A core, rotatably fitted within a body of a manifold assembly, includes a flow channel configured so that, when the core is rotated 360 degrees, fluid communication between ports of the body is only established by the channel at a first position, between first and second ports, and at a second position, between third and fourth ports. The channel may define an angle greater than 90 degrees and less than 180 degrees, preferably 120 degrees； and, the rotation, between first and second positions, may be approximately 180 degrees. In a medical injection system, the first and second ports are fill ports of the assembly, the first being coupled to a reservoir, and the second being coupled to a pump； and the third and fourth ports are injection ports of the assembly, the third being coupled to the pump, and the fourth being coupled to an injection line.
