Abstract:
A medical device delivery system including a mechanism to concurrently move an inner member and an outer member in opposite directions and at pre-set speed ratio can be operated, for example, to reconstrain a foreshortening self-expanding stent with a known foreshortening ratio between the crimped diameter in an intraluminal catheter based delivery system and the nominal deployed diameter in the body lumen. The mechanism can include two oppositely handed lead screws that concurrently turn and two followers, each follower operatively connected to one of the two shafts (e.g., the inner and outer member).

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority to U.S. Provisional Patent Application No. 62/074,609, filed Nov. 3, 2014, which is expressly incorporated in its entirety. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The invention relates to the field of medical devices, and more particularly medical devices or delivery systems for and methods of controllably deploying stents and reconstraining partially deployed stents. 
         [0004]    In some applications, the invention relates to systems for delivering a self-expandable intraluminal graft (“stents”) for use within a body passageway or duct which are particularly useful for repairing blood vessels narrowed or occluded by disease. 
         [0005]    2. Related Devices and Methods 
         [0006]    Transluminal prostheses have been widely used in the medical arts for implantation in blood vessels, biliary ducts, or other similar lumens of the living body. These prostheses are commonly known as stents and are used to maintain, open, or dilate tubular structures. An example of a commonly used stent is given in U.S. Pat. No. 4,733,665 filed by Palmaz on Nov. 7, 1985, which is hereby incorporated in its entirety herein by reference. Such stents are often referred to as balloon expandable stents. Typically the stent is made from a solid tube of stainless steel. Thereafter, a series of cuts are made in the wall of the stent. The stent has a first smaller diameter which permits the stent to be delivered through the human vasculature by being crimped onto a balloon catheter. The stent also has a second, expanded diameter, upon the application, by the balloon catheter, from the interior of the tubular shaped member of a radially, outwardly extending force. 
         [0007]    However, such stents are often impractical for use in some vessels such as the carotid artery or the superficial femoral artery. The carotid artery is easily accessible from the exterior of the human body, and is often visible by looking at one&#39;s neck. A patient having a balloon expandable stent made from stainless steel, or the like, placed in his or her carotid artery might be susceptible to severe injury through day-to-day activity. A sufficient force placed on the patient&#39;s neck, such as by falling, could cause the stent to collapse resulting in injury to the patient. In order to prevent this and to address other shortcomings of balloon expandable stents, self-expanding stents were developed. Self-expanding stents act like springs and will recover to their expanded or implanted configuration after being crushed. 
         [0008]    One type of self-expanding stent is disclosed in U.S. Pat. No. 4,665,771, which stent has a radially and axially flexible, elastic tubular body with a predetermined diameter that is variable under axial movement of ends of the body relative to each other and which is composed of a plurality of individually rigid but flexible and elastic thread elements defining a radially self-expanding helix. This type of stent is known in the art as a “braided stent” and is so designated herein. 
         [0009]    Other types of self-expanding stents use alloys such as Nitinol (Ni—Ti alloy) which have shape memory and/or superelastic characteristics in medical devices that are designed to be inserted into a patient&#39;s body. The shape memory characteristics allow the devices to be deformed to facilitate their insertion into a body lumen or cavity and then be heated within the body so that the device returns to its “memorized” shape. Superelastic characteristics on the other hand generally allow the metal to be deformed and restrained in the deformed condition to facilitate the insertion of the medical device containing the metal into a patient&#39;s body, with such deformation causing the phase transformation. Once within the body lumen the restraint on the superelastic member can be removed, thereby reducing the stress therein so that the superelastic member can return to its original un-deformed shape by the transformation back to the original phase, or close to it (as the implanted shape is designed to have some deformation to provide a force to prop open the vessel in which it is implanted). 
         [0010]    Alloys having shape memory/superelastic characteristics generally have at least two phases. These phases are a martensitic phase, which has a relatively low tensile strength and which is stable at relatively low temperatures, and an austenitic phase, which has a relatively high tensile strength and which is stable at temperatures higher than the martensitic phase. 
         [0011]    When stress is applied to a specimen of a metal such as Nitinol exhibiting superelastic characteristics at a temperature above which the austenite is stable (i.e. the temperature at which the transformation of martensitic phase to the austenite phase is complete), the specimen deforms elastically until it reaches a particular stress level where the alloy then undergoes a stress-induced phase transformation from the austenitic phase to the martensite phase. As the phase transformation proceeds, the alloy undergoes significant increases in strain but with little or no corresponding increases in stress. The strain increases while the stress remains essentially constant until the transformation of the austenite phase to the martensite phase is complete. Thereafter, further increase in stress is necessary to cause further deformation. The martensitic metal first deforms elastically upon the application of additional stress and then plastically with permanent residual deformation. 
