A fluid injection arrangement, in the context of patient imaging systems, in which phases of contrast medium injection and flushing medium injection can be freely and selectably ordered so as to make available to the operator and patient a vast array of possible protocols that has hitherto been essentially unattainable. Also contemplated is the use of a “hold” phase, involving an indefinite pause between phases of a protocol, in connection with such imaging systems. Further contemplated is the use of a “pause” phase in which a pause of fixed duration is pre-programmed into the protocols of MRI injector systems.