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Effects of intravoxel velocity distributions on the accuracy of the phase‐mapping method in phase‐contrast MR angiography
Author(s) -
Hamilton Craig A.,
Moran Paul R.,
Rajala Sarah A.
Publication year - 1994
Publication title -
journal of magnetic resonance imaging
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.563
H-Index - 160
eISSN - 1522-2586
pISSN - 1053-1807
DOI - 10.1002/jmri.1880040520
Subject(s) - voxel , imaging phantom , laminar flow , physics , flow velocity , contrast (vision) , aliasing , phase (matter) , asymmetry , flow (mathematics) , thermal velocity , mathematics , nuclear magnetic resonance , optics , mechanics , computer science , filter (signal processing) , quantum mechanics , artificial intelligence , computer vision
The phase‐mapping method of phase‐contrast magnetic resonance angiography is shown to be based on an implicit assumption that the intravoxel velocity distribution is symmetric about its mean velocity. The effect of asymmetric distributions on the accuracy of quantitative average velocity measurements is determined analytically and verified experimentally. An explicit formulation is developed for the estimated average velocity in a voxel as a function of the true average velocity and the asymmetry of the distribution about the true average velocity. Worst‐case distributions are determined for unidirectional and bidirectional flow, and the special case of laminar flow is also investigated. Computer simulations and phantom imaging experiments demonstrate the accuracy of the analysis. For voxels with unidirectional flow, the phase‐mapping method produces accurate estimates of average velocity, while results for bidirectional flow indicate possible large errors unless the aliasing velocity is increased. which decreases the signal‐to‐noise ratio in the resultant velocity map image.