Patent Publication Number: US-2023158229-A1

Title: Fluid injector with syringe engagement mechanism

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation Application of U.S. application Ser. No. 16/341,285, filed Apr. 11, 2019, which is a § 371 national phase application of PCT Application No. PCT/US2017/056731, filed Oct. 16, 2017 and claims priority to U.S. Provisional Application No. 62/409,044 filed Oct. 17, 2016; and U.S. Provisional Application No. 62/545,693, filed Aug. 15, 2017, the disclosures of which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     Field of the Disclosure 
     The present disclosure relates to medical fluid injectors and, more particularly, to fluid injectors having syringe engagement mechanisms for engaging a syringe with a flexible sidewall and a piston engagement portion on a proximal end of the sidewall. 
     Description of Related Art 
     In many medical diagnostic and therapeutic procedures, a practitioner, such as a physician, injects a patient with one or more medical fluids. In recent years, a number of injector-actuated syringes and powered fluid injectors for pressurized injection of medical fluids, such as a contrast solution (often referred to as “contrast”), a flushing agent, such as saline, and other medical fluids, have been developed for procedures such as angiography, computed tomography (CT), ultrasound, magnetic resonance imaging (MRI), positron emission tomography (PET), and other imaging procedures. In general, these fluid injectors are designed to deliver a preset amount of medical fluid at a preset pressure and/or flow rate. 
     Typically, powered injectors have pistons that connect to a syringe plunger that is slidably disposed within the syringe. The syringe generally includes a rigid barrel with the syringe plunger being slidably disposed within the barrel. The piston drives the plunger in a direction of a longitudinal axis of the barrel to draw fluid into the syringe barrel with a proximal movement of the piston or deliver the fluid from the syringe barrel with a distal movement of the piston. While various connection mechanisms exist in the art for engaging the piston of the fluid injector with the syringe, it remains desirable to develop improved designs of syringes and syringe engagement mechanisms to facilitate injection procedures. 
     SUMMARY OF THE DISCLOSURE 
     The present disclosure generally relates to fluid injectors having a syringe engagement mechanism for engaging a syringe with a flexible sidewall and a piston engagement portion on at least a portion of the flexible sidewall. 
     In some examples of the present disclosure, an engagement mechanism may be associated with a reciprocally movable piston of a fluid injector. The engagement mechanism may be configured for releasably engaging an engagement portion at a proximal end of a rolling diaphragm syringe having a flexible sidewall configured for rolling upon itself when acted upon by the piston. The engagement mechanism may have a plurality of engagement elements reversibly and pivotally movable about a pivot pin relative to the engagement portion of the syringe between a first position, where the plurality of engagement elements are disengaged from the engagement portion of the syringe, and a second position, where the plurality of engagement elements are pivotally movable about the pivot pin in a radially inward direction to engage with the engagement portion of the syringe. The engagement mechanism may further have a drive mechanism for moving the plurality of engagement elements between the first position and the second position. 
     In other examples of the present disclosure, the plurality of engagement elements may be progressively movable from the first position to the second position with movement of the piston in a proximal direction to continuously increase a gripping force on the engagement portion of the syringe. The drive mechanism may be operatively connected to the piston such that the plurality of engagement elements are movable from the first position to the second position with movement of the piston in a proximal direction. The plurality of engagement elements may be movable from the second positon to the first position with movement of the piston in a distal direction. The drive mechanism may move the plurality of engagement elements between the first position and the second position independently of movement of the piston in a proximal direction or a distal direction. The drive mechanism may have at least one of the following: a linear electric motor or actuator, a rotary electric motor or actuator, a solenoid, a pneumatic mechanism, a hydraulic mechanism, an electromagnetic mechanism, an electroactive polymer mechanism, a nitinol wire-based mechanism, and any combination thereof. The drive mechanism may have a rod linearly or rotatably movable by a motor. Linear or rotary movement of the rod may reversibly move the plurality of engagement members between the first position and the second position. The plurality of engagement elements may be biased to one of the first position or the second position by a biasing mechanism. The biasing mechanism may be a spring. 
     In other examples of the present disclosure, an engagement mechanism may be associated with a reciprocally movable piston of a fluid injector. The engagement mechanism may be configured for releasably engaging an engagement portion at a proximal end of a rolling diaphragm syringe having a flexible sidewall configured for rolling upon itself when acted upon by the piston. The engagement mechanism may have a plurality of engagement elements reversibly and pivotally movable about a pivot pin relative to the engagement portion of the syringe between a first position, where the plurality of engagement elements are disengaged from the engagement portion of the syringe, and a second position, where the plurality of engagement elements are pivotally movable about the pivot pin in a radially inward direction to engage with the engagement portion of the syringe. The engagement mechanism may further have a drive mechanism for moving the plurality of engagement elements between the first position and the second position. The drive mechanism may have an outer piston sleeve fixed relative to the piston of the fluid injector and an abutment section movably received within the outer piston sleeve at a distal end of the outer piston sleeve. The abutment section may be operatively engaged with the plurality of engagement members. The drive mechanism may further have an inner piston sleeve movably received within the outer piston sleeve and connected with the abutment section such that movement of the inner piston sleeve causes movement of the abutment section. The inner piston sleeve may be movable by a piston rod movably coupled to the piston. Movement of the piston in a proximal direction may moves the outer piston sleeve proximally relative to the abutment section, and proximal movement of the outer piston sleeve relative to the abutment section may move the plurality of engagement members from the first position to the second position. 
     In other examples of the present disclosure, the abutment section has an outer engagement surface configured for contacting a closed end wall of the syringe at a central opening on the outer engagement surface configured for receiving the engagement portion of the syringe. the plurality of engagement elements are progressively movable from the first position to the second position with movement of the piston in a proximal direction to continuously increase a gripping force on the engagement portion of the syringe. At least one of the plurality of engagement elements may have a pointed distal end configured for at least partially embedding into the engagement portion of the syringe when the plurality of engagement elements are in the second position. The plurality of engagement elements may be movable from the second positon to the first position with movement of the piston in the distal direction. The plurality of engagement elements may be biased to one of the first position or the second position by a biasing mechanism, such as a spring. 
     In other examples of the present disclosure, a fluid injector may have at least one injector head with at least one reciprocally movable piston and an engagement mechanism associated with the at least one piston and configured for releasably engaging an engagement portion at a proximal end of a rolling diaphragm syringe having a flexible sidewall configured for rolling upon itself when acted upon by the piston. The engagement mechanism may have a plurality of engagement elements reversibly and pivotally movable about a pivot pin relative to the engagement portion of the syringe between a first position, where the plurality of engagement elements are disengaged from the engagement portion of the syringe, and a second position, where the plurality of engagement elements are pivotally movable about the pivot pin in a radially inward direction to engage with the engagement portion of the syringe. The fluid injector may further have a drive mechanism for moving the plurality of engagement elements between the first position and the second position. 
     In other examples of the present disclosure, the drive mechanism may have at least one of the following: a linear electric motor or actuator, a rotary electric motor or actuator, a solenoid, a pneumatic mechanism, a hydraulic mechanism, an electromagnetic mechanism, an electroactive polymer mechanism, a nitinol wire-based mechanism, and any combination thereof. The drive mechanism may have a rod linearly or rotatably movable by a motor. Linear or rotary movement of the rod may reversibly move the plurality of engagement members between the first position and the second position. 
     In other examples of the present disclosure, the drive mechanism may have an outer piston sleeve fixed relative to the piston of the fluid injector and an abutment section movably received within the outer piston sleeve at a distal end of the outer piston sleeve. The abutment section may be operatively engaged with the plurality of engagement members. The drive mechanism may further have an inner piston sleeve movably received within the outer piston sleeve and connected with the abutment section such that movement of the inner piston sleeve causes movement of the abutment section. The inner piston sleeve may be movable by a piston rod movably coupled to the piston. Movement of the piston in a proximal direction may move the outer piston sleeve proximally relative to the abutment section. Proximal movement of the outer piston sleeve relative to the abutment section may move the plurality of engagement members from the first position to the second position. 
     Various other examples of the present disclosure are recited in one or more of the following enumerated clauses: 
     Clause 1: An engagement mechanism associated with a reciprocally movable piston of a fluid injector and configured for releasably engaging an engagement portion at a proximal end of a rolling diaphragm syringe having a flexible sidewall configured for rolling upon itself when acted upon by the piston, the engagement mechanism comprising: a plurality of engagement elements reversibly and pivotally movable about a pivot pin relative to the engagement portion of the syringe between a first position, where the plurality of engagement elements are disengaged from the engagement portion of the syringe, and a second position, where the plurality of engagement elements are pivotally movable about the pivot pin in a radially inward direction to engage with the engagement portion of the syringe; and a drive mechanism for moving the plurality of engagement elements between the first position and the second position. 
     Clause 2: The engagement mechanism of clause 1, wherein the plurality of engagement elements are progressively movable from the first position to the second position with movement of the piston in a proximal direction to continuously increase a gripping force on the engagement portion of the syringe. 
     Clause 3: The engagement mechanism of clauses 1 or 2, wherein the drive mechanism is operatively connected to the piston such that the plurality of engagement elements are movable from the first position to the second position with movement of the piston in a proximal direction. 
     Clause 4: The engagement mechanism of clause 3, wherein the plurality of engagement elements are movable from the second positon to the first position with movement of the piston in a distal direction. 
     Clause 5: The engagement mechanism of clauses 1 or 2, wherein the drive mechanism moves the plurality of engagement elements between the first position and second position independently of movement of the piston in a proximal direction or a distal direction. 
     Clause 6: The engagement mechanism of any of clauses 1 to 5, wherein the drive mechanism comprises at least one of the following: a linear electric motor or actuator, a rotary electric motor or actuator, a solenoid, a pneumatic mechanism, a hydraulic mechanism, an electromagnetic mechanism, an electroactive polymer mechanism, a nitinol wire-based mechanism, and any combination thereof. 
     Clause 7: The engagement mechanism of any of clauses 1 to 6, wherein the drive mechanism comprises a rod linearly or rotatably movable by a motor, and wherein linear or rotary movement of the rod reversibly moves the plurality of engagement members between the first position and the second position. 
