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

Tae Kim, Yoojin Lee, Tiejun Zhao, Hoby P. Hetherington, Jullie W. Pan
<span title="2016-12-01">2016</span> <i title="Wiley"> <a target="_blank" rel="noopener" href="https://fatcat.wiki/container/34p2n5u2vjfgrf7j2rmkmfhogu" style="color: black;">Magnetic Resonance in Medicine</a> </i> &nbsp;
Purpose: To quantitatively assess the effects of high degree and order (1 st -4 thþ ) relative to 1 st -2 nd degree B 0 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 (R Ã 2 ), BOLD % signal change and activated pixel counts in a breath-hold task. Results: Comparing
more &raquo; ... the 1 st -4 thþ degree with 1 st -2 nd degree shimmed B 0 maps generated spatially varying regions of DjB 0 j ¼ jB 1À2 0 j À jB 1À4þ 0 j. As binned in 10-Hz intervals, the two center DjB 0 j (610 Hz) bins maintained the B 0 offset of 48.6% of gray-matter pixels. In the positive DjB 0 j bins greater than 10 Hz, the 1 st -4 thþ degree shimming improved the B 0 offset in 41.1%; in negative DjB 0 j bins less than À10 Hz, the offset worsened in 10.2% of the pixels. In the positive DjB 0 j bins, we found variable but significant increases in BOLD sensitivity; the negative DjB 0 j bins showed significant decreases. In the breath-hold studies, positive bins showed significantly increased activated pixel numbers (þ5-29%), whereas negative bins showed À18 to 0% decline. Conclusion: 1 st -4 thþ degree shimming maintained B 0 homogeneity over central brain regions while improving most of the other regions, including the inferior frontal lobe. Magn Reson Med 78:1734-1745,
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