Abstract: The present invention provides an injection system and a pump system for use therein for pressurizing a liquid medium for injection into a patient. In general, the pump system comprises a pressurizing unit having at least one chamber. Each chamber has disposed therein a pressurizing mechanism to pressurize liquid medium within the chamber. Preferably, the pressurizing mechanism positively displaces the liquid medium through generally linear motion of the pressurizing mechanism within the chamber. Through reciprocating linear motion of the pressurizing mechanism (for example, a piston), the liquid medium is alternatively drawn into the chamber from a source of liquid medium (for example, a container) and forced out of the chamber under a desired pressure. Each chamber comprises an inlet port and an outlet port.