     Clause 8: The engagement mechanism of any of clauses 1 to 7, wherein the plurality of engagement elements are biased to one of the first position or the second position by a biasing mechanism. 
     Clause 9: The engagement mechanism of clauses 8, wherein the biasing mechanism is a spring. 
     Clause 10: An engagement mechanism associated with a reciprocally movable piston of a fluid injector and configured for releasably engaging an engagement portion at a proximal end of a rolling diaphragm syringe having a flexible sidewall configured for rolling upon itself when acted upon by the piston, the engagement mechanism comprising: a plurality of engagement elements reversibly and pivotally movable about a pivot pin relative to the engagement portion of the syringe between a first position, where the plurality of engagement elements are disengaged from the engagement portion of the syringe, and a second position, where the plurality of engagement elements are pivotally movable about the pivot pin in a radially inward direction to engage with the engagement portion of the syringe; and a drive mechanism for moving the plurality of engagement elements between the first position and the second position, the drive mechanism comprising: an outer piston sleeve fixed relative to the piston of the fluid injector; an abutment section movably received within the outer piston sleeve at a distal end of the outer piston sleeve, wherein the abutment section is operatively engaged with the plurality of engagement members; and an inner piston sleeve movably received within the outer piston sleeve and connected with the abutment section such that movement of the inner piston sleeve causes movement of the abutment section, wherein the inner piston sleeve is movable by a piston rod movably coupled to the piston, wherein movement of the piston in a proximal direction moves the outer piston sleeve proximally relative to the abutment section, and wherein proximal movement of the outer piston sleeve relative to the abutment section moves the plurality of engagement members from the first position to the second position. 
     Clause 11: The engagement mechanism of clause 10, wherein the abutment section has an outer engagement surface configured for contacting a closed end wall of the syringe at a central opening on the outer engagement surface configured for receiving the engagement portion of the syringe. 
     Clause 12: The engagement mechanism of clauses 10 or 11, wherein the plurality of engagement elements are progressively movable from the first position to the second position with movement of the piston in a proximal direction to continuously increase a gripping force on the engagement portion of the syringe. 
     Clause 13: The engagement mechanism of any of clauses 10 to 12, wherein at least one of the plurality of engagement elements has a pointed distal end configured for at least partially embedding into the engagement portion of the syringe when the plurality of engagement elements are in the second position. 
     Clause 14: The engagement mechanism of any of clauses 10 to 13, wherein the plurality of engagement elements are movable from the second positon to the first position with movement of the piston in the distal direction. 
     Clause 15: The engagement mechanism of any of clauses 10 to 14, wherein the plurality of engagement elements are biased to one of the first position or the second position by a biasing mechanism. 
     Clause 16: The engagement mechanism of clause 15, wherein the biasing mechanism is a spring. 
     Clause 17: A fluid injector comprising: at least one injector head comprising at least one reciprocally movable piston; an engagement mechanism associated with the at least one piston and configured for releasably engaging an engagement portion at a proximal end of a rolling diaphragm syringe having a flexible sidewall configured for rolling upon itself when acted upon by the piston, the engagement mechanism comprising: a plurality of engagement elements reversibly and pivotally movable about a pivot pin relative to the engagement portion of the syringe between a first position, where the plurality of engagement elements are disengaged from the engagement portion of the syringe, and a second position, where the plurality of engagement elements are pivotally movable about the pivot pin in a radially inward direction to engage with the engagement portion of the syringe; and a drive mechanism for moving the plurality of engagement elements between the first position and the second position. 
     Clause 18: The fluid injector of clause 17, wherein the drive mechanism comprises at least one of the following: a linear electric motor or actuator, a rotary electric motor or actuator, a solenoid, a pneumatic mechanism, a hydraulic mechanism, an electromagnetic mechanism, an electroactive polymer mechanism, a nitinol wire-based mechanism, and any combination thereof. 
     Clause 19: The fluid injector of clauses 17 or 18, wherein the drive mechanism comprises a rod linearly or rotatably movable by a motor, and wherein linear or rotary movement of the rod reversibly moves the plurality of engagement members between the first position and the second position. 
     Clause 20: The fluid injector of clause 17, wherein the drive mechanism comprises: an outer piston sleeve fixed relative to the piston of the fluid injector; an abutment section movably received within the outer piston sleeve at a distal end of the outer piston sleeve, wherein the abutment section is operatively engaged with the plurality of engagement members; and an inner piston sleeve movably received within the outer piston sleeve and connected with the abutment section such that movement of the inner piston sleeve causes movement of the abutment section, wherein the inner piston sleeve is movable by a piston rod movably coupled to the piston, wherein movement of the piston in a proximal direction moves the outer piston sleeve proximally relative to the abutment section, and wherein proximal movement of the outer piston sleeve relative to the abutment section moves the plurality of engagement members from the first position to the second position. 
     Further details and advantages of the various examples described in detail herein will become clear upon reviewing the following detailed description in conjunction with the accompanying drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a front perspective view of a fluid injector having a pair of pressure jackets and syringes in accordance with one example of the present disclosure; 
         FIG.  2 A  is a side cross-sectional view of a syringe in accordance with one example of the present disclosure, with the syringe shown in an unrolled configuration; 
         FIG.  2 B  is a side cross-sectional view of the syringe of  FIG.  2 A  shown in a rolled configuration; 
         FIG.  3 A  is a side cross-sectional view of a syringe and a piston having a syringe engagement mechanism in accordance with one example of the present disclosure shown in an open state or configuration; 
         FIG.  3 B  is a side cross-sectional view of the syringe and the piston with the syringe engagement mechanism of  FIG.  3 A  shown in a closed state or configuration; 
         FIG.  4 A  is a side cross-sectional view of a syringe and a piston having a syringe engagement mechanism in accordance with one example of the present disclosure; 
         FIG.  4 B  is an exploded view of the piston and the syringe with the engagement mechanism shown in  FIG.  4 A ; 
         FIG.  5 A  is a side cross-sectional view of a syringe and a piston having a syringe engagement mechanism in accordance with one example of the present disclosure shown in an open state or configuration; 
         FIGS.  5 B- 5 C  are side cross-sectional views of the syringe and the piston with the syringe engagement mechanism of  FIG.  5 A  showing movement of the syringe engagement mechanism from the open state or configuration to a closed state or configuration; 
         FIGS.  5 D- 5 E  are side cross-sectional views of the syringe and the piston with the syringe engagement mechanism of  FIG.  5 A  showing movement of the syringe engagement mechanism from the closed state or configuration to the open state or configuration; 
         FIGS.  6 A- 6 C  are side views of engagement arms of a syringe engagement mechanism in accordance with one example of the present disclosure showing movement of the engagement arms between an open state or configuration and a closed state or configuration; 
         FIG.  7 A  is a side cross-sectional view of a syringe and a piston having a syringe engagement mechanism in accordance with one example of the present disclosure shown in an open state or configuration; 
         FIG.  7 B  is a side cross-sectional view of the syringe and the piston with the syringe engagement mechanism of  FIG.  7 A  shown in a closed state or configuration; 
         FIG.  8 A  is a side cross-sectional view of a syringe and a piston having a syringe engagement mechanism in accordance with one example of the present disclosure shown in an open state or configuration; 
         FIG.  8 B  is a side cross-sectional view of the syringe and the piston with the syringe engagement mechanism of  FIG.  8 A  shown in a closed state or configuration; 
         FIG.  8 C  is a side cross-sectional view of the syringe and the piston with the syringe engagement mechanism of  FIG.  8 A  shown in the open state or configuration; 
         FIG.  9 A  is a side cross-sectional view of a syringe and a piston having a syringe engagement mechanism in accordance with one example of the present disclosure shown in an open state or configuration; 
         FIG.  9 B  is a side cross-sectional view of the syringe and the piston with the syringe engagement mechanism of  FIG.  9 A  shown in a closed state or configuration; 
         FIGS.  9 C- 9 D  are side cross-sectional views of the syringe and the piston with the syringe engagement mechanism of  FIG.  9 A  showing movement of the syringe engagement mechanism from the closed state or configuration to the open state or configuration; 
         FIG.  10 A  is a perspective, partial cross-sectional view of a syringe and a piston having a syringe engagement mechanism in accordance with one example of the present disclosure shown in an open state or configuration; 
         FIG.  10 B  is a side cross-sectional view of the syringe and the piston with the syringe engagement mechanism shown in  FIG.  10 A ; 
         FIG.  10 C  is a perspective, partial cross-sectional view of the syringe and the piston with the syringe engagement mechanism shown in  FIG.  10 A  with the syringe engagement mechanism shown in a closed state or configuration; 
         FIG.  10 D  is a side cross-sectional view of the syringe and the piston with the syringe engagement mechanism shown in  FIG.  10 C ; 
         FIG.  10 E  is a side cross-sectional view of a syringe and a piston having a syringe engagement mechanism in accordance with one example of the present disclosure shown in an open state or configuration; 
         FIG.  10 F  is a side cross-sectional view of the syringe and the piston with the syringe engagement mechanism shown in  FIG.  10 E  with the syringe engagement mechanism shown in a closed state or configuration; 
         FIG.  10 G  is a side cross-sectional view of a syringe and a piston having a syringe engagement mechanism in accordance with one example of the present disclosure shown in an open state or configuration; 
         FIG.  1011    is a side cross-sectional view of the syringe and the piston with the syringe engagement mechanism shown in  FIG.  10 G  with the syringe engagement mechanism shown in a closed state or configuration; 
         FIG.  11 A  is a perspective, partial cross-sectional view of a syringe and a piston having a syringe engagement mechanism in accordance with one example of the present disclosure shown in an open state or configuration; 
         FIG.  11 B  is a side cross-sectional view of the syringe and the piston with the syringe engagement mechanism shown in  FIG.  11 A ; 
         FIG.  11 C  is a perspective, partial cross-sectional view of the syringe and piston with the syringe engagement mechanism shown in  FIG.  11 A  with the syringe engagement mechanism shown in a closed state or configuration; 
         FIG.  11 D  is a side cross-sectional view of the syringe and the piston with the syringe engagement mechanism shown in  FIG.  11 C ; 
         FIG.  12    is a side cross-sectional view of a syringe and a piston having a syringe engagement mechanism in accordance with one example of the present disclosure; and 
         FIG.  13    is a side cross-sectional view of a syringe and a piston having a syringe engagement mechanism in accordance with one example of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     As used in the specification, the singular form of “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. 
