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Abstract #3060

Characterisation of the flip angle dependence of R2* in Multi-Parameter Mapping

Giorgia Milotta1, Nadège Corbin1,2, Christian Lambert1, Antoine Lutti3, Siawoosh Mohammadi4,5, and Martina Callaghan1
1Wellcome Centre for Human Neuroimaging, UCL Queen Square Institute of Neurology, University College London, London, United Kingdom, 2Centre de Résonance Magnétique des Systèmes Biologiques, UMR5536, CNRS/University Bordeaux, Bordeaux, France, 3Laboratory for Research in Neuroimaging, Department for Clinical Neuroscience, Lausanne University Hospital and University of Lausanne, Lausanne, Switzerland, 4Department of Systems Neurosciences, University Medical Center Hamburg-Eppendorf, Hamburg, Germany, 5Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany

The apparent transverse relaxation rate (R2*) has biologically-relevant dependence on iron content and myelination. However confounding factors, e.g. flip angle dependence owing to differential longitudinal relaxation rates of sub-compartments, hinder interpretation. Multi-compartment models have been used to estimate myelin-water fraction from multi-echo spoiled GRE images, but require rich datasets for reliable estimation leading to extended acquisition times. A time-efficient alternative is to assume mono-exponential intra-voxel decay. In this work, we characterise the residual FA-dependence of such R2* estimates in vivo, and explore the biological origin of this dependence via simulations.

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