Abstract:
The present invention provides prefillable syringes and injectors for use therewith that expand and/or facilitate a variety of medical procedures involving the injection of a liquid medium. In several embodiments, the present syringes and injectors enable the use of current syringe materials at higher pressures than previously attainable or the use of other materials not previously usable with current high pressure-syringe and injector designs. In one embodiment, a syringe comprises an elongated cylindrical main body having a first pair and a second pair of mounting flanges encompassing collectively an arcuate length equal to at least approximately 180° of the circumference of the rear portion of the cylindrical main body for releasably mounting the syringe in a desired position relative to the front wall of the injector housing. Injectors for use with such syringes comprise a housing having a front wall and a retainer on the front wall which cooperates with the first and second pairs of mounting flanges of the syringe to releasably mount the syringe on the injector.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of application Ser. No. 08/748,230, filed on Nov. 12, 1996 which issued as U.S. Pat. No. 5,944,694, the contents of which are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to medical syringes, and more particularly to prefillable syringes and injectors for use therewith. 
     BACKGROUND OF THE INVENTION 
     A number of injector-actuated syringes and powered injectors for use in medical procedures such as angiography, computer tomography and NMR/MRI, have been developed. For example, U.S. Pat. No. 4,006,736 discloses an apparatus for injecting fluid into the vascular system of a human being or an animal. Likewise, U.S. Pat. No. 4,677,980 discloses an angiographic injector and syringe wherein the drive member of the injector can be connected to, or disconnected from, the syringe plunger at any point along the travel path of the plunger via a releasable mechanism requiring rotation of the syringe plunger relative to the piston. 
     Numerous advances have been made in the area of injector-actuated syringes and powered injectors for use therewith. Nonetheless, newly developed and developing medical procedures constantly test the limits of current injector systems. For example, some procedures require the use of high pressures but also require physiochemical properties of the syringe (for example chemical and biochemical compatibility with the liquid injection medium) that make attainment of high, pressures difficult. 
     It is, therefore, very desirable to develop new syringes and injectors usable in a wide variety of medical procedures. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention provides injector-actuated syringes and injectors for use therewith that enable and/or facilitate a variety of medical procedures involving the injection of a liquid medium. In several embodiments, the present syringes and injectors enable the use of current syringe fabrication materials at higher pressures than previously attainable or the use of other fabrication materials not previously usable with high pressure-syringe and injector designs. 
     For example, the present invention provides generally a front-loading syringe comprising an elongated cylindrical main body and a releasable mounting mechanism. Known front-loading syringes with readily releasable mounting mechanisms are described in U.S. Pat. No. 5,383,858. The releasable mounting mechanism of the present invention comprises at least one mounting flange connected to a rear portion of the cylindrical main body and enables releasable mounting of the syringe in a desired position relative to a front wall of an injector housing. The mounting flange preferably encompasses an arcuate length equal to at least approximately one half (that is, approximately 180°) of the circumference of the rear portion of the cylindrical main body. It is understood that the mounting flange can encompass an arcuate length greater than 360° of the circumference of the rear portion of the cylindrical main body. 
     The releasable mounting mechanism preferably comprises more than one mounting flange. For example, the releasable mounting mechanism may comprise at least two radially projecting mounting flanges that encompass collectively an arcuate length equal to at least approximately 180° of the circumference of rear portion of the cylindrical main body. In one embodiment, the releasable mounting mechanism comprises at least a first pair and a second pair of radially projecting mounting flanges. The first pair of the mounting flanges is preferably positioned at a first axial location, and the second pair of the mounting flanges is preferably positioned at a second axial location. As set forth above, these four mounting flanges encompass collectively an arcuate length equal to at least approximately 180° of the circumference of rear portion of the cylindrical main body. It is understood that these four mounting flanges can encompass collectively an arcuate length greater than 360° of the circumference of rear portion of the cylindrical main body. Preferably, the mounting flanges of each pair of mounting flanges are positioned to be opposing (that is, positioned symmetrically with respect to each other about the axis of the cylindrical main body) to assist in eliminating uneven loading forces and torque imparted on the syringe when the injector drive member is activated. 
     The first pair of mounting flanges and the second pair of mounting flanges may be in general alignment. In another embodiment, the first pair of mounting flanges are offset from the second pair of mounting flanges. Preferably, the first pair of mounting flanges are offset from the second pair of mounting flanges by approximately 90°. Offsetting of the pairs of mounting flanges assists in evenly distributing forces over the entire circumference of the syringe. 
     The present invention also provides injectors for use with the above syringes. In general, the injectors comprise a housing having a front wall, a cooperating retainer and a powered drive member. The cooperating retainer comprises at least one slot for receiving therethrough the at least one cooperating mounting flange on the syringe. The cooperating retainer further comprises at least one retaining flange to releasably engage the at least one cooperating mounting flange over substantially the entire arcuate length of the cooperating mounting flange when the syringe is inserted into and rotated within the cooperating retainer. The syringe is thereby releasably mountable in a desired position relative to the front wall of the injector housing. 
     In cases in which the syringe comprises at least two mounting flanges, the cooperating retainer preferably comprises at least two slots for receiving therethrough the at least two cooperating mounting flanges on the syringe. The cooperating retainer further comprises at least two retaining flanges to releasably engage the at least two cooperating mounting flange over substantially the entire arcuate length of the cooperating mounting flanges. 
     In cases in which the syringe comprises multiple pairs of mounting flanges positioned at different axial positions on the syringe, but in general alignment, the cooperating retainer may comprise two slots for receiving therethrough the multiple pairs of mounting flanges on the syringe. The cooperating retainer further comprises at least one retaining flange to releasably engage each cooperating mounting flange. For example, in the case of a syringe comprising two pairs of cooperating mounting flanges, the retainer preferably comprises a first pair of retaining flanges positioned at a first axial location on the cooperating retainer to engage the first pair of opposing mounting flanges and a second pair of retaining flanges positioned at a second axial location on the cooperating retainer to engage the second pair of opposing mounting flanges. 