     For purposes of the description hereinafter, the terms “upper”, “lower”, “right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, “lateral”, “longitudinal”, and derivatives thereof shall relate to the disclosure as it is oriented in the drawing figures. 
     Spatial or directional terms, such as “left”, “right”, “inner”, “outer”, “above”, “below”, and the like, are not to be considered as limiting as the invention can assume various alternative orientations. 
     When used in relation to a syringe and/or a pressure jacket, the term “proximal” refers to a portion of a syringe and/or a pressure jacket nearest to an injector when a syringe and/or a pressure jacket is oriented for connecting to an injector. 
     The term “distal” refers to a portion of a syringe and/or pressure jacket farthest away from an injector when a oriented for connecting to the injector. 
     The term “radial” refers to a direction in a cross-sectional plane normal to a longitudinal axis of a syringe and/or pressure jacket extending between proximal and distal ends. 
     The term “circumferential” refers to a direction around an inner or outer surface of a sidewall of a syringe and/or a pressure jacket. 
     The term “axial” refers to a direction along a longitudinal axis of a syringe and/or a pressure jacket extending between the proximal and distal ends. 
     The term “flexible”, when used in connection with a syringe, means that at least a portion of a syringe, such as a sidewall of a syringe, is capable of bending or being bent, for example up to 180°, to change a direction in which it extends. 
     The terms “roll over”, “rolling over”, and “rolls upon itself” refer to an ability of a first portion of a syringe, such as a proximal portion of a sidewall of a syringe, to bend approximately 180° relative to a second portion of a syringe, such as a distal portion of a sidewall of a syringe, when urged by a piston of a fluid injector. 
     All numbers used in the specification and claims are to be understood as being modified in all instances by the term “about”. The term “about” means a range of plus or minus ten percent of the stated value. 
     Unless otherwise indicated, all ranges or ratios disclosed herein are to be understood to encompass any and all subranges or subratios subsumed therein. For example, a stated range or ratio of “1 to 10” should be considered to include any and all subranges between (and inclusive of) the minimum value of 1 and the maximum value of 10; that is, all subranges or subratios beginning with a minimum value of 1 or more and ending with a maximum value of 10 or less, such as but not limited to, 1 to 6.1, 3.5 to 7.8, and 5.5 to 10. 
     The term “at least” means “greater than or equal to”. 
     The term “includes” is synonymous with “comprises”. 
     It is to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification, are simply exemplary examples of the disclosure. Hence, specific dimensions and other physical characteristics related to the examples disclosed herein are not to be considered as limiting. 
     All documents, such as but not limited to issued patents and patent applications, referred to herein, and unless otherwise indicated, are to be considered to be “incorporated by reference” in their entirety. 
     Referring to the drawings in which like reference characters refer to like parts throughout the several views thereof, the present disclosure is generally directed to fluid injectors having a syringe engagement mechanism for engaging a syringe with a flexible sidewall and a piston engagement portion on at least a portion of the flexible sidewall. The syringe engagement mechanism has a plurality of engagement elements movable in a radial direction relative to the engagement portion of the syringe from a first position, wherein the plurality of engagement elements are disengaged from the engagement portion of the syringe, and a second position, wherein the plurality of engagement elements are engaged with the engagement portion of the syringe. 
     With reference to  FIG.  1   , a fluid injector  10  includes at least one injector head  12  and an injector housing  14 . The injector  10  may be supported on a support structure  13 . In some examples, as shown in  FIG.  1   , the fluid injector  10  may include two injector heads  12  arranged in a side-by-side orientation. Each injector head  12  may be formed at a front end of the injector housing  14  and may be configured for receiving and retaining at least one pressure jacket  16 . While  FIG.  1    illustrates the fluid injector  10  with two injector heads  12 , each with a corresponding pressure jacket  16 , other examples of the fluid injector  10  may include a single injector head  12  and a corresponding pressure jacket  16  or more than two injector heads  12  with a corresponding number of pressure jackets  16 . The pressure jacket  16  may be removably attached to the injector head  12  with one or more engagement elements, for example the one or more engagement elements described in PCT International Publications WO 2016/069714 and WO 2016/069711, the disclosures of which are incorporated herein by this reference. 
     Each injector head  12  includes a drive member, such as a reciprocally driven piston  19  (shown in  FIGS.  3 A- 3 B ), moved by a motor, the movement of which is controlled by a controller. Each piston  19  may be configured to extend into and from the respective injector head  12  through an opening in the front end of the injector housing  14 . Each piston  19  imparts a motive force to at least a portion of the syringe or to a plunger within the syringe disposed in the respective pressure jacket  16 , as described herein. 
     With continued reference to  FIG.  1   , the fluid injector  10  is configured to receive a syringe  20  within each pressure jacket  16 . The at least one pressure jacket  16  is typically a reusable component, while the syringe  20  is typically a single-use component. In some examples, the syringe  20  may be a multi-use component. The fluid injector  10  may have at least one bulk fluid source for filling the syringes  20  with fluid. At least one fluid path set may be fluidly connected with a discharge end of each syringe  20  for delivering fluid from the syringes  20  through tubing connected to a catheter, needle, or other fluid delivery connection (not shown) inserted into a patient at a vascular access site. Fluid flow into and from the at least one syringe  20  may be regulated by a fluid control module (not shown). The fluid control module may operate various pistons, valves, and/or flow regulating structures to regulate the delivery of the medical fluid, such as saline solution and contrast, to the patient based on user selected injection parameters, such as injection flow rate, duration, total injection volume, and/or ratio of contrast media and saline. Examples of suitable front-loading fluid injectors that may be used or modified for use with the herein-described system, including at least one pressure jacket  16  and syringe  20 , are disclosed in PCT Application Publication No. WO 2015/164783 and PCT Application Publication No. WO 2016/172467, the disclosures of which are incorporated herein by reference. 
     With reference to  FIGS.  2 A- 2 B , in certain examples, the syringe  20  generally includes a hollow body  25  defining an interior volume  27 . The body  25  has a forward or distal end  28 , a rearward or proximal end  30 , and a flexible sidewall  32  extending therebetween. The sidewall  32  of the syringe  20  defines a soft, pliable or flexible, yet self-supporting body that is configured to roll upon itself, as a rolling diaphragm, under the action of the piston  19 . In particular, the sidewall  32  is configured to roll such that its outer surface is folded and inverted in a radially inward direction as the piston  19  is moved in a distal direction ( FIG.  2 B ) and unrolled and unfolded in the opposite manner in a radially outward direction as the piston  19  is retracted in a proximal direction ( FIG.  2 A ). The sidewall  32  may have a smooth, substantially uniform structure, or it may have one or more ribs provided thereon to facilitate the rollover during an injection procedure. In some examples, the sidewall  32  and/or the end wall  34  may have a textured surface, or a combination of a smooth surface and a textured surface. One or more indicia (not shown) may be formed on the sidewall  32 . In some examples, the sidewall  32  may have a uniform thickness along its longitudinal length. In other examples, the sidewall  32  may have a non-uniform thickness along its longitudinal length. In specific examples, the sidewall  32  at or near the distal end  28  may be substantially rigid. As will be understood by one of skill in the art in view of the present disclosure, the engagement mechanisms described herein may also be used to engage a plunger slidably disposed within the barrel of a syringe, such as described, for example in U.S. Pat. Nos. 6,652,489; 9,173,995; and 9,199,033, the disclosures of which are incorporated by reference herein. According to these embodiments, the plunger may have a piston engagement portion, such as described herein, located on a proximal end of the plunger to interact with the plurality of engagement elements of the various embodiments of the engagement mechanisms described herein. 
     With continued reference to  FIGS.  2 A- 2 B , the rearward or proximal portion of the sidewall  32  connects to a closed end wall  34 , and a forward or distal portion  28  of the sidewall  32  defines a discharge neck  36  opposite the closed end wall  34 . The closed end wall  34  may have a concave shape to facilitate the initiation of the inversion or rolling of the sidewall  32  and/or to provide a receiving pocket to receive a distal end of piston  19 . For example, the closed end wall  34  may define a receiving end pocket  38  for interfacing directly with a similarly-shaped piston  19 . In particular examples, at least a portion of the piston  19  may be shaped to substantially match the shape of the closed end wall  34  or, alternatively, pressure from the piston  19  as it is moved distally may conform the end wall  34  to substantially match the shape of at least a portion of the piston  19 . The closed end wall  34  may have a non-uniform thickness, for example in a radial direction extending from a central longitudinal axis of the syringe  20 . In certain examples, at least a portion of the end wall  34  may be thicker near the center and thinner near the connection with the sidewall  32 . 
     With continued reference to  FIGS.  2 A- 2 B , the body  25  of the syringe  20  is adapted to be removably received in the interior portion of the pressure jacket  16 . The distal end  28  of the syringe  20  may be secured removably or permanently to a cap (not shown), removably attachable to the pressure jacket  16 , or configured with a retention surface to interact with a retaining force to retain the syringe  20  within the pressure jacket  16 . For example, the syringe  20  may be secured to the cap by an adhesive, solvent welding, or laser welding, or be removably secured to the cap, such as by a friction fit connection or other suitable mechanical connection. The distal end  28  may have a frusto-conical shape that gradually narrows from the sidewall  32  to the discharge neck  36 . In certain examples, the discharge neck  36  may terminate in a discharge port  40  having a connection member  42  for connecting to a cap, fluid path set, or other connection element. In some examples, the connection member  42  is a threaded interface having one or more threads. In other examples, the connection member  42  may have a luer-type connection. In further examples, the side wall  32  may have one or more lips or grooves that interact with corresponding grooves or lips on the pressure jacket  16  to releasably or non-releasably retain the syringe  20  within the pressure jacket  16 . 
