the present invention embodies a method and an injector adapted to incorporate this method , for keeping a patient &# 39 ; s vein open during an intravenous contrast injector procedure without injecting a saline solution from a separate syringe . the injector includes a controller having a programable software module to allow an operator to configure the injector to push some contrast media fluid through an injection site and then retract a plunger drive ram . a syringe is adapted to allow a patient &# 39 ; s blood pressure to move the syringe plunger back towards its starting position , thus enabling a patient &# 39 ; s blood to pass through the injection site . alternatively , the syringe is adapted with an elastic plunger which as it enlarges and contracts facilitates fluid communication through the injection site . additionally , the plunger drive ram can be adapted to gradually pull as well as push the plunger , thereby causing fluid to flow across the injection site .