     In cases in which the syringe comprises more than two mounting flanges having offset positions on the syringe, the retainer preferably has more than two slots to receive the mounting flanges. In one embodiment described above, for example, the syringe comprises a first pair of opposing mounting flanges positioned at a first axial location on the syringe and a second pair of opposing mounting flanges being positioned at a second axial location on the syringe, the first pair of opposing mounting flanges being offset from the second pair of opposing mounting flanges by approximately 90°. For releasable mounting of such a syringe, the cooperating retainer comprises four slots (two pairs of slots offset by approximately 90°) for receiving therethrough the at least four cooperating mounting flanges on the syringe. The cooperating retainer further comprising at least four retaining flanges to releasably engage the four cooperating mounting flanges. A first pair of retaining flanges is positioned at a first axial location on the cooperating retainer to engage the first pair of mounting flanges, and a second pair of retaining flanges being positioned at a second axial location on the cooperating retainer to engage the second pair of mounting flanges. The first pair of retaining flanges are offset from the second pair of retaining flanges by approximately 90°. 
     The present invention also provides a number of novel syringes that expand the pressure range of syringe fabrication material for use in front-loading or rear-loading injectors. In one embodiment, the syringe comprises an elongated cylindrical main body and a generally conical transition region positioned at a end portion of the elongated cylindrical main body. The wall thickness of the conical transition region and the wall thickness of the elongated cylindrical main body are thickened in the vicinity of the intersection of the elongated cylindrical main body and the generally conical transition region (as compared to the wall thickness of the elongated cylindrical main body) to structurally reinforce the syringe in the vicinity of the intersection region to withstand relatively high internal pressures without failure. Preferably, the wall thickness of the entire conical transition region is thickened. 
     In another embodiment, the present invention provides a syringe for use with a powered injector comprising an elongated cylindrical main body, an elongated injection region having a diameter less than the elongated cylindrical main body and a transition region connecting the elongated cylindrical main body and the elongated ejection region. The transition region has a generally hemispherical shape to withstand relatively high internal pressures without failure. 
     The syringes and injectors of the present invention are particularly useful in the development of prefillable syringes suitable to contain the injection fluid for extended periods of time. There are significant advantages, in developing syringe systems in which the syringe may be prefilled with the liquid medium to be injected. For example, use of a prefilled syringe saves the user time, minimizes the potential for mislabeling of the liquid medium, minimizes the potential of contamination of the liquid medium and also minimizes the possibility of injecting air into the patient. Current prefilled systems, such as disclosed in U.S. Pat. No. 4,628,969, require use of a pressure jacket. Such current prefilled systems are “breach-loading” and are much less convenient for the user than a front-loading system and/or a jacketless system. 
     The material from which such a syringe is fabricated must be compatible with the injection fluid (such as an angiography contrast medium) for extended periods of time. In other words, neither the injection fluid nor the fabrication material should detrimentally effect the performance of the other. In that regard, the fabrication material must be “chemically compatible” with the injection fluid. For example, the material for the syringe must maintain its structural integrity when in contact with the injection fluid for extended periods and must not leach any substance into the injection fluid which will impair the functionality of the injection fluid. The fabrication material must also be “biochemically compatible” with the injection fluid. For example, the fabrication material must not leach any substance into the injection fluid which will endanger the patient (animal or human) into which the injection fluid is to be injected. As used herein, the term “biochemically compatible” thus refers generally to a material that will not result in unacceptable harm to living tissue or organisms as used in connection with the present invention. 
     The construction material for the syringe should be chemically and biochemically compatible with the injection medium over extended periods of time. Although it is recommended that prefilled syringes be used as soon as possible after filling of the syringe, prefilled syringes preferably have a shelf life of at least approximately six (6) months. More preferably, the prefilled syringes have a shelf life of at least approximately three (3) years. 
     The construction material(s) for the syringe also preferably exhibit good barrier properties, for example, low water vapor transmission rate, because changes in moisture content can detrimentally affect the ionic character of certain injection fluids. Moreover, unlike syringes designed to be filled after mounting on a powered injector, prefilled syringes containing injection fluid must be sterilized. Therefore, in addition to being chemically and biochemically compatible with the injection fluid as describe above, the construction material for the syringe must exhibit physical characteristics suitable to withstand the pressures, temperatures and other forces experienced during sterilization, such as autoclave sterilization. For example, externally applied pressures of up to approximately 44-53 PSIA and temperatures of approximately 120° to 124° C. (255° F.) are often experienced during autoclave sterilization. Further, like all angiographic syringes, the material of the syringe must have physical characteristics suitable to withstand pressure and other forces experienced during injection. Finally, it is desirable that the syringe material be clear so that the injection fluid contained in the syringe can be viewed. 
     While certain materials exhibit suitable long-term chemical and biochemical compatibility characteristics, such materials have generally been found to be structurally weaker (that is, to have lower tensile strength and/or lower elasticity) than materials commonly used in current syringes. Examples of such current fabrication materials include polyethylene terephthalate (PET) or other dense or crosslinked plastic materials. 
     The novel structural changes in the syringe and injectors of the present invention enable syringes of a variety of fabrication materials to withstand the forces experienced in typical motorized injector applications. An example of a syringe fabrication material suitable for use with a variety of liquid media under the present invention is polypropylene. 
     The present invention also provides a plunger for use in a syringe including a dynamic seal which improves the sealing engagement between the plunger cover and syringe barrel. The syringe comprises an elongated main body, an elongated injection region having a smaller diameter than the elongated main body, and a transition region connecting the elongated main body and the elongated injection region. The plunger comprises a plunger surface or a cover surface preferably fabricated from an elastic material. In the case of a prefillable syringe, the elastic material must also be chemically and biochemically compatible with the liquid medium for extended periods of time. 
