Abstract:
An injector for injecting a fluid from a syringe (which syringe includes a body, a plunger moveably positioned within the body, and an encoding device providing syringe information)r includes a housing, a motor disposed within the housing, a controller operably associated with the motor, a sensor operably associated with the controller and operable to read the encoded syringe information provided by the encoding device when the syringe is attached to the injector, a drive member disposed in the housing and powered by the motor, the drive member operable to automatically advance and engage the plunger when the sensor reads the syringe information provided by the encoding device, and a plunger engagement detection device operably associated with the controller and operable to indicate when the drive member of the injector has engaged the plunger of the syringe.

Description:
FIELD OF THE INVENTION 
   The present invention relates to injectors and injector systems, and, more particularly, to injectors and injector systems in which a syringe is connected to or loaded upon the injector in a powered or manual manner. 
   BACKGROUND OF THE INVENTION 
   A number of injector-actuated syringes and powered injectors for use in medical procedures such as angiography, computed tomography and NMR/MRI have been developed. For example, U.S. Pat. No. 4,006,736 discloses an apparatus for injecting fluid into the vascular system of a human being or an animal. Likewise, U.S. Pat. No. 4,677,980 discloses an angiographic injector and syringe wherein the drive member of the injector can be connected to, or disconnected from, the syringe plunger at any point along the travel path of the plunger via a releasable mechanism requiring rotation of the syringe plunger relative to the piston. Each of the injectors disclosed in U.S. Pat. Nos. 4,006,736 and 4,677,980 includes a pressure jacket that is breach or rear loaded with a syringe. 
   U.S. Pat. No. 5,300,031 discloses an injector system in which a syringe is loadable in and unloadable from a pressure jacket of an injector through an open front end in the pressure jacket. The injector system of U.S. Pat. No. 5,300,031 permits replacement of a syringe without retraction of the syringe plunger drive or disconnection of injection tubing connected to the syringe. 
   A front-loading syringe and injector system is disclosed in U.S. Pat. No. 5,383,858. The syringes disclosed in U.S. Pat. No. 5,383,858 can be readily and securely front-loaded directly and accurately on the injector or on a pressure jacket attached to the injector, thereby facilitating the loading-unloading operation as compared to prior systems. In the front-loading system of U.S. Pat. No. 5,383,858 and other currently available front loading systems, a user manually aligns the syringe in a desired orientation relative to the injector and manually inserts and locks the syringe in place. 
   In the system of U.S. Pat. No. 5,383,858, for example, an interlocking, releasable mechanism is activated and released upon proper axial and radial alignment and subsequent manual rotation of a rearward portion of a syringe relative to a front wall of the injector housing. In one embodiment, the releasable mechanism includes slots on the front wall of the housing for receiving retaining flanges on the rearward end of the syringe. The syringe is manually rotatable to engage the retaining flanges with associated or cooperating flanges on the injector mounting mechanism. The releasable mechanism also includes an annular sealing member on the injector housing front wall against which a resilient annular sealing member or flange on the syringe becomes seated as the syringe is positioned on the mounting mechanism. The resilient annular sealing member and the retaining flanges on the syringe receive the flanges on the injector mounting mechanism therebetween with an interference fit. 
   The syringe plunger of U.S. Pat. No. 5,383,858 must be appropriately axially and radially positioned relative to the drive member during loading of the syringe upon that injector system so that rotation of the syringe during loading will also cause engagement of the drive member and the syringe plunger. 
   Although front-loading syringes represent a significant advancement in the area of injector-actuated syringes and powered injectors for use therewith, the loading and unloading procedures therewith require significant operator time/involvement to ensure secure engagement. For example, the operator must ensure that the syringes of current front-loading systems are first properly aligned with and then securely connected to the injector and that the plunger is engaged by the injector drive member. These steps can require substantial time, dexterity and strength as a result of, for example, alignment requirements, awkward and complex motions and close design tolerances. In many cases the injector may also be positioned so that it is difficult for the operator to access the injector to load a syringe thereon. Moreover, injector heads are typically not securely anchored and can move during syringe loading, further complicating loading of a syringe thereon. 
