Scan-rescan Reproducibility of Myelin Sensitive MRI Techniques

Magnetization Transfer Imaging (MTI) permits the assessment of the integrity of macromolecules in brain tissue, such as myelin and cellular/axonal membrane components.

Multi-echo Susceptibility-Based imaging (SBI) provides quantitative susceptibility maps and T2* maps that - when combined - permit the disentanglement of myelin from iron and various phases of myelin degradation.

Myelin Water Imaging (MWI) quantifies the water trapped between myelin layers by separating the multiple water components in T2 relaxometry data. In fact, the presence of myelin on water pools bound to it provokes a loss in magnetic resonance (MR)-signal coherence, which is more rapid than the one characterizing the water pools located within the axons or in the cytoplasm.

A method based on a spiral acquisition that achieves a myelin-specific signal in clinically compatible scan times is currently applied: T1 relaxometry (quantitative T1, qT1) - which measures the time that a perturbed nuclear spin distribution needs to get back to equilibrium in the longitudinal plane- is sensitive to a number of components of the brain tissue such as myelin, axonal diameter and the overall architectural organization of the brain tissue.

Finally, multi-shell diffusion allows the application of mathematical models of diffusion compartments, which in part are influenced by myelin integrity.