The invention provides a fluid injector assembly for the injection of a fluid including an injector body having distal and proximal ends, a fluid inlet disposed towards the proximal end, a fluid outlet disposed towards the distal end, and a fluid pathway extending therebetween the inlet and the outlet. An injector needle is rotatably disposed at least partially in the injector body and is moveable between an open and closed position. The proximal end of the injector needle has a tip that is configured to sealably close the fluid outlet. The fluid injector assembly includes a first threaded region that cooperates with a corresponding threaded region on the needle, and first and second cooperating coupling members that are arranged axially of the injector needle. The first coupling member is attached to a motor, and the second coupling member is attached to a distal end of the injector needle. The motor is configured to rotate the injector needle within the injector body which causes the threaded region of the needle to be driven in the first threaded region of the fluid injector assembly to thereby move the injector needle along a longitudinal axis of the fluid injector assembly between the open and closed positions.