         [0012]    If the load on the specimen is removed before any permanent deformation has occurred, the martensitic specimen will elastically recover and transform back to the austenite phase. The reduction in stress first causes a decrease in strain. As stress reduction reaches the level at which the martensitic phase transforms back into the austenite phase, the stress level in the specimen will remain essentially constant (but substantially less than the constant stress level at which the austenite transforms to the martensite) until the transformation back to the austenite phase is complete, i.e. there is significant recovery in strain with only negligible corresponding stress reduction. After the transformation back to austenite is complete, further stress reduction results in elastic strain reduction. This ability to incur significant strain at relatively constant stress upon the application of a load and to recover from the deformation upon the removal of the load is commonly referred to as superelasticity or pseudoelasticity. It is this property of the material which makes it useful in manufacturing tube cut self-expanding stents. The prior art makes reference to the use of metal alloys having superelastic characteristics in medical devices which are intended to be inserted or otherwise used within a patient&#39;s body. See for example, U.S. Pat. No. 4,665,905 (Jervis) and U.S. Pat. No. 4,925,445 (Sakamoto et al.). 
         [0013]    A now conventional delivery system for a self-expanding stent is a so-called “pin and pull” system. The following is an example of a “pin and pull” system. The delivery system includes an outer sheath, which is an elongated tubular member having a distal end and a proximal end and a lumen therethrough. A typical outer sheath is made from an outer polymeric layer, an inner polymeric layer, and a braided reinforcing layer between the inner and outer layers. The reinforcing layer is more rigid than the inner and outer layers. It is this outer sheath which is “pulled” in the “pin &amp; pull” system. The “pin &amp; pull” system further includes an inner shaft located coaxially within the outer sheath. The shaft has a distal end, extending distal of the distal end of the sheath, and a proximal end, extending proximal of the proximal end of the sheath. It is this shaft which is “pinned” in the “pin &amp; pull” system. A “pin &amp; pull” system further has a structure to limit the proximal motion of the self-expanding stent relative to the shaft. This “stent stopping” structure is located proximal to the distal end of the sheath. Lastly, a “pin &amp; pull” system includes a self-expanding stent located within the sheath. The stent in its reduced diameter state for delivery makes frictional contact with the inner diameter of the outer sheath, more specifically, with the inner diameter of the inner layer of the outer sheath. The stent is located between the stop structure and the distal end of the sheath, with a portion of the shaft disposed coaxially within a lumen of the stent. The stent makes contact with the stop structure during deployment as the sheath is withdrawn and moves the stent with it (due to the frictional contact between the stent and the inner diameter of the sheath). The proximal motion of the proximal end of the stent is stopped as it comes into contact with the stop structure and the stop structure provides a counteracting force on the stent, equal and opposite to the frictional force from the sheath on the stent. 
         [0014]    To deploy a stent from a “pin &amp; pull” system, the system is navigated to the treatment location. Then the inner shaft, which extends proximal of the proximal end of the outer sheath is held fixed against the patient with one hand of the operator (medical professional). This action fixes the location of the inner shaft along a longitudinal axis of the patient&#39;s lumen being stented. This action is the “pin” step in the “pin &amp; pull” system. The physician takes his or her other hand and pulls the outer sheath proximally (drawing some of it out of the patient toward the “pinning” hand) to unconstrain, expose, and deploy the stent. This action is the “pull” step in the “pin &amp; pull” system. 
         [0015]    An early example of another “pin &amp; pull” system is the Gianturco stent delivery system as described in U.S. Pat. No. 4,580,568 issued Apr. 8, 1986. In this prior art delivery system, the outer sheath is a tube of a single material, which does not have a reinforcing structure within it. A cylindrical flat end pusher, having a diameter almost equal to the inside diameter of the sheath is inserted into the sheath behind the stent. The pusher or inner shaft is then used to push the stent from the proximal end of the sheath to the distal end of the sheath. Deployment of the stent is accomplished by holding the inner shaft fixed with respect to the patient&#39;s body and pulling back on the sheath to expose the stent, which expands upon removal of the radially restraining force, as illustrated in FIGS. 4 &amp; 5 of U.S. Pat. No. 4,580,568, which are incorporated herein by reference. 
