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Abstract
We investigate the utility of RF parallel transmission (pTx) for whole-brain resting-state
functional MRI (rfMRI) acquisition at 7 Tesla (7T). To this end, Human Connectome
Project (HCP)-style data acquisitions were chosen as a showcase example. Five healthy
subjects were scanned in pTx and single-channel transmit (1Tx) modes. The pTx data
were acquired using a prototype 16-channel transmit system and a commercially available
Nova 8-channel transmit 32-channel receive RF head coil. Additionally, pTx single-spoke
multiband (MB) pulses were designed to image sagittal slices. HCP-style 7T rfMRI data
(1.6-mm isotropic resolution, 5-fold slice and 2-fold inplane acceleration, 3600 volumes
and ~ 1-hour scan) were acquired with pTx and the results were compared to those acquired
with the original 7T HCP rfMRI protocol. The use of pTx significantly improved flip-angle
uniformity across the brain, with coefficient of variation (i.e., std/mean) of whole-brain
flip-angle distribution reduced on average by ~39%. This in turn yielded ~17% increase
in group temporal SNR (tSNR) as averaged across the entire brain and ~10% increase
in group functional contrast-to-noise ratio (fCNR) as averaged across the grayordinate
space (including cortical surfaces and subcortical voxels). Furthermore, when placing
a seed in either the posterior parietal lobe or putamen estimate seed-based dense
connectome, the increase in fCNR was observed to translate into stronger correlation
of the seed with the rest of the grayordinate space. We have demonstrated the utility
of pTx for slice-accelerated highresolution whole-brain rfMRI at 7T; as compared to
current state-of-the-art, the use of pTx improves flip-angle uniformity, increases
tSNR, enhances fCNR and strengthens functional connectivity estimation.