Rua Catarina, Wastling Stephen J, Costagli Mauro, Symms Mark R, Biagi Laura, Cosottini Mirco, Del Guerra Alberto, Tosetti Michela, Barker Gareth J
Department of Physics, University of Pisa, Largo B. Pontecorvo 3, Pisa, Italy.
Imago7 Foundation, Viale del Tirreno 331, Calambrone, Italy.
MAGMA. 2018 Apr;31(2):257-267. doi: 10.1007/s10334-017-0652-x. Epub 2017 Sep 20.
Signal drop-off occurs in echo-planar imaging in inferior brain areas due to field gradients from susceptibility differences between air and tissue. Tailored-RF pulses based on a hyperbolic secant (HS) have been shown to partially recover signal at 3 T, but have not been tested at higher fields.
The aim of this study was to compare the performance of an optimized tailored-RF gradient-echo echo-planar imaging (TRF GRE-EPI) sequence with standard GRE-EPI at 7 T, in a passive viewing of faces or objects fMRI paradigm in healthy subjects.
Increased temporal-SNR (tSNR) was observed in the middle and inferior temporal lobes and orbitofrontal cortex of all subjects scanned, but elsewhere tSNR decreased relative to the standard acquisition. In the TRF GRE-EPI, increased functional signal was observed in the fusiform, lateral occipital cortex, and occipital pole, regions known to be part of the visual pathway involved in face-object perception.
This work highlights the potential of TRF approaches at 7 T. Paired with a reversed-gradient distortion correction to compensate for in-plane susceptibility gradients, it provides an improved acquisition strategy for future neurocognitive studies at ultra-high field imaging in areas suffering from static magnetic field inhomogeneities.
