Diffusion-weighted imaging of biliopancreatic disorders: Correlation with conventional magnetic resonance imaging

Figure 2 Diagram of diffusion-weighted sequence. DWI 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 perfectly by the second diffusion gradient; therefore measured high signal intensity is preserved. In contrast, moving molecules undergo dephasing but are not entirely rephased by the second gradient because of their motion, thereby resulting in signal loss. DWI: Diffusion-weighted magnetic resonance imaging; RF: Radiofrequency.