Front-loading medical injector and syringes, syringe interfaces, syringe adapters and syringe plungers for use therewithAbstract Claims 1. A syringe for use with an injector comprising a syringe retaining mechanism, the syringe comprising: a body comprising a rear end and a front end; a plunger movably disposed within the body; and at least one attachment member associated with the body, the at least one attachment member adapted to releasably engage the syringe retaining mechanism of the injector regardless of the orientation of the syringe with respect to the injector. 2. The syringe of claim 1 wherein the at least one attachment member comprises an annular ridge disposed on the body. 3. The syringe of claim 1, further comprising one or more projections associated with the body, the one or more projections adapted to engage corresponding members of the syringe retaining mechanism to enable release of the syringe from the injector through rotational motion. 4. The syringe of claim 1 wherein the at least one attachment member comprises one or more tab members. 5. The syringe of claim 4 wherein each of the tab members comprises a first tab end attached to the body and a second tab end adapted to engage the syringe retaining mechanism of the injector. 6. The syringe of claim 4 wherein the tab members are resilient members. 7. The syringe of claim 4 wherein the tab members are integrally formed with the body. 8. The syringe of claim 1, further comprising a flange associated with the body and adapted to engage a corresponding surface of the injector when the syringe is releasably engaged therewith. 9. The syringe of claim 8 wherein the flange is adapted to substantially prevent fluid from entering the interior of the injector. 10. The syringe of claim 1 wherein the at least one attachment member is moved in an axial direction to releasably engage the injector. 11. The syringe of claim 1 wherein the at least one attachment member is moved in a vertical direction to releasably engage the injector. 12. The syringe of claim 1 wherein the at least one attachment member is associated with the rear end of the body. 13. The syringe of claim 1 wherein the at least one attachment member is associated with the front end of the body. 14. The syringe of claim 1, further comprising an encoding device operable to provide syringe information to the injector. 15. An injector for injecting fluid from a syringe mounted thereon, the injector comprising: a housing; a drive member at least partially disposed within the housing and operable to engage a plunger of the syringe; and a syringe retaining mechanism associated with the housing, the syringe retaining mechanism adapted to releasably engage the syringe regardless of the orientation of the syringe with respect to the injector. 16. The injector of claim 15 wherein the syringe retaining mechanism comprises one or more capture members adapted to releasably engage corresponding members of the syringe. 17. The injector of claim 16, further comprising an actuator member adapted to engage the corresponding members of the syringe to urge them out of engagement with the one or more capture members to release the syringe from the injector. 18. The injector of claim 16 wherein the one or more capture members are resilient or movable members. 19. The injector of claim 18 wherein the one or more capture members are manipulated to urge them out of engagement with the corresponding members of the syringe to release the syringe from the injector. 20. The injector of claim 18, further comprising an actuator member associated with the one or more capture members, the actuator member adapted to be rotated by the syringe to urge the one or more capture members out of engagement with the corresponding members of the syringe to release the syringe from the injector. 21. The injector of claim 16 wherein the one or more capture members are spring-loaded members. 22. The injector of claim 21 wherein movement of the syringe against the one or more capture members to overcome the spring force urges the one or more capture members out of engagement with the corresponding members of the syringe to release the syringe from the injector. 23. The injector of claim 21 wherein manipulation of the one or more capture members to overcome the spring force urges the one or more capture members out of engagement with the corresponding members of the syringe to release the syringe from the injector. 24. The injector of claim 15 wherein the syringe retaining mechanism is adapted to releasably engage the syringe in an axial direction. 25. The injector of claim 15 wherein the syringe retaining mechanism is adapted to releasably engage the syringe in a vertical direction. 26. The injector of claim 15, further comprising a sensor adapted to read syringe information provided by an encoding device on a syringe. 27. A method of connecting a syringe comprising at least one attachment member to an injector comprising a syringe retaining mechanism, the method comprising: moving the at least one attachment member of the syringe into the syringe retaining mechanism without regard to the orientation of the syringe to the injector; and releasably engaging the at least one attachment member of the syringe with the syringe retaining mechanism of the injector. 28. The method of claim 27 wherein the moving step comprises axially moving the syringe into the syringe retaining mechanism. 29. The method of claim 28 wherein the moving step comprises vertically moving the syringe into the syringe retaining mechanism. 30. The method of claim 27, further comprising: providing an actuator member associated with the syringe retaining mechanism and adapted to be rotated by the syringe to urge the syringe retaining mechanism out of engagement with the at least one attachment member of the syringe; and rotating the syringe to release the at least one attachment member from the syringe retaining mechanism. 31. The method of claim 27, further comprising the step of manipulating the syringe retaining mechanism to release the at least one attachment member therefrom. 32. The method of claim 27, further comprising the step of moving the syringe against the syringe retaining mechanism to release the at least one attachment member therefrom. 33. The method of claim 27, further comprising: providing an actuator member adapted to engage the at least one attachment member of the syringe; activating the actuator member to urge the at least one attachment member out of engagement with the syringe retaining mechanism to release the syringe from the injector 34. The method of claim 27, further comprising: providing an encoding device adapted to provide syringe information on the syringe; providing a sensor adapted to read syringe information on the injector; and reading the syringe information as the syringe is connected to the injector. 35. An injector for injecting fluid from a syringe mounted thereon, the injector comprising: a housing; and a retaining member associated with the housing for releasably engaging the syringe, the retaining member being movable upon rotation of the syringe between a relaxed state, where the syringe is engaged by the retaining member, and a tensioned state, where the syringe is released from the retaining member. 36. The injector of claim 35 wherein the retaining member comprises a substantially elliptical, flexible ring. 37. The injector of claim 35 wherein the retaining member comprises a substantially circular, flexible ring. 38. The injector of claim 35 wherein the retaining member comprises a plurality of segments. 39. The injector of claim 35, further comprising a grooved, rotating ring operatively connected to the retaining member, wherein rotation of the rotating ring manipulates the retaining member from the relaxed state to the tensioned state. 40. An injector system comprising an injector and a syringe, the injector system comprising: a syringe comprising: a body comprising a forward end and a rearward end; and a plunger movably disposed in the body; and an injector comprising: a housing; and a piston movably disposed at least partially within the housing and operable to drive the plunger of the syringe in a forward direction without a connective engagement therebetween to dispense fluid from the forward end of the body during an injection procedure, wherein the piston connectively engages the plunger to retract the plunger within the syringe. 41. The injector system of claim 40 wherein the piston comprises a collet member comprising one or more segment members adapted to deflect in a radial direction to engage the plunger when the piston is retracted. 42. The injector system of claim 40 wherein the piston comprises an elastomeric member adapted to expand in a radial direction to engage the plunger when the piston is retracted. 43. The injector system of claim 40, further comprising: a sleeve member associated with the piston; and one or more plunger gripper members associated with the piston and adapted to be biased by the sleeve member into engagement with the plunger upon retraction of the piston. 44. The injector system of claim 43, further comprising: a collar connected to one end of the piston sleeve, the collar defining an opening through which the piston extends; a plunger cap connected to the collar, the plunger cap defining an interior space and a plurality of slots formed in a side thereof; a gripper extender disposed on an end of the piston within the interior space of the plunger cap; a plurality of grippers disposed through the slots and engageable with the gripper extender; and a biasing member in contact with the piston sleeve; whereby, upon movement of the piston in a rearward direction, the biasing member biases movement of the piston sleeve to substantially prevent movement of the piston sleeve in the rearward direction to cause the gripper extender to push the plurality of grippers through the slots in the plunger cap into engagement with the plunger within the syringe. 45. The injector system of claim 40 wherein the piston is adapted to engage the plunger without regard to the orientation of the plunger with respect to the piston. 46. The injector system of claim 40 wherein the piston is adapted to drive the plunger without regard to the orientation of the plunger with respect to the piston. 47. A method of preparing an injector comprising a drive piston for a procedure, the method comprising: mounting a syringe comprising a plunger on the injector; sensing that the syringe is mounted on the injector; and advancing the piston of the injector to engage the plunger of the syringe. 48. The method of claim 47, further comprising the step of advancing the plunger to a distal end of the syringe to expel air therefrom. 49. The method of claim 48, further comprising the step of filling the syringe with fluid by retracting the piston to aspirate fluid into the syringe. 50. The method of claim 47, further comprising the step of advancing the piston to prime the syringe and a tube connected to the syringe. 51. The method of claim 50, further comprising the step of advancing the piston to expel fluid from the syringe. 52. The method of claim 47, further comprising the step of retracting the piston after the syringe is removed from the injector. 53. The method of claim 47 wherein the step of advancing the piston to engage the plunger is automatically conducted by the injector. 54. A syringe for use with an injector comprising a syringe retaining mechanism, the syringe comprising: a body comprising a rearward end and a forward end; a plunger movably disposed within the body; at least one attachment member associated with the body; and at least one rotation member associated with the body for releasably engaging a corresponding member of the syringe retaining mechanism of the injector. 55. The syringe of claim 54 wherein the at least one rotation member comprises a recess formed in the body. 56. The syringe of claim 54 wherein the at least one rotation member comprises a projection. 57. A syringe adapter for use with an injector, the syringe adapter comprising: a rear mounting member adapted to engage a syringe retaining mechanism associated with the injector; and a front mounting member adapted to engage a corresponding mounting member associated with a syringe to install the syringe on the injector. 58. The syringe adapter of claim 57 wherein the front mounting member comprises at least one capture member adapted to engage the corresponding mounting member associated with the syringe. 59. The syringe adapter of claim 58 wherein the at least one capture member is movable to engage the corresponding mounting member associated with the syringe. 60. The syringe adapter of claim 57 wherein the rear mounting member comprises at least one attachment member adapted to engage the syringe retaining mechanism of the injector. 61. The syringe adapter of claim 60 wherein the at least one attachment member comprises an annular ridge disposed on the body. 62. The syringe adapter of claim 60 wherein the rear mounting member further comprises one or more projections adapted to engage corresponding members of the syringe retaining mechanism to enable release of the syringe from the injector through rotational motion. 63. The syringe adapter of claim 60 wherein the at least one attachment member comprises one or more tab members. 