Asymmetric spin-echo (ASE) spiral improves BOLD fMRI in inhomogeneous regions

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Journal titleNMR in Biomedicine
Pages654662; # of pages: 9
SubjectfMRI; blood oxygen-level-dependent Contrast (BOLD); susceptibility artifacts; pulse sequence design; spiral; asymmetric spin-echo spiral
AbstractFunctional MRI (fMRI) is of limited use in areas such as the orbitofrontal and inferior temporal lobes due to the presence of local susceptibility-induced field gradients (SFGs), which result in severe image artifacts. Several techniques have been developed to reduce these artifacts, the most common being the dual-echo spiral sequences (spiral-in/out and spiral-in/in). In this study, a new multiple spiral acquisition technique was developed, in which the later spiral acquisitions are acquired asymmetrically with the peak of a spin-echo causing increased R2-weighting but matched R2′-weighting. This sequence, called asymmetric spin-echo (ASE) spiral, has demonstrated significant improvements in minimizing the signal loss and increasing the image quality as well as optimal blood-oxygen-level-dependent (BOLD)-weighting. The ASE spiral is compared to conventional spiral-out using both signal-to-noise ratio (SNR) and whole brain fMRI activation volumes from a breath-hold task acquired at 4 Tesla. The ASE dual spiral has exhibited SNR increases of up to 300% in areas where strong SFGs are present. As a result, the ASE spiral is highly efficient for recovering lost activation in areas of SFGs, as demonstrated by a 16% increase in the total number of activated voxels over the whole brain. Post spin-echo ASE spiral images have decreasing SNR due to R2 signal losses, however the increase in R2-weighting leads to a higher percentage of signal changes producing ASE spiral images with equivalent contrast-to-noise ratio (CNR) for each echo. The use of this sequence allows for recovery of BOLD activation in areas of SFG without sacrificing the CNR over the whole brain.
Publication date
AffiliationNRC Institute for Biodiagnostics; National Research Council Canada
Peer reviewedYes
NPARC number20171302
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Record identifier70343209-63bf-46b8-b609-1fcd2895b73a
Record created2012-06-22
Record modified2016-05-09
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