A medical injection system comprising a pump and a tubing circuit, the pump including a fill port and an injection port, and the tubing circuit including a fill tubing line coupled to a fluid reservoir and an injection tubing line; and wherein the system further comprises a manifold assembly for coupling the tubing circuit to the pump, the manifold assembly being located between the pump and tubing circuit such that the assembly has a circuit side and a pump side, opposite the circuit side; and the manifold assembly comprising: a flow control core including a longitudinal axis, an outer perimeter surface, and a single flow channel, the flow channel including a first section extending inward, toward the axis, from a first opening at the outer perimeter surface, and a second section extending inward, toward the axis, from a second opening at the outer perimeter surface; and a body including a longitudinal axis, an inner perimeter surface, a first fill port, a second fill port, a first injection port, and a second injection port, each port extending from a corresponding opening at the inner perimeter surface to a corresponding opening at an exterior of the body, and each port opening at the inner perimeter surface being located in a separate quadrant of four quadrants into which the inner surface is divided; whereby the first fill port and the second injection port are located at the fluid circuit side and the second fill port and the first injection port are located at the pump side; and wherein the flow control core is fitted within the inner perimeter surface of the body such that the outer perimeter surface of the core seals against the inner perimeter surface of the body, the axis of the core is approximately aligned with the axis of the body, and the core is rotatable about the axis thereof between a first position (P-1) and a second position (P-2); when the core is at the first position, the first opening of the flow channel aligns with the inner surface opening of the first fill port of the body, and the second opening of the flow channel aligns with the inner surface opening of the second fill port of the body, such that the channel allows fluid communication between the first and second fill ports; when the core is at the second position, the first opening of the flow channel aligns with the inner surface opening of the first injection port of the body, and the second opening of the flow channel aligns with the inner surface opening of the second injection port of the body, such that the channel allows fluid communication between the first and second injection ports; and when the flow control core is rotated 360 degrees about the axis thereof, fluid communication between any ports of the body is prevented except at the first and second positions. a flow control core including a longitudinal axis, an outer perimeter surface, and a single flow channel, the flow channel including a first section extending inward, toward the axis, from a first opening at the outer perimeter surface, and a second section extending inward, toward the axis, from a second opening at the outer perimeter surface; and a body including a longitudinal axis, an inner perimeter surface, a first fill port, a second fill port, a first injection port, and a second injection port, each port extending from a corresponding opening at the inner perimeter surface to a corresponding opening at an exterior of the body, and each port opening at the inner perimeter surface being located in a separate quadrant of four quadrants into which the inner surface is divided; whereby the first fill port and the second injection port are located at the fluid circuit side and the second fill port and the first injection port are located at the pump side; and wherein the flow control core is fitted within the inner perimeter surface of the body such that the outer perimeter surface of the core seals against the inner perimeter surface of the body, the axis of the core is approximately aligned with the axis of the body, and the core is rotatable about the axis thereof between a first position (P-1) and a second position (P-2); when the core is at the first position, the first opening of the flow channel aligns with the inner surface opening of the first fill port of the body, and the second opening of the flow channel aligns with the inner surface opening of the second fill port of the body, such that the channel allows fluid communication between the first and second fill ports; when the core is at the second position, the first opening of the flow channel aligns with the inner surface opening of the first injection port of the body, and the second opening of the flow channel aligns with the inner surface opening of the second injection port of the body, such that the channel allows fluid communication between the first and second injection ports; and when the flow control core is rotated 360 degrees about the axis thereof, fluid communication between any ports of the body is prevented except at the first and second positions.