  440  may be released following venous insertion. A system to provide a releasable stretched balloon  440  may include an elastic balloon that contains an inner self-sealing valve. A spring ball retainer  442  is attached to the inner aspect of the self-sealing valve. The spring ball retainer  442  may be a sphere constructed of spring material such as stainless spring steel or a high durometer polymeric material such as polycarbonate or Ultem. The sphere  442  is centrally slotted along the majority of its length, and it contains a through hole in the center of its posterior aspect. The spring ball  442  retainer resides in a normally closed position. When a wire stylet  444  is inserted through the posterior hole in the spring ball retainer  442 , the ball pivots open to present an enlarged vertical profile. A catheter designed to deliver and release a stretched balloon  440  contains a distal claw and an inner lumen that accommodates a wire stylet  444 . The opening in the distal claw of the balloon release catheter is sized such that the balloon  440  containing a closed spring ball retainer  442  slides into the inside of the claw. However, when the wire stylet  444  is advanced through the self-sealing valve and the spring ball retainer  442 , the ball retainer  442  opens in a clamshell fashion to lock the balloon  440  inside the distal claw. The wire stylet  444  is advanced further to stretch the balloon  440  axially, thereby decreasing its profile diameter. 
     In order to release the stretched balloon  440 , the wire stylet  444  is pulled out of the spring ball retainer  442  and the self-sealing valve, causing the spring ball retainer  442  to close and the balloon  440  to exit the distal claw in the balloon release catheter. The releasable stretched balloon concept may be combined with the curable fluid filled balloon concept, but substituting the wire stylet  444  with a single or double lumen tubular stylet containing one or both of a fluid injection lumen and a curing agent lumen (e.g., a light carrying fiber optic cable). The balloon  440  may be inflated with curable fluid, the tubular stylet may be withdrawn from the spring ball retainer but not the self-sealing valve to release the balloon  440  from the distal claw, and light may be transmitted into the balloon to cure the fluid adhesive inside the balloon  440 . Removal of the tubular stylet out of the self-sealing valve releases the expanded balloon  440 . 
     Referring now to  FIGS. 16A and 16B , in some embodiments of a vascular prosthetic valve, a ball  454  may be connected to the self-expanding valve anchoring frame  452  via an elastic tether (not visible, because inside of the frame  452 ). One end of the elastic tether is attached to the valve frame near or at the location of the valve seat, and the other end of the tether is attached to the ball  454 . As in  FIG. 16A , for delivery, the elastic tether is stretched to position the ball  454  outside of the distal end of the valve frame  452 . The valve frame  452  is loaded into the delivery catheter  450  in a compressed configuration, with the tethered ball  454  positioned immediately distal to the valve frame  452  in the tip of the delivery catheter  450 . Upon ejection of the implant from the delivery catheter  450 , as in  FIG. 16B , the valve frame  452  expands, and the elastic tether contracts to pull the ball  454  into the valve frame  452 . This design allows the maximal diameter of ball  454  to be accommodated inside a delivery catheter  450 . 
     With reference to  FIGS. 17A and 17B , in some embodiments, a ball  464  may be tethered via an inelastic tether  466  that is of sufficient length to allow the ball  464  to reside distal to the self-expanding frame  462  when the frame  462  is compressed inside the delivery catheter  460 . In this design, the ball  464  has a long excursion between its closed position, in contact with the valve seat, and its open position, where it extends past the distal end of the expanded valve frame  462 . This embodiment and the previously described embodiment allow for a smaller delivery catheter by moving the ball outside of the anchoring frame during loading and delivery. 
     Referring to  FIG. 18 , in one embodiment, a vascular prosthetic valve delivery device  470  may include two portions—a small diameter catheter portion  472  and a larger diameter catheter portion  474 . The larger diameter portion  474  may be sized to accommodate the prosthetic valve implant  476 , while smaller diameter portion  472  is designed for easier advancement and maneuverability through the blood vessel. This embodiment may be combined with other approaches described in this application. 
     Referring now to  FIG. 19A , in one embodiment of a vascular valve prosthesis  480 , the valve seat may include a semi-rigid ring  484  made from material such as FEP, PTFE, or the like, attached to the anchoring frame  482 . The ring  484  is configured to resist deformation post-implantation of the device  480 . In this embodiment, the ring  484  is attached to an inner surface of the anchoring frame  482 . 
