1. A method for generating a B 1 map in an MRI system, said method comprising using an MRI system to: (a) acquire at least one set of B 1 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 to produce at least two sub-sets of frequency-filtered k-space data: (i) a baseline low-frequency sub-set, and (ii) at least one of a positive higher frequency sub-set including a harmonic version of said baseline sub-set and a negative higher frequency sub-set including a harmonic version of said baseline sub-set; (c) separately transform each of said sub-sets to respectively corresponding spatial domain data sets: (i) a baseline magnitude set, and (ii) at least one of a positive harmonic magnitude set and a negative harmonic magnitude set; (d) arithmetically combine said baseline magnitude set with said at least one of the harmonic magnitude sets on a pixel-by-pixel basis to provide upper and lower magnitude data sets; (e) process said upper and lower magnitude data set values on a pixel-by-pixel basis to generate a B 1 map value based on value related to a ratio of said upper and lower pixel data values at a given pixel location in the spatial domain; and (f) store said B 1 map of values in a computer accessible and readable memory device for subsequent use by said MRI system.