   It is very desirable to develop new syringes, injectors, injector systems and methods to reduce operator time/involvement in loading the syringe onto the injector and/or in connecting the syringe plunger to the injector drive member, while ensuring secure engagement between the syringe (including the syringe plunger) and the injector. 
   SUMMARY OF THE INVENTION 
   The present invention provides improved injectors, injector systems, syringes and methods in which the syringe is loaded upon and/or unloaded from the injector in a powered or manual manner. The loading/connecting features of the present invention greatly simplify the process of loading a front-loading syringe onto an injector and frees valuable operator time to accomplish other tasks. 
   The powered loading features of the present invention also provide greater confidence of proper and secure engagement of the syringe to the injector and/or the syringe plunger to the injector drive member. Moreover, because the loading procedure is powered, tighter tolerances can be designed into the mounting and retaining mechanisms of the present invention than with previous front-loading systems in which tolerances were limited or loosened to facilitate manual loading. The tighter tolerances of the present invention substantially reduce or eliminate play or movement of the syringe after connection thereof to the injector, thereby facilitating more accurate control of the injector. 
   In one aspect, the present invention provides an injector for injecting a fluid from a syringe. The syringe includes an elongated body and a mounting member positioned on a rear portion of the body. The syringe further includes a plunger moveably positioned within the body of the syringe. The injector includes a housing having a front wall and a retainer on the front wall. The retainer is adapted to cooperate with the mounting member to retain the syringe on the front wall of the injector. Preferably, the syringe is releasably retained upon the front wall of the injector. The retainer includes a powered loader adapted to bring the mounting member and the retainer into secure engagement to securely connect the syringe to the injector. The injector further includes a powered drive member in the housing. The drive member is adapted to engage the plunger and control the movement of the plunger. 
   The mounting member of the syringe may be formed integrally with the remainder of the syringe in, for example, a polymer molding procedure. Alternatively, the mounting member may be formed separately from the syringe and attached thereto. For example, an adapter including the mounting member can be fabricated to be separate from and attachable to a syringe body. The adapter can, for example, be designed to accept a syringe such as disclosed in U.S. Pat. No. 5,383,858 to adapt that syringe or other syringes for use in the present invention. Preferably, the adapter is releasably connectible to the injector. The adapter is also preferably releasably connected or attached to the syringe. 
   Likewise, syringes for use in the present invention are readily adapted for use with other injectors through use of an adapter. Such an adapter can, for example, be used to load a syringe of the present invention on an injector as disclosed in U.S. Pat. No. 5,383,858. 
   In several embodiments, the powered loader of the present invention moves one or more components of the retainer to engage the mounting member and to bring the mounting member and the retainer into secure connection, thereby securely connecting the syringe to the injector. For example, the mounting member may include threading and the retainer may include a cooperating threaded member. The powered loader may rotate the threaded member of the retainer relative to the threading on the syringe to engage the threading on the syringe and securely connect the syringe to the injector. 
   In general, many types of cooperating attachment members can be used for the mounting member and the retainer. The mounting member may, for example, include a mounting flange or flanges (for example, a single annular flange or a plurality of flanges positioned about the circumference of a syringe or adapter) and the retainer may include a cooperating retaining flange or flanges. In this embodiment, the powered loader preferably moves the retainer to cause the retainer flange(s) to engage the mounting flange(s) to securely connect the syringe to the injector. 
   The injector may also include a loading or mounting sensor to determine when the syringe is in position for the powered loader to bring the mounting member and the retainer into secure engagement. The powered loading procedure can thereby be automatically initiated when the syringe is in position. The injector may also include one or more sensors to read information encoded upon the syringe. In another embodiment, a single sensor can be used to both read encoded syringe information and to initiate the powered loading process. 
   The syringe (or an adapter that is attached to the rear of the syringe as described above) may include a generally annular flange preferably positioned forward of the mounting flange(s) that forms a sealing engagement with a forward surface of the retainer to assist in creating a secure engagement of the syringe to the injector and to assist in preventing leakage of fluids into the injector. 
