Accuracy of MR phase contrast velocity measurements for unsteady flow

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Abstract
The accuracy of MR phase contrast (PC) velocity measurements for unsteady flow has been quantitatively assessed. Spatially resolved velocity fields were measured in a long straight tube using a gated PC technique. and the resulting MR PC velocity data were compared with velocities derived from the analytic Womeraley solution to the Navier-Stokes equations governing fluid flow. The overall root-meansquare (rms) difference between the measured and analytic velocities was 1.6 cm s−1 for nominally sinusoidal flow waveforms with peak velocities ranging from 51.6 cm s−1 to 59.8 cm s−1 This rms difference corresponded to 7.5% of the mean fluid velocity, which is similar to the cited accuracy of approximately 5% for MR PC velocimetry for steady flows. Linear regression between the PC velocity measurements and the velocities obtained using the analytic expression was highly significant (r2 = 0.997) and yielded a slope of 0.998, close to the expected value of 1. We conclude that the gated MR PC velocity measurements in unsteady flow are accurate.