     The outer diameter of the syringe  20  may be dimensioned such that the syringe  20  fits within the interior space defined by the throughbore and inner surface of the pressure jacket  16 . In one example, the syringe  20  fits snuggly but removably within the pressure jacket  16  such that the outer surface of the syringe  20  abuts at least a portion of the inner surface of the walls of the pressure jacket  16 . In another example, the syringe  20  fits loosely within the pressure jacket  16  such that there is a gap between at least a portion of the outer surface of the syringe  20  and the inner surface of the pressure jacket  16 . The syringe  20  may be expanded under pressure during an injection procedure such that the outer surface of the syringe  20  abuts the inner surface of the pressure jacket  16 . Examples of suitable pressure jacket features are described in PCT International Application No. PCT/US2017/051473, the disclosure of which is incorporated herein by this reference. 
     The end wall  34  may have a central portion  44  having a substantially dome-shaped structure and a piston engagement portion  46  (hereinafter referred to as “engagement portion  46 ”) extending proximally from the central portion  44 . In some examples, the engagement portion  46  may extend in a proximal direction along a longitudinal axis of the syringe  20  from an approximate midpoint of the central portion  44 . In some examples, a diameter of the engagement portion  46  may be uniform, such that the engagement portion  46  has a substantially cylindrical structure. In other examples, the diameter of the engagement portion  46  may be non-uniform. For example, the diameter of the engagement portion  46  may gradually decrease or increase in the proximal direction. While the engagement portion  46  is shown in  FIGS.  2 A- 2 B  as being substantially flush with the proximal end  30  of the syringe  20 , in certain examples the engagement portion  46  may extend proximally beyond the proximal end  30  of the syringe  20 . 
     The engagement portion  46  may be monolithically formed with the syringe body  25 , or it may be removably or non-removably attached to the central portion  44  of the end wall  34 , such as by welding, adhesion, or clip attachment, or other fastening mechanism. The engagement portion  46  is configured for interacting with an engagement mechanism on the piston  19  of the fluid injector  10 , as described herein. 
     The syringe  20  may be made of any suitable medical-grade plastic or polymeric material, desirably a clear or substantially translucent plastic material. The material of the syringe  20  is desirably selected to meet the required tensile and planar stress requirements, water vapor transmission, and chemical/biological compatibility. 
     In certain embodiments, suitable syringes  20  include a rolling diaphragm-type syringe as described in WO 2015/164783 and WO 2016/172467 having a flexible thin sidewall which rolls upon itself when acted upon by the piston  19  such that an outer surface of the sidewall at a folding region is folded in a radially inward direction as the piston  19  is advanced from the proximal end to the distal end  28  and such that the outer surface of the sidewall  32  at the folding region is unfolded in a radially outward direction as the piston  19  is retracted from the distal end  28  toward the proximal end  30 . Such rolling diaphragm syringes may be made from a suitable medical-grade plastic and have a sidewall thickness ranging from 0.0050 inches to 0.20 inches, or in other embodiments from 0.010 inches-0.15 inches. Upon pressurization of the syringe  20  by distal movement of the piston  19 , the fluid pressure within the rolling diaphragm syringe causes the sidewall to expand radially outward. This effect is enhanced by the relative thinness of the syringe sidewall compared to conventional syringes. As the syringe sidewall expands radially outward, it contacts the interior surface of the pressure jacket  16 , which limits further expansion of the syringe sidewall, thereby preventing breaking of the syringe wall. 
       FIGS.  3 A- 3 B  show the syringe  20  in combination with a syringe engagement mechanism  48  (hereinafter referred to as “engagement mechanism  48 ”) of the piston  19  in accordance with one example of the present disclosure. The components of the syringe  20  shown in  FIGS.  3 A- 3 B  are substantially similar to the components of the syringe  20  described herein with reference to  FIGS.  2 A- 2 B . The engagement portion  46  of the syringe  20  is configured for interacting with one or more engagement pins or surfaces of the engagement mechanism  48  that reversibly move radially inward and outward to engage and disengage, respectively, the engagement portion  46  of the syringe  20 . 
     In various examples, the engagement mechanism  48  has one or more engagement elements  56 , such as engagement fingers or surfaces, movable in a radial direction relative to the engagement  46  portion of the syringe  20  between a first position, where the plurality of engagement elements  56  are disengaged from the engagement portion  46  of the syringe  20 , and a second position, where the plurality of engagement elements  56  are engaged with the engagement portion  46  of the syringe  20 . The engagement mechanism  48  further has a drive mechanism for moving the plurality of engagement elements  56  such as fingers or surfaces between the first position and the second position. 
     In various examples, the inward/outward radial movement of the engagement elements  56  may be effected by a proximal/distal movement of the piston  19 . The engagement elements  56  may be moved radially inward/outward via linear movement, arcuate movement, or a combination of linear and arcuate movement. In various examples, movement of the piston  19  in the proximal direction may cause the engagement elements  56  to contact and lock onto the engagement portion  46  of the syringe  20  so that the distal end  30  of the syringe  20  may be pulled by the piston  19  in a proximal direction to fill the syringe  20  with a medical fluid. Conversely, movement of the piston  19  in a distal direction may cause the engagement elements  56  to be released from contacting the engagement portion  46  of the syringe  20  such that the syringe  20  may be removed from the pressure jacket  16  and the injector  10 . In various examples, the piston  19  and/or the engagement elements  56  may be movable by a motor drive, a solenoid drive, a pneumatic drive, a hydraulic drive, or due to an activation of an electro-active polymer, an electromagnetic mechanism, or a nitinol wire or other shape memory alloy-based mechanism, as discussed herein. 
     With continued reference to  FIGS.  3 A- 3 B , the drive mechanism of the engagement mechanism  48  is contained at least partially within the piston  19 . In some examples, the drive mechanism has a plurality of parts operatively connected with the piston  19  for moving the plurality of engagement elements  56  between the first position and the second position. In some examples, the drive mechanism has an outer piston sleeve  50  and an abutment section  52  movably received within the outer piston sleeve  50  at a distal end thereof. The outer piston sleeve  50  has a substantially cylindrical structure with an open proximal end and an open distal end. The abutment section  52  has an outer engagement surface  54  at its distal end for engaging at least a portion of the distal surface  44  of the syringe  20  when the piston  19  is advanced distally to engage with the syringe  20 . In some examples, the abutment section  52  of the piston  19  may contact at least a portion of the proximal end  30  of the syringe  20 , such as the distal surface  44  of the end wall  34 . The outer engagement surface  54  may be shaped to correspond to the shape of the end wall  34  such that the outer engagement surface  54  is in surface-to-surface contact with at least a portion of the end wall  34  of the syringe  20 . The outer engagement surface  54  and outer piston sleeve  50  define a surface over which the sidewall  32  of the syringe  20  may roll over during a fluid filling or a fluid delivery process due to proximal or distal movement of the piston  19 , respectively. An opening  55  is formed in a central portion of the abutment section  52 . The opening  55  is configured to receive at least a portion of the engagement portion  46  of the syringe  20  when the abutment section  52  substantially contacts the end wall  34  of syringe  20 . Desirably, an inner diameter of the opening  55  is larger than an outer diameter of the widest portion of the engagement portion  46  to allow free insertion of the engagement portion  46  into the opening  55  during distal movement of the piston  19  toward the end wall  34  of syringe  20  or proximal movement of the end wall  34  of syringe  20  toward the piston  19 , for example during insertion of the syringe  20  into the pressure jacket  16 . 
     The abutment section  52  is axially movable relative to the outer piston sleeve  50 , which is held in a substantially fixed position, for example due to friction between the outer piston sleeve  50  and the piston. The abutment section  52  is movable or slidable in an axial direction relative to the outer piston sleeve  50  to control the state or position of one or more engagement elements  56 , such as one or more engagement elements, as described herein. The movement of the abutment section  52  relative to the outer piston sleeve  50  is configured to allow engagement or disengagement of the one or more engagement elements  56  with the engagement portion  46  of the syringe  20 . 
     The piston  19  also has an inner piston sleeve  58  that is axially movable relative to the outer piston sleeve  50 . The inner piston sleeve  58  is connected to the abutment section  52  such that movement of the abutment section  52  results in a corresponding movement of the inner piston sleeve  58 , and vice versa. A collar  60  is fixedly mounted within the outer piston sleeve  50 . In some examples, the collar  60  may have a circumferential recess  59  that is configured to engage a projection  61  protruding from an inner surface of the outer piston sleeve  50 . The collar  60  has a longitudinal opening  66  configured to receive at least a portion of the engagement portion  46  of the syringe  20 . An inner diameter of the longitudinal opening  66  may be larger than an outer diameter of the widest portion of the engagement portion  46  to allow free insertion of the engagement portion  46  into longitudinal opening  66 . 
     With continued reference to  FIGS.  3 A- 3 B , the abutment section  52  is connected to the inner piston sleeve  58 , such as by one or more fasteners  57  (shown in  FIG.  4 B ). In this manner, axial movement of the inner piston sleeve  58  results in a corresponding axial movement of the abutment section  52 , and vice versa. 
     The inner piston sleeve  58  and the abutment section  52  are movable or slidable in an axial direction relative to the outer piston sleeve  50  and the collar  60  with movement of the piston rod  64 . For example, the inner piston sleeve  58  and the abutment section  52  may be movable between a first position ( FIG.  3 A ), where the one or more engagement elements  56  are disengaged from the engagement portion  46  of the syringe  20  and a second position ( FIG.  3 B ), wherein the one or more engagement elements  56  are engaged with the engagement portion  46 . In some examples, the inner piston sleeve  58  and the abutment portion  52  may be biased to the second position by a biasing mechanism, such as a spring  76 . A biasing force of the spring  76  may be adjustable by moving the adjustment element  77  in a distal direction (to increase the biasing force) or in a proximal direction (to reduce the biasing force) or vice versa. The adjustment element  77  may be a screw that is threadably engaged with the collar  60  such that the spring  76  is disposed between the head of the screw and the proximal surface of the inner piston sleeve  58  or a washer  81  abutting the proximal surface of the inner piston sleeve  58 . The adjustment element  76  desirably extends through an opening in the inner piston sleeve  58 . In some examples, inner piston sleeve  58  and the abutment section  52  may be movable or slidable in an axial direction relative to the outer piston sleeve  50  and the collar  60  by way of an electrical, pneumatic, electromagnetic, electroactive polymer-based, shape memory alloy-based or hydraulic actuation mechanism that is operable independent of the direction of movement of the piston  19 . 
