Researchers at the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) developed an MRI-method that is based on the acquisition of multiple pulsed field gradient (m-PFG) rather than single-pulsed field gradient (s-PFG) MRI sequences. In particular, double PFG (dPFG) MRI sequences offer higher sensitivity and greater robustness, as they are more sensitive to the effects of “restriction;” i.e., to water trapped within the axon’s intracellular space, and thus to the diameter of the axons. Thus, it renders the MRI data more sensitive to “pore size” and “pore shape,” making the measurement of the average axon diameter (AAD), and the axon diameter distribution (ADD) more sensitive and accurate. Moreover, measurements using the multiple-PFG sequence can be performed readily at ‘low b” or “low q” – making it biologically relevant and clinically feasible.