Method of forming medical devices; intravascular occlusion devices |
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申请号 | EP09075025.8 | 申请日 | 1995-07-10 | 公开(公告)号 | EP2055263B1 | 公开(公告)日 | 2014-06-18 |
申请人 | AGA Medical Corporation; | 发明人 | Amplatz, Curtis; | ||||
摘要 | |||||||
权利要求 | |||||||
说明书全文 | The present invention generally relates to intravascular devices for treating certain medical conditions and, more particularly, provides a method of forming intravascular devices and certain novel intravascular occlusion devices. The devices made in accordance with the invention are particularly well suited for delivery through a catheter or the like to a remote location in a patient's vascular system or in analogous vessels within a patient's body. A wide variety of intravascular devices are used in various medical procedures. Certain intravascular devices, such as catheters and guidewires, are generally used simply to deliver fluids or other medical devices to specific locations within a patient's body, such as a selective site within the vascular system. Other, frequently more complex, devices are used in treating specific conditions, such as devices used in removing vascular occlusions or for treating septal defects and the like. In certain circumstances, it may be necessary to occlude a patient's vessel, such as to stop blood flow through an artery to a tumor or other lesion. Presently, this is commonly accomplished simply by inserting, e.g. Ivalon particles, a trade name for vascular occlusion particles, and short sections of coil springs into a vessel at a desired location. These "embolization agents" will eventually become lodged in the vessel, frequently floating downstream of the site at which they are released before blocking the vessel. In part due to the inability to precisely position the embolization agents, this procedure is often limited in its utility. Detachable balloon catheters are also used to block patients' vessels. When using such a catheter, an expandable balloon is carried on a distal end of a catheter. When the catheter is guided to the desired location, the balloon is filled with a fluid until it substantially fills the vessel and becomes lodged therein. Resins which will harden inside the balloon, such as an acrylonitrile, can be employed to permanently fix the size and shape of the balloon. The balloon can then be detached from the end of the catheter and left in place. Such balloon embolizations are also prone to certain safety problems, though. For example, if the balloon is not filled enough, it will not be firmly fixed in the vessel and may drift downstream within the vessel to another location, much like the loose embolization agents noted above. In order to avoid this problem, physicians may overfill the balloons; it is not uncommon for balloons to rupture and release the resin into the patient's bloodstream. Mechanical embolization devices, filters and traps have been proposed in the past. Even if some of those devices have proven effective, they tend to be rather expensive and time-consuming to manufacture. For example, some intravascular blood filters suggested by others are formed of a plurality of specially-shaped legs which are adapted to fill the vessel and dig into the vessel walls. In making most such filters, the legs must be individually formed and then painstakingly attached to one another, frequently entirely by hand, to assemble the final filter. Not only does this take significant skilled manpower, and hence increase the costs of such devices, the fact that each item must be made by hand tends to make quality control more difficult. This same difficulty and expense of manufacturing is not limited to such filters, but is experienced in many other intravascular devices as well. Accordingly, it would be desirable to provide a method for forming devices for deployment in a vessel in a patient's body which is both economical and yields consistent, reproducible results. It would also be advantageous to provide a reliable embolization device which is both easy to deploy and can be accurately placed in a vessel. The medical device and method of the invention are as set out in the claims. According to an aspect of the present invention a method of forming a medical device for deployment in a channel in a patient's body, the device having a preset expanded configuration and a collapsed configuration enabling passage of the device through a catheter, comprising the steps of:
In the method of the invention, a metal fabric formed of a plurality of resilient strands is provided, with the wires being formed of a resilient material which can be heat treated to substantially set a desired shape. This fabric is then deformed to generally conform to a molding surface of a molding element and the fabric is heat treated in contact with the surface of the molding element at an elevated temperature. The time and temperature of the heat treatment is selected to substantially set the fabric in its deformed state. After the heat treatment, the fabric is removed from contact with the molding element and will substantially retain its shape in the deformed state. The fabric so treated defines an expanded state of a medical device which can be deployed through a catheter into a channel in a patient's body. A distal end of a catheter can be positioned in a channel in a patient's body to position the distal end of the catheter adjacent a treatment site for treating a physiological condition. A medical device made in accordance with the process outlined above can be collapsed and inserted into the lumen of the catheter. The device is urged through the catheter and out the distal end, whereupon it will tend to return to its expanded state adjacent the treatment site. Further embodiments of the present invention also provide specific medical devices which may be made in accordance with the present invention. Such devices of the invention are formed of a metal fabric and have an expanded configuration and a collapsed configuration. The devices are collapsed for deployment through a catheter and, upon exiting the distal end of the catheter in a patient's channel, will resiliently substantially return to their expanded configuration. In accordance with a first of these embodiments, a generally elongate medical device has a generally tubular middle portion and a pair of expanded diameter portions, with one expanded diameter portion positioned at either end of the middle portion.