   Preferably, the drive member of the injector includes an engagement member on a forward end thereof. The engagement member is preferably adapted to connect or dock to the plunger upon forward advancement of the drive member. Preferably, the engagement member is suitable to connect to the plunger regardless of the axial position of the plunger within the syringe and regardless of the relative angular positions of the drive member and plunger about a generally common axis. Preferably, the drive member automatically connects to the plunger either during or shortly after the power loading or manual loading of the syringe onto the injector. 
   The drive member may, for example, be automatically advanced forward upon loading of the syringe on the injector to connect the drive member to the plunger. Whether the drive member is connected to the plunger automatically or by manual control, the injector preferably controls the motion of the drive member based upon syringe information encoded upon the syringe. For example, if the injector determines that the syringe is empty from the syringe information encoded upon the syringe, the injector preferably causes the drive member to advance the plunger forward to expel air from the syringe in preparation for loading the syringe with fluid. However, if the injector determines that the syringe is prefilled from the syringe information encoded upon the syringe, the injector preferably stops forward advancement of the drive member upon connection of the drive member with the plunger to prevent undesirable expelling of injection fluid. Controlling the drive member, for example, to perform certain preinjection procedures in a manner that depends upon the type of syringe loaded upon the injector can save valuable user time and helps standardize injection procedures. 
   In another aspect, the present invention provides a system for injecting a liquid medium that includes a front-loading syringe for injecting a fluid into a patient and a powered injector. The syringe preferably includes: an elongated body; a mounting member positioned on a rear portion of the body, and a plunger moveably positioned within the body of the syringe. The injector preferably includes: a housing having a front wall and a retainer on the front wall that is adapted to retain the syringe on the front wall. The retainer preferably includes a powered loader adapted to bring the mounting member and the retainer into secure engagement to securely connect the syringe to the injector. The injector further includes a powered drive member in the housing that is adapted to engage the plunger and control the movement of the plunger. 
   In a further aspect, the present invention provides a method of connecting a front-loading syringe to a powered injector including the steps of: positioning the syringe in a mounting position on the injector; and moving a retaining member of the injector in a powered manner to engage the syringe and connect the syringe to the injector. 
   In another aspect, the present invention provides a syringe for use with a powered injector including: an elongated body, a plunger moveably positioned within the body of the syringe, and a threaded mounting member positioned on a rear portion of the syringe to retain the syringe on the injector. The syringe preferably further includes a stop member to prevent rotation of the syringe relative to a threaded retaining member of the injector when the threaded retaining member is rotated relative to the threaded mounting member to engage the threaded mounting member and connect the syringe to the injector. 
   In a further aspect, the present invention provides an injector for injecting a fluid from a syringe. The syringe includes an elongated body, a mounting member positioned on a rear portion of the body, a plunger moveably positioned within the body of the syringe, and encoded syringe information. The injector preferably includes: a sensor to read the encoded syringe information and a powered drive member adapted to engage the plunger and control the movement of the plunger. The drive member preferably controls the movement of the plunger in accordance with the encoded syringe information. 
   In still another aspect, the present invention provides a method of connecting a syringe to an injector for injection of a fluid into a patient, the syringe including a plunger positioned therein and encoded syringe information. The method includes the steps of: connecting the syringe to the injector; having the injector read the syringe information; and having the injector control the motion of the plunger in a manner that is dependent upon the encoded syringe information. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other aspects of the invention and their advantages will be discerned from the following detailed description when read in connection with the accompanying drawings, in which: 
       FIG. 1  illustrates a front perspective view an embodiment of an injector system of the present invention; 
       FIG. 2A  illustrates a rear perspective view of an embodiment of a syringe and injector retainer in a disassembled state; 
       FIG. 2B  illustrates a rear perspective view of a syringe and an adapter in a disassembled state; 
       FIG. 2C  illustrates a rear perspective view of a syringe and an adapter in a disassembled state; 
       FIG. 3  illustrates a front perspective view of the syringe and retainer of  FIG. 2A  in a disassembled state; 
       FIG. 4A  illustrates a side view of an embodiment of a plunger, retainer, piston and plunger release mechanism in which the piston is engaged by the plunger. 
