Abstract #3060

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

Giorgia Milotta¹, Nadège Corbin^1,2, Christian Lambert¹, Antoine Lutti³, Siawoosh Mohammadi^4,5, 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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