title: Gradient-echo EPI using a high-degree shim insert coil at 7 T: Implications for BOLD fMRI.
abstract: To quantitatively assess the effects of high degree and order (1st-4th+) relative to 1st-2nddegree B0shimming at 7 Tesla (T) on gradient-echo echo planar imaging (GE-EPI) and blood-oxygen-level dependent (BOLD) activation.
  
  
  
  Simulations and GE-EPI were performed at (2mm)3and (3mm)3resolution, evaluating the temporal signal-to-noise ratio (tSNR), transverse relaxivity ( R2*), BOLD % signal change and activated pixel counts in a breath-hold task.
  
  
  
  Comparing the 1st-4th+degree with 1st-2nddegree shimmed B0maps generated spatially varying regions of Δ|B0|=|B01-2|-|B01-4+|. As binned in 10-Hz intervals, the two center Δ|B0| (±10 Hz) bins maintained the B0offset of 48.6% of gray-matter pixels. In the positive Δ|B0| bins greater than 10 Hz, the 1st-4th+degree shimming improved the B0offset in 41.1%; in negative Δ|B0| bins less than -10 Hz, the offset worsened in 10.2% of the pixels. In the positive Δ|B0| bins, we found variable but significant increases in BOLD sensitivity; the negative Δ|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.
  
  
  
  1st-4th+degree shimming maintained B0homogeneity 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.
authors.affiliation: Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.|Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
authors.forename: Tae
authors.initials: T
authors.lastname: Kim
authors.affiliation: Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
authors.forename: Yoojin
authors.initials: Y
authors.lastname: Lee
authors.affiliation: Siemens Healthineers, USA, Siemens Medical Solution USA, Pittsburgh, Pennsylvania, USA.
authors.forename: Tiejun
authors.initials: T
authors.lastname: Zhao
authors.affiliation: Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
authors.forename: Hoby P
authors.initials: HP
authors.lastname: Hetherington
authors.affiliation: Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.|Department of Neurology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
authors.forename: Jullie W
authors.initials: JW
authors.lastname: Pan
mesh_terms: D000328:Adult; D000465:Algorithms; D001921:Brain / Q000000981:diagnostic imaging*; D017352:Echo-Planar Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged
keywords: B0 mapping; BOLD; functional MRI; high magnetic field; shimming