Table 1.

Performance of currently available structural MRI tools to track disease progression in the early stage of PD

Criteria	T1-weighted MRI			dMRI			Iron-sensitive imaging
	VBM	Cortical thickness	NMI	One tensor	Bi-tensor	DKI	R2*	QSM
1. Describe PD neurodegeneration	✔	✔	✔	✔	✔	✔	✔	✔
2. Sensitive to reflect small changes in disease progression	✖	NA	NA	NA	✔	NA	✖	✖
3. Good test-retest reliability	✔	✔	✔	✔	✔	NA	✔	✔
4. Reproducible across multisites	NA	NA	NA	✔	✔	NA	NA	✔
5. Not influenced by symptomatic treatment	NA	NA	NA	NA	✔	NA	NA	NA
6. Relate to clinical outcome	✔	✔	NA	NA	✔	NA	NA	NA
7. Robust longitudinal data allowing sample size calculations	NA	NA	NA	NA	✔	NA	NA	NA
8. Be relatively inexpensive and easy to use	✔	✔	✔	✔	✔	✔	✔	✔

VBM, voxel-based morphometry; dMRI, diffusion-weighted MRI; DKI, diffusion kurtosis imaging; NMI, neuromelanin-sensitive imaging; QSM, quantitative susceptibility mapping; NA, has not been studied sufficiently to draw a conclusion; check mark, yes; X mark, no