On the accuracy of EPI-based phase contrast velocimetry

For over a decade, echo-planar imaging (EPI) has been used in both the medical and applied sciences to capture velocity fields of fluid flows. However, previous studies have not rigorously confirmed the accuracy of the measurements or sought to understand the limitations of the technique. In this st...

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Bibliographic Details
Published in:Magnetic resonance imaging 2000-11, Vol.18 (9), p.1115-1123
Main Authors: Moser, Kevin W., Georgiadis, John G., Buckius, Richard O.
Format: Article
Language:English
Subjects:
Biological and medical sciences
Blood Flow Velocity - physiology
Cardiovascular system
Constriction, Pathologic - physiopathology
Echo-Planar Imaging - methods
EPI
Humans
Image Processing, Computer-Assisted
Investigative techniques, diagnostic techniques (general aspects)
Medical sciences
Miscellaneous. Technology
Models, Cardiovascular
NMR flow imaging
Phantoms, Imaging
Phase contrast velocimetry
Radiodiagnosis. Nmr imagery. Nmr spectrometry
Rheology
Stenosis
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Summary:For over a decade, echo-planar imaging (EPI) has been used in both the medical and applied sciences to capture velocity fields of fluid flows. However, previous studies have not rigorously confirmed the accuracy of the measurements or sought to understand the limitations of the technique. In this study, a bipolar gradient was added to a flow-compensated EPI pulse sequence to obtain rapid phase contrast images of steady and unsteady flows through two step stenoses. For steady Re = 100 and 258 flows, accuracy was measured through systematic comparisons with CFD simulations, mass flow rate measurements, and spin echo phase contrast images. On average, the EPI image data exhibited velocity errors of 5 to 10 percent, while mass was conserved to within 5.6 percent at each axial position. Compared to spin-echo phase contrast images, the EPI images have 50 percent lower signal-to-noise ratio, larger local velocity errors, and similar mass conservation characteristics. An unsteady flow was then examined by starting a pump and allowing it to reach a steady Re = 100 flow. Accuracy in this case was measured by the consistency between mass flow rate measurements at different axial positions. Images taken at 0.3 s intervals captured the velocity field evolution and showed that 50 to 100 percent errors occur when the flow changes on a time scale faster than the image acquisition time.
ISSN:0730-725X
1873-5894
DOI:10.1016/S0730-725X(00)00189-2