Abstract #3452

GRAPE-based slab-selective universal parallel transmit excitation pulses for whole-brain MRSI at 7 Tesla

Yannik Völzke^1,2, Daniel Löwen², Eberhard Daniel Pracht², Alexander Radbruch^1,2, Bernhard Strasser³, Lukas Hingerl³, Gilbert Hangel³, Philipp Lazen³, Wolgang Bogner³, and Tony Stöcker^2,4

¹Department of Neuroradiology, University Clinic Bonn, Bonn, Germany, ²German Center for Neurodegenerative Diseases, Bonn, Germany, ³High-Field MR Center, Department of Biomedical Imaging and Image-Guided Therapy, Medical University of Vienna, Vienna, Austria, ⁴Department of Physics and Astronomy, University of Bonn, Bonn, Germany

Synopsis

Keywords: Parallel Transmit & Multiband, Spectroscopy

Motivation: Whole-brain MRSI at ultra-high field is hampered by excitation field inhomogeneities which cause flip angle variations and, consequently, reduced SNR, especially in the cerebellum.

Goal(s): To improve the flip angle homogeneity and, consequently, increase the SNR of whole-brain ultra-high field MRSI by utilizing universal pTx-pulses.

Approach: Frequency-selective universal pTx-pulses(UP) were designed for homogeneous excitation with the GRAPE approach and implemented in a pulse-acquire-based MRSI sequence with concentric-ring readout at 7T. The spectral SNR was estimated with LCModel and compared to CP excitation.

Results: GRAPE-UP excitation achieves a mean SNR increase of 23% in the cerebellum and slight SNR increase over the whole brain.

Impact: This work shows the feasibility of GRAPE-based frequency-selective universal parallel transmit excitation pulses for whole-brain MRSI. These reduce spatial flip angle variations, and the resulting SNR loss, which is one of the main difficulties in whole-brain MRSI at ultra-high field.

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