fig1 illustrates a power injector 10 of a type , for example , that is used for angiographic and ct injection . one such injector is described and illustrated in u . s . pat . no . 5 , 279 , 569 , which is assigned to the assignee of the present invention , and is expressly incorporated herein by reference herein . the injector 10 includes an injector housing 11 that contains a power driven ram 12 . the ram 12 is longitudinally extendable from the housing 11 in a direction normal to the front of the housing 11 by activation of a motor ( not shown ) contained within the housing 11 . the forward end of the ram 12 is extendable from a retracted position in which its forward end is located inside the housing 11 , as illustrated in fig1 to an extended position in which its forward end has been advanced a considerable distance outside the front wall of the housing 11 , as more fully explained in the incorporated u . s . pat . no . 5 , 279 , 569 . the injector described in that cited patent has a door assembly that constitutes a syringe mounting head of a front loading type for receiving a front loadable syringe with the syringe being loaded therein by translating it rearwardly , back end first , into the front of the mounting head . the embodiment of the invention illustrated in fig1 is , however , equipped with a faceplate in the form of a syringe mounting head 15 that is an alternative to , or a replacement for , or otherwise exchangeable with , the front loading head described in the patent which is configured to receive a syringe that is particularly designed for front loading , and which has a rearward end of the same outer diameter and cross - section as the syringe body . the mounting head 15 of the embodiment of fig1 is rather configured to receive a syringe 40 of a type that has been designed for breech loading into an injector of the rear loading type , where the syringe 40 is translated , front end first , through an opening from the rearward side of a loading door , which must be opened for the purpose of loading or unloading a syringe 40 . the syringe 40 typically has a cylindrical syringe body 41 with a frusto conical front end 42 having a conical injection nozzle 43 at the front thereof . the syringe body 41 has a rearward end 44 provided with a radially outwardly extending flange 45 . the flange 45 is typically of uniform thickness and integrally formed with the syringe body 41 at its extreme rearward end . the flange 45 may be a ring shaped annular flange with a circular outer edge , but usually is provided with at least one flat edge or notch to angularly align the syringe or to prevent the syringe from rotating about its longitudinal axis . the flange 45 of the syringe 40 has a polygonal outer edge that will angularly orient , or prevent rotation of , the syringe 40 when mounted in an injector . as illustrated in fig1 the syringe 40 is provided with a flange 45 having an outer edge of octagonal shape . within the body 41 of the syringe 40 is a plunger 47 formed of a hard polymeric material which forms a slidable but sealable contact with the inside of the syringe body 41 and defines along with the body 41 a sealed cavity 48 within the body 41 which contains injection fluid 49 , preferably the syringe 40 when supplied from the manufacturer , that is , a prefilled syringe . the head 15 preferably includes a casting 17 removably pivotally connected to the front of the housing 11 to a pivot shaft 16 and with a locking mechanism 25 , which illustrated in part in fig1 - 3 , and as is more particularly described in the incorporated u . s . pat . no . 5 , 279 , 569 . the mechanism 25 functions to lock and unlock of the head 15 to and from the housing 11 , to couple the ram 12 to plunger 47 within the body 41 of the syringe 40 , and to lock the syringe 40 to the injector 10 . the mechanism 25 is provided with an operating lever 26 , illustrated in an unlocked or loading position in fig1 and 2 ., which is the position which allows the head 15 to be opened , removed and replaced and which allows syringes 40 to be loaded and unloaded from the mounting head 15 . the lever or handle 26 is connected to a disc 27 rotatably mounted to the casting 17 . the handle 26 is moveable to a locked position , illustrated in fig3 which is the position at which the head 15 is locked to the injector 10 , the ram 12 is coupled to the syringe ram and the syringe 40 is locked to the injector 10 . the casting 17 of the head 15 has an opening 30 therethrough , which is preferably of the same shape as the flange 45 of the syringe 40 and slightly larger in size to allow the flange 45 to be inserted into