     The cover surface comprises a forward portion which contacts the liquid medium. The forward portion preferably has the general shape of the transition region of the syringe. The cover surface further comprises a seal portion having a generally cylindrical exterior surface. The seal portion contacts the inner wall of the elongated cylindrical main body of the syringe and forms a seal therewith. The plunger also comprises a base over which the cover surface is placed. The base comprises a forward base portion having generally the shape of the forward portion of the cover surface. The base also comprises a side portion having an angle of taper wherein the diameter of the side portion decreases from a rearward axial position to a forward axial position thereof The diameter of an inner wall of the seal portion of the cover surface decreases from rearward to a forward axial position at an angle approximately the same as the angle of taper of the side portion of the base. The side portion of the base and the seal portion create a dynamic seal with increases of internal pressure within the syringe. 
     The present invention also provides a plunger comprising a releasable connection mechanism adapted to make a releasable connection with the drive member of an injector at any plunger position within the syringe barrel. The connection mechanism comprises at least two relatively flexible capture members projecting rearwardly from a rear surface of the plunger. The capture members flex radially outwardly when contacted by a forward, relatively rigid piston head of the drive member during forward advancement of the piston head to form a releasable connection with the piston head. The drive member of the injector preferably comprises a piston including a piston head positioned at forward end thereof The piston head is preferably formed of a relatively rigid material. Preferably, the capture members include shoulders or abutment surfaces that abut the piston head to prevent disengagement of the piston head and the capture members upon rearward motion of the piston. The plunger is preferably readily releasable from the piston head upon relative rotation of the plunger and the piston head, such that the piston head is no longer abutted by the abutment shoulders, thus permitting subsequent rearward motion of the piston without retracting the plunger. Known readily releasable mechanisms are described in U.S. Pat. Nos. 4,677,980 and 5,383,858. 
     In an alternative embodiment, the capture members are rigid and the piston head comprises flexible members which flex to allow capture and retention thereof by the capture member. Once again, the plunger is preferably readily releasable from the piston head upon relative rotation of the plunger and the piston head. 
     Finally, the present invention provides a plunger that results in less waste of contrast medium than current plunger designs. Numerous syringes comprise an elongated main body, an elongated injection region having a smaller diameter than the elongated main body, and a transition region connecting the elongated main body and the elongated injection region. The plunger of the present invention comprises a cover surface including a forward portion which contacts the liquid medium. The cover surface also comprises a protruding member at a forward end of the forward portion. The protruding member is adapted to enter the elongated injection region of the syringe when the plunger is advanced to expel liquid medium contained in the elongated injection region. The forward portion preferably has, for example, a generally conical shape or a generally hemispherical shape depending on the shape of the transition region of the syringe. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other aspects of the invention and their advantages will be discerned from the following detailed description when read in connection with the accompanying drawings, in which: 
     FIG. 1A illustrates an embodiment of an injector system of the present invention in which the syringe comprises two pairs of mounting flanges in general alignment; 
     FIG. 1B illustrates an embodiment of an injector system of the present invention in which the syringe comprises two pairs of radially offset mounting flanges; 
     FIG. 2A illustrates an axial cross section of the injector system of FIG. 1A; 
     FIG. 2B illustrates an axial cross section of the injector system of FIG. 1B, 
     FIG. 3A illustrates a front elevational view of the front wall of FIG. 1A; 
     FIG. 3B illustrates a front elevational view of the front wall of FIG.  1 B. 
     FIG. 4 illustrates a front view of the front wall of FIG. 3B; 
     FIG. 5 illustrates a cross-sectional view of the front wall and a forward portion of the injector of FIG. 1B; 
     FIG. 6A illustrates a plan view of an embodiment of a syringe of the present invention; 
     FIG. 6B illustrates a plan view of another embodiment of a syringe of the present invention; 
     FIG. 7A illustrates a cross-sectional view of the syringe of FIG. 6A; 
     FIG. 7B illustrates a second, cross-sectional view of the syringe of FIG. 6A rotated approximately 90° from the view of FIG. 7A; 
     FIG. 8 illustrates a front view of the syringe of FIG. 7A; 
     FIG. 9 illustrates a rear view of the syringe of FIG. 7A; 
     FIG. 10 illustrates a rear, partially cross-sectional view of the syringe of FIG. 7A; 
     FIG. 11 illustrates a cross-sectional view of a plunger of the present invention; 
     FIG. 12A illustrates an elevational view of an embodiment of a cover surface of a plunger of the present invention; 
     FIG. 12B illustrates an elevational view of a first base member of a two-piece base for use with the cover surface of FIG. 12A; 
     FIG. 12C illustrates an elevational view of a second base member (central yoke member) of the two-piece base for use with the first base member of FIG. 12B; 
     FIG. 13A illustrates a perspective view of the cover surface of FIG. 12A; 
     FIG. 13B illustrates a bottom perspective view of the first base member of FIG. 12B; 
     FIGS. 13C illustrates a perspective view of an assembled plunger of the present invention; 
     FIG. 14 illustrates a prefilled syringe including a connector tube; 
     FIG. 15 illustrates an enlarged cross-sectional view of an embodiment of a swivel nut and syringe tip; 
     FIG. 16 illustrates a perspective view of the swivel nut of FIG. 15; and 
     FIG. 17 illustrates a cross-sectional view of an embodiment of a tip seal. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Two embodiments of front-loading injector systems  5  and  5 ′ of the present invention are illustrated in FIGS. 1A and 1B, respectively. A front-loading syringe and injector system is also disclosed in U.S. Pat. No. 5,383,858, the disclosure of which is incorporated herein by reference. Injector systems  5  and  5 ′ generally differ substantially only in the manner in which the syringes are mounted upon the corresponding injector. Like entities in each of systems  5  and  5 ′ are numbered the same. 