     In alternative embodiments, the valve seat may be formed as part of the anchoring frame or as part of a material used to cover or coat the anchoring frame. In these embodiments, therefore, the valve seat is not a separate piece attached to the anchoring frame. For example, the valve seat in some embodiments might be a thickened portion of the anchoring frame. Alternatively, a coating substance, such as PTFE, might be used to form the valve seat. The ring embodiments of  FIGS. 19A and 19B  are thus merely examples. 
     In the embodiment of  FIG. 19B , the valve prosthesis  490  includes a ring  494  attached to an external surface of the anchoring frame  492 . In this embodiment, the ring  494  acts as part of the anchoring member  492 . In either embodiment, the ring  484 ,  494  may be covered or coated in the same continuous layer of material (such as PTFE) as the rest of the anchoring frame  482 ,  492  to allow a smooth continuous surface exposed to the blood. 
     In either of the two embodiments just described, as well as in any other alternative embodiments, the valve seat  484 ,  494  and anchoring frame  482 ,  492  may be sized, along with the ball, to optimize blood flow through the valve. For example, to evaluate or explain blood flow through the prosthetic valve, two different areas may be compared—the area of the opening of the valve seat and the area around the ball, between the ball and the inner wall of the anchoring member when the valve is in the open position (a flat donut shape around the ball). In some embodiments, these two areas may be designed to be exactly or approximately the same, and this may provide an advantageous flow through the valve. In other embodiments, the two areas might be within 50 percent of each other, or more ideally within 25 percent of each other, or even more ideally within 10 percent of each other. 
     Referring now to  FIG. 20 , in another alternative embodiment, a vascular valve prosthetic implant  500  may include an asymmetric anchoring frame  502  with a valve seat  512 , and a ball  508  disposed in the anchoring frame  502 . The anchoring frame  502  has an asymmetrical shape, with a downstream end  506  that has a small diameter and an upstream end  504  that has a large diameter. The small downstream end  506  is small enough to constrain the ball  508 , so that the ball  508  cannot escape the anchoring frame  502  from that end  506 . Thus, this small diameter end  506  acts as a ball retention member or feature, so that no additional ball retention members are needed. The large diameter end  504  is large enough to anchor the anchoring frame  502  in the vein. As seen in front view in the two right hand panels, this configuration includes an elliptical valve exit orifice with two side channels  510  for blood flow around the ball  508 , through the implant  500 . In an alternative embodiment, the downstream end  506  could include a wide, larger diameter portion after the narrowed, small diameter portion, to prevent flow between the device and vessel wall. This would allow the same flow area at the necked down portion, while allowing device symmetry and stability at the inflow and outflow regions. Similarly, and also optionally, the small diameter end  506  may also include a large diameter anchoring portion (not shown) around the smaller, inner portion, such that both ends  504 ,  506  anchor in the blood vessel, even though a portion of the small diameter end  506  is still configured to trap the ball  508 . 
     Referring now to  FIG. 21 , another embodiment of a vascular valve prosthesis  520  is illustrated. The anchoring frame  522  is again asymmetric, with a wider end  524  and a narrower end  526 . Also included are a ball  528  and a valve seat  532 . As seen in the front views of the right hand two panels, this embodiment includes an X-shaped opening  530 , which may provide for more assured constriction of the ball  528 . The constricted, upstream end  526  of the superelastic frame  502  contains the ball  508  within at all times, even upon compression of the frame  502  from different directions. Following implantation, compression of the patient&#39;s thigh may occur due to applied external forces. Therefore, in this embodiment, the opening  530  includes multiple indentations to prevent the opening  530  from becoming deformed in a way that would allow the ball  528  to escape. Compression of this exit orifice  530  from any direction will collapse the crossed exit orifice  530  inwards, thereby preventing release of the ball  528 . The blood flow area between the outer surface of the ball and the outline of the crossed exit orifice  530  may be greater than that of a symmetrical design. Again, the small diameter end  526  may optinally include a large diameter anchoring portion (not shown) around the smaller, inner portion, such that both ends  524 ,  526  anchor in the blood vessel. 
