Effect of Venc on accuracy of velocity profiles in multi-slice phase-contrast MR imaging of stenotic flow

Phase-contrast MRI (PC MRI) is a powerful technique for imaging the flow velocities in-vivo. In PC MRI, the velocity encoding parameter, V_enc, plays a central role in fidelity of velocities acquired with this technique. Typically V_enc is chosen to be the highest velocity in the flow. However, when acquiring velocity images at a number of slice locations, it may be advantageous to change the V_enc as a function of position. The goal of this study was to determine the effect of V_enc on the accuracy of the estimated velocity profiles in a range of locations in a phantom model of a 90% area stenosis. To this end, velocities from PC MRI were compared with velocities from computational fluid dynamics (CFD) simulations for identical geometry and flow conditions. Our results confirm that although using smaller V_enc´s leads to wrapping artifact, it provides more accurate velocity profiles. However, there is a lower limit to setting the V_enc, beyond which phase-unwrapping becomes uncertain.