     The motion of the abutment section  52  relative to the outer piston sleeve  50  and the collar  60  is limited to allow engagement or disengagement of the one or more engagement elements  56  with the engagement portion  46  of the syringe  20 . For example, with reference to  FIG.  4 A , such relative motion can be limited using a metal rod, polymer rod, or dowel  63  fixed to the piston rod  64 , where the dowel  63  passes through and seats within a slot  65  (shown in  FIG.  4 B ) formed in the inner piston sleeve  58  that is directly connected to the collar  60  and the abutment section  52 . In some examples, the abutment section  52  may be movable by about 0.100 to 0.150 inches, for example 0.125 inches, with the movement of the inner piston sleeve  58  before the outer piston sleeve  50  and the abutment section  52  move at the same time. In some examples, the inner piston sleeve  58  may be in frictional contact with an inner sidewall of the injector head (not shown). This frictional contact may be used to restrain the inner piston sleeve  58  while allowing the piston rod  64  to move, thereby moving the dowel  63  within the slot  65 . Once the dowel  63  engages the proximal or distal end of the slot  65 , the frictional force holding the inner piston sleeve  58  is overcome, and the piston rod  64  and the inner piston sleeve  58  may be moved together. 
     Using this range of movement of the abutment section  52 , the collar  60 , and the inner piston sleeve  58  relative to the piston rod  64  and the outer piston sleeve  50  (delimited by the longitudinal length of the slot  65 ), the one or more engagement elements  56  can be moved between the first (open) position ( FIG.  3 A ) and a second (closed) position ( FIG.  3 B ). For example, initial movement of the piston rod  64  in the distal direction may cause the outer piston sleeve  50  to move distally relative to the abutment section  52 , which is restrained due to the frictional engagement of the inner piston sleeve  58  with the injector head. Such relative movement of the abutment section  52  and the outer piston sleeve  50  may cause the one or more engagement elements  56  to be retracted in a radially outward direction to allow the syringe  20  to be removed from (on installed on) the injector  10 . Conversely, movement of the piston rod  64  in the proximal direction may cause the outer piston sleeve  50  to move proximally relative to the abutment section  52 , which is restrained due to the frictional engagement of the inner piston sleeve  58  with the injector head  12 . Such relative movement of the abutment section  52  and the outer piston sleeve  50  may cause the one or more engagement elements  56  to be extended in a radially inward direction to engage the engagement portion  46  of syringe  20  to allow for retraction of end wall  34  and filling of syringe  20 . 
     With continued reference to  FIGS.  3 A- 3 B , the engagement elements  56  may be at least one, and optionally, a plurality of engagement elements  56  spaced apart circumferentially around a cavity  78  of the inner piston sleeve  58 . In some examples, a single engagement element  56  may be configured to contact the engagement portion  46  of the syringe  20 . The engagement elements  56  may be spaced apart at equal or unequal angular intervals from one another. The engagement elements  56  may be movable between a first position ( FIG.  3 A ), where the engagement elements  56  do not contact the engagement portion  46  of the syringe  20 , and a second position ( FIG.  3 B ), wherein the engagement elements  56  contact the outer surface of the engagement portion  46  of the syringe  20 . In some examples, the engagement elements  56  may have a pointed terminal end  86  or tooth configured for at least partially embedding into the material of the engagement portion  46  of the syringe  20  when the engagement elements  56  are positioned in the second position ( FIG.  3 B ). In some examples, the engagement elements  56  may be configured to move from the first position to the second position immediately upon proximal movement of the piston  19 . In other examples, the engagement elements  56  may be configured to gradually and progressively move from the first position toward the second position with proximal movement of the piston  19  to continuously increase the gripping force between the engagement element  56  and the engagement portion  46  of the syringe  20 . For example, the pointed terminal end  86  may be under a continually increasing force to increase the “bite” with the engagement portion  46  as the piston is moved in a proximal direction. 
     In some examples, the engagement elements  56  may be pivotable about a pivot pin  80  on the inner piston sleeve  58  to move the engagement element  56  between the first position and the second position. Movement of the engagement elements  56  may be constrained by a pin  83  on the collar  60  that is received within a track  85  on each of the engagement elements  56 . The track  85  may be offset from the pivot pin  80  and may be shaped such that it directs the movement of the engagement elements  56  between the first and the second position in an arcuate motion about the pivot pin  80 . The engagement elements  56  may also be biased by a biasing mechanism (not shown) to one of the first position and the second position. To move the engagement elements  56  from the second position to the first position, at least a portion of each engagement element  56  may be engaged by the outer engagement surface  54  of the abutment section  52 . Because the engagement elements  56  are retained on the collar  60 , movement of the abutment section  52  relative to the collar  60  causes the outer engagement surface  54  of the abutment section  52  to contact a distal surface of the engagement elements  56 . Continued movement of the abutment section  52  relative to the collar  60  causes the engagement elements  56  to be deflected in a radially outward direction to the first position. In this manner, the engagement elements  56  can be disengaged from contacting the engagement portion  46  of the syringe  20 . 
     Fluid can be delivered from the interior volume  27  of the syringe  20  by driving the piston  19  in the distal direction. If the interior volume  27  of the syringe  20  is fully or partially filled, fluid can be delivered from the syringe  20  by rolling over the sidewall  32  upon itself with the distal movement of the piston  19 . During movement of the piston  19  in the distal direction, such as shown by arrow A in  FIG.  3 A , the abutment section  52  contacts the proximal surface of the end wall  34  of the syringe  20 . The abutment section  52  is moved to the first position without rolling over the sidewall  32  of the syringe  20  because the piston rod  64  is moved only to allow the dowel  63  to contact the distal end of the slot  65 , thereby moving the engagement elements  56  to the first position. In particular, initial distal movement of the piston  19  urges the outer engagement surface  54  of the abutment section  52  in contact with at least a portion of each engagement element  56  and causes the engagement elements  56  to be deflected in a radially outward direction, thereby opening a clearance space between the engagement elements  56  to allow insertion or removal of the engagement portion  46  of the syringe  20  in the space between the engagement elements  56 . 
     To fill the syringe  20  with fluid, the piston  19  is moved in a proximal direction in the direction of arrow B in  FIG.  3 B . During movement of the piston  19  in the proximal direction, such as shown by arrow B in  FIG.  3 B , the abutment section  52  moves relative to the outer sleeve  50 . During such movement, the engagement elements  56  are moved to the second position toward the engagement portion  46  of the syringe  20  in a radially inward direction by pivoting about the pivot pin  80 . The pointed terminal end  86  digs into the outer surface of the engagement portion  46  of the syringe  20  as described herein, to provide a grabbing force between the engagement elements  56  and the engagement portion  46 . 
       FIGS.  5 A- 5 E  show the proximal end  30  of the syringe  20  in combination with an engagement mechanism  48  of the piston  19  in accordance with various aspects of the present disclosure. The components of the syringe  20  shown in  FIGS.  5 A- 5 E  are substantially similar to the components of the syringe  20  described herein with reference to  FIGS.  2 A- 2 B . The engagement portion  46  of the syringe  20  is configured for interacting with one or more engagement elements  56 , such as one or more engagement elements  56  of the engagement mechanism  48 . The engagement elements  56  are configured to move between the first position and the second position by moving radially inward and outward to engage and disengage, respectively, the engagement portion  46  of the syringe  20  in a manner similar to the engagement of the engagement elements  56  of the engagement mechanism  48  with the engagement portion  46  of the syringe  20  described herein with reference to  FIGS.  3 A- 3 B . 
     The engagement mechanism  48  has a drive mechanism  88  for moving the plurality of engagement elements  56  between a first position, wherein the plurality of engagement elements  56  are disengaged from the engagement portion  46  of the syringe  20 , and a second position, wherein the plurality of engagement elements  56  are engaged with the engagement portion  46  of the syringe  20 . The drive mechanism  88  has an outer piston sleeve  50  and an abutment section  52  fixed relative to the outer piston sleeve  50  at a distal end thereof. The outer piston sleeve  50  has a substantially cylindrical structure with an open proximal end and an open distal end. The abutment section  52  has an outer engagement surface  54  for contacting at least a portion of the proximal end  30  of the syringe  20 , such as the end wall  34 . An opening  55  is formed in a central portion of the abutment section  52  and is configured to receive at least a portion of the engagement portion  46  of the syringe  20  when the abutment section  52  contacts the proximal end  30  of the syringe  20 . 
     The drive mechanism  88  further has an inner piston sleeve  58  that is axially movable relative to the outer piston sleeve  50 . The inner piston sleeve  58  may be biased to the first position (shown in  FIG.  5 A ) or the second position (not shown) by a biasing mechanism, such as a spring  79 . Movement of the inner piston sleeve  58  in a distal direction and toward the outer piston sleeve  58  in a direction of arrow A in  FIG.  5 B  compresses the spring  79  from a first state ( FIG.  5 A ) to a second state ( FIG.  5 B ). 