         [0016]    Another early self-expanding stent on the market was the Wallstent. It was braided and changed both length, which shortened, and diameter, which increased, when it was deployed, and the change to its length was appreciable. U.S. Pat. No. 4,655,771 to Wallsten, herein after “Wallsten”, describes a couple of delivery systems for a braided stent, called a “tubular body” in the patent. One of the delivery systems is illustrated in FIG. 11 of Wallsten, which is described as follows, “[i]In FIG. 11 there is shown another embodiment of the assembly for use in expanding the tubular body. This assembly constitutes a flexible instrument intended to introduce the tubular body in contracted state into for example a blood vessel and then to expand the body when located therein. The parts of the instrument consist of an outer flexible tube 61 and a concentric also flexible inner tube 62. At one end of the outer tube an operational member 63 is arranged. Another operational member 64 is attached to the free end of inner tube 62. In this manner the inner tube 62 is axially displaceable in relation to the outer tube 61. At the other end of inner tube 62 a piston 65 is attached which when moving runs along the inner wall of outer tube 61. When the instrument is to be used the tubular expansible body 69 in contracted state is first placed inside tube 61, the inner tube 62 with the piston 65 being located in the rear part 66 of outer tube 61. The starting position of piston 65 is shown by dashed lines at 67 in FIG. 11. In this manner part of tube 61 is filled with the contracted tubular body 69 in the starting position. During implantation the flexible tubular part of the device is inserted to the location of a blood vessel intended for implantation. Member 64 is then moved in the direction of arrow 68, the contracted body 69 being pushed out through end 70 of tube 61, the part of the tubular body 69 leaving tube end 70 expanding until in its expanded position 71 it is brought to engagement with the interior of vascular wall 72. The tubular body 69, 71 is for sake of simplicity shown in FIG. 11 as two sinus-shaped lines. To the extent that the expanded body 21 comes into engagement with vascular wall 72 tube end 70 is moved by moving member 63 in the direction of arrow 73. The contracted body 69 is moved by the piston 65 pushing against one end of the body. Thus, the implantation takes place by simultaneous oppositely directed movements of members 64 and 63, the displacement of member 64 being larger than that of member 63.” Like the delivery system for the Gianturco stent, its sheath was not reinforced, but was a single material tube, and its inner shaft did not extend through the stent, but terminated at the proximal end of the stent constrained at the distal end of the outer sheath. The inner shaft was coaxial with the outer sheath, and had an outer diameter that was larger than the inner diameter of the reduced diameter “constrained” or crimped stent. 
         [0017]    Many conventional self-expanding stents are designed to limit the stent foreshortening to an amount that is not appreciable (e.g., less than 10%). Stent foreshortening is a measure of change in length of the stent from the crimped or radially compressed state as when the stent is loaded on or in a delivery catheter to the expanded state. Percent foreshortening is typically defined as the change in stent length between the delivery catheter loaded condition (crimped) and the nominal deployed diameter (i.e., the labeled diameter which the stent is intended to have when deployed, i.e., a “10 mm stent” has a nominal deployed diameter of 10 mm.) divided by the length of the stent in the delivery catheter loaded condition (crimped), multiplied by 100. Stents that foreshorten an appreciable amount (e.g., equal to or more than [insert a value here]) can be more difficult to deploy where intended axially when being deployed in a body lumen or cavity, such as a vessel, artery, vein, or duct. The distal end of the stent has a tendency to move in a proximal direction as the stent is being deployed in the body lumen or cavity. And, in conditions where the distal end is stationary with respect to the vessel wall, the proximal end of the stent will move distally as a function of the foreshortening upon expansion. Thus foreshortening may lead to a stent being placed in an incorrect or suboptimal location. Delivery systems that can compensate for stent foreshortening would have many advantages over delivery systems that do not. 
         [0018]    When a self-expanding stent is deployed in the vessel in an unintended location, an additional stent may be required to cover the full length of the diseased portion of the vessel, and some stent overlap may occur. Obviously, the ability to reposition a stent to correctly deploy it in the intended location is preferred. Often, repositioning a stent requires that the stent first be reconstrained within the outer tubular member of the delivery system (often referred to as a “sheath”). To reconstrain a stent, the outer tubular member is pushed distally to slide over the stent and radially compress it back to its crimped diameter. To resist the axial force of the sheath on the stent due to friction, the proximal end of the stent which is still in the sheath is typically restrained from distal motion relative to the sheath and inner member. A number of delivery system designs provide features to restrain the proximal end of the stent from distal motion, see, e.g., U.S. patent application Ser. No. 12/573,527, Attorney docket number FSS5004USNP, filed Oct. 5, 2009, and Ser. No. 13/494,567, Attorney docket number FSS5004USCIP, filed Jun. 12, 2012, and European Patent Publication No. 0696442 A2, and U.S. Patent Publication No. 2007/0233224 A1. 
