Figure 11

Pulse sequences used for diffusion imaging of the myocardium. The diffusion-encoding gradients are represented by the black rectangles, TD is the trigger delay, δ describes the duration of the diffusion-encoding gradient and Δ the diffusion time interval. Single-shot EPI readouts are used in all cases. (A) In the Stejskal-Tanner sequence diffusion-encoding gradients are placed on either side of a 180° refocusing pulse. This sequence can be used to image the myocardium ex-vivo but cannot be used to image moving tissues. (B-D): Cardiac gated sequences. The two vertical lines breaking the baseline of the ECG indicate that the timeline of the diffusion-encoding gradients is not drawn to the same scale as the ECG. (B) Diffusion-encoded stimulated echo sequence used to image the myocardium in-vivo [47]. The diffusion time (Δ) equals TE/2 plus the mixing time (TM) and is thus much longer than TE. (C) Stimulated echo sequence with bipolar diffusion-encoding gradients [12]. No diffusion encoding occurs between the second and third RF pulses with this sequence. With standard gradient strengths, the time needed to achieve an adequate b-value with the bipolar gradients lengthens the TE significantly and becomes limiting. (D) Modified (flow-compensated) Stejskal-Tanner sequence with bipolar diffusion-encoding gradients. Implementation of this sequence in-vivo was feasible on a clinical 3T scanner with gradient strengths greater than 80 mT/m [52].