     With reference now to  FIG. 22 , in one embodiment, a vascular valve prosthetic implant  540  may include an anchoring frame, a tether  544 , a valve seat  546  and a collapsible ball  548 . In previously described embodiments, ball tethers were shown as being attached at one end to the ball and at an opposite end to the valve seat or anchoring member. In this embodiment, by contrast, the tether  544  is attached at one end to the ball  548  and has an opposite end that is V-shaped and attaches to two places on the anchoring frame  542 . Alternatively, the V-shaped end may split into three, four or any other number of ends that attach to the anchoring frame  542 . The V-shaped, two-point attachment of the tether  544  allows the ball  548  to be placed at maximal points of shear—i.e., in the center of the valve implant  540  and may also enhance strength of the tether connection. 
       FIG. 23  illustrates another embodiment of a vascular valve prosthetic implant  550 , including an anchoring frame  552 , two tethers  554 , a valve seat  556  and a collapsible ball  558 . In this embodiment, the two tethers  554  are attached between the ball  548  and the anchoring frame  552 . Alternatively, three, four or any other number of tethers  554  may be used. 
       FIG. 24  illustrates another embodiment of a vascular valve prosthetic implant  560 , including an anchoring frame  562 , two tethers  564 , a valve seat  566  and a collapsible ball  568 . In this embodiment, the two tethers  564  are attached between the ball  568  and the anchoring frame  562 . Alternatively, three, four or any other number of tethers  564  may be used. In alternative embodiments, any suitable number, length and configuration of tethers may be used. 
     Referring now to  FIG. 25 , in some embodiments, such as those just described, the attachment locations of the tether to the anchor frame  578  and the ball  576  may be selected at least in part to try to limit clot formation at the attachment points by positioning the attachment points at locations of maximal shear (with blood flow). For example, the tether (not shown in this illustration, since these principles may be applied to many different embodiments) may be attached to the ball  576  along an area of maximal shear  570  of blood flowing around the ball  576 . The tethers may also be attached to the anchoring frame  578  anywhere around the circumference of the inlet  572  that lead up to the valve seat or to the valve seat itself. These areas for locating the attachment points may help decrease the risk for thrombosis (clot formation), since they represent the areas of lowest risk for blood stagnation. 
     When the tether is attached to the stent valve anchor, it may be threaded through the wall of the device and tied around the outer portion of the device. It may also be fused directly to the wall of the device or valve seat of the device. Additional materials may be used or fused to cover any exit points from the device. When the tether is attached to the ball, it may be tunneled through the ball and knotted on the other end to hold it in place. It may also be tunneled and molded directly to the ball itself. It may also be one continuous piece of material. The process of attachment to the device and to the ball is important, since any disruption or irregularity in material may act as a nidus for clot formation. 
     Referring now to  FIG. 26 , another embodiment of a vascular prosthetic valve implant  580  includes an anchoring frame  582 , a tether  584 , a valve seat  586  and a compressible ball  588 . In this embodiment, the tether  584  is attaching to the inlet portion of the anchoring frame  582 . The length of the tether  584  can be important, as it controls the location of the ball  588 , which can impact clot formation. In this embodiment, the tether  584  is relatively short, so that when the valve is open, the ball  588  is located just in front of the valve seat. This may optimize flow around the ball  588 , increase shear to decrease clot formation, and help hold the ball  588  in the center of the lumen of the implant  580 . In various alternative embodiments, the tether  584  may have a length ranging from about 0.1 millimeters to about 25 millimeters, or more ideally between about 0.5 millimeters and about 10 millimeters. 
     Referring to  FIG. 27 , an alternative embodiment of a vascular prosthetic valve implant  590  includes an anchoring frame  592 , a tether  594 , a valve seat  596  and a compressible ball  598 . In this embodiment, the tether  594  is longer and extends beyond the end of the implant  590 , such that the ball  598  sits outside the anchoring frame  592  and rests in the native vein, thus preventing foreign material from resting on foreign material. The venous wall is known to have anti-thrombotic properties, and these may prevent thrombus formation at the area of ball-wall contact. 
     Referring to  FIG. 28 , in the venous system, there is a balance between minimizing the amount of material in the blood and separating the valve portion of the device from the edge, where there is the potential for edge stenosis. The embodiment of a vascular valve prosthesis  600  in  FIG. 28  includes an asymmetrical design, where the anchoring frame  602  includes a long end  603 . This allows the edge that is at risk for stenosis that can lead to valve complications to be further separated from the valve itself. Depending on the vessel being treated, the long end  603  may either be proximal or distal. Also depicted in  FIG. 28  are a tether  604 , valve seat  606  and ball  608 . 
