Elimination of oblique flow artifacts in magnetic resonance imaging.

We present an analysis of how flow oblique to the frequency-encoding direction generates displacement artifacts in MR imaging and show that for flow which has constant velocity between the start of the phase encoding and the center of the echo it is possible to eliminate these artifacts by gradient moment nulling in the phase-encoding direction. However, unlike the standard moment nulling calculations for flow compensating the frequency-encode and slice-selection gradients, the phase-encoding first moment must be nulled specifically with respect to the echo center. Limitations of this method imposed by finite gradient strengths are analyzed. In 3D volume acquisitions with two axes phase encoded it is possible to correct for oblique flow in all directions, and this is demonstrated in images of a human volunteer. Correction for oblique flow displacement artifacts may be particularly useful in quantitative flow and angiographic applications.