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To compare in vivo real-time Fourier velocity encoding (FVE), spectral-Doppler ultrasound, and phase-contrast (PC) magnetic-resonance (MR) imaging.In vivo velocity spectra were measured in the suprarenal and infrarenal aorta and the hepatic segment of the inferior vena cava of eight normal volunteers using FVE, and compared to similar measurements using Doppler ultrasound and gated PC MR imaging. In vivo waveforms were compared qualitatively according to flow pattern appearance (number, shape, and position of velocity peaks) and quantitatively according to peak velocity.Good agreement was obtained between peak velocities measured in vitro using FVE and PC MR imaging (R2 = 0.99, P = 2.10−6, slope = 0.97 ± 0.05). Qualitatively, the FVE and ultrasound measurements agreed closely in the majority of in vivo cases (excellent or good in 21/24 cases) while the PC MR method resolved fewer velocity peaks due to the inherent temporal averaging of cardiac-gated studies (excellent or good agreement with FVE in 13/24 cases). Quantitatively, the FVE measurement of peak velocity correlated strongly with both ultrasound (R2 = 0.71, P = 2.10−7, slope = 0.81 ± 0.08) and PC MR (R2 = 0.85, P = 2.10−10, slope = 1.04 ± 0.08).Real-time MR assessment of blood-flow velocity correlated well with spectral Doppler ultrasound. Such new methods may allow hemodynamic information to be acquired in vessels inaccessible to ultrasound or in patients for whom respiratory compensation is not possible. J. Magn. Reson. Imaging 2005;21:297–304. © 2005 Wiley-Liss, Inc.