       FIG. 4B  illustrates a side view of the plunger, retainer, piston and plunger release mechanism of  FIG. 4A  in which the plunger release mechanism has been advanced to allow disengagement of the plunger from the piston. 
       FIG. 4C  illustrates a rear perspective view of the piston and plunger release mechanism of  FIGS. 4A and 4B  in a disassembled state. 
       FIG. 4D  illustrates a side view of the syringe, retainer, and plunger release mechanism of  FIGS. 4A ,  4 B and  4 C. 
       FIG. 4E  illustrates a cross-sectional view of an embodiment of a design of a drive member including a sensor to detect plunger position. 
       FIG. 5A  illustrates a cross-sectional view of another embodiment of an injector system of the present invention in which the syringe is being brought into position for loading upon the injector. 
       FIG. 5B  illustrates a cross-sectional view of the embodiment of  FIG. 5A  in which the syringe is in secure connection with the injector. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   An embodiment of a front-loading injector system  10  of the present invention is illustrated in  FIGS. 1 through 4D . Injector system  10  includes a syringe  100  and an injector  200 . Injector housing  210  of injector  200  preferably includes a reciprocating piston  220  (see, for example,  FIGS. 4A and 4C ) therein which cooperates with a syringe plunger  110  disposed within an elongated cylindrical body  120  of syringe  100  to inject an injection fluid (for example, a liquid contrast medium) from the interior of syringe  100  into a patient. Piston  220  is preferably extendible and retractable via a powered means as known in the art (not shown) that is preferably contained within injection housing  210  and includes, for example, a motor or hydraulic system, including appropriate gearing (not shown). As also known in the art, injector  200  also preferably includes a motor controller for controlling operation of a motor and thereby controlling operation of piston  220 . The operation of injector  200  can, for example, be controlled by a computer  150  including a processing unit  152  and memory  154 . 
   As used herein to describe system  10 , the terms “axial” or “axially” refer generally to an axis A around which system  10  (including, for example, piston  220  and syringe  10 ) is preferably formed (although not necessarily symmetrically therearound). The terms “proximal” or “rearward” refer generally to an axial direction toward the end of injector housing  210  opposite the end to which syringe  10  is mounted. The terms “distal” or “forward” refer generally to an axial direction toward a syringe tip  124  of syringe  10 . The term “radial” refers generally to a direction normal to axis A. 
   Piston  220  moves axially forward and rearward through an opening  232  in a retainer  230  that includes a face plate  240  that is attached to or formed integrally with the front wall of housing  210 . As illustrated in  FIGS. 1  through  3 , retainer  230  preferably further includes a generally annular retaining member  250  that rotatably seats in a seating area  234  in retainer  230 . Retaining member  250  may, for example, include threading  252  on an inner surface thereof. Threading  252  cooperates with threading  130  positioned on a rearward portion of syringe body  120  to load and retain syringe  100  on injector  200 . 
   During loading of syringe  100  onto injector  200 , an operator inserts the rear portion of syringe  100  within opening  232  in face plate  240  so that, for example, one or more guide or stop members  140  are aligned with corresponding slot(s)  260  formed in face plate  240 . Retainer  230  may include a sensor bank  264  (seated, for example, in seating area  266  formed in face plate  240 ) including a loading sensor or sensors  270  to sense the presence of syringe  100  and begin rotation of retaining member  250  to draw syringe  100  rearward with the opening in face plate  240  and create a secure engagement between syringe  100  and injector  200 . Many types of sensors as known in the art can be used as loading sensor(s)  270 . For example, loading sensor  270  can include a switch mechanism that is triggered by contact with stop member  240 . Alternatively, a manual switch (not shown) located on injector  200  or remote therefrom can be used to begin rotation of retaining member  250  once syringe  100  is in position. 
