Injector systems which include a syringe and a powered injector to inject a fluid into a patient are described. The powered injector includes a drive member, an energy source, at least one sensor for detecting energy from the energy source, and at least one contact member axially movable in the injector and in communication with the sensor. The syringe includes at least one indicator positioned at a predetermined position, such as on a rear surface of an attachment flange, which may transmit or reflect energy from the energy source to the sensor. The contact member may contact and be moved by the indicator when the syringe is attached to the powered injector, so that the energy detected by the sensor may be determined by the position of the indicator. The position of the indicator thereby provides information about the syringe configuration.