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Parallel transmit (pTx) with online pulse design for task-based fMRI at 7 T.

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Ding, Belinda 
Dragonu, Iulius 
Rua, Catarina 
Carlin, Johan D 
Halai, Ajay D 


PURPOSE: Parallel transmission (pTx) is an approach to improve image uniformity for ultra-high field imaging. In this study, we modified an echo planar imaging (EPI) sequence to design subject-specific pTx pulses online. We compared its performance against EPI with conventional circularly polarised (CP) pulses. METHODS: We compared the pTx-EPI and CP-EPI sequences in a short EPI acquisition protocol and for two different functional paradigms in six healthy volunteers (2 female, aged 23-36 years, mean age 29.2 years). We chose two paradigms that are typically affected by signal dropout at 7 T: a visual objects localiser to determine face/scene selective brain regions and a semantic-processing task. RESULTS: Across all subjects, pTx-EPI improved whole-brain mean temporal signal-to-noise ratio (tSNR) by 11.0% compared to CP-EPI. We also compared the ability of pTx-EPI and CP-EPI to detect functional activation for three contrasts over the two paradigms: face > object and scene > object for the visual objects localiser and semantic association > pattern matching for the semantic-processing paradigm. Across all three contrasts, pTx-EPI showed higher median z-scores and detected more active voxels in relevant areas, as determined from previous 3 T studies. CONCLUSION: We have demonstrated a workflow for EPI acquisitions with online per-subject pulse calculations. We saw improved performance in both tSNR and functional acquisitions from pTx-EPI. Thus, we believe that online calculation pTx-EPI is robust enough for future fMRI studies, especially where activation is expected in brain areas liable to significant signal dropout.



7 T, Parallel transmit, Spokes, Ultra-high field, fMRI, Adult, Brain, Brain Mapping, Contrast Media, Echo-Planar Imaging, Female, Humans, Magnetic Resonance Imaging, Signal-To-Noise Ratio

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Magn Reson Imaging

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Elsevier BV
Wellcome Trust (Unknown)
Wellcome Trust (098436/Z/12/B)
National Institute for Health and Care Research (IS-BRC-1215-20014)
MRC (MR/V031481/1)
BD was funded by Gates Cambridge Trust. CR was funded by the Cambridge Centre for Parkinson- Plus. CTR was funded by a Sir Henry Dale Fellowship from the Wellcome Trust and the Royal Society [098436/Z/12/B]. This research was supported by the NIHR Cambridge Biomedical Research Centre (BRC-1215-20014). The views expressed are those of the author(s) and not necessarily those of the NIHR or the Department of Health and Social Care.