the opening 30 . the opening 30 is preferably flared outwardly on the forward side thereof to guide the flange 45 of a syringe 40 into the opening 30 when the syringe 40 is being loaded . the opening 30 is centered on an axis 31 which is perpendicular to the front of the housing 11 . the axis 31 is parallel to the path of the ram 12 and generally lies on the centerline of the ram 12 when the lever 26 is in its locked position . behind the opening 30 is an annular stop 32 ( fig4 ), which lies in a plane that is oriented perpendicular to the axis 31 . the stop 32 may be integrally formed of or otherwise fixed to the disc 27 , which is centered to pivot on the axis 31 . the stop 32 lies at the back of a recess 34 formed in the disc 27 . the recess 34 has a depth approximately equal to the thickness of the flange 45 . the recess 34 is preferably of the same shape as the flange 45 to hold the syringe 40 against rotation in the opening 30 once the syringe 40 is mounted in the opening 30 . the stop 32 has an opening 33 therein to allow passage of the ram 12 . when the flange 45 of a syringe 40 is inserted through the opening 30 and is seated against the stop 32 , the axis of the syringe 40 coincides with the axis 31 of the opening 30 , whereby the syringe 40 is perpendicular to the faceplate 15 , and the syringe 40 is in its operating position on the injector 10 . according to one embodiment of the invention , the locking mechanism 25 includes a iris - like gripping mechanism 50 for holding the syringe 40 firmly in its operating position in the holder 15 . the gripping mechanism 50 includes a plurality of gripping elements which preferably have gripping surfaces that encircle most of the circumference of the syringe body 31 . in this embodiment , a pair of jaws 51 , 52 , is provided , each jaw being pivotally connected to the housing 17 of the head 15 at respective pivot pins 53 , 54 which are fixed to the housing 17 . the jaws 51 , 52 have inner concave gripping surfaces 55 , 56 having curvatures that correspond to the curvature of the outer surface of the body 41 of syringe 40 . preferably , the surfaces 55 , 56 of the jaws 51 , 52 each encompass an arc of between 90 ° and 180 °, so that when the jaws 51 , 52 are closed ( fig3 ) the surfaces 55 , 56 substantially surround the body 41 of the syringe 40 and securely hold the syringe in the operating position . the jaws 51 , 52 are spaced forward of the stop 32 so that , when the syringe 40 is in its operating position , the syringe flange 45 is held flat against the stop 32 by the jaws 51 , 52 . the jaws 51 , 52 are simultaneously moved between retracted positions ( fig2 ) and locked positions ( fig3 ) by a camming action of the mechanism 25 , which is provided by a pair of cam follower pins 57 , 58 mounted on the ring 27 to move with and be actuated by the handle 26 . a magnet 88 is provided on the jaw 52 which can be detected by a sensor ( not shown ) in the injector housing 11 in order to determine that the mechanism 25 is in its locked condition which enables , through controls ( not shown ) in the housing , the operation of the ram 12 . the pins 57 , 58 scribe an arc on a circle 60 , centered on the axis 31 , when the handle 26 is operated . the pins 57 , 58 move in arcuate slots 61 , 62 in the jaws 51 , 52 , respectively , so that , when the handle 26 is operated , the pins 57 , 58 move the slots 61 , 62 generally radially and thereby cam the jaws 51 , 52 to pivot on their respective pins 53 , 54 between their retracted positions , in which the surfaces 55 , 56 are displaced radially outward of the flange 45 to provide clearance for the flange 45 when the flange 45 moves between the opening 30 and the backplate 32 during loading and unloading , and their locked positions in which the jaws 51 , 52 seat snugly against the outside of the body 41 of the syringe 40 immediately forward of the flange 45 . when so actuated , the jaws 51 , 52 move generally radially inwardly or outwardly along a path that may be , but is not necessary normal to the outer surface 41 of the syringe 40 . according to another embodiment of the invention , an alternative head 15 a is provided in which the syringe 40 is held in its operating position by an alternative gripping mechanism 50 a having a set of four slidable jaws 71 - 74 , as illustrated in fig5 - 7 . each of the jaws 71 - 74 has a rectangular cross - section when viewed from the axis 31 , and each is trapped to slide radially in a respective one of four rectangular slots 75 formed between respective pairs of adjacent ones of a set of four wedges 76 , which are fixed to the ring 27 , and between the