     FIG. 2B  illustrates another embodiment of a syringe  100 A which cooperates with an adapter  100 B to connect to retainer. Adapter  100 B preferably includes threading  130 B, a guide or stop member  140 B and a flange  160 B that cooperate with retainer  230  as described above. Syringe  100 A may, for example, be a syringe as disclosed in U.S. Pat. No. 5,383,858 that connects to adapter  100 B in the manner that is described in U.S. Pat. No. 5,383,858 for connection of syringe  100 A to the injector of U.S. Pat. No. 5,383,858. In that regard, adapter  100 B includes retaining flanges (not shown) for receiving mounting flanges  102 A on the rearward end of the syringe  100 A. Syringe is manually rotated to engage the mounting flanges behind the associated or cooperating flanges on the adapter. Use of an adapter such as adapter  100 B enables use of a wide variety of syringes with the retainers of the present invention. With use of an adaptor, many types of syringes can be used to take advantage of the benefits of the injectors of the present invention. 
   Similarly, syringe  100  can easily be adapted for use with other injectors through use of an adapter such as adapter  100 C illustrated in  FIG. 2C . Adapter  100 C can, for example, be designed to adapt syringe  100  for use in current manually loaded injectors such as described in U.S. Pat. No. 5,383,858. In that regard, adapter  100 C includes on a rearward end thereof retaining flanges  102 C that cooperate with the injector of U.S. Pat. No. 5,383,858 as described therein. On a front end thereof, adapter  100 C also includes an opening having a slot  140 C on the perimeter thereof through which guide member  140  passes to allow threading  130  of syringe  100  to engage threading  130 C of adapter  100 C to connect syringe  100  to adapter  100 C. 
   Sensor  270  or a manual switch as described above is preferably in communication with a power source such as an electric motor  300  so that motor  300  is switched on when syringe  100  is sensed by sensor  270  or when an operator selects the manually operated loading switch. In the embodiment of  FIGS. 1 through 4D , motor  300  is in operative connection with a gear  310  that is rotatably seated within a seating area  280  within retainer  230  to mesh with an outer geared surface  254  of retaining member  250 . Rotational motion of motor  300  is thus translated to rotation of rotating member  250 . Abutment of stop member  140  with the sides of slot  260  prevents syringe  100  from rotating relative to retaining member  250  when retaining member  250  is rotated to engage syringe threading  130 , thereby facilitating threaded engagement between retaining member  250  and syringe  100 . Limit switches (not shown), position sensors (not shown) and/or measurement of motor current of motor  300  can, for example, be used to control movement of retaining member  250  to ensure that syringe  100 A is properly loaded and excess stresses are not placed thereon. 
   Using cooperating threaded elements, syringe  100  can be loaded upon injector  200  in either a powered or manual manner. For example, if it is desirable to load syringe  100  onto injector  200  in a manual manner, retaining member  250  can be advanced to its forward position and held in that position. Syringe  100  can then me manually rotated to engage threading  130  with threading  252  of retaining member  250 . 
   Syringe  100  preferably also includes a generally annular flange  160  positioned forward of threading  130 . Flange  160  is preferably drawn securely against a portion of a front or forward surface of face plate  240  when syringe  100  is fully engaged within injector  200 . Flange  160  assists in forming a secure interference fit and also assists in preventing leakage of fluids into injector  200 . 