       SUMMARY OF THE INVENTION 
       [0019]    One aspect of the invention is a method of reconstraining a partially deployed self-expanding stent that uses a mechanism to move the inner shaft and the outer tubular member in opposite directions at rates that are proportional to each other in accordance to the foreshortening ratio of the stent being reconstrained. 
         [0020]    Another aspect of the invention is a number of hand or motor actuated mechanisms that may be actuated to perform the above method. 
         [0021]    One invention described and claimed herein is a method of reconstraining a foreshortening self-expanding stent with a known foreshortening ratio between the crimped diameter in an intraluminal catheter based delivery system and the nominal deployed diameter in the body lumen, wherein the proximal end of the stent is in releasable fixed relation about a location along the length of an inner member of a stent delivery system, the method comprising translating proximally the outer member with respect to the stent at a first rate, thereby exposing at least a portion of the stent, at the same time that the outer member is translating proximally, translating distally the inner member, thereby translating distally the proximal end of the stent at a rate equal to the known foreshortening ratio multiplied by the first rate at which the outer member is translating proximally, after exposing at least a length of the stent, but before translating proximally the distal end of the outer member past the proximal end of the stent, deciding to reconstrain the partially deployed stent, subsequently translating distally the outer member with respect to the stent at a second rate, thereby reconstraining the length of the stent exposed in the previous translating proximally step, and at the same time that the outer member is translating distally, translating proximally the inner member at a rate equal to the known foreshortening ratio multiplied by the second rate at which the outer member is translating distally. 
         [0022]    Another invention described and claimed herein is a medical device delivery system comprising a first lead screw having a right-handed thread and a central longitudinal axis, a second lead screw having a left-handed thread and a central longitudinal axis, a first follower operationally coupled to the right-handed thread to translate without rotating, a second follower operationally coupled to the left-handed thread to translate without rotating, wherein when the first and second lead screws rotate, the first follower translates parallel to the central longitudinal axis of the first lead screw in a first linear direction and the second follower translates parallel to the central longitudinal axis of the second lead screw in a linear direction opposite the first linear direction. 
         [0023]    Yet another invention described and claimed herein is a medical device delivery system comprising a first lead screw having a right-handed thread and a central longitudinal axis, a second lead screw having a left-handed thread and a central longitudinal axis, a first follower operationally coupled to the right-handed thread to translate without rotating, a second follower operationally coupled to the left-handed thread to translate without rotating, wherein the central longitudinal axis of the first and second lead screws are on a common line and are coupled together to rotate about the common line in the same rotational direction and at the same time, such that when the first and second lead screws rotate, the first follower translates parallel to the common line in a first linear direction and the second follower translates parallel to the common line in a linear direction opposite the first linear direction. 
         [0024]    These and other features, benefits, and advantages of the present invention will be made apparent with reference to the following detailed description, appended claims, and accompanying figures, wherein like reference numerals refer to structures that are either the same structures, or perform the same functions as other structures, across the several views. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0025]    The figures are merely exemplary and are not meant to limit the present invention. 
           [0026]      FIG. 1  illustrates a stent delivery system; 
           [0027]      FIG. 2A  illustrates a self-expanding stent in a constrained diameter and length; 
           [0028]      FIG. 2B  illustrates a self-expanding stent in a nominal deployment diameter and length; 
           [0029]      FIG. 3  illustrates an assembly of two lead screws and two followers; 
           [0030]      FIG. 4  illustrates the assembly of  FIG. 3  connected to two elongated members; 
           [0031]      FIG. 5  illustrates a side view of a handle of a medical device delivery system including an embodiment of one aspect of the present invention; 
           [0032]      FIG. 6  illustrates a front view of the handle of  FIG. 5 ; 
           [0033]      FIG. 7  illustrates a front view of another embodiment of one aspect of the present invention; 
           [0034]      FIG. 8  illustrates a front view of yet another embodiment of one aspect of the present invention; 
           [0035]      FIG. 9  illustrates a partial side view of the embodiment of  FIG. 8 ; 
           [0036]      FIG. 10  illustrates a front view of fourth embodiment of one aspect of the present invention; 
           [0037]      FIG. 11  illustrates a partial side view of the embodiment of  FIG. 10 ; 
           [0038]      FIG. 12  illustrates a front view of an embodiment of a follower; 
           [0039]      FIG. 13  illustrates a front view of an embodiment of a follower with bearings; 
           [0040]      FIG. 14  illustrates a side view of yet another alternative embodiment of the mechanism, in which the first and second lead screws can have their central longitudinal axes parallel to one another; and 
           [0041]      FIG. 15  illustrates a front view of the embodiment of  FIG. 14 . 
