Table 1.

Summary of MRI techniques, models and derived parameters used in the present study.

Imaging technique	Model	Measure	Abbreviation	Measure relates to	Scale
Diffusion MRI (dMRI)	DTI	Fractional anisotropy	FA	Presence of preferred direction of diffusion (i.e. tissue anisotropy)	0–1 (0 = most isotropic, 1 = most anisotropic)
		Mean diffusivity	MD	Amount of isotropic diffusion (i.e. not bounded by membranes, e.g. in CSF)	Continuous increasing value = increasing amount of diffusion
		Axial diffusivity	AD	Amount of isotropic diffusion along direction of maximal diffusion	Continuous increasing value = increasing amount of diffusion
		Radial diffusivity	RD	Amount of isotropic diffusion perpendicular to direction of maximal diffusion	Continuous increasing value = increasing amount of diffusion
	DKI	Mean kurtosis	MK	Presence of compartments that do not have a Gaussian diffusion profile (i.e. bounded by membranes)	Continuous increasing value = more compartmentalization
	NODDI	Neurite density index	NDI	Density of axons and dendrites based on intracellular diffusion	0–1 (0 = most extracellular diffusion, 1 = most intracellular diffusion)
		Orientation dispersion index	ODI	Dispersion of axons and dendrites in the intracellular compartment	0–1 (0 = well-aligned neurites, 1 = highly dispersed neurites)
		Fraction of isotropic compartment	FISO	Cerebrospinal fluid (isotropic Gaussian diffusion)	0–1 (0 = no CSF-like fluid, 1 = most CSF-like fluid)
Multi-exponential T2 relaxation (MET2)	MET2	Myelin water fraction	MWF	Myelin content	0–1 (0 = least myelin, 1 = most myelin)
		Intra- and extracellular water fraction	IEWF	Water molecules in and between axons (or having similar properties)	0–1 (0 = no intra- or extracellular water, 1 = mostly intra- and extracellular water)
		Geometric mean T2 time	IEW-gmT2	Intra- and extra-axonal mobility of water molecules (e.g. long T2 time = high mobility)	Continuous increasing value = more loosely bound water molecules