1. In an NMR system for acquiring NMR data from a subject and reconstructing an image from the data, the method comprising: a) acquiring two NMR data sets from which two separate images are reconstructed, the two NMR data sets being acquired with different velocity encoding magnetic field gradients applied to the subject; b) producing a phase difference array by calculating the phase of each value in the two NMR data sets and calculating the difference between the phases of corresponding values in each of the two NMR data sets; c) producing a complex difference array by calculating the square root of the sum of the squares of the differences between corresponding real values in the two NMR data sets and the differences between corresponding quadrature values in the two NMR data sets; d) correcting the complex difference array for saturation effects using velocity information derived from the phase difference array; and e) producing a flow image from the corrected complex difference array.