1. A method for correcting the background phase in magnetic resonance phase contrast flow images, the method comprising the steps of: providing a time series of anatomical magnetic resonance images and velocity encoded magnetic resonance images of a patient, wherein said time series of velocity encoded images comprises for each time point a phase contrast image wherein a pixel intensity is proportional to a flow velocity; computing, for each pixel, an intensity variance over the time series of phase contrast images and an intensity variance over the time series of anatomical images; selecting, for each pixel, the maximum of the intensity variance over the phase contrast images and the intensity variance over the anatomical images as a measure of temporal variance for each pixel; forming a histogram of the intensity variance of all pixels; determining a threshold from said histogram, wherein pixels whose intensity change is less than the threshold are considered as stationary pixels, and pixels whose intensity change is greater than the threshold are considered as moving pixels; and calculating a correction field for the stationary pixels, wherein said correction field represents a background phase to be subtracted from the phase contrast image.