64. The syringe adapter of claim 63 wherein each of the tab members comprises a first tab end attached to the adapter and a second tab end adapted to engage the syringe retaining mechanism of the injector. 65. The syringe adapter of claim 63 wherein the tab members are resilient members. 66. The syringe adapter of claim 63 wherein the tab members are integrally formed with the adapter. 67. The syringe adapter of claim 57 wherein the rear mounting member is moved in an axial direction to engage the syringe retaining mechanism of the injector. 68. The syringe adapter of claim 57 wherein the rear mounting member is moved in a vertical direction to engage the syringe retaining mechanism of the injector. 69. The syringe adapter of claim 57 wherein the rear mounting member is adapted to engage the syringe retaining mechanism of the injector regardless of the orientation of the syringe adapter with respect to the injector. 70. A method of adapting an injector to accept a syringe, the method comprising: installing an adapter configured to accept the syringe on the injector; and mounting the syringe on the adapter. 71. The method of claim 70 wherein the adapter may be installed on the injector without regard to the orientation of the adapter with respect to the injector. Description [0001] This application is a continuation-in-part of application Ser. No. 09/718,230, filed on Nov. 21, 2000, and claims priority to Provisional Application Ser. No. 60/180,647, filed on Feb. 7, 2000, and to Provisional Application Ser. No. 60/229,550, filed on Sep. 5, 2000. BACKGROUND OF THE INVENTION [0002] This invention relates to medical injectors, and syringes, syringe interfaces, syringe adapters and syringe plungers for use therewith. More particularly, the present invention relates to front-loading medical injectors, and syringes, syringe interfaces, syringe plungers and adapters for use with new or existing medical injectors wherein a syringe of special construction is mountable upon and removable from the injectors by a releasable mechanism. [0003] Medical injectors and syringes for injecting contrast media into a patient for imaging biological structures are known in the art. For example, U.S. Pat. No. 4,677,980, issued to D. M. Reilly et al. on Jul. 7, 1987, and entitled "Angiographic Injector and Angiographic Syringe for Use Therewith," which is assigned to the same Assignee as the subject application, discloses an angiographic injector apparatus. The apparatus is designed for injecting contrast media into the vascular system of an animal, in which syringes are rear-loaded into a pressure jacket of the injector. More specifically, the apparatus comprises a rotatable turret which carries a pair of the pressure jackets and which is rotatable so that when one of the pressure jackets, into which a syringe has been rear-loaded, is in an injection position, the other pressure jacket is in a position in which an associated syringe can be rear-loaded. Subsequently, when injection of contrast media from the first syringe is completed, the turret is rotated to move the first syringe to an unloading-loading position, with the second pressure jacket and the syringe concurrently being moved into the injection position. [0004] In the apparatus disclosed in the '980 patent, a drive member of the angiographic injector can be drivingly connected to, or disconnected from, a plunger of a syringe at any point along the path of travel of the syringe plunger by a releasable mechanism. However, for the releasable mechanism to correctly operate, the syringe plunger must be properly oriented to mate with the injector piston. Further, during loading of the syringe on the injector, the syringe must be correctly aligned within a respective pressure jacket to allow the syringe plunger and the injector piston to connect to and disconnect from each other. [0005] An improved apparatus over the '980 patent apparatus is disclosed in U.S. Pat. No. 5,383,858, issued to D. M. Reilly et al. on Jan. 24, 1995, and entitled "Front-Loading Medical Injector and Syringe for Use Therewith." which is also assigned to the same Assignee as the present application. In the apparatus described in the '858 patent, the syringe is front-loaded onto, in at least one embodiment, a pressure jacket-less injector, overcoming one of the drawbacks of the '980 patent injector apparatus. [0006] The injector described in the '858 patent has a first release mechanism for attaching and releasing the syringe from the injector. In addition, the apparatus includes a second release mechanism that engages and disengages the injector piston from the syringe plunger. Upon rotation of the syringe, the syringe is attached to or released from the injector and, simultaneously, the plunger is attached to or released from the piston. The structure disclosed requires that the syringe be installed on the injector in a specific orientation so that the syringe can releasably engage the injector and, simultaneously, the plunger can releasably engage the piston. In addition, as with the syringe disclosed in the '980 patent, during assembly the syringe plunger must be correctly oriented within the syringe. [0007] Another injector apparatus is disclosed in U.S. Pat. No. 5,300,031, issued to C. Neer et al. on Apr. 5, 1994, and entitled "Apparatus for Injecting Fluid into Animals and Disposable Front Loadable Syringe Therefor." The '031 patent discloses various embodiments of a pressure-jacketed injector wherein a syringe is loaded into and removed from an injector pressure jacket through an opening provided in the front end of the pressure jacket. To retain the syringe within the pressure jacket, for example, during an injection operation, the front end of the syringe is locked to the front end of the pressure jacket. To correctly connect the syringe to the pressure jacket, the syringe may only be inserted into the pressure jacket in one orientation. [0008] In each example discussed above, the syringe must be connected to the injector in a specific orientation to assure proper syringe mounting. Proper alignment is required to assure that the syringe may be operated properly during a medical imaging procedure. The required orientation, however, hinders rapid attachment and replacement of the syringe. The required orientation may also increase the manufacturing assembly cost and complexity of the syringe. [0009] Accordingly, while the above injector and syringe apparatuses have proven effective, a need has arisen for a simpler front-loading medical injector. More specifically, to facilitate further the loading operation, a need has arisen for a syringe that can be easily connected to the injector without regard for the specific orientation of the syringe and/or syringe plunger. In addition, to simplify assembly of the syringe components, a need has arisen for a syringe with a plunger that does not need to be oriented in a specific relation to the barrel or base of the syringe. Furthermore, to minimize the time required to prepare an injector for an injection procedure, a need has arisen for injectors providing automated features. SUMMARY OF THE INVENTION [0010] The present invention provides medical injectors, syringe interfaces, syringe adapters, syringe plungers and syringes for use therewith which address the needs that have arisen for a simpler injector and syringe system. Specifically, the present invention provides, in one aspect, a syringe interface and a mating syringe that cooperate to allow the syringe to be easily, readily and securely fastened to a medical injector. The syringe need not be oriented in any particular manner before being connected to the injector. In addition, the plunger need not be oriented in any particular manner with respect to the barrel of the syringe. The syringe and plunger both are provided with release mechanisms so that the syringe can be quickly installed on and unloaded from the injector and replaced with a new syringe. [0011] To accomplish these objectives, the present invention provides a syringe for engaging an injector. In a preferred embodiment, the syringe includes a syringe body having a syringe forward end adapted to dispense fluid and a syringe rearward end adapted to engage with the injector. A plunger or plunger cover is axially reciprocable within the syringe body. A flange member is disposed at the syringe rearward end. The flange is adapted to engage a flexible ring within a connector mechanism on the injector housing, or on a syringe interface or an adapter connected to the injector housing. The flange and flex ring combination provide for engagement of the syringe to and release of the syringe from the injector. Further, the syringe includes one or more members for engaging the flexible ring to permit disengagement of the syringe therefrom. [0012] In an alternate embodiment, the flange member may be disposed at the syringe forward end and the flexible ring may be disposed on a forward end of a pressure jacket connected to an injector. [0013] In another embodiment, the syringe includes a syringe body having a syringe forward end adapted to dispense fluid and a syringe rearward end adapted to engage with the injector. A plunger or plunger cover is axially reciprocable within the syringe body. At least one tab or flange member (which may be resilient) is disposed at the syringe rearward end. The at least one tab or flange is adapted to engage a wall portion on an injector, or a syringe interface or an adapter connected to the injector, when the syringe engages with the injector. The at least one tab or flange provides for engagement of the syringe to and release of the syringe from the injector. [0014] In still another embodiment, the syringe includes a syringe body having a syringe forward end adapted to dispense fluid and a syringe rearward end adapted to engage with the injector. A plunger is axially reciprocable within the syringe body. At least one resilient tab is disposed at the syringe rearward end. The at least one resilient tab is adapted to engage a wall portion on the injector, or a syringe interface or an adapter connected to the injector, when the syringe engages with the injector. The at least one tab provides for engagement of the syringe to and release of the syringe from the injector. [0015] In an alternate embodiment, the syringe includes at least two resilient tabs adapted to engage the wall portion of the injector when the syringe engages the injector. In still another embodiment, the syringe includes more than two tabs that are arranged around its base so that the syringe securely engages the injector. [0016] The present invention further provides an injector system combining a syringe and an injector. The syringes have the same general constructions as described above. The injector includes an interface adapted to receive the rearward end of the syringe. In a preferred embodiment, the interface of the injector includes a flexible ring for engaging a flange member disposed on the syringe. In an alternate embodiment, the flexible ring may be disposed on a forward end of a pressure jacket connected to the injector, and the flange member may be disposed on the forward end of the syringe to engage the flexible ring. [0017] In another embodiment, the injector includes a forward portion having a first diameter adapted to receive the syringe rearward end. The injector interface also includes a rearward portion having a second diameter, larger than the first diameter, and a ledge disposed between the forward portion and the rearward portion, joining the forward portion and the rearward portion together. The at least one tab on the syringe is adapted to resiliently engage the ledge when the syringe is engaged with the injector. The interface of the injector further includes a collar, reciprocable within the rearward portion adjacent a wall therein, adapted to urge the at least one tab inwardly to disengage the at least one tab from the ledge, thereby enabling removal of the syringe from the injector. [0018] The present invention further provides an injector piston, a syringe plunger assembly and a combined piston/plunger assembly. In a preferred embodiment, the syringe plunger assembly includes a plunger cover and an associated plunger cover support ring disposed within the syringe. In an alternate embodiment, the syringe plunger assembly includes only a plunger cover disposed within the syringe. The injector piston is preferably shaped to complement the shape of the plunger cover. In addition, the injector piston is preferably adapted to push the syringe plunger cover during forward axial movement, without an actual connection being made therebetween. During retraction of the plunger, however, the injector piston is adapter to connectively engage the plunger or plunger cover. [0019] In one embodiment, the piston/plunger assembly includes a piston associated with an injector, a piston sleeve surrounding the piston, a collar connected to one end of the piston sleeve, the collar defining an opening through which the piston extends, a plunger cap connected to the collar, the plunger cap defining an interior space, a gripper extender disposed on an end of the piston within the interior space of the plunger cap, a plurality of slots through a side of the plunger cap, a plurality of grippers disposed through the slots