casting 17 and the rotatable ring 27 . the jaws 71 - 74 have inner concave gripping surfaces 77 having curvatures that correspond to the curvature of the outer surface of the body 41 of syringe 40 , so that when the jaws 71 - 74 are closed ( fig3 ) the surfaces 77 substantially surround the body 41 of the syringe 40 and securely hold the syringe in the operating position . the jaws 71 - 74 are spaced forward of the stop 32 so that , when the syringe 40 is in its operating position , the syringe flange 45 is held flat against the stop 32 by the jaws 71 - 74 . the jaws 71 - 74 rotate with the ring 27 and also simultaneously move between retracted positions ( fig5 ) and locked positions ( fig6 ) by the camming action of the mechanism 25 a . the gripping surfaces 77 of the jaws 71 - 75 have v - shaped notches 89 therein which line up with the corners of the recess 34 in the ring 26 . each one of the jaws 71 - 74 is provided with a cam follower slot 78 in which is located a cam pin 79 which is fixed to the casting 17 and lies on a circle centered on the axis 31 . when the handle 26 is operated to move the ring 27 , the wedges 76 move with the ring 27 and rotate with them the jaws 71 - 74 . the movement of the jaws 71 - 74 moves the slots 78 along the fixed pins 79 , which causes the jaws 71 - 74 to move radially when the handle 26 is operated between their retracted positions , in which the gripping surfaces 77 are displaced radially outward of the flange 45 to provide clearance as the flange 45 during loading and unloading of the syringe 40 , and their locked positions snugly against the outside of the body 41 of the syringe 40 immediately forward of the flange 45 to hold the syringe 40 in position for operation . preferably , as illustrated in fig3 the gripping surfaces , such as surfaces 55 , 56 of jaws 51 , 52 , span at least approximately 25 % of the circumference of the syringe for many syringes . in the embodiment illustrated , the jaws 51 , 52 have spaces 81 , 82 between them that each span no more than approximately 10 - 20 % of the circumference . with some syringes , it is preferred that the gripping surfaces span at least approximately 65 % of the circumference and in addition or in the alternative , that spaces between contacting portions of the surfaces by not more than approximately 95 % of the circumference of the syringe . for example , surfaces 77 of jaws 71 - 74 in fig6 each have two arcs spaced by a v - shaped notch 89 of less than about 3 to 5 % of the circumference , with the spaces 83 between the jaws 71 - 74 , when the jaws are in the locked position , being also spanning less than approximately 3 to 5 % of the circumference , leaving about 65 % of the circumference cumulatively spanned by the surfaces 77 . while the jaws 51 , 52 and 71 - 74 are referred to herein as gripping jaws , these jaws may or may not actually squeeze radially inward on the syringe 40 . what is preferred is that they contribute to the holding of the syringe in the opening 30 , particularly resisting the force exerted by the ram 12 in moving the plunger 47 . it is also important that , whatever holding action is performed by the gripping structure , the syringe 40 be held against the forces of operation without subjecting it to such forces and stresses that would cause any portion of the syringe 40 to fail . to this end , it is preferred that the jaws 51 , 52 or 71 - 74 engage the syringe 40 close to the body 41 of the syringe 40 , at the intersection of the flange 45 with the syringe body 41 , in a way that concentrates axial forces on the syringe 40 on the flange 45 as close to the body 41 as possible . this may be accomplished by configuring the rear edge of the inner surfaces 55 , 56 or 77 of the jaws 51 , 52 or 71 - 74 with a smaller radius than the radius 85 between the flange 45 and the outside of the syringe body 41 , as illustrated in fig6 . this leaves small spaces 86 between the jaws and the syringe body 41 and spaces 87 between the jaws and the syringe flange 45 . to load a syringe 40 into an injector 10 , a faceplate 15 or 15 a having a gripping mechanism 50 or 50 a is mounted onto the injector housing 11 , for example as a replacement to the standard faceplate with which the injector 10 is provided . if the syringe 40 has a plunger coupling that is not compatible with the coupling in the ram 12 of the injector 10 , a ram coupling adapter may be attached to the end of the ram 12 to provide coupling between the ram 12 and the coupling element ( not shown ) on the rear side of the plunger 47 . with the lever 26 in its unlocked position , a syringe 40 is loaded into the opening 30 