     Referring to  FIG. 29 , an anchoring frame  610  for any of the valve prosthesis embodiments described herein may have an inlet taper angle  612  and/or an outlet taper angle  614  designed to optimize flow through the implant and prevent clot formation. In various embodiments, the angles  612 ,  614  may be the same or different. In general, a more gradual taper is preferred. For example, the anchoring frame  610  may have an inlet taper angle  612  and outlet taper angle  614  in the range of between about 5 degrees and about 60 degrees, or more ideally between about 15 degrees and about 35 degrees. 
     Referring to  FIG. 30 , in some embodiments, a prosthetic vein valve implant  620  may have an anchoring frame  622  with a coated portion  624  and an uncoated portion  626 . Additionally or alternatively, the implant  620  may be positioned within a vein V such that it lies within a native valve NV. Either or both of these features (the uncoated portion  626  and the placement in the native valve NV) may help stimulate the vein V to secrete anti-thrombotic agents. For example, if the entire portion  626  of the implant  620  after the valve seat is not coated with a hemostatic layer, blood will accumulate in the space between the implant  620  and the wall of the vein V. The vein&#39;s antithrombotic agents can decrease likelihood of clot in that area, similar to the natural vein valve NV. Similarly, if the implant  620  is placed such that the native valve NV lies on the implant  620 , it can further decrease risk of clotting via native anti-coagulant. This also creates a more physiologic space similar to the native leaflet valve NV. 
       FIGS. 31A-31C  depict yet another alternative embodiment of a venous valve prosthesis  630 , in this case it includes an anchoring frame  632 , a ball retention member  636 , a flap valve  634  with an opening  635  that acts as the valve seat, and a ball  638 .  FIG. 31A  is a partial cross-sectional view, depicting the ball  638  seated in the opening  635  of the flap valve  634  (front view in  FIG. 31B ), such that the implant  630  is in its closed position. In  FIG. 31C , the valve implant  630  is in the open position, with the flap valve  634  oriented in the opposite direction and the ball  638  located between the flap valve  634  and the ball retention member  636 . The flap valve  634  may be made of a thin material that can invert and evert, as illustrated in  FIGS. 31A and 31C . Blood flows through the opening  635  in one direction, but when blood flows in the other direction the ball  638  seals the hole  635  and prevents retrograde flow. In an alternative embodiment, a tether may be used instead of the ball retention member  636 . 
     Referring now to  FIG. 32 , in some embodiments, an anchoring frame  640  for a vascular valve prosthesis may include multiple anti-migration barbs  642  that are located apart from either of the two extreme ends of the frame  640 . Anti-migration features (such as barbs  642 ) were explained above and are generally configured to prevent the anchoring frame  640  from moving within the vein or other blood vessel after it has been delivered. As opposed to some of the embodiments described above, the barbs  642  of this embodiment of the anchoring frame  640  are positioned away from the two extreme ends of the anchoring frame  640 . Barbs  642  in this location help anchor the valve implant and prevent device migration and may also be less prone to the fibrotic reaction that may be promoted by barbs positioned at the proximal and distal edges of an anchoring frame. The barbs  642  are not in an area at high risk for stenosis and are not exposed to the flow of blood, due to the continuous layer of PTFE over the anchoring frame. This is important in decreasing the risk of edge stenosis and potential failure of the device. In alternative embodiments, the barbs  642  may be positioned only towards one end of the anchoring frame  640 , rather than near both ends as depicted in  FIG. 32 . 
     With reference now to  FIG. 33 , in another embodiment, a venous valve implant  650  may include an anchoring frame  652  with multiple anti-migration V-shaped protrusions  654 , rather than single-point barbs. The V-shaped protrusions  654  may also be located away from either of the extreme ends of the anchoring frame  652 , and they may help maintain the valve implant  650  in the blood vessel and prevent it from migrating. Alternative embodiments may include U-shaped protrusions, hooks or any other configuration of anti-migration members. And again, the V-shaped protrusions  654  may be located near either end of the anchoring frame  652  in some embodiments and need not be near both ends. 
     In various embodiments, the anti-migration barbs  642 , V-shaped protrusions  654  or other anti-migration features may form any of a range of angles, relative to the adjacent portion of the anchoring frame  640 ,  650  from which they protrude. For example, in some embodiments, the anti-migration features may form an angle with the anchoring frame  640 ,  650  of between about 15 degrees and about 60 degrees, or more ideally between about 25 degrees and about 45 degrees. 