     The inner piston sleeve  58  has a bar or a link  152  with a distal end pivotally movable about a pivot point  154  fixed relative to the outer piston sleeve  50  and a second end received within a slot  156 . Movement of the inner piston sleeve  58  in the distal direction and toward the outer piston sleeve  58  moves the second end of the link  152  from a distal end toward a proximal end of the slot  156  ( FIG.  5 B ). Continued movement of the inner piston sleeve  58  in the distal direction and toward the outer piston sleeve  50  further moves the link  152  proximally within the slot  156  such that a distal end  158  of the inner piston sleeve  58  contacts a proximal end  75  of the engagement elements  56 . The contact between the distal end  158  of the inner piston sleeve  58  with the proximal end  75  of the engagement elements  56  urges the engagement elements  56  in a radially inward direction due to the angled shape of the distal end  158  of the inner piston sleeve  58  ( FIG.  5 C ). As the engagement elements  56  are urged in a radially inward direction, the engagement elements  56  engage the engagement portion  46  of the syringe  20  to allow the end wall  34  of the syringe  20  to be moved in a proximal direction during filling of the syringe  20 . As shown in  FIG.  5 C , the proximal second end of link  152  is secured in the inverted proximal vee  173  of slot  156 , reversibly locking the engagement mechanism in the second engaged positon with the engagement elements  56  engaged with the engagement portion  46  of syringe  20 , for example by where the pointed terminal ends  86  of the engagement elements  56  having dug into the surface of engagement portion  46 . Movement of the engagement elements  56  from the first position ( FIG.  5 A ) to the second position ( FIG.  5 C ) may bias an engagement element biasing mechanism, such as a spring  160 , from a first position to a second position. In this position ( FIG.  5 C ), the piston  19  may be retracted in the proximal direction with concomitant unrolling and filling of the syringe  20  with a medical fluid 
     With reference to  FIG.  5 D , after retraction of the piston  19  to fill syringe  20  with the fluid, delivery of the fluid by distal movement of the piston  19  also disengages the proximal second end  175  of link  152  from the inverted proximal vee  173  of slot  156 , at this point movement of the inner piston sleeve  58  in a proximal direction of arrow B after fluid delivery moves the second end of the link  152  from the proximal end toward the distal end of the slot  156 , thereby disengaging the distal end  158  of the inner piston sleeve  58  from contacting the proximal end  75  of the engagement elements  56 . The engagement elements  56  can then be retracted to the first position ( FIG.  5 E ) due to the restoring force of the spring  160 . Movement of the engagement elements  56  from the second position ( FIG.  5 C ) to the first position ( FIG.  5 D ) disengages the engagement elements  56  from the engagement portion  46  of the syringe  20  to allow removal of the syringe  20  ( FIG.  5 E ). 
     With reference to  FIGS.  6 A- 6 C , each engagement element  56  may be movable between the first position, where the engagement element  56  is disengaged from the engagement portion  46  of the syringe  20  (not shown), and a second position, where the engagement element  56  is engaged with the engagement portion  46  of the syringe with axial movement of a drive mechanism  88 . The engagement element  56  shown in  FIGS.  6 A- 6 C  may have the same structure as the engagement elements  56  shown in  FIGS.  3 A- 3 B  including pointed terminal ends  86  or teeth for digging into the surface of engagement portion  46  to provide a secure connection between the engagement element  56  and engagement portion  46 . The engagement element  56  may be pivotable about a pivot pin  80 . Movement of the engagement element  56  may be constrained by a pin  83  that is received within a track  85 . The track  85  is offset from the pivot pin  80  and may be shaped such that it directs the movement of the engagement elements  56  from the first to the second position in an arcuate motion about the pivot pin  80 . The drive mechanism  88  may be operated by distal and proximal movement of the piston or may be an activatable drive mechanism, for example a mechanism that is activated by one or more of a linear electric motor or actuator, a rotary electric motor or actuator, a solenoid, a pneumatic mechanism, a hydraulic mechanism, an electromagnetic mechanism, an electroactive polymer mechanism, a shape-memory alloy (such as nitinol wire)-based mechanism, and any combination thereof. 
     With continued reference to  FIGS.  6 A- 6 C , according the various aspects, the drive mechanism  88  may be formed on or within the piston  19  (not shown). According to certain aspects, the drive mechanism  88  may have a first sloped surface  88   a  and a second sloped surface  88   b  axially offset from the first sloped surface  88   a . The first and second sloped surfaces  88   a ,  88   b  are angled in a direction pointing radially and proximally away from the engagement portion  46 . The drive mechanism  88  is movable from a first position (shown in  FIG.  6 A ) to a second position (shown in  FIG.  6 B ) via axial movement in a direction of arrow G in  FIG.  6 A  and from the second position to the first position by axial movement in a direction opposite of arrow G. In the first position, the first sloped surface  88   a  is axially offset from a distal end  75  of the engagement element  56 . With distal movement of the drive mechanism  88 , the first sloped surface  88   a  contacts the distal end  75  of the engagement element  56 , forcing the distal end  75  to slide along the first sloped surface  88   a . Such sliding movement of the distal end  75  of the engagement element  56  causes the engagement element  56  to pivot about the pivot pin  80  and the pin  83  to move from a first end to a second end of the track  85 . The pivoting movement of the engagement element  56  results in the pointed terminal end  86  moving radially inward such that it contacts the engagement portion  46  of the syringe ( FIG.  6 B ). Continued distal movement of the drive mechanism  88  engages the distal end  75  of the engagement element  56  with the second sloped surface  88   b  ( FIG.  6 C ). Such engagement between the distal end  75  of the engagement element  56  and the second sloped surface  88   b  further forces the pointed terminal end  86  to move radially inward such that the pointed terminal end  86  digs into and becomes embedded into the material of the engagement portion  46  of the syringe. With such engagement, the piston (not shown), can be moved proximally and retract the engagement portion  46  and distal end  30  of syringe  20  (see  FIGS.  2 A- 2 B ), to fill the syringe with fluid, as described herein with reference to  FIGS.  3 A- 3 B . 
       FIGS.  7 A- 7 B  show the proximal end  30  of the syringe  20  in combination with an engagement mechanism  48  of the piston  19  in accordance with various examples of the present disclosure. The components of syringe  20  shown in  FIGS.  7 A- 7 B  are substantially similar to the components of the syringe  20  described herein with reference to  FIGS.  2 A- 2 B . The engagement portion  46  of the syringe  20  is configured for interacting with one or more engagement elements, such as one or more engagement elements  56  of the engagement mechanism  48 . The engagement elements  56  are configured to move radially inward and outward to engage and disengage, respectively, the engagement portion  46  of the syringe  20  in a manner similar to the engagement of the engagement elements  56  of the engagement mechanism  48  with the engagement portion  46  of the syringe  20  described herein with reference to  FIGS.  3 A- 3 B . According to various embodiments, the inward/outward movement of the engagement elements  56  in  FIGS.  7 A- 7 B  may occur independently of the proximal/distal movement of the piston  19  due to operation of a drive mechanism  88 . 
     With continued reference to  FIGS.  7 A- 7 B , the drive mechanism  88  is configured for controlling the movement of the engagement elements  56  between a first, or disengaged position ( FIG.  7 A ) and a second, engaged position ( FIG.  7 B ). The drive mechanism  88  is disposed within the outer piston sleeve  50 . Similar to the piston  19  shown in  FIGS.  3 A- 3 B , the piston  19  in  FIGS.  7 A- 7 B  has the abutment section  52  at a distal end thereof for engaging with the end wall  34  of the syringe  20 . Activation of the drive mechanism  88  moves the abutment section  52  relative to the outer sleeve  50 , such as by advancing the abutment section  52  in a distal direction. Such movement of the abutment section  52  moves the engagement elements  56  in a radially inward direction to engage the engagement portion  46  of the syringe  20 . The engagement elements  56  may be movable between a first position ( FIG.  7 A ), where the engagement elements  56  do not contact the engagement portion  46  of the syringe  20 , and a second position ( FIG.  7 B ), wherein the engagement elements  56  contact the outer surface of the engagement portion  46  of the syringe  20  and the pointed terminal end  86  digs into and becomes embedded into the material of the engagement portion  46 . In some examples, radial movement of the engagement elements  56  may further be a function of proximal movement of the piston  19  in a direction of arrow B shown in  FIG.  7 B . That is, as the piston  19  is moved further in the proximal direction, the force of the “bite” or radially inward force between the engagement elements  56  and the pointed terminal ends  86  with the engagement portion  46  increases so that any proximal slipping of the pointed terminal ends  86  through the material of the engagement portion  46  is counteracted. For example, during initial movement of the piston  19  in the proximal direction, the engagement elements  56  may be advanced radially inward to an initial contact position where the engagement elements  56  contact the outer surface of the engagement portion  46  of the syringe  20 . With continued proximal movement of the piston  19 , the engagement elements  56  may continue to move in a radially inward direction from the initial contact position such that the engagement elements  56  and pointed terminal ends  86  dig into or become embedded within the material of the engagement portion  46  of the syringe  20  to increase the holding force on the syringe  20 . The engagement elements  56  may move to a final contact position having a maximum radial displacement from the initial contact position at a final proximal position of the piston  19 . In other examples, radial movement of the engagement elements  56  may be controlled independent of the proximal or distal movement of the piston  19 . A linkage mechanism  73  connects the drive mechanism  88  with the engagement elements  56  to effect the movement of the engagement elements  56  with actuation of the drive mechanism  88 . 
     Various embodiments of the drive mechanism  88  may be mechanically, electrically, pneumatically, and/or hydraulically operated. For example, the drive mechanism  88  may have an electric or electromechanical mechanism, such as a linear or rotary electric motor, or a solenoid. In other examples, the drive mechanism  88  may be activated/deactivated by an electromagnetic mechanism, an electroactive polymer mechanism, or a shape-memory alloy (such as nitinol wire)-based mechanism. Various combinations of these mechanisms is also contemplated at being within the scope of the present disclosure. In some examples, the drive mechanism  88  may be selectively energized, such as during proximal or distal movement of the piston  19 . In other examples, the drive mechanism  88  may be constantly energized, regardless of whether the piston  19  is stationary, or moving in the proximal or distal direction. 
     In certain embodiments, movement of the drive mechanism  88  relative to the outer piston sleeve  50  is configured to allow engagement or disengagement of the engagement elements  56  with engagement portion  46  of the syringe  20 . In some examples, movement of the abutment section  52  in a proximal direction relative to the outer piston sleeve  50  and away the syringe  20  may result in the drive mechanism  88  retracting the engagement elements  56  in a radially outward direction to allow the syringe  20  to be removed from the injector  10 . Conversely, movement of the abutment section  52  in a distal direction relative to the outer piston sleeve  50  and toward the syringe  20  may result in the drive mechanism  88  extending the engagement elements  56  in a radially inward direction to engage the engagement portion  46  of the syringe  20 . In other examples, operation or activation of the drive mechanism  88  may be independent of the movement of the abutment section  52 , the outer piston sleeve  50 , and/or the piston  19 , such that the engagement elements  56  can be selectively moved between the first position and the second position based upon operation of the drive mechanism  88  only. 