     Injector system  5  includes an injector  20  and a syringe  10 . Injector housing  21  of injector  20  preferably includes a reciprocating piston  22  therein which cooperates with a syringe plunger  15  to inject an injection fluid or liquid medium from the interior of syringe  10  into a patient. Piston  22  is extendible and retractable via a powered means preferably contained within injection housing  21  and comprising, for example, a motor or hydraulic system, including appropriate gearing (not shown). As known in the art, injector housing  21  also preferably includes a motor controller for controlling operation of a motor and thereby controlling operation of piston  22 . 
     As used herein to describe systems  5  and  5 ′, the terms “axial” or “axially” refer generally to an axis A around which systems  5  and  5 ′ (including, for example, piston  22  and syringes  10  and  10 ′) are preferably formed (although not necessarily symmetrically therearound). The terms “proximal” or “rearward” refer generally to an axial direction toward the end of injector housing  21  opposite the end to which syringe  10  is mounted. The terms “distal” or “forward” refer generally to an axial direction toward a syringe tip  24  of syringe  10 . The term “radial” refers generally to a direction normal to axis A. 
     Referring to FIG. 1A, piston  22  moves axially forwardly and rearwardly through a retainer  25  comprising an opening  26  formed in a front wall  28 ′ of injector housing  21 . Opening  26  and syringe  10  preferably comprise cooperating means for securely affixing syringe  10  to front wall  28 ′. Preferably, such securing means comprise a cooperating mounting mechanism formed upon the rearward portion of syringe  10  and a cooperating retainer  25  formed upon injector front wall  28 ′. 
     In the embodiment of FIGS. 1A,  2 A and  3 A, opening  26  comprises a pair of opposed, axially extending slots  30  and  32 . Slots  30  and  32  preferably separate and define a first pair of radially inwardly projecting syringe retaining flanges  34  and  36  formed around the circumference of the opening  26 . To the rear of first retaining flanges  34  and  36  is a first circumferential groove or channel  38 , which is in communication with the axial slots  30  and  32 . 
     As shown in FIG. 3A, to the rear of channel  38 , are preferably a pair of second, radially inwardly projecting retaining flanges  40  and  42 . Retaining flange  42  is shown in FIG. 2A, and is preferably substantially identical to retaining flange  40 . Retaining flanges  34  and  40  are preferably generally symmetrically aligned with retaining flanges  36  and  42 , respectively, about axis A. A second circumferential channel  44  (see FIG.  2 A), also in communication with slots  30  and  32 , is preferably formed between the rear radial sidewalls of mounting flanges  40  and  42  and a rear abutment member  46 . Retainer  25  (including first retaining flanges  34  and  36  and second retaining flanges  40  and  42 ) is preferably formed as a portion of injector front wall  28 ′. 
     Front wall  28 ′ and retainer  25  may, for example, be machined out of aluminum or other suitable material such as plastic. Certain plastics may be preferable because of their “low friction” characteristics. In that regard, the relatively large surface of the mounting flanges and the drip flange of the present syringes may result in significant friction when installing the syringe in the injector. Any material suitable to lower frictional forces would be beneficial. Plastics such as polyacetal may offer such a benefit. 
     Opening  26  of retainer  25  receives and firmly secures syringe  10  to injector front wall  28 ′. In that regard, syringe  10  preferably comprises an elongated, generally cylindrical body  50  including a rear portion  52  which preferably includes a first set of radially extending mounting flanges  54  and  56  and a second set of radially extending mounting flanges  58  and  60 . A radially extending drip flange  62  is preferably formed forwardly from first mounting flanges  54  and  56  on body  50 . Drip flange  62  assists in proper axial positioning of syringe  10  with respect to front wall  28 ′ by preferably abutting the face of front wall  28 ′ when syringe  10  is properly positioned. Drip flange  62  further substantially prevents liquid from leaking into injector housing  21 . Such leakage into injector housing  21  may cause damage to injector  20 . Drip flange  62  also provides structural reinforcement for syringe body  50 . As illustrated, syringe  10  is preferably formed around axis A such that its components are generally symmetrical with respect to axis A. 
     The structure of second mounting flanges  58  and  60  is preferably similar to the structure of first mounting flanges  54  and  56 . Each of first mounting flanges  54  and  56  and second mounting flanges  58  and  60  preferably includes a plurality of ribs  63 . In the embodiment of FIGS. 1A,  2 A and  3 A, ribs  63  provide improved strength at reduced material cost and minimize the potential f or material shrinkage that can occur during injection molding. 
     During mounting of syringe  10  in front wall  28 , first mounting flanges  54  and  56  of the syringe  10  are preferably rotatably and closely received in first circumferential channel  38  to be retained by first retaining flanges  34  and respectively  36 . Second mounting flanges  58  and  60  are preferably similarly received in second channel  44  to be retained by second retaining flanges  40  and  42 , respectively. 
     First channel  38  is preferably dimensioned differently from (for example, deeper and/or narrower than) second channel  44 . Accordingly, first mounting flanges  54  and  56  are correspondingly narrower and/or more radially extensive than second mounting flanges  58  and  60 . The dimensional differences in the mounting flanges and their respective channels substantially prevent mis-mounting or partial mounting of syringe  10  in retainer  25 . For example, if the user mistakenly aligns second retaining flanges  58  and  60  with first channel  38  and attempts to rotate second mounting flanges  58  and  60  behind first retaining flanges  34  and  36 , the dimensions of channel  38  will prevent such rotation. The user must (1) insert syringe  10  rearwardly to abut a stop member or such that drip flange  62  abuts the front face of front wall  28 ′ and then (2) rotate syringe mounting flanges  56 ,  54 ,  58  and  60  relative to retainer  25  so that they will occupy the channels, immediately behind respective retaining flanges  34 ,  36 ,  40  and  42 . In this way, both sets of syringe mounting flanges will be securely and fully engaged and available to resist forward force exerted on syringe  10  by piston  22 . 
