A syringe for use with a medical injector system includes a barrel and a semi-rigid hub, the hub having an outer surface adapted to slidingly move within the barrel, and an inner surface having a continous circumferential wall. The hub further includes an annular engaging portion recessed within at least part of the continous circumferential wall forming a groove, at least one radially extendable and retractable retention member disposed at partially within a proximal cylindrical portion of the hub, and the elastometric seal engaged with a seal engaging portion on the hub and slidingly engaged with the barrel of the syringe. The semi-rigid hub and the elastomeric seal are reciprocally slidable within the barrel, and the at least one radially entendable and retractable retention member is configured to releasably engage the groove upon retraction of the plunger to permit the semi-rigid hub to be selectively withdrawn within the barrel.
