The effects of periodic velocity fluctuations on magnetic resonance flow images are investigated experimentally and theoretically. In the experiments, laminar pipe flow of water was examined. The flow was driven by a constant pressure head with a superimposed sinusoidal component with the frequency m, varied from 0 to 1 Hz, whereas in the simulations omega(z) was between 0 to 65 Hz. The velocity profiles obtained from the experimental results compare well with the theoretical calculations. Both theory and experiment show that flow fluctuations produce artifacts in the form of "ghosts" of the primary image, which are spaced at equal intervals in the phase encoding (flow) direction. The distance between ghosts depends on the fluctuation frequency and on the experimentally specified parameters (phase encoding gradient step, repetition time, phase encoding duration, and time difference between phase encoding gradient lobes). The amplitudes of the ghosts depend on amplitude of the flow fluctuation and diminish at frequencies higher than 30 Hz. (C) 2004 American Institute of Chemical Engineers.