   Upon secure connection of syringe  100  to injector  200  as described above (in either a powered or manual loading procedure), a preferably releasable connection between plunger  110  and piston  220  is preferably made. A number of manners of forming a releasable connection between a plunger and a piston in a front-loading injector system are disclosed in U.S. Pat. Nos. 4,677,980, 5,383,858, 5,873,861 and 5,947,935, the disclosures of which are incorporated herein by reference. In the embodiment illustrated in  FIGS. 4A through 4D , plunger  110  includes capture legs  112  that extend rearward from a rear surface of plunger  110 . Capture legs  112  include radially inward extending abutment members  114  that cooperate with a radially outward extending flange  224  of a piston head  222  to releasably connect plunger  110  to piston  220 . Capture legs  112  are cantilevered such that, when abutment members  114  are contacted by flange  224  upon forward advancement of piston  220  relative to plunger  110 , capture legs  112  are forced radially outward to allow piston head  222  to pass therebetween. Capture legs  112  spring radially inward once flange  224  passes abutment members  114  so that abutment members  114  engage flange  224  to releasably connect plunger  110  to piston  220  as illustrated in  FIG. 4A . Flange  224  is preferably generally circular in shape so that the relative angular positions (as rotated about the common axis A) of plunger  110  and drive member  220  are unimportant to the ability to connect plunger  110  and drive member  220 . 
   In the embodiment of  FIGS. 4A through 4D , plunger  110  is preferably released from piston  220  by forward advancement of a release cylinder  400  that contacts capture legs  112  to force capture legs radially outward as illustrated in  FIG. 4B . Piston  220  can then be drawn rearward to release plunger  110  from connection therewith. During operation of injector  200 , release cylinder  400  is in a retracted position as illustrated in  FIG. 4A  and travels generally in unison with piston  220 , which is disposed within release cylinder  400 . Upon, for example, completion of an injection procedure, an operator can preferably depress a release switch  212  on injector housing  210  to initiate release of plunger  110  (and, preferably, release of syringe  100  from injector  200 ). Upon depression of switch  212 , a plunger release motor  410  is preferably activated to advance release cylinder  400  to release plunger  110 . 
   Upon release of the connection of plunger  110  from piston  220  via release switch  212 , syringe  100  can be released from injector  200  by simply activating retaining member  250  to disconnect threading  252  thereof from threading  130  on the rear of syringe  100 . Preferably, such activation of retaining member  250  occurs automatically upon release of plunger  100 . Upon disconnection, syringe  100  preferably remains releasably seated in opening  232  of retainer  230  until removed by the operator. 
   Depending, for example, upon the nature of syringe  110 , and regardless of whether syringe  100  is loaded in a powered or manual manner, different operations may be performed upon connection of syringe  100  to injector  200 . It is particularly advantageous to control and/or automate certain preinjection procedures. For example, in the case of an empty syringe, it may be desirable to advance plunger  110  within syringe  100  to expel air therefrom and, subsequently, to draw injection fluid into syringe  100 . One or more of these steps may be accomplished through manual control by an operator or automatically via, for example, control from computer  150 . 
   In the case of a prefilled syringe, on the other hand, after connection of syringe  100  to injector  200 , caution should be exercised in advancing piston  220  any farther forward than required to connect piston  220  to plunger  110 . Excess forward motion of piston  110  will result in expelling injection fluid in a prefilled syringe. 
   Although the determination of the type of syringe connected to injector  200  can be made by the operator and injector  200  controlled appropriately, it is also possible to have injector  200  detect the type of syringe  100 , the contents thereof, the volume thereof etc. In that regard, one or more sensors  290  can be positioned on retainer  230  to detect syringe information that can be encoded on, for example, area  142  on syringe  100  (see  FIG. 3 ). Methods and systems for reading encoded syringe information are disclosed, for example, in U.S. Pat. No. 5,383,858 and PCT International Patent Application Serial No. PCT/US99/13360 filed Jun. 15, 1999, assigned to the assignee of the present invention, the disclosures of which are incorporated herein by reference. In one embodiment, sensors  270  and  290  are combined in a single sensor. 
   Moreover, in the case that a prefilled syringe is connected to injector  200 , the position of syringe plunger  100  may be detected by injector  200  to ensure that piston  220  is not advanced too far forward in connecting piston  220  to plunger  110 . The detection of plunger position can be accomplished in numerous ways. For example, motor current in injector  200  can be measured. The greater resistance to advancement of piston  220  upon contact thereof with plunger  110  can be sensed by measuring motor current and the advancement of piston  220  stopped. Likewise, a sensor can be placed on piston head  222  and or plunger  110  to detect contact of piston  220  with plunger  110 . For example, plunger  110  can include a light source  116  and a light sensor  116 ′ (see  FIG. 4B ). Connection of drive member  220  with plunger  110  will prevent light from light source  116  from reaching light sensor  116 ′ and thereby provide an indication that connection has been made. 
