On the nature and reduction of the displacement artifact in flow images

In flow-imaging experiments with 2-D Fourier transform sequences, the time difference between phase encoding and readout leads to a potentially misleading displacement artifact. This artifact arises in regions of rapid flow and high shear, and manifests as an intensity distortion in addition to a bulk shift. We have studied methods of mitigating the artifact, including offset-echo acquisition, backward-evolving phase encoding, moment-compensated phase encoding, and projection-reconstruction imaging. Experiments on flow phantoms verified the nature and reduction of this displacement artifact. Of the four methods studied, the projection-reconstruction sequence proved to be the most effective, completely eliminating the artifact.