Figure 1.

Diagram of diffusion-weighted sequence. It is based on T2-weighted spin-echo sequencing with application of two equal gradient pulses (a dephasing gradient and a rephasing gradient) on each side of the 180° radiofrequency pulse. Static molecules are dephased by the first diffusion gradient and rephased by the second diffusion gradient; therefore measured high signal intensity is maintained. In contrast, moving molecules undergo dephasing by the first diffusion gradient but are not entirely rephased by the second gradient because of their motion, thereby resulting in signal loss. Diffusion sensitizing is commonly applied in three orthogonal directions at the same time for DW-MRI.