A method of imaging two chemical species using magnetic resonance imaging with signal separation for the two chemical species, the method comprising predetermining different echo times, wherein said predetermination comprises: - selecting or calibrating a spectral signal model of at least one of the chemical species, - calculating the evolution of the amplitude and phase over echo time of the signal of at least one of the chemical species, described by time variant complex weights, and - selecting echo times for which these complex weights satisfy predefined constraints, by which the number of voxels for which the modelling yields more than one mathematical solution is minimized in the signal separation, the method further comprising: - acquiring first and second echo data using the selected echo times resulting in a first and second acquired complex dataset, - modelling the first and second acquired dataset, said modelling comprising said selected or calibrated spectral signal model, wherein the signal S of each dataset in image space is modeled as S = ( W + cF) e iφ, where W and F denote the signals of the two chemical species, and φ and e iφ denote a phase error and a corresponding phasor, the complex factor c being given by c = ∑ m w m e iθ m, where w m denotes weights that add up to one, and θ m equals 2πΔ f m TE, with Δ f m, being the offset in resonance frequency of the m -th peak of the spectrum of the chemical species F with respect to the chemical species W, and TE being the respective echo time, - identifying in the first and second acquired dataset the voxels for which the modelling yields a single, unambiguous mathematical solution for the signal separation, and - resolving the ambiguity for the voxels for which the modelling yields more than one mathematical solution, if any such voxels remain. - selecting or calibrating a spectral signal model of at least one of the chemical species, - calculating the evolution of the amplitude and phase over echo time of the signal of at least one of the chemical species, described by time variant complex weights, and - selecting echo times for which these complex weights satisfy predefined constraints, by which the number of voxels for which the modelling yields more than one mathematical solution is minimized in the signal separation, - acquiring first and second echo data using the selected echo times resulting in a first and second acquired complex dataset, - modelling the first and second acquired dataset, said modelling comprising said selected or calibrated spectral signal model, wherein the signal S of each dataset in image space is modeled as S = ( W + cF) e iφ, where W and F denote the signals of the two chemical species, and φ and e iφ denote a phase error and a corresponding phasor, the complex factor c being given by c = ∑ m w m e iθ m, where w m denotes weights that add up to one, and θ m equals 2πΔ f m TE, with Δ f m, being the offset in resonance frequency of the m -th peak of the spectrum of the chemical species F with respect to the chemical species W, and TE being the respective echo time, - identifying in the first and second acquired dataset the voxels for which the modelling yields a single, unambiguous mathematical solution for the signal separation, and - resolving the ambiguity for the voxels for which the modelling yields more than one mathematical solution, if any such voxels remain.