       
    
    
     DETAILED DESCRIPTION 
       [0042]    As used herein, “foreshortening ratio” is defined as the result of dividing the value of the length of the nominal diameter stent subtracted from the length of the crimped diameter stent by the length of the crimped diameter stent. 
         [0043]    In  FIG. 1 , a stent delivery system  10  includes a self-expanding stent  12  at the distal end  14  of the lumen  16  of a flexible tubular member  18 , which surrounds a smaller diameter flexible tubular member  20 . Each of the tubular members is connected to a hard plastic structure ( 21 ,  24 ), which serves, among other functions, as the piece with which to manipulate the tubular member. At the proximal end, the smaller diameter flexible tubular member  20  is connected to a stiffer tubular member  22 , which may be a hypotube, and the grip or handle  24  is connected to the proximal end of the hypotube  22 . Stiffer tubular member  22  and flexible tubular member  20  may have a lumen for tracking over a guidewire  25 . Structure  26  mounted on flexible tubular member  20  functions to keep stent  12  is releasable fixed relation to a longitudinal point on the length of tubular member  20 . Finally, stent delivery system may include a distal tip that is distal to the distal end of flexible tubular member  18  and acts as a dilator when entering the body, a blood vessel in particular. 
         [0044]    The stents that are delivered to the treatment location may be self-expanding.  FIG. 2A  is a schematic representation of a fully connected, helical geometry self-expanding stent  29  in a state of crimped diameter and length. This is the state of the stent when completely constrained in the lumen of the outer tubular member of the stent delivery system.  FIG. 2B  is a schematic representation of the same stent  29  in the nominal deployed state, which has a larger diameter and a shorter length. The difference between the crimped length and the nominal deployed length is considered significant if it is greater than 10%. When deployed, if the distal end of the stent contacts the vessel wall when it expands, the distal end is then stationary with respect to the vessel. In these conditions, the proximal end of the stent must move distally from that time on to permit the stent to expand as it deploys. 
         [0045]    Reconstraining includes pushing the outer tubular member distally to slide over the expanded stent until the tubular member constrains the entire length of the stent and the stent is no longer in contact with the vessel wall, and can be repositioned without risk of stretching the vessel which may lead to injury. Just as the proximal stent stop applied counteracting distal forces to the proximal end of the stent to counteract the proximal friction forces along the outer diameter of the stent in contact with the proximally translating outer tubular member, and allowed the tubular member to be withdrawn to expose the stent, a structure is needed to apply proximally acting forces to the stent to counteract the distally acting friction forces of the distally translating tubular member on the outer diameter of the stent. If insufficient counteracting force is provided, when the tubular member is advanced distally, since the distal end of the stent is in contact with the vessel wall, which resists distal motion, one possible outcome is that the tubular member does not slide over the stent, such that the portion of the stent that is exposed and unconstrained begins to evert around the advancing distal end of the tubular member as the constrained portion of the stent at a smaller diameter is advanced toward a relatively stationary expanded diameter distal end of the stent. Systems are known in the art for providing structures to provide such a counteracting proximal force, and examples are U.S. patent application Ser. No. 12/573,527, Attorney docket number FSS5004USNP, filed Oct. 5, 2009, (a rotatable band which interfaces with the inner diameter of the crimped stent, protruding through it and holding that part of the stent in place, when against a stop on the inner shaft) and Ser. No. 13/494,567, Attorney docket number FSS5004USCIP, filed Jun. 12, 2012, (a rotatable stent lock with has axially extending protrusions that interface with the proximal end of the stent at the same radial location as the crimped stent, when against a stop on the inner shaft) and European Patent Publication No. 0696442 A2 (four radially projecting members fixes to the inner shaft which mechanically interfere with axial motion of the crimped stent (proximal or distal)), and U.S. Patent Publication No. 2007/0233224 A1 (rotatable, but axially fixed (to the inner shaft) bumpers that stick to the inner diameter of the crimped stent). However, when a stent has an appreciable (relative to the length of the section of the vessel being treated) increase in length upon constraining (or, i.e., crimping), proximal motion of the structure that provides these counteracting forces may provide optimal conditions for reconstraining a stent. 