     Referring to  FIGS. 34A-34C , in some embodiments, it may be desirable to remove the ball from a vascular valve implant, for example to replace it with a new ball. As illustrated in  FIG. 34A , a vascular valve implant  660  includes an expandable anchoring frame  662 , a ball  664  and a tether  666 , as described above in relation to many embodiments. A ball removal device  670  may be advanced into the vein to remove the ball  664 . The ball removal device  670  includes a catheter  672 , a grasper  674  and a tether cutter  676 . In  FIG. 34A , the grasper  674  is advanced out of the catheter  672  toward the ball  664 . In  FIG. 34B , the grasper  674  has been used to grasp the ball  664 , and the tether cutter  676  is advanced to cut the tether  666 . In  FIG. 34C , the cutter  676  has cut the tether  666  and has been retracted back into the catheter  672 . The grasper  674  may then be used to pull the ball  664  out of the valve implant  660 . The grasper  674  may attach to the ball  664  via suction, magnetic attraction, adhesion, or any other suitable mechanical attachment or modality. The ball  664  may then be pulled toward the catheter  672  to draw the tether  666  taught before using the cutter  676 . The cutter  676  may have a scissors end or any other suitable cutting device end. After the ball  664  is removed, the anchoring frame  662  may remain in place in the vessel. The ball  664  may be replaced by a new ball, in some embodiments. 
     In alternative embodiments, the valve implant may not include a tether, and the tether cutter  676  may not be needed. Thus, a ball removal device, in an alternative embodiment, may include only the catheter  672  and the grasper  674 . 
     Referring to  FIGS. 35A and 35B , in one alternative embodiment, a venous valve implant  700  may include an expandable anchoring frame  702  and a single leaflet flap valve  704 .  FIG. 35A  shows the valve  704  in the open position allowing blood  706  to flow though the implant  700 .  FIG. 35B  shows the valve  704  in the closed position, preventing retrograde blood flow  708  through the implant  700 . 
     In another alternative embodiment, shown in  FIGS. 36A and 36B , a venous valve implant  710  may include an expandable anchoring frame  712  and a two leaflet flap valve  714 .  FIG. 36A  shows the valve  714  in the open position allowing blood  716  to flow though the implant  710 .  FIG. 36B  shows the valve  714  in the closed position, preventing retrograde blood flow  718  through the implant  710 . In either of the two leaflet valve embodiments 700, 710, the flap(s) of the valve  704 ,  714  may be made of delrin, titanium, silastic, Teflon, silicone coated Teflon, pyrolyte, or any other suitable leaflet material. The valves  704 ,  714  are mechanical valves and are thus different than prior leaflet valves, which are bioprosthetic, thin, and more prone to failure. Further, placement in the expandable/collapsible anchoring frame  702 ,  712  allows for easier delivery in a percutaneous system. 
       FIGS. 37A and 37B  illustrate the effect of gravity on one embodiment of a venous valve prosthetic implant  720 , which includes an expandable anchoring frame  722 , a tether  724  and a ball  726 . In certain non-symmetric embodiments, such as one leveraging a single tether  724 , orientation of the implant  720  can alter how the ball  726  moves and rests in the vascular system. For example, if the patient is in a sitting or supine position, gravity will push the ball  726  downward, and the flow of blood will push the ball sideways, as depicted in  FIGS. 37A and 37B . The tether attachment location, relative to the direction of the gravitational force, can impact the likelihood that the ball gets “kicked up” by the blood flow and moves within the implant  720 .  FIG. 37A  depicts the forces and a tether orientation that will enhance ball movement. The tether orientation depicted in  FIG. 37B  is less likely to enhance ball movement. Increased ball movement leads to fewer areas of stasis or minimized blood flow, and therefore decreases likelihood of clot. Therefore, orientation of the venous valve implant  720  can play an important role in the success of the implant  720 . In this or other embodiments, one or more radiopaque markers may be placed on the implant  720  and/or on the delivery catheter to visualize orientation of the implant  720  on fluoroscopy during implantation. The delivery catheter can be rotated in order to orient the valve implant  720  appropriately prior to deployment from the catheter. This allows control of orientation upon deployment. Alternatively, the delivery catheter handle can have a demarcation or indicator that corresponds to the orientation of the valve implant  720  in the sheath. This catheter can then be appropriately rotated in order to orient the valve prior to deployment. 
