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A Velocity k ‐Space Analysis of Flow Effects in Echo‐Planar and Spiral Imaging
Author(s) -
Nishimura Dwight G.,
Irarrazabal Pablo,
Meyer Craig H.
Publication year - 1995
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/mrm.1910330414
Subject(s) - planar , spiral (railway) , physics , ghosting , position (finance) , k space , orientation (vector space) , formalism (music) , optics , geometry , mathematics , mathematical analysis , fourier transform , computer science , art , economics , visual arts , musical , computer graphics (images) , finance , quantum mechanics
A velocity k ‐space formalism facilitates the analysis of flow effects for imaging sequences involving time‐varying gradients such as echo‐planar and spiral. For each sequence, the velocity k ‐space trajectory can be represented by k v (k) r ; that is, its velocity‐frequency (k r ) position as a function of spatial‐frequency (k r ) position. In an echo‐planar sequence, k r is discontinuous and asymmetric. However, in a spiral sequence, k r is smoothly varying, circularly symmetric, and small near the k r origin. To compare the effects of these trajectory differences, simulated images were generated by computing the k ‐space values for an in‐plane vessel with parabolic flow. Whereas the resulting echo‐planar images demonstrate distortions and ghosting that depend on the vessel orientation, the spiral images exhibit minimal artifacts.