Figure 1.

Pulse-sequence diagram of a diffusion-weighted spin-echo sequence based on a Stejskal-Tanner encoding scheme. Two precisely matched diffusion-sensitizing gradients are inserted before and after a 180° radiofrequency refocusing pulse. Important factors defining the degree of diffusion sensitization (‘b value’) are the gradient amplitude (G), duration (δ), and the time between the two sensitizing gradients (Δ). The resulting signal is reduced in proportion to the water mobility, with less restricted environments exhibiting larger decreases in signal.