Fat suppression using dynamic parallel transmission at 7T: application to whole-brain CEST MRI
Simon Lévy1, Jürgen Herrler2, Andrzej Liebert1, Katharina Tkotz1, Moritz S. Fabian2, Christian Eisen1, Michael Uder1, David Grodzki3, Moritz Zaiss2, and Armin M. Nagel1,4
1Institute of Radiology, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany, 2Department of Neuroradiology, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany, 3MR Application Predevelopment, Siemens Healthcare, Erlangen, Germany, 4Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
Fat signal can cause strong artifacts in MR images and/or bias measurements such as in Chemical Exchange Saturation Transfer (CEST) where metabolites peaks are reduced. At 7T, the signal-to-noise ratio and the peak separation are increased but the Specific Absorption Rate (SAR) constraints too, limiting the use of fat suppression pulses. Parallel transmit dynamic pulses for fat saturation (using kT-points) and water-selection (using a Spiral Non-Selective trajectory) were implemented for a whole-brain CEST protocol and optimized to reduce SAR compared to the standard circularly-polarized approach. Results showed high improvements in flip angle homogeneity and fat suppression efficiency, with reduced SAR.
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