Final answer:
An 18 gauge needle allows for the highest rate of injection for an intravenous contrast injection in a CT procedure, as its larger diameter permits a greater flow of fluid compared to the higher numbered gauges.
Step-by-step explanation:
Intravenous contrast injection for a CT procedure implies the use of a cannula of a certain gauge, which indicates the size of the needle. Among the options provided, an 18 gauge needle allows for a higher rate of injection because the smaller the gauge number, the larger the diameter of the needle. Larger diameters permit greater fluid flow. Gauges such as 20 gauge, 22 gauge, and 25 gauge have smaller diameters and thus a slower rate of injection compared to an 18 gauge needle. The gauge of a needle impacts how the pressure results in a force that is converted (or transduced) into some type of readout. In the context of IV injections, this translates into the speed and volume of contrast medium that can be delivered into the bloodstream.