       FIGS.  8 A- 8 C  show the proximal end  30  of the syringe  20  in combination with an engagement mechanism  48  of the piston  19  in accordance with various examples of the present disclosure. The components of the syringe  20  shown in  FIGS.  8 A- 8 C  are substantially similar to the components of the syringe  20  described herein with reference to  FIGS.  2 A- 2 B . The engagement portion  46  of the syringe  20  is configured for interacting with one or more engagement elements, such as one or more engagement elements  56  of the engagement mechanism  48 . The engagement elements  56  are configured to move radially inward and outward to engage and disengage, respectively, the engagement portion  46  of the syringe  20  in a manner similar to the movement of the engagement elements  56  relative to the engagement portion  46  of the syringe  20  described herein with reference to  FIGS.  3 A- 3 B . 
     Radial movement of the engagement elements  56  may be controlled independently of the proximal or distal movement of the piston  19 . For example, after the piston  19  is advanced in a distal direction such that the abutment section  52  contacts the proximal end  30  of the syringe  20 , the engagement elements  56  may be advanced radially inward with actuation of the drive mechanism  88 , such as a solenoid operated piston  188 . In some examples, the drive mechanism  88  may rotate each of the engagement elements  56  about the pivot pin  80  in a direction of arrows C in  FIG.  8 B  to engage ( FIG.  8 A ) or disengage ( FIG.  8 C ) the engagement elements  56  from the engagement portion  46 . The engagement elements  56  may be biased to move in a radially inward direction from their initial position to a final position due to a biasing mechanism such as a spring. Movement of the engagement elements  56  radially inwardly may cause the material of the engagement portion  46  of the syringe  20  is at least partially deformed. For example, the engagement elements  56  may be at least partially embedded into the material of the engagement portion  46  such that the post of the engagement portion  46  is deformed from its initial configuration ( FIG.  8 A ) to a final configuration ( FIGS.  8 B- 8 C ) due to the force applied by the biasing mechanism. In some examples, the deformed engagement portion  46  may have an inverted “T” shape, wherein the engagement elements  56  engage at least a portion of the deformed engagement portion  46 . Activation of the solenoid operated piston  188  moves the solenoid operated piston  188  in a distal direction, causing the engagement elements to move against the biasing force of the biasing mechanism and actively engage or disengage from the engagement portion  46 . 
       FIGS.  9 A- 9 D  show the proximal end  30  of the syringe  20  in combination with an engagement mechanism  48  of the piston  19  in accordance with other examples of the present disclosure. The components of the syringe  20  shown in  FIGS.  9 A- 9 D  are substantially similar to the components of the syringe  20  described herein with reference to  FIGS.  2 A- 2 B . The engagement portion  46  of the syringe  20  is configured for interacting with one or more engagement elements, such as one or more engagement elements  56 , of the engagement mechanism  48 . The engagement elements  56  are configured to move radially inward and outward to engage and disengage, respectively, the engagement portion  46  of the syringe  20  in a manner similar to the movement of the engagement elements  56  relative to the engagement portion  46  of the syringe  20  described herein with reference to  FIGS.  3 A- 3 B . 
     With continued reference to  FIGS.  9 A- 9 D , the engagement mechanism  48  has a drive mechanism  88  for moving the plurality of engagement elements  56  between a first position, wherein the plurality of engagement elements  56  are disengaged from the engagement portion  46  of the syringe  20 , and a second position, wherein the plurality of engagement elements  56  are engaged with the engagement portion  46  of the syringe  20 . The engagement mechanism  48  has an outer piston sleeve  50  and an abutment section  52  fixed relative to the outer piston sleeve  50  at a distal end thereof. The outer piston sleeve  50  has a substantially cylindrical structure with an open proximal end and an open distal end. The abutment section  52  has an outer engagement surface  54  for contacting at least a portion of the proximal end  30  of the syringe  20 , such as the end wall  34 . An opening  55  is formed in a central portion of the abutment section  52  and is configured to receive at least a portion of the engagement portion  46  of the syringe  20  when abutment section  52  contacts the syringe  20 . 
     The engagement mechanism  48  further has an inner piston sleeve  58  that is axially movable relative to the outer piston sleeve  50 . The inner piston sleeve  58  may be biased to a first position (shown in  FIG.  9 A ) by a biasing mechanism, such as a spring  79 . Movement of the inner piston sleeve  58  in a distal direction and relative to the outer piston sleeve  58  in a direction of arrow A in  FIG.  9 B  compresses the spring  79  from a first state ( FIG.  9 A ) to a second state ( FIG.  9 B ). 
     With continued reference to  FIGS.  9 A- 9 D , the drive mechanism  88  has a solenoid  165  having a two or more locking levers  166  at a proximal end of the solenoid  165 . Each locking lever  166  is rotatably mounted on a pivot pin  168  such that each locking lever  166  is rotatable about the pivot pin  168 . In some examples, the locking levers  166  may be biased in a radially outward direction by a biasing mechanism (not shown). Proximal ends of the locking levers  166  are configured for being received within a groove  170  on an inside surface of the outer piston sleeve  50 . Movement of the inner piston sleeve  58  in the distal direction relative to the outer piston sleeve  58 , such as due to movement of the piston  19 , moves the locking levers  166  to a position where the locking levers  166  can be expanded radially outward by rotating in a direction of arrow C in  FIG.  9 B  when the locking levers  166  are axially aligned within the groove  170 . Movement of the locking levers  166  in a radially outward direction into the groove  170  locks the locking levers  166 , and thereby the inner piston sleeve  58  from moving proximally relative to the outer piston sleeve  50 . Distal movement of the inner piston sleeve  58  relative to the outer piston sleeve  50  is permitted due to an angled surface  172  of the groove  170  deflecting the proximal ends of the locking levers  166  in a radially inward direction ( FIG.  9 C ). 
     Concurrent with movement of the inner piston sleeve  58  in the distal direction relative to the outer piston sleeve  58 , the inner piston sleeve  58  urges a distal end  158  of the inner piston sleeve  58  to contact a proximal end  75  of the engagement elements  56 . Contact between the distal end  158  of the inner piston sleeve  58  with the proximal end  75  of the engagement elements  56  urges distal ends of the engagement elements  56  and the pointed terminal ends  86  in a radially inward direction due to the angled shape of the distal end  158  of the inner piston sleeve  58  with the proximal end  75  of the engagement elements  56  ( FIG.  9 C ). As the engagement elements  56  are urged in a radially inward direction, the engagement elements  56  engage the engagement portion  46  of the syringe  20  to allow the end wall  34  of the syringe  20  to be moved in a proximal direction during filling of the syringe  20  and in a distal direction during a fluid delivery from syringe  20 . Movement of the engagement elements  56  from the first position ( FIG.  9 A ) to the second position ( FIG.  9 C ) may bias an engagement element biasing mechanism, such as a spring  160 , from a first position to a second position. 
     With reference to  FIG.  9 D , when the solenoid  165  is energized, the locking levers  166  are rotated about the pivot pins  168  radially inward in a direction of arrow D, thereby disengaging the proximal ends of the locking levers  166  from the grooves  170 . This allows the inner piston sleeve  58  to be moved proximally relative to the outer piston sleeve  50 , thereby disengaging the distal end  158  of the inner piston sleeve  58  from contacting the proximal end  75  of the engagement elements  56 . The engagement elements  56  are subsequently retracted to the first position ( FIG.  9 D ), for example due to the restoring force of the spring  160 . Movement of the engagement elements  56  from the second position ( FIG.  9 C ) to the first position ( FIG.  9 D ) disengages the engagement elements  56  from the engagement portion  46  of the syringe  20  to allow removal of the syringe  20 . 
       FIGS.  10 A- 10 D  show the proximal end  30  of the syringe  20  in combination with an engagement mechanism  48  of the piston  19  in accordance with various aspects of the present disclosure. The components of the syringe  20  shown in  FIGS.  10 A- 10 D  are substantially similar or identical to the components of the syringe  20  described herein with reference to  FIGS.  2 A- 2 B . The engagement portion  46  of the syringe  20  is configured for interacting with one or more surfaces of the engagement mechanism  48  that engage and disengage the engagement portion  46  of the syringe  20  with movement of a central rod  37 . For example, the engagement portion  46  of the syringe  20  is configured for interacting with one or more engagement elements  56 , such as one or more engagement arms  68 , of the engagement mechanism  48  that move radially inward and outward to engage and disengage, respectively, the engagement portion  46  of the syringe  20 . 
     In various examples, the engagement mechanism  48  has the one or more engagement elements  56 , such as the one or more engagement arms  68 , movable in a radial direction relative to the engagement portion of the syringe  20  between a first position, where the engagement arms  68  are disengaged from the engagement portion  46  of the syringe  20 , and a second position, where the engagement arms  68  are engaged with the engagement portion  46  of the syringe  20 . The engagement mechanism  48  further has a drive mechanism  88  for moving the engagement arms  68  between the first position and the second position. 
     The engagement arms  68  each include a proximal end  69  configured for interacting with a central rod  37  operably connected to the piston  19 . A distal end  70  of the engagement arms  68  is configured for engagement with the engagement portion  46  of the syringe  20 . Each arm  68  is pivotable about a pivot pin  80  between a first position, where the engagement portion  46  of the syringe  20  can be freely inserted into and removed from the space between the arms  68 , a second position, such as an opening  55  in an outer engagement surface  54  of the piston  19 , wherein the distal end  70  of the arms  68  engages at least a portion of the engagement portion  46  of the syringe  20 , for example by digging one or more pointed terminal ends  86  into a surface of the engagement portion  46 . In the example shown in  FIGS.  10 A- 10 D , the central rod  37  is configured to move relative to the piston  19  in the proximal/distal direction.  FIGS.  10 A- 10 B  show the central rod  37  in a proximally retracted position, such that the engagement arms  68  are disengaged from the engagement portion  46  of the syringe  20 .  FIGS.  10 C- 10 D  show the central rod  37  in a distally extended position, such that a widened portion of central rod  37  abuts the proximal ends  69  of the engagement arms  68 , causing the engagement arms  68  to rotate about respective pivot pins  80  to engage the distal end  70  of the engagement arms  68  with the engagement portion  46  of the syringe  20 . In various examples, proximal/distal movement of the central rod  37  may be effected by and/or dependent upon proximal/distal movement of the piston  19 . In other examples, proximal/distal movement of central rod  37  may be independent of the proximal/distal movement of piston  19 , such as by a drive mechanism  88  substantially similar or identical to the drive mechanism  88 , such as any of the drive mechanisms described herein. 
