Table 1.
The average value and the Results of the heritability analysis for the parameters of the diffusion models are shown. DTI: diffusion tensor imaging model. PD: permeability-diffusivity model. Mu is the compartmental fraction of the signal that comes from the compartment with unrestricted diffusion. NODDI: the Neurite Orientation Dispersion and Density Imaging model. ODI: the orientation dispersion index. MIC: the fraction for the intra-cellular compartment, thought to represent neurite density in the voxel space. Miso: the fraction for the isotropic diffusion compartment, thought to represent free standing water in the voxel space, e.g., cerebrospinal fluid. Bolded statistics were significant after Bonferroni correction for eight tests in the WM (p<0.00625) and five tests in the GM (p<0.01).
| White Matter: Corpus Callosum |
Variable | Symbol | Average ± std. dev. |
h2 | SE | p-value | Significant Covariates (p<0.05) |
|---|---|---|---|---|---|---|---|
| DTI | Fractional Anisotropy |
FA | .69±0.03 | .67 | .25 | .001 | Age |
| Axial Diffusivity |
DA | 1.43±.09*10−3 | .41 | .35 | .10 | none | |
| Radial Diffusivity |
DR | .50±.04*10−3 | .72 | .22 | .001 | Age | |
| PD Model | Permeability- diffusivity Index |
PDI | .04±.01 | .64 | .24 | .001 | Age |
| Compartmental Fraction |
Mu | .56±.04 | .33 | .31 | .16 | Age | |
| NODDI Model | Orientation Dispersion Index |
ODI | .08±.01 | .42 | .31 | .08 | Age |
| Neurite Density | MIC | .59±.07 | .70 | .21 | .005 | Age | |
| Isotropic Water Volume |
MISO | .36±.12 | .41 | .45 | .25 | Age | |
| Gray Matter: Cingulate |
|||||||
| PD Model | Permeability- Diffusivity Index |
PDI | .08±.02 | .84 | .27 | .0007 | Age |
| Compartmental Fraction |
Mu | .67±.05 | .53 | .37 | .09 | Age | |
| NODDI Model | Orientation Dispersion Index |
ODI | .40±.13 | .68 | .30 | .01 | Age |
| Neurite Density | MIC | .42±.09 | .55 | .24 | .01 | Age | |
| Isotropic Water Volume |
MISO | .27±.08 | .44 | .25 | .06 | Age |