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.
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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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