A method for post-processing images of a region of interest in a subject, the images being acquired with a magnetic resonance imaging technique, the magnetic resonance imaging technique involving successive echoes of a multiple-gradient echo sequence with bipolar readout gradients, each image associating to each pixel of the image the amplitude of the measured signal in the magnetic resonance imaging technique and the phase of the measured signal in the magnetic resonance imaging technique, the method for post-processing comprising at least the steps of: - unwrapping the phase of each image, to obtain unwrapped images, - extracting a complex signal over echo time for at least one pixel of the unwrapped images, to obtain at least one extracted complex signal, and - calculating fat characterization parameters by using a fitting technique applied on a model, the model being a function which associates to a plurality of parameters each extracted complex signal, the plurality of parameters comprising at least two fat characterization parameters, the magnitude error generated by the use of the bipolar readout gradients and the phase error generated by the use of the bipolar readout gradients, the model further depending on the complex intensity of water, the complex intensity of fat and a complex field map taking into account the effect of transversal relaxivity rate and the field inhomogeneity in the magnetic field used in the magnetic resonance imaging technique, and the fat characterization parameters being chosen in the group consisting of the number of double bounds, the number of methylene-interrupted double bounds and the chain length, and whereby, at the step of calculating, the parameters are derived by using the fitting technique, the fitting technique being a non-linear least-square fitting technique using pseudo-random initial conditions. - unwrapping the phase of each image, to obtain unwrapped images, - extracting a complex signal over echo time for at least one pixel of the unwrapped images, to obtain at least one extracted complex signal, and - calculating fat characterization parameters by using a fitting technique applied on a model, the model being a function which associates to a plurality of parameters each extracted complex signal, the plurality of parameters comprising at least two fat characterization parameters, the magnitude error generated by the use of the bipolar readout gradients and the phase error generated by the use of the bipolar readout gradients, the model further depending on the complex intensity of water, the complex intensity of fat and a complex field map taking into account the effect of transversal relaxivity rate and the field inhomogeneity in the magnetic field used in the magnetic resonance imaging technique, and the fat characterization parameters being chosen in the group consisting of the number of double bounds, the number of methylene-interrupted double bounds and the chain length, the model being a function which associates to a plurality of parameters each extracted complex signal, the plurality of parameters comprising at least two fat characterization parameters, the magnitude error generated by the use of the bipolar readout gradients and the phase error generated by the use of the bipolar readout gradients, the model further depending on the complex intensity of water, the complex intensity of fat and a complex field map taking into account the effect of transversal relaxivity rate and the field inhomogeneity in the magnetic field used in the magnetic resonance imaging technique, and the fat characterization parameters being chosen in the group consisting of the number of double bounds, the number of methylene-interrupted double bounds and the chain length,