Signal displacement in spiral-in acquisitions : simulations and implications for imaging in SFG regions

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DOITrouver le DOI : http://doi.org/10.1016/j.mri.2012.02.014
AuteurRechercher : ; Rechercher : ; Rechercher : ; Rechercher : ; Rechercher :
TypeArticle
Titre de la revueMagnetic Resonance Imaging
Volume30
Numéro6
Pages753763; nbre. de pages : 11
SujetFunctional MRI; Susceptibility; Artifacts; Spiral
RésuméSusceptibility field gradients (SFGs) cause problems for functional magnetic resonance imaging (fMRI) in regions like the orbital frontal lobes, leading to signal loss and image artifacts (signal displacement and “pile-up”). Pulse sequences with spiral-in k-space trajectories are often used when acquiring fMRI in SFG regions such as inferior/medial temporal cortex because it is believed that they have improved signal recovery and decreased signal displacement properties. Previously postulated theories explain differing reasons why spiral-in appears to perform better than spiral-out; however it is clear that multiple mechanisms are occurring in parallel. This study explores differences in spiral-in and spiral-out images using human and phantom empirical data, as well as simulations consistent with the phantom model. Using image simulations, the displacement of signal was characterized using point spread functions (PSFs) and target maps, the latter of which are conceptually inverse PSFs describing which spatial locations contribute signal to a particular voxel. The magnitude of both PSFs and target maps was found to be identical for spiral-out and spiral-in acquisitions, with signal in target maps being displaced from distant regions in both cases. However, differences in the phase of the signal displacement patterns that consequently lead to changes in the intervoxel phase coherence were found to be a significant mechanism explaining differences between the spiral sequences. The results demonstrate that spiral-in trajectories do preserve more total signal in SFG regions than spiral-out; however, spiral-in does not in fact exhibit decreased signal displacement. Given that this signal can be displaced by significant distances, its recovery may not be preferable for all fMRI applications.
Date de publication
Langueanglais
AffiliationConseil national de recherches Canada; Dispositifs médicaux
Publications évaluées par des pairsOui
Numéro NPARC21267974
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Identificateur de l’enregistrement6ce4bad9-8dd2-4c49-8b42-0f15ca517b1d
Enregistrement créé2013-03-27
Enregistrement modifié2016-05-09
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