Sub-millimeter T2 weighted fMRI at 7 T: comparison of 3D-GRASE and 2D SE-EPI

V.G. Kemper, F. de Martino, A.T. Vu, B.A. Poser, D.A. Feinberg, R. Goebel, E. Yacoub

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Abstract

Functional magnetic resonance imaging (fMRI) allows studying human brain function non-invasively up to the spatial resolution of cortical columns and layers. Most fMRI acquisitions rely on the blood oxygenation level dependent (BOLD) contrast employing T(*) 2 weighted 2D multi-slice echo-planar imaging (EPI). At ultra-high magnetic field (i.e., 7 T and above), it has been shown experimentally and by simulation, that T2 weighted acquisitions yield a signal that is spatially more specific to the site of neuronal activity at the cost of functional sensitivity. This study compared two T2 weighted imaging sequences, inner-volume 3D Gradient-and-Spin-Echo (3D-GRASE) and 2D Spin-Echo EPI (SE-EPI), with evaluation of their imaging point-spread function (PSF), functional specificity, and functional sensitivity at sub-millimeter resolution. Simulations and measurements of the imaging PSF revealed that the strongest anisotropic blurring in 3D-GRASE (along the second phase-encoding direction) was about 60% higher than the strongest anisotropic blurring in 2D SE-EPI (along the phase-encoding direction). In a visual paradigm, the BOLD sensitivity of 3D-GRASE was found to be superior due to its higher temporal signal-to-noise ratio (tSNR). High resolution cortical depth profiles suggested that the contrast mechanisms are similar between the two sequences, however, 2D SE-EPI had a higher surface bias owing to the higher T(*) 2 contribution of the longer in-plane EPI echo-train for full field of view compared to the reduced field of view of zoomed 3D-GRASE.
Original languageEnglish
Article number163
Number of pages14
JournalFrontiers in Neuroscience
Volume9
DOIs
Publication statusPublished - 5 May 2015

Keywords

  • 3D-GRASE
  • Spin-Echo EPI
  • T2
  • T2*
  • point-spread function
  • high-resolution BOLD fMRI
  • POINT-SPREAD FUNCTION
  • SPIN-ECHO FMRI
  • 2D-SELECTIVE RF EXCITATIONS
  • BOLD FUNCTIONAL MRI
  • HIGH MAGNETIC-FIELD
  • HUMAN BRAIN
  • GRADIENT-ECHO
  • HIGH-RESOLUTION
  • SIGNAL CHANGES
  • OF-VIEW

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