     The mounting flanges and corresponding retaining flanges must provide enough area of contact to adequately retain syringe  10  without mechanical failure during injection procedures. Preferably, one or more mounting flanges are provided around the circumference of the rear portion of syringe  10  such that the one or more flanges encompass cumulatively an arcuate length equal to at least approximately one-half of the circumference of the rear portion of syringe  10  (that is, approximately 180°). This result may be accomplished using multiple flanges as described above or using a single helical or screw-like flange (not shown). It is understood that the one or more mounting flanges may encompass cumulatively an arcuate length greater than 360° of the circumference of the rear portion of syringe  10 . The one or more mounting flanges are preferably positioned symmetrically around the body of syringe  10 , however, to prevent unequal flange loading or torque when piston  22  engages plunger  15  to push plunger  15  forward. 
     In the embodiment illustrated in FIG. 1A, first pair of mounting flanges  54  and  56  are in general alignment with second pair of mounting flanges  58  and  60 . In an alternative embodiment (not shown), the centers of the first pair of mounting flanges  54  and  56  are positioned or rotated approximately 90° from the centers of second pair of mounting flanges  58  and  60 . In the corresponding injector, the center of channel  38  is positioned or rotated approximately 90° from the center of channel  44 , and the center of retaining flange  34  is positioned or rotated approximately 90° from the center of retaining flange  40 , so as to accomotate the offset syringe mounting flanges  54  and  56 , and  58  and  60 . The benefits of offsetting the centers of the syringe mounting flanges are discussed below in connection with the embodiment shown in FIG. 1B,  2 B and  3 B. 
     In the embodiment of injector system  5 ′, as best illustrated in FIG. 1B,  2 B and  3 B, opening  26 ′ comprises two pairs of opposed, axially extending slots  112  and  112 ′ and  118  and  118 ′. The centers of first pair of slots  112  and  112 ′ are positioned or rotated approximately 90° from the centers of second pair of slots  118  and  118 ′. Slots  112  and  112 ′ preferably separate and define at least a first pair of radially inwardly projecting syringe retaining flanges  120  and  120 ′ formed around the circumference of the opening  26 ′. To the rear of first retaining flanges  120  and  120 ′ is a first circumferential groove or channel  124 , which is in communication with the axial slots  112  and  112 ′. 
     To the rear of channel  124 , are preferably a pair of second, radially inwardly projecting retaining flanges  128  and  128 ′. Retaining flanges  128  and  128 ′ are preferably generally aligned with retaining flanges  120  and  120 ′. Retaining flange  128  is not shown in FIG. 3B, but is identical to retaining flange  128 ′. A second circumferential channel  130  (preferably also in communication with slots  112  and  112 ′) is preferably formed between the rear of mounting flanges  128  and  128 ′ and a rearward ledge  132  (see FIG.  3 B). 
     Slots  118  and  118 ′ are preferably formed as radially inward projecting slots in retaining flanges  120  and  120 ′ and  128  and  128 ′. Preferably, the depth of slots  118  and  118 ′ is somewhat less than that the radial width of retaining flanges  120  and  120 ′. As shown in FIG. 4, slots  118  and  118 ′ preferably separate and frame at least third pair of radially inwardly projecting syringe retaining flanges  140  and  140 ′ formed around the circumference of the opening  26 ′ and  128  and  128 ′. 
     Syringe  10 ′ preferably comprises a body  50 ′ comprising a rear portion  52 ′ which preferably includes a first pair of radially extending mounting flanges  164  and  164 ′ and a second pair of radially extending mounting flanges  166  and  166 ′. A radially extending drip flange  62 ′ is preferably formed forwardly from first mounting flanges  164  and  164 ′ on body  50 ′. First mounting flanges  164  and  164 ′ and second mounting flanges  166  and  166 ′ are preferably in general alignment. The structure of second mounting flanges  166  and  166 ′ is preferably similar to the structure of first mounting flanges  164  and  164 ′. 
     In the case of some fabrication materials, uneven distribution of forces over the circumference of the syringe  10 ′ can result in undesirably quick failure of the syringe  10 ′. Therefore, syringe body  50 ′ also preferably comprises a third pair of radially extending mounting flanges  170  and  170 ′. The centers of third mounting flanges  170  and  170 ′ are preferably offset or rotated approximately 90°(around axis A) from the centers of first mounting flanges  164  and  164 ′. Thus, offsetting of mounting flanges, as illustrated in FIG. 1B, assists in evenly distributing forces over the circumference of syringe  10 ′. 
     As described above for injector system  5 , opening  26 ′ receives and firmly secures syringe  10 ′ to injector front wall  28 ′. During mounting, third pair of mounting flanges  170  and  170 ′ pass through second pair of slots  118  and  118 ′, respectively. First pair of mounting flanges  164  and  164 ′and second pair of mounting flanges  166  and  166 ′ pass through first pair of slots  112 ′ and  112 , respectively. Upon, for example, abutment of drip flange  62 ′ with the face of front wall  28 ′, syringe  10 ′ is rotated clockwise relative to retainer  25 ′ approximately 90° to firmly and releasably mount syringe  10 ′ on injector housing  21 ′ of injector  20 ′. To release syringe  10 ′ from injector  20 ′, the process of mounting is simple reversed. 