         [0046]      FIG. 3  illustrates a side view of a mechanism  30  that can provide constant ratio relative motion by either advancing the inner tubular member while retracting the outer tubular member (for exposing and deploying a stent) or by alternatively retracting the inner tubular member while advancing the outer tubular member (for reconstraining a partially deployed stent). Thus when the proximal end of the stent is fixed longitudinally with respect to the longitudinal axis of the inner tubular member, the proximal end of the stent is translated the expected distance to account for the expected foreshortening distally upon deployment or forelengthening proximally into the outer tubular member during reconstraining. Turning to mechanism  30 , it includes a first lead screw  32  with a helical thread  34  over length L 1 . In the illustrated mechanism, helical thread  34  is right handed and has a predetermined pitch. Mechanism  30  includes a second lead screw  36  with a helical thread  38  over length L 2 . In the illustrated mechanism, helical thread  38  is left handed and has a predetermined pitch. First and second lead screws both have central longitudinal axes which are axially aligned along a common line  40 . In the illustrated mechanism  30 , first and second lead screws are fixedly connected to a smaller diameter shaft  42 , used for mounting the assembly of lead screws to a frame (not shown). Mechanism  30  includes a first follower  50 , illustrated in  FIG. 3  as a square. First follower  50  interfaces with lead screw  32  and when constrained from rotating, translates parallel to common line  40 , when lead screw  32  rotates. Mechanism  30  includes a second follower  52 , illustrated in  FIG. 3  as a square. Second follower  52  interfaces with lead screw  36  and when constrained from rotating, translates parallel to common line  40 , when lead screw  36  rotates. Initial positions of followers  50  and  52  are depicted in solid lines and final positions are depicted in broken lines. Arrows illustrate the translation parallel to common line  40  between the initial and final positions. The ratio of the pitches of the helical threads is, in the depicted embodiment, equal to the ratio of L 1  to L 2 . In  FIG. 3 , it can be seen that followers  50  and  52  move in opposite directions, and at different rates given the same rotational input of their respective lead screw. 
         [0047]    Mechanism  30  can be operated to translate at the same time two members in opposite directions at different rates with a single rotational input. In  FIG. 4 , mechanism  30  is illustrated connected to two elongated tubular members. The first elongated tubular member  60  is operatively connected to follower  50  at its distal end  62 . As illustrated elongated tubular member  60  is hollow and has a lumen  64 . A second elongated tubular member  70  is operatively connected with follower  52  at its proximal end  72 . Elongated tubular member  70  has a smaller outer diameter than the inner diameter of elongated tubular member  60 , and as illustrated, a length less than the total length of 70 is inside the lumen  64  and co-axial with elongated tubular member  60 . When shaft  42  is rotated, follower  50  will translate proximally and elongated member  60  will translate an equal amount at the same time due to the operative connection between them. When shaft  42  is rotated, follower  52  will translate distally and elongated member  70  will translate an equal amount at the same time due to the operative connection between them. 
         [0048]      FIG. 5  illustrates the assembly of mechanism  30  and elongated members  60  and  70  in half of a housing  90 . Housing  90  substantially encloses mechanism  30 , in addition to enclosing the proximal portions of elongated members  60  and  70 . Housing  90  defines opening  92  at its distal tip for the elongated members  60  and  70  to translate through. Housing  90  defines an opening  94  for a portion of a follower that may be used as an input  114  to the system by manipulation by a user. In some embodiments, opening  94  is a straight slot. Housing  90  defines an opening  96  to accommodate a rotatable input  110  operatively connected to shaft  42 . Shaft  42  is mounted in bearings  100  to housing  90 . In some embodiments, not depicted, housing  90  defines additional openings. In some embodiments of the present invention, housing  90  functions as a handle to a medical device delivery system. In some embodiments of the present invention, housing  90  is sized to be grasped by a human hand. Such sizing does not necessarily impact the length of housing  90 , just the circumference of a transverse cross section to common line  40  (like shown in  FIG. 6 ). As housing  90  substantially encloses mechanism  30 , mechanism  30  is accordingly sized to housing  90 . 
         [0049]    Input  110  as illustrated in  FIG. 5  is a short cylinder with a knurled or otherwise grippable surface, for example, using facets  112  about the generally cylindrical circumference. It is envisioned that an operator of mechanism  30  may use a thumb or finger to apply tangential force to input  110  to rotate it about common line  40 . Input  110  is operatively connected to the two lead screws, such that rotation of input  110  results in rotation (in the same direction) of lead screws  32  and  36 , and translation of followers  50  and  52 , and translation of elongated members  60  and  70 . The larger the diameter of input  110 , the greater the mechanical advantage to operate the mechanism. 