       FIG. 38  depicts an alternate embodiment of a venous valve implant  730 , which includes an expandable anchoring frame  732  with two end portions and a central round portion  734 , a valve seat  736 , a ball retention member  738  and a ball  740 . The central round portion  734  of the anchoring frame  732  may provide for more uniform forward blood flow around the ball  740 , with decreased areas of stasis due to sudden changes in geometry or angles. As the geometry of the anchoring frame  732  encourages blood flow back behind the ball  740 , this helps prevent an area of stasis that would otherwise be seen behind the ball  740 . More uniform blood flow and decreased areas of stasis help prevent thrombus formation and device failure. In alternative embodiments, the central round portion  734  may be more elongate, more oval-shaped or the like. In other alternative embodiments, a tether may be used to retain the ball  740 . 
     Previously disclosed ball-valve type venous valve prostheses include a self-expanding anchor frame and a polymer ball with a density greater than the density of blood, to ensure that the ball would move into contact with the valve seat and close properly when the patient is in either an upright or a supine position. In one embodiment, for example, the density of the polymer ball may be approximately 2.2 g/cm3, while the density of blood is approximately 1.06 g/cm3. In alternative embodiments, it may be advantageous to use a ball that has a lower density than 2.2 g/cm3. Some embodiments of the venous valve implant, for example, may use polymer balls of a density nearly or approximately equal to the density of blood (1.06 g/cm3). Such a ball is referred to as a “neutral density ball” in this disclosure. Active movement of the neutral density ball may help prevent thrombus formation on the ball. In various embodiments, the neutral density ball of a venous ball valve prosthesis may have a density of less than about 2.2 g/cm3. More preferably, the ball may have a density between about 0.9 g/cm3 and about 1.2 g/cm3. In one embodiment, the ball may have a density of about 1.06 g/cm3. The neutral density of the ball may be achieved in any of several suitable ways. First, a material that has a natural density within that range (e.g., polyurethane) may be used. Alternatively, a material with a natural density lower than that range may be weighted to have an effective density within the range. 
     As discussed above, it is also desirable for the ball of the venous valve implant to be compressible, as this allows the implant to be introduced via a smaller diameter catheter. The compressible ball may be made of a biocompatible flexible foam, such as polyurethane or silicone rubber. A foam ball that exhibits a significant degree of compressibility is also characterized by a low density. For example, a 7 mm diameter polyurethane foam ball that may be compressed to fit into a catheter with a 4 mm inner diameter may have a density of 0.064 g/cc, compared to the density of blood at 1.06 g/ml. Thus, the foam is approximately 1/16th the density of blood, and weight must be added to the foam ball to render it functional as a valve. 
     Referring now to  FIGS. 39A and 39B , in one embodiment, a ball  740  of a venous valve implant may include a compressible foam outer portion  742  and a weighted core  744 , which may be a spherical stainless steel ball, for example. As depicted in  FIG. 39B , the compressible foam outer portion  742  and the core  744  may both have an aperture, through which a tether  746  may pass. (The aperture is not visible in the drawing.) The aperture may pass all the way through the core  744 , so that the tether  746  may be knotted  748  outside of one end of the aperture. The tether  746  may be any suitable tether material, as described above, such as a monofilament formed of polytetrafluoroethylene (PTFE). 
     Referring now to  FIG. 40 , in an alternative embodiment of a venous valve implant, a foam ball  752  (or other lightweight ball material) may be used without a weight but instead with an elastic tether  754 . The compressible foam ball  752  resides on one side of the valve seat, and the elastic tether  754  is attached to the valve frame (not illustrated) on the opposite side of the valve seat. The elastic tether  754  is attached to the frame under tension, so the compressible foam ball is biased against the valve seat with a calibrated force. The calibrated force may be equivalent to a ball of identical outer diameter containing a density close to the density of blood. The elastic tether  754  may extend through the diameter of the compressible foam ball  752 . The distal end of the elastic tether  754  may be knotted, and the knot  756  may be retracted into a cutaway in the foam ball  752 . The knot  756  may be covered with implantable grade adhesive filler  758  to yield a smooth contour to the surface of the foam ball  752  at the site of the knot  756 . The elastic tether  754  may be constructed of silicone rubber, polyurethane, or other elastic material. It may be a solid strand containing a round cross-section, with an outer diameter of approximately 0.1-0.2 mm. 
