Fig 3. Pulse sequence diagrams show the benefits of parallel imaging for DWI. At an acceleration factor of R = 2, the echo-train length for the single-shot EPI acquisition is only half as long. This is reflected in a shorter readout time (t_acq) and allows the echo train to be better centered at the peak of the spin-echo, improving SNR, decreasing T2 and T2* contrast blurring, and reducing off-resonance artifacts that cause geometric distortions. The shorter readout time also enables a reduction of TE, further improving SNR and reducing geometric distortion. However, the use of parallel imaging results in an intrinsic loss of SNR that may offset the aforementioned SNR gains. RF indicates radio-frequency.