     The distinctive positioning and sizing of the mounting flanges and corresponding retainers of systems  5  and  5 ′ substantially ensure proper axial mounting alignment. Systems  5  and  5 ′ are preferably also provided with one or more means for ensuring that syringes  10  and  10 ′ are properly and securely rotatably mounted in retainers  25  and  25 ′, respectively. Referring to FIG. 3A, for example, second channel  44  preferably terminates in a transverse stop  46  to abut an edge of one of second mounting flanges  58  and  60  upon full rotation of syringe  10 . Likewise, and referring to FIG. 3B retainer  25 ′ preferably includes a transverse stop  146  to abut an edge of one of third mounting flanges  170  and  170 ′ upon full rotation of syringe  10 ′. 
     Another means of ensuring proper engagement of the syringe mounting flanges behind their corresponding retaining flanges is to provide means for providing feedback to a user once proper engagement has been effected. Such feedback may be audio, visual and/or tactile. For example, indentations  150  and  152  (see FIG. 3B) may be provided on retainer  25 ′ of injector front wall  28 ′ to receive corresponding projections  156  and  158  formed on the rear surface of drip flange  62 ′ (see FIG.  6 A). Projections  156  and  158  fall into place within indentations  150  and  152  to create an audible “click” sound when syringe  10 ′ is properly secured. 
     Visual indications that syringe  10 ′ is properly secured may also be provided. For example, and as best illustrated in FIG. 8, a pair of indicator arrows  180  and  182  are preferably formed on a forward surface  184  of drip flange  62 ′. When syringe  10 ′ has been fully locked into place in opening  26 ′ of retainer  25 ′, indicator arrows  180  and  182  are preferably in alignment with suitable visual indicators  186  and  188  (see FIG. 4) preferably formed on the front face of injector front wall  28 . 
     Preferably, projection  156  is formed at the same angular location as indicator arrow  180 , while projection  158  is formed at the same angular location as indicator arrow  182 . In this manner indicator arrows  180  and  182  provide a visual indication of the position of projections  156  and  158  as syringe  10 ′ is rotated into place. 
     Syringe  10 ′ and injector  20 ′ are preferably further provided with cooperating data exchange mechanisms for exchanging information between syringe  10 ′ and injector  20 ′. As best illustrated in FIG. 9, for example, third mounting flanges  170  and  170 ′ may be provided with recesses or depressions  190  and  192 , respectively, formed therein to convey information concerning syringe  10 ′ or its contents to the injector  20 ′. Varying the presence, type and/or location of such depressions may be used to encode information. 
     As illustrated in FIG. 5, a spring-actuated sensor switch  194  may be appropriately positioned to be activated by one of depressions  190  or  192  to indicate, for example, the type of syringe which has been installed, the identity of the fluid contained therein and/or the amount of fluid contained therein. 
     Similarly, other depressions may be selectively formed in substantially any area of any mounting flange, as long as the structural integrity of the mounting flanges is not compromised. Similar cooperating sensor elements can also be used to ensure fill engagement of syringe  10 ′. For example appropriate logic may be provided in a manner clear to one of skill in the art such that without full engagement, injector piston  22  will not be actuated by the injector motor and no injection will take place. Cooperating depressions and sensor switches may also function in a timed mode, such that the sensor switches read information from a series of depressions as they are moved past the sensor switches by the action of rotating syringe  10 ′ into place. 
     As illustrated in FIGS. 6A,  7 A and  7 B, the forward end of the syringe  10 ′ preferably includes a conical transition region  210  that provides a transition between main cylindrical body  50 ′ and syringe tip  24 ′. A corner or intersection  212  is formed between cylindrical main body  50 ′ and conical portion  210  on the syringe  10 ′. Intersection  212  is a critical zone which is likely to fail under pressure more quickly than either of the sections it joins. For this reason, intersection  212  is preferably provided with means for reinforcing structural integrity in that area. In a preferred embodiment, the wall thickness in the vicinity of intersection  212  is greater than the general wall thickness of cylindrical main body  50 ′. Preferably, the wall thickness of the entire conical transition region  210  is likewise increased. Reinforcing the structural integrity of intersection  212  and conical transition region  210  enables the use of a number of materials (for example, which are chemically and biochemically compatible with the injection fluid) which would otherwise be unsuitable because of mechanical failure at high pressure. 
     Increasing the wall thickness of intersection  212  and conical transition region  210  reduces bending stress experienced during injection. Alternatively, but at increased fabrication cost, the wall thickness of syringe  10 ′ may be uniformly increased throughout syringe  10 ′ such that bending, meridianal, and circumferential (hoop) stresses are below the tensile yield stress of the syringe material used (or within the elastic region of the stress-strain curve). 
     FIG. 6B illustrates an embodiment of a syringe  220  in which the likelihood of failure under high internal pressure is decreased by providing a transition region  230  of a generally hemispherical shape to connect cylindrical main body  250  with syringe tip or injection region  260 . 
     As best illustrated in FIGS. 11 through 13C, plunger  15 , which is slidably disposed inside cylindrical main body  50 ′, preferably comprises an elastomeric cover surface or sealing cover  310  and a base  312 . In the case of a prefillable syringe, cover  310  is preferably injection-fluid-compatible (that is, chemically compatible and biochemically compatible with the injection fluid). Any contact with the injection fluid is preferably made only with cover  310  and, therefore, base  312  need not be fabricated from a long-term chemically and biochemically compatible material in the case of a prefillable syringe. Base  312  is preferably fabricated from a relatively structurally strong material such as a nylon or polycarbonate. In the embodiment illustrated in FIGS. 11 through 13C, for ease of fabrication base  312  comprises a first base member  320  and a second base member or yoke member  322 . Base  312  can, however, be fabricated to be integral. 
     In the case of a prefillable syringe, sealing cover  310  of plunger  15  may comprise, for example, an elastomeric material such as a thermoplastic elastomer or a synthetic. Such elastomeric materials for sealing cover  310  preferably generally have a hardness in the range of approximately 50-60 Shore A, low compression set characteristic at elevated temperatures (for example, at autoclave temperatures), high chemical resistance and isotropic behavior. Moreover, such elastomeric materials should have no plasticizers and have very low levels of organic and metallic extractables. 
     Cover  310  preferably includes a forward portion  326  having the general shape of the inner wall of the transition region (for example, conical or hemispherical) of the syringe in which plunger  15  is to be used. Cover  310  also preferably includes a protuberance or nose  328  shaped to occupy at least a portion of syringe tip  24  when plunger  15  is in a forward position. Nose  328  decreases the amount of injection fluid which remains inside syringe  10 ′ after plunger  15  is advanced forward to mate with, for example, conical transition region  210 . 
     A side portion of cover  310  forms a cylindrical sealing engagement with the inner sidewall of cylindrical main body  50 ′. In a preferred embodiment, plunger cover  310  has a plurality of circumferential seal ribs  330  (preferably, at least three) which protrude from the outer perimeter of the cover  310  to more effectively create a seal between cover  310  and the inner sidewall of cylindrical main body  50 ′ for the containment and storage of parenteral agents. Seal ribs  330  also assist in maintaining the position of the plunger assembly during autoclave processes. Plunger  15  is properly positioned within the syringe barrel  50  when plunger axis A (shown in FIG. 11) is parallel to barrel axis A (shown in FIG.  1 A). A linear distance L between the leading edge of the forwardmost rib  330  of cover  310  and the trailing edge of the rearwardmost rib  330  of cover  310  is preferable at least 30% of the syringe internal diameter. Such an approximately 3:1 ratio limits misalignment of the plunger axis A and barrel axis A which may occur during the autoclave cycle. 
     In a preferred embodiment, sidewall  340  of base  312  has a slope or angle of taper represented by the angle Φ (see FIG.  11 ), which is preferably greater than approximately 0° and less that approximately 90° (as measured from the horizontal as depicted in FIG.  11 ). More preferably, Φ is in the range of approximately 3° to approximately 15°. Even more preferably, Φ is in the range of approximately 4° to approximately 10°. The rear diameter of sidewall  340  is thus greater than the forward diameter of sidewall  340 , forming the general shape of a fulcrum. Cover  310  is preferably fabricated such that the thickness of a side engaging or seal portion  350  thereof is greater at the forward portion thereof than at the rearward portion thereof Thus, while the slope or exterior sidewall of side engaging portion  350  of cover  310 , which contacts the inner sidewall of cylindrical main body  50 ′, is generally flat (that is, forming an angle of approximately 0° with the horizontal as illustrated in FIG.  11 ), the slope of the interior sidewall of engaging portion  350  is preferably approximately the same as the slope or angle of taper of sidewall  340  of base  312 . A surface preparation or lubricant as known in the art, such as a silicone oil, is preferably provided between cover  310  and base  312  to facilitate relevant movement therebetween, thereby ensuring adequate dynamic function. The above construction of plunger  15  improves the sealing engagement between plunger  15  and the inner sidewall of cylindrical main body  50 ′ of syringe  10 ′ by minimizing the negative effects of compression set which may be experienced by some cover materials during sterilization. Further, this plunger construction assists in minimizing unwanted (and potentially irreversible) plunger movement during sterilization. 
     As the internal pressure of the syringe system increases, the elastomeric material in the region of  350  of seal cover  310  tends to slide along surface  340  of base  312  parallel to axis A of plunger  15 . The sliding action of these components in response to increased internal syringe pressure forces seal cover  310  to exert a radial force on the inside wall of syringe barrel  50 ′, thereby creating a dynamic “wedge” seal system. 
     In the case of “static” seal systems (for example O-rings), used on current syringe systems, as the internal syringe pressure increases, the radial expansion of the vessel must be minimal to ensure an adequate seal. Such static sealing systems are thus generally acceptable in a syringe barrel system where radial barrel growth is negligible. In a prefillable syringe system, however, radial growth in response to increases in internal pressure can be substantial due to the weakness of certain syringe materials, and the lack of a pressure jacket. For example, radial growth of the barrel  50  is typically observed under internal pressures achieved during a powered injection. The wedge dynamic seal provides a dynamic seal within such a relatively flexible, radially expanding syringe barrel under relatively high internal pressures. 
     As also best illustrated in FIG. 11, seal cover  310  preferably has an inwardly projecting circumferential attachment member  360 . Attachment member  360  is designed to seat in a channel  362  of base  312  to hold seal cover  310  on base  312 . 
     As discussed above, piston  22  cooperates with plunger  15  to impart reciprocal motion thereto. Piston  22  preferably comprises a stem  410  and a piston head  412  formed on a distal end of stem  410 . Piston head  412  preferably extends radially outwardly beyond the radial edge of stem  410 . In the embodiment illustrated in FIG. 1A through 2B, piston head  412  comprises two opposing piston flanges  414  and  416 . 
     Base  312  of plunger  15  preferably includes capture members  420  and  422  protruding rearwardly beyond the rear surface of base  312  by an amount sufficient to capture and retain flanges  414  and  416  of the piston head  412  (see, for example, FIG.  2 B). Capture members  420  and  422  are preferably constructed of a flexible material such that capture members  420  and  422  flex radially outwardly when contacted by piston flanges  414  and  416  and subsequently “snap back” to capture piston flanges  414  and  416 . While only two capture members  414  and  416  are shown, as clear of one skilled in the art, more than two capture members  414  and  416  can be used with a corresponding change in the shape of the piston head  412 . 
     In a preferred embodiment, as piston  22  moves forward to contact plunger  15  a pair of preferably beveled surfaces  424  and  426  are aligned with and engaged by piston flanges  414  and  416  and are forced radially outwardly until piston head flanges  414  and  416  pass beyond and over inner shoulders  428  and  430 . This design enables piston  22  to engage plunger  15  easily at any axial position of plunger  15 , thus permitting use of various injection liquid fill volumes in syringes. In a preferred embodiment, beveled surfaces  424  and  426  are aligned for engagement with piston flanges  414  and  416  when syringe  10 ′ is properly mounted in retainer  25 ′. Likewise, disengaging rotation of capture members  420  and  422  relative to piston  22  preferably corresponds to the rotation of syringe  10 ′ required to dismount syringe  10 ′ from retainer  25 ′ so that plunger  15  (which preferably rotates with syringe  10 ′) is disengaged from piston head  412  when syringe  10 ′ is rotated and dismounted from retainer  25 ′. 
     In another embodiment, capture members  420  and  422  can be fabricated to be substantially rigid and piston flanges  414  and  416  (shown in FIG. 1A) can be fabricated to be flexible or spring-loaded such that piston flanges  414  and  416  deflect radially inwardly (with respect to axis A) to allow passage of piston head  412  between capture members  420  and  422  and retention of piston head  412  by capture members  420  and  422 . 
     After retention of piston head  412  by capture members  420  and  422 , plunger  15  preferably resists disconnection from piston  22  upon rearward movement of piston  22 . In one embodiment, capture members  420  and  422  are designed such that the forces exerted upon capture members  420  and  422  upon rearward movement of piston  22  substantially prevent radially outward deflection (or bending) of capture members  420  and  422 . In the embodiment (best illustrated in FIG.  11 ), for example, retention members  440  of capture members  420  and  422  are positioned such that the load experienced upon rearward movement of piston  22  (represented by arrow F) is experienced at a position equal or greater in radial distance (relative to axis A) than points C where stems  444  of cantilevered capture members  420  and  422  are attached to base  312 . The bending moment created by rearward motion of piston  22  thus tends to cause capture members  420  and  422  to deflect radially inwardly and assists in preventing disconnection of plunger  15  from piston  22 . 
     During use, syringe  10 ′, for example, is attached to a connecting tube which transports the injection fluid as known in the art to a hollow needle or the like inserted into the patient. As illustrated in FIG. 14, a prefilled syringe  10 ′ may be provided as a unit with a connecting tube  510 . In this embodiment, connecting tube  510  and syringe  10 ′ are permanently affixed (for example, via an adhesive) to each other at syringe tip  24 ′. This joined nature allows both syringe  10 ′ and tube  510  to be filled as a unit with an injection fluid, filling the entire volume of connecting tube  510  and a predetermined portion of elongated cylindrical main body  50 ′. 
     Syringe tip  24 ′ may be terminated in any one of several manners. In the embodiment of syringe  10 ′ illustrated in FIGS. 6A,  7 A and  7 B, for example, syringe tip  24 ′ terminates in a standard male luer connection  520 . Luer connection  520  comprises an inner tubular member  522  designed to mate with a standard female luer connector (not shown) on the flexible connector tube  510  as illustrated in FIG.  14 . Syringe tip  24 ′ also comprises a threaded outer wall  524  having an interior diameter that grips the luer connector of connector tube  510 . Outer wall  524  preferably comprises a double-start, right-hand threaded luer lock fitting. 
     In another embodiment illustrated in FIG. 15, a syringe  610  is terminated in a long, relatively thin tube section  612  which preferably has a standard luer taper. Tube  612  preferably includes an annular channel  614  extending radially inwardly from the generally cylindrical exterior surface of tube section  612 . 
     A generally cylindrical swivel nut  620  preferably comprises a radially inwardly projecting engaging flange  622 . The width of retaining flange  622  is slightly smaller than the width of channel  614 . Swivel nut  620  is preferably manufactured from a relatively tough and resilient material such as polycarbonate and preferably includes a series of exterior ribs  624  to aid the user in gripping and rotating swivel nut  620 . Ribs  624  preferably extend in a direction parallel to the axis around which the syringe  610  is formed. 
     To attach swivel nut  620  to syringe  610 , swivel nut  620  is placed over tube  612  and moved rearwardly, applying sufficient force to swivel nut  620 , to cause retaining flange  622  to snap over retaining flange  616  to seat in channel  614 . Further rearward movement of swivel nut  620  is prevented by a second retaining flange  618 . Once swivel nut  620  has been snapped into place with respect to channel  614 , it may rotate freely with respect to the syringe tube  612 . 
     As best illustrated in FIG. 16, swivel nut  620  preferably comprises a plurality of interior threads  626  for engagement of the outside flange of a female luer fitting positioned at the end of an elastomeric connector tube. Preferably, threads  626  are double start right-handed threads (for example, according to MD-70 standards). In use, swivel nut  620  is simply rotated to screw onto a connector tube which occupies the space between the exterior sidewall of tube  612  and threads  626 . 
     FIG. 17 is a cross-sectional illustration of a syringe tip seal  720  which is fluid-tight with respect to the injection fluid within a syringe. The embodiment of tip seal  720  illustrated in FIG. 17 is designed for use, for example, with a syringe tip terminating in a standard luer fitting as illustrated in FIGS. 6A,  7 A,  7 B and  14 . Tip seal  720  is preferably fabricated from an elastomeric material that is chemically and biochemically compatible with the injection fluid. For example, tip seal  720  may be fabricated from a thermoplastic elastomer or synthetic halobutyl isoprene. Tip seal  720  preferably comprises an outer, generally cylindrical, seal member  722 . Seal member  722  preferably has a tapered inner surface which forms a seal with the outer diameter of outer wall  524  of luer connection  520 . Tip seal  720  also preferably comprises an inner, generally cylindrical, seal member  724 . Inner seal member  724  preferably comprises a tapered inner surface which forms a seal with the outer diameter of inner tubular member  522  of luer connection  520 . 
     Although the present invention has been described in detail in connection with the above examples, it is to be understood that such detail is solely for that purpose and that variations can be made by those skilled in the art without departing from the spirit of the invention except as it may be limited by the following claims.