The present invention provides a reproducible, relatively inexpensive method of forming devices for use in channels in patients' bodies, such as vascular channels, urinary tracts, biliary ducts and the like, as well as devices which may be made via that method. In forming a medical device via the method of the invention, a metal fabric 10 is provided. The fabric is formed of a plurality of wire strands having a predetermined relative orientation between the strands. In the fabric of The pitch of the wire strands (i.e. the angle defined between the turns of the wire and the axis of the braid) and the pick of the fabric (i.e. the number of turns per unit length) may be adjusted as desired for a particular application. For example, if the medical device to be formed is to be used to occlude the channel in which it is placed, the pitch and pick of the fabric will tend to be higher than if the device is simply intended to filter bodily fluid passing therethrough. For example, in using a tubular braid such as that shown in The wire strands of the metal fabric used in the present method should be formed of a material which is both resilient and can be heat treated to substantially set a desired shape. Materials which are believed to be suitable for this purpose include a cobalt-based low thermal expansion alloy referred to in the field as Elgiloy, nickel-based high-temperature high-strength "superalloys" commercially available from Haynes International under the trade name Hastelloy, nickel-based heat treatable alloys sold under the name Incoloy by International Nickel, and a number of different grades of stainless steel. The important factor in choosing a suitable material for the wires is that the wires retain a suitable amount of the deformation induced by the molding surface (as described below) when subjected to a predetermined heat treatment. One class of materials which meet these qualifications are so-called shape memory alloys. Such alloys tend to have a temperature induced phase change which will cause the material to have a preferred configuration which can be fixed by heating the material above a certain transition temperature to induce a change in the phase of the material. When the alloy is cooled back down, the alloy will "remember" the shape it was in during the heat treatment and will tend to assume that configuration unless constrained from so doing. One particularly preferred shape memory alloy for use in the present method is nitinol, an approximately stoichiometric alloy of nickel and titanium, which may also include other minor amounts of other metals to achieve desired properties. NiTi alloys such as nitinol, including appropriate compositions and handling requirements, are well known in the art and such alloys need not be discussed in detail here. For example, The wire strands can comprise a standard monofilament of the selected material, i.e. a standard wire stock may be used. If so desired, though, the individual wire strands may be formed from "cables" made up of a plurality of individual wires. For example, cables formed of metal wires where several wires are helically wrapped about a central wire are commercially available and NiTi cables having an outer diameter of 0.0076 cm (0.003 inches) or less can be purchased. One advantage of certain cables is that they tend to be "softer" than monofilament wires having the same diameter and formed of the same material. Additionally, if the device being formed from the wire strands is to be used to occlude a vessel, the use of a cable can increase the effective surface area of the wire strand, which will tend to promote thrombosis. In preparation of forming a medical device in keeping with the invention, an appropriately sized piece of the metal fabric is cut from the larger piece of fabric which is formed, for example, by braiding wire strands to form a long tubular braid. The dimensions of the piece of fabric to be cut will depend, in large part, upon the size and shape of the medical device to be formed therefrom. When cutting the fabric to the desired dimensions, care should be taken to ensure that the fabric will not unravel. In the case of tubular braids formed of NiTi alloys, for example, the individual wire strands will tend to return to their heat-set configuration unless constrained. If the braid is heat treated to set the strands in the braided configuration, they will tend to remain in the braided form and only the ends will become frayed. However, it may be more economical to simply form the braid without beat treating the braid since the fabric will be heat treated again in forming the medical device, as noted below. In such untreated NiTi fabrics, the strands will tend to return to their unbraided configuration and the braid can unravel fairly quickly unless the ends of the length of braid cut to form the device are constrained relative to one another. One method which has proven to be useful to prevent the braid from unraveling is to clamp the braid at two locations and cut the braid to leave a length of the braid having clamps (15 in Alternatively, one can solder, braze, weld or otherwise affix the ends of the desired length together (e.g. with a biocompatible cementitious organic material) before cutting the braid. Although soldering and brazing of NiTi alloys has proven to be fairly difficult, the ends can be welded together, such as by spot welding with a laser