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Abstract #5634

Rapid B1 mapping based on the Bloch-Siegert shift using a single offset frequency and multi-echo readout

Nadège Corbin1, Julio Acosta-Cabronero1, Oliver Josephs1, Nikolaus Weiskopf1,2, and Martina F Callaghan1

1Functional Imaging Laboratory (FIL) & Wellcome Center for Human Neuroimaging, UCL Institute of Neurology, London, United Kingdom, 2Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany

The advance towards in vivo histology benefits greatly from the quantification of specific physical parameters1. The longitudinal relaxation rate (R1) has proven a reliable surrogate for myelination, facilitating investigation of the relationship between brain microstructure and function in vivo2–5. R1 maps can be estimated by combining spoiled gradient-echo volumes, acquired with variable flip angles, and calibration data correcting for flip angle inhomogeneities. The Bloch-Siegert shift (BSS) approach6 is a relatively time-efficient method that allows the calibration data to be acquired with an identical gradient-echo readout thereby matching distortions across all data needed to map R1. However, it requires data to be acquired at two off-resonance frequencies to remove B0 dependence up to second order and suffers from high specific-absorption-rate (SAR). Here, we investigate a modified BSS-based B1+ mapping approach that aimed to overcome these shortcomings by using a single offset frequency and a multi-echo readout.

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