and being engageable with the gripper extender, and a biasing member in contact with the piston sleeve. Upon movement of the piston in a direction, the biasing member biases movement of the piston sleeve to restrict movement in the same direction to cause the gripper extender to push the plurality of grippers through the slots in the plunger cap for engagement with a plunger or rubber cover within a syringe. [0020] In other embodiments, the plunger and piston may be adapted to connect together electromechanically or electromagnetically. [0021] Further in accordance with the embodiments set forth above, the present invention also provides an adapter for receiving a syringe. The adapter engages with an injector and is disposed between the injector and the syringe. The adapter includes an adapter forward end adapted to engage the syringe. In one embodiment, the adapter rearward end has at least one resilient tab that is adapted to engage with the injector. [0022] The present invention further provides for an adapter assembly. The adapter assembly includes an adapter and a syringe for use therewith. In a preferred embodiment, the adapter includes an adapter rearward end comprising a flange member adapted to engage with a flexible ring of an injector. In this embodiment, the adapter would allow an injector designed according to the present invention to accept conventional syringes. [0023] In an alternate embodiment, the adapter may have a rearward end including a mechanism allowing it to mate with existing injectors (such as the injectors disclosed in U.S. Pat. Nos. 4,677,980, 5,383,858 and 5,300,031, the disclosures of which are hereby incorporated by reference) and a forward end including a flexible ring or a ledge or shoulder member allowing it to mate with syringes designed according to the present invention. In this embodiment, the adapter would allow conventional or existing injectors to accept syringes designed according to the present invention. [0024] In addition, the present invention provides methods for engaging or installing the front-loading syringes and adapters of the present invention and/or existing syringes with the front-loading injectors of the present invention and/or existing injectors. [0025] Furthermore, the present invention provides injectors and injector systems having certain automated features that facilitate the preparation thereof for injection procedures. [0026] The present invention offers many advantages over the prior art. For example, the present invention provides a syringe that does not have to be aligned and/or oriented with respect to an injector for installation thereon. Further, the present invention provides a syringe in which alignment, either radially or axially, between the plunger and syringe is not required. [0027] Moreover, the piston of the present invention may be designed so that it does not permanently engage the plunger. So designed, the plunger acts primarily as a pusher during the injection operation. Only when the plunger must be retracted, for example, to aspirate fluid into the syringe, may an engagement mechanism be activated so that the piston connects to the plunger. By virtue of this arrangement, the plunger may be left in any position when the syringe is removed from the injector system. [0028] The present invention, along with the attributes and attendant advantages thereof, will best be appreciated and understood in view of the following detailed description taken in conjunction with, the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS [0029] The various embodiments of the present invention are described in connection with the figures appended hereto, in which: [0030] FIG. 1 is a perspective view of an injector apparatus in accordance with the present invention, showing an injector housing and a syringe in a disassembled relationship; [0031] FIG. 2 is an enlarged perspective view of the syringe illustrated in FIG. 1, shown connected to a front wall of the injector housing, illustrating how a flange disposed at a rearward end of the syringe may prevent leaking fluid from entering the injector housing; [0032] FIG. 3 is an enlarged cross-sectional view of the syringe shown in FIGS. 1 and 2, illustrating the construction of a forward end of the syringe; [0033] FIG. 4 is a perspective view of another embodiment of the present invention, illustrating a syringe and a pressure-jacketed injector in a disassembled relationship; [0034] FIG. 5 is another perspective view of the embodiment illustrated in FIG. 4, showing a piston displaced at a more forward position than that illustrated in FIG. 4; [0035] FIG. 6 is a cross-sectional view of the syringe and housing illustrated in FIGS. 1 and 2, showing the secure connection of the syringe to the front wall of the injector housing through tabs attached at the rearward end of the syringe; [0036] FIG. 7 is an enlarged cross-sectional view of the structures enclosed by circle VII in FIG. 6, showing in greater detail the connection of the syringe to the front wall of the injector housing; [0037] FIG. 8 is an enlarged perspective view of the tabs illustrated in FIG. 7 that are connected to the rearward end of the syringe illustrated in FIG. 1; [0038] FIG. 9 is an enlarged cross-section of an alternate embodiment of tabs attached at the rearward end of a syringe for engagement with a front wall of an injector, showing essentially the same structures illustrated in FIG. 7; [0039] FIG. 10 is an enlarged perspective view of yet another embodiment of a syringe in accordance with the present invention, illustrating at least one tab at a base of the syringe for engagement with a ledge defined in an interface of an injector housing; [0040] FIG. 11 is an enlarged perspective view of the syringe illustrated in FIG. 10, showing the at least one tab from the rearward end (or base side) of the syringe; [0041] FIG. 12 is an enlarged perspective view of another embodiment of a syringe in accordance with the teachings of the present invention, illustrating two tabs at the base of the syringe for engagement with the injector housing; [0042] FIG. 13 is an enlarged perspective view of the syringe shown in FIG. 12, illustrating the two tabs at the rearward end of the syringe; [0043] FIG. 14 is an enlarged perspective view of still another embodiment of a syringe in accordance with the present invention, illustrating more than two tabs at a base of the syringe for engagement with an injector housing; [0044] FIG. 15 is an enlarged perspective view of the syringe illustrated in FIG. 14, showing the base end of the syringe with the plurality of tabs; [0045] FIG. 16 is a partial, enlarged perspective view of an alternate embodiment of the tab arrangement illustrated in FIGS. 1 and 8; [0046] FIG. 17 is a cross-sectional view of the tab arrangement illustrated in FIG. 16, taken along line XVII-XVII; [0047] FIG. 18 is a cross-sectional view of the syringe illustrated in FIGS. 14 and 15 with a portion of a front wall of an injector housing, showing a ledge that is securely engaged by tabs at the base of the syringe, and also showing a reciprocating collar that disengages the tabs from the ledge; [0048] FIG. 19 is a cross-sectional illustration of the embodiment illustrated in FIG. 18, showing the tabs engaging the ledge so that the syringe securely engages the injector housing; [0049] FIG. 20 is a cross-sectional illustration of the embodiment shown in FIGS. 18 and 19, showing the engagement of the reciprocating collar with the tabs to disengage them from the ledge of the injector housing; [0050] FIG. 21 is a cross-sectional view of an adapter assembly connected to the syringe illustrated in FIGS. 14 and 15; [0051] FIG. 22 is a cross-sectional view of an alternate embodiment of the adapter assembly illustrated in FIG. 21, where the adapter includes a tabbed opening for engagement with the injector housing; [0052] FIG. 23 is a perspective view of the adapter and syringe illustrated in FIG. 22; [0053] FIG. 24 is another perspective view of the adapter and syringe illustrated in FIG. 22; [0054] FIG. 25 is a cross-sectional view of an embodiment of a plunger and piston according to the teachings of the present invention, showing an electromagnetic mechanism that causes the plunger and piston to be attracted to one another during operation of the apparatus; [0055] FIG. 26 is a partial cross-sectional view of an other embodiment of a plunger and piston, showing an electromechanical mechanism that causes the plunger and piston to be releasably attached to one another during operation of the apparatus; [0056] FIG. 27 is an enlarged cross-sectional view of the piston and plunger illustrated in FIG. 26, showing the piston engaging the plunger; [0057] FIG. 28 is a cross-sectional view of the combination of the piston and the plunger shown in FIG. 27, the view taken along line XXVIII-XXVIII, showing two protrusions extended so that the piston engages the plunger; [0058] FIG. 29 is a cross-sectional view of the combination of the piston and the plunger shown in FIGS. 26-28, with the two protrusions retracted so that the piston can disengage from the plunger; [0059] FIG. 30 is an enlarged cross-sectional view of a plunger according to the teachings of the present invention, illustrating the placement of a pressure-sensing device in the plunger; [0060] FIG. 31 is an enlarged cross-sectional view of the plunger illustrated in FIG. 30, showing the plunger subjected to a pressure from the fluid contained in a syringe (not illustrated); [0061] FIG. 32 is a side view illustration of an alternate embodiment of the present invention where tabs are added to a syringe cap that engages the end of a pressure jacket; [0062] FIG. 33 is an enlarged cross-sectional view of an alternate embodiment of the apparatus shown in FIG. 7; [0063] FIG. 34 is an enlarged cross-sectional view of the alternate embodiment of the apparatus shown in FIG. 33; [0064] FIG. 35 is a side view illustration of another embodiment of the apparatus that releasably connects the plunger and piston to one another; [0065] FIG. 36 is a side view illustration of still another embodiment of the apparatus that releasably connects the plunger and piston to one another; [0066] FIG. 37 is an end view illustration of the separable members shown in FIG. 36; [0067] FIG. 38 is a perspective cut-away illustration of a pressure jacket embodiment of the present invention showing the reciprocating collar disposed within the pressure jacket; [0068] FIG. 39 is a cross-sectional view of the pressure jacket embodiment illustrated in FIG. 38, taken along line XXXIX-XXXIX; [0069] FIG. 40A is an exploded, perspective view of another embodiment of a front-loading syringe interface and syringe system in accordance with the present invention; [0070] FIG. 40B is a perspective view of the system shown in FIG. 40A in an installed position; [0071] FIG. 40C is a perspective view of the syringe interface shown in FIG. 40A in an open position; [0072] FIG. 41A is an assembled, perspective view of another embodiment of a front-loading syringe interface and syringe system in accordance with the present invention; [0073] FIG. 41B is a perspective view of the system shown in FIG. 41A in an open position; [0074] FIG. 41C is a front, perspective view of the syringe interface shown in FIG. 41A in an open position; [0075] FIG. 41D is a rear, perspective view of the syringe interface shown in FIG. 41A in an open position; [0076] FIG. 42A is an assembled, perspective view of an alternate embodiment of the embodiment of the front-loading syringe interface and syringe system shown in FIGS. 41A-41D; [0077] FIG. 42B is a perspective view of the system shown in FIG. 42A in a disengaged position; [0078] FIG. 42C is a front, perspective view of the syringe interface shown in FIG. 42A in a closed position; [0079] FIG. 42D is a plan, perspective view of the syringe interface shown in FIG. 42A in a closed position; [0080] FIG. 43A is an exploded, perspective view of another alternate embodiment of the embodiment of the front-loading syringe interface and syringe system shown in FIGS. 41A-41D; [0081] FIG. 43B is a perspective view of the syringe interface shown in FIG. 43A in a closed position; [0082] FIG. 43C is a side, perspective view of the system shown in FIG. 43A in a first disengaged position; [0083] FIG. 43D is a perspective view of the system shown in FIG. 43A in an installed position; [0084] FIG. 43E is a perspective view of the system shown in FIG. 43A in a second disengaged position; [0085] FIG. 43F is a perspective view of the system shown in FIG. 43A in an open position for syringe removal; [0086] FIG. 43G is an exploded, perspective view of the system shown in FIG. 43A with the syringe interface in an open position; [0087] FIG. 43H is a front, perspective view of the syringe interface shown in FIG. 43A in an open position; [0088] FIG. 43I is a rear, perspective view of the syringe interface shown in FIG. 43A in an open position; [0089] FIG. 44A is a perspective view of a slightly altered version of the syringe interface shown in FIGS. 43A-43I incorporated in or mounted on an injector head; [0090] FIG. 44B is a rear, perspective view of the syringe interface and injector head shown in FIG. 44A; [0091] FIG. 45A is a perspective view of a second, slightly altered version of the syringe interface shown in FIGS. 43A-43I