welder. The same problems present themselves when a flat sheet of fabric such as the woven fabric shown in Once an appropriately sized piece of the metal fabric is obtained, the fabric is deformed to generally conform to a surface of a molding element. As will be appreciated more fully from the discussion below in connection with The molding element can be a single piece, or it can be formed of a series of mold pieces which together define the surface to which the fabric will generally conform. The molding element can be positioned within a space enclosed by the fabric or can be external of such a space, or can even be both inside and outside such a space. In order to illustrate one example of how such a mold may be configured and how it may be used in accordance with the method of the invention, reference will be had to In the molding element illustrated in The overall shape and dimensions of the center section can be varied as desired; it is generally the size of the central recesses 34 and the forming port 36 which will define the size and shape of the middle of the finished device, as explained below. If so desired, each half 32 may be provided with a manually graspable projection 38. In the embodiment shown in the drawings, this projection 38 is provided at a location disposed away from the abutting faces of the respective halves. Such a manually graspable projection 38 will simply enable an operator to more easily join the two halves to define the recesses 34 and forming port 36. The center section is adapted to cooperatively engage a pair of end plates 40 for forming the desired device. In the embodiment shown in One or more channels 48 for receiving bolts and the like may also be provided through each of the end plates and through the center section 30. By passing bolts through these channels 48, one can assemble the molding element 20 and retain the metal fabric in the desired shape during the heat treatment process, as outlined below. In utilizing the molding element 20 shown in A central portion of the length of the metal braid may be positioned within one of the two halves of the forming port 36 and the opposed halves 32 of the center section may be joined to abut one another to restrain a central portion of the metal braid within the central forming port 36 through the center section. The tubular braid will tend to have a natural, relaxed diameter which is defined, in large part, when the tubular braid is formed. Unless the tubular braid is otherwise deformed, when the wire strands are in their relaxed state they will tend to define a generally hollow tube having the predetermined diameter. The outer diameter of the relaxed braid may be, for example, about 4 mm. The relative size of the forming port 36 in the central section 30 of the molding element and the natural, relaxed outer diameter of the tubular braid may be varied as desired to achieve the desired shape of the medical device being formed. In the embodiment shown in If so desired, a generally cylindrical internal molding section (not shown) may also be provided. This internal molding section has a slightly smaller diameter than the inner diameter of the forming port 36. In use, the internal molding section is placed within the length of the metal fabric, such as by manually moving the wire strands of the fabric apart to form an opening through which the internal molding section can be passed. This internal molding section should be positioned within the tubular braid at a location where it will be disposed within the forming port 36 of the center section when the molding element is assembled. There should be a sufficient space between the outer surface of the interior molding section and the inner surface of the forming port 36 to permit the wire strands of the fabric 10 to be received therebetween. By using such an internal molding section, the dimensions of the central portion of the finished medical device can be fairly accurately controlled. Such an internal molding section may be necessary in circumstances where the natural, relaxed outer diameter of the tubular braid 10 is less than the inner diameter of the forming port 36 to ensure that the braid conforms to the inner surface of that forming port. However, it is not believed that such an internal molding section would be necessary if the natural, relaxed outer diameter of the braid were larger than the inner diameter of the forming port 36. As noted above, the ends of the tubular braid should be secured in order to prevent the braid from unraveling. Each end of the metal fabric 10 is desirably received within a cavity 46 formed in one of the two end plates 40. If a clamp (15 in As best seen in In the molding element 20 shown in It should be understood that the specific shape of the particular molding element 20 shown in Accordingly, the specific molding element 20 shown in Once the molding element 20 is assembled with the metal fabric generally conforming to a molding surface of that element, the fabric can be subjected to a heat treatment while it remains in contact with that molding surface. This heat treatment will depend in large part upon the material of which the wire strands of the metal fabric are formed, but the time and temperature of the heat treatment should be selected to substantially set the fabric in its deformed state, i.e., wherein the wire strands are in their reoriented relative configuration