by translating the syringe 40 in a rearward axial direction , rear end first , until the flange 45 on the rearward end 44 of the syringe 40 passes through the opening 30 and rests in the recess 34 and against the stop plate 32 in the ring 27 . the tapered front of the opening 30 in the casting 17 guides the flange 45 such that the shaped perimeter thereof lines up with the similarly shaped periphery of the recess 34 . with the lever 26 so unlocked , the jaws 51 , 52 or 71 - 74 are in their retracted positions out of the path of the flange 45 as it is inserted into the opening . when the rearward end 44 of the syringe 40 is completely seated in the opening , the lever 26 is moved to its locked position , which causes the jaws 51 , 52 or 71 - 74 , to move to their closed positions against the outside of the body 41 of the syringe 40 , gripping the body 41 and trapping the flange 45 between the jaws 51 , 52 or 71 - 74 and the ring 27 . this locking motion securely holds the syringe in position in the holder 15 on the housing 11 of the injector 10 , with its plunger 47 in line with the ram 12 and its centerline on the centerline of the holder 31 in alignment with the centerline of the path of the ram 12 . removal of the syringe is accomplished by moving the lever 26 to its unlocked position to move the jaws 51 , 52 or 71 - 74 to their retracted positions . with the injector that is disclosed in u . s . pat . no . 5 , 279 , 569 , this movement of the lever causes the locking mechanism 25 , 25 a to slightly rotate the head 15 on the housing 11 , which translates the ram 12 out of alignment with the centerline 31 of the opening , thereby shifting the syringe 40 sideways and uncoupling the ram 12 from the syringe plunger 47 . the syringe 40 can thereby be manually removed from the injector 10 by translating it forwardly in the axial direction . if there is used injection tubing connected to the nozzle 43 after the use of the syringe 40 , the syringe 40 can nonetheless be removed without disconnecting the tubing from the syringe nozzle 43 . insertion of the syringe 40 into the injector 10 can also be carried out with a simple one handed motion , without separately operating the lever 26 . this is accomplished by inserting the syringe in the opening 30 and translating it axially rearwardly until the flange 45 is seated against the stop plate 32 in the recess 34 . then by twisting the syringe 40 in the opening by less than 90 °, preferably by about 45 °, the ring 26 will turn , operating the locking mechanism 25 , which moves the faceplate 15 and syringe plunger 47 into alignment with the ram 12 and operates the gripping mechanism 50 , 50 a to move the jaws 51 , 52 or 71 - 74 to their locked position . the invention provides the user of a power injector with the ability to front load an otherwise rear loadable syringe , particularly a rear loadable syringe having a flange at the rearward end thereof . this provides the user with the advantages of front loadability . those skilled in the art will appreciate that the applications of the present invention herein are varied , and that the invention is described in preferred embodiments . accordingly , additions and modifications can be made to the embodiments of the invention illustrated and described herein without departing from the principles of the invention .
a power injector and a removable replacement faceplate therefor are provided along with a method of front loading syringes , particularly prefilled syringes , which have outwardly extending structure such as flanges which have been typically breech loaded or side loaded into injectors or operated in a hand held fashion . the holder or faceplate of or for the injector is provided with a set of jaws spaced around a syringe receiving opening into which a syringe is loaded , rearward end first , with the jaws in a retracted position , until the flange or other outwardly extending structure on the syringe is rearward of the syringe is beyond a locking position of the jaws . the jaws are then actuated , either by operating an actuator on the faceplate or injector or by twisting the syringe in the opening , so that the jaws move radially inward and close in iris - like fashion about the syringe . the jaws preferably engage a narrow ring along a juncture of the flange or other structure and the body of the syringe and make sufficient contact around the circumference of the syringe , with sufficiently small spaces between the contacting surfaces to avoid damaging deformation of the syringe during use and to effectively hold the syringe against forward forces exerted by the ram of the injector .