Phase-contrast CMR enables the measurement of blood flow velocity across the cardiac valves and the great vessels with a high
temporal and spatial resolution. As blood flows through the static magnetic field gradient, the precession frequency of the
hydrogen atoms change. This frequency change results in a dephasing effect on the magnetization of the atoms. The net
dephasing of the spins is a function of the velocity of the blood flow as well as the direction.
CMR flow imaging has been useful in the diagnosis of valvular regurgitation, aortic stenosis, and has even been used for angiography.