1. A method of separating and imaging at least two species using magnetic resonance imaging (MRI) comprising steps of: a) acquiring low resolution image information at multiple echo times, b) acquiring some fraction of the higher resolution information at multiple echo times, c) estimating low resolution images of species content and a low resolution field map estimate from (a), d) using the low resolution images of species content and low resolution field map estimates in (c) to reconstruct higher resolution species images from the partial information in (b).