1. A method for generating a B0 map in an MRI system, said method comprising using an MRI system to: (a) acquire at least one set of amplitude tagged MRI data signals in spatial frequency domain k-space from MR nuclei within an imaged volume of the MRI system; (b) process said k-space data with at least one data processor in order to produce at least two sub-sets of frequency-filtered k-space data including at least two of: (i) a baseline low-frequency sub-set, (ii) a positive higher frequency sub-set including a harmonic version of said baseline sub-set, and (iii) a negative higher frequency sub-set including a harmonic version of said baseline sub-set; (c) separately Fourier transform each of said at least two sub-sets in order to produce at least two respectively corresponding complex-valued spatial domain data sets; (d) arithmetically combine said at least two complex-valued spatial domain data sets on a pixel-by-pixel basis in order to generate and provide an off-resonance phase set of pixel data representing a B0 map value; and (e) store said B0 map values in a non-transitory computer accessible and readable memory device that is subsequently usable by said MRI system.