Table 2.

Diffusion Metrics

Groups/Statistics	Free-Water	Bi-Tensor FA	Bi-Tensor MD	Single-Tensor FA	Single-Tensor MD
Anterior Substantia Nigra
HC	0.19 (.006)	0.57 (.009)	0.56 (.005)	0.50 (.008)	0.76 (.015)
PD	0.19 (.005)	0.58 (.007)	0.56 (.003)	0.48 (.006)	0.76 (.011)
MSA	0.19 (.008)	0.60 (.011)	0.57 (.006)	0.48 (.011)	0.77 (.019)
PSP	0.22 (.008)	0.61 (.011)	0.57 (.006)	0.46 (.010)	0.79 (.019)
Full model F statistic	7.96	3.93	4.53	2.58	3.19
Group F statistic	3.80	3.59	2.10	3.55	0.98
Partial η2	0.027	0.025	0.015	0.025	0.007
Significant Covariate	Age, Site	Site	Site	N/A	N/A
Group P-value	0.01	0.014	0.10	0.015	0.40
P-value corrected	0.02	0.0214	0.13	0.021	0.44
Post Hoc	PSP > HC|PD	PSP>PD|HC	N/A	PSP<HC	N/A
Posterior Substantia Nigra
HC	0.19 (.007)	0.60 (.009)	0.57 (.005)	0.49 (.008)	0.79 (.013)
PD	0.22 (.005)	0.59 (.006)	0.57 (.004)	0.48 (.006)	0.80 (.010)
MSA	0.24 (.008)	0.62 (.011)	0.57 (.007)	0.45 (.010)	0.88 (.017)
PSP	0.28 (.008)	0.65 (.011)	0.57 (.006)	0.45 (.009)	0.88 (.016)
Full model F statistic	21.51	5.41	6.08	4.25	8.11
Group F statistic	23.64	9.26	0.40	4.11	10.86
Partial η2	0.145	0.062	0.003	0.029	0.072
Significant Covariate	Age, Sex, Site	Site	Site	Age	N/A
Group P-value	3.75E-14	6E-6	0.75	0.007	6.98E-07
P-value corrected	3.75E-13	2e-5	0.75	0.018	3.49E-06
Post Hoc	PSP>MSA| PD>HC	PSP>PD|HC	N/A	PSP|MSA<HC	PSP|MSA> PD|HC

ROI data represent the mean (standard error) adjusted for age and sex, with the statistics for the comparisons and significant covariates listed below. Abbreviations: FA = fractional anisotropy, HC = healthy controls, MD = mean diffusivity, MSA = multiple system atrophy, PD = Parkinson’s disease, PSP = progressive supranuclear palsy.