incorporated in or mounted on an injector head; [0092] FIG. 45B is a rear, perspective view of the syringe interface and injector head shown in FIG. 45A; [0093] FIG. 46A is an exploded, perspective view of a first preferred embodiment of a front-loading syringe interface and syringe system in accordance with the present invention; [0094] FIG. 46B is an assembled, perspective view of the syringe interface shown in FIG. 46A; [0095] FIG. 46C is a perspective view of the system shown in FIG. 46A in a disengaged position; [0096] FIG. 46D is a perspective view of the system shown in FIG. 46A in an installed position; [0097] FIG. 47A is a perspective view of an alternate embodiment of the first preferred embodiment of the front-loading syringe interface and syringe system shown in FIGS. 46A-46D in an installed position; [0098] FIG. 47B is a perspective view of the system shown in FIG. 47A in a disengaged position; [0099] FIG. 47C is an exploded, perspective view of the system shown in FIG. 47A; [0100] FIG. 47D is an exploded, perspective view of the syringe interface shown in FIG. 47A; [0101] FIG. 47E is a rear, partially assembled, perspective view of the syringe interface shown in FIG. 47A; [0102] FIG. 47F is a rear, exploded, perspective view of the syringe interface shown in FIG. 47A; [0103] FIG. 48A is an exploded, perspective view of still another embodiment of a front-loading syringe interface and syringe system in accordance with the present invention; [0104] FIG. 48B is a perspective view of the system shown in FIG. 48A in a disengaged position; [0105] FIG. 48C is a perspective view of the system shown in FIG. 48A in an installed position; [0106] FIG. 49A is an assembled, perspective view of another embodiment of an injector piston and syringe plunger interface system of the present invention; [0107] FIG. 49B is an exploded perspective view of the piston/plunger system shown in FIG. 49A; [0108] FIG. 49C is a perspective view of the piston/plunger system shown in FIG. 49B with the plunger base separated from the plunger cover and associated with the piston; [0109] FIG. 49D is a perspective of the piston/plunger system shown in FIG. 49B with the plunger, including the plunger base and the plunger cover, separated from the piston; [0110] FIG. 49E is a rear, perspective view of the piston/plunger system shown in FIG. 49A in a disengaged position; [0111] FIG. 49F is an exploded, perspective view of the plunger base and the plunger cover shown in FIGS. 49C and 49D; [0112] FIG. 50A is an exploded, perspective view of another embodiment of an injector piston and syringe plunger interface system of the present invention; [0113] FIG. 50B is an enlarged view, partially in cross-section, of the plunger base and the piston shown in FIG. 50A in an engaged position; [0114] FIG. 51A is an exploded, perspective view of an alternate embodiment of the injector piston and syringe plunger interface system shown in FIGS. 50A and 50B; [0115] FIG. 51B is a perspective view of the piston/plunger system shown in FIG. 51A with the plunger base separated from the plunger cover and associated with the piston; [0116] FIG. 51C is an enlarged view, partially in cross-section, of the plunger base and the piston shown in FIG. 51A in an engaged position; [0117] FIG. 52A is an exploded, perspective view of still another embodiment of an injector piston and syringe plunger interface system of the present invention; [0118] FIG. 52B is an exploded perspective view of the piston/plunger system shown in FIG. 52A; [0119] FIG. 52C is a rear, perspective view of the piston/plunger system shown in FIG. 52A in a disengaged position; [0120] FIG. 53A is an exploded, perspective view of an alternate embodiment of the injector piston and syringe plunger interface systems shown in FIGS. 51A-51C and 52A-52C; [0121] FIG. 53B is an enlarged, perspective view of the piston/plunger system shown in FIG. 53A in a disengaged position; [0122] FIG. 53C is a cross-sectional view of the piston/plunger system shown in FIG. 53A; [0123] FIG. 53D is an exploded, perspective view of the piston/plunger system shown in FIG. 53A; [0124] FIG. 54A is a perspective view of a current syringe plunger; [0125] FIG. 54B is an exploded, perspective of the plunger shown in FIG. 54A; [0126] FIG. 54C is a perspective view of an embodiment of a syringe plunger of the present invention; [0127] FIG. 54D is an exploded, perspective of the plunger shown in FIG. 54C; [0128] FIG. 54E is a perspective view of another embodiment of a syringe plunger of the present invention; [0129] FIG. 54F is an exploded, perspective view of the syringe plunger shown in FIG. 54E; [0130] FIG. 54G is a perspective view of yet another embodiment of the syringe plunger of the present invention; [0131] FIG. 54H is an exploded, perspective view of the syringe plunger shown in FIG. 54G; [0132] FIG. 55 is a side view schematic illustration of a second preferred embodiment of a front-loading syringe interface and syringe system in accordance with the present invention, illustrating a release mechanism for connecting a syringe to an injector housing; [0133] FIG. 56 is an exploded, isometric, front view perspective of the syringe interface and syringe system shown in FIG. 55; [0134] FIG. 57 is an exploded, isometric, rear view perspective of the syringe interface and syringe system shown in FIG. 56; [0135] FIG. 58 is an exploded, isometric, rear view perspective of a portion of the syringe interface and syringe system shown in FIGS. 55-57; [0136] FIG. 59 is an exploded, isometric, rear view perspective of another portion of the syringe interface and syringe system shown in FIGS. 55-57, showing in detail the rear of a portion of a flex ring and a rotating ring of the interface/release mechanism; [0137] FIG. 60 is an isometric, rear view of the syringe interface and syringe system shown in FIGS. 55-59, detailing the connection of the syringe to the release mechanism; [0138] FIG. 61 is an exploded, isometric, front view perspective illustration of the portion of the present invention as shown in FIG. 59, detailing the front of the rotating ring and a portion of the flex ring thereof, [0139] FIG. 62 is a partial, isometric, front view, perspective illustration of the rear portion of the syringe of the second preferred embodiment of the present invention, detailing the ridge and flange structure thereof; [0140] FIG. 63 is a partial, isometric, rear view, perspective illustration of the syringe shown in FIG. 62; [0141] FIG. 64 is an isometric, rear view perspective illustration of the front plate of the release mechanism of the second preferred embodiment of the present invention; [0142] FIG. 65 is an isometric, front view perspective illustration of the front plate shown in FIG. 64; [0143] FIG. 66 is an isometric, front view perspective illustration of the flex ring element of the release mechanism of the second preferred embodiment of the present invention, detailing several aspects thereof; [0144] FIG. 67 is an isometric, rear view perspective illustration of the flex ring shown in FIG. 66; [0145] FIG. 68 is an isometric, front view perspective illustration of the rotating ring element of the release mechanism of the second preferred embodiment of the present invention, detailing several aspects thereof; [0146] FIG. 69 is an isometric, rear view perspective illustration of the rotating ring shown in FIG. 68; [0147] FIG. 70 is an isometric, front view perspective illustration of the rear plate of the second preferred embodiment of the release mechanism of the present invention, detailing several aspects thereof; [0148] FIG. 71 is an isometric, rear view perspective illustration of the rear plate shown in FIG. 70; [0149] FIG. 72 is an isometric, front view perspective illustration of the syringe interface and syringe system of the second preferred embodiment of the present invention; [0150] FIG. 73 is an isometric, rear view perspective illustration of the syringe interface and syringe system shown in FIG. 72; [0151] FIG. 74 is a cross-sectional schematic illustration of a portion of the syringe interface/release mechanism of the second preferred embodiment of the present invention before insertion of the syringe into the interface/release mechanism; [0152] FIG. 75 is a side view, cross-sectional schematic illustration of the same elements shown in FIG. 74, with the syringe partially inserted into the interface/release mechanism; [0153] FIG. 76 is a side view, cross-sectional schematic illustration of the same features of the second preferred embodiment of the present invention as shown in FIGS. 74 and 75, in this case illustrating the syringe after it has been fully inserted into the interface/release mechanism; [0154] FIG. 77 is an end view, cross-sectional schematic illustration of the syringe and flex ring elements of the present invention as shown in FIG. 76, depicting the engagement of the syringe by the flex ring; [0155] FIG. 78 is an end view, cross-sectional schematic illustration of the syringe and flex ring of the second preferred embodiment of the present invention, depicting the disengagement of the syringe from the flex ring after rotation of the syringe through a one quarter turn; [0156] FIG. 79 is a perspective illustration of a related art syringe, showing the efficacy of the flange on the syringe for preventing contrast media from entering the injector housing; [0157] FIG. 80 is an isometric, front view, perspective illustration of a first preferred embodiment of the injector piston and syringe plunger interface system of the present invention; [0158] FIG. 81 is an isometric, rear view perspective illustration of the piston/plunger assembly depicted in FIG. 80; [0159] FIG. 82 is an exploded, isometric view of the piston/plunger assembly depicted in FIGS. 80 and 81; [0160] FIG. 83 is an exploded, isometric rear perspective illustration of the front end of the first preferred embodiment of the piston/plunger assembly of the present invention; [0161] FIG. 84 is an exploded, isometric view of the same features of the piston/plunger assembly illustrated in FIG. 83, taken from a slightly different angle from the view shown in FIG. 83; [0162] FIG. 85 is an isometric, front view illustration of the piston from the piston/plunger assembly illustrated in FIGS. 80-82; [0163] FIG. 86 is an isometric, side view illustration of the piston illustrated in FIG. 85; [0164] FIG. 87 is an isometric, front view illustration of the piston sleeve of the piston/plunger assembly shown in FIGS. 80-82; [0165] FIG. 88 is an isometric illustration of the collar element of the piston/plunger assembly shown in FIGS. 80-82; [0166] FIG. 89 is another isometric view of the collar depicted in FIG. 88; [0167] FIG. 90 is a third isometric view of the collar element depicted in FIG. 88; [0168] FIG. 91 is an isometric end view illustration of the gripper expander element of the first preferred embodiment of the piston/plunger assembly of the present invention; [0169] FIG. 92 is a second isometric illustration of the gripper expander depicted in FIG. 91; [0170] FIG. 93 is a third isometric illustration of the gripper expander depicted in FIGS. 91 and 92; [0171] FIG. 94 is a first isometric illustration of one of the support ring grippers of the first preferred embodiment of the piston/plunger assembly of the present invention; [0172] FIG. 95 is a second isometric illustration of the support ring gripper shown in FIG. 94; [0173] FIG. 96 is another isometric illustration of the support ring gripper shown in FIGS. 94 and 95; [0174] FIG. 97 is a first isometric illustration of the plunger cap element of the first preferred embodiment of the piston/plunger assembly of the present invention; [0175] FIG. 98 is a second isometric illustration of the plunger cap shown in FIG. 97; [0176] FIG. 99 is another isometric illustration of the plunger cap shown in FIGS. 97 and 98; [0177] FIG. 100 is a fourth isometric illustration of the plunger cap element shown in FIGS. 97-99; [0178] FIG. 101 is a first isometric illustration of the rubber cover support ring element of the first preferred embodiment of the piston/plunger assembly of the present invention; [0179] FIG. 102 is a second isometric illustration of the rubber cover support ring element shown in FIG. 101; [0180] FIG. 103 is a third isometric illustration of the rubber cover support ring element shown in FIGS. 101 and 102; [0181] FIG. 104 is a fourth isometric illustration of the rubber cover support ring element depicted in FIGS. 101-103; [0182] FIG. 105 is an isometric, side view illustration of the rubber cover of the plunger of the first preferred embodiment of the piston/plunger assembly of the present invention; [0183] FIG. 106 is a second isometric illustration of the rubber cover shown in FIG. 105; [0184] FIG. 107 is a side view schematic illustration of a portion of the first preferred embodiment of the piston/plunger assembly of the present invention, showing the interrelation of the piston, collar, gripper expander, support ring grippers and plunger cap thereof, the illustration showing the relationship of these elements when at rest or when the piston is moved toward the front end of the syringe; [0185] FIG. 108 is a side view schematic illustration of the portion of the piston/plunger assembly depicted in FIG. 107, in this case showing the interrelation of the piston, collar, gripper