         [0050]    In the illustrated embodiment of  FIGS. 5 &amp; 6 , mechanism  30  is configured such that follower  50  can be used as an input to the system. To accommodate such manipulation of follower  50  in embodiments with a housing, follower  50  is configured to project through opening  94  to present a tab or other suitable structure for a user to manipulate by translation within opening  94 . Such structure is alternatively referred to herein as an input  114 . If a user translates input  114 , lead screw  50  rotates, resulting in lead screw  52  rotating in the same direction as lead screw  50 , follower  52  translating in an opposite direction from the input translation, and input  110  rotating in the same direction as lead screw  50 . Of course, due to the operative connections of elongated tubular members to the respective followers, translating input  114  will also translate the elongated members in opposite directions. 
         [0051]    Gripping the outer elongated tubular member outside of the housing and translating it along its longitudinal axis is, in some embodiments, an acceptable input to the mechanism as well, resulting in the translation of the follower to which it is operatively connected to translate in the same direction, rotating the first lead screw, and producing the rest of the motions the mechanism is configured to produce as described above. 
         [0052]    Thus, in some embodiments of a device incorporating such a mechanism  30 , a user may achieve the desired exposure of a constrained stent or reconstraint of a partially deployed stent by rotating input  110 , translating input  114 , or translating outer tubular member  60  external to the housing  90  and patient in the desired direction to accomplish the desired exposure or reconstraint. 
         [0053]      FIG. 6  illustrates a front view of the complete housing in phantom lines, and the input  110 , shaft  42 , follower  50 , input  114 , follower  52  and elongated tubular members  60  and  70  to show other aspects of mechanism  30 . In the illustrated embodiment, a follower interfaces with its respective lead screw over an internal angle alpha, α, of less than 180 degrees, and more closely approximating 90 degrees. As long as the follower interfaces sufficiently with the threads of the lead screw, such an angle measurement over which the two parts are in contact is not necessary. Alternatively, followers  50  and  52  could be annular rings, like a nut, about and co-axial with the lead screw and its longitudinal axis, here the common line  40 . The follower must be prevented from rotating, so that elongated tubular members can translate in a straight line through housing  90  and out opening  92 . Another aspect illustrated in  FIG. 6  is the portion of input  110  which extends through opening  96  in housing  90 . Here the knurled or faceted ring-like surface of input  110  may be manipulated by a user&#39;s thumb or finger for one handed operation (i.e., hold the handle and rotate input  110  with the thumb of the same hand, or by one or more digits on the hand not holding the handle for two handed operation via input  110 .  FIG. 6  also illustrates input  114  extending through opening  94  to provide a structure that can be manipulated by the user to translate (in and out of the page in the view of  FIG. 6 ) to actuate mechanism  30  and provide opposite and scaled translation between the two tubular members of the device. 
         [0054]    Another embodiment of a rotatable input (with respect to the housing  90 ) is illustrated in  FIG. 7 , which is another front view, to most easily show difference between this embodiment and the last. Here input  110  is an internal gear  120  with a larger diameter than the short cylinder illustrated in  FIGS. 5 and 6 . The internal gear  120  has teeth  122  that engage mating teeth  124  of a spur gear  126  located within the internal opening of the internal gear  120 . Spur gear  126  is axially aligned with common line  40  and is operatively connected to lead screw  50  (and the rest of mechanism  30 ). Thus a greater mechanical advantage is obtained using the illustrated embodiment, and all other things being the same about mechanism  30 , fewer rotations of input  110  are needed to fully expose or reconstrain a stent with a delivery system including this embodiment. 
         [0055]    Yet another embodiment of rotatable input  110  is illustrated in a front view in  FIG. 8  and a partial side view in  FIG. 9 . This input to the mechanism rotates about an axis  130  that is perpendicular to the common line  40 , and relies on a face gear  132 , that is, one with teeth  134  projecting along the axis  130  of the gear off of one “face” of the gear  132 , rather than projecting radially inward (as in an internal ring gear) or radially outward (as in an external ring gear). Here again, housing  90  is drawn in phantom lines to more clearly see arrangement of new components. Face gear  132  engages with a spur gear  136 , the same as or similar to the one illustrated in  FIG. 7 , but the user interface is different. Instead of rotating the input  110  across the handle, a user rotates the input  110  in-line with the longitudinal axis of the handle. As illustrated, the rotatable input  110  would be on one lateral side or the other with respect to the longitudinal midplane  140  of the handle. 
