Dataset Information

Gradient-echo EPI using a high-degree shim insert coil at 7?T: Implications for BOLD fMRI.

ABSTRACT:

Purpose

To quantitatively assess the effects of high degree and order (1^st -4^th+ ) relative to 1^st -2^nd degree B₀ shimming at 7 Tesla (T) on gradient-echo echo planar imaging (GE-EPI) and blood-oxygen-level dependent (BOLD) activation.

Methods

Simulations and GE-EPI were performed at (2mm)³ and (3mm)³ resolution, evaluating the temporal signal-to-noise ratio (tSNR), transverse relaxivity ( R2*), BOLD % signal change and activated pixel counts in a breath-hold task.

Results

Comparing the 1^st -4^th+ degree with 1^st -2^nd degree shimmed B₀ maps generated spatially varying regions of ?|B0|=|B01-2|-|B01-4+|. As binned in 10-Hz intervals, the two center ?|B₀ | (±10?Hz) bins maintained the B₀ offset of 48.6% of gray-matter pixels. In the positive ?|B₀ | bins greater than 10?Hz, the 1^st -4^th+ degree shimming improved the B₀ offset in 41.1%; in negative ?|B₀ | bins less than -10?Hz, the offset worsened in 10.2% of the pixels. In the positive ?|B₀ | bins, we found variable but significant increases in BOLD sensitivity; the negative ?|B₀ | bins showed significant decreases. In the breath-hold studies, positive bins showed significantly increased activated pixel numbers (+5-29%), whereas negative bins showed -18 to 0% decline.

Conclusion

1^st -4^th+ degree shimming maintained B₀ homogeneity over central brain regions while improving most of the other regions, including the inferior frontal lobe. Magn Reson Med 78:1734-1745, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

SUBMITTER: Kim T

PROVIDER: S-EPMC6084307 | biostudies-literature | 2017 Nov

REPOSITORIES: biostudies-literature

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Publications

Gradient-echo EPI using a high-degree shim insert coil at 7 T: Implications for BOLD fMRI.

Kim Tae T Lee Yoojin Y Zhao Tiejun T Hetherington Hoby P HP Pan Jullie W JW

Magnetic resonance in medicine 20161201 5

<h4>Purpose</h4>To quantitatively assess the effects of high degree and order (1<sup>st</sup> -4<sup>th+</sup> ) relative to 1<sup>st</sup> -2<sup>nd</sup> degree B<sub>0</sub> shimming at 7 Tesla (T) on gradient-echo echo planar imaging (GE-EPI) and blood-oxygen-level dependent (BOLD) activation.<h4>Methods</h4>Simulations and GE-EPI were performed at (2mm)<sup>3</sup> and (3mm)<sup>3</sup> resolution, evaluating the temporal signal-to-noise ratio (tSNR), transverse relaxivity ( R2*), BOLD % si ...[more]

PMID: 27910126

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