Table 2.
Comparisons of summary statistics derived from histograms between MCI and control groups, before and after correction with Free Water Elimination. Mean and modal values of the histogram distribution for fractional anisotropy (FA, no unit), mean diffusivity (MD, 10− 3 mm2 s− 1), axial diffusivity (AD, 10− 3 mm2 s− 1) and radial diffusivity (RD, 10− 3 mm2 s− 1) and corresponding histogram peak heights (proportion of voxels at modal value) for patients with mild cognitive impairment (MCI) and healthy elderly controls (HC) in the uncorrected dataset, and after correcting for partial volume effect using the free-water elimination (FWE) approach. Examples where CSF contamination altered the qualitative interpretation of results are highlighted in bold.
| Group | Uncorrected |
FWE-corrected |
||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Mean (SD) | T(df = 43) | p | d | Mean (SD) | T(df = 43) | p | d | |||
| FA | Mean | MCI | 0.323 (0.029) | − 3.08 | .004** | 0.353 (0.028) | − 3.01 | .005** | ||
| HC | 0.345 (0.017) | .93++ | 0.373 (0.015) | .85++ | ||||||
| Mode | MCI | 0.262 (0.039) | − 3.45 | .001** | 0.284 (0.062) | − 3.40 | .002** | |||
| HC | 0.300 (0.034) | 1.0++ | 0.336 (0.038) | .97++ | ||||||
| Peak height | MCI | 0.0145 (0.0015) | 1.33 | .19 | 0.0130 (0.0020) | 0.95 | .35 | |||
| HC | 0.0139 (0.0009) | .40+ | 0.0127 (0.0008) | .28 | ||||||
| MD | Mean | MCI | 0.871 (0.066) | 2.35 | .023* | 0.780 (0.039) | 2.31 | .026* | ||
| HC | 0.833 (0.033) | .70+ | 0.757 (0.021) | .69+ | ||||||
| Mode | MCI | 0.803 (0.040) | 1.87 | .069 | 0.753 (0.029) | 2.04 | .048* | |||
| HC | 0.784 (0.030) | .56+ | 0.737 (0.020) | .61+ | ||||||
| Peak height | MCI | 0.0340 (0.0070) | − 3.76 | .001** | 0.0529 (0.0107) | − 3.66 | .001** | |||
| HC | 0.0411 (0.0053) | 1.1++ | 0.0634 (0.0079) | 1.1++ | ||||||
| AD | Mean | MCI | 1.166 (0.055) | 1.64 | .11 | 1.071 (0.029) | 0.98 | .33 | ||
| HC | 1.143 (0.031) | .49 | 1.064 (0.018) | .29 | ||||||
| Mode | MCI | 1.068 (0.042) | 0.84 | .41 | 0.997 (0.031) | 1.74 | .088 | |||
| HC | 1.059 (0.029) | .25 | 0.983 (0.019) | .52+ | ||||||
| Peak height | MCI | 0.0196 (0.0044) | − 2.58 | .013* | 0.0249 (0.0022) | − 2.35 | .024* | |||
| HC | 0.0223 (0.0014) | .77+ | 0.0262 (0.0013) | .70+ | ||||||
| RD | Mean | MCI | 0.723 (0.073) | 2.77 | .009** | 0.634 (0.046) | 2.70 | .010* | ||
| HC | 0.677 (0.035) | .78+ | 0.604 (0.024) | .81++ | ||||||
| Mode | MCI | 0.661 (0.045) | 2.03 | .048* | 0.618 (0.033) | 1.87 | .069 | |||
| HC | 0.637 (0.033) | .61+ | 0.601 (0.025) | .60+ | ||||||
| Peak height | MCI | 0.0285 (0.0048) | − 3.45 | .001** | 0.0370 (0.0048) | − 3.32 | .002** | |||
| HC | 0.0326 (0.0027) | 1.0++ | 0.0410 (0.0028) | 1.0++ | ||||||
Significance: *p < .05, **p < .01.
Effect sizes: + medium (d > .5), ++ large (d > .8).