     Referring to  FIG. 41 , in another embodiment, a compressible ball  760  for a vascular valve implant may include a compressible ball portion  762  with multiple higher density weights  764 , such as stainless steel microspheres, dispersed throughout the ball portion  762 . This allows the ball  760  to have the same overall desired density, while allowing more complete compressibility. The ball  760  may also include an aperture extending through its diameter to accommodate a tether  766 , as described above. 
     As mentioned previously, a venous valve prosthesis with a tethered ball having a density nearly neutral to blood and also being compressible and self-expanding is advantageous, as it allows the prosthesis to be delivered via a delivery catheter with a significantly smaller outer diameter than is possible with a rigid, non-compressible ball. A compressible ball may be constructed of flexible polyurethane foam, as polyurethane foam is biocompatible and relatively non-thrombogenic. Flexible polyurethane foam is available that may be molded from two-part liquid mixtures that are combined and subsequently self-expand to form a compressible solid. Some of these foams form an outer skin that renders them fluid-tight. 
     In order to form flexible foam that is characterized by high compressibility; e.g.  10 : 1  compressibility, the resultant solid foam typically needs to have a density much lower than blood (e.g. 0.064 g/cm3 compared to the density of blood at 1.06 g/cm3). Weight may be added to such a compressible foam ball, to render it density-neutral to blood. Biocompatible weights  764 , such as stainless-steel microspheres, may be added to the mold during the formation of the foam ball  760 . For example, microspheres of 0.5 mm to 1.0 mm may be distributed within the flexible foam ball portion  762 , providing a ball density neutral to blood while still allowing it to be compressed substantially within the valve frame for insertion via a small diameter delivery catheter. The stainless-steel microspheres  764  incorporated in the polyurethane foam ball portion  762  render the ball  760  radiopaque for visibility during fluoroscopic examination. Alternatively, barium sulfate powder may be mixed into the polyurethane foam, to provide sufficient weight to form a blood neutral density foam ball  760  that is also radiopaque. 
     The inelastic tether that attaches the foam ball to the valve frame may be composed of PTFE monofilament suture, for example. Attachment of the tether to the foam ball may be performed in several ways. In one embodiment, a knot is tied near the end of the PTFE suture, the knotted suture is pulled into a central channel formed in the foam ball, and ultraviolet curable adhesive is used to glue the suture inside the channel. In another embodiment, a short length of thick-walled stainless-steel tubing is crimped near the distal end of the suture, and the crimped suture is glued into the central channel in the foam ball. Alternatively, the foam may be molded around the suture or a knotted end of the suture. In other alternative embodiments, the suture may be attached to one of the microspheres with foam subsequently being molded over it. 
     Alternatively, mechanical means can be used to hold the ball in the central lumen of the device to avoid ball to wall device contact. For example, a semi-rigid tether (e.g., Nitinol) can be used to allow the ball to translate proximally and distally in the body and device, but not medially or laterally to rest on the wall of the device. This allows the ball to still act as a functional valve, while avoiding ball to wall contact. 
     Referring to  FIGS. 42A and 42B , in some embodiments, compressibility of a vascular valve implant  770  may be limited or focused in certain dimensions. For example, in the depicted embodiment, the implant  770  includes an expandable anchoring frame  772 , a collapsible ball  774 , a tether  778  and a valve seat  779 , among other features. The ball  774  includes a central rod  776 , which may be made of metal, plastic or other rigid material. As illustrated in  FIG. 42A , when the rod  776  is oriented longitudinally, the ball  774  and the anchoring frame  772  may be collapsed, such as for delivery through a delivery catheter. As illustrated in  FIG. 42B , when the rod  776  is oriented horizontally (or perpendicular to the longitudinal axis of the anchoring frame  772 ), the rod  776  prevents the ball from collapsing inwards toward the center of the frame  772 . In other words, the rod  776  allows the ball  774  to compress in two dimensions, but not three. In some embodiments, the tether  778  may be attached to the rod  776 . By orienting the tether  778  perpendicular to the central rod/restrictor  776 , when the device  770  is deployed ( FIG. 42B ), the ball  774  will be prevented from squeezing through, or wedging into, the valve seat  779 . This design allows the ball  774  to be of lower density and compressible, while also preventing the ball  774  from being compressed and squeezed through the valve seat  779  due to backpressure.