and the fabric generally conforms to the molding surface. The time and temperature of the heat treatment can vary greatly depending upon the material used in forming the wire strands. As noted above, one preferred class of materials for forming the wire stands are shape memory alloys, with nitinol, a nickel titanium alloy, being particularly preferred. If nitinol is used in making the wire strands of the fabric, the wire strands will tend to be very elastic when the metal is in its austenitic phase; this very elastic phase is frequently referred to as a "superelastic" or "pseudoelastic" phase. By heating the nitinol above a certain phase transition temperature, the crystal structure of the nitinol metal when in its austenitic phase can be set. This will tend to "set" the shape of the fabric and the relative configuration of the wire strands in the positions in which they are held during the heat treatment. Suitable heat treatments of nitinol wire to set a desired shape are well known in the art. Spirally wound nitinol coils, for example, are used in a number of medical applications, such as in forming the coils commonly carried around distal lengths of guidewires. A wide body of knowledge exists for forming nitinol in such medical devices, so there is no need to go into great detail here on the parameters of a heat treatment for the nitinol fabric preferred for use in the present invention. Briefly, though, it has been found that holding a nitinol fabric at about 500°C to about 550°C for a period of about 1 to about 30 minutes, depending on the softness or harness of the device to be made, will tend to set the fabric in its deformed state, i.e. wherein it conforms to the molding surface of the molding element. At lower temperatures the heat treatment time will tend to be greater (e.g. about one hour at about 350°C) and at higher temperatures the time will tend to be shorter (e.g. about 30 seconds at about 900°C). These parameters can be varied as necessary to accommodate variations in the exact composition of the nitinol, prior heat treatment of the nitinol, the desired properties of the nitinol in the finished article, and other factors which will be well known to those skilled in this field. Instead of relying on convection heating or the like, it is also known in the art to apply an electrical current to the nitinol to heat it. In the present invention, this can be accomplished by, for example, hooking electrodes to the clamps 15 carried at either end of the metal fabric illustrated in After the heat treatment, the fabric is removed from contact with the molding element and will substantially retain its shape in a deformed state. When the molding element 20 illustrated in The vascular occlusion device 60 of The relative sizes of the tubular middle section and the expanded diameter portions can be varied as desired. In this particular embodiment, the medical device is intended to be used as a vascular occlusion device to substantially stop the flow of blood through a patient's blood vessel. When the device 60 is deployed within a patient's blood vessel, as detailed below, it will be positioned within the vessel such that its axis generally coincides with the axis of the vessel. The dumbbell-shape of the present device is intended to limit the ability of the vascular occlusion device 60 to turn at an angle with respect to the axis of the blood vessel to ensure that it remains in substantially the same position in which the operator deploys it within the vessel. Although the illustrated embodiments of this invention only have two expanded diameter portions, it should be understood that the device could have more than two such expanded diameter portions. For example, if the device has three expanded diameter portions, each expanded diameter portion is separated from at least one other expanded diameter portion by a tubular portion having a smaller diameter. If so desired, the diameters of each of the expanded diameter portions can be the same, but they need not be the same. In order to relatively strongly engage the lumen of the blood vessel, the maximum diameter of the expanded diameter portions 64 (which occurs along the middle ridge 66 in this embodiment) should be selected so that it is at least as great as the diameter of the lumen of the vessel in which it is to be deployed, and is optimally slightly greater than that diameter. When it is deployed within the patient's vessel, the vascular occlusion device 60 will engage the lumen at two spaced-apart locations. The device 60 is desirably longer along its axis than the dimension of its greatest diameter. This will substantially prevent the vascular occlusion device 60 from turning within the lumen at an angle to its axis, essentially preventing the device from becoming dislodged and tumbling along the vessel with blood flowing through the vessel. The relative sizes of the generally tubular middle portion 62 and expanded diameter portion 64 of the vascular occlusion device 60 can be varied as desired for any particular application. For example, the outer diameter of the middle portion 62 may range between about one quarter and about one third of the maximum diameter of the expanded diameter portions 64 and the length of the middle portion 62 may comprise about 20% to about 50% of the overall length of the device. Although these dimensions are suitable if the device 60 is to be used solely for