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Sampling and reconstruction effects due to motion in diffusion‐weighted interleaved echo planar imaging
Author(s) -
Atkinson David,
Porter David A.,
Hill Derek L.G.,
Calamante Fernando,
Connelly Alan
Publication year - 2000
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/1522-2594(200007)44:1<101::aid-mrm15>3.0.co;2-s
Subject(s) - diffusion mri , nyquist–shannon sampling theorem , nuclear magnetic resonance , sampling (signal processing) , echo planar imaging , planar , diffusion , computer science , nyquist frequency , computer vision , physics , artificial intelligence , mathematics , magnetic resonance imaging , medicine , radiology , computer graphics (images) , filter (signal processing) , thermodynamics
Subject motion during diffusion‐weighted interleaved echo‐planar imaging causes k‐ space offsets which lead to irregular sampling in the phase‐encode direction. For each image, the k ‐space shifts are monitored using 2D navigator echoes, and are shown to lead to a frequent violation of the Nyquist condition when an ungated sequence is used on seven subjects. Combining data from four repeat acquisitions allows the Nyquist condition to be satisfied in all but 1% of images. Reconstruction of the irregularly‐sampled data can be performed using a matrix inversion technique. The repeated acquisitions make the inversion more stable and additionally improve the signal‐to‐noise ratio. The resultant isotropic diffusion‐weighted images and average apparent diffusion coefficient (ADC) maps show high resolution and enable clear localization of a stroke lesion. Residual ADC artifacts with a slow spatial variation are observed and assumed to originate from non‐rigid pulsatile brain motion. Magn Reson Med 44:101–109, 2000. © 2000 Wiley‐Liss, Inc.