1. A method of MR imaging of at least two chemical species having different MR spectra, the method comprising the steps of: a) generating at least one echo signal by subjecting a body placed in the examination volume of a MR device to an imaging sequence of RF pulses and switched magnetic field gradients; b) acquiring the at least one echo signal; c) separating signal contributions of the at least two chemical species to the at least one acquired echo signal on the basis of a multi-peak spectral model for at least one of the chemical species and the prior knowledge about spatial variations of the main magnetic field B 0 in the examination volume; and wherein a phase evolution of the signal contributions of the at least two chemical species over the respective echo time on the order of π, 2π, or more is predicted according to the spatial variations of the main magnetic field B 0 , wherein the prediction of the phase evolution of the signal contributions of the at least two chemical species over the respective echo time is used to demodulate the phase of these signal contributions before the separation on the basis of the multi-peak spectral model, wherein the multi-peak spectral model on which the separation is based considers phase errors reflecting further main magnetic field variations, wherein the prior knowledge about the spatial variations of the main magnetic field B 0 is gained from: design parameters of a main magnet coil of the MR device and/or from shimming parameters; a measurement by means of magnetic field probes; or a B 0 map obtained from a separate MR scan; and d) reconstructing a MR image from the signal contributions of at least one of the chemical species.