occluding a vascular vessel, it is to be understood that these dimensions may be varied if the device is to be used in other applications, such as where the device is intended to be used simply as a vascular filter rather than to substantially occlude the entire vessel or where the device is deployed in a different channel in a patient's body. The aspect ratio (i.e., the ratio of the length of the device over its maximum diameter or width) of the device 60 illustrated in The pick and pitch of the metal fabric 10 used in forming the device 60, as well as some other factors such as the number of wires employed in a tubular braid, are important in determining a number of the properties of the device. For example, the greater the pick and pitch of the fabric, and hence the greater the density of the wire strands in the fabric, the stiffer the device will be. Having a greater wire density will also provide the device with a greater wire surface area, which will generally enhance the tendency of the device to occlude a blood vessel in which it is deployed. This thrombogenicity can be either enhanced, e.g. by a coating of a thrombolytic agent or by attaching silk or wool fabric to the device, or abated, e.g. by a coating of a lubricious, anti-thrombogenic compound. A variety of materials and techniques for enhancing or reducing thrombogenicity are well known in the art and need not be detailed here. When the device is deployed in a patient's vessel, thrombi will tend to collect on the surface of the wires. By having a greater wire density, the total surface area of the wires will be increased, increasing the thrombolytic activity of the device and permitting it to relatively rapidly occlude the vessel in which it is deployed. It is believed that forming the occlusion device 60 from a 4 mm diameter tubular braid having a pick of at least about 40 and a pitch of at least about 30° will provide sufficient surface area to substantially completely occlude a blood vessel of 2 mm to about 4 mm in inner diameter in a suitable period of time. If it is desired to increase the rate at which the device 60 occludes the vessel in which it is deployed, any of a wide variety of known thrombolytic agents can be applied to the device. As explained more fully below in connection with The base 88 desirably flares out relatively rapidly to define a shoulder tapering radially outwardly from the middle 86 of the body. When the device is deployed in a vessel, this shoulder will abut the lumen of one of the vessels being treated. The forward end 84 is retained within the vessel and urges the base 88 of the body open to ensure that the shoulder engages the wall of the vessel to prevent the device 80 fmm becoming dislodged from within the shunt. As detailed above, in making a device of the invention it is desirable to attach the ends of the wire strands forming the metal fabric 10 to one another to prevent the fabric from unraveling. In the illustrations of The rearward ends of the wire strands are shown as being attached to one another by an alternative clamping means 90. This clamp 90 serves the same purpose as the schematically illustrated clamp 15, namely to interconnect the ends of the wires. However the clamp 90 also serves to connect the device 80 to a delivery system (not shown). In the embodiment shown, the clamp 90 is generally cylindrical in shape and has a recess for receiving the ends of the wires to substantially prevent the wires from moving relative to one another, and a threaded outer surface. The threaded outer surface is adapted to be received within a cylindrical recess (not shown) on a distal end of a delivery device and to engage the threaded inner surface of the delivery device's recess. The delivery device (not shown) can take any suitable shape, but desirably comprises an elongate, flexible metal shaft having such a recess at its distal end. The delivery device can be used to urge the PDA occlusion device 80 through the lumen of a catheter for deployment in a channel of the patient's body, as outlined below. When the device is deployed out the distal end of the catheter, the device will still be retained by the delivery device. Once the proper position of the device 80 in the shunt is confirmed, the shaft of the delivery device can be rotated about its axis to unscrew the clamp 90 from the recess in the delivery means. By keeping the PDA device 80 attached to the delivery means, the operator could still retract the device for repositioning if it is determined that the device is not properly positioned in the first attempt. This threaded attachment will also allow the operator to control the manner in which the device 80 is deployed out of the distal end of the catheter. As explained below, when the device exits the catheter it will tend to resiliently return to a preferred expanded shape which is set when the fabric is heat treated. When the device springs back into this shape, it may tend to act against the distal end of the catheter, effectively urging itself forward beyond the end of the catheter. This spring action could conceivably result in improper positioning of the device if the location of the device within a channel is critical, such as where it is being positioned in a shunt between two vessels. Since the threaded clamp 90 can enable the operator to maintain a hold on the device during deployment, the spring action of the device can be