Accuracy of phase-contrast velocimetry in systems with skewed intravoxel velocity distributions

Vallatos, A. , Al Mubarak, H. F.I., Mullin, J. M. and Holmes, W. M. (2018) Accuracy of phase-contrast velocimetry in systems with skewed intravoxel velocity distributions. Journal of Magnetic Resonance, 296, pp. 121-129. (doi: 10.1016/j.jmr.2018.09.002) (PMID:30245475)

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Abstract

Phase contrast velocimetry (PCV) has been widely used to investigate flow properties in numerous systems. Several authors have reported errors in velocity measurements and have speculated on the sources, which have ranged from eddy current effects to acceleration artefacts. An often overlooked assumption in the theory of PCV, which may not be met in complex or unsteady flows, is that the intravoxel displacement distributions (propagators) are symmetric. Here, the effect of the higher moments of the displacement distribution (variance, skewness and kurtosis) on the accuracy of PCV is investigated experimentally and theoretically. Phase and propagator measurements are performed on tailored intravoxel distributions, achieved using a simple phantom combined with a single large voxel. Asymmetric distributions (Skewness ≠ 0) are shown to generate important phase measurement errors that lead to significant velocimetry errors. Simulations of the phase of the spin vector sum, based on experimentally measured propagators, are shown to quantitatively reproduce the relationship between measured phase and experimental parameters. These allow relating the observed velocimetry errors to a discrepancy between the average phase of intravoxel spins considered in PCV theory and the vector phase actually measured by a PFG experiment. A theoretical expression is derived for PCV velocimetry errors as a function of the moments of the displacement distribution. Positively skewed distributions result in an underestimation of the true mean velocity, while negatively skewed distributions result in an overestimation. The magnitude of these errors is shown to increase with the variance and decrease with the kurtosis of the intravoxel displacement distribution.

Item Type:Articles
Additional Information:H. Al-Mubarak would like to thanks the Ministry of Higher Education and Scientific Research in Iraq for financial support.
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Mullin, Mr James and Holmes, Dr William and Vallatos, Dr Antoine
Authors: Vallatos, A., Al Mubarak, H. F.I., Mullin, J. M., and Holmes, W. M.
College/School:College of Medical Veterinary and Life Sciences > School of Psychology & Neuroscience
Journal Name:Journal of Magnetic Resonance
Publisher:Elsevier
ISSN:1090-7807
ISSN (Online):1096-0856
Published Online:05 September 2018
Copyright Holders:Copyright © 2018 Elsevier Inc.
First Published:First published in Journal of Magnetic Resonance 296:121-129
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher

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