     With reference to  FIG.  10 B , the central rod  37  has a proximal portion  37   a  having a first diameter that is larger than a space between the engagement arms  68  and a distal portion  37   b  having a second diameter that is smaller or equal to the space between the engagement arms  68 , when the engagement arms  68  are in the first position. The proximal and distal portions  37   a ,  37   b  may be connected by a ramp  37   c . The engagement arms  68  are positioned in the first position away from the engagement portion  46  of the syringe  20  when the distal portion  37   b  of the central rod  37  is positioned between the proximal ends  69  of the engagement arms  68 . With a distal movement of the central rod  37 , such as due to actuation of the drive mechanism  88 , the ramp  37   c  engages the proximal ends  69  of the engagement arms  68  to spread the proximal ends  69  radially apart from each other to allow the proximal portion  37   a  of the central rod  37  to be inserted therebetween. Spreading of the proximal ends  69  of the engagement arms  68  moves the distal ends  70  thereof radially closer together and into engagement with the engagement portion  46  of the syringe  20  into the second positon. Proximal retraction of the central rod  37  reverses the process and disengages the distal ends  70  from the engagement portion  46  of the syringe  20  to allow removal of the syringe  20  from the injector. In some examples, a biasing mechanism, such as a spring, may be provided to bias the engagement arms to the first (open) position or the second (closed) position. 
     According to other aspects, such as shown in  FIGS.  10 E- 10 F , the central rod  37  has a proximal portion  37   a  having a first diameter that is smaller than a space between the engagement arms  68  and a distal portion  37   b  having a second diameter that is larger or equal to the space between the engagement arms  68 . The proximal and distal portions  37   a ,  37   b  may be connected by the ramp  37   c . The engagement arms  68  are positioned away from the engagement portion  46  of the syringe  20  when the proximal portion  37   a  of the central rod  37  is positioned between the proximal ends  69  of the engagement arms  68 . With a proximal movement of the central rod  37 , such as due to actuation of the drive mechanism  88 , the ramp  37   c  engages the proximal ends  69  of the engagement arms  68  to spread the proximal ends  69  apart from each other to allow the distal portion  37   b  of the central rod  37  to be inserted therebetween. Spreading of the proximal ends  69  of the engagement arms  68  moves the distal ends  70  thereof closer together and into engagement with the engagement portion  46  of the syringe  20 . Distal extension of the central rod  37  reverses the process and disengages the distal ends  70  from the engagement portion  46  of the syringe  20  to allow removal of the syringe  20  from the injector. 
     In further examples, the central rod  37  may have a conical shape without a distinct ramp  37   c  between the proximal and distal portions  37   a ,  37   b , respectively. The central rod  37  may be movable in a proximal direction with actuation of the drive mechanism  88  to engage the engagement arms  68  with the engagement portion  46  of the syringe  20 . In other examples, central rod  37  may be movable in a distal direction with actuation of drive mechanism  88  to engage engagement arms  68  with the engagement portion  46  of syringe  20 . 
     In some examples, such as shown in  FIGS.  10 G- 10 H , the central rod  37  may have two or more links  41   a ,  41   b  pivotally connected at their first end to a distal end  37   d  of the central rod  37 . A second end of each link  41   a ,  41   b  is pivotally connected to a proximal end  69  of one of the engagement arms  68 . In this manner, movement of the central rod  37  in a proximal/distal direction causes the links  41   a ,  41   b  to pivot about their pivot points on the distal end  37   d  of the central rod  37  and the proximal ends  69  of the engagement arms  68 . In certain embodiments, the length of each of the two links  41   a ,  41   b  may be selected such that when the links  41   a ,  41   b  are oriented substantially perpendicular to a longitudinal axis of the central rod  37 , the distal ends  70  of the engagement arms  68  are engaged with the engagement portion  46  of the syringe  20  ( FIG.  1011   ). With movement of the central rod  37  in a proximal direction or distal direction from the position shown in  FIG.  1011   , the links  41   a ,  41   b  are pivoted to a second position, wherein distal ends  70  of the engagement arms  68  are disengaged from the engagement portion  46  of the syringe  20 . In other embodiments, the length of each of the two links  41   a ,  41   b  may be selected such that the links  41   a ,  41   b  remain angled relative to a longitudinal axis of the central rod  37  when the distal ends  70  of the engagement arms  68  are engaged with the engagement portion  46  of the syringe  20  (not shown). According to these embodiments, further proximal retraction of the piston may also cause retraction of the central rod  37  relative to the links  41   a ,  41   b , causing links  41   a ,  41   b  to apply a further radially extending force to the proximal ends  69  of the engagement arms  68  and creating a greater engagement or “biting” force between the distal ends  70  of the engagement arms  68  with the engagement portion  46  of the syringe  20 . 
     According to other examples, as shown in  FIGS.  11 A- 11 D , the central rod  37  may have an elliptical, oval, or rectangular cam  38  positioned between the proximal ends  69  of the engagement arms  68 . The cam  38  has a minor axis and a major axis, wherein the minor axis is shorter than the major axis. The central rod  37  may be rotatable about its longitudinal axis between a disengaged, first position shown in  FIGS.  11 A- 11 B  and an engaged, second position shown in  FIGS.  11 C- 11 D . In the disengaged, first position, the central rod  37  is positioned such that the proximal ends  69  of the engagement arms  68  are substantially aligned parallel with a minor axis of the cam  38 . In the engaged, second position, the central rod  37  is rotated about the longitudinal axis such that the proximal ends  69  of the engagement arms  68  are substantially aligned parallel with the major axis of the cam  38 , causing the proximal ends  69  to move radially outward with respect to the central rod  37 . Spreading of the proximal ends  69  of the engagement arms  68  moves the distal ends  70  thereof closer together and into engagement with the engagement portion  46  of the syringe  20 , resulting in digging one or more pointed terminal ends  86  into a surface of the engagement portion  46 . Rotation of the central rod  37  between the major and minor axes being in alignment with the proximal ends  69  of the engagement arms  68  selectively moves the mechanism between the first, disengaged position and the second, engaged position. Rotation of the central rod  37  may be effected by a drive mechanism  88 , such as by a drive mechanism  88  substantially similar or identical to the drive mechanism  88 , such as any of the drive mechanisms described herein. 
     In other examples similar to that depicted in  FIGS.  11 A- 11 D , the cam  38  may be substituted with a disc having slots each corresponding to and interacting with the proximal end  69  of one of the engagement arms  68 . In particular, each slot defines a track for the proximal ends  69 , such that as the disc is rotated by the drive mechanism  88 , the proximal ends  69  of the engagement arms  68  are caused to move radially outward and inward with respect to the central rod  37 . Consequently, the engagement arms  68  are forced to rotate about respective pivot pins  80  to engage the engagement portion  46  of the syringe  20 . 
     Referring now to  FIG.  12   , an engagement mechanism  48  in accordance with other aspects of the present disclosure is shown in combination with the proximal end  30  of a syringe  20 . The components of the syringe  20  shown in  FIG.  12    are substantially similar or identical to the components of the syringe  20  described herein with reference to  FIGS.  2 A- 2 B . The engagement mechanism  48  includes one or more engagement arms  68  rotatable around respective pivot pins  80 , substantially similar to the engagement arms  68  and pivot pins  80  described herein with reference to  FIGS.  10 A- 11 D . The engagement arms  68  differ from those of  FIGS.  10 A- 11 D  in that the each engagement arm  68  further includes a lobe  71  between the proximal and distal ends of the engagement arm  68 . The lobe  71  of each engagement arm  68  is configured to interact with a deactivating pin  74  moveable in the proximal/distal direction. In an unlocked state shown in  FIG.  12   , the deactivating pin  74  is extended in the distal direction such that the lobe  71  of each engagement arm  68  abuts the deactivating pin  74 , thereby preventing the distal ends  70  of the respective engagement arms  68  from engaging the engagement portion  46  of the syringe  20 . The deactivating pin  74  may be retracted in the proximal direction to achieve a locked position in which the lobes  71  are disengaged from the deactivating pin  74  and the pointed terminal ends  86  of the engagement arms  68  are permitted to engage the engagement portion  46  of the syringe  20  by rotation around pivot pins  80 . 
     Proximal/distal movement of the deactivating pin  74  may be controlled by a drive mechanism, substantially similar or identical to the drive mechanism  88  described herein with reference to  FIGS.  7 A- 7 B . In some embodiments, the engagement arms  68  may be biased toward the locked position (i.e., normally closed) such that additional mechanisms are not required to maintain engagement between the engagement arms  68  and the engagement portion  46  of the syringe  20 . In other embodiments, the engagement arms  68  may be biased toward the unlocked position (i.e., normally open) such that actuation of the deactivating pin  74  or another actuation mechanism is required to engage the engagement arms  68  with the engagement portion  46  of the syringe  20 . 
     With reference to  FIG.  13   , an engagement mechanism  48  of a piston  19  is shown in accordance with other examples of the present disclosure. The engagement mechanism  48  includes at least a pair of engagement arms  68  that are pivotally connected to the piston  19  via a cam member  15 . In one example, the engagement arms  68  are configured to move between an open first position and a closed second position to grip the engagement portion  46  of the syringe  20 . A band  23 , may be configured as an electro-active polymer is positioned on each of the engagement arms  68 . In some examples, the band  23  may be a nitinol wire or other shape-memory alloy. To move the engagement arms  68  from the open position to the closed position, an electrical charge may be applied or directed to the band  23  to cause the band  23  to contract, thereby reducing the diameter of the band  23 . As the band  23  is contracted, the engagement arms  68  are brought towards one another to clamp on the engagement portion  46  of the syringe  20 . 
     While examples of a fluid delivery system and a syringe for use therefor were provided in the foregoing description, those skilled in the art may make modifications and alterations to these examples without departing from the scope and spirit of the disclosure. Accordingly, the foregoing description is intended to be illustrative rather than restrictive. The disclosure described hereinabove is defined by the appended claims, and all changes to the disclosure that fall within the meaning and the range of equivalency of the claims are to be embraced within their scope.