Improving fMRI in signal drop-out regions at 7 T by using tailored radio-frequency pulses: application to the ventral occipito-temporal cortex
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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.
Materials and methods
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.
KeywordsFunctional MRI Ultra high field Tailored radio-frequency pulse Signal drop-out recovery
This work was supported by the Initial Training Network, HiMR, funded by the FP7 Marie Curie Actions of the European Commission (FP7-PEOPLE-2012-ITN-316716).
CR Project development, data collection and data analysis. SJW Project development and data collection. MC Project development, data collection and data analysis. MRS Project development, data collection and data analysis. LB Project development and data collection. MC Project development and data management. ADG Project development. MT Project development and data management. GJB Project development and data management.
Compliance with ethical standards
CR was supported by the Initial Training Network, HiMR, funded by the FP7 Marie Curie Actions of the European Commission (FP7-PEOPLE-2012-ITN-316716).
Conflict of interest
MRS is employed by General Electric Healthcare. GJB receives honoraria for teaching from General Electric Healthcare, who also part fund a PhD studentship. GJB acts as a consultant for IXICO.
All procedures involving human participants were in accordance with the ethical standards of the competent ethics committee and with the 1964 Helsinki declaration and its later amendments.
Written informed consent was obtained from all individual participants included in the study.
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