expander, support ring grippers and plunger cap thereof when the piston is moved/retracted toward the rear end of the syringe; [0186] FIG. 109 is a side view schematic illustration of a portion of the piston/plunger assembly and the syringe, showing the interrelation of the syringe, rubber cover, support ring grippers, and rubber cover support ring when the piston is moved/retracted toward the rear end of the syringe and the support ring grippers engage the rubber cover support ring; [0187] FIG. 110 is an isometric illustration of an alternate embodiment of a rubber cover for use with a plunger of the present invention; [0188] FIG. 111 is a side view illustration of the rubber cover illustrated in FIG. 110; [0189] FIG. 112 is a top view illustration of the rubber cover illustrated in FIG. 110; [0190] FIG. 113 is a cross-sectional illustration of the rubber cover depicted in FIG. 110; [0191] FIG. 114 is an isometric, exploded illustration of an alternate embodiment of the syringe interface/release mechanism of the present invention; [0192] FIG. 115 is an end-view, schematic illustration of another embodiment of the syringe interface/release mechanism of the present invention; [0193] FIG. 116 is a cross-sectional illustration of an end portion of the second preferred embodiment of the syringe according to the present invention; [0194] FIG. 117 is a cross-sectional illustration of an alternate embodiment of the syringe shown in FIG. 116; [0195] FIG. 118 is a schematic representation of three embodiments of grooves that are provided in the rotating ring of the second preferred embodiment of the syringe interface/release mechanism of the present invention; [0196] FIG. 119 is an isometric, exploded illustration of another embodiment of a syringe interface/release mechanism according to the teachings of the present invention; [0197] FIG. 120 is an isometric, exploded illustration of still another embodiment of a syringe interface/release mechanism according to the teachings of the present invention; [0198] FIG. 121 is a front view illustration of yet another embodiment of a syringe interface/release mechanism according to the teachings of the present invention; [0199] FIG. 122 is a side view illustration of the syringe interface/release mechanism illustrated in FIG. 121; [0200] FIG. 123 is an isometric, front view perspective of an alternate embodiment of the syringe shown in FIGS. 55-57; [0201] FIG. 124 is an exploded, isometric, front view perspective of a third preferred embodiment of a front-loading syringe interface and syringe system in accordance with the present invention; [0202] FIG. 125 is an exploded, isometric, rear view perspective of the syringe interface and syringe system shown in FIG. 124; and [0203] FIG. 126 is an isometric, front view perspective of a syringe incorporating syringe encoding. DETAILED DESCRIPTION OF THE INVENTION [0204] FIG. 1 discloses an injector apparatus 10 of the general type disclosed in U.S. Pat. No. 5,383,858 for injecting a liquid contrast media into a vascular system of an animal. Injector apparatus 10 has a front-loading construction. The apparatus of FIG. 1 utilizes a syringe 12 capable of being front-loaded into a mounting assembly 14 associated with a front wall 16 of a housing 18 of an injector 20 by a first releasable mechanism 22. Syringe 12 is capable of functioning in an injection operation without the use of a pressure jacket (although the syringe may be used in an injector with a pressure jacket, as will be described in greater detail in connection with FIGS. 4 and 5, below). To the extent not inconsistent with this disclosure, the disclosure of the '858 patent, which is assigned to Medrad, Inc., the Assignee of the subject application, is incorporated herein by reference. [0205] With reference to FIG. 1 and the first releasable mechanism 22, the mounting assembly 14 is provided with an essentially cylindrical interface 26 for receiving a rearward end of syringe 12. Interface 26 includes an annular surface 28, which may be cylindrical or conically tapered. As best shown in FIGS. 6 and 7, annular surface 28 includes a distal ledge 29, which is engaged by tabs 30 on the rearward end of syringe 12. Syringe 12 is inserted into cylindrical interface 26 until tabs 30 engage ledge 29 to secure syringe 12 to the injector 20. [0206] Among other things, tabs 30 distribute the attachment force of syringe 12 to ledge 29 equally around the syringe. This helps to maintain a connection between syringe 12 and ledge 29 even if syringe 12 deforms or "ovals" under pressure during use. This overcomes a potential shortfall with conventional front-loading injector systems, which may not function as well if the syringe ovals under pressure during use. [0207] Referring again to FIG. 1, syringe 12 comprises an elongated main tubular body or barrel 32 and a coaxial discharge injection section 34, interconnected by an intermediate conical portion 36. A plunger 38 is slidably positioned within the tubular body 32 and is connectable to a second releasable mechanism 40 on a piston 42 in the injector housing 18. Second releasable mechanism 40 is formed in part by plunger 38 and in part by piston 42, as set forth in greater detail below. [0208] Piston 42 and plunger 38 cooperate to eject fluid contained within syringe 12 in a desired quantity and at a desired rate. Second releasable mechanism 40 is designed to facilitate axial movement of plunger 38 in either direction when actuated. Second releasable mechanism 40 is also designed to engage or disengage plunger 38 from piston 42 no matter where plunger 38 sits in tubular body 32. Further in this connection, the actuating mechanism, which reciprocates the plunger 38 in the syringe tubular body 32, comprises piston 42 or a reciprocable drive member. The drive member or piston 42, while reciprocable, does not need to be rotatable. [0209] With reference to FIG. 1, to be mounted, syringe 32 is inserted into interface 26 in mounting assembly 14. As best shown in FIGS. 6 and 7, tabs 30 initially move past annular surface 28 where they engage ledge 29 to securely hold syringe 12 to mounting assembly 14. As best shown in FIGS. 2 and 7, mounting assembly 14 further includes a forwardly projecting annular ring or collar 44, which functions to assure perpendicular engagement between plunger 38 and piston 42. As explained above, forwardly projecting annular ring or collar 44 also functions as a seal between a flange 46 on syringe 32 and mounting assembly 14. [0210] Resilient annular sealing flange 46 surrounds tubular body 32 of syringe 12 and is disposed forward of tabs 30 a preselected distance essentially equal to a width of annular surface 28. Thus, when syringe 12 is inserted into interface 26 in mounting assembly 14 until sealing flange 46 engages annular ring 44, annular ring 44 and flange 46 create a seal between syringe 12 and mounting assembly 14. [0211] The foregoing mounting arrangement possesses a number of advantages. The attachment of tabs 30 to the periphery of the rearward portion of syringe 12 minimizes wobble of syringe 12 during an injection operation. While minimizing wobble, tabs 30 also permit syringe 12 to rotate freely within interface 26. Tabs 30 also prevent syringe 12 from disengaging from injector 20. The seal between annular ring 44 and flange 46 also prevents contrast media spilled from discharge end 34 of syringe 12 from flowing into injector housing 18 (as illustrated in FIG. 2) and eliminates the need for constructing the respective parts to excessively tight tolerances. To enhance the sealing capability between flange 46 and annular ring 44, a suitable O-ring (not shown) may be provided optionally therebetween. [0212] With further reference to FIG. 1, the apparatus also includes a system for transmitting syringe information from syringe 12 to an injector controller 51. Syringe 12 is provided with an encoding device 48 forward of tabs 30 but rearward of flange 46. Encoding device 48 may be a bar code or any other suitable encoding device known to those skilled in the art. When attaching syringe 12 to the mounting assembly 14, if syringe 12 is rotated after tabs 30 engage ledge 29, a sensor 50 is provided in annular surface 28 to read the encoding device 48. Sensor 50 then forwards the associated signals to injector controller 51, which interprets the signals and modifies the function of the injector 20 accordingly. Examples of the information which could be encoded on encoding device 48 include dimensions of syringe 12, volume of syringe 12, content of syringe 12 (in the case of a pre-filled syringe), manufacturing information such as lot numbers, dates and tool cavity number, recommended contrast media flow rates and pressures, and loading/injection sequences. [0213] As an alternative to encoding device 48 being a bar code, encoding device 48 also could include machine-readable raised or recessed surfaces. The raised or recessed surfaces could then be read by injector sensor 50, mounted in annular surface 28, in a manner similar to that for reading a bar code. In addition to encoding device 48, one might also use a mechanically readable device (e.g. a slot, hole, or projection on the syringe 12 or plunger 38) to register against a switch on the mounting assembly 14. Alternatively, an optically readable device (e.g. characters, dots and other geometric shapes) could be employed to send information concerning the type of syringe used to the intelligent circuits of injector 20. [0214] In FIG. 1, since syringe 12 is being used in this embodiment without a pressure jacket, for strength and visibility of the contents of syringe 12, the syringe 12 may be formed of a clear PET polyester material. In the alternative, the wall of syringe 12 may be formed of polypropylene reinforced by providing a series of annular ribs on tubular body 32 of syringe 12 in longitudinally spaced relationship. (This arrangement is illustrated in FIG. 5 of the '858 patent.) As discussed in the '858 patent, by suitably spacing the ribs along the length of tubular body 32, such as in equal increments, the ribs also can perform the dual function of serving as volumetric gradations for the purpose of indicating the amount of contrast media in syringe 12. [0215] With reference to FIGS. 1 and 2, tubular body 32 of syringe 12 also may be provided with an indicating mechanism 52 for readily detecting the presence or absence of a liquid contrast media in syringe 12. In this instance, detecting mechanism 52 includes a plurality of integrally molded, textured dots on syringe 12, which provide a visual indication of whether the syringe contains liquid or air. More specifically, when viewed against an air background, dots 52 appear oval-shaped, but when viewed against a liquid contrast media background, which has a different index of refraction than air, dots 52 appear circular. The details of indicating mechanism 52 are described in detail in U.S. Pat. No. 4,452,251, assigned to Medrad, Inc., the Assignee of the subject application. To the extent not inconsistent with the present disclosure, the contents of U.S. Pat. No. 4,452,251 are incorporated herein by reference. [0216] FIG. 3 illustrates the internal construction of the syringe discharge end 34. Specifically, while a rearward portion 54 of discharge end 34 is of tapered conical construction, a forward connector portion 56 is of generally cylindrical construction and formed with internal screw threads 58 for attaching a connecting tube to discharge end 34. Further, an injection nozzle 60 of reduced diameter is disposed within the screw-threaded cylindrical connector portion 56 and is integrally molded with tapered rearward portion 54 of discharge end 34 adjacent the point at which the tapered and cylindrical portions merge together. [0217] FIGS. 4 and 5 illustrate an alternate embodiment of the present invention in which a front-loading syringe 112 is mounted on the front of a pressure jacket 170, preferably formed of a strong clear plastic, such as polycarbonate. Pressure jacket 170 is in the form of an elongated tubular member that is suitably mounted at its rearward end in a mounting assembly 124 on housing front wall 116, by fitting the flange of pressure jacket 170 into the collar on the mounting assembly 124. Pressure jacket 170 also has a forward open end 172 for receiving the syringe 112. [0218] In this embodiment, an annular surface 174 with a distal ledge 175 is provided adjacent to the forward open end 172 of the pressure jacket 170. Annular surface 174 is similar in construction to annular surface 28 in the embodiment illustrated in FIGS. 1 and 7. Similarly, a tubular body 132 of syringe 112 includes tabs 180 at a position adjacent its forward end for engagement with ledge 175 when tubular body 132 has been inserted into pressure jacket 170. [0219] In addition, at the forward end of syringe 112, on opposite sides of a discharge end 134, a pair of reinforcing, loop-shaped handles 162, for facilitating handling of the syringe 112, is integrally molded with discharge end 134 and a tapered conical intermediate portion 136. In other respects, while not specifically disclosed and described, it is to be understood that various other features of the embodiment of the invention disclosed in FIGS. 1-3, 6 and 7 may be incorporated into the embodiment of FIGS. 4 and 5, as desired. [0220] In