1. A method for producing an image with an MRI system, the steps comprising: a) acquiring a first NMR signal at a first echo time and a second NMR signal at a second echo time; b) repeating step a) a plurality of times to sample a corresponding plurality of first and second NMR signals; c) forming a first k-space data set with the plurality of first NMR signals acquired in steps a) and b); d) forming a second k-space data set with the plurality of second NMR signals acquired in steps a) and b); e) producing a phase difference image by: e)i) producing a first phase image from the first k-space data set formed in step c); e)ii) producing a second phase image from the second k-space data set formed in step d); e)iii) subtracting the first phase image and the second phase image to produce the phase difference image; f) producing a phase shifted k-space data set by rotating a phase of the acquired k-space samples in the first k-space data set formed in step c); g) producing a combined k-space data set by combining the phase shifted k-space data set produced in step f) with the second k-space data set formed in step d); h) reconstructing a combined image from the combined k-space data set produced in step g); and i) producing an image having a substantially suppressed signal contribution from an unwanted spin species by thresholding the combined image reconstructed in step h) based on image intensity values in the phase difference image produced in step e).