A method of determining fractional flow reserve (FFR) in a blood vessel having stenosis includes injecting fluid into the blood vessel upstream of the stenosis using a power fluid injector, measuring pressure drop across the stenosis, and calculating FFR from measured pressure drop. The injected fluid may comprise a contrast medium. Further actions may include placing a pressure sensor proximal of the stenosis, injecting fluid into the blood vessel upstream of the stenosis using the power fluid injector, and measuring pressure in the blood vessel proximal of the stenosis. The pressure sensor may then be repositioned to a position distal of the stenosis, fluid may be reinjected into the blood vessel upstream of the stenosis using the power fluid injector, and pressure may be measured in the blood vessel distal of the stenosis.