controlled and the operator can control the deployment to ensure proper positioning. A PDA occlusion device 80 of this embodiment can advantageously be made in accordance with the method outlined above, namely deforming a metal fabric to generally conform to a molding surface of a molding element and heat treating the fabric to substantially set the fabric in its deformed state. The molding element 100 generally comprises a body portion 110 and an end plate 120. The body portion 110 is adapted to receive and form the body 82 of the device 80 while the end plate is adapted to compress against the metal fabric to form the forward end 84. The body portion 110 includes an elongate, generally tubular central segment 112 which is sized to receive the elongate body 82 of the device. The central segment 112 of the molding element 100 optimally has an internal diameter slightly less than the natural, relaxed outer diameter of the tubular braid of which the device is formed. This compression of the braid will help yield devices with reproducibly sized bodies 82. The forward end of the body portion 110 includes a back plate 114 which has a generally annular sidewall 116 depending downwardly therefrom. The sidewall defines a recess 118 which is generally circular in shape. The end plate 120 of the molding element 100 has a generally disc-shaped face 122, which desirably has a clamp port 124 approximately centered therein for receiving a clamp 15 attached to the metal fabric, as noted above. The end plate also has an annular sidewall 126 which extends generally upwardly from the face 122 to define a generally cylindrical recess 128 in the end plate 120. The sidewall 116 of the body portion 110 is sized to be received within the recess 128 of the end plate. In use, the metal fabric is placed in the molding element and the body portion 110 and the end plate 120 are brought toward one another The inner face of the back plate 114 will engage the fabric and tend to urge it under compression generally radially outwardly. The fabric will then be enclosed generally within the recess 118 of the body portion and will generally conform to the inner surface of that recess. If one prevents the entire clamp 15 from passing through the clamp port 124, the fabric will be spaced slightly away from the inner surface of the face 122, yielding a slight dome shape in the forward end 84 of the device, as illustrated in Once the fabric is compressed in the molding element 100 so that it generally conforms to the molding surface of the molding element, the fabric can be subjected to a heat treatment such as is outlined above. When the molding element is opened again by moving the body portion 110 and the end plate 120 away from one another again, the fabric will generally retain its deformed, compressed configuration. The device can then be collapsed, such as by urging the clamps 15, 90 generally axially away from one another, which will tend to collapse the device toward its axis. The collapsed device 80 can then be passed through a catheter for deployment in a channel in a patient's vascular system. The device can then be retracted so that the forward end 84 engages the wall of the pulmonary artery P. If one continues to retract the catheter, the engagement of the device with the wall of the pulmonary artery will tend to naturally pull the body portion 82 of the device from the catheter, which will permit the body portion to return to its expanded configuration. The body portion should be sized so that it will frictionally engage the lumen of the PDA's shunt. The device 80 will then be held in place by the combination of the friction between the body portion and the lumen of the shunt and the engagement between the wall of the pulmonary artery and the forward end 84 of the device. Over a relatively short period of time, thrombi will form in and on the device 80 and the thrombi will occlude the PDA. If so desired, the device may be coated with a suitable thrombolytic agent to speed up the occlusion of the PDA. This filter 180 has a generally conical configuration, tapering generally radially outwardly from its rearward end 182 to its forward end 184. A length of the device adjacent its forward end is adapted to engage the walls of a lumen of a channel. The maximum diameter of the filter device 180 is therefore at least as large as the inner diameter of the channel in which it is to be positioned so that at least the forward end will engage the wall of the vessel to substantially lock the device in place. Having a series of unsecured ends 185 of the wire strands adjacent the forward end of the device will assist in seating the device in the channel because the ends of the wires will tend to dig into the vessel wall slightly as the forward end of the device urges itself toward its fully expanded configuration within the vessel. The combination of the friction between the outwardly urging forward end of the device and the tendency of the wire ends to dig into the vessel walls will help ensure that the device remains in place where it is deployed rather than floating freely within a vessel to reach an undesired location. The method in which the device 180 is deployed may vary depending on the nature of the physiological condition to be treated. For example, in treating an arteriovenous fistula, the device may be carefully positioned, as described above, to occlude the flow of blood at