         [0056]    Yet another embodiment of rotatable input  110  is illustrated in a front view in  FIG. 10  and a partial side view in  FIG. 11  to illustrate differences between this embodiment and the others. This embodiment builds on the last embodiment by incorporating an “in-line” rotatable input  110  on the handle, but additionally, it centers the input  110  along the longitudinal midplane  140  of the handle. This requires an additional rotatable structure, here the combination of a knurled short cylinder  144  fixedly connected to a spur gear  146 . The face gear of the last embodiment additionally must have external teeth  148  with which to engage the spur gear  136 , thus being a combination face and external gear  150 . The housing  90  and gears can be sized to optimize the desired ease of handling and gear ratio between the input and the gears in the chain (here  146 ,  150 , and  136 ) that operate mechanism  30  and result in opposite movement of the two tubular members operatively connected to the followers. 
         [0057]    A follower that is also going to function as a translatable input to the mechanism can have different forms than depicted in  FIGS. 5-11 .  FIG. 12  illustrates a front view of a follower  156  that provides a projection ( 158 ,  160 ) laterally on either side of a vertical midplane  140  of the handle. Housing  90  is accordingly adjusted moving opening  94  from the “bottom” of the handle to a side and also defining an additional opening  162  for the lateral projection on the opposite side of the follower. That way, translating the lateral projection of the follower on either side of the handle can be used to actuate mechanism  30  and provide translation in opposite directions of the two elongated tubular members operatively connected to the two followers. 
         [0058]    And an additional design option for operation requiring less actuating force is illustrated in  FIG. 13 , which illustrates the incorporation of bearings into a mechanism utilizing followers similar to that illustrated in  FIG. 12 . In this embodiment, followers  50  and  52  define an additional through-hole  164  which is a bearing surface against a bearing rod  166 , which runs parallel to common line  40 . Additionally, a round bearing  170 , the inner race of which surrounds a vertical post  172  extending down from the follower  50 , counteracts the moment exerted on the follower  50  from the rotation of the lead screw  32 . The lower bearing  170  rotates against one of two vertical walls  174 ,  176  provided in housing  90  to prevent rotation of follower  50 . 
         [0059]    In order to reduce system friction, it may be desirable to exchange the “threads” of lead screw and follower with more of a cam-follower setup. In this embodiment, follower  50  contains a bearing in contact with it and the leadscrew, which now longer is strictly a lead screw (as there are not interfacing grooves, i.e., mating threads, in follower  50 ). Instead structure  50  is actually a helical cam for that bearing to follow. 
         [0060]    Reducing system friction to negligible amounts increases efficiency and allows backdriving so that translation of translatable input  114  can rotate lead screw  32 . The cam/bearing method is one way to achieve this. Also a ball nut could be used or simply very low friction materials, lubricants, etc. 
         [0061]      FIGS. 14 and 15  illustrate an alternative embodiment of the mechanism, in which the first lead screw  32  and second lead screw  36  have parallel central longitudinal axes ( 184 ,  186 ), rather than axially aligned ones. The elongated members  60 ,  70  attached to the first and second followers  50 ,  52  have a common central longitudinal axis  182  parallel to each of the respective central longitudinal axis of the first and second lead screw. In such an embodiment, a single rotatable input  110  may be an internal ring gear  120  engaging with two spur gears  126 ,  180 , one for each of the two parallel lead screws, similar to the embodiment depicted in  FIG. 7 . In this embodiment, the axis of rotation  190  for the rotatable input is parallel to the central longitudinal axes of the first and second lead screws. The axis of rotation  190  of the rotatable input may be axially aligned with the common central longitudinal axis of the first and second elongated members, or it may be parallel to it, as depicted in  FIG. 15 . The teeth of internal gear  120  and spur gears  126 ,  180  are not shown, and instead the pitch circles of such gears are illustrated for ease. 
         [0062]    Aspects of the present invention have been described herein with reference to certain exemplary or preferred embodiments. These embodiments are offered as merely illustrative, not limiting, of the scope of the present invention. Certain alterations or modifications which are possible include the substitution of selected features from one embodiment to another, the combination of selected features from more than one embodiment, and the elimination of certain features of described embodiments. Other alterations or modifications may be apparent to those skilled in the art in light of instant disclosure without departing from the spirit or scope of the present invention, which is defined solely with reference to the following appended claims.