Article (Scientific journals)
Improved shimming for fMRI specifically optimizing the local BOLD sensitivity
Balteau, Evelyne; Hutton, Chloe; Weiskopf, Nikolaus
2010In NeuroImage, 49, p. 327-336
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Keywords :
BOLD sensitivity; Shimming; fMRI
Abstract :
[en] In functional MRI, magnetic field inhomogeneities due to air-tissue susceptibility differences may lead to severe signal dropouts and geometric distortions in echo-planar images. Therefore, the inhomogeneities in the field are routinely minimized by shimming prior to imaging. However in fMRI, the Blood Oxygen Level Dependent (BOLD) effect is the measure of interest, so the BOLD sensitivity (BS) should be optimized rather than the magnetic field homogeneity. The analytical expression for an estimate of the BOLD sensitivity has been recently developed, allowing for the computation of BOLD sensitivity maps from echo-planar images and field maps. This report describes a novel shimming procedure that optimizes the local BOLD sensitivity over a region of interest. The method is applied in vivo and compared to a standard global shimming procedure. A breath-holding experiment was carried out and demonstrated that the BS-based shimming significantly improved the detection of activation in a target region of interest, the medial orbitofrontal cortex.
Disciplines :
Anatomy (cytology, histology, embryology...) & physiology
Physics
Author, co-author :
Balteau, Evelyne ;  Université de Liège - ULiège > Centre de recherches du cyclotron
Hutton, Chloe;  University College London - UCL > Wellcome Trust Centre for Neuroimaging
Weiskopf, Nikolaus;  University College London - UCL > Wellcome Trust Centre for Neuroimaging
Language :
English
Title :
Improved shimming for fMRI specifically optimizing the local BOLD sensitivity
Publication date :
2010
Journal title :
NeuroImage
ISSN :
1053-8119
eISSN :
1095-9572
Publisher :
Elsevier Science, Orlando, United States - Florida
Volume :
49
Pages :
327-336
Peer reviewed :
Peer Reviewed verified by ORBi
Funders :
F.R.S.-FNRS - Fonds de la Recherche Scientifique [BE]
Wellcome Trust [GB]
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