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Background

Random motion of water molecules (diffusion) in the presence of a strong magnetic gradient results in MR signal loss as a result of the dephasing of spin coherence (Fig. 1). The application of a pair of strong gradients to elicit differences in the diffusivity of water molecules among various biologic tissues is known as diffusion sensitization or diffusion weighting [22, 23]. The degree of diffusion weighting is described by the b value, a parameter that is determined by the type of sensitizing gradient scheme implemented in the MR experiment. For the Stejskal-Tanner spin-echo scheme [24](Fig. 2)—a pulsed pair of approximately rectangular gradients around a 180 radiofrequency pulse that is most commonly implemented on clinical MR scanners—the b value is determined by the duration (δ) and strength (G) of the sensitizing pulsed gradients, and the time interval between the two pulsed gradients (Δ) is …