a fairly specific location. In treating other conditions (e.g. an arteriovenous malformation), however, if may be desired to simply release a number of these devices upstream of the malformation in a vessel having a larger lumen and simply allow the devices to drift from the treatment site to lodge in smaller vessels downstream. The decision as to whether the device 180 should be precisely positioned at an exact location within the channel in a patient's body or whether it is more desirable to allow the device(s) to float to their final lodging site will depend on the size of the channels involved and the specific condition to be treated. This decision should be left to the individual operator to be made on a case-by-case basis as his or her experience dictates; there is no one right or wrong way to deploy the device 180 without regard to the conditions at hand. In the embodiment shown in The ends of the wire strands at the rearward end 182 of the device are secured with respect to one another, such as by means of a threaded clamp 90 such as that described above in connection with In the embodiment illustrated in When the a tubular braid is used in forming this device, the tubular metal fabric may be applied to the molding element by placing the molding element within the tubular braid and clamping the ends of the braid about the molding element before cutting the braid to the desired length. In order to better facilitate the attachment of the clamps 90 to the ends of the tubular braid, the ends 206 of the molding element may be rounded, as shown, rather than tapering to a sharper point at the ends of the molding element. In order to ensure that the braid more closely conforms to the outer surface of the molding element 200, i.e. the molding element's molding surface, the natural, relaxed diameter of the braid should be less than the maximum diameter of the element, which occurs at its middle 204. This will place the metal fabric in tension about the middle of the element and, in combination with the clamps at the ends of the braid, cause the braid to generally conform to the molding surface. The two molding sections should be readily attached to one another with the larger, open ends 226 of the sections abutting one another. The mold sections can simply be clamped together, such as by providing a reusable jig (not shown) which can be used to properly position the sections 214, 216 with respect to one another. If so desired, bolt holes 228 or the like may be provided to allow a nut and bolt, or any similar attachment system, to be passed through the holes and attach the sections 214, 216 together. In use, a suitably sized piece of a metal fabric, optimally a length of a tubular braid, is placed in the recess 212 of the molding element and the two molding sections 214, 216 are urged toward one another. The fabric should have a relaxed axial length longer than the axial length of the recess 212 so that bringing the sections toward one another will axially compress the fabric. This axial compression will tend to urge the wire strands of the braid radially outwardly away from the axis of the braid and toward engagement with the molding surface of the element 210, which is defined by the surface of the recess 212. Once the metal fabric is deformed to generally conform to the molding surface of either molding element 200 or 210, the fabric can be heat treated to substantially set the shape of the fabric in its deformed state. If molding element 200 is used, it can then be removed from the interior of the metal fabric. If there is sufficient room between the resilient wire strands, the molding element can simply be removed by opening the web of wire strands and pulling the molding element out of the interior of the metal fabric. If molding element 210 is employed, the two molding sections 214, 216 can be moved away from one another and the molded fabric can be retrieved from the recess 212. Depending on the shape of the molding surface, the resulting formed shape may resemble either a pair of abutting hollow cones or, as noted above, a football, with clamps, welds or the like provided at either end of the shape. This shape can then be cut into two halves by cutting the wires in a direction generally perpendicular to the shared axis of the cones (or the major axis of the ovoid shape) at a location about midway along its length. This will produce two separate filter devices 180 substantially as illustrated in In an alternative embodiment of this method, the molding element 200 is formed of a material selected to permit the molding element to be destroyed for removal from the interior of the metal fabric. For example, the molding element may be formed of a brittle or friable material, such as glass. Once the material has been heat treated in contact with the molding surface of the molding element, the molding element can be broken into smaller pieces which can be readily removed from within the metal fabric. If this material is glass, for example, the molding element and the metal fabric can be struck against a hard surface, causing the glass to shatter. The glass shards can then be removed from the enclosure of the metal fabric. The resultant shape can be used in its generally conical shape, or it can be cut into two separate halves to produce a device substantially as shown in Alternatively, the molding element 200 can be formed of a material which