The effect of diffusion-weighted gradient direction number on the reliability of LDH.

<p>(a) Ten voxels (red) were randomly selected to test the reliability of LDH. (b)–(d) Intra-class coefficient (ICC) of LDH07, LDH19 and LDH27 as a function of the number of diffusion-weighted gradient directions (6∼63). The curves represent the mean ICC minus 1std (i.e., mean-1std) of ICC across the samples. This result represents the lower limit (i.e., the worst case) of ICC across samples (50 in total). Each curve is calculated for one voxel (10 in total). The cutoff value for the criterion of excellent reliability (i.e., ICC = 0.75) is denoted by the grey dashed line.</p

The percentage of voxels showing significant correlations (p<0.05, FDR corrected) between the LDH and FA/MD metrics on the WM skeleton (123081 voxels in total).

<p>The percentage of voxels showing significant correlations (p<0.05, FDR corrected) between the LDH and FA/MD metrics on the WM skeleton (123081 voxels in total).</p

Correlations between the LDH07 and FA/MD metrics across subjects.

<p>To highlight the potential differences between the metrics, voxels that did not exhibit significant correlations (p>0.05, FDR corrected) between the metrics were color-coded. (a)–(b)The panels depict the spatial pattern of voxels exhibiting non-significant correlations between LDH07 and FA as well as LDH07 and MD. The statistical analysis was performed on the WM skeleton derived from TBSS. The results were ‘thickened’ for better visualization (<a href="http://www.fmrib.ox.ac.uk/fsl/tbss/index.html#display" target="_blank">http://www.fmrib.ox.ac.uk/fsl/tbss/index.html#display</a>).</p

The extraction of voxel-wise diffusivity series.

<p>(a) Schematic diagram showing the processing procedures for calculating the diffusivity (D) along the gradient directions. The vector from the center of the sphere to a red circle on the surface represents a diffusion gradient direction. For each gradient direction, one diffusion-weighted image (DWI) was collected and used to calculate the diffusivity images. (b) The diffusivity series for a sample voxel (the red voxel). A dataset with 64 gradient directions was analyzed.</p

Maps showing the spatial consistencies and inconsistencies between LDH and FA/MD in the detection of age-related effects.

<p>(a) The voxels showing significant age-related effects that were detected by both FA and LDH07. (b) The voxels showing significant age-related effects that were detected by either FA or LDH07 alone. The yellow-red represents significant age-related effects that were only detected by FA but not on LDH07. Bright blue represents significant age-related effects that were only detected by LDH07 but not FA. (c) The voxels showing significant age-related effects that were detected by both MD and LDH07. (d) The voxels in which an age-related effect was only detected by either MD or LDH07. The yellow-red represents significant age-related effects that were detected only by MD but not by LDH07. Bright blue represents significant age-related effects that were only detected by LDH07 but not MD. All of these results were also ‘thickened’ for visualization.</p

Correlations between the LDH and FA/MD metrics across space.

<p>(a)–(f) Representative scatter plot between the LDH and FA/MD metrics across the WM skeleton of one subject. Each circle represents one voxel on the skeleton. (g)–(i) The Pearson correlation between the LDHs and FA/MD metrics for all subjects.</p

LDH and FA/MD across the entire brain.

<p>(a) Representative LDH and FA/MD images from one subject in the native space. The number in the bracket (i.e., 7, 19, 27) represents the size of the nearest neighborhood. (b) The average LDH and FA/MD images across the entire sample of 40 subjects. The images were nonlinearly registered into the standard space using the TBSS framework.</p

The significant age-related WM changes revealed by the LDH, FA and MD metrics.

<p>(a) Significant FA reduction (p<0.05, FDR corrected) in elderly individuals. (b) Significant LDH07 reduction (p<0.05, FDR corrected) in elderly individuals. (c) Significant MD increase (p<0.05, FDR corrected) in elderly individuals. The statistical analysis shown in this figure was performed only on the WM skeleton derived from TBSS. The results were ‘thickened’ for better visualization.</p

Voxels showing significant age-related effects as measured by both the LDH and FA/MD metrics (FDR corrected p<0.05).

<p>Voxels showing significant age-related effects as measured by both the LDH and FA/MD metrics (FDR corrected p<0.05).</p

TRT reliability of nodal degree for brain networks in different frequency bands.

<p>TRT reliability values of nodal degree were projected onto MNI brain surface using the BrainNet viewer (<a href="http://www.nitrc.org/projects/bnv/" target="_blank">http://www.nitrc.org/projects/bnv/</a>) for (A) short-term scans and (B) long-term scans in slow-5 and slow-4. Significant differences were found in TRT reliability of nodal degree driven by different frequency bands for (C) short-term and (D) long-term scans. Nodal degree in brain networks in slow-4 band showed higher ICC values. The asterisk indicates p<0.05. L, left hemisphere; R, right hemisphere.</p