A method of analysing the magnitude of Magnetic Resonance Imaging (MRI) data to determine the relative signal contributions of at least two species to each voxel of the images, the method comprising the steps of: using the magnitude only of the multi-echo MRI data of images from the subject, where the images are acquired at arbitrarily timed echoes including at least one echo time where water and fat are not substantially in-phase with each other; fitting the magnitude of said multi-echo MRI data to a single signal model to produce a plurality of potential solutions for the relative signal contributions for each of the at least two species from the model, by using a plurality of different starting conditions to generate a particular cost function value for each of the plurality of starting conditions, where said cost function values are independent of a field map term for the MRI data; and analysing said cost function values to calculate the relative signal separation contribution for each species at each voxel of the images.
A METHOD OF ANALYSING MAGNETIC RESONANCE IMAGING IMAGES