Table 2.

Overview of the quantitative microstructural indices and their interpretation in grey matter.

MRI modality	Index	Apparent grey matter property	Hypothesised changes with LOAD risk
Diffusion NODDI	ICSF	Neurite density	Increases with tau pathology55/Reduction in MCI and AD patients52–54
	ODI	Neurite dispersion	Increase/Reduction
	ISOSF	Free water	Increase
qMT	MPF	Macromolecules (e.g. myelin)	Reduction
	kf	Mitochondrial metabolism	Increase in acute inflammation83; Reduction in low-level inflammation125 and in MCI and AD patients59–61
Relaxometry	R1	free water, myelin, iron	Increase/Reduction62

AD Alzheimer's disease, ICSF intracellular signal fraction, ISOSF isotropic signal fraction, k_f forward exchange rate, MCI mild cognitive impairment, MPF macromolecular proton fraction, NODDI neurite orientation dispersion and density imaging, ODI orientation dispersion index, qMT quantitative magnetization transfer.