ACCURACY OF MR PHASE-CONTRAST VELOCITY-MEASUREMENTS FOR UNSTEADY-FLOW

The accuracy of MR phase contrast (PC) velocity measurements for unste ady flow has been quantitatively assessed. Spatially resolved velocity fields were measured in a long straight tube using a gated PC techniq ue, and the resulting MR PC velocity data were compared with velocitie s derived from the analytic Womersley solution to the Navier-Stokes eq uations governing fluid now. The overall root-mean-square [rms] differ ence 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 re gression between the PC velocity measurements and the velocities obtai ned using the analytic expression was highly significant [r(2) = 0.997 ] and yielded a slope of 0.998, close to the expected value of 1. We c onclude that the gated MR PC velocity measurements in unsteady flow ar e accurate.