use, the syringe 112 of FIGS. 4 and 5 may be mounted in pressure jacket 170 with piston 142 of injector 120 either in a retracted position, as shown in FIG. 4, or in an advanced position, as shown in FIG. 5. For example, with piston 142 in the retracted position, as shown in FIG. 4, plunger 138 is disposed at the rearward end of syringe 112. Syringe 112 then is inserted into the open end 172 of the forward end of pressure jacket 170 until second releasable mechanism 140 engages with plunger 138. [0221] In FIG. 5, in which piston 142 is in a forward position, the mounting of syringe 112 into pressure jacket 170 is the same as shown in FIG. 4, except that plunger 138 also is in its forward position in syringe 112. In other respects, the mounting of syringe 112 on pressure jacket 170 is essentially the same as previously described with respect to FIG. 4. However, having syringe plunger 138 and piston 142 in their forward positions, as shown in FIG. 5, has several advantages over the rearward position arrangement of FIG. 4. For example, because syringe plunger 138 and piston 142 are already in their forward positions, it is not necessary to move them forward to expel air from the syringe 112 in preparation for a syringe-filling operation. Rather, plunger 138 and piston 142 can immediately be retracted to aspirate fluid into the syringe 112. Similarly, after an injection operation has been completed, additional time is saved by not having to retract plunger 138 and piston 142 in preparation for a next injection operation. [0222] In summary, a new and improved system by which an injection syringe, such as syringe 12 in the embodiment of FIGS. 1-3, can be readily mounted upon and/or removed from injector housing 18, has been disclosed. For this purpose, the first releasable mechanism 22, by which syringe 12 is attached to or removed from injector housing 18, and second releasable mechanism 40, by which plunger 38 of syringe 12 is drivingly connected to or released from piston 42 of injector 20 cooperate to produce their respective connections and disconnections simultaneously and/or independently. Another advantage is that plunger 38 is capable of being placed in a driven or undriven state at any point along its path, whereby syringe 12 may be disengaged from injector 20 without having to retract piston 42, or having to first disconnect syringe 12 from a patient being injected before retracting piston 42. [0223] Other desirable features of the invention include the construction of first releasable mechanism 22, in which syringe 12 is mounted upon injector housing 18 with a secure fit, which is advantageous from the standpoint of minimizing syringe wobble and disengagement during an injection operation, and eliminating the need for excessively tight manufacturing tolerances. Encoding device 48 on syringe 12, in cooperation with sensor 50 on injector 20, also is advantageous from the standpoint of providing "custom programming" of injector 20. Elimination of a pressure jacket also is desirable from the standpoint of better visibility of the contents of syringe 12, better heat transfer to the syringe contents and decreased cleaning and maintenance otherwise needed due to, e.g., scratching or contamination with contrast media of the pressure jacket. [0224] In order to eliminate the need for a pressure jacket, syringe 12 also may be made of a relatively strong clear plastic, or may be provided with annular reinforcing ribs (not shown), which may be spaced to function as volumetric gradations. Further, detection of the presence of air in syringe 12 is facilitated by the indicating mechanism 52 in FIGS. 1 and 2, in the form of dots 52 molded into syringe tubular body 32. Dots 52 appear visually as either oval-shaped or circular, depending upon whether the tubular body contains air or liquid, respectively. In addition to functioning as a part of first releasable mechanism 22 for syringe 12, syringe resilient annular flange 46 also cooperates with annular ring 44 to create a seal to prevent contrast media spilled from the injection end of syringe 12, from flowing into injector 20, as shown in FIG. 2. The embodiment of the invention shown in FIGS. 4 and 5 provides a system by which various other advantages, including time savings in syringe-filling and syringe-changing operations, can be achieved utilizing a pressure jacket, such as pressure jacket 170 mounted on injector housing front wall 116. [0225] FIG. 6 illustrates a cross-section of syringe 12 after it has been inserted into injector 20 so that tabs 30 engage ledge 29. Tabs 30 are preferably substantially V-shaped members that preferably form a ring encircling the rearward end of tubular body 32. Alternately, one or more tabs may be separately disposed around the rearward end of the body 32. Each of tabs 30 on the ring has a first end 62 and a second end 64. (An enlarged, perspective illustration of the ring of tabs 30 is shown in FIG. 8.) As shown in FIG. 8, first ends 62 of tabs 30 engage ledge 29 when syringe 12 is inserted into interface 26 of injector 20. First ends 62 of tabs 30 are separated from one another by gaps 66 around the periphery of tubular body 32 so that they are flexible and can easily compress. Second ends 64 of tabs 30, on the other hand, form a ring that attaches to tubular body 32. [0226] Syringe 12, therefore, is easily connected to the injector 20 simply by inserting the rearward end of tubular body 32 into cylindrical interface 26. During insertion of tubular body 32 into cylindrical interface 26, annular surface 28 compress first ends 62 of tabs 30 until first tabs 62 clear ledge 29. Once first ends 62 clear ledge 29, they spring open and engage ledge 29 to prevent the removal of tubular body 32 from interface 26. [0227] Removal of syringe 12 from housing 20 is enabled by a reciprocating collar 68 that is disposed within injector 20 at a location behind syringe 12 (once inserted into cylindrical interface 26). Reciprocating collar 68 is preferably a cylindrical member that can move in both forward and rearward directions, as illustrated by the arrow in FIG. 7. During an injection operation, reciprocating collar 68 is in its rest position behind tabs 30 so that first ends 62 remain engaged with ledge 29. Upon completion of the injection operation, in order to remove syringe 12 from interface 26, reciprocating collar 68 is pushed forward toward ledge 29 by an actuating mechanism (not shown) or manually so that it compresses first ends 62 so that they can easily slide out from behind ledge 29. Syringe 12 then can be easily removed from injector 20. [0228] Alternatively, tabs 30 may be caused to disengage from ledge 29 by retracting annular surface 28 in the direction of arrow 1100 in FIG. 33. To do this, annular surface 28 is made of a number of segments 1102, all of which can retract to release syringe 32. In still another alternative embodiment as illustrated in FIG. 34, a portion of the inner surface 1104 may be moved inwardly in the direction indicated by arrow 1106 to collapse tabs 30 so that syringe 32 may be disengaged from ledge 29. Other embodiments of these two arrangements will be readily understood by those skilled in the art. [0229] In the case where syringe 112 is to be inserted into a pressure jacket 170 (as illustrated in FIGS. 4 and 5), tabs 180 serve the same function as tabs 30, except of course that they are located toward the forward end of syringe 112. In fact, but for the location of tabs 180 on tubular body 132, it is contemplated for the present invention that tabs 180 have the same construction as tabs 30. When tabs 180 are inserted through open end 172 of pressure jacket 170, annular surface 174 compresses first ends 62 of tabs 180 until they clear ledge 175. Syringe 112 is then securely held in place. When it becomes necessary to remove syringe 112 from pressure jacket 170, a reciprocating collar 68 extends forward within the pressure jacket 170 (as described in more detail below) to compress first ends 62 so that they no longer engage ledge 174. Syringe 112 can then be removed from pressure jacket 170. [0230] It is not necessary for tabs 30, 180 to have a V-shaped appearance as illustrated in FIGS. 1 and 4-8, however. It is contemplated for the second embodiment of tabs 30 that they have a b-shaped appearance, as illustrated in FIG. 9. When tabs 30 have a b-shaped appearance, they may be formed integrally with the end of syringe 412. Tabs 30, when they have a b-shaped appearance, have bulbous first ends 70 that extend outwardly from second ends 72, which are separated from adjacent tabs 30 by gaps 71 (as best shown in FIGS. 14 and 15). As with first ends 62, first ends 70 engage ledge 29 when syringe has been inserted into injector housing 18. As with first ends 62, reciprocating collar 68 acts upon first ends 70 to disengage them from ledge 29 when syringe 412 is to be removed from injector 20. [0231] For each of the embodiments of tabs 30 contemplated by the present invention, it is also contemplated that the number of tabs used may be varied while remaining within the scope of the present invention. For example, for syringe 212, illustrated in FIGS. 10 and 11, it is contemplated that only one tab is provided at the end of the syringe. In FIGS. 10 and 11, only one tab 30 with first end 70 and second end 72 is illustrated. It should be understood, however, that tab 30 with first end 62 and second end 64 could be easily substituted therefor. [0232] While a single tab 30 may be used, preferably the syringe has at least two tabs, because the tabs should flex in order to function optimally. Such a syringe 312, with at least two tabs, is illustrated in FIGS. 12 and 13. When two tabs are included on syringe 312, it is contemplated that they be disposed on opposite sides of tubular body 32 to add stability to the secure engagement of syringe 312 to injector 20. The tabs may be appropriately sized and optionally may be of different circumferential dimension. [0233] In an alternate embodiment of the pressure-jacketed injector system shown in FIG. 32, it is contemplated that a syringe cap 1000 could be provided at the end of the pressure jacket 1002 to hold a syringe 1032 therein. Alternately, cap 1000 could be attached to or molded as a part of syringe 1032 and need not be a separate element. As shown in FIG. 32, pressure jacket 1002 is a modified version of pressure jacket 170 illustrated in FIGS. 4 and 5. According to the teachings of the present invention, cap 1000 includes tabs 1004 about its periphery. Tabs 1004 engage a ridge 1006 that encircles the end of pressure jacket 1002. To disengage tabs 1004 from ridge 1006, a reciprocating ring 1008 slides along the exterior of pressure jacket 1002. Ring 1008 includes a tapered surface 1010 to facilitate removal of tabs 1004 from ridge 1006. The actuator of ring 1008 is not shown. However, those skilled in the art will readily recognize that ring 1008 may be operated either manually, mechanically, or electrically (or in any other fashion suitable to disengage tabs 1004 from ridge 1006). [0234] In another alternate embodiment of the apparatus described in relation to FIG. 32, the tabs could extend from the cap (which could be separate from, attached to, or molded with the syringe) to engage annular member 174 at the end of pressure jacket 170 in the same way that tabs 180 engage annular member 174 in the embodiment illustrated in FIGS. 4 and 5. As with the embodiment illustrated and described in relation to FIGS. 4 and 5, a reciprocating collar should then be positioned within pressure jacket 170 to disengage the tabs from the annular member. [0235] The elements for the releasing mechanism are illustrated in FIGS. 38 and 39. There, reciprocating collar 1402 is shown internal to pressure jacket 170. As illustrated, reciprocating collar 1402 is disposed at the end of at least two supports 1404 that are also within the interior of pressure jacket 170. To accommodate supports 1404, interior wall 1406 of pressure jacket 170 includes at least two tracks 1408 in which supports 1404 slide. When syringe 1032 is to be removed from pressure jacket 170, reciprocating collar 1402 is moved forward within pressure jacket 170 to disengage the tabs on syringe 1032 from engagement with annular member 174. [0236] This arrangement also may be used in connection with the pressure jacket system illustrated and described in connection with FIGS. 4 and 5. When syringe 132 is to be removed from pressure jacket 170, reciprocating collar 1402 is moved forward within pressure jacket 170 to compress tabs 180 so that they no longer engage annular member 174. Once tabs 180 are clear of annular member 174, syringe 132 may be removed from pressure jacket 170. [0237] In the case where syringe 112 is to be inserted into pressure jacket 170 as shown in FIGS. 4 and 5, b-shaped tabs 190 may be added to the forward end of syringe 112 in the same manner that tabs 180 were applied. As shown in FIG. 16, tabs 190 essentially comprise a ring 74 from which second ends 72 of tabs 190 extend in a rearward direction. Ring 74 with tabs 190 form a V-shaped structure in cross-section, as illustrated in FIG. 17. As with tabs 180, when tabs 190 are inserted into pressure jacket 170 (as illustrated in FIGS. 4 and 5), they are compressed until they clear annular surface 174, whereupon they expand to engage