1. A method for using a magnetic resonance imaging (MRI) system to produce an image representative of the vasculature of a subject, said method comprising: (a) applying a non-contrast MRI pulse sequence to acquire MRI k-space data from non-stationary nuclei flowing in a selected spatial region of a subject after nuclei within said region have been subjected to spatially non-uniform pre-saturation of nuclear magnetic resonant (NMR) magnetization by a pre-saturation pulse having a non-uniform profile in the spatial domain across the region for the purpose of suppressing subsequent MRI signals emanating from background nuclei located within said region during said pre-saturation; and (b) using the acquired MRI k-space data to reconstruct an image representing vasculature of said subject.