Fluid injector with syringe engagement mechanism

The invention relates to a fluid injector comprising an engagement mechanism associated with a reciprocally movable piston of the fluid injector and configured to releasably engage an engagement portion at a proximal end of a rolling diaphragm barrel having a flexible sidewall configured to roll over itself when acted by the piston. The engagement mechanism has a plurality of engagement elements reversibly and pivotally movable about a pivot pin relative to an engagement portion of the needle cylinder between a first position in which the plurality of engagement elements are disengaged from the engagement portion of the needle cylinder and a second position in which the plurality of engagement elements are disengaged from the engagement portion of the needle cylinder. The plurality of engagement elements are pivotally movable in a radially inward direction about the pivot pin at the second position to engage with an engagement portion of the syringe. The engagement mechanism also has a drive mechanism to move