ledge 175. Tabs 190 hold syringe 112 securely in pressure jacket 170 until disengaged by reciprocating collar 68. [0238] The installation and removal of syringe 412 is illustrated in FIGS. 18-20. In FIG. 18, syringe 412 is shown prior to insertion into injector front wall 16. Reciprocating collar 68 is shown in a rest state behind where first ends 70 of tabs 30 will rest after they clear annular surface 128 and rest against distal ledge 129. In this embodiment, annular surface 128 is illustrated with a tapered cross-section rather than the cylindrical cross-section shown in FIGS. 7 and 9. A tapered cross-section may facilitate insertion of syringe 412 into interface 26 because the taper may help to squeeze first ends 70 of tabs 30 during insertion of syringe 412 into injector 20. In addition, annular surface 128, when tapered, acts as a guiding surface for syringe 412 (or any other embodiment disclosed) so that syringe 412 may be inserted into front wall 16 at even greater angular approaches. In other words, syringe 412 may be inserted easily into front wall 16 even when syringe 412 is not oriented exactly with the central axis of interface 26. [0239] Once syringe 412 has been fully inserted into front wall 16, tabs 30 expand to engage ledge 129, as illustrated in FIG. 19. Syringe 412 is then securely held in place. As shown in FIG. 19, reciprocating collar 68 remains in its rest position until after the injection operation is completed. [0240] After the injection operation is completed, reciprocating collar 68 is moved forward to compress first ends 70 of tabs 30 to disengage tabs 30 from ledge 129. FIG. 20 shows reciprocating collar 68 in this forward position. The compression of tabs 30 is also illustrated. The syringe 412 may then be removed from injector 20. [0241] The present invention also contemplates that it may be desirable to connect a syringe to an adapter 500 before connecting the syringe to injector 20. The adapters could be disposable or reuseable, as would be understood by those skilled in the art. The syringe may be of different construction from that disclosed herein, as would be understood by those skilled in the art. An adapter for a syringe is described in U.S. Pat. No. 5,535,746, issued to Hoover et al. on Jul. 16, 1996, the disclosure of which is incorporated herein by reference. Other patents that are exemplary of adapters include U.S. Pat. No. 5,520,653 and WO 97/36635, both of which are assigned to the Assignee of the present application and are incorporated herein by reference. [0242] In the embodiment illustrated in FIG. 21, a syringe 412 with tabs 30 having a b-shaped appearance snap-fits into a forward end 502 of adapter 500. Of course, tabs with the V-shaped cross-section may be substituted therefor. Adapter 500 includes a annular surface 528 with a distal ledge 529 within its forward end 502 to which first ends 70 of tabs 30 engage to hold syringe 412 securely in place. Flange 46 of syringe 412 may or may not be included to engage with forward end 502 of adapter 500 to prevent contrast medium, should it leak, from entering injector housing 18 through adapter 500. The rearward end 504 of adapter 500 also preferably includes a flange 546 that mates with annular ring 44 on mounting assembly 14 of injector 20. Flange 546 serves the same function as flange 46 on syringe 12, namely to prevent contrast medium (or whatever fluid is included in syringe) from entering the injector 20. [0243] If adapter 500 is attached to syringe 32, piston 42 may need to be adapted to accommodate the increased length of the overall construction. If so, a piston extender or adapter (not shown) may be attached to the end of piston 42, as would be understood by those skilled in the art. Alternatively, piston 42 could be constructed so that it is long enough to accommodate syringes 32 of varying lengths. [0244] In this particular embodiment, adapter 500 includes conventional connector elements 506, such as those described in U.S. Pat. No.5,535,746 or U.S. Pat. No.5,383,858. So designed, adapter 500 permits syringe 412 to be connected to an injector that is designed to accept only syringes with conventional connector elements 506. [0245] As shown in FIG. 22, in an alternate embodiment of the adapter, it may be necessary to adapt a conventional syringe for use in an injector designed to accept the syringes of the present invention. Here, adapter 600 includes tabs 630 at its rearward end 604. Tabs 630 act and function like tabs 30 to secure adapter to housing 18 by engaging ledge 29 on mounting assembly 14. Tabs 630 are disengaged from ledge 29 by reciprocating collar 68. Adapter 600 may also include a flange 646 as in the other embodiments that have been described above. While adapter 600 is shown with a syringe having a ridged end inserted therein, it should be understood that adapter 600 could be easily designed so that its forward end 602 can accept conventional connector elements, such as those described in U.S. Pat. No. 5,535,746 or U.S. Pat. No. 5,383,858. [0246] FIGS. 23 and 24 illustrate two perspective views of the combination of the syringe 412 and adapter 600. In this embodiment, flange 46 has been omitted. However, as illustrated in FIG. 22, flange 46 may be included. Naturally, as with syringe 212 (shown in FIGS. 10 and 11) and with syringe 312 (shown in FIGS. 12 and 13), the adapter may include only one tab, two tabs, or more than two tabs 630. FIGS. 23 and 24 illustrate adapter 600 with a plurality of tabs. [0247] Two embodiments of second releasable mechanism 40 for engaging and releasing the syringe plunger and the injector piston will now be described with respect to FIGS. 25-29. FIG. 25 illustrates an electromagnetic release mechanism. FIGS. 26-29 illustrate an electromechanical release mechanism. [0248] As shown in FIG. 25, plunger 738 may be releasably connected to piston 742 through an electromagnetic device. A forward end 702 of piston 742 is provided with an electromagnetic coil 704 that can be activated by applying a current through leads 706 that extend through piston 742. At its rearward end 707, plunger 738 includes a magnetically attractive ring 708, made of iron, for example, which is attracted to electromagnetic coil 704 when electromagnetic coil 704 is activated. The cross-sections of forward end 702 of piston 742 and of recess 710 in rearward end 707 of plunger 738 are cylindrical. This permits the engagement of piston 742 with plunger 738 regardless of the orientation of plunger 738 in the syringe. [0249] Second releasable mechanism 40, as illustrated in FIG. 25, operates as follows. When a syringe has been inserted into the interface on the injector housing 18, piston 742 is extended into the syringe until its forward end 702 mates with recess 710 of plunger 738. Electromagnetic coil 704 may then be activated to retract plunger 738. The attraction between magnetically attractive ring 708 and electromagnetic coil 704 holds plunger 738 to the end of piston 742 during rearward movement of piston 742. Alternatively, electromagnetic coil 704 may be activated before piston 742 is extended into the syringe to mate with plunger 738. Once plunger 738 and piston 742 are electromagnetically attracted to one another, piston 742 may be moved as required within the syringe. To disengage piston 742 from plunger 738, or to retract piston 742 without retracting plunger 738, one need only disengage the power supplied to electromagnetic coil 704. Of course, the piston 742 may advance the plunger 738, for example, during an injection, without activating electromagnetic coil 704. [0250] The second embodiment contemplated for second releasable mechanism 40 involves an electromechanical connection between the piston and the plunger. This embodiment is illustrated in FIGS. 26-29. [0251] In FIGS. 26-29, piston 842 has a forward end 802 that engages with a recessed area 804 formed in a rearward end 806 of plunger 838. Forward end 802 of piston 842 includes protrusions 808 that retractably extend therefrom. Protrusions 808 engage an indentation or channel 810 formed in the plunger 838, as illustrated in FIG. 27. A member 812 is enclosed by piston 842 and forward end 802. Member 812 is actuated by mechanism 814, also contained within piston 842. Mechanism 814 receives power through leads 816. [0252] As shown in FIGS. 28 and 29, protrusions 808 are essentially rectangular. They are connected to one another through resilient members 818. Resilient members 818 bias protrusions 808 so that they do not protrude from forward end 802 of piston 842, as shown in FIG. 29. [0253] The operation of second releasable mechanism 40 will now be described in connection with FIGS. 26-29. When a syringe has been inserted into front wall 16 of injector 20, piston 842 is extended forward to meet with plunger 838. When piston 842 extends forward, mechanism 814 is deactivated so that member 812 is in a retracted condition, as shown in FIG. 29. In other words, member 812 is retracted so that it does not sit between protrusions 808. As a result, resilient members 818 bias protrusions 808 so that they do not extend outside of forward end 802 of piston 842, as shown in FIG. 29. [0254] Once forward end 802 of piston 842 mates with recessed area 804 in plunger 838, mechanism 814 is activated so that member 812 extends forward to sit between protrusions 808, thereby forcing protrusions 808 to extend outside of forward end 802 of piston 842. Protrusions 808, once extended, extend into channel 810 within plunger 838. Once so arranged, piston 842 is connected to plunger 838 so that rearward movement of piston 842 translates directly into a corresponding rearward movement of plunger 838. [0255] When it becomes necessary to disengage the syringe from the injector, or to retract piston 842 without retracting plunger 838, mechanism 814 is activated to withdraw member 812 from between protrusions 808. Once withdrawn, resilient members 818 bias protrusions 808 so that they no longer engage channel 810. Piston 842 may then be withdrawn from plunger 838. [0256] Two additional second releasable mechanisms 40 will now be described with reference to FIGS. 35-37. [0257] In the embodiment illustrated in FIG. 35, plunger 1238 may be releasably connected to piston 1242 through expansion of an elastomeric member 1202 disposed at a forward end thereof. Elastomeric member 1202 is a cylindrical element with external walls 1204 and internal walls 1206. A rod 1208 extends through piston 1242 and connects to an actuator 1210 at a forward end of rod 1208 closest to plunger 1238. Actuator 1210 has a frustoconical shape on a side facing elastomeric member 1202. The frustoconical shape defines an inclined surface 1212 on actuator 1210. The diameter of elastomeric member 1202 is slightly smaller than the diameter of the hole 1214 in plunger 1238. Also, the diameter of actuator 1210 is smaller than the diameter of hole 1214. [0258] The operation of the second releasable mechanism 40 illustrated in FIG. 35 will now be described. Because the diameter of hole 1214 in plunger 1238 is larger than the diameter of elastomeric member 1202 and of actuator 1210, when piston 1242 is pushed forward, elastomeric member 1202 and actuator 1210 easily fit into hole 1214. Plunger 1238 can then be advanced by piston 1242 without a connective engagement existing therebetween. However, once positioned in this manner, to connectively engage the plunger 1238 (e.g., to retract plunger) actuator 1210 is pulled toward elastomeric member 1202 by rod 1208, as shown by arrow 1216 in FIG. 35. The pressure from actuator 1210 compresses elastomeric member 1202 so that external sides 1204 swell or expand from their unstressed condition. The approximate shape of the swelled walls 1218 of elastomeric member 1202 is shown in dotted line format in FIG. 35. Swelled walls 1218 engage walls 1220 of hole 1214 so that piston 1242 releasably engages plunger 1238. Plunger 1238 can now be retracted to, for example, aspirate fluid into the syringe. [0259] The embodiment of second releasable mechanism 40 shown in FIGS. 36-37 will now be described. As shown in FIGS. 36-37, plunger 1338 engages piston 1342 through segmented member 1302. Segmented member 1302 is made of a number of separate elements 1304 as shown in the end view illustration of FIG. 37. Separate elements 1304 may be made from any suitable material, such as an elastomeric material, so long as the material preferably (1) can substantially withstand repeated deformation and (2) returns substantially to its original condition when no longer subject to a deforming stress. Segmented member 1302 is disposed at a forward end of piston 1342. A rod 1306 extends through the middle of piston 1342 and extends at least partially into a central bore 1308 of segmented member 1302. [0260] To releasably connect plunger 1338 with piston 1342, piston 1342 is moved forward until segmented member 1302 is disposed within a hole 1310 formed in plunger 1338. Rod 1306 is then moved forward, in the direction shown by arrow 1312, until rod 1306 is at least partially disposed within segmented member 1302. Since the diameter of rod 1306 is greater than the diameter of bore 1308, the insertion of rod 1306 into bore 1308 pushes segmented members 1304 outwardly until they reach a deformed position 1314 shown in dotted lines in both FIG. 36 and FIG. 37. When