How to Avoid Artifacts from the FID of the First RF Pulse in a Twice-Refocused Spin-Echo Diffusion-Weighted Sequence

Zoltan Nagy¹, Nikolaus Weiskopf¹, David L. Thomas²

In the twice-refocused spin echo sequence for diffusion encoding several pathways may lead to a measurable signal, of which, only the twice-refocused spin echo should be acquired. Here we show that there is adequate signal from FID of the 1st RF pulse and care must be taken to make sure the diffusion-weighting and crusher gradients do not cancel each other for any of the diffusion-encoding directions. A general solution is hard to achieve because the gradient timings depend on the TE, gradient amplitude, etc but one solution may be to always use crushers orthogonal to the diffusion encoding direction.