Frontiers in Neuroscience (May 2015)

Sub-Millimeter T2 Weighted fMRI at 7 T: Comparison of 3D-GRASE and 2D SE-EPI

  • Valentin G. Kemper,
  • Federico eDe Martino,
  • Federico eDe Martino,
  • An T. Vu,
  • Benedikt A. Poser,
  • David A. Feinberg,
  • David A. Feinberg,
  • Rainer eGoebel,
  • Essa eYacoub

DOI
https://doi.org/10.3389/fnins.2015.00163
Journal volume & issue
Vol. 9

Abstract

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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 T2* 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, functional specificity, and functional sensitivity at sub-millimeter resolution. Simulations and measurements of the imaging point-spread function 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. 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 T2* 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.

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