     FIG. 4E  illustrates an alternative embodiment of a plunger  110 ′ having capture members  112 ′. In this embodiment, plunger  110 ′ includes a rearward projecting element  114 ′ that inserts into a passage  222 ′ of a piston head  224 ′ of a piston  220 ′ upon connection of piston  220 ′ and plunger  110 ′. Disposed on one side of passage  222 ′ is a light source  226 ′, and on an opposing side thereof is a light sensor  226 ″. Connection of drive member  220 ′ with plunger  110 ′ will cause projecting element  114 ′ to enter passage  222 ′ and prevent light from light source  226 ′ from reaching light sensor  226 ″, thereby providing an indication that connection has been made. 
   During loading of syringe  100  onto injector  200  as described above, an operator inserts the rear portion of syringe  100  within opening  232 . Loading sensor(s)  270  sense the presence of syringe  100  and begin loading syringe  100  upon injector  200 . The type of syringe is sensed by sensor  290 . Docking of piston  220  to plunger  110 , as described above, is preferably automatically initiated upon loading of syringe  100  into injector  200 . If injector  200  senses that an empty syringe has been loaded thereupon, injector  200  preferably advanced piston  220  to engage plunger  110 . After engagement of plunger  110 , piston  220  preferably continues to advance forward to expel air from syringe  100  and prepare syringe  100  for filling with injection fluid. Should injector  200  sense that a prefilled syringe has been loaded thereupon, however, piston  220  preferably engages plunger  110  and discontinues any further advancement until an injection procedure begins. 
   An alternative embodiment of a syringe mounting and retaining mechanism is illustrated in  FIGS. 5A and 5B . In this embodiment, syringe  600  includes a generally annular mounting flange  630  formed on a rearward portion thereof. Syringe  600  also includes a generally annular flange or sealing member  650  formed forward of mounting flange  630 . Injector  700  includes a retainer  730  to securely connect syringe  600  to injector  700 . Retainer  730  includes, for example, a retaining member  750 . Retaining member  750  preferably includes a plurality of capture members  752  that are preferably positioned around the circumference of retaining member  750 . Each of capture members  752  preferably includes an abutment member  754  on a forward end thereof that is adapted to form an abutting connection with mounting flange  730 . 
   Before loading of syringe  600  on injector  700 , capture members  752  are in an open position as illustrated in  FIG. 5A  in which capture members  752  are flared radially outward so that mounting flange  630  can pass by abutment members  754 . Once syringe  600  is placed in loading position by an operator, retaining member  750  is drawn rearward, for example, via cooperation of threading  756  with a cooperating threaded member (not shown). As retaining member  750  is drawn rearward, the radially outer edges of capture members  652  contact a radially inward extending surface  732  of retainer  730 , thereby drawing abutment members  754  radially inward to engage mounting flange  630 . 
   After abutment members  754  engage mounting flange  630  and retainer  650  is drawn further rearward, syringe  600  is drawn rearward until flange  650  is drawn into secure engagement with a front surface of retainer  630  as illustrated in  FIG. 5B . Sensors (not shown) can be provided to ensure that secure engagement has been achieved. Capture members  752  and abutment members  754  are preferably forced radially inward by abutment with a beveled or chamfered surface  760  of retainer  730 . Syringe  600  is thereby securely engaged within injector  300 . To release syringe  600 , retaining member  650  is moved forward so that capture members  752  are allowed to expand in a radial outward manner as illustrated in  FIG. 5A . 
   Although the present invention has been described in detail in connection with the above examples, it is to be understood that such detail is solely for that purpose and that variations can be made by those skilled in the art without departing from the spirit of the invention except as it may be limited by the following claims.