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Phase Errors in Diffusion-Weighted Imaging 

Phase Errors in Diffusion-Weighted Imaging
Chapter:
Phase Errors in Diffusion-Weighted Imaging
Author(s):

Roland Bammer

, Samantha J. Holdsworth

, Murat Aksoy

, and Stefan T. Skare

DOI:
10.1093/med/9780195369779.003.0014
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date: 17 July 2018

One of the greatest technical challenges for diffusion-weighted imaging (DWI) is overcoming the phase errors originating from macroscopic motion, that is from bulk and physiologic motion, while simultaneously retaining its sensitivity to microscopic motion. Due to the randomness of motion the phase of the echo in a standard spin-warp acquisition will be perturbed differently and in an unpredictable fashion, ultimately leading to substantial ghosting artifacts in the final images. Moreover, this additional phase impressed on the spins will also challenge the phase requirements between transverse magnetization and radio-frequency (RF) pulses for FSE and driven-equilibrium (DE) approaches. Controlling phase errors is not only the gatekeeper for high-resolution multi-shot DTI, but also for improving the quality and reproducibility of such sequences. This chapter describes the origins of such motion effects, how they can be entered into the MR signal model for a diffusion sequence for both image encoding and radio-frequency excitation/refocusing, and how such effects can be corrected for.

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