A complex‐difference phase‐contrast technique for measurement of volume flow rates

Magnetic resonance (MR) phase‐difference methods work well for measuring volumetric flow rates when the vessel diameter is large compared with the in‐plane voxel dimensions. For small vessels (eg, coronary arteries), partial‐volume effects introduce substantial errors in the measured volume flow rate. To correctly measure flow rates through a voxel, both the fraction of the voxel containing moving spins and the phase shift imparted to those spins must be known. The authors propose a flow measurement method that combines information obtained with both the complex‐difference and phase‐difference processing techniques and thereby provides the fractional volume occupied by the moving spins and the phase of those spins. The complex‐difference flow map method proposed results in improved accuracy of MR phase‐contrast flow measurements in the presence of partial‐volume effects.