deformed, segmented members 1304 engage walls 1316 of hole 1310 in plunger 1338 to create a releasable engagement between plunger 1338 and piston 1342. [0261] For each of the second releasable mechanisms described in FIGS. 25-29 and 35-37, the advantage that the mechanisms provide is that the piston need not be oriented in any specific manner with the plunger in order to facilitate a connection between the piston and plunger. Regardless of the orientation of the piston and the plunger, the two can easily mate with one another and can be easily disengaged from one another. [0262] In addition, if for example a prefilled syringe is mounted on the injector, it may not be necessary to retract the plunger within the syringe to draw fluid within the syringe for subsequent injection. In such a case, the piston may be operated in a "push-only" mode that does not require engagement between the piston and the plunger. If operated in this manner, the engagement mechanism need not be activated at all. Alternatively, if the injector is designed to handle only prefilled syringes, no readily releasable mechanism need be provided. [0263] The plunger of the present invention may also include a pressure sensor like the sensors described in U.S. Pat. No. 5,808,203, issued to Nolan, Jr. et al. on Sep. 15, 1998, and assigned to the Assignee of the present application. The disclosure of U.S. Pat. No. 5,808,203 is incorporated herein by reference, to the extent that it is not inconsistent with the instant disclosure. [0264] FIGS. 30 and 31 illustrate the sensor that can be included in the plunger of the present invention. Plunger 938 preferably comprises a base 902 with a passage 904 therethrough. A sensing member 906 is disposed within passage 904 to be in operative contact with a portion P of contact surface 908. Sensing member 906 is preferably biased forward, for example, via a spring 910. As fluid pressure within the syringe (not shown) increases, portion P of contact surface 908 is deformed as shown in FIG. 31. This deformation of portion P causes sensing member 906 to move rearward through passages 904 and 912 and 914 in piston 942. The movement of sensing member 906 is monitored with a sensor 916 preferably disposed within piston 942. Because the degree of movement of sensing member 906 is a function of the pressure of the fluid medium within the syringe, the pressure of the fluid medium can be determined therefrom. Sensor 916 is preferably connected to a data collection and/or control device via leads 918. [0265] While FIGS. 30 and 31 describe one possible embodiment of a sensor that can be incorporated into the plunger of the present invention, it should be noted that any other suitable sensor may be included. In addition, the sensor need not detect only the pressure of the fluid. As would be understood by those skilled in the art, the sensor may measure a number of different parameters including amount, pressure and density of the fluid in the syringe. [0266] Also, the plunger may contain encoding elements that are read or sensed by the injector or injector piston to identify the syringe and/or its contents. In this embodiment, the encoding elements, such as an integrated circuit, are included on the plunger rather than the syringe. The encoded elements then may be read electronically when the plunger contacts the piston. The plunger may contain information such as the contents and volume of the syringe as well as other information needed for the procedure or for billing purposes. One example of such a system is described in PCT Publication No. WO 99/65548, which is incorporated herein by reference. [0267] The present invention is often shown and described herein in terms of cooperating syringe interfaces and syringes. The terms "syringe interface" and "syringe interfaces" as used herein can be incorporated in or integrated with new medical injectors or configured as syringe adapters mountable on or associated with existing or conventional medical injectors, such as the injector shown and described in U.S. Pat. No. 5,383,858, the contents of which are hereby incorporated by reference, to allow the installation of the syringes of the present invention thereon. [0268] FIGS. 40A-40C illustrate another embodiment of a front-loading syringe interface and syringe system 1500 in accordance with the present invention. The system 1500 includes a syringe 1512 and a syringe interface 1514. The syringe 1512 includes a body or barrel portion 1516 having a rear end 1520 and a front end 1517 defining a fluid discharge end 1518. Preferably, at least one tab or mounting member 1522 is associated with the barrel portion 1516 adjacent to or at the rear end 1520 of the syringe 1512. In addition, a flange 1524 is preferably positioned forward of the mounting member 1522 to facilitate the engagement of the syringe 1512 to the syringe interface 1514 and/or to prevent fluid expelled from the discharge end 1518 of the syringe from entering into the syringe interface 1514 and the injector (not shown), as described in more detail in U.S. Pat. No. 5,383,858. [0269] Preferably, the mounting member 1522 is disposed around the circumference of the barrel portion 1516 and includes an inclined surface 1526 that defines a shoulder 1528. The function of the mounting member 1522 will be described in more detail below. Alternately, the mounting member 1522 may extend around only a portion of the circumference of the barrel portion 1516 or may be formed in discrete segments. [0270] (Unless otherwise noted, the syringe 1512 (and its components parts) described above applies to the remaining embodiments of the present invention discussed and described below with respect to FIGS. 40A-47F.) [0271] As best shown in FIGS. 40A and 40C, the syringe interface 1514 is in an "open" position ready to accept the syringe 1512. The syringe interface 1514 includes a base member 1530 and two cooperating syringe-retaining members 1532. However, in alternate embodiments, three or more retaining members 1532 could be provided. Preferably, each of the retaining members 1532 is associated with the base member 1530 by means of two angled rail members 1534. However, in alternate embodiments, one, three or more members 1534 may be used to associate each retaining member 1532 with the base member 1530. [0272] Further, each retaining member 1532 preferably defines a contact surface 1533 and a channel 1536 to capture and retain the mounting member 1522 on the syringe 1512. In addition, the retaining members 1532 are preferably associated with one another by means of two rail members 1538. Once again, in alternate embodiments, one, three or more rail members 1538 may be used to associate the retaining members 1532 with one another. [0273] To install the syringe 1512 on the syringe interface 1514, the syringe 1512 is moved axially (in the direction of Arrow A in FIG. 40A) into the space defined between the retaining members 1532. When the flange 1524 on the syringe 1512 engages the contact surfaces 1533 on the retaining members 1532, the retaining members 1532 are urged toward the base member 1530 along the rail members 1534. Because the rail members 1534 are angled in toward the center of the base member 1530, the rail members 1534 operate to cause the retaining members 1532 to move toward each other along the rail members 1538 and to "collapse" around the rear end 1520 of the syringe 1512. As the retaining members 1532 collapse on the syringe 1512, the retaining members 1532 cooperate to capture the mounting member 1522 within the channels 1536 to securely engage the syringe 1512 with the syringe interface 1514. [0274] Any suitable type of locking mechanism (not shown), as is known in the art, may be used to secure the retaining members 1532 together to retain the syringe 1512 within the syringe interface 1514. To remove the syringe 1512 from the syringe interface 1514, the lock must first be unlocked and the retaining members 1532 moved apart (e.g., by hand or by means of a lever or any other suitable art-recognized manipulative device) to free the mounting member 1522 from the channels 1536. [0275] Another embodiment of the syringe interface and syringe system 1600 is shown in FIGS. 41A-41D. The system 1600 includes a syringe 1512 and a syringe interface 1614. As best shown in FIGS. 41B and 41C, the syringe interface 1614 is in an "open" position ready to accept the syringe 1512. The syringe interface 1614 includes a base member 1630 and two cooperating syringe-retaining members 1632. The retaining members 1632 are preferably connected together and associated with the base member 1630 by means of a pivot pin 1631 or other suitable mechanism (see FIG. 41D). In addition, the retaining members 1632 are associated with the base member 1630 by means of pins 1629 (see FIG. 41D) that are associated with the retaining members 1632 and captured within slots 1635 defined in the base member 1630. [0276] Further, each retaining member 1632 preferably defines a channel 1636 to capture and retain the mounting member 1522 on the syringe 1512. As best shown in FIGS. 41B and 41C, a spring pin 1637 (or other suitable locking mechanism) is connected to one retaining member 1632 and a channel with a pin recess 1640 is defined in the other retaining member 1632. In addition, two barrel guide rails 1639 are preferably defined in the base member 1630. [0277] To install the syringe 1512 on the syringe interface 1614, the syringe 1512 is moved downwardly (in the direction of Arrow B in FIG. 41B) into the space defined between the retaining members 1632. The barrel 1516 of the syringe 1512 is guided into position between the retaining members 1632 by the barrel guide rails 1639 in the base member 1630. When the syringe barrel 1516 engages the pivot ends 1651 of the retaining members 1632 (see FIG. 41C), the retaining members 1632 are urged to collapse around the rear end 1520 of the syringe 1512. The pins 1629, riding in slots 1635 defined in the base member 1630, direct and control the arcuate motion of the retaining members 1632 into engagement around the syringe 1512. As the retaining members 1632 collapse on the syringe 1512, the retaining members 1632 cooperate to capture the mounting member 1522 within the channels 1636 to securely engage the syringe 1512 with the syringe interface 1614. [0278] Further, when the retaining members 1632 collapse around the syringe 1512, the spring pin 1637 runs along the channel and locks into the pin recess 1640 to secure the syringe 1512 within the syringe interface 1614. To remove the syringe 1512 from the syringe interface 1614, the spring pin 1637 must be removed from the pin recess 1640 to unlock the retaining members 1632 and the retaining members 1632 moved (e.g., by hand or by any suitable lever means) from engagement with the syringe 1512. At this point, the syringe 1512 can be removed by either moving the syringe 1512 upwardly (in the opposite direction of Arrow B) or axially (in the direction of Arrow C in FIG. 41B). [0279] FIGS. 42A-42D illustrate an alternate embodiment 1700 of the syringe interface and syringe system 1600 shown in FIGS. 41A-41D. The system 1700 includes a syringe 1512 and a syringe interface 1714. The syringe interface 1714, as best shown in FIGS. 42C and 42D, differs from the syringe interface 1614 in FIGS. 41A-41D in that the retaining members 1732 include pivot ends 1751 located at the ends of the retaining members 1732 remote from the pivot pin 1731. Further, the retaining members 1732 are preferably spring-biased in the "closed" or "engaged" position, as best shown in FIG. 42D, to retain the syringe 1512 within the syringe interface 1714. [0280] To install the syringe 1512 on the syringe interface 1714, the syringe 1512 is moved downwardly (in the direction of Arrow D in FIG. 42B) into engagement with the retaining members 1732. When the syringe barrel 1516 engages the pivot ends 1751 of the retaining members 1732, the retaining members 1732 are urged apart against the spring force to allow the syringe barrel 1516 to pass between the pivot ends 1751 and into the space defined between the retaining members 1732. The syringe mounting member 1522 is guided by the channels 1736 defined in the retaining members 1732 to correctly position the syringe 1512 within the syringe interface 1714. Once the syringe 1512 passes the pivot ends 1751, the retaining members 1732 are urged by the spring force to collapse around the rear end 1520 of the syringe 1512. The pins 1729, riding in slots 1735 defined in the base member 1730, direct and control the arcuate motion of the retaining members 1732 into engagement around the syringe 1512. As the retaining members 1732 collapse on the syringe 1512, the retaining members 1732 cooperate to capture the mounting member 1522 within the channels 1736 to securely engage the syringe 1512 within the syringe interface 1714. [0281] To remove the syringe 1512 from the syringe interface 1714, the syringe 1512 is moved upwardly (in the opposite direction of Arrow D) against the pivot ends 1751 of the retaining members 1732. When the upward force on the syringe 1512 overcomes the spring force holding the retaining members 1732 together, the retaining members 1732 will move apart and allow the syringe 1512 to slide free from the syringe interface 1714. [0282] FIGS. 43A-43I illustrate another alternate |