can be chemically dissolved, or otherwise broken down, by a chemical agent which will not substantially adversely affect the properties of the metal wire strands. For example, the molding element can be formed of a temperature-resistant plastic resin which is capable of being dissolved with a suitable organic solvent. The fabric and the molding element can be subjected to a heat treatment to substantially set the shape of the fabric in conformance with the surface of the molding element, whereupon the molding element and the metal fabric can be immersed in the solvent. Once the molding element is substantially dissolved, the metal fabric can be removed and either used in its current shape or cut into separate halves, as outlined above. Care should be taken to ensure that the material selected to form the molding element is capable of withstanding the heat treatment without losing its shape, at least until the shape of the fabric has been set. For example, the molding element could be formed of a material having a melting point above the temperature necessary to set the shape of the wire strands, but below the melting point of the metal forming the strands. The molding element and metal fabric can then be heat treated to set the shape of the metal fabric, whereupon the temperature can be increased to substantially completely melt the molding element, thereby removing the molding element from within the metal fabric. It should be understood that the methods outlined immediately above for removing the metal fabric 10 from the molding element 200 can be used in connection with other shapes, as well. Although these methods may not be necessary or desirable if the molding element is carried about the exterior of the metal fabric (such as are elements 30-40 of the molding element 20 of This molding element 230 can be used with a metal fabric which is in the form of a tubular braid. If such a fabric is used and a clamp 15 (not shown in this drawing) or the like is provided to connect the ends of the wire strands adjacent one end of the device, a recess (not shown) analogous to the cavity 46 in the face of the compression disk 44 of molding element 20 ( However, the present molding element 230 can be used quite readily with a flat woven piece of metal fabric, such as is illustrated in As can be seen by the discussion of the various molding elements 200, 210 and 230 in We further provide a method of treating a physiological condition of a patient. In accordance with this method, a medical device suitable for treating the condition, which may be substantially in accordance with one of the embodiments outlined above, is selected. For example, if a patent ductus arteriosus is to be treated, the PDA occlusion device 80 of Medical devices made in accordance with the method of the invention outlined above have a preset expanded configuration and a collapsed configuration which allows the device to be passed through a catheter. The expanded configuration is generally defined by the shape of the medical fabric when it is deformed to generally conform to the molding surface of the molding element. Heat treating the metal fabric substantially sets the shapes of the wire strands in the reoriented relative positions when the fabric conforms to the molding surface. When the metal fabric is then removed from the molding element, the fabric may define a medical device in its preset expanded configuration. The medical device can be collapsed into its collapsed configuration and inserted into the lumen of the catheter. The collapsed configuration of the device may be of any shape suitable for easy passage through the lumen of a catheter and proper deployment out the distal end of the catheter. For example, the devices shown in Once the medical device is collapsed and inserted into the catheter, it may be urged along the lumen of the catheter toward the distal end of the catheter. This may be accomplished by using a guidewire or the like to abut against the device and urge it along the catheter. When the device begins to exit the distal end of the catheter, which is positioned adjacent the desired treatment site, it will tend to resiliently return substantially entirely to its preset expanded configuration. Superelastic alloys, such as nitinol, are particularly useful in this application because of their ability to readily return to a particular configuration after being elastically deformed to a great extent. Hence, simply urging the medical device out of the distal end of the catheter tend to properly deploy the device at the treatment site. Although the device will tend to resiliently return to its initial expanded configuration (i.e. its shape prior to being collapsed for passage through the catheter), it should be understood that it may not always return entirely to that shape. For example, the device 60 of If the device is to be used to permanently occlude a channel in the patient's body, such as the devices 60 and 80 described above may be, one can simply retract the catheter and remove it from the patient's body. This will leave the medical device deployed in the patient's vascular system so that it may occlude the blood vessel or other channel in the patient's body. In some circumstances, the medical device may be attached to a delivery system in such a manner as to secure the device to the end of the delivery means, such as when the threaded clamp 90 shown in |