1. A computerized method of generating a myelin tissue fraction map of a brain in a displayable form, comprising: generating at least one magnetic resonance (MR) sequence of the brain with an MR scanner, thereby producing a range of images having different signal intensities; generating, in a computer based on using the range of images, a map of two or more observed physical properties of the brain, wherein a respective set of the two or more observed physical properties is determined for each voxel of the map; and the two or more physical properties include at least two of longitudinal relaxation time T1, transverse relaxation time T2, and proton density PD or at least two properties based on longitudinal relaxation time T1, transverse relaxation time T2, and proton density (PD); forming, in the computer, a simulation model by: partitioning each voxel into at least a myelin fraction, a cellular fraction, and a free water fraction, each of the myelin, cellular, and free water fractions having corresponding longitudinal relaxation rate (R1), a corresponding transversal relaxation rate (R2) and a corresponding PD, determining a first magnetic evolution coupling between the myelin fraction and the cellular fraction, and determining a second magnetic evolution coupling between the cellular fraction and the free water fraction, providing values for the myelin, cellular, and free water fractions, and generating values of longitudinal relaxation rate (R1), transversal relaxation rate (R2) and PD corresponding to the provided values of the myelin, cellular, and free water fractions based on the provided values and the first and second magnetic evolution couplings; and assigning, in the computer to each voxel of the map, at least a myelin tissue fraction by matching the voxels' observed R1, R2, and PD to a set of R1, R2, and PD generated by the simulation model, the myelin tissue fraction assigned corresponding to a myelin fraction used in the simulation model to generate the set of R1, R2, and PD, thereby generating the myelin tissue fraction map of the brain.