1. A method for using a magnetic resonance imaging (MRI) system to produce an image representative of flowing nuclei within a subject, said method comprising: (a) for each of plural MRI data acquisition sequences, applying a non-contrast pulsed ASL (arterial spin labeling) pre-sequence to flowing nuclei in a tagging region during a tagging period which occurs prior to MRI data acquisition from a selected downstream image region, said ASL pre-sequence comprising plural different elapsed tagging times at which a radio frequency (RF) nuclear magnetic resonant (NMR) nutation tagging pulse occurs or does not occur in accordance with different predetermined patterns for corresponding different ones of said data acquisition sequences; (b) decoding said acquired MRI data in accordance with said predetermined patterns to thereby detect MRI signal emanating from different cohorts of flowing nuclei that have been subjected to different combinations of said nutation pulses; and (c) using the acquired MRI data to reconstruct at least one image representing said flowing nuclei within said selected image region.