1. A method for measuring a transverse magnetization relaxation rate that is corrected for macroscopic magnetic field inhomogeneities in a subject with a magnetic resonance imaging (MRI) system, the steps of the method comprising: a) acquiring image data with the MRI system by sampling a plurality of different echo signals occurring at a respective plurality of different echo times; b) forming for each of the plurality of different echo signals, a signal model that accounts for relative signal components for each of a plurality of different chemical species; c) estimating magnetic field inhomogeneity values associated with the MRI system by fitting the image data acquired in step a) to the signal models formed in step b); d) forming for each of the plurality of different echo signals using the magnetic field inhomogeneity values estimated in step c), a signal model that accounts for relative signal components for each of a plurality of different chemical species and for signal decay resulting from macroscopic variations in a main magnetic field of the MRI system; and e) estimating a transverse relaxation rate for at least one of the plurality of different chemical species by fitting the image data acquired in step a) to the signal models formed in step d).