Disclosed herein is a method for defining a localized excitation volume within a localizer image, comprising: choosing a region of interest within the localizer image, prescribing at least one imaging slab, and defining a localized excitation volume contained within the region of interest and encompasses a portion of the at least one imaging slab. Further disclosed herein is a method for measuring an accurate center frequency, comprising: prescribing a region of interest within a localizer image, prescribing at least one imaging slab bisecting the region of interest, defining a localized excitation volume that is substantially contained within the region of interest and encompassing a portion of the imaging slab, exciting the localized excitation volume, and calculating a center frequency peak for the localized excitation volume in spectral domain after a fast Fourier transform (FFT) process.