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Abstract #4745

Further Insights into (ih)MT: Four-Pool Model Analysis Accounting for Dipolar Order in ex vivo White Matter

Niklas Wallstein1, André Pampel1, Anders Dyhr Sandgaard2, Carsten Jäger3,4, Roland Müller1, and Harald Möller1,5
1NMR Methods & Development Group, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, 2Department of Clinical Medicine, Center of Functionally Integrative Neuroscience, Aarhus University, Aarhus, Denmark, 3Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, 4Center of Neuropathology and Brain Research, Medical Faculty, University of Leipzig, Paul Flechsig Institute, Leipzig, Germany, 5Institute for Solid State Physics, Leipzig University, Leipzig, Germany

Synopsis

Keywords: Microstructure, Relaxometry, Four-Pool Model, inhomogeneous Magnetization Transfer (ihMT)

Motivation: Recent findings indicate that simplified two-pool models are inadequate for modelling MR behaviour of white matter, suggesting a sophisticated four-pool model (4PM) consisting of two aqueous and two non-aqueous reservoirs.

Goal(s): To extend the four-pool model to include effects of dipolar order created by off-resonant RF pulses and to address the question of appropriate RF absorption lineshapes.

Approach: Comprehensive set of MR relaxometry acquisitions was performed in fixated nervus opticus with a custom-made setup at physiological temperature.

Results: The fit of the ‘extended 4PM’ demonstrates the existence of (at least) two dipolar order relaxation times (T1D) and remarkable deviations from super-Lorentzian absorption behaviour.

Impact: Experimental evidence was provided for the need for an ‘extended 4PM’ with dipolar reservoirs. Systematic deviations in the z-spectra were resolved by a ‘free lineshape’ model, providing